JP2008004135A - Leakage prism and optical pickup - Google Patents

Abstract

A leakage prism that separates an appropriate amount for a front monitor from the amount of light emitted from each laser diode in a 405 nm band, a 650 nm band, and a 780 nm band, and 3 using the same
Get with wave light pickup.
Three laser diodes (LD) 2, 6, 8 for CD, DVD and blue wavelength band
And three diffraction gratings 3, 7, and 9 for CD, DVD, and blue wavelength band, a first wavelength synthesis prism 4 that synthesizes light for CD and DVD, and for CD, DVD, and blue wavelength band. Second to synthesize light
Wavelength synthesis prism 5, leakage prism 10, CD, DVD, P for blue wavelength band
A BS 11, a quarter-wave plate 12, a collimating lens 13, a photodetector 15, and a front monitor 16 are provided.
[Selection] Figure 1

Description

The present invention relates to an optical pickup used for recording and reproduction of CD (Compact disc), DVD (Digital Versatile Disc) and optical discs in a blue wavelength band, and in particular, a leakage prism improved so as to monitor the amount of laser light, and the use thereof The present invention relates to a three-wavelength optical pickup.

In recent years, an optical pickup used in an optical disk recording / reproducing apparatus is a CD (780 nm band).
In addition, an optical pickup in which a plurality of laser beams having different wavelengths are integrated according to applications such as DVD (650 nm band) is employed. An example using a CD / DVD both-recording type optical pickup is disclosed in Patent Document 1. FIG. 9 is a schematic diagram showing the configuration of a two-wave (CD, DVD) optical pickup 31, which includes semiconductor laser diodes (hereinafter referred to as LDs) 32 and 35, diffraction gratings 33 and 36, and first and second elements. Polarization beam splitters (hereinafter referred to as PBS) 34, 38
A front monitor 37, a quarter-wave plate 39, a collimating lens 40, a rising mirror 41, an objective lens 42, a sensor lens 43, and a photodetector 44.

FIG. 10A shows a polarizing film 34 of a first polarizing beam splitter (hereinafter referred to as PBS) 34.
a is a diagram showing the spectral characteristics of a, and P-polarized light having a wavelength of about 780 nm used for CD is a polarizing film 3
With 4a, about 10% of the light quantity is transmitted and about 90% is reflected. About 90% of the light amount of P-polarized light having a wavelength of about 650 nm used for DVD is transmitted by the polarizing film 34a, and about 10% of the light amount is reflected. FIG. 10B is a diagram showing the spectral characteristics of the polarizing film 38a of the second PBS 38, in which P-polarized light is transmitted and S-polarized light is reflected.

The P-polarized light having a wavelength of 780 nm that is emitted from the LD 32 in FIG. 9 is divided into three beams by the diffraction grating 33, is incident on the first PBS 34, and about 90% of the light quantity is reflected by the polarizing film 34a. , The traveling direction is changed by 90 degrees and the light is incident on the second PBS 38. About 10% of P-polarized light that has passed through the polarizing film 34 a enters the front monitor 37. On the other hand, P-polarized light having a wavelength of 650 nm band emitted from the LD 35 is divided into three beams by the diffraction grating 36, and the first P
About 90% of the amount of light is incident on the BS 34 and transmitted by the polarizing film 34a, and the second PBS.
Proceed to 38. About 10% of P-polarized light reflected by the polarizing film 34 a enters the front monitor 37. Nearly 100% of the P-polarized light having wavelengths of about 650 nm and 780 nm incident on the second PBS 38 is transmitted due to the characteristics of the polarizing film 38a, enters the quarter-wave plate 39, is converted into circularly polarized light, and is further collimated. The light is converted into parallel light by the lens 40, converted upward 90 degrees by the rising mirror 41, collected by the objective lens 42, and focused on the surface of the optical disk (not shown).

The reflected light from the surface of the optical disk becomes reversely polarized circularly polarized light, enters the quarter-wave plate 39 through the objective lens 42, the rising mirror 41, and the collimating lens 40, and is converted into S-polarized light. 2 enters the PBS 38. The incident S-polarized light is the polarizing film 38 of the second PBS 38.
The light is totally reflected by a, enters the photodetector 44 through the sensor lens 43, and the information is decoded. In addition, about 10% of the amount of light emitted from the LDs 32 and 35 is guided to the monitor 37. By an APC (auto power controller) connected to the front monitor 37,
The drive signal levels of the drivers of the LDs 32 and 35 are controlled so that the signal level of the front monitor 37 becomes the reference level. APC including this monitor is described in detail in Patent Document 2.
JP 2004-110897 A JP 2002-185073 A

However, the first PBS 34 for pickup of the conventional DVD and CD corresponding to two wavelengths is used.
The polarizing film 34a is composed of several tens of layers, and a blue wavelength band, DVD,
When trying to manufacture a polarizing film that transmits about 95% of the light of three waves of CD and reflects about 5%, there is a problem that the film thickness accuracy of each layer becomes extremely strict. Further, the polarizing film has wavelength dependency, and it is difficult to meet the required specifications, and there is a problem that the manufacturing yield is extremely poor.
The present invention reflects a leakage prism that reflects about 5% and transmits about 95% of the amount of light emitted from each light emitting diode in the blue wavelength band, DVD, and CD, and 3 using this.
The object is to provide an optical pickup for wavelength.

The present invention is to improve a leakage prism in order to accurately and easily manufacture an optical device for separating the monitoring light quantity of a three-wavelength optical pickup, and to form an optical pickup that supports three wavelengths by using this. It is characterized by. A hexahedral prism formed by bonding two triangular prisms each having an angle of 45 degrees with an inclined surface to each other and an optical adhesive, and an approximately 52 nm SiO ₂ thin film is provided on one of the inclined surfaces. The leakage prism is configured to transmit about 95% of S-polarized light having a wavelength of 370 nm to 850 nm and reflect about 5%.
When the leakage prism is configured as described above, there is a feature that a polarizing film can be easily configured, and a polarizing film that can be accurately separated with no wavelength dependency can be obtained.

Two triangular prisms each having an angle of 45 degrees with a surface opposed to the inclined surface are hexahedral prisms formed by bonding the inclined surfaces to each other with an optical adhesive, and a plurality of dielectric thin films are provided on one of the inclined surfaces, A leakage prism having a wavelength of 370 nm to 850 nm S-polarized light and transmitting about 95% and reflecting about 5% is configured.
When the leakage prism is configured as described above, there is a feature that a polarizing film can be easily configured, and a polarizing film that can be accurately separated with no wavelength dependency can be obtained.

A leakage prism is formed using SiO ₂ , Al ₂ O ₃ , lanthanum aluminate, or the like as the multilayer dielectric.
When the leakage prism is configured as described above, there is a feature that a polarizing film can be easily configured, and a polarizing film that can be accurately separated with no wavelength dependency can be obtained.

The present invention also provides a light source that emits light of three different wavelengths, a diffraction grating that corresponds to three different wavelengths, an objective lens that focuses the emitted light from the light source onto an optical recording medium, and the light source that is emitted from the light source. A light amount detecting means for detecting the amount of light detected and a light detecting means for detecting the reflected light from the optical recording medium, and recording or / and reproducing information detected by the light detecting means on the optical recording medium. A three-wave optical pickup, in the optical path between the light source and the objective lens,
The leakage prism according to the present invention is arranged to split the light emitted from the light source to the light amount detecting means.
When an optical pickup for three wavelengths is configured in this way, a light quantity separation device can be easily configured, and the wavelength dependence is good and the separation accuracy is good, and the characteristics of the APC function are improved.

The parts arranged adjacent to each other in the optical component are bonded together using an optical adhesive.
An optical pickup for wavelength is configured.
Thus, when the optical pickup for three wavelengths is configured, there is an effect that the optical pickup can be miniaturized.

Embodiments according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of a 780 nm band CD, a 650 nm band DVD, and a 405 nm band (blue-violet wavelength band) optical pickup 1 according to the present invention. First laser diode (LD) 2, 6, 8, CD, DVD, three diffraction gratings 3, 7, 9 for blue wavelength band, and light for CD, DVD Wavelength synthesis prism 4 and CD, D
A second wavelength synthesis prism 5 that synthesizes light for VD and blue wavelength bands, and a leakage prism 1
0, CD, DVD, PBS 11 for blue wavelength band, quarter wavelength plate 12, collimator lens 13, photodetector 15, and front monitor 16. Where CD, D
It is assumed that S-polarized laser beams S1, S2, and S3 are emitted from the three LDs 2, 6, and 8 for the VD and blue wavelength bands, respectively.

Before describing the operation of the optical pickup 1 shown in FIG. 1, an optical device used for this will be described. FIG. 2 is a perspective view showing the configuration of the leakage prism 10 according to the present invention. A hexahedral prism (leakage prism) in which two triangular prisms each having an angle of 45 degrees with an inclined surface are bonded to each other with an optical adhesive, and the one shown in FIG. As shown in Example 1, this is a leakage prism provided with a SiO ₂ thin film of approximately 52 nm. The spectral characteristic of this leakage prism is a wavelength of 3 as indicated by Ts in FIG.
Transmits about 95% of S-polarized laser light of 70 nm to 850 nm, and the spectral characteristic R in FIG.
As shown by s, this is a leakage prism having a characteristic of reflecting about 5% of S-polarized laser light. As described above, the light quantity separation of the leakage prism is characterized by high accuracy and very little wavelength dependency.

