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WO2012004991A1 - Détecteur optique, tête optique et dispositif optique de lecture d'informations - Google Patents

Détecteur optique, tête optique et dispositif optique de lecture d'informations Download PDF

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Publication number
WO2012004991A1
WO2012004991A1 PCT/JP2011/003867 JP2011003867W WO2012004991A1 WO 2012004991 A1 WO2012004991 A1 WO 2012004991A1 JP 2011003867 W JP2011003867 W JP 2011003867W WO 2012004991 A1 WO2012004991 A1 WO 2012004991A1
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WO
WIPO (PCT)
Prior art keywords
light
light receiving
photodetector
layer
light beam
Prior art date
Application number
PCT/JP2011/003867
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English (en)
Japanese (ja)
Inventor
秀輝 中田
秀彦 和田
泰守 日野
Original Assignee
パナソニック株式会社
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Filing date
Publication date
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Publication of WO2012004991A1 publication Critical patent/WO2012004991A1/fr

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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/13—Optical detectors therefor
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
    • G11B7/1381—Non-lens elements for altering the properties of the beam, e.g. knife edges, slits, filters or stops
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/13—Optical detectors therefor
    • G11B7/131—Arrangement of detectors in a multiple array

Definitions

  • the present invention relates to a photodetector, an optical head, and an optical information device for recording or reproducing information on an information recording medium such as an optical disk or an optical card.
  • FIG. 24A is a perspective view showing a configuration of the photodetector of the first conventional example
  • FIG. 24B is a cross-sectional view of the photodetector of FIG.
  • the photodetector 4 is disposed on the metal holder 9 in a state where a light receiving unit and a circuit that receive light are disposed on the bare chip 12.
  • Each connection terminal 12a of the bare chip 12 is connected to an electrode 34 formed on the holder 9 by a wire 35 (wire bonding).
  • the portion 12 c other than the incident portion 12 b where the reflected light beam enters is sealed with a thermosetting liquid sealing resin 36.
  • the light incident portion 12b is not covered with the thermosetting liquid sealing resin 36, but is kept exposed to the atmosphere, so that the blue laser light passes through the resin. Deterioration is prevented (see, for example, Patent Document 1).
  • FIG. 25A is a plan view showing the configuration of the photodetector of the second conventional example
  • FIG. 25B is a cross-sectional view of the photodetector of FIG.
  • the light beam having a wavelength of 405 nm incident on the first light receiving portion 2 is transmitted in the order of air, the silicon nitride film 8, the silicon oxide film 7, the silicon nitride film 6, and the silicon oxide film 5.
  • a four-layer antireflection film is essential.
  • the DVD light flux having a wavelength of 650 nm and the CD light flux having a wavelength of 780 nm that are incident on the second light receiving unit 3 are transmitted through the air, the silicon nitride film 6 and the silicon oxide film 5 in this order.
  • a two-layer antireflection film is essential (see, for example, Patent Document 2).
  • the transmittance with respect to the light beam with a wavelength of 405 nm when the transmittance with respect to the light beam with a wavelength of 405 nm is maximized, the transmittance with respect to the light beam with a wavelength of 405 nm is 67%, and the light with respect to the light beam with a wavelength of 650 nm is transmitted.
  • the rate is 83%, and the transmittance for a light beam having a wavelength of 780 nm is 83%.
  • the transmittance with respect to the light beam with a wavelength of 405 nm when the transmittance with respect to the light beam with a wavelength of 405 nm is maximized, the transmittance with respect to the light beam with a wavelength of 405 nm is 84%, and the transmittance with respect to the light beam with a wavelength of 650 nm. Is 92%, and the transmittance for a light beam having a wavelength of 780 nm is 91%.
  • the transmittance with respect to the light beam with a wavelength of 405 nm when the transmittance with respect to the light beam with a wavelength of 405 nm is maximized, the transmittance with respect to the light beam with a wavelength of 405 nm is 95%, and the transmittance with respect to the light beam with a wavelength of 650 nm. Is 82%, and the transmittance for a light beam having a wavelength of 780 nm is 79%.
  • the transmittance with respect to the light flux with a wavelength of 650 nm for DVD when the transmittance with respect to the light flux with a wavelength of 650 nm for DVD is maximized, the transmittance with respect to the light flux with a wavelength of 405 nm is 74%, and the light flux with a wavelength of 650 nm. Is 95%, and the transmittance for a light beam having a wavelength of 780 nm is 95%. Therefore, in order to increase the transmittance with respect to the light beam having a wavelength of 405 nm, it is essential to form four or more antireflection films.
  • FIG. 26A is a view of semiconductor silicon of a conventional photodetector as viewed from the incident light beam side
  • FIG. 26B is a cross-sectional view of the conventional photodetector
  • FIG. It is the figure which looked at the conventional photodetector from the light beam entrance side.
  • the photodetector 409 includes a semiconductor silicon (multilayer silicon wafer) 431, a resin package 441, a wiring board 442, and an FPC board (flexible printed circuit board). 445.
  • the semiconductor silicon 431 includes a quadrant light receiving unit 420, a sub beam light receiving unit 421, an arithmetic circuit 432, and a signal output unit 433.
  • the arithmetic circuit 432 converts the light amount of the light beam received by the four-divided light receiving unit 420 and the sub beam light receiving unit 421 into a voltage and performs a predetermined calculation.
  • the signal output unit 433 is connected to the arithmetic circuit 432 and outputs a voltage that is an output signal from the arithmetic circuit 432.
  • the pad portion 443 formed on the wiring substrate 442 is connected to the signal output portion 433 by wire bonding 446.
  • the resin package 441 covers the four-divided light receiving unit 420, the sub-beam light receiving unit 421, the arithmetic circuit 432, the signal output unit 433, and the wiring substrate 442.
  • the wiring substrate 442 includes a terminal portion 444 that is electrically connected to the pad portion 443, and the terminal portion 444 is mounted and fixed to the FPC board 445.
  • FIG. 27 is a diagram showing a configuration of an optical system of a conventional optical head 400.
  • the optical head 400 includes a semiconductor laser 401, a diffraction grating 402, a beam splitter 403, a collimator lens 404, an objective lens 405, an objective lens actuator 406, a cylindrical lens 408, a photodetector 409, and a holder 410.
  • the light beam emitted from the semiconductor laser 401 is separated into a plurality of different light beams by the diffraction grating 402.
  • the light beam transmitted through the diffraction grating 402 is reflected by the beam splitter 403 and converted into a parallel light beam by the collimator lens 404. Then, the light flux enters the objective lens 405 and becomes so-called three-beam convergent light. This convergent light is applied to the recording layer of the optical disc 407.
  • the light beam reflected and diffracted by the recording layer of the optical disc 407 passes through the objective lens 405 again and passes through the beam splitter 403.
  • the objective lens 405 is driven in the optical axis direction (focus direction) and the radial direction (radial direction) of the optical disk 407 by an objective lens actuator 406 (details not shown).
  • the light beam that has passed through the beam splitter 403 passes through the cylindrical lens 408 and enters the photodetector 409.
  • the photodetector 409 is fixed to the holder 410 and receives the light beam that has passed through the holder 410.
  • the photodetector receives the reflected light from the recording layer, converts it into a voltage signal, and outputs it. At this time, the reflected light from the multilayer optical disk having a low reflectance particularly causes the S / N of the reproduction signal to deteriorate, and the reproduction signal is greatly deteriorated.
  • the reflectivity of each recording layer of a multi-layer optical disc of BD-R (Blu-ray Disc Recordable) and BD-RE (Blu-ray Disc Rewritable) is about 2% to 4%.
  • the reflectivity of the multilayer optical disc is 20% for the BD-R single-layer optical disc, and about 8% for the BD-R double-layer optical disc. Therefore, the reflectance of the multilayer optical disk is very small compared to the reflectance of the BD-R single-layer optical disk and the reflectance of the BD-R double-layer optical disk.
  • the photodetector and optical head corresponding to the light sources having three wavelengths of 405 nm, 650 nm, and 780 nm not only the BD (wavelength 405 nm) but also the reproduction signal for each of DVD (wavelength 650 nm) and CD (wavelength 780 nm). It is also necessary to increase the S / N.
  • the portion through which the light beam having a wavelength of 405 nm is transmitted is configured with a four-layer antireflection film, and the portion through which the light beam with a wavelength of 650 nm and wavelength is 780 nm is configured with a two-layer antireflection film.
  • the focal length of the objective lens 405 of the optical head 400, the collimator lens 404, the cylindrical lens 408, and the light It is necessary to increase the lateral magnification of the so-called detection optical system, which is the ratio with the focal length of the optical component composed of the detector 409.
  • the stray light reflected by the recording layer other than the recording layer on which the light of the multilayer optical disc is collected is not incident on the sub-beam light receiving unit 421 for detecting the tracking error signal, and the forward detection optical system is provided. It is necessary to reduce the size.
  • the stray light reflected by the other recording layer of the optical disk 407 can be prevented from entering the sub-beam light receiving unit 421, and the detection optical system of the return path of the optical head 400 can be downsized, and the optical element and the photodetector The size in the height direction of the optical head 400 can be reduced by downsizing 409.
  • the signal output portion 433 of the semiconductor silicon 431 and the pad portion 443 formed on the wiring substrate 442 are connected to each other by wires.
  • an area for forming the pad portion 443 on the wiring substrate 442 is required. Therefore, when the number of signal output units 433 increases, the number of pad units 443 also increases, making it difficult to reduce the size of the photodetector 409. In this case, the volume of the resin package 441 that holds the semiconductor silicon 431 and the wiring substrate 442 becomes larger, and it becomes more difficult to reduce the size of the photodetector 409.
  • a preferable size of the photodetector when the photodetector is mounted on a so-called slim-size optical disc drive (optical information device) will be described below.
  • the dimension of the photodetector in the Y direction is desirably 4 mm or less.
  • the dimension in the X direction is about 7 mm
  • the dimension in the Y direction is about 5 mm
  • the dimension in the Z direction is about 3 mm.
  • FIG. 28 illustrates the relationship between the magnification of the detection optical system and the interval between the main beam and the sub beam on the photodetector, and the relationship between the magnification of the detection optical system and the interval between the two sub beams on the photodetector. It is a figure for doing.
  • Table 1 shows the relationship between the magnification of the detection optical system and the interval between the main beam and the sub beam on the photodetector, and the relationship between the magnification of the detection optical system and the interval between the two sub beams on the photodetector. It is a table
  • the focus error signal is calculated based on the following formula (1)
  • the tracking error signal is calculated based on the following formula (2).
