JP3047351B2 - Optical head device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device for recording and reproducing information on and from an optical recording medium, and more particularly to an optical head device for recording and reproducing information on and from two types of optical recording media having different substrate thicknesses. The present invention relates to a hook device.

[0002]

2. Description of the Related Art In recent years, standardization of large-capacity optical disks such as digital video disks has been promoted. One of the standards for digital video discs is to use a disc having a substrate thickness of 0.6 mm. On the other hand, in a standard such as a conventional compact disk, a disk having a substrate thickness of 1.2 mm is used. Therefore, an optical head device capable of reproducing both a digital video disk and a compact disk is desired. However, in an ordinary optical head device, since the objective lens is designed to cancel spherical aberration with respect to a disk having a certain substrate thickness, spherical aberration remains with respect to a disk having a different substrate thickness. , Can not be played correctly.

As a conventional optical head device capable of reproducing both a digital video disk and a compact disk,
There is an example described in Optical Review, Vol. 1, No. 1, pp. 27-29. FIG. 22 shows a configuration of a conventional optical head device. A hologram optical element 145 is provided in the optical system, and the transmitted light (0th-order light) is used for reproducing a disk having a substrate thickness of 0.6 mm, and the + 1st-order diffracted light is used for reproducing a disk having a substrate thickness of 1.2 mm. About half of the light emitted from the semiconductor laser 143 is reflected by the half mirror 144, is collimated by the collimator lens 4, and becomes a hologram optical element 145.
Incident on. The light transmitted through the hologram optical element 145 is incident on the objective lens 6 as parallel light, and is focused on the disk 7 having a substrate thickness of 0.6 mm. The reflected light from the disk 7 passes through the objective lens 6 in the opposite direction, and is again divided into transmitted light and + 1st-order diffracted light by the hologram optical element 145. on the other hand,
The + 1st-order diffracted light of the hologram optical element 145 is incident on the objective lens 6 as divergent light, and is converged on the disk 8 having a substrate thickness of 1.2 mm. The reflected light from the disk 8 is transmitted through the objective lens 6 in the opposite direction, and again the hologram optical element 14
At 5, the light is divided into transmitted light and + 1st-order diffracted light. Of the reflected light from the disk 7, the transmitted light of the hologram optical element 145,
The + 1st-order diffracted light of the hologram optical element 145 among the reflected light from the disk 8 is incident on the collimator lens 4 as parallel light. About half of the transmitted light of the collimator lens 4 is transmitted through the half mirror 144 and the concave lens 146
And is received by the photodetector 147. Photodetector 14
Reference numeral 7 denotes a four-division light receiving unit. The focus error signal is detected by an astigmatism method using astigmatism generated by the half mirror 144, and the track / error signal is detected by a push-pull method. The reproduced signal is detected from the sum of the outputs of the four-divided light receiving unit.

The objective lens 6 has a spherical aberration for canceling a spherical aberration generated when light emitted from the objective lens 6 passes through a substrate having a thickness of 0.6 mm.
Reference numeral 5 denotes a spherical surface for canceling the sum of the spherical aberration generated when the light emitted from the objective lens 6 passes through the 1.2 mm-thick substrate and the spherical aberration of the objective lens 6 with respect to the + 1st-order diffracted light of the hologram optical element 145. Has aberration. Therefore, the transmitted light of the hologram optical element 145 is condensed on the disk 7 by the objective lens 6 without aberration, and the + 1st-order diffracted light of the hologram optical element 145 is collected by the objective lens 6 on the disk 8.
It is condensed on the top without aberration. FIG. 23 is a plan view of the hologram optical element 145. The hologram optical element 145 has a pattern of concentric interference fringes, and functions as a concave lens for the + 1st-order diffracted light together with the above-described spherical aberration correction. Therefore, the focusing position of the + 1st-order diffracted light on the disk 8 can be made farther than the focusing position of the transmitted light on the disk 7 with respect to the objective lens 6, and the distance from the objective lens 6 to the surface of the disks 7, 8 can be reduced. Can be almost equal.

[0005]

In the conventional optical head device shown in FIG. 22, since the incident light is divided into transmitted light and + 1st-order diffracted light by the hologram optical element 145, the utilization efficiency for each light is reduced. There was a problem. FIG. 24 is a sectional view of the hologram optical element 145. FIG.
(A) is a case where the cross section is rectangular, and unnecessary -1st-order diffracted light is generated with the same efficiency as the + 1st-order diffracted light. FIG. 24B shows a case where the cross section is saw-toothed, and the efficiency of + 1st-order diffracted light increases and the efficiency of unnecessary -1st-order diffracted light decreases. At this time,
The height of the sawtooth region is 2 h, the refractive index is n, and the wavelength of the incident light is λ.
Then, the transmittance η ₀ and the + 1st-order diffraction efficiency η ₊₁ are given by the following equations. η ₀ = sin ² φ / φ ² (1) η ₊₁ = sin ² φ / (φ−π) ² (2) where φ = 2π (n−1) h / λ (3) φ = π / 2 When η ₀ and η ₊₁ are equal, η ₀ = η ₊₁ =
0.405. The round trip utilization efficiency in this case is η ₀ ²
= Η ₊ ¹² = 0.164. Therefore, the semiconductor laser 1
Assuming that the output of 43 is the same as that of a normal optical head device, the amount of light received by the photodetector 147 is only 0.164 times that of the normal optical head device, and the S / N of the reproduction signal is reduced. In order for the amount of light received by the photodetector 147 to be the same as that of a normal optical head device, the output of the semiconductor laser 143 needs to be increased to 6.10 times that of a normal optical head device. In order to perform recording as well as reproduction of the disks 7 and 8, it is necessary to further increase the output of the semiconductor laser 143, which is practically impossible.

The conventional optical head device shown in FIG. 22 also has a problem with the wavelength of the semiconductor laser. The digital video disk standard uses a semiconductor laser having a wavelength of 635 nm to 655 nm, whereas the conventional compact disk standard uses a semiconductor laser having a wavelength of 785 nm. In the conventional optical head device, in order to reproduce a digital video disk having a higher density than a compact disk, it is necessary to use a semiconductor laser having a wavelength of 635 nm to 655 nm, which can reduce the focused spot diameter as compared with the wavelength of 785 nm. On the other hand, as one type of compact disc, there is a write-once compact disc called CD-R. This uses an organic dye as a recording medium. A high reflectance of 70% or more can be obtained at a wavelength of 785 nm, but a very low reflectance of about 10% can be obtained at a wavelength of 635 nm to 655 nm. For this reason, the conventional optical head device cannot reproduce a write-once compact disc.

Therefore, the problem to be solved by the present invention is:
For two types of disks having different substrate thicknesses, the S / N of the reproduced signal can be maintained at the same level as when a disk having one type of substrate thickness is used, without increasing the output of the semiconductor laser. An object of the present invention is to provide an optical head device capable of reproducing data including a write-once compact disc and also capable of recording.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical head device comprising two semiconductor lasers oscillating at different wavelengths, an optical multiplex that transmits light of one wavelength and reflects light of the other wavelength. Means for transmitting light of one wavelength substantially 100%,
The problem can be solved by providing a hologram optical element capable of extracting the −1st or + 1st order diffracted light of the light of the other wavelength with high efficiency.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical head device according to the present invention comprises a first semiconductor laser oscillating at a first wavelength, a second semiconductor laser oscillating at a second wavelength, and the first semiconductor laser. Multiplexing means capable of multiplexing the outgoing light of the second semiconductor laser and the outgoing light of the second semiconductor laser, a hologram optical element for guiding the outgoing light of each semiconductor laser to the first or second optical recording medium, and an objective A lens and a light detection unit that receives reflected light from an optical recording medium of light emitted from the first and second semiconductor lasers and is provided on an optically opposite side of the optical multiplexing unit on the hologram optical element side. With, before
Transmittance of the hologram optical element for the first wavelength
Is higher than the transmittance for the second wavelength, and
The −1st order diffraction efficiency for the second wavelength is higher than the first wavelength.
Against have been made higher than the -1-order diffraction efficiency, by using the -1-order diffracted light of the hologram the by the optical element the first semiconductor laser transmitted beam and the second semiconductor laser, or of the hologram optical element Said
The + 1st-order diffraction efficiency for the first wavelength is higher than the second wavelength.
Higher than the + 1st-order diffraction efficiency, and the second wavelength
Is higher than the transmittance for the first wavelength.
By using + 1st-order diffracted light of the first semiconductor laser by the hologram optical element and transmitted light of the second semiconductor laser, the emitted light of the first semiconductor laser is subjected to first optical recording. Medium, guide the emitted light of the second semiconductor laser to a second optical recording medium thicker than the first semiconductor laser, so that reproduction or reproduction and recording can be performed on each optical recording medium. It was done.

[0010] More preferably, the objective lens has a spherical aberration for canceling a spherical aberration generated when light transmitted from the hologram optical element passes through a substrate of an optical recording medium to which the transmitted light is guided, The hologram optical element has a spherical aberration and a + 1st-order diffracted light or a -1st-order diffracted light of the hologram optical element, which are generated when light emitted from the objective lens passes through a substrate of an optical recording medium to which the emitted light is guided. The objective lens has a spherical aberration that cancels the sum of the spherical aberration and the objective lens.

As described above, the optical head device of the present invention has a semiconductor laser and a hologram optical element having two different wavelengths, and uses one of the semiconductor lasers and transmitted light of the hologram optical element to emit one of the discs. Play,
Using the + 1st-order or -1st-order diffracted light of the hologram optical element emitted from the other semiconductor laser, the other disc having a substrate thickness different from that of one disc is reproduced. Since the transmittance of the hologram optical element and the ± first-order diffraction efficiency depend on the wavelength of the incident light, a transmittance close to 100% is obtained for the wavelength of one semiconductor laser, and the transmittance for the wavelength of the other semiconductor laser is obtained. Higher + 1st order diffraction efficiency or -1
By designing such that the next diffraction efficiency can be obtained, the S / N of the reproduced signal becomes almost the same as usual, the output of the semiconductor laser is almost the same as usual, and not only reproduction but also recording can be performed. Become. By setting the wavelength of one of the semiconductor lasers to 785 nm, it is possible to reproduce a write-once compact disc.

[0012]

Next, an embodiment of the present invention will be described with reference to the drawings. [First Embodiment] FIG. 1 shows the structure of an optical head device according to a first embodiment of the present invention. Each of the modules 1 and 2 includes a semiconductor laser and a detection optical system that receives light reflected from a disk. The wavelength of the semiconductor laser in the module 1 is 635 nm, and the wavelength of the semiconductor laser in the module 2 is 785 nm. Wavelength filter 3
Transmits light with a wavelength of 635 nm almost completely, and a wavelength of 7
It functions to reflect 85 nm light almost completely. Light emitted from the semiconductor laser in the module 1 passes through the wavelength filter 3, is collimated by the collimator lens 4, and enters the hologram optical element 5. The light transmitted through the hologram optical element 5 enters the objective lens 6 as parallel light, and is focused on a disk 7 having a substrate thickness of 0.6 mm. The reflected light from the disk 7 passes through the objective lens 6 in the opposite direction, and again enters the hologram optical element 5. The transmitted light of the hologram optical element 5 enters the collimator lens 4 as parallel light.
The transmitted light of the collimator lens 4 passes through the wavelength filter 3 and is received by the detection optical system in the module 1.

On the other hand, light emitted from the semiconductor laser in the module 2 is reflected by the wavelength filter 3, collimated by the collimator lens 4, and enters the hologram optical element 5. The -1st-order diffracted light from the hologram optical element 5 enters the objective lens 6 as divergent light, and is condensed on a disk 8 having a substrate thickness of 1.2 mm. The reflected light from the disk 8 is transmitted through the objective lens 6 in the opposite direction, and is incident on the hologram optical element 5 again. The -1st-order diffracted light of the hologram optical element 5 enters the collimator lens 4 as parallel light. Light transmitted through the collimator lens 4 is reflected by the wavelength filter 3 and received by the detection optical system in the module 2. The hologram optical element 5 and the objective lens 6 are driven integrally by an actuator.

The objective lens 6 has a spherical aberration for canceling a spherical aberration generated when light emitted from the objective lens 6 having a wavelength of 635 nm passes through a substrate having a thickness of 0.6 mm. Spherical aberration that cancels out the sum of the spherical aberration generated when the outgoing light from the objective lens 6 having a wavelength of 785 nm passes through a substrate having a thickness of 1.2 mm and the spherical aberration of the objective lens 6 with respect to the -1st-order diffracted light of the element 5 Having. Therefore, the transmitted light of the hologram optical element 5 having a wavelength of 635 nm is converged on the disk 7 by the objective lens 6 without aberration, and the -1st-order diffracted light of the hologram optical element 5 having the wavelength of 785 nm is not collected on the disk 8 by the objective lens 6. It is collected by aberration. The hologram optical element 5 is configured as shown in FIG.
Has a pattern of concentric interference fringes like the hologram optical element 145 shown in (1), and functions as a concave lens for the -1st-order diffracted light together with the above-described spherical aberration correction.
Therefore, with respect to the objective lens 6, the condensing position of the −1st-order diffracted light on the disk 8 can be made farther than the condensing position of the transmitted light on the disk 7.
Can be made substantially equal in distance to the surface.

FIG. 2 is an enlarged view of a cross section of the hologram optical element 5. By making the cross section not a rectangular shape but a step shape of four levels as shown in the figure, the efficiency of the -1st-order diffracted light increases and the efficiency of the unnecessary + 1st-order diffracted light decreases. FIG. 2A shows a case where SiO ₂ 10 is deposited on a glass substrate 9, and FIG. 2B shows a case where the glass substrate 14 is etched. In both cases, two photomasks are used for fabrication. In FIG. 2A, deposition of the region 11 is performed using the first photomask, and deposition of the regions 12 and 13 is performed using the second photomask. FIG. 2 (b)
Then, the region 15 is etched using the first photomask, and the region 1 is etched using the second photomask.
6 and 17 parts are etched.

At this time, the height or depth of each step is defined as h /
2. Assuming that the refractive index is n and the wavelength of the incident light is λ, the transmittance η
₀ , the + 1st-order diffraction efficiency η ₊₁ , and the -1st-order diffraction efficiency η _-1 are given by the following equations. η ₀ = cos ² (φ / 2) cos ² (φ / 4) (4) η ₊₁ = (8 / π ² ) sin ² (φ / 2) cos ² [(φ-π) / 4] (5 ) Η ₋₁ = (8 / π ² ) sin ² (φ / 2) cos ² [(φ + π) / 4] (6) where φ = 2π (n−1) h / λ (7) For example, h = 2 .76 μm, n = 1.46, λ = 6
Since φ = 4π for 35 nm, η ₀ = 1, η ₊₁
= 0, η _-1 = 0, and for λ = 785 nm, φ =
Since 3.23π, η ₀ = 0.085, η ₊₁ = 0.0
23, η _-1 = 0.686. In this case, the round trip utilization efficiency is η ₀ ² = 1 for λ = 635 nm, and
= The eta _-1 ² = 0.471 for 785 nm.

Accordingly, with respect to the wavelength of 635 nm, the S / N of the reproduction signal of the disk 7 is almost the same as usual, and the output of the semiconductor laser in the module 1 is almost the same as usual. It is also possible to record. On the other hand, regarding the wavelength of 785 nm, assuming that the output of the semiconductor laser in the module 2 is the same as that of a normal optical head device, the amount of light received by the detection optical system in the module 2 is 0.471 times that of the normal optical head device. However, at this level, the S / N of the reproduced signal of the disk 8 hardly decreases. Further, in order for the amount of light received by the detection optical system in the module 2 to be the same as that of a normal optical head device, the output of the semiconductor laser in the module 2 is set to 2.
Although it is necessary to increase it by a factor of 12, it can be easily realized with this degree. In addition, since the wavelength of the semiconductor laser in the module 2 is 785 nm, reproduction is possible even when the disk 8 is a write-once compact disk.

FIG. 3 is an overall sectional view of the hologram optical element 5. Assuming that the effective diameter of the objective lens 6 is 2a, the pattern of the interference fringes is formed only in the area of the smaller diameter 2b. Outside the region of the diameter 2b, the wavelength 635n
The light of m, 785 nm is completely transmitted through the hologram optical element 5. Therefore, the light having the wavelength of 635 nm causes the hologram optical element 5 to be 100% over the entire area of the diameter 2a.
The transmitted light having a wavelength of 785 nm is 68.8% as -1st-order diffracted light by the hologram optical element 5 in the area of the light 2b.
Is diffracted, and is not diffracted at all outside the region of the diameter 2b.
Assuming that the focal length of the objective lens 6 is f, a wavelength of 635 n
The effective numerical apertures for light of m and 785 nm are given by a / f and b / f, respectively. For example, f = 2.6m
If m, a = 1.56 mm and b = 1.17 mm, a
/F=0.6 and b / f = 0.45.

[Second Embodiment] FIG. 4 shows the configuration of an optical head device according to a second embodiment of the present invention. Each of the modules 1 and 2 includes a semiconductor laser and a detection optical system that receives light reflected from a disk. The wavelength of the semiconductor laser in the module 1 is 635 nm, and the wavelength of the semiconductor laser in the module 2 is 785 nm. The wavelength filter 3 has a function of transmitting light having a wavelength of 635 nm almost completely and reflecting light having a wavelength of 785 nm almost completely. Light emitted from the semiconductor laser in the module 1 passes through the wavelength filter 3, is collimated by the collimator lens 4, and enters the hologram optical element 18. The + 1st-order diffracted light of the hologram optical element 18 enters the objective lens 19 as convergent light, and is condensed on the disk 7 having a substrate thickness of 0.6 mm. The reflected light from the disk 7 passes through the objective lens 19 in the opposite direction, and enters the hologram optical element 18 again. The + 1st-order diffracted light of the hologram optical element 18 enters the collimator lens 4 as parallel light. The transmitted light of the collimator lens 4 passes through the wavelength filter 3 and is received by the detection optical system in the module 1. On the other hand, the emitted light from the semiconductor laser in the module 2 is reflected by the wavelength filter 3,
The light is collimated by the collimator lens 4 and enters the hologram optical element 18. The light transmitted through the hologram optical element 18 enters the objective lens 19 as parallel light and has a substrate thickness of 1.2.
The light is condensed on a disc 8 mm. The reflected light from the disk 8 passes through the objective lens 19 in the opposite direction, and again enters the hologram optical element 18. The transmitted light of the hologram optical element 18 enters the collimator lens 4 as parallel light.
Light transmitted through the collimator lens 4 is reflected by the wavelength filter 3 and received by the detection optical system in the module 2. The hologram optical element 18 and the objective lens 19 are driven integrally by an actuator.

The objective lens 19 has a spherical aberration that cancels the spherical aberration generated when the light emitted from the objective lens 19 having a wavelength of 785 nm passes through a substrate having a thickness of 1.2 mm. + Of element 18
The first-order diffracted light has spherical aberration that cancels out the sum of the spherical aberration generated when the light emitted from the objective lens 19 having a wavelength of 635 nm passes through the substrate having a thickness of 0.6 mm and the spherical aberration of the objective lens 19. Therefore, the + 1st-order diffracted light of the hologram optical element 18 having a wavelength of 635 nm is
Is focused on the disk 7 with no aberration, and the wavelength is 785n
m of the hologram optical element 18 is transmitted through the objective lens 19
As a result, the light is focused on the disk 8 with no aberration. The hologram optical element 18 is a hologram optical element 14 shown in FIG.
Similar to 5, it has a pattern of concentric interference fringes, and acts as a convex lens for the + 1st-order diffracted light together with the above-described spherical aberration correction. Therefore, the focusing position of the + 1st-order diffracted light on the disk 7 can be closer to the objective lens 19 than the focusing position of the transmitted light on the disk 8, and the distance from the objective lens 19 to the surfaces of the disks 7 and 8 can be reduced. Can be almost equal.

FIG. 5 is an enlarged view of a cross section of the hologram optical element 18. By making the cross section not a rectangular shape but a step shape of four levels as shown in the figure, the efficiency of the + 1st-order diffracted light increases and the efficiency of the unnecessary -1st-order diffracted light decreases. FIG. 5A shows a case in which SiO ₂ 21 is deposited on a glass substrate 20 to produce the substrate. FIG. 5B shows a case in which the glass substrate 25 is produced by etching. In both cases, two photomasks are used for fabrication. In FIG. 5A, deposition is performed on the region 22 using the first photomask, and deposition is performed on the regions 23 and 24 using the second photomask. FIG.
In (b), the region 26 is etched using the first photomask, and the regions 27 and 28 are etched using the second photomask. At this time, assuming that the height or depth of each step is h / 2, the refractive index is n, and the wavelength of the incident light is λ, the transmittance η ₀ , the + 1st-order diffraction efficiency η ₊₁ , and the −1st-order diffraction efficiency η _{− 1} is given by equations (4) to (7). For example, when h = 3.45 μm and n = 1.46, λ = 635n
Since φ = 5π for m, η ₀ = 0, η ₊₁ = 0.
811, η _-1 = 0, and φ for λ = 785 nm
= 4.04π, η ₀ = 0.995, η ₊₁ = 0.
002, η _-1 = 0.001. The round trip utilization efficiency in this case is η _{+ 1} ² = 0.65 for λ = 635 nm.
8 and η ₀ ² = 0.990 for λ = 785 nm
Becomes

Therefore, assuming that the output of the semiconductor laser in the module 1 is the same as that of the ordinary light head device for the wavelength of 635 nm, the amount of light received by the detection optical system in the module 1 is 0 in the ordinary optical head device. .658 times,
At this level, the S / N of the reproduction signal of the disk 7 hardly decreases. Also, in order for the amount of light received by the detection optical system in the module 1 to be the same as that of a normal optical head device, it is necessary to increase the output of the semiconductor laser in the module 1 to 1.52 times that of a normal optical head device. There is, however, such a degree can be easily realized. On the other hand, with respect to the wavelength of 785 nm, the S / N of the reproduction signal of the disk 8 is about the same as usual, the output of the semiconductor laser in the module 2 is about the same as usual, and not only the reproduction of the disc 8 but also the recording is performed. It is also possible. In addition, since the wavelength of the semiconductor laser in the module 2 is 785 nm, reproduction is possible even when the disk 8 is a write-once compact disk.

FIG. 6 is an overall view of a cross section of the hologram optical element 18. When the effective diameter of the objective lens 19 is 2a, the pattern of interference fringes is formed over the entire area of the diameter 2a. Further, the wavelength filter film 29 and the phase compensation film 30 are formed only outside the region having the smaller diameter 2b. The wavelength filter film 29 has a wavelength of 635
nm has a function of transmitting light of a wavelength of approximately nm, and reflecting light of a wavelength of 785 nm almost completely. The phase compensation film 30
With respect to the wavelength of 635 nm, it functions to adjust the phase difference between the light passing through the wavelength filter film 29 and the phase compensation film 30 and the light passing through the air to 2π. That is, outside the region of the diameter 2b, the light having the wavelength of 635 nm is completely transmitted through the hologram optical element 18, and the light having the wavelength of 785 nm is completely reflected by the hologram optical element 18. Accordingly, 81.1% of the light having a wavelength of 635 nm is diffracted as + 1st-order diffracted light by the hologram optical element 18 over the entire area of the diameter 2a,
99.5% of the light having a wavelength of 785 nm is transmitted through the hologram optical element 18 in the region of the diameter 2b, and is not transmitted at all outside the region of the diameter 2b. Let the focal length of the objective lens 19 be f
Then, the effective numerical apertures for light with wavelengths of 635 nm and 785 nm are given by a / f and b / f, respectively. For example, f = 2.6 mm, a = 1.56 mm, b =
Assuming 1.17 mm, a / f = 0.8, b / f ==
0.45.

The hologram optical element 5 can be manufactured by integral molding of plastic or glass. The part of the hologram optical element 18 other than the wavelength filter film 29 can also be manufactured by integral molding of plastic or glass. Further, the hologram optical elements 5 and 18 can be formed directly on the objective lenses 6 and 19, respectively.

FIG. 7 shows a configuration of a wavelength filter used in an embodiment of the optical head device according to the present invention. The wavelength filter 3 shown in FIG. 7A is obtained by bonding two glass blocks via a dielectric multilayer film 34. Wavelength 635n
The m incident light 31 is incident on the dielectric multilayer film 34 at an incident angle of 45 degrees, is transmitted almost completely, and travels straight. On the other hand, the wavelength 78
The incident light 32 of 5 nm is incident on the dielectric multilayer film 34 at an incident angle 45.
And the light is almost completely reflected and the traveling direction is bent by 90 degrees. The wavelength filter 33 shown in FIG. 7B is obtained by bonding three glass blocks via dielectric multilayer films 35 and 36. Incident light 31 having a wavelength of 635 nm
Enters the dielectric multilayer film 35 at an incident angle of 22.5 degrees, travels almost completely, and goes straight. On the other hand, the incident light 32 having a wavelength of 785 nm is incident on the dielectric multilayer films 35 and 36 at an incident angle of 22.5.
Incident at 90 degrees, almost completely reflected twice, and the traveling direction is 90
Bendable. In general, the design of the wavelength filter is easier as the incident angle on the dielectric multilayer film is smaller.

The wavelength filters 3 and 33 shown in FIG. 7 transmit light having a wavelength of 635 nm almost completely, and have a wavelength of 785 nm.
Is designed to almost completely reflect the light of wavelength 785 nm.
It is also possible to design to reflect the light of 35 nm almost completely. When this is used, the wavelength of the semiconductor laser in the module 1 of FIGS.
m, the wavelength of the semiconductor laser in the module 2 is 635 nm
And it is sufficient. Also, when the polarization direction of the light emitted from the semiconductor laser is the same as the polarization direction of the light reflected from the disk,
It is also possible to use a polarization beam splitter instead of the wavelength filter. For example, light having a wavelength of 635 nm is made to enter a polarization beam splitter as P-polarized light,
If the light of nm is incident on the polarizing beam splitter as S-polarized light, the former is almost completely transmitted and the latter is almost completely reflected.

FIG. 8 shows the configuration of a module when the embodiment of the optical head device of the present invention is applied to a read-only disk. This module includes a package 39 containing a semiconductor laser 37 and a photodetector 38, and a package 39.
Diffraction grating 4 provided in a window portion with a spacer 42 interposed therebetween
0, a hologram optical element 41. The diffraction grating 40 and the hologram optical element 41 have a structure in which a pattern is formed of SiO ₂ on a glass substrate, and have a function of transmitting a part of incident light and diffracting a part of the incident light. The light emitted from the semiconductor laser 37 is divided by the diffraction grating 40 into three lights, that is, transmitted light and ± first-order diffracted light, and about 50% of the light is transmitted through the hologram optical element 41 toward the disk. The three lights reflected by the disk are each diffracted by the hologram optical element 41 as ± first-order diffracted light by about 40%, transmitted through the diffraction grating 40, and received by the photodetector 38.

FIG. 9 shows an embodiment of mounting the semiconductor laser 37 on the photodetector 38 in the module shown in FIG. FIG.
(A) is a case where a glass mirror is used. The semiconductor laser 37 is installed on a photodetector 38 via a heat sink 43. Light emitted laterally from the semiconductor laser 37 is reflected by a glass mirror 44 and travels upward. On the other hand, FIG. 9B shows a case where a mirror formed by etching is used for the photodetector. The semiconductor laser 37 is
The photodetector 38 is provided in a recess formed by etching. The light emitted laterally from the semiconductor laser 37 is
The light is reflected by a mirror formed by etching on the photodetector 38 and goes upward.

FIG. 10A shows a diffraction grating 40 and FIG.
(B) shows patterns of interference fringes of the hologram optical element 41. The diffraction grating 40 has a pattern only in a region 45 near the center. Light emitted from the semiconductor laser 37 passes through the inside of the region 45, and light reflected from the disk passes outside the region 45. The hologram optical element 41 has an off-axis concentric pattern, and functions as a convex lens for + 1st-order diffracted light and as a concave lens for -1st-order diffracted light.

FIG. 11 shows the pattern of the light receiving section of the photodetector 38 and the arrangement of the light spots on the light receiving section. Of the light transmitted through the diffraction grating 40 on the outward path, the hologram optical element 41 on the return path
+ 1st-order diffracted light forms a light spot 56 on the light receiving sections 46 to 48 divided into three, and the hologram optical element 4
The -1st-order diffracted light of 1 forms a light spot 57 on the light receiving sections 49 to 51 divided into three. Also, the diffraction grating 4 on the outward path
Hologram optical element 4 on the return path of the + 1st-order diffracted light of 0
The ± 1st-order diffracted light of 1 forms light spots 58 and 59 on the light receiving sections 52 and 53, respectively, and
Of the first-order diffracted light, ± of the hologram optical element 41 on the return path
The first-order diffracted light forms light spots 60 and 61 on the light receiving portions 54 and 55, respectively. Light receiving units 46 to 48, 52, 5
4 is located behind the converging point, and the light receiving sections 49 to 51,
53 and 55 are located in front of the converging point. Light receiving section 46
When the outputs from .about.55 are respectively represented by V46 to V55, the focus error signal is (V46 + V48 + V50)-(V47 + V49 +) by the known spot size method.
V51), the track error signal is obtained by the known three-beam method by (V52 + V53)-(V54 + V
55). Also, the reproduction signal of the disc is V46 + V47 + V48 + V49 + V50 + V51.
From the calculation of

FIG. 12 shows the configuration of a module when the embodiment of the optical head device of the present invention is applied to a write-once disc or a rewritable phase change disc. This module includes a package 64 containing a semiconductor laser 62 and a photodetector 63, a polarizing hologram optical element 65 provided in a window of the package 64, and a 板 wavelength plate 66. As shown in FIG. 13, the polarizing hologram optical element 65 has a structure in which a pattern is formed by a proton exchange region 68 and a phase compensation film 69 on a lithium niobate substrate 67 having birefringence. It transmits all ordinary light and diffracts all extraordinary light. The outgoing light from the semiconductor laser 62 is incident on the polarizing hologram optical element 65 as ordinary light, passes through it, is converted from linearly polarized light into circularly polarized light by the quarter wavelength plate 66, and travels toward the disk. The reflected light from the disk is converted from circularly polarized light into linearly polarized light by the quarter wavelength plate 66, enters the polarizing hologram optical element 65 as extraordinary light, and is diffracted by about 80% as ± 1st-order diffracted light to detect light. The light is received by the device 63. The mounting form of the semiconductor laser 62 on the photodetector 63 is the same as that of FIG.

FIG. 14 shows a pattern of interference fringes of the polarizing hologram optical element 65. Polarizing hologram optical element 65
Is divided into four regions 70 to 73. The optical axis 74 of the polarizing hologram optical element 65 is set in a direction perpendicular to the polarization direction of the light emitted from the semiconductor laser 62. FIG. 15 shows the pattern of the light receiving unit of the photodetector 63,
4 shows an arrangement of light spots on a light receiving unit. The + 1st-order diffracted light from the region 70 of the polarizing hologram optical element 65 forms a light spot 83 on the dividing line of the light receiving units 75 and 76, and the -1st-order diffracted light from the region 70 is on the light receiving unit 82. A light spot 87 is formed. The + 1st-order diffracted light from the region 71 of the polarizing hologram optical element 65 forms a light spot 84 on the dividing line of the light receiving units 77 and 78 divided into two,
The −1st-order diffracted light from the region 71 forms a light spot 88 on the light receiving section 81. The polarizing hologram optical element 6
The ± 1st-order diffracted light from the area 72 of the light receiving section 7
Light spots 85 and 89 are formed on the areas 9 and 82,
The ± 1st-order diffracted lights from the light source form light spots 86 and 90 on the light receiving portions 80 and 81, respectively. When the outputs from the light receiving sections 75 to 82 are respectively represented by V75 to V82, the focus error signal is (V75 + V
78)-(V76 + V77), and the track error signal is obtained by the known push-pull method using the V79-V
Obtained from 80 operations. Also, the reproduction signal of the disc is obtained from the calculation of V81 + V82.

FIG. 16 shows the configuration of a module when the embodiment of the optical head device of the present invention is applied to a rewritable magneto-optical disk. This module includes a semiconductor laser 91,
A package 95 containing a photodetector 92, microprisms 93 and 94, and a spacer 9
The hologram optical element 97 is composed of a polarizing diffraction grating 96 and a hologram optical element 97 provided therebetween. The polarizing diffraction grating 96
It has the same structure as that of the polarizing hologram optical element 65 shown in FIG. 13, and has a function of transmitting part of ordinary light, diffracting part of incident light, and diffracting all extraordinary light. The light emitted from the semiconductor laser 91 passes through the hologram optical element 97 by about 8
0% of the light is transmitted and enters the polarizing diffraction grating 96 as ordinary light, and about 90% of the light is transmitted to the disk. Of the reflected light from the disk, about 8% of the ordinary light component and about 80% of the extraordinary light component are diffracted by the polarizing diffraction grating 96 as ± 1st-order diffracted light, the + 1st-order diffracted light is the microprism 93, and the −1st-order diffracted light is The light is received by the photodetector 92 via the microprism 94. About 90% of the ordinary light component passes through the polarizing diffraction grating 96 and is incident on the hologram optical element 97, and ± 1%
About 16% is diffracted as next-order diffracted light and received by the photodetector 92. The mode of mounting the semiconductor laser 91 on the photodetector 92 is the same as that in FIG.

FIG. 17A shows a polarizing diffraction grating 96, and FIG.
FIG. 7B shows patterns of interference fringes of the hologram optical element 97, respectively. The optical axis 99 of the polarizing diffraction grating 96 is set in a direction perpendicular to the polarization direction of the light emitted from the semiconductor laser 91. The hologram optical element 97 has a pattern only near the center and is divided into four regions 100 to 103. Of the reflected light from the disk, the transmitted light of the polarizing diffraction grating 96 passes through the regions 100 to 103, and the ± 1st-order diffracted light of the polarizing diffraction grating 96 is the region 100 to 103.
It passes outside 103. Region 1 of hologram optical element 97
Reference numerals 00 and 101 each have an off-axis concentric pattern and function as a convex lens for + 1st-order diffracted light and as a concave lens for -1st-order diffracted light.

FIG. 18 shows the structure of the microprism 93. The microprism 93 is formed by bonding three glass blocks via dielectric multilayer films 107 and 108. The P-polarized component of the incident light 104 is the dielectric multilayer 1
07 is transmitted almost completely to become transmitted light 105, and the S-polarized light component of the incident light 104 is almost completely reflected twice by the dielectric multilayer films 107 and 108 to become reflected light 106. The configuration of the microprism 94 is the same. FIG. 19 shows the pattern of the light receiving unit of the photodetector 92 and the arrangement of the light spots on the light receiving unit. The + 1st-order diffracted light from the polarizing diffraction grating 96 is separated into transmitted light and reflected light by using the microprism 93 as an analyzer.
The reflected light forms light spots 124 on the light receiving unit 110, respectively. The -1st-order diffracted light from the polarizing diffraction grating 96 is separated into transmitted light and reflected light using the microprism 94 as an analyzer. , Light spots 126 are formed respectively. On the other hand, the + 1st-order diffracted light from the regions 100 and 101 of the hologram optical element 97 respectively has light spots 127 and 127 on the light receiving units 113 to 115 divided into three.
128, and the -1st-order diffracted lights from the regions 100 and 101 form light spots 129 and 130 on the three divided light receiving units 116 to 118, respectively. Light receiving unit 113-
Reference numeral 115 is located behind the light-collecting point,
Reference numeral 118 is located in front of the focal point. The ± 1st-order diffracted light from the region 102 of the hologram optical element 97 is applied to the light spots 131 and 1 on the light receiving sections 119 and 122, respectively.
33, and ± 1st-order diffracted lights from the region 103 are projected onto the light receiving portions 120 and 121, respectively.
4 is formed. When the outputs from the light receiving units 109 to 122 are respectively represented by V109 to V122, the focus error signal is (V113 + V1) by a known spot size method.
15 + V117)-(V114 + V116 + V118)
The track error signal is obtained by the known push-pull method by (V119 + V122)-(V120 +
V121). Also, the reproduced signal of the disc is (V109 + V111)-(V110 + V11
It is obtained from the operation of 2).

Each of the embodiments of the optical head device of the present invention shown in FIGS. 1 and 4 has a configuration using two modules each containing a semiconductor laser and a detection optical system for miniaturization. A configuration using two sets of blocks provided with a laser and a detection optical system separately is also possible.

[Third Embodiment] FIG. 20 shows the configuration of a third embodiment of the optical head device according to the present invention. Module 13
6 includes a semiconductor laser and a detection optical system for receiving light reflected from the disk. Semiconductor laser 135
Is 635 nm, and the wavelength of the semiconductor laser in the module 136 is 785 nm. The wavelength filter 137 is
P-polarized light having a wavelength of 635 nm is transmitted almost completely,
It functions to reflect S-polarized light of 35 nm and light of wavelength 785 nm almost completely. The 波長 wavelength plate 138 has a wavelength of 6
It is optimally designed for 35 nm.

The light emitted from the semiconductor laser 135 is incident on the wavelength filter 137 as P-polarized light, passes through the whole, is collimated by the collimator lens 4, and becomes a quarter-wave plate 138.
Is converted from linearly polarized light into circularly polarized light and enters the hologram optical element 5. The light transmitted through the hologram optical element 5 enters the objective lens 6 as parallel light, and is focused on a disk 7 having a substrate thickness of 0.6 mm. The reflected light from the disk 7 passes through the objective lens 6 in the opposite direction, and again enters the hologram optical element 5. The transmitted light of the hologram optical element 5 is 1 /
The light is converted from circularly polarized light into linearly polarized light by the four-wavelength plate 138 and enters the collimator lens 4 as parallel light. The light transmitted through the collimator lens 4 enters the wavelength filter 137 as S-polarized light, is totally reflected, and is received by the detection optical system in the module 138. On the other hand, the light emitted from the semiconductor laser in the module 138 is reflected by the wavelength filter 137, is collimated by the collimator lens 4, and becomes a quarter-wave plate 138.
Is converted from linearly polarized light into elliptically polarized light and enters the hologram optical element 5. The -1st-order diffracted light of the hologram optical element 5 enters the objective lens 6 as divergent light, and has a substrate thickness of 1.2.
The light is condensed on a disc 8 mm. The reflected light from the disk 8 is transmitted through the objective lens 6 in the opposite direction, and is incident on the hologram optical element 5 again. The -1st-order diffracted light of the hologram optical element 5 is converted from elliptically polarized light to another elliptically polarized light by the quarter-wave plate 138, and is incident on the collimator lens 4 as parallel light. The transmitted light of the collimator lens 4 is the wavelength filter 1
The light is reflected at 37 and received by the detection optical system in the module 136. The hologram optical element 5 and the objective lens 6 are driven integrally by an actuator. The configuration of the module 136 is obtained by removing the 波長 wavelength plate 66 from the configuration of the module shown in FIG.

[Fourth Embodiment] FIG. 21 shows the configuration of an optical head device according to a fourth embodiment of the present invention. Module 13
9 has a built-in semiconductor laser and a detection optical system for receiving the reflected light from the disk. The wavelength of the semiconductor laser in the module 139 is 635 nm,
The wavelength of 0 is 785 nm. The wavelength filter 141 is
It functions to transmit the light having a wavelength of 635 nm and the P-polarized light having a wavelength of 785 nm almost completely and reflect the S-polarized light having a wavelength of 785 nm almost completely. The 波長 wavelength plate 142 has a wavelength of 7
It is optimally designed for 85 nm.

The light emitted from the semiconductor laser in the module 139 passes through the wavelength filter 141, is collimated by the collimator lens 4, converted from linearly polarized light to elliptically polarized light by the １ ／ wavelength plate 142, and Incident on. The light transmitted through the hologram optical element 5 enters the objective lens 6 as parallel light, and is focused on a disk 7 having a substrate thickness of 0.6 mm. The reflected light from the disk 7 is
Is transmitted in the opposite direction, and is incident on the hologram optical element 5 again. The transmitted light of the hologram optical element 5 is a 波長 wavelength plate 1
At 42, the elliptically polarized light is converted into another elliptically polarized light, and enters the collimator lens 4 as parallel light. The transmitted light of the collimator lens 4 passes through the wavelength filter 141 and is received by the detection optical system in the module 139.

On the other hand, the light emitted from the semiconductor laser 140 enters the wavelength filter 141 as S-polarized light, is totally reflected, is collimated by the collimator lens 4, and is converted from linearly polarized light to circularly polarized light by the quarter wavelength plate 142. The light is converted and enters the hologram optical element 5. Hologram optical element 5-1
The next-order diffracted light enters the objective lens 6 as divergent light, and is converged on a disk 8 having a substrate thickness of 1.2 mm. Disk 8
Is transmitted through the objective lens 6 in the opposite direction, and then enters the hologram optical element 5 again. Hologram optical element 5
Is converted from circularly polarized light into linearly polarized light by the quarter-wave plate 142 and enters the collimator lens 4 as parallel light. The transmitted light of the collimator lens 4 is incident on the wavelength filter 141 as P-polarized light, is entirely transmitted, and is received by the detection optical system in the module 139. The hologram optical element 5 and the objective lens 6 are driven integrally by an actuator. The configuration of the module 139 is obtained by removing the ４ wavelength plate 66 from the configuration of the module shown in FIG.

Each of the embodiments of the optical head device of the present invention shown in FIGS. 20 and 21 has a configuration using one module and one semiconductor laser incorporating a semiconductor laser and a detection optical system for miniaturization. However, a configuration using a set of blocks separately provided with a semiconductor laser and a detection optical system and one semiconductor laser is also possible.

[0043]

As described above, the optical head device of the present invention has a semiconductor laser and a hologram optical element of two different wavelengths, and uses the transmitted light of the hologram optical element emitted from one of the semiconductor lasers. One disk is recorded / reproduced using the + 1st-order or -1st-order diffracted light of the hologram optical element emitted from the other semiconductor laser to record / reproduce the other disc having a thickness different from that of the one disc.
Since the transmittance and the ± first-order diffraction efficiency of the hologram optical element depend on the wavelength of the incident light, a transmittance close to 100% can be obtained for the wavelength of one of the semiconductor lasers. By designing so as to obtain a high + 1st-order or -1st-order diffraction efficiency with respect to the wavelength of the other semiconductor laser, the S / N of the reproduction signal becomes almost the same as usual, and the output of the semiconductor laser also becomes normal. Is the same as
An optical head device capable of performing not only reproduction but also recording can be realized. Further, according to the present invention, by setting the wavelength of one semiconductor laser to 785 nm, it is possible to realize an optical head device capable of reproducing a write-once compact disc.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of an optical head device according to the present invention.

FIG. 2 is an enlarged cross-sectional view of a hologram optical element used in the first embodiment of the optical head device according to the present invention.

FIG. 3 is an overall cross-sectional view of a hologram optical element used in the first embodiment of the optical head device according to the present invention.

FIG. 4 is a diagram showing a configuration of an optical head device according to a second embodiment of the present invention.

FIG. 5 is an enlarged cross-sectional view of a hologram optical element used in a second embodiment of the optical head device according to the present invention.

FIG. 6 is an overall cross-sectional view of a hologram optical element used in a second embodiment of the optical head device of the present invention.

FIG. 7 is a diagram showing a configuration of a wavelength filter used in the first and second embodiments of the optical head device of the present invention.

FIG. 8 is a diagram showing the configuration of a module when the embodiment of the optical head device of the present invention is applied to a read-only disc.

FIG. 9 is a diagram showing a mounting mode of a semiconductor laser on a photodetector in the module of FIG. 8 used in the embodiment of the optical head device of the present invention.

FIG. 10 shows an embodiment of the optical head device according to the present invention.
FIG. 8 is a diagram showing patterns of interference fringes of a diffraction grating and a hologram optical element in the module of FIG.

FIG. 11 shows an embodiment of the optical head device according to the present invention.
FIG. 7 is a diagram showing a pattern of a light receiving unit of a photodetector and an arrangement of light spots on the light receiving unit in the module of FIG.

FIG. 12 is a diagram showing the configuration of a module when the embodiment of the optical head device of the present invention is applied to a write-once disc or a rewritable phase change disc.

FIG. 13 shows an embodiment of an optical head device according to the present invention.
FIG. 8 is a diagram illustrating a structure of a polarizing hologram optical element in a second module.

FIG. 14 shows an embodiment of an optical head device according to the present invention.
FIG. 9 is a diagram showing a pattern of interference fringes of a polarizing hologram optical element in the module No. 2;

FIG. 15 shows an embodiment of the optical head device according to the present invention.
FIG. 8 is a diagram showing a pattern of a light receiving unit of a photodetector and an arrangement of light spots on the light receiving unit in the second module.

FIG. 16 is a diagram showing a configuration of a module when an embodiment of the optical head device of the present invention is applied to a rewritable magneto-optical disk.

FIG. 17 shows an embodiment of an optical head device according to the present invention.
FIG. 18 is a diagram illustrating a pattern of interference fringes of the polarizing diffraction grating and the hologram optical element in the module No. 8;

FIG. 18 shows an embodiment of an optical head device according to the present invention.
It is a figure which shows the structure of the microprism in the module of No. 6.

FIG. 19 is a diagram illustrating an optical head device according to an embodiment of the present invention;
FIG. 13 is a diagram illustrating a pattern of a light receiving unit of a photodetector and an arrangement of light spots on the light receiving unit in the module No. 6;

FIG. 20 is a diagram showing a configuration of a third embodiment of the optical head device according to the present invention.

FIG. 21 is a diagram showing the configuration of a fourth embodiment of the optical head device according to the present invention.

FIG. 22 is a diagram showing a configuration of a conventional optical head device.

FIG. 23 is a plan view of a hologram optical element used in a conventional optical head device.

FIG. 24 is a sectional view of a hologram optical element used in a conventional optical head device.

[Explanation of symbols]

1, 2 module 3 wavelength filter 4 collimator lens 5 hologram optical element 6 objective lens 7, 8 disk 9 glass substrate 10 SiO ₂ 11 to 13 region 14 glass substrate 15 to 17 region 18 hologram optical element 19 objective lens 20 glass substrate 21 SiO ₂ 22-24 region 25 glass substrate 26-28 region 29 wavelength filter film 30 phase compensation film 31, 32 incident light 33 wavelength filter 34-36 dielectric multilayer film 37 semiconductor laser 38 photodetector 39 package 40 diffraction grating 41 hologram optics Element 42 Spacer 43 Heat sink 44 Mirror 45 Area 46 to 55 Light receiving section 56 to 61 Light spot 62 Semiconductor laser 63 Photodetector 64 Package 65 Polarizing hologram optical element 66 Quarter wave plate 67 Lithium niobate Plate 68 proton exchange region 69 phase compensation film 70 to 73 region 74 optical axis 75 to 82 light receiving unit 83 to 90 light spot 91 semiconductor laser 92 photodetector 93, 94 microprism 95 package 96 polarizing diffraction grating 97 hologram optical element 98 Spacer 99 Optical axis 100-103 Area 104 Incident light 105 Transmitted light 106 Reflected light 107, 108 Dielectric multilayer film 109-122 Light receiving section 123-134 Light spot 135 Semiconductor laser 136 module 137 Wavelength filter 138 Quarter-wave plate 139 Module 140 semiconductor laser 141 wavelength filter 142 quarter wavelength plate 143 semiconductor laser 144 half mirror 145 hologram optical element 146 concave lens 147 photodetector

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11B 7/135

Claims (9)

(57) [Claims] 1. A first semiconductor laser oscillating at a first wavelength, a second semiconductor laser oscillating at a second wavelength, light emitted from the first semiconductor laser, and the second semiconductor laser. Multiplexing means capable of multiplexing outgoing light from the hologram, a hologram optical element and an objective lens for guiding outgoing light of each semiconductor laser to the first or second optical recording medium, and the hologram of the optical multiplexing means An optical detector provided on the optically opposite side of the optical element side, and a light detector for receiving reflected light from the optical recording medium of emitted light of the first and second semiconductor lasers, and The transmittance for the first wavelength is higher than the transmittance for the second wavelength, and the -1st-order diffraction efficiency for the second wavelength is higher than the -1st-order diffraction efficiency for the first wavelength. And said By using the transmitted light of the first semiconductor laser by the hologram optical element and the -1st-order diffracted light of the second semiconductor laser, or by increasing the + 1st-order diffraction efficiency of the hologram optical element with respect to the first wavelength, Higher than the + 1st-order diffraction efficiency for the second wavelength, and the transmittance for the second wavelength is made higher than the transmittance for the first wavelength, and the + 1st time of the first semiconductor laser by the hologram optical element. By using the folded light and the transmitted light of the second semiconductor laser, the emitted light of the first semiconductor laser is guided to a first optical recording medium, and the emitted light of the second semiconductor laser is converted to the first light. Leading to a second optical recording medium thicker than the recording medium,
It is configured to perform reproduction or reproduction and recording on each optical recording medium , wherein the objective lens is
Optical recording in which transmitted light from a ram optical element is guided by the transmitted light
A sphere that cancels out the spherical aberration that occurs when transmitting through a medium substrