JP2000048392A - Optical pickup device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To obtain a low-priced, compact, lightweight and highly reliable optical pickup device. SOLUTION: An aperture and a diffraction grating are formed on a first entrance / exit surface 3a of a prism 3, and a hologram is formed on a second entrance / exit surface 3b. After the diameter of the light beam generated by the light beam generation unit 2 is selected by the aperture, the light beam is separated into three incident beams by a diffraction phenomenon by the diffraction grating. The incident beam is incident on the first slope 3c.
After that, the light is reflected by the second inclined surface 3d and reaches the second input / output surface 3b. Then, the light is condensed by the hologram diffraction phenomenon, and is irradiated on the surface of the recording medium 1 as an irradiation beam. The reflected beam reflected on the surface of the recording medium 1 is condensed by the hologram, and the second slope 3
After being deflected by d and reflected by the first slope 3c,
The light is detected by the light detection unit 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device, and more particularly to an optical pickup device that performs tracking control by a tracking error signal detection method using a three-beam method.

[0002]

2. Description of the Related Art In recent years, increasing the capacity of recording media such as optical disks and floppy disks has been promoted. Data recorded on the optical disk track is read using a light beam, but a light beam from a semiconductor laser or the like is used to keep the light beam at the pit position on the track following surface deflection due to rotation of the optical disk. Optical tracking control is performed. Further, not only optical disks but also magnetic disks such as floppy disks can be provided with a tracking pit array and by performing the same optical tracking control as an optical disk, data can be read reliably, and Reliability can be improved. For optical tracking control when reading data recorded on a floppy disk,
For example, Proceedings of the 58th JSAP Academic Lecture Meeting 5a-Z
Proceedings of E-6 and the 45th Alliance Lectures on Applied Physics 29
It is described in p-ZK-2.

FIG. 23 is a schematic diagram showing a configuration of a conventional optical pickup device. The coordinate system is set as shown in FIG. Reference numeral 100 denotes a recording medium such as an optical disk or a floppy disk,
A pit row for tracking is provided. Code 10
Reference numeral 1 denotes a light beam generator configured by, for example, a semiconductor laser or the like, which generates a light beam. Also, reference numeral 102
Is a diffraction grating, which deflects part of the incident light according to the pitch of the grating, thereby separating the incident light into a plurality of lights. Reference numeral 103 denotes an aperture, which passes only light having a required diameter among incident light and blocks other light. Reference numeral 104 denotes a beam splitter, as shown in FIG.
Incident light traveling in the plus Z direction passes through as it is, while incident light traveling in the minus Z direction is deflected in the minus Y direction. Reference numeral 105 denotes a lens, and reference numeral 106 denotes a light detection unit.

Next, the operation will be described. The light beam generator 101 generates a light beam, and the light beam is applied to the diffraction grating 102. The diffraction grating 102 converts the light beam emitted from the light beam generation unit 101 into a main beam IB0 corresponding to the zero-order diffracted light, a sub-beam IB + corresponding to the plus first-order diffracted light having a component in the plus X direction, and a minus X direction. The light beam is split into three light beams of a sub-beam IB- corresponding to the minus first-order diffracted light having the component. Main beam I separated by diffraction grating 102
B0 and sub-beams IB + and IB-
3 is incident. Then, beams other than the required diameter are blocked by the aperture 103, and only the light beam having the required diameter passes through the aperture 103. The main beam IB0 and the sub-beams IB +, I which have passed through the aperture 103
B- passes through the beam splitter 104 and passes through the lens 10
5 is irradiated. The lens 105 is the beam splitter 1
The main beam IB0 and the sub-beams IB + and IB- irradiated from the light source 04 are condensed and irradiated as an irradiation beam on a portion of the recording medium 100 where a pit row is formed. The irradiation beam applied to the recording medium 100
The reflected beam is condensed by the lens 105, deflected by the beam splitter 104 in the negative Y direction, and detected by the light detection unit 106.