  • A1 to A4 represent outputs of the respective light receiving areas of the four-divided light receiving unit 420, and B1 and B2 represent the sub beam light receiving unit 421 divided into two. It represents the output of each light receiving area, and k represents the gain.
  • the gain k is normally set to a value of about 1 to 5.
  • the lateral magnification of a detection optical system generally used in a conventional optical head is about 6 times, and assuming that the distance between the main beam and the sub beam on the optical disk is 20 ⁇ m, the main beam 422 and the sub beam on the photodetector 409 are assumed.
  • An interval P with respect to 423 is 120 ⁇ m.
  • the interval P between the main beam 422 and the sub beam 423 on the photodetector 409 increases to 280 ⁇ m to 320 ⁇ m.
  • the interval Q between the two sub-beams 423 also increases nearly three times.
  • the size R in the Y direction of the semiconductor silicon 431 having the four-divided light receiving unit 420, the sub beam light receiving unit 421, and the arithmetic circuit increases.
  • the size R of the semiconductor silicon 431 in the Y direction increases, the size of the photodetector 409 including the resin package becomes too large, and the photodetector 409 does not enter the slim optical disc drive. Therefore, it is necessary to make the dimension (size R) of the photodetector 409 in the Y direction as small as possible.
  • the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a photodetector, an optical head, and an optical information device that can be miniaturized.
  • a photodetector is a photodetector that detects a light beam reflected by an information recording medium, and photoelectrically converts a light receiving unit that receives the light beam and a light beam received by the light receiving unit. And a substrate formed with a calculation unit that performs a predetermined calculation on the electric signal obtained by this, and at least reflected on the incident information recording medium formed on the light receiving unit and the calculation unit.
  • a multilayer antireflection layer including a plurality of antireflection films to be prevented, a glass package that covers the multilayer antireflection layer, and an adhesive layer that bonds the multilayer antireflection layer and the glass package.
  • the substrate includes the light receiving unit that receives the light beam and the calculation unit that performs a predetermined calculation on the electrical signal obtained by photoelectrically converting the light beam received by the light receiving unit.
  • the multilayer antireflection layer includes a plurality of antireflection films that are formed on at least the light receiving unit and the calculation unit and prevent reflection of a light beam reflected by an incident information recording medium.
  • the glass package covers the multilayer antireflection layer.
  • the adhesive layer bonds the multilayer antireflection layer and the glass package.
  • the photodetector by comprising a substrate, a multilayer antireflection layer, an adhesive layer, and a glass package, even if the magnification of the detection optical system is increased, wire bonding and a resin package are not required, and the photodetector is It can be downsized.
  • (A) is a front view which shows the structure of the photodetector in Embodiment 1 of this invention
  • (B) is a side view which shows the structure of the photodetector in Embodiment 1 of this invention
  • (C) is a back view which shows the structure of the photodetector in Embodiment 1 of this invention.
  • It is a schematic diagram which shows the structure of the multilayer antireflection layer in Embodiment 1 of this invention.
  • it is a figure which shows the calculated value of the transmittance
  • (A) is a figure which shows the relationship between the thickness of the contact bonding layer in Embodiment 1 of this invention, and adhesive strength
  • (B) is the thickness of the contact bonding layer in Embodiment 1 of this invention, integrated light quantity
  • (C) is a figure which shows the relationship between the thickness of the contact bonding layer in Embodiment 1 of this invention, and the transmittance
  • (A) is the schematic for demonstrating the surface reflection from the other layer in a two-layer optical disk
  • (B) is the schematic for demonstrating the surface reflection from the other layer in a multilayer optical disk.
  • (A) is a figure which shows the relationship between the distance of the main beam and sub beam on the photodetector of the conventional optical head, and other-layer stray light
  • (B) is the optical of Embodiment 2 of this invention. It is a figure which shows the relationship between the distance of the main beam on a photodetector of a head, and a sub beam, and other layer stray light. It is a figure which shows the structure of the optical system of the optical head in Embodiment 3 of this invention.
  • FIG. (A) is a side view which shows the structure of the photodetector in Embodiment 3 of this invention
  • (B) is a front view which shows the structure of the photodetector in Embodiment 3 of this invention. It is a figure for demonstrating the calculation method of the tracking error signal in Embodiment 3 of this invention.
  • (A) is a figure which shows another example of the multilayer antireflection film of the photodetector in Embodiment 2 of this invention
  • (B) is the multilayer reflection of the photodetector in Embodiment 3 of this invention. It is a figure which shows another example of a prevention film.
  • FIG. 4 It is a figure which shows the structure of the optical system of the optical head in Embodiment 4 of this invention. It is a front view which shows the structure of the photodetector in Embodiment 4 of this invention. It is a figure which shows the partial structure of the arithmetic circuit of the photodetector in FIG. It is a reverse view of the photodetector in Embodiment 5 of this invention. It is a figure which shows the amplifier noise in the non-low noise mode and low noise mode using the 1st amplification gain of the 1st differential amplifier circuit.
  • A is a perspective view which shows the structure of the photodetector of a 1st prior art example
  • (B) is sectional drawing of the photodetector of FIG.
  • FIG. 24 (A).
  • (A) is a top view which shows the structure of the photodetector of the 2nd prior art example
  • (B) is sectional drawing of the photodetector of FIG. 25 (A).
  • (A) is the figure which looked at the semiconductor silicon of the conventional photodetector from the incident light beam side
  • (B) is a sectional view of the conventional photodetector
  • (C) is the conventional photodetector. It is the figure which looked at from the light beam entrance side. It is a figure which shows the structure of the optical system of the conventional optical head.
  • FIG. 1 (A) to FIG. 1 (C) are diagrams showing the configuration of the photodetector in the first embodiment of the present invention.
  • FIG. 1A is a front view of the photodetector 120 according to Embodiment 1 of the present invention as viewed from the light incident side
  • FIG. 1B is the photodetector 120 according to Embodiment 1 of the present invention.
  • FIG. 1C is a back view of the photodetector 120 according to Embodiment 1 of the present invention.
  • the photodetector 120 includes a semiconductor substrate (for example, semiconductor silicon) 121, an adhesive layer 124, a glass package 125, a multilayer antireflection layer 128, and a signal output unit 130.
  • a semiconductor substrate for example, semiconductor silicon
  • an adhesive layer 124 for example, adhesive
  • a glass package 125 for example, glass package 125
  • a multilayer antireflection layer 128, and a signal output unit 130 In the semiconductor silicon 121, a light receiving portion 123, an arithmetic circuit 122, and a signal output portion 130 are formed.
  • the light receiving unit 123 receives the reflected light beam reflected by the optical disc 21.
  • the arithmetic circuit 122 performs a predetermined operation on the electrical signal obtained by photoelectrically converting the light beam received by the light receiving unit 123.
  • the signal output unit 130 is connected to the arithmetic circuit 122 and outputs a voltage that is an output signal from the arithmetic circuit 122.
  • the light receiving portion 123 and the arithmetic circuit 122 are formed on the light incident side surface of the semiconductor silicon 121, and the signal output portion 130 is formed on the surface facing the light incident side surface.
  • the multilayer antireflection layer 128 is formed on at least the light receiving portion 123 and the arithmetic circuit 122, and includes a plurality of antireflection films for preventing the reflection of the light beam reflected by the incident optical disk.
  • the glass package 125 is made of transparent glass. The glass package 125 covers the multilayer antireflection layer 128 and the semiconductor silicon 121.
  • the adhesive layer 124 bonds the multilayer antireflection layer 128 and the glass package 125.
  • the glass package 125 is bonded to the multilayer antireflection layer 128 and the semiconductor silicon 121 by the adhesive layer 124.
  • the adhesive layer 124 is made of a silicon resin that has a transmittance of 99% or more for a light beam having a wavelength of 405 nm when the thickness is 30 ⁇ m or less. Further, a multilayer antireflection layer 128 is provided on the light incident side surface of the semiconductor silicon 121, and the multilayer antireflection layer 128 is formed between the light receiving portion 123 and the adhesive layer 124.
  • the thickness of the semiconductor silicon 121 is about 0.3 mm
  • the thickness of the glass package 125 is about 0.7 mm
  • the thickness of the photodetector 120 is about 1 mm.
  • the lengths of the photodetector 120 in the X direction and the Y direction are about 2.5 mm, respectively, and even in the projection area, the size of the conventional photodetector is greatly reduced. .
  • the signal output unit 130 and the arithmetic circuit 122 are connected by wiring from the side surface of the photodetector 120 or connected to the signal output unit 130 on the bottom surface by providing a via hole or the like in the arithmetic circuit 122 configured by a laminated circuit. It is configured to do.
  • the signal output unit 130 is mounted on a flexible printed circuit board (FPC board) 126, and servo signals and reproduction signals are output from the signal output unit 130.
  • the adhesive layer 124 may be formed only on the entire surface on the light incident side of the light receiving unit 123, or may be formed on the entire surface on the light incident side of the semiconductor silicon 121 including the light receiving unit 123 and the arithmetic circuit 122.
  • the photodetector 120 has a structure that does not use a resin package and wire bonding, so that both the thickness and the projected area are greatly reduced, and the volume is 1/10 or less of the conventional one.
  • the light receiving portion 123 corresponds to an example of a light receiving portion
  • the arithmetic circuit 122 corresponds to an example of an arithmetic portion
  • the semiconductor silicon 121 corresponds to an example of a substrate
  • the multilayer antireflection layer 128 includes a multilayer.
  • the glass package 125 corresponds to an example of an antireflection layer
  • the glass package 125 corresponds to an example of a glass package
  • the adhesive layer 124 corresponds to an example of an adhesive layer.
  • FIG. 2 is a schematic diagram showing the configuration of the multilayer antireflection layer 128 according to Embodiment 1 of the present invention.
  • the dimension in the thickness direction is shown partially enlarged.
  • a multilayer antireflection layer 128 composed of three antireflection films formed by vacuum deposition such as sputtering is formed.
  • the multilayer antireflection layer 128 includes a silicon-based nitride film 128a, a silicon-based oxide film 128b, and a silicon-based nitride film 128c in order from the light incident surface side.
  • the refractive index of the silicon-based nitride films 128a and 128c is 2.07, and the refractive index of the silicon-based oxide film 128b is 1.47.
  • the refractive indexes of the silicon-based nitride films 128a and 128c and the silicon-based oxide film 128b may each have a refractive index change of ⁇ 5%.
  • the thickness of each antireflection film of the multilayer antireflection layer 128 is 44.1 nm, 73.6 nm, and 47.1 nm in order from the light beam incident surface side. Each antireflection film may have a thickness change of ⁇ 10%.
  • the refractive index of the glass package 125 and the silicon resin adhesive layer 124 is 1.57, the refractive index of the silicon nitride film is 2.07, and the refractive index of the silicon oxide film is 1.47. It is.
  • the refractive indexes of the glass package 125, the adhesive layer 124, the silicon nitride film, and the silicon oxide film may have a refractive index change of ⁇ 5%.
  • an antireflection film (AR coating) 112 is formed on the light incident surface of the glass package 125, and no antireflection film (AR coating) is formed between the glass package 125 and the adhesive layer 124. .
  • the adhesive layer 124 (silicon resin) is formed on the multilayer antireflection layer 128, so that the number of films of the multilayer antireflection layer 128 can be reduced to three.
  • the transmittance from 125 to the light receiving unit 123 can be greatly improved.
  • the transmittance from the glass package 125 to the light receiving portion 123 can be significantly improved with respect to a light flux having a wavelength of 650 nm and a wavelength of 780 nm.
  • the number of deposition steps for the multilayer antireflection layer 128 can be reduced.
  • the light receiving sensitivity of the photodetector 120 when receiving a light beam having a wavelength of 405 nm can be greatly improved.
  • FIG. 3 is a diagram showing a calculated value of the transmittance with respect to the wavelength of the incident light beam in the photodetector according to the first embodiment of the present invention.
  • the transmittance for the light flux with a wavelength of 650 nm for DVD and the light flux with a wavelength of 780 nm for CD can be 77% or more, and a photodetector with high light receiving sensitivity corresponding to a light source with three wavelengths can be realized.
  • the transmittance with respect to the light beam having a wavelength of 405 nm is 98%, the transmittance of 80% or more can be realized for both the light beam with a wavelength of 650 nm and the light beam with a wavelength of 780 nm with the same multilayer antireflection layer. .
  • the antireflection film (AR coating) is not provided on the boundary surface between the glass package 125 and the adhesive layer 124, and the glass package 125 and the adhesive layer are directly bonded. With this configuration, the adhesive strength between the glass package 125 and the adhesive layer 124 can be increased.
  • FIG. 4A is a diagram showing the relationship between the thickness of the adhesive layer 124 and the adhesive strength in the first embodiment of the present invention
  • FIG. 4B is the adhesive layer 124 in the first embodiment of the present invention
  • FIG. 4C is a diagram showing the relationship between the thickness of the adhesive layer 124 and the transmittance in the first embodiment of the present invention.
  • FIG. 4A is a graph showing an example of the result of measuring the relationship between the thickness of the adhesive layer 124 and the adhesive strength.
  • the horizontal axis indicates the thickness of the adhesive layer 124, and the vertical axis indicates the adhesive strength (N). If the thickness of the adhesive layer 124 is 5 ⁇ m or more, the required adhesive strength of 15 (N) or more is satisfied.
  • FIG. 4B is a graph showing an example of the result of measuring the relationship between the thickness of the adhesive layer 124 and blue light deterioration.
  • the horizontal axis indicates the thickness of the adhesive layer 124
  • the vertical axis indicates the integrated light amount (Wh / mm 2 ). If the thickness of the adhesive layer 124 is less than 6 ⁇ m, the thickness of the layer is thin, so that the adhesive layer 124 is cracked by expansion and contraction, and if the thickness of the adhesive layer 124 exceeds 25 ⁇ m, bubbles are generated inside the adhesive layer 124. It tends to occur. Therefore, when the thickness of the adhesive layer 124 is in the range of 5 ⁇ m to 25 ⁇ m, 250 (Wh / mm 2 ) that is an integrated light amount necessary for detection is satisfied.
  • FIG. 4C is a graph showing an example of the result of measuring the relationship between the thickness of the adhesive layer 124 and the transmittance for a light beam having a wavelength of 405 nm.
  • the transmittance can be greatly improved by reducing the thickness of the adhesive layer 124.
  • the transmittance with respect to a light beam having a wavelength of 405 nm can be set to 99.5% or more.
  • the thickness of the adhesive layer 124 is indispensable to be 5 ⁇ m or more and 25 ⁇ m or less, and preferably in the range of 10 ⁇ m or more and 20 ⁇ m or less.
  • the adhesive layer 124 has a thickness in the range of 5 ⁇ m to 25 ⁇ m and is applied to the entire surface between the glass package 125 and the semiconductor silicon 121.
  • the thickness of the adhesive layer 124 can suppress so-called blue light deterioration due to the light beam (wavelength 405 nm) from the blue laser light source while maintaining high adhesive strength without deteriorating the transmittance with respect to the light beam with a wavelength of 405 nm.
  • the adhesive strength can be increased by applying the adhesive layer 124 to the entire surface of the semiconductor silicon 121. Further, the light incident side of the light receiving unit 123 is covered with the adhesive layer 124, and no air layer is present on the light receiving unit 123. As a result, it is possible to prevent impurities from adhering to the light receiving portion 123 and the glass package 125 due to the so-called blue light optical tweezer effect.
  • the adhesive layer 124 made of silicon resin is formed on the light beam incident side surface of the multilayer antireflection layer 128 deposited on the light beam incident side surface of the semiconductor silicon 121.
  • the number of antireflection films constituting the multilayer antireflection layer 128 can be reduced to three.
  • the light loss in the multilayer antireflection layer 128 is reduced, and the transmittance with respect to an incident light beam having a wavelength of 405 nm can be improved to 99% or more.
  • the glass package 125 having a refractive index of 1.57 is formed on the light incident side of the adhesive layer 124 made of silicon resin, so that the semiconductor silicon 121 can be held by the glass package 125.
  • a small photodetector 120 having a CSP (chip size package) configuration without a resin package and wire bonding can be realized.
  • the chip size package means that the area of the light incident side surface of the photodetector is the same as the area of the light incident side surface of the semiconductor silicon 121.
  • an antireflection film (AR coating) 112 is formed only on the light incident side of the glass package 125.
  • an antireflection film (AR coating) is not formed between the glass package 125 and the adhesive layer 124.
  • the adhesive layer 124 is made of a transparent silicon resin having a transmittance of 99% or more for light in the wavelength region of 400 to 800 nm when the thickness is 30 ⁇ m or less. Desirably, the adhesive layer 124 is preferably made of a silicon resin having a transmittance of 99.5% or more when light having a wavelength of about 405 nm is incident when the thickness is 25 ⁇ m.
  • the glass package 125 is made of a glass material.
  • the materials of the adhesive layer 124 and the glass package 125 are not limited to the above materials.
  • the material of the adhesive layer 124 may be any material that does not deteriorate the transmittance, suppresses blue light deterioration, maintains high adhesive strength, and enhances component strength.
  • the material of the glass package 125 is preferably a material that can reinforce the semiconductor silicon 121 and can secure a certain degree of flatness.
  • the adhesive layer 124 is formed on the light receiving portion 123, the diameter of the reflected light beam when passing through the adhesive layer 124 is very small. For this reason, when the photodetector 120 is combined with an optical system using high-power blue light having a wavelength of about 405 nm, strong energy of blue light flux is applied to the adhesive layer 124, and the adhesive layer 124 may be deteriorated. As described above, when the adhesive layer 124 is deteriorated, the light transmittance of the adhesive layer 124 is lowered, and the signal characteristic of the signal observed by the photodetector 120 is deteriorated. Note that even when a silicon resin is used for the adhesive layer 124, the silicon resin may be deteriorated by blue light (light beam having a wavelength of 405 nm).
  • the adhesive layer 124 has a composition that does not include an epoxy compound.
  • a silicon resin synthesized by removing an epoxy resin from a raw material is used as the adhesive layer 124, a composition that does not include an epoxy compound can be obtained.
  • the photodetector 120 is arranged at a position where the reflected light beam of blue light is incident, the photodetector 120 is excellent in that the signal characteristics are hardly deteriorated by the blue light. It will have blue resistance.
  • FIG. 5 is a diagram showing a configuration of the photodetector in the modification of the first embodiment of the present invention.
  • the multilayer antireflection layer 128 and the adhesive layer 124 are in close contact with each other, and there are no other components between the multilayer antireflection layer 128 and the adhesive layer 124.
  • the present invention is not particularly limited to this.
  • a protective film 114 may be provided between the multilayer antireflection layer 128 and the adhesive layer 124 as long as the refractive index and transmittance are similar to those of the adhesive layer 124. Further, the protective film 114 may have a multilayer structure.
  • the second embodiment shows a configuration of an optical head using the photodetector 120 of the first embodiment.
  • FIG. 6 is a diagram showing the configuration of the optical system of the optical head according to Embodiment 2 of the present invention.
  • the signal output unit 130 is mounted on the FPC board 126 and soldered, so that the signal detected by the light receiving unit 123 is transmitted from the optical head to the main board of the optical information device main body.
  • an optical head 10 includes a semiconductor laser (light source) 101, a diffraction grating 102, a beam splitter 103, a collimator lens 104, an objective lens 105, an objective lens actuator 106, a cylindrical lens 108, a metal holder 110, and a photodetector 120. And an FPC board (flexible printed circuit board) 126.
  • the semiconductor laser 101 emits a light beam.
  • the light beam emitted from the semiconductor laser 101 as the light source is separated into a plurality of different light beams by the diffraction grating 102.
  • the diffraction grating 102 splits the light beam emitted from the semiconductor laser 101.
  • the diffraction grating 102 divides the incident light beam into a main beam and first and second sub beams.
  • the light beam transmitted through the diffraction grating 102 is reflected by the beam splitter 103, converted into a parallel light beam by the collimator lens 104, and enters the objective lens 105.
  • the objective lens 105 focuses the light beam emitted from the semiconductor laser 101 on the optical disk 21.
  • the light beam incident on the objective lens 105 becomes so-called three-beam convergent light and is applied to the optical disc 21.
  • the objective lens 105 is driven in the optical axis direction (focus direction) and the tracking direction (radial direction) of the optical disk 21 by an objective lens actuator 106 (not shown in detail).
  • the light beam reflected and diffracted by the recording layer of the optical disc 21 passes through the objective lens 105 and the collimator lens 104 again and enters the beam splitter 103.
  • the light beam that has passed through the beam splitter 103 enters the cylindrical lens 108.
  • the cylindrical lens 108 generates astigmatism in the reflected light beam reflected by the optical disk 21.
  • the light beam that has passed through the cylindrical lens 108 enters the photodetector 120.
  • the photodetector 120 detects a reflected light beam in which astigmatism is generated by the cylindrical lens 108.
  • FIG. 7 is a diagram showing the configuration of the light receiving unit 123 of the photodetector 120 and the configuration of the arithmetic circuit 122 according to the second embodiment of the present invention.
  • the light receiving unit 123 includes a four-divided light receiving region 140, a first sub-beam light receiving region 141a, and a second sub-beam light receiving region 141b.
  • the arithmetic circuit 122 includes first to seventh addition amplifiers 144a to 144g and first to fourth differential amplifiers 145a to 145d.
  • the four-divided light receiving region 140 receives the main beam 142 among the light beams that have passed through the cylindrical lens 108.
  • the first differential amplifier 145a calculates the difference between the diagonal sum signals of the four-divided light receiving region 140, thereby detecting a focus error signal.
  • the first summing amplifier 144a calculates the sum of all signals in the four-divided light receiving area 140, thereby detecting an RF signal (a reproduction signal of a signal recorded on the optical disc 21).
  • the second addition amplifier 144b and the third addition amplifier 144c each add a signal output from a region located diagonally to the four-divided light receiving region 140.
  • the first differential amplifier 145a calculates a difference between the sum signal output from the second addition amplifier 144b and the sum signal output from the third addition amplifier 144c.
  • the first addition amplifier 144a adds the sum signal output from the second addition amplifier 144b and the sum signal output from the third addition amplifier 144c.
  • the first sub-beam light-receiving area 141a and the second sub-beam light-receiving area 141b of the photodetector 120 are condensed and reflected on the track of the recording layer of the optical disc 21 and are reflected by the first sub-beam in the so-called three-beam method.
  • 143a and the second sub beam 143b are received.
  • the first sub-beam 143a and the second sub-beam 143b are received by the first sub-beam receiving area 141a and the first sub-beam receiving area 141b.
  • the first sub-beam light receiving area 141a and the second sub-beam light receiving area 141b are each divided into two areas along the Y direction (direction perpendicular to the tracking direction).
  • a push-pull signal calculated based on the main beam 142 received by the four-divided light receiving region 140 and a signal corresponding to the amount of light received by the first sub-beam light receiving region 141a and the second sub-beam light receiving region 141b are the sixth.
  • the seventh addition amplifiers 144f and 144g and the second to fourth differential amplifiers 145b to 145d are generated.
  • the tracking error signal is used when performing tracking servo for causing the objective lens 105 to follow the track of the recording layer of the optical disc 21.
  • the fourth addition amplifier 144d and the fifth addition amplifier 144e each add a signal output from a region adjacent to the X direction (tracking direction) of the four-divided light receiving region 140.
  • the third differential amplifier 145c calculates a difference between the sum signal output from the fourth summing amplifier 144d and the sum signal output from the fifth summing amplifier 144e.
  • the sixth addition amplifier 144f adds the signal output from the upper region of the first sub-beam light receiving region 141a and the signal output from the upper region of the second sub-beam light receiving region 141b.
  • the seventh addition amplifier 144g adds the signal output from the area below the first sub-beam light receiving area 141a and the signal output from the area below the second sub-beam light receiving area 141b.
  • the second differential amplifier 145b calculates a difference between the sum signal output from the sixth addition amplifier 144f and the sum signal output from the seventh addition amplifier 144g.
  • the fourth differential amplifier 145d calculates a difference between the differential signal output from the second differential amplifier 145b and the differential signal output from the third differential amplifier 145c.
  • the quadrant light receiving region 140 corresponds to an example of a first light receiving region
  • the first sub-beam light receiving region 141a and the second sub-beam light receiving region 141b correspond to an example of a second light receiving region.
  • FIG. 8 is a diagram showing a configuration of a detection optical system including a cylindrical lens according to Embodiment 2 of the present invention.
  • the cylindrical lens 108 has a cylindrical cylindrical surface 108a on the incident surface side of the light beam, and a concave lens surface 108b having lens power on the exit surface side.
  • the cylindrical surface 108a generates astigmatic differences with different focal positions at an angle of 90 degrees in a plane orthogonal to the optical axis. Further, the direction of the cylindrical surface 108 a is arranged at an angle inclined by approximately 45 degrees with respect to the four-divided light receiving region 140 of the photodetector 120.
  • FIG. 9 is a diagram showing the shape of the main beam on the 4-split light receiving area 140 at the front focal line, the rear focal line, and the focal position.
  • the main beam 142a at the focal position has a circular shape
  • the main beam 142b at the front focal line and the main beam 142c at the rear focal line have elliptical shapes orthogonal to each other.
  • a light beam as shown in FIG. 9 is formed at the front focal line and the rear focal line.
  • the light receiving unit 123 is arranged at the focal position in FIG.
  • the lateral magnification ( ⁇ ) of the detection optical system is determined by the focal length of the objective lens 105, the focal length of the collimator lens 104, and the optical power of the concave lens surface 108b of the cylindrical lens 108.
  • FIG. 10 is a cross-sectional view showing a partial configuration from the collimator lens 104 to the FPC board 126 of the optical head according to the second embodiment of the present invention.
  • the optical base 111 includes a semiconductor laser 101 (not shown), a diffraction grating 102 (not shown), a beam splitter 103, a collimator lens 104, an objective lens actuator 106 (not shown) for driving the objective lens 105, and a cylindrical lens 108. Hold.
  • the photodetector 120 is fixed to the metal holder 110.
  • the metal holder 110 is placed on the optical base 111 in the Z direction (optical axis direction) and the XY plane (in the plane perpendicular to the optical axis) with respect to the optical base 111 by an external jig (not shown).
  • the configuration is adjustable.
  • the position of the photodetector 120 in the XY plane is adjusted so that the main beam 142 incident on the quadrant light receiving region 140 of the photodetector 120 enters the approximate center of the quadrant light receiving region 140.
  • the position of the photodetector 120 in the Z direction is finely adjusted so that the light receiving unit 123 is disposed at the astigmatic focal position in a state where the objective lens 105 is focused on the recording layer of the optical disc 21.
  • the By adjusting in the Z direction the main beam 142 incident on the four-divided light receiving region 140 becomes circular, and the focus error signal has no offset. At this time, the output of the focus error signal becomes 0 in a state where the objective lens 105 is focused on the recording layer of the optical disc 21.
  • the rotation adjustment (around the optical axis) of the photodetector 120 is performed so that the first sub-beam 143a and the second sub-beam 143b are incident on substantially the center of the first sub-beam light-receiving area 141a and the second sub-beam light-receiving area 141b.
  • ⁇ Z is performed.
  • the focus error signal balance is adjusted by adjusting the position of the XY plane, the tracking error signal is adjusted in detail by adjusting the rotation around the optical axis ( ⁇ Z), and the focus offset of the focus error signal is adjusted by adjusting the position in the Z direction. Adjustments are made.
  • the first sub beam 143a and the second sub beam 143b are optically designed to be substantially incident on the first sub beam light receiving region 141a and the second sub beam light receiving region 141b. . Further, the entire photodetector 120 is rotationally adjusted around the optical axis center so that the amplitude of the tracking error signal is maximized. As a result, fine adjustment of the positional relationship between the first sub-beam 143a and the second sub-beam 143b and the first sub-beam light-receiving area 141a and the second sub-beam light-receiving area 141b is performed.
  • the RF signal is detected by adding all signals corresponding to the light amount of the light beam received by the four-divided light receiving region 140.
  • the metal holder 110 and the optical base 111 are bonded and fixed by the adhesive layer 113.
  • the optical axis of the photodetector 120 is adjusted so that the main beam 142 enters the approximate center of the four-divided light receiving region 140. Done.
  • the photodetector 120 and the metal holder 110 are fixed to the optical base 111 with the photodetector 120 positioned.
  • FIG. 11 is a diagram showing a configuration of the optical disc drive according to the second embodiment of the present invention.
  • the optical disk drive 20 includes an optical head 10, a motor 203, a traverse 204, a control circuit 205, a signal processing circuit 206, and an input / output circuit 207.
  • the optical disc 21 is sandwiched and fixed between a clamper 201 and a turntable 202 and is rotated by a motor (rotating system) 203.
  • the motor 203 rotates the optical disc 21.
  • the optical head 10 is on a traverse (transfer system) 204.
  • the traverse 204 moves the optical head 10 in the radial direction of the optical disc 21. Thereby, the irradiated light can be moved from the inner periphery to the outer periphery of the optical disc 21.
  • the control circuit 205 controls the optical head 10 and the motor 203.
  • the control circuit 205 performs focus control, tracking control, traverse control, rotation control of the motor 203, and the like based on the signal received from the optical head 10.
  • the signal processing circuit 206 reproduces information from the reproduction signal and outputs the information to the input / output circuit 207 or sends the recording signal input from the input / output circuit 207 to the optical head 10 through the control circuit 205.
  • the optical disk drive 20 corresponds to an example of an optical information device
  • the optical head 10 corresponds to an example of an optical head
  • the motor 203 corresponds to an example of a drive unit
  • the control circuit 205 corresponds to a control unit. It corresponds to an example.
  • FIG. 12A is a schematic diagram for explaining surface reflection from another layer in the two-layer optical disc 21, and FIG. 12B explains surface reflection from another layer in the multilayer optical disc 31.
  • FIG. 12A shows the configuration of the optical disc 21 having two recording layers, and shows how stray light is generated from other layers when the convergent light 300 is condensed on a certain recording layer.
  • the first recording layer L0 is focused, and in this case, the light reflected by the second recording layer L1 becomes the other layer stray light.
  • FIG. 12B shows the configuration of the optical disc 31 having four recording layers, and shows how stray light is generated from other layers when the convergent light 300 is condensed on a certain recording layer.
  • the third recording layer L2 is focused, and the light reflected by the first recording layer L0, the second recording layer L1, and the fourth recording layer L3 becomes the other layer stray light. .
  • the layer interval d2 between the first recording layer L0 and the second recording layer L1 is defined as 25 ⁇ 5 ⁇ m in the standard, and is 20 ⁇ m at the minimum or 20 ⁇ m at the maximum. 30 ⁇ m. Therefore, the magnitude of the other layer stray light on the photodetector 120 is limited to some extent.
  • the smallest layer interval d4min is likely to be smaller than that of the two-layer optical disc 21.
  • the layer interval between the third recording layer L2 and the fourth recording layer L3 is the layer interval d4min.
  • the farthest separated layer interval d4max is larger than that of the two-layer optical disc 21.
  • the magnitude of the other-layer stray light in the photodetector 120 is significantly larger than that of the two-layer optical disk 21.
  • the layer interval between the first recording layer L0 and the fourth recording layer L3 is the layer interval d4max.
  • the detection optical system has a larger magnification (lateral magnification ⁇ ) to receive a four-divided light receiving region 140 that receives the main beam 142, and a first sub beam that receives the first sub beam 143a and the second sub beam 143b.
  • the distance between the light receiving region 141a and the second sub-beam light receiving region 141b needs to be greatly separated.
  • FIG. 13A is a diagram showing the relationship between the distance between the main beam and the sub beam on the photodetector of the conventional optical head and the stray light in other layers
  • FIG. 13B is a diagram illustrating the implementation of the present invention. It is a figure which shows the relationship between the distance of the main beam on a photodetector of the optical head of form 2, and a sub beam, and other layer stray light.
  • the distance between the main beam 142 and the first sub beam 143a (or the second sub beam 143b) on the photodetector 120 is such that the main beam 142 and the first sub beam 143a (focused on the recording layer track of the optical disc 21).
  • the distance from the second sub beam 143b) is multiplied by the lateral magnification of the detection optical system.
  • the main beam 142 on the photodetector 120 is The distance from the first sub beam 143a (or the second sub beam 143b) is about 120 ⁇ m.
  • the lateral magnification of the detection optical system is about 10 to detect a stable tracking error signal. Double is required.
  • the distance between the main beam 142 and the first sub beam 143a (or the second sub beam 143b) is about 200 ⁇ m.
  • the interval between the main beam 142 and the first sub beam 143a (or the second sub beam 143b) on the track of the recording layer of the multilayer optical disk 31 is set to approximately 20 ⁇ m. Since this affects the offset of the tracking error when moving from the circumference to the circumference, the value is preset for each device, and a value in the range of 10 ⁇ m to 20 ⁇ m is generally selected.
  • the detection optical system in order to realize the miniaturization of the optical head 10, it is necessary to reduce the size of the detection optical system, and it is necessary to reduce the size of the detection optical system in consideration of the influence of other layer stray light. In consideration of the adverse effect of other layer stray light, it is necessary to increase the magnification of the detection optical system.
  • the detection optical system can be downsized with only the objective lens 105 and the collimator lens 104 while maintaining the lateral magnification.
  • the quadrant light receiving region 140, the first sub beam receiving region 141a, and the first sub light receiving region 141a and the first sub beam receiving region 141a and the first sub beam receiving region 141b are prevented from entering other layer stray light.
  • the lateral magnification of the detection optical system constituted by the concave lens surfaces of the objective lens 105, the collimator lens 104, and the cylindrical lens 108 is set to a range of about 14 to 16 times. It is desirable.
  • the distance between the four-divided light receiving region 140 and the first sub-beam light receiving region 141a and the first sub-beam light receiving region 141b is increased, so that the other layer stray light becomes the first sub-beam light receiving region 141a and By not entering the first sub-beam light receiving region 141b, a stable tracking error signal free from stray light offset and interference can be obtained.
  • the photodetector 120 does not include a resin package and wire bonding, but includes a glass package 125 and an adhesive layer 124, so that the quadrant light receiving region 140, the first sub-beam light receiving region 141a, and the first sub-beam light receiving region 141b are provided.
  • the photodetector 120 can be significantly downsized even if the area of the semiconductor silicon 121 is increased.
  • the photodetector 120 can be made small and thin, and the size can be reduced while increasing the magnification of the detection optical system in the return path of the optical head 10.
  • the optical head 10 can be miniaturized, and the optical disc drive 20 that can be miniaturized and compatible with multilayer optical discs can be realized.
  • the specifications of the multilayer antireflection layer 128, the glass package 125, the adhesive layer 124, and the like are configured so that the transmittance is maximized with respect to a light beam having a wavelength of 405 nm.
  • the transmittance in the quadrant light receiving region 140, the first sub-beam light receiving region 141a, and the first sub-beam light receiving region 141b with respect to an incident light beam having a wavelength of 405 nm can be 99% or more. Can significantly improve the light receiving sensitivity (mA / ⁇ W). Further, the S / N ratio of the RF signal can be greatly improved even when reproducing the multilayer optical disk 31 having a low reflectance.
  • the RF signal is generated from an addition signal obtained by adding a signal corresponding to the light beam received by the four-divided light receiving region 140.
  • the light beam for generating the RF signal is received exclusively.
  • An RF signal light receiving region may be provided, or an RF signal may be generated from the light beam received by the first sub-beam light receiving region 141a and the first sub-beam light receiving region 141b.
  • the cylindrical surface 108a is formed on the light incident side of the cylindrical lens 108 and the concave lens surface 108b is formed on the light emitting side.
  • the present invention is not particularly limited to this, and the cylindrical lens 108 is formed.
  • a concave lens surface may be formed on the light beam incident side, and a cylindrical surface may be formed on the light beam emission side.
  • the optical head in the third embodiment is different from the second embodiment in the tracking error signal detection method.
  • the tracking error signal is detected by the so-called three-beam method using the diffraction grating 102.
  • the so-called one-beam method (APP (advanced push-pull) method) using a hologram element is used. Tracking error signal is detected.
  • the arrangement of the light receiving regions of the light receiving unit 123 differs with the change in the tracking error signal detection method.
  • FIG. 14 is a diagram showing the configuration of the optical system of the optical head according to Embodiment 3 of the present invention.
  • an optical head 13 includes a semiconductor laser 101, a beam splitter 103, a collimator lens 104, an objective lens 105, an objective lens actuator 106, a cylindrical lens 108, a hologram element 150, a metal holder 110, a photodetector 220, and an FPC board. 126.
  • the semiconductor laser 101 emits a light beam having an oscillation wavelength of about 405 nm.
  • the hologram element 150 is disposed between the beam splitter 103 and the cylindrical lens 108, and divides an incident light beam into a light beam for generating a tracking error signal by a so-called one beam method (APP method).
  • the light beam emitted from the semiconductor laser 101 is reflected by the beam splitter 103, converted into a parallel light beam by the collimator lens 104, and enters the objective lens 105.
  • the objective lens 105 focuses the light beam emitted from the semiconductor laser 101 on the optical disk 21.
  • the objective lens 105 is driven in the optical axis direction (focus direction) and the tracking direction (radial direction) of the optical disk 21 by an objective lens actuator 106 (not shown in detail).
  • the light beam reflected and diffracted by the recording layer of the optical disc 21 passes through the objective lens 105 and the collimator lens 104 again and enters the beam splitter 103.
  • the light beam that has passed through the beam splitter 103 is divided into a plurality of parts by the hologram element 150 and enters the cylindrical lens 108.
  • the cylindrical lens 108 generates astigmatism in the reflected light beam reflected by the optical disk 21.
  • the light beam that has passed through the cylindrical lens 108 enters the photodetector 220.
  • the photodetector 220 detects a reflected light beam in which astigmatism is generated by the cylindrical lens 108.
  • FIG. 15 is a diagram showing a configuration of the hologram element 150 shown in FIG.
  • the solid line indicates the division pattern of the hologram element 150
  • the broken line indicates the shape of the light beam that passes through the hologram element 150.
  • the hologram element 150 includes a main beam region 151 where a main beam is incident, and first and second APPs where interference light between ⁇ first order light and zeroth order light diffracted by the recording layer of the optical disc 21 (31) is incident. It includes main regions 152 and 153 and first and second APP sub-regions 154 and 155 in which only the 0th-order light is incident.
  • the lateral magnification ( ⁇ ) of the detection optical system in the third embodiment is set to 14 to 16 times as in the second embodiment.
  • FIG. 16A is a side view showing the configuration of the photodetector in the third embodiment of the present invention
  • FIG. 16B is a front view showing the configuration of the photodetector in the third embodiment of the present invention.
  • the photodetector 220 includes a semiconductor silicon 221, an adhesive layer 124, a glass package 125, a multilayer antireflection layer 128, and a signal output unit 130.
  • the semiconductor silicon 221 includes a light receiving unit 223 and an arithmetic circuit 122. Note that a hatched line in FIG. 16B indicates a region where the adhesive layer 124 is formed.
  • a multilayer antireflection layer 128 having the same specifications as in the first embodiment is formed between the adhesive layer 124 and the semiconductor silicon 121.
  • a light receiving portion 223, an arithmetic circuit 122, and a signal output portion 130 are formed, and the glass package 125 is bonded onto the semiconductor silicon 221 with an adhesive layer 124.
  • a light receiving unit 223 and an arithmetic circuit 122 are formed on the light incident side surface of the semiconductor silicon 221, and a signal output unit 130 is formed on the surface facing the light incident side surface.
  • the configuration of the photodetector 220 other than the light receiving unit 223 is the same as the configuration of the photodetector 120 of the first embodiment.
  • the light receiving unit 223 receives the reflected light beam reflected by the optical disc 21.
  • the arithmetic circuit 122 performs a predetermined operation on the electrical signal obtained by photoelectrically converting the reflected light beam received by the light receiving unit 223.
  • the glass package 125 covers the light receiving unit 223 and the arithmetic circuit 122.
  • the light receiving unit 223 includes a quadrant light receiving region 240, a first APP main beam light receiving region 156, a second APP main beam light receiving region 157, a first APP sub beam light receiving region 158, and a second APP sub beam light receiving region 159. .
  • the light beam that has passed through each divided region of the hologram element 150 enters each light receiving region.
  • the light beam (main beam 142) transmitted through the main beam region 151 is incident on the four-divided light receiving region 240.
  • the light beam (APP main beam 165) transmitted through the first and second APP main regions 152 and 153 is incident on the first APP main beam light receiving region 156 and the second APP main beam light receiving region 157.
  • the light beam (APP sub-beam 166) transmitted through the first and second APP sub-regions 154 and 155 is incident on the first APP sub-beam receiving region 158 and the second APP sub-beam receiving region 159.
  • the focus error signal is generated by calculating the differential of the diagonal sum signal of the quadrant light receiving area 240, and the RF signal is generated by calculating the sum of all the signals of the quadrant light receiving area 240. .
  • a so-called push-pull signal is generated by obtaining a differential signal between the first and second APP main beam light receiving regions 156 and 157, and the generated push-pull signal and the first and second push-pull signals are generated.
  • a tracking error signal in the so-called APP method is generated.
  • FIG. 17 is a diagram for explaining a tracking error signal calculation method according to Embodiment 3 of the present invention.
  • the tracking error signal is calculated based on the following equation (3).
  • Tracking error signal (B1-B2) -k (B3-B4) (3)
  • B1 represents the output of the first APP main beam light receiving region 156
  • B2 represents the output of the second APP main beam light receiving region 157
  • B3 represents the first
  • the output of the APP sub-beam light receiving area 158 is represented
  • B4 represents the output of the second APP sub-beam light receiving area 159
  • k represents the gain.
  • the gain k is usually set to 0.5 to 5.
  • the photodetector can be greatly reduced in size, and the tracking error signal becomes a servo signal that is not affected by interference from other layers of stray light, and stable recording is achieved.
  • An optical head having performance and reproduction performance can be realized.
  • an optical head in which a tracking error signal is detected by the APP method can be reduced in size and can be adapted to the multilayer optical disk 31.
  • the four-divided light receiving region 240 corresponds to an example of the first light receiving region
  • 158 and 159 correspond to an example of a second light receiving region.
  • the multilayer antireflection layer 128 is formed between the semiconductor silicon 121 (221) and the adhesive layer 124, and the entire surface of the semiconductor silicon 121 (221) on the light beam incident side.
  • the present invention is not particularly limited to this.
  • FIG. 18 (A) is a diagram showing another example of the multilayer antireflection film of the photodetector in the second embodiment of the present invention
  • FIG. 18 (B) is a photodetection in the third embodiment of the present invention. It is a figure which shows another example of the multilayer antireflection film of a vessel.
  • the multilayer antireflection layer 128 is formed only on the surface of the four-divided light receiving region 140 (240) for generating an RF signal.
  • the multilayer antireflection layer on at least the quadrant light receiving region 140 (240) is composed of three or more antireflection films, and at least a part of the semiconductor silicon 121 (221) other than the quadrant light receiving region 140 (240).
  • the multilayer antireflection layer comprises a single layer or two layers of antireflection films.
  • the area of the multilayer antireflection layer 128 where the three antireflection films are deposited can be greatly reduced.
  • the time and man-hour required for the deposition of the antireflection film can be greatly reduced, and the thickness and refractive index specifications of each antireflection film can be relaxed.
  • the three-layer portion (first antireflection layer 128x) of the multilayer antireflection layer 128 is composed of a silicon-based nitride film, a silicon-based oxide film, and a silicon-based nitride film in order from the light beam incident side.
  • the silicon-based nitride film has a refractive index of 2.07
  • the silicon-based oxide film has a refractive index of 1.47
  • both the silicon-based nitride film and the silicon oxide film have a refractive index change of ⁇ 5%. .
  • each antireflection film of the three-layer portion (first antireflection layer 128x) of the multilayer antireflection layer 128 is 44.1 nm, 73.6 nm, and 47.1 nm in order from the light beam incident side.
  • Each antireflection film has a thickness change of ⁇ 10%.
  • the first antireflection layer 128x is not limited to three antireflection films, and may include four or more antireflection films.
  • the two-layer portion (second antireflection layer 128y) of the multilayer antireflection layer 128 is composed of a silicon-based oxide film and a silicon-based nitride film in order from the light beam incident side.
  • the silicon-based nitride film has a refractive index of 2.07
  • the silicon-based oxide film has a refractive index of 1.47
  • both the silicon-based nitride film and the silicon oxide film have a refractive index change of ⁇ 5%.
  • the thickness of each antireflection film of the two-layer portion (second antireflection layer 128y) of the multilayer antireflection layer 128 is 73.6 nm and 47.1 nm in order from the light beam incident side. Both have a thickness change of ⁇ 10%.
  • the antireflection film is composed of either a silicon nitride film or a silicon oxide film.
  • the optical head of the fourth embodiment is different from the second and third embodiments in that it is not only for a BD light source that emits light having a wavelength of 405 nm but also for a DVD that emits light having a wavelength of 650 nm. And a light source for CD that emits light having a wavelength of 780 nm are mounted, and it is possible to cope with multilayer BD, DVD and CD.
  • FIG. 19 is a diagram showing the configuration of the optical system of the optical head according to Embodiment 4 of the present invention.
  • the optical head 14 includes a diffraction grating 102, a beam splitter 103, a collimator lens 104, an objective lens 105, an objective lens actuator 106, a cylindrical lens 108, a metal holder 110, a photodetector 320, an FPC board 126, and a hologram element.
  • 150 a flat plate beam splitter 170, a blue semiconductor laser 191 and a two-wavelength semiconductor laser 192.
  • Blue semiconductor laser 191 emits blue light having a wavelength of 405 nm.
  • the two-wavelength semiconductor laser 192 emits red light having a wavelength of 650 nm and emits infrared light having a wavelength of 780 nm.
  • the flat beam splitter 170 reflects red light or infrared light emitted from the two-wavelength semiconductor laser 192 toward the objective lens 105 and reflects light (blue light, red light or red light) reflected by the optical disc 21 (31). Infrared light) is transmitted.
  • the photodetector 320 detects a reflected light beam in which astigmatism is generated by the cylindrical lens 108.
  • FIG. 20 is a front view showing the configuration of the photodetector in the fourth embodiment of the present invention.
  • the photodetector 320 includes a semiconductor silicon 321, an adhesive layer 124, a multilayer antireflection layer (not shown), and a glass package (not shown).
  • the semiconductor silicon 321 includes a light receiving unit 323, an arithmetic circuit 122, and a signal output unit (not shown). Note that hatched lines in FIG. 20 indicate regions where the adhesive layer 124 is formed.
  • the glass package is bonded to the multilayer antireflection layer by the adhesive layer 124.
  • the light receiving portion 323 and the arithmetic circuit 122 are formed on the light incident side surface of the semiconductor silicon 321, and the signal output portion is formed on the surface facing the light incident side surface.
  • the adhesive layer 124 is formed on the entire surface of the semiconductor silicon 321.
  • the configuration of the photodetector 320 other than the light receiving unit 323 is the same as that of the photodetector 120 of the first embodiment.
  • the light receiving unit 323 receives the reflected light beam reflected by the optical disc 21 (31).
  • the arithmetic circuit 122 performs a predetermined operation on the electrical signal obtained by photoelectrically converting the reflected light beam received by the light receiving unit 323.
  • the glass package covers the light receiving portion 323 and the arithmetic circuit 122.
  • the light receiving unit 323 includes a first four-divided light receiving region 180, a second four-divided light receiving region 161, a first APP main beam light receiving region 156, a second APP main beam light receiving region 157, and a first APP sub beam receiving region. 158, a second APP sub-beam receiving area 159, a first sub-beam receiving area 160a, a second sub-beam receiving area 160b, a third sub-beam receiving area 162a, and a fourth sub-beam receiving area 162b.
  • the first four-divided light receiving region 180 receives the blue main beam 142 having a wavelength of 405 nm and the red main beam 242 having a wavelength of 650 nm.
  • the first and second APP main beam light receiving regions 156 and 157 receive the blue light APP main beam 165 having a wavelength of 405 nm.
  • the first and second APP sub-beam light receiving regions 158 and 159 receive the blue light APP sub-beam 166 having a wavelength of 405 nm.
  • the first sub-beam receiving region 160a receives a first sub-beam 243a of red light having a wavelength of 650 nm
  • the second sub-beam receiving region 160b receives a second sub-beam 243b of red light having a wavelength of 650 nm.
  • a focus error signal is detected based on the main beam 242
  • a tracking error signal in the so-called three-beam method is detected based on the push-pull signal of the main beam 242 and the signals of the first sub beam 243a and the second sub beam 243b. Is done.
  • the second quadrant light receiving region 161 receives an infrared main beam 342 having a wavelength of 780 nm.
  • the third sub-beam receiving region 162a receives a first sub-beam 343a of infrared light having a wavelength of 780 nm
  • the fourth sub-beam receiving region 162b receives a second sub-beam 343b of infrared light having a wavelength of 780 nm. Is received.
  • a focus error signal is detected based on the main beam 342, and a tracking error signal in the so-called three-beam method is detected based on the push-pull signal of the main beam 342 and the signals of the first sub beam 343a and the second sub beam 343b. Is done.
  • BD and DVD RF signals are generated based on the amounts of light beams having a wavelength of 405 nm and a wavelength of 650 nm received by the first four-divided light receiving region 180, respectively. Further, an RF signal of the CD is generated based on the light amount of the light beam having a wavelength of 780 nm received by the second four-divided light receiving region 161.
  • the first antireflection layer 128x having three antireflection films, and the first four divisions.
  • a region other than the light receiving region 180 is configured by the second antireflection layer 128y having two antireflection films.
  • information can be recorded or reproduced on an optical disc (BD, DVD or CD) corresponding to light beams having three different wavelengths, and a single-layer or double-layer optical disc 21 is used.
  • information can be recorded on or reproduced from the multilayer optical disk 31. Therefore, it is possible to realize a small optical head and optical disk drive that have excellent recording characteristics and reproduction characteristics.
  • the first four-divided light receiving region 180 corresponds to an example of the first light receiving region
  • the sub beam receiving areas 158 and 159 correspond to an example of a second light receiving area.
  • the BD tracking error signal detection method in the fourth embodiment is a one-beam method (APP method), it is needless to say that a three-beam method may be used.
  • the fifth embodiment differs from the first to fourth embodiments in that the arithmetic circuit 122 does not improve the S / N of the reproduction signal by increasing the transmittance of the light receiving portions 123, 223, and 323.
  • the S / N of the reproduction signal is improved by reducing the noise level of the reproduction signal to be generated.
  • FIG. 21 is a diagram showing a partial configuration of the arithmetic circuit 122 of the photodetector 320 in FIG.
  • the configurations of the optical head and the photodetector in the fifth embodiment are the same as the configurations of the optical head 14 and the photodetector 320 in the fourth embodiment.
  • a light receiving region 180a indicates a 1ch light receiving region in the first four-divided light receiving region 180 in FIG. 20, and receives light beams for BD and DVD.
  • the first four-divided light receiving region 180 includes four light receiving regions 180a, 180b, 180c, and 180d.
  • the light receiving area 161a indicates a 1ch light receiving area in the second four-divided light receiving area 161 in FIG. 20, and receives a light beam for CD.
  • the second quadrant light receiving region 161 includes four light receiving regions 180a, 180b, 180c, and 180d.
  • the arithmetic circuit 122 includes a first differential amplifier circuit 182, a second differential amplifier circuit 183, a voltage amplifier circuit 184, and a switch 185.
  • the first differential amplifier circuit 182 shows a part of the first-stage current / voltage conversion circuit (I / V amplifier) for BD and DVD.
  • the first differential amplifier circuit 182 converts a current generated according to the amount of light received by the light receiving region 180a into a voltage using an amplification gain. That is, the first differential amplifier circuit 182 converts a current corresponding to the amount of light received by the light receiving region 180a into a voltage based on a plurality of preset gain modes.
  • the first differential amplifier circuit 182 includes a differential amplifier 41, first to third amplification gains 42, 43, 44, first to third switches 45, 46, 47, and a bias current output unit 48.
  • the differential amplifier 41 is shared by a plurality of gain modes.
  • the first to third amplification gains 42, 43, and 44 each have a predetermined resistance value.
  • the resistance values of the first to third amplification gains 42, 43, and 44 are 100 K ⁇ , 50 K ⁇ , and 30 K ⁇ .
  • the first switch 45 connects the differential amplifier 41 and the first amplification gain 42
  • the second switch 46 connects the differential amplifier 41 and the second amplification gain 43
  • the third switch 47 connects the differential amplifier 41 and the third amplification gain 44.
  • the photodetector 120 further includes a gain setting terminal unit to which a gain mode switching signal for switching a plurality of gain modes is input.
  • FIG. 22 is a back view of photodetector 120 in the fifth embodiment of the present invention. As shown in FIG. 22, the gain setting terminal portion 131 is formed along with the signal output portion 130 on the surface of the semiconductor silicon 121 facing the light incident side surface. A gain mode switching signal for switching a plurality of gain modes is input to the arithmetic circuit 122 via the gain setting terminal unit 131.
  • the plurality of gain modes include, for example, three gain modes, and any one of the first to third switches 45, 46, and 47 is turned on according to the gain mode switching signal.
  • the bias current output unit 48 outputs a bias current to the differential amplifier 41.
  • the second differential amplifier circuit 183 is a part of the first-stage current / voltage conversion circuit (I / V amplifier) for CD.
  • the second differential amplifier circuit 183 converts a current generated according to the amount of light received by the light receiving region 161a into a voltage using an amplification gain.
  • the second differential amplifier circuit 183 includes a differential amplifier 51, first to third amplification gains 52, 53, and 54, first to third switches 55, 56, and 57, and a bias current output unit 58.
  • the differential amplifier 51 is shared by a plurality of gain modes.
  • the first to third amplification gains 52, 53, and 54 each have a predetermined resistance value.
  • the resistance values of the first to third amplification gains 52, 53, and 54 are 100 K ⁇ , 50 K ⁇ , and 30 K ⁇ .
  • the first switch 55 connects the differential amplifier 51 and the first amplification gain 52
  • the second switch 56 connects the differential amplifier 51 and the second amplification gain 53
  • the third switch 57 connects the differential amplifier 51 and the third amplification gain 54.
  • a gain mode switching signal for switching a plurality of gain modes is input to the arithmetic circuit 122 via the gain setting terminal unit 131.
  • the plurality of gain modes include, for example, three gain modes, and one of the first to third switches 55, 56, and 57 is turned on in response to the gain mode switching signal.
  • the bias current output unit 58 outputs a bias current to the differential amplifier 51.
  • the voltage amplifying circuit 184 includes the first differential amplifying circuit 182 and the first amplifying circuit 182 so that the RF output has an optimum amplitude according to the set values of the differential amplifier 61 and the first to third amplification gains 62, 63, and 64.
  • the reproduction signal output from the second differential amplifier circuit 183 is amplified.
  • the voltage amplifier circuit 184 includes a differential amplifier 61, first to third amplification gains 62, 63, 64, first to third switches 65, 66, 67, and a bias current output unit 68.
  • the differential amplifier 61 is shared by a plurality of gain modes.
  • the first to third amplification gains 62, 63, 64 each have a predetermined resistance value.
  • the resistance values of the first to third amplification gains 62, 63, 64 are 100 K ⁇ , 50 K ⁇ , and 30 K ⁇ .
  • the first switch 65 connects the differential amplifier 61 and the first amplification gain 62
  • the second switch 66 connects the differential amplifier 61 and the second amplification gain 63
  • the third switch 67 connects the differential amplifier 61 and the third amplification gain 64.
  • a gain mode switching signal for switching a plurality of gain modes is input to the arithmetic circuit 122 via the gain setting terminal unit 131.
  • the plurality of gain modes include, for example, three gain modes, and one of the first to third switches 65, 66, and 67 is turned on according to the gain mode switching signal.
  • the bias current output unit 68 outputs a bias current to the differential amplifier 61.
  • the switch 185 is disposed between the first differential amplifier circuit 182, the second differential amplifier circuit 183, and the voltage amplifier circuit 184.
  • the switch 185 When recording or reproducing information on a BD or DVD, the switch 185 When the differential amplifier circuit 182 and the voltage amplifier circuit 184 are connected and information is recorded on or reproduced from the CD, the second differential amplifier circuit 183 and the voltage amplifier circuit 184 are connected.
  • the light receiving region 180a has a radiation sensitivity of 0.3 A / W with respect to a light beam having a wavelength of 405 nm.
  • the resistance value of the amplification gain 42 is 100 K ⁇
  • the I / V conversion gain is 30 mV / ⁇ W.
  • the first differential amplifier circuit 182 outputs a voltage of 300 mV
  • the voltage amplifier circuit 184 is output by the first differential amplifier circuit 182. The voltage is further amplified and output as an RF signal.
  • the light receiving area 180a shown in FIG. 21 is one channel among the four divided light receiving areas 180, and the four divided light receiving area 180 includes four light receiving areas 180a, 180b, 180c, and 180d.
  • Four first differential amplifier circuits 182 connected to the regions 180a, 180b, 180c, and 180d are provided. Therefore, in practice, all the signals output from the four first differential amplifier circuits 182 are added, input to the voltage amplifier circuit 184, and output from the voltage amplifier circuit 184 as an RF signal (reproduced signal).
  • the four-divided light receiving region 161 includes four light receiving regions 161a, 161b, 161c, and 161d, and the arithmetic circuit 122 includes four second differential amplifications connected to the respective light receiving regions 161a, 161b, 161c, and 161d.
  • a circuit 183 is provided.
  • the amplification factor of the first amplification gain 42 is the largest. Therefore, the first amplification gain 42 is used for reproducing a multilayer BD (optical disc 31) having a low reflectance.
  • the second amplification gain 43 is used for reproducing a single-layer or two-layer BD (optical disc 21) having a relatively high reflectance
  • the third amplification gain 44 having the lowest amplification factor is the optical disc 21 or the multilayer. Is used for recording on the optical disc 31 of the above. In the case of DVD, it is set separately.
  • the amplification gain of the voltage amplification circuit 184 is set in the same manner as described above.
  • the differential amplifier 41 when reproducing information from the multi-layer optical disk 31, the differential amplifier 41 is configured to lower the value of the bias current 49 of the differential amplifier 41 in order to reduce the noise of the reproduced signal and improve the S / N of the reproduced signal. Add low noise mode to switch internal resistance. That is, the differential amplifier 41 switches between a low noise mode that reduces noise included in the reproduction signal and a non-low noise mode that does not reduce noise included in the reproduction signal, and sets the bias current value in the low noise mode to non-low noise. Smaller than the bias current value in the mode.
  • the first amplifier gain 42 is used and the differential amplifier 41 is switched to the non-low noise mode.
  • the bias current value is about 200 ⁇ A.
  • the first amplifier gain 42 is used and the differential amplifier 41 is switched to the low noise mode.
  • the bias current value is about 100 ⁇ A.
  • the amplifier noise of the first differential amplifier circuit 182 at the first stage can be reduced by 2 to 3 dBm, the noise level of the RF signal (reproduced signal) can be greatly reduced, and the multilayer optical disk 31 can be reduced. Even in the reproduction of the reproduction signal, a reproduction signal excellent in S / N can be realized.
  • the same first amplification gain 42 is used in the non-low noise mode and the low noise mode, it is not necessary to provide different amplification gains in the non-low noise mode and the low noise mode, and the arithmetic circuit 122 is greatly reduced. Miniaturization can also be realized.
  • the differential amplifier 41 switches to the low noise mode when switching to the gain mode having the highest gain setting value among the plurality of gain modes, that is, the first amplification gain 42.
  • the higher the gain setting value the greater the noise, so if you switch to the gain mode with the highest gain setting value among multiple gain modes, you can reduce the noise by switching to the low noise mode, The S / N of the reproduction signal can be improved.
  • the first differential amplifier circuit 182 corresponds to an example of a current / voltage conversion circuit
  • the gain setting terminal unit 131 corresponds to an example of a gain setting terminal unit
  • the differential amplifier 41 is a difference. This corresponds to an example of a dynamic amplifier.
  • FIG. 23 is a diagram illustrating amplifier noise in the non-low noise mode and the low noise mode using the first amplification gain 42 of the first differential amplifier circuit 182.
  • the horizontal axis represents frequency
  • the vertical axis represents noise level.
  • FIG. 23 shows the relationship between the frequency and the noise level in the low noise mode and the relationship between the frequency and the noise level in the non-low noise mode.
  • FIG. 23 shows the result of measurement with a predetermined light receiving sensitivity, and noise reduction of 2 dB to 3 dB is possible in the frequency band (around 33 MHz) required when reproducing the multilayer optical disc 31 at double speed. Become.
  • the amplifier noise of the differential amplifier 41 can be reduced, but the frequency characteristic (f characteristic) of the RF signal is lowered.
  • the frequency when 3 dB is reduced is about 50 MHz
  • the frequency when 3 dB is reduced is about 100 MHz.
  • the four-divided light receiving region for receiving the DVD light beam is the same as the four-divided light receiving region for receiving the BD light beam.
  • the four-divided light receiving area for receiving the luminous flux for DVD may be the same, or the four-divided light receiving area for receiving the luminous flux for DVD and the four-divided light receiving area for receiving the luminous flux for CD may be the same.
  • the photodetector includes a four-divided light receiving region for receiving a DVD light beam and a four-divided light receiving region for receiving a CD light beam, but receives a BD light beam 4. Only a divided light receiving region may be provided.
  • the first-stage first differential amplifier circuit 182 has three amplification gains, but it goes without saying that the amplification gain may be increased or decreased according to the application.
  • the second differential amplifier circuit 183 and the voltage amplifier circuit 184 each have three amplification gains, but the amplification gain may be increased or decreased according to the application.
  • the first differential amplifier circuit 182 in the first stage is a so-called inverting amplification method, but may be a so-called non-inverting amplification method.
  • the second differential amplifier circuit 183 and the voltage amplifier circuit 184 may be a non-inverting amplifier system.
  • the photodetector 120 further includes a noise setting terminal unit 132 to which a noise mode switching signal for switching between a low noise mode and a non-low noise mode is input.
  • a noise setting terminal portion 132 is formed on the surface of the semiconductor silicon 121 that faces the light incident side surface together with the signal output portion 130 and the gain setting terminal portion 131.
  • a noise mode switching signal for switching between the low noise mode and the non-low noise mode is input to the arithmetic circuit 122 via the noise setting terminal unit 132.
  • the differential amplifier 41 switches the internal resistance in accordance with the noise mode switching signal and changes the bias current.
  • the bias current value in the low noise mode is 1 ⁇ 2 of the bias current value in the non-low noise mode.
  • the bias current value in the low noise mode is not low from the viewpoint of noise reduction. It may be 2/3 or less of the bias current value in the noise mode.
  • the first differential amplifier circuit 182 is preferably set to the gain mode with the largest amplification gain from the viewpoint of noise reduction.
  • a photodetector is a photodetector that detects a light beam reflected by an information recording medium, and photoelectrically converts a light receiving unit that receives the light beam and a light beam received by the light receiving unit. And a substrate formed with a calculation unit that performs a predetermined calculation on the electric signal obtained by this, and at least reflected on the incident information recording medium formed on the light receiving unit and the calculation unit.
  • a multilayer antireflection layer including a plurality of antireflection films to be prevented, a glass package that covers the multilayer antireflection layer, and an adhesive layer that bonds the multilayer antireflection layer and the glass package.
  • the substrate includes the light receiving unit that receives the light beam and the calculation unit that performs a predetermined calculation on the electrical signal obtained by photoelectrically converting the light beam received by the light receiving unit.
  • the multilayer antireflection layer includes a plurality of antireflection films that are formed on at least the light receiving unit and the calculation unit and prevent reflection of a light beam reflected by an incident information recording medium.
  • the glass package covers the multilayer antireflection layer.
  • the adhesive layer bonds the multilayer antireflection layer and the glass package.
  • the photodetector can be downsized. Can do.
  • the multilayer antireflection layer includes three layers of the antireflection film, and the three layers of antireflection films are sequentially formed from a light incident side, a silicon nitride film and a silicon oxide film.
  • a silicon nitride film is preferable.
  • the transmittance for a light beam having a wavelength of 405 nm between the glass package and the light receiving portion can be significantly improved without increasing the number of antireflection films included in the multilayer antireflection layer, and a wavelength of 650 nm.
  • the transmittance can be greatly improved even for a light beam having a wavelength of 780 nm.
  • the multilayer antireflection layer can be composed of three antireflection films, the number of steps for depositing the antireflection film can be greatly reduced.
  • the thickness of the adhesive layer is 30 ⁇ m or less, the transmittance of the adhesive layer is 99% or more with respect to a light beam having a wavelength of 405 nm, and the adhesive layer is made of silicon.
  • the antireflection film is formed on the surface of the glass package on which the light beam reflected by the information recording medium is incident, and the antireflection film is formed between the glass package and the adhesive layer. It is preferably not formed.
  • the S / N is excellent even if the reflectance of the information recording medium is low and the amount of reflected light from the information recording medium is small. Playback signal can be realized. Moreover, the adhesive strength between the glass package and the adhesive layer can be increased. Further, even if there is no antireflection film at the interface with the adhesive layer of the glass package, the transmittance is not lowered, and a photodetector with high reliability and excellent S / N can be realized.
  • the thickness of the adhesive layer is preferably 5 ⁇ m or more and 25 ⁇ m or less.
  • the thickness of the adhesive layer is not less than 5 ⁇ m and not more than 25 ⁇ m, so-called blue light by the light beam having a wavelength of 405 nm is maintained while maintaining high adhesive strength without deteriorating the transmittance for the light beam having a wavelength of 405 nm. Deterioration can be suppressed.
  • the adhesive layer is preferably formed on the entire surface between the glass package and the multilayer antireflection layer.
  • the adhesive layer is formed on the entire surface between the glass package and the multilayer antireflection layer, the adhesive strength can be increased.
  • the surface of the light receiving portion on the light beam incident side is covered with an adhesive layer, it is possible to prevent impurities from adhering to the light receiving portion and the glass package without an air layer on the light receiving portion. Therefore, a photodetector with excellent reliability can be realized.
  • the light receiving unit receives a first light receiving region for receiving a light beam for calculating a focus error signal, and a second light receiving region for receiving a light beam for calculating a tracking error signal.
  • the calculation unit preferably calculates a reproduction signal of the information recording medium based on a light beam received by the first light receiving region.
  • the light beam for calculating the focus error signal is received by the first light receiving region, and the light beam for calculating the tracking error signal is received by the second light receiving region.
  • the computing unit computes a reproduction signal of the information recording medium based on the light beam received by the first light receiving region.
  • the reproduction signal of the information recording medium is calculated based on the light beam received by the first light receiving region where the light beam for calculating the focus error signal is received, the light receiving region is calculated in order to calculate the focus error signal. Therefore, it is not necessary to prepare a light receiving region for calculating the reproduction signal separately, and the area of the light receiving unit can be reduced.
  • At least the multilayer antireflection layer on the first light receiving region includes three or more layers of the antireflection film, and at least a part of the substrate other than the first region.
  • the multilayer antireflection layer preferably comprises a single layer or two layers of the antireflection film.
  • the region where the antireflection film having three or more layers is formed is only at least on the first light receiving region, thereby reducing the region where the antireflection film having three or more layers is formed on the substrate.
  • the number of steps for depositing the antireflection film can be greatly reduced.
  • the calculation unit includes a current / voltage conversion circuit that converts a current corresponding to a light amount of a light beam received by the light receiving unit into a voltage based on a plurality of preset gain modes.
  • the photodetector further includes a gain setting terminal unit that is connected to the arithmetic unit and receives a signal for switching the plurality of gain modes, and the current / voltage conversion circuit includes the plurality of gain modes.
  • the differential amplifier switches between a low noise mode that reduces noise included in the reproduction signal and a non-low noise mode that does not reduce noise included in the reproduction signal.
  • the bias current value in the noise mode is preferably smaller than the bias current value in the non-low noise mode.
  • the current / voltage conversion circuit converts the current corresponding to the light amount of the light beam received by the light receiving unit into a voltage based on a plurality of preset gain modes.
  • a signal for switching a plurality of gain modes is input by a gain setting terminal unit connected to the calculation unit.
  • the current / voltage conversion circuit has a differential amplifier shared by a plurality of gain modes. The differential amplifier switches between a low noise mode that reduces the noise contained in the reproduced signal and a non-low noise mode that does not reduce the noise contained in the reproduced signal, and the bias current value in the low noise mode is biased in the non-low noise mode. Make it smaller than the current value.
  • the optimum gain mode can be selected according to the reproduction speed of the information recording medium and the reflectance of the recording layer. For example, when the reflectance of the recording layer is low or the information recording medium is reproduced at a low speed, the frequency characteristic of the reproduced signal is sacrificed by switching to a low noise mode that reduces noise contained in the reproduced signal. Noise can be reduced, and a reproduction signal with excellent S / N can be obtained. On the other hand, when the reflectivity of the recording layer is relatively high or when the information recording medium is played back at a high speed, reproduction with excellent frequency characteristics is possible by switching to a non-low noise mode that does not reduce the noise contained in the playback signal. A signal can be obtained.
  • the low-noise mode and the non-low-noise mode can be switched by the same differential amplifier, the area of the arithmetic unit does not increase even if the gain mode is increased, and the photodetector is further downsized. Can do. In addition, it is possible to cope with higher speed and lower noise of the reproduction signal.
  • the differential amplifier preferably sets the bias current value in the low noise mode to 2/3 or less of the bias current value in the non-low noise mode.
  • the amplifier noise is reduced and the S / N of the reproduction signal is greatly improved. be able to.
  • the mode when the gain mode having the highest gain setting value among the plurality of gain modes is switched, the mode is switched to the low noise mode. Therefore, the higher the gain setting value, the greater the noise, so when switching to the gain mode with the highest gain setting value among multiple gain modes, switching to the low noise mode can reduce the noise. And the S / N of the reproduction signal can be improved.
  • An optical head is an optical head for recording or reproducing information on an information recording medium having a recording layer, the light source emitting a light beam, and the light beam emitted from the light source as the information recording medium.
  • An objective lens that collects light on the light source, and a photodetector according to any one of the above that detects a light beam reflected by the information recording medium. According to this configuration, the above-described photodetector can be applied to the optical head.
  • An optical information device includes the above-described optical head, a drive unit for rotating an information recording medium, and a control unit that controls the optical head and the drive unit. According to this configuration, the optical head described above can be applied to an optical information device.
  • the photodetector, the optical head, and the optical information device according to the present invention can realize a stable tracking control function and a low information error rate, realize recording or reproduction of information on a multilayer information recording medium, and recording performance and reproduction. It is useful as an external storage device for a thin (slim size) computer with stable performance.
  • the photodetector, the optical head, and the optical information device according to the present invention are a video recording device such as a DVD recorder, a BD recorder, or an HD-DVD recorder, or a video reproducing device such as a DVD player, a BD player, or an HD-DVD player. It can also be applied to. Furthermore, the photodetector, the optical head, and the optical information device according to the present invention can be applied to a storage device of a car navigation system, a portable music player, a digital still camera, or a digital video camera.

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  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Head (AREA)
  • Light Receiving Elements (AREA)

Abstract

L'invention concerne un détecteur optique, une tête optique et un dispositif optique de lecture d'informations pouvant être de petite taille. Ledit détecteur optique (120) comporte : du silicium semi-conducteur (121) formant une unité optique de réception (123) qui permet de recevoir un faisceau lumineux, et un circuit de calcul (122) qui applique une opération donnée sur un signal électrique obtenu par conversion photoélectrique du faisceau lumineux reçu par ladite unité optique de réception (123) ; une couche anti-réflexion multicouche (128) qui se trouve au moins sur l'unité optique de réception (123) et sur le circuit de calcul (122) et qui comprend une pluralité de couches anti-réflexion servant à empêcher la réflexion d'un faisceau lumineux qui est incident sur un disque optique et réfléchi par ce dernier ; un boîtier en verre (125) qui recouvre la couche anti-réflexion multicouche (128) ; et une couche adhésive (124) qui assemble ladite couche anti-réflexion multicouche (128) et le boîtier en verre (125).
PCT/JP2011/003867 2010-07-09 2011-07-06 Détecteur optique, tête optique et dispositif optique de lecture d'informations WO2012004991A1 (fr)

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JP2008053583A (ja) * 2006-08-28 2008-03-06 Nec Corp 半導体受光素子及び半導体光集積素子
JP2009094573A (ja) * 2007-10-03 2009-04-30 Panasonic Corp 受光増幅装置

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