4, 5, and 6 respectively show a first wavelength synthesis prism 4, a second wavelength synthesis prism 5,
This is an example of the spectral characteristics of the PBS 11 and designed by a well-known optical filter theory. The first wavelength combining prism 4 has a 780 nm band (for CD) as shown in the spectral characteristics of FIG.
The S-polarized laser beam is reflected, and the S-polarized laser beam in the 650 nm band (for DVD) is transmitted. The second wavelength combining prism 5 has C as shown in the spectral characteristics of FIG.
S-polarized laser light for D and DVD is transmitted, and S-polarized laser light in the 405 nm band is reflected. PBS 11 is a CD, as shown in the spectral characteristics of FIG.
DVD, S-polarized laser light for blue wavelength band is reflected and P-polarized laser light is transmitted. Here, Rs in FIG. 6 represents the reflectance of S-polarized light, and Tp represents the transmittance of P-polarized light.

The S-polarized laser light (S1) emitted from the LD 2 for CD shown in FIG. 1 is transmitted through the diffraction grating 3, reflected by the polarizing film 4a of the first wavelength synthesis prism 4, and changes the traveling direction by 90 degrees. Then, the light enters the second wavelength combining prism 5. On the other hand, the S-polarized laser light (S2) emitted from the LD 6 for DVD passes through the diffraction grating 7 and enters the first wavelength combining prism 4. First
The S-polarized light S2 incident on the wavelength combining prism 4 passes through the polarizing film 4a and enters the second wavelength combining prism 5. S-polarized laser beams S 1 and S 2 for CD and DVD pass through the polarizing film 5 a of the second wavelength combining prism 5 and enter the leakage prism 10. On the other hand, the S-polarized laser light (S3) emitted from the LD 8 for the blue wavelength band passes through the diffraction grating 9, enters the second wavelength combining prism 5, is reflected by the polarizing film 5a, and travels in the traveling direction. The light is incident on the leakage prism 10 by changing it by 90 degrees.

S-polarized laser light S for CD, DVD, and blue wavelength band incident on the leakage prism 10
In S 1, S 2, and S 3, about 95% of the amount of incident light is transmitted through the polarizing film 10 a as indicated by Ts in the spectral characteristics of FIG. On the other hand, the spectral characteristic R in FIG.
As shown in s, about 5% of the incident light quantity is reflected and enters the front monitor 16. S-polarized laser light for CD, DVD, and blue wavelength band incident on the polarizing beam splitter 11 is substantially reflected by the polarizing film 11a, and is incident on the quarter-wave plate 12 by changing the traveling direction by 90 degrees. When transmitting, it is converted to circularly polarized light. The circularly polarized light emitted from the quarter-wave plate 12 is converted into parallel light by the collimator lens 13, collected by an objective lens (not shown), and focused on the surface of the optical disk 14.

The circularly polarized light reflected from the surface of the optical disk 14 becomes reversely rotated circularly polarized light, enters the quarter-wave plate 12 through an objective lens and a collimating lens 13 (not shown), and passes through this when passing through it.
It is converted into polarized light (P1, P2, P3) and enters the PBS 11. P incident on PBS11
The polarized light passes through the polarizing film 11a of the PBS 11 and enters the photodetector 15, and the information is decoded.
As described in the prior art, about 5% of the light incident on the front monitor 16 controls the drive signal levels of the drivers of the LD2, 6, and 8 so that the signal level of the front monitor 16 becomes the reference level. Used.

Conventionally, about 10% of the amount of light was separated by PBS and made incident on the front monitor. However, when trying to produce a polarizing film of PBS for CD, DVD, and blue wavelength band of 3 wavelengths, several tens of thin films are stacked. In addition, the film thickness required strict accuracy. In addition, the polarizing film has wavelength dependency and it is extremely difficult to satisfy the required specifications. As shown in FIGS. 2 and 3, the present invention is characterized by using a leakage prism in which a single SiO ₂ thin film of approximately 52 nm is formed.
The amount of light for the front monitor can be separated. As shown in FIG. 3, the leakage prism according to the present invention has a feature that it is not dependent on wavelength and is easy to manufacture.

In addition to the 52 nm SiO ₂ thin film of Example 1 shown in FIG. 2, a leakage prism having a thin film configuration of Examples 2, 3 and the like shown in FIG. Example 2 is a leakage prism having a three-layer thin film structure, in which 100 nm of SiO ₂ , 22 nm of Al ₂ O ₃ , and 62 nm of SiO ₂ are laminated on the slope of the prism. The spectral characteristics of Example 2 are shown in FIG. Ts and Rs represent S-polarized light transmittance (%) and reflectance (%), respectively. As is apparent from this figure, the wavelength is 370 n.
For S-polarized light from m to 850 nm, the transmittance Ts (%) and the reflectance Rs (%) are about 9 respectively.
5%, about 5%. The transmittance (%) and reflectance (%) for P-polarized light are indicated by Tp and Rp.

Example 3 is a leakage prism having a 6-layer thin film structure, and a 9 nm Al ₂ O ₃ film is formed on the slope of the prism.
, 99 nm lanthanum aluminate (mixed oxide of La and Al ₂ O ₃ ), 35 nm Si
O ₂ , 53 nm Al ₂ O ₃ , 49 nm SiO ₂ , and 15 nm Al ₂ O ₃ are laminated. The spectral characteristics of Example 3 are shown in FIG. The spectral characteristics of FIG. 8 also show substantially the same characteristics as the spectral characteristics shown in FIG.
In addition to the examples shown in the first to third embodiments, various types of leakage prisms can be designed.

In this embodiment, the leakage prism 10 is arranged at the subsequent stage of the second wavelength synthesis prism 5, but this is only an example, and the leakage prism 10 includes an objective lens (not shown) and a second wavelength. It can be placed at any position in the optical path to the combining prism 5.

In order to explain the function of each optical component in the three-wavelength optical pickup shown in FIG.
Although shown individually, the pickup can be miniaturized by bonding two or more parts together. In FIG. 1, four prisms, that is, the first wavelength synthesis prism 4, the second wavelength synthesis prism 5, the leakage prism 10, and the PBS 11 are used, but for example, the first wavelength synthesis prism 4 and The second wavelength synthesis prism 5 may be bonded together, or the second wavelength synthesis prism 5, the leakage prism 10 and the PBS 11 may be bonded together. PBS
11 and the quarter wave plate 12 may be bonded together.

1 is a schematic configuration diagram showing a configuration of an optical pickup according to the present invention. The perspective view which shows the structure of the leakage prism concerning this invention The spectral characteristic figure of the leakage prism concerning this invention. The spectral characteristic figure of a 1st wavelength synthetic | combination prism. The spectral characteristic figure of a 2nd wavelength synthetic | combination prism. The spectral characteristic figure of a polarization beam splitter. FIG. 6 is a spectral characteristic diagram of a leakage prism of Example 2 according to the present invention. FIG. 6 is a spectral characteristic diagram of a leakage prism according to a third embodiment of the present invention. The schematic block diagram which showed the structure of the conventional 2 wave optical pick-up. (A), (b) is a spectral characteristic figure of a polarization beam splitter, respectively.

Explanation of symbols

1, 3 wave optical pickup, 2, 6, 8 laser diode, 3, 7, 9 diffraction grating, 4
First wavelength combining prism, 4a, 5a, 10a Polarizing film, 5 Second wavelength combining prism, 10 Leakage prism, 11 Polarizing beam splitter, 12 1/4 wavelength plate, 13
Collimating lens, 14 optical disc, 15 photodetector, 16 front monitor, S1
, S2, S3 S polarized light, P1, P2, P3 P polarized light, Ts S polarized light transmittance, Rs S polarized light reflectance, Tp P polarized light transmittance

Claims (5)

A prism prism formed by bonding two triangular prisms each having an angle of 45 degrees with an inclined surface to each other, and attaching the inclined surfaces to each other with an optical adhesive,
A leakage prism having an approximately 52 nm SiO ₂ thin film on one of the inclined surfaces, transmitting about 95% of S-polarized light having a wavelength of 370 nm to 850 nm and reflecting about 5%. A leakage prism comprising two triangular prisms each having an angle of 45 degrees with a surface opposed to a slope, wherein the slopes are bonded together with an optical adhesive,
A leakage prism comprising a plurality of dielectric thin films provided on one of the inclined surfaces, and transmitting about 95% of light having a wavelength of 370 nm to 850 nm and reflecting about 5%. The SiO _2, Al ₂ O ₃ as a dielectric, Lee Kek di prism according to claim 2, characterized by using a lanthanum aluminate. A light source that emits light of three different wavelengths, a diffraction grating corresponding to three different wavelengths, an objective lens that collects the emitted light from the light source onto an optical recording medium, and the amount of light emitted from the light source are detected. A light amount detecting means, and a light detecting means for detecting reflected light from the optical recording medium,
A three-wavelength optical pickup for recording or / and reproducing information detected by the light detection means on the optical recording medium;
4. The leakage prism according to claim 1, wherein light leakage from the light source is split into the light amount detection unit in an optical path between the light source and the objective lens. 5. Features an optical pickup. The optical pickup according to claim 4, wherein the components arranged adjacent to each other in the optical component are bonded together using an optical adhesive.

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