FIG. 24 is a schematic view showing a state in which the surface of the recording medium 100 is irradiated with an irradiation beam. Recording medium 1
A plurality of pits 1 having a three-dimensional shape
There is provided a pit row for tracking in which 07 are arranged in a predetermined direction. The spots S +, S0, S- are beam spots corresponding to the sub beam IB +, the main beam IB0, and the sub beam IB-, respectively. As shown in the figure, spots S +, S0, S− are recorded on the recording medium 10.
0 in the X direction on the surface. At this time, spots S +,
The direction in which S0 and S− are arranged is slightly inclined with respect to the direction in which the pits 107 are arranged. The spot diameter of each spot is determined by the numerical aperture (NA) set by the aperture 103 and the lens 105.

FIG. 25 is a plan view schematically showing a state in which a reflected beam is applied to the light detecting section 106. FIG. The light detection unit 106 outputs the reflected beam R corresponding to the main beam IB0.
It has a light receiving unit 1060 for receiving B0, a light receiving unit 106+ for receiving a reflected beam RB + corresponding to the sub beam IB +, and a light receiving unit 106- for receiving a reflected beam RB- corresponding to the sub beam IB-. Light receiving unit 106+, 1
06-reflected beams RB + and RB-
Is converted into a voltage value and input to the two input terminals of the differential amplifier, whereby a tracking error signal can be obtained as an output of the differential amplifier.

[0007]

Since the conventional optical pickup device is configured as described above, the number of elements constituting the optical pickup device is large, and each element is independently configured. Therefore, it is difficult to reduce the cost, reduce the size and weight, and furthermore, it is difficult to set the optical arrangement, which is disadvantageous in terms of mass productivity.

The present invention has been made to solve such a problem, and an object of the present invention is to provide an inexpensive, compact, lightweight, and highly reliable optical pickup device.

[0009]

Means for Solving the Problems Claim 1 of the present invention
The optical pickup device described in the above, a light source, disposed between the light source and the tracking target, incident light from the light source is incident, a prism that irradiates the tracking target with irradiation light,
Light detection means for receiving reflected light from the tracking target with respect to the irradiation light and obtaining a tracking error signal,
The prism reflects an incident surface for irradiating incident light from the light source to the inside of the prism, an irradiating surface for irradiating the irradiation light from the inside of the prism to the tracking target, and reflects the incident light incident to the inside of the prism And a first reflection surface for separating the incident light into at least three or more light beams on one of the incident surface and the first reflection surface. Is a device in which light condensing means for converging three of the plurality of lights to obtain irradiation light is formed.

According to a second aspect of the present invention, there is provided the optical pickup device according to the first aspect, wherein the light having a predetermined diameter out of the light emitted from the light source is provided on the incident surface. A light diameter selecting means for obtaining incident light by passing through only the light path.

According to a third aspect of the present invention, there is provided the optical pickup device according to the first aspect, wherein the light separating means is a diffraction grating, and the diffraction grating is a first reflection device. It is characterized by being formed on a surface.

According to a fourth aspect of the present invention, there is provided the optical pickup device according to the second aspect, wherein the prism reflects the incident light reflected by the first reflecting surface. A second reflection surface for guiding the light to the irradiation surface, and the reflected light from the tracking target is made incident on the inside of the prism via the condensing means, and the first reflection surface is provided on the second reflection surface. Deflection means for deflecting the reflected light incident inside the prism is formed such that the reflected light travels on an optical path different from the optical path on which the incident light travels between the surface and the second reflecting surface, The light detecting means receives the reflected light deflected by the deflecting means.

According to a fifth aspect of the present invention, there is provided the optical pickup device according to the fourth aspect, wherein the surfaces of the first and second reflection surfaces are respectively covered with a metal film. It is characterized by being performed.

According to a sixth aspect of the present invention, there is provided an optical pickup device according to the first aspect, wherein the condensing means is a hologram having a sawtooth cross section. It is a feature.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a side view schematically showing a configuration of the optical pickup device according to Embodiment 1 of the present invention. The coordinate system is set as shown in FIG. In FIG. 1, reference numeral 1 denotes a recording medium such as an optical disk or a floppy disk, which has a pit array for tracking. Reference numeral 2 denotes a light beam generation unit constituted by, for example, a semiconductor laser or the like, which generates a light beam. Reference numeral 4 denotes a light detection unit. Reference numeral 3 denotes a prism disposed between the light beam generator 2 and the recording medium 1, and is formed as one block of, for example, a plastic material. As shown in FIG.
The first input / output surface 3a facing the light beam generator 2 and the photodetector 4, the second input / output surface 3b facing the recording medium 1, and the first input / output surface 3a are at 45 °. It has a first slope 3c intersecting at an angle, and a second slope 3d intersecting at 45 ° with the second entrance / exit surface 3b. Here, the first entrance / exit surface 3a and the second entrance / exit surface 3b are surfaces through which the light beam passes, and the first slope 3c and the second slope 3d are surfaces which internally reflect the light beam.

FIGS. 2 to 4 are diagrams specifically showing the structure of the first entrance / exit surface 3a. An aperture 5 and a diffraction grating 6 are formed on the first entrance / exit surface 3a. FIG. 2 shows the aperture 5 and the diffraction grating 6 of the first entrance / exit surface 3a from the X direction and FIG. Is equivalent to looking at each of the portions where. FIG. 4 shows the aperture 5 and the diffraction grating 6 viewed from the Z direction. FIG.
As shown in FIGS. 1 to 4, a conical taper in which the diameter of the upper surface circle is smaller than the diameter of the bottom surface circle is formed on the first entrance / exit surface 3 a, and the slope portion of the taper functions as the aperture 5. On the upper surface circle of the taper, uneven fringes extending in the Y direction are formed, and the uneven fringes function as the diffraction grating 6.

FIGS. 5 to 7 are views specifically showing the structure of the second slope 3d. The diffraction grating 7 is formed on the second inclined surface 3d, and FIG. 5 corresponds to a portion of the second inclined surface 3d where the diffraction grating 7 is formed viewed from the X direction. 6 shows the diffraction grating 7 from the Y direction, and FIG. 7 shows the diffraction grating 7 from the Z direction. As shown in FIGS. 5 to 7, uneven stripes extending in the X direction are formed on the second slope 3 d, and the uneven stripes function as the diffraction grating 7.

FIGS. 8 to 10 are diagrams specifically showing the structure of the second entrance / exit surface 3b. A hologram 8 is formed on the second entrance / exit surface 3b. FIG. 8 shows a portion of the second entrance / exit surface 3b where the hologram 8 is formed, as viewed from the X direction and FIG. Equivalent to what you saw.
FIG. 10 shows the hologram 8 viewed from the Z direction. As shown in FIGS. 8 to 10, the second entrance / exit surface 3 b
A pattern having a sawtooth cross section is formed symmetrically with respect to the Z axis, and this pattern functions as the hologram 8. This pattern can be formed by machining (turning) using a diamond tool or the like. FIG. 11 is a side view showing another structure of the hologram, and corresponds to a portion of the second entrance / exit surface 3b where the hologram 9 is formed, viewed from the X direction. FIG. 8 shows the hologram 8 having a sawtooth cross section,
As in the hologram 9 shown in FIG. 11, the cross-sectional shape may be stepped. The hologram has a function of condensing a light beam by utilizing a diffraction phenomenon. The hologram 8 having a sawtooth cross-sectional shape has a higher light-collecting efficiency than the hologram 9 having a step-like cross-sectional shape. ing. However, the hologram 9 can be formed by etching or the like, and is effective when a sawtooth pattern cannot be formed by machining. In a broad sense, the entire prism 3 shown in FIG. 1 can be called a hologram, but in the present specification, only the patterns shown in FIGS.

Next, a specific operation of the optical pickup device will be described. First, the light beam generator 2 generates a light beam (FIG. 1), and this light beam is applied to the aperture 5 (FIG. 2). The outer peripheral portion having a large diameter indicated by a broken line in FIG.
The light is applied to the tapered slope. The light beam applied to the slope of the taper is refracted as shown in the figure, and is not used for the optical pickup operation. On the other hand, aperture 5
The central portion having a small diameter indicated by a solid line in FIG. 2 of the light beam irradiated to the taper is irradiated to the tapered upper surface circular portion and used for the optical pickup operation. As described above, the aperture 5 has a function of selecting the diameter of the light beam emitted from the light beam generating unit 2, and the diameter of the light beam used for the optical pickup operation is determined by the diameter of the tapered upper surface circle. Can be set.

As shown in FIG. 3, a diffraction grating 6 is formed on the upper circular portion of the taper. Therefore, the light beam applied to the upper circular portion of the taper is changed by the diffraction phenomenon by the diffraction grating 6 into the main beam I corresponding to the zero-order diffracted light.
B0, a sub-beam IB + corresponding to a plus first-order diffracted light having a component in the plus X direction, and a sub-beam IB corresponding to a minus first-order diffracted light having a component in the minus X direction
The light beam is split into three light beams of-and is incident on the inside of the prism 3 as an incident beam. The incident beam that has entered the prism 3 is reflected by the first slope 3c in the plus Y direction as shown in FIG. 1 and reaches the second slope 3d.

As shown in FIG. 5, a diffraction grating 7 is formed on the second slope 3d. Therefore, the incident beam that has reached the second slope 3d from the first slope 3c is
In addition to the 0th-order diffracted light shown by the solid line in FIG. 5, for example, the first-order diffracted light shown by the broken line in FIG. These diffracted lights are reflected by the second inclined surface 3d as shown in FIG. 5, and reach the second input / output surface 3b.

As shown in FIG. 9, a hologram 8 is formed on the second entrance / exit surface 3b. Of the plurality of diffracted lights generated by the diffraction phenomenon by the diffraction grating 7, only the 0th-order diffracted light indicated by the solid line in FIG. Then, the light is condensed by the diffraction phenomenon of the hologram 8 and is irradiated as an irradiation beam on the surface of the recording medium 1 as shown in FIG. At this time, the irradiation beam applied to the hologram 8 includes components of a main beam IB0 shown by a solid line, a sub-beam IB + shown by a broken line, and a sub-beam IB- shown by a dashed line in FIG. Since the main beam IB0 and the sub-beams IB + and IB− have different positions when entering the hologram 8, the irradiation beam emitted from the hologram 8 is also an irradiation beam corresponding to the main beam IB0 and an irradiation beam corresponding to the sub-beam IB +. , And the irradiation beam corresponding to the sub-beam IB-.

FIG. 12 is a schematic diagram showing a state in which the surface of the recording medium 1 is irradiated with an irradiation beam. On the surface of the recording medium 1, there is provided a pit row for tracking in which a plurality of pits 10 having a three-dimensional shape are arranged in a predetermined direction. The spots S +, S0, S− are respectively a sub beam IB +, a main beam IB0, and a sub beam IB−.
Is a beam spot corresponding to. As shown in the figure,
The spots S +, S0, and S− are X on the surface of the recording medium 1.
Line up in the direction. At this time, the direction in which the spots S +, S0, S- are arranged is slightly inclined with respect to the direction in which the pits 10 are arranged. The spot diameter of each spot is determined by the numerical aperture (N) set by the aperture 5 and the hologram 8.
A).

The irradiation beam applied to the recording medium 1 is reflected on the surface of the recording medium 1, and the reflected beam is applied to the hologram 8
And reaches the second slope 3d. FIG.
FIG. 9 is a side view showing a state where the reflected beam is irradiated on the second inclined surface 3d, and corresponds to a portion of the second inclined surface 3d where the diffraction grating 7 is formed, viewed from the X direction. The reflected beam that has reached the second slope 3d from the hologram 8 is
The light is deflected by the second inclined surface 3d and reaches the first inclined surface 3c. At this time, the light is separated by a diffraction phenomenon by the diffraction grating 7, and in addition to the 0th-order diffracted light shown by the solid line in FIG. A first-order diffracted light is generated as shown in FIG. In detecting the reflected beam, the first-order diffracted light among these diffracted lights is used. By using the first-order diffracted light instead of the zero-order diffracted light for the detection of the reflected beam in this manner, the optical path in which the incident beam travels from the first slope 3c to the second slope 3d and the reflected beam is shifted to the second slope 3d
And the optical path traveling to the first slope 3c can be separated.

The reflected beam reaching the first slope 3c is
As shown in FIG. 1, the light is reflected by the first slope 3c and reaches a portion of the first entrance / exit surface 3a where the aperture 5 is not formed. Then, the light is refracted by the first entrance / exit surface 3 a and is irradiated on the light detection unit 4.

FIG. 14 is a plan view schematically showing a state in which a reflected beam is applied to the light detecting section 4, and corresponds to a view of the light receiving surface of the light detecting section 4 from the Z direction. Light detector 4
Is a light receiving unit 40 for receiving the reflected beam RB0 corresponding to the main beam IB0, a light receiving unit 4+ for receiving the reflected beam RB + corresponding to the sub beam IB +, and the sub beam I
A light-receiving unit 4 for receiving a reflected beam RB- corresponding to B-
have. By converting the irradiation amounts of the reflected beams RB + and RB- respectively radiated to the light receiving units 4+ and 4- into voltage values and inputting them to the two input terminals of the differential amplifier, respectively, the tracking error is output as the differential amplifier output. A signal can be obtained. Since the light detection unit 4 detects the first-order diffracted light in the diffraction grating 7 as a reflected beam, the beam spot on the light receiving surface of the light detection unit 4 becomes elliptical due to the effect of astigmatism. Therefore, as shown in FIG. 14, it is desirable that the shape of the light receiving sections 40, 4+, 4- be rectangular in accordance with this.

FIG. 15 is a side view schematically showing the structure of the prism 3 and corresponds to a view of the entire prism 3 viewed from the X direction. As shown in the figure, an antireflection film 15 is provided on the surface of the first entrance / exit surface 3a,
An anti-reflection film 16 may be provided on the surface b. In FIG. 15, hatched portions are ends of the antireflection films 15 and 16. Thereby, reflection when the incident beam or the reflected beam passes through the first and second entrance / exit surfaces 3a and 3b can be suppressed, and the utilization efficiency of the light beam can be increased.

As described above, according to the optical pickup device according to the first embodiment, the elements such as the diffraction grating 6 and the hologram 8 constituting the optical pickup device are formed in one block as the prism 3. Compared with the device, it is possible to reduce the cost and size and weight. Further, once the prism 3 is formed, there is no need to set the optical arrangement between the elements, so that the effect of excellent mass productivity and high reliability can be obtained.

Embodiment 2 In the first embodiment, the case where the diffraction grating 6 is formed on the first entrance / exit surface 3a has been described. However, instead of the first entrance / exit surface 3a, the first slope 3
c. 16 to 19 are diagrams schematically showing a structure of an optical pickup device according to Embodiment 2 of the present invention. In particular, FIG. 16 corresponds to a portion of the first entrance / exit surface 3a where the aperture 5 is formed and a portion of the first inclined surface 3c where the diffraction grating 12 is formed as viewed from the X direction. I do. 17 shows the diffraction grating 12 from the Y direction and FIG. 18 shows the diffraction grating 12 from the Z direction. Further, FIG. 19 is a cross-sectional view showing a cross-sectional structure of the diffraction grating 12, which corresponds to a cross-section of the diffraction grating 12 viewed from the YZ direction shown in FIG. As shown in FIGS. 16 to 19, the first inclined surface 3 c is formed with uneven stripes extending in the YZ directions shown in FIG. 16, and the uneven stripes function as the diffraction grating 12. An aperture 5 having the same structure and function as in the first embodiment is formed on the first entrance / exit surface 3a. The other structure of the optical pickup device according to the second embodiment is the same as that of the first embodiment.

Next, the operation will be described. As shown in FIG. 16, the incident beam that has entered the inside of the prism 3 from the aperture 5 reaches the first slope 3c,
Is reflected in the plus Y direction by the inclined surface 3c. At this time, the diffraction grating 12 is formed on the first slope 3c. Therefore, as shown in FIG. 19, the incident beam that has reached the first inclined surface 3c is converted into a main beam IB0 corresponding to the zero-order diffracted light and a plus first-order diffracted light having a component in the plus X direction by the diffraction phenomenon of the diffraction grating 12. And a sub-beam IB- corresponding to the minus first-order diffracted light having a component in the minus X direction.

The subsequent operation of the optical pickup device is the same as in the first embodiment. That is, the main beam IB0 and the sub beam IB separated by the diffraction grating 12
+, IB- are reflected in the plus Z direction on the second inclined surface 3d, condensed by the hologram 8, and radiated to the recording medium 1. Then, the reflected beam from the recording medium 1 enters the prism 3 through the hologram 8, is reflected by the second inclined surface 3d and the first inclined surface 3c, and is refracted by the first entrance / exit surface 3a. After that, the light is irradiated on the light detection unit 4.

FIG. 20 is a plan view schematically showing a state in which the surface of the recording medium 1 is irradiated with an irradiation beam. FIG.
As described above, in the optical pickup device according to the second embodiment, the diffraction grating 12 is formed not on the first entrance / exit surface 3a but on the first slope 3c. Therefore, the diffraction grating 1
The arrangement of the beam spots S00, S +, S- corresponding to the main beam IB0 and the sub-beams IB +, IB- separated by 2 deviates from the straight line on the surface of the recording medium 1 as shown in FIG. The amount of misalignment of the beam spots S00, S +, S- on the surface of the recording medium 1 is determined by the configuration of the prism 3. Therefore,
When obtaining a tracking error signal in the light detection unit 4,
A tracking error signal can be appropriately obtained by performing a process of electrically correcting the misalignment of the beam spots S00, S +, and S- in consideration of the misalignment.

As described above, according to the optical pickup device of the second embodiment, unlike the first embodiment, the diffraction grating 12 is not the first entrance / exit surface 3a but the first inclined surface 3a.
c. Therefore, the distance that the incident beam travels between the diffraction grating 12 and the hologram 8 in the second embodiment is longer than the distance that the incident beam travels between the diffraction grating 6 and the hologram 8 in the first embodiment. Be shorter. Therefore, the pitch between the gratings of the diffraction grating 12 according to the second embodiment can be set larger than that of the diffraction grating 6 according to the first embodiment.

Embodiment 3 FIG. 21 shows the first slope 3 of the optical pickup device according to Embodiment 3 of the present invention.
It is sectional drawing which expands and shows the structure of c. As shown in the figure, AI or Au having a high reflectance is provided on the surface of the first slope 3c.
A metal film 13 is provided. The metal film 13 can be added to the surface of the prism 3 by a method such as vapor deposition. In FIG. 21, the diffraction grating 12 is provided on the first slope 3c.
However, the metal film 13 may be provided on the surface of the first slope 3c in the first embodiment where the diffraction grating 12 is not formed.

FIG. 22 is an enlarged sectional view showing the structure of the second inclined surface 3d in the optical pickup device according to the third embodiment of the present invention. As shown in FIG.
The metal film 14 is provided on the surface of the inclined surface 3d. Metal film 14
Is made of AI, Au, or the like, like the metal film 13, and can be added to the surface of the prism 3 by a method such as vapor deposition.

Other structures and operations of the optical pickup device according to the third embodiment are the same as those of the above embodiments.

As described above, according to the optical pickup device of the third embodiment, the first slope 3c and the second slope 3c
Metal films 13 and 14 having high reflectivity were provided on the surface of d. Therefore, when the original plates of the diffraction gratings 12 and 7 are formed or when the prism 3 is formed, the surfaces of the first inclined surface 3c and the second inclined surface 3d become rough, and the light is incident on the first inclined surface 3c or the second inclined surface 3d. Even when a part of the beam or the reflected beam is scattered, it is possible to prevent the scattered light from leaking to the outside of the prism 3, and it is possible to increase the utilization efficiency of the light beam.

More specifically, as for the incident beam, of the incident beam scattered on the first slope 3c, the one reflected by the metal film 13 in the Y direction shown in FIG. 1 or on the second slope 3d. Among the scattered incident beams, those reflected by the metal film 14 in the Z direction shown in FIG. 1 can be used for the optical pickup operation.

Regarding the reflected beams, of the reflected beams scattered on the second inclined surface 3d or the first inclined surface 3c, respectively, in the direction in which the regular reflected beams not scattered by the metal films 14 and 13 travel. The reflected light can be used for the optical pickup operation.

[0040]

According to the first aspect of the present invention, the incident light is separated into a plurality of lights by the light separating means, and three of the lights are condensed by the light condensing means and directed to the tracking target. Irradiated. Then, the tracking error signal can be obtained by detecting the reflected light from the tracking target by the light detecting means. In addition, since the light separating means and the light condensing means are formed as one prism as one block, the cost and size and weight of the apparatus can be reduced as compared with a conventional optical pickup device in which these means are independently configured. In addition to this, once formed as a prism, it is not necessary to set the optical arrangement between the light separating means and the light collecting means.

According to the second aspect of the present invention, the diameter of the incident beam used for the optical pickup operation can be set by the light diameter selecting means.
In addition, since the light diameter selecting means is not formed independently of the light separating means and the condensing means, but is formed as a prism together with the light separating means and the condensing means, the cost and size and weight of the apparatus are reduced. Can be further promoted.

According to the third aspect of the present invention, the diffraction grating is formed on the first reflecting surface. Therefore, as compared with the case where the diffraction grating is formed on the incident surface, the distance that the incident light travels between the diffraction grating and the light condensing unit is shorter, so that the diffraction angle when the diffraction grating separates the incident light is smaller. That is, the pitch between the diffraction gratings can be set large.

According to the fourth aspect of the present invention, the deflecting means allows the incident light to travel from the first reflecting surface to the second reflecting surface.
And the optical path in which reflected light travels from the second reflective surface to the first reflective surface. Therefore, the tracking error signal can be appropriately obtained by the photodetector receiving the reflected light traveling on the optical path separated from the optical path of the incident light. Moreover, since the deflecting means is not formed independently of the light separating means and the condensing means, but is formed as a prism together with the light separating means and the condensing means, the cost and size and weight of the apparatus can be further reduced. Can be promoted.

According to the fifth aspect of the present invention, since the surfaces of the first and second reflecting surfaces are covered with a metal film having a high reflectivity, the surfaces of the first and second reflecting surfaces are covered. Even if some of the incident light and the reflected light are scattered on the surfaces of the first and second reflection surfaces, it is possible to prevent the scattered light from leaking out of the prism.

According to the sixth aspect of the present invention, the hologram, which is the light condensing means, has a sawtooth cross section, so that the light condensing efficiency of the incident light can be increased.

[Brief description of the drawings]

FIG. 1 is a side view schematically showing a configuration of an optical pickup device according to Embodiment 1 of the present invention.

FIG. 2 is a diagram specifically showing a structure of a first entrance / exit surface.

FIG. 3 is a view specifically showing a structure of a first entrance / exit surface.

FIG. 4 is a view specifically showing a structure of a first entrance / exit surface.

FIG. 5 is a view specifically showing a structure of a second slope.

FIG. 6 is a view specifically showing a structure of a second slope.

FIG. 7 is a view specifically showing a structure of a second slope.

FIG. 8 is a view specifically showing a structure of a second entrance / exit surface.

FIG. 9 is a view specifically showing a structure of a second entrance / exit surface.

FIG. 10 is a diagram specifically showing a structure of a second entrance / exit surface.

FIG. 11 is a side view showing another structure of the hologram.

FIG. 12 is a schematic diagram illustrating a state in which a surface of a recording medium is irradiated with an irradiation beam.

FIG. 13 is a side view showing a state where the second inclined surface is irradiated with a reflected beam.

FIG. 14 is a plan view schematically showing a state in which a light detection unit is irradiated with a reflected beam.

FIG. 15 is a side view schematically showing a structure of a prism.

FIG. 16 is a diagram schematically showing a structure of an optical pickup device according to a second embodiment of the present invention.

FIG. 17 is a drawing schematically showing a structure of an optical pickup device according to Embodiment 2 of the present invention.

FIG. 18 is a drawing schematically showing a structure of an optical pickup device according to Embodiment 2 of the present invention.

FIG. 19 is a view schematically showing a structure of an optical pickup device according to Embodiment 2 of the present invention.

FIG. 20 is a plan view schematically showing a state in which the surface of a recording medium is irradiated with an irradiation beam.

FIG. 21 is an enlarged sectional view showing a structure of a first slope in the optical pickup device according to Embodiment 3 of the present invention.

FIG. 22 is an enlarged sectional view showing the structure of a second slope in the optical pickup device according to Embodiment 3 of the present invention.

FIG. 23 is a view schematically showing a configuration of a conventional optical pickup device.

FIG. 24 is a plan view schematically showing a state in which a surface of a recording medium is irradiated with an irradiation beam.

FIG. 25 is a plan view schematically showing a state in which a light detection unit is irradiated with a reflected beam.

[Explanation of symbols]

1 recording medium, 2 light beam generator, 3 prism, 3
a first entrance / exit surface, 3b second entrance / exit surface, 3c first slope, 3d second slope, 4 photodetector, 5 aperture, 6, 7, 12 diffraction grating, 8, 9 hologram, 13 , 14 metal films.

Continued on the front page (72) Inventor Tatsunori Hihara 2-3-2 Marunouchi, Chiyoda-ku, Tokyo, Japan Mitsubishi Electric Corporation (72) Inventor Naoto Sugawa 2-3-2, Marunouchi, Chiyoda-ku, Tokyo, Mitsubishi F-term (reference) in Denki Co., Ltd. 5D119 AA01 AA04 AA40 AA43 BB03 DA01 DA05 EA02 JA07 JA13 JA30 JA47

Claims (6)

[Claims] 1. A light source, a prism disposed between the light source and a tracking target, a prism that receives incident light from the light source and irradiates the tracking target with irradiation light, and a prism that irradiates the tracking target with the irradiation light. And a light detecting means for receiving a reflected light of the prism to obtain a tracking error signal, wherein the prism is configured to input the incident light from the light source to the inside of the prism; Having an irradiation surface for irradiating the tracking target from inside of the prism, and a first reflection surface for reflecting the incident light incident on the inside of the prism, wherein the incident surface and the first reflection On one of the faces,
A light separating means for separating the incident light into at least three or more lights is formed, and a light collecting means for collecting three lights of the plurality of lights to obtain the irradiation light on the irradiation surface. Optical pickup device on which is formed. 2. The light incident surface according to claim 1, wherein a light diameter selecting means for obtaining the incident light by passing only light having a predetermined diameter out of the light emitted from the light source is formed on the incident surface. Optical pickup device. 3. The optical pickup device according to claim 1, wherein said light separating means is a diffraction grating, and said diffraction grating is formed on said first reflection surface. 4. The prism further includes a second reflection surface for reflecting the incident light reflected on the first reflection surface and guiding the incident light to the irradiation surface, and the reflection from the tracking target. Light is incident on the inside of the prism via the condensing means, and the incident light travels between the first reflection surface and the second reflection surface on the second reflection surface. A deflecting unit for deflecting the reflected light incident inside the prism is formed such that the reflected light travels along an optical path different from the optical path, and the light detection unit is deflected by the deflecting unit. The optical pickup device according to claim 2, wherein the optical pickup device receives the reflected light. 5. The optical pickup device according to claim 4, wherein the surfaces of the first and second reflection surfaces are respectively covered with a metal film. 6. The optical pickup device according to claim 1, wherein the light condensing means is a hologram having a sawtooth cross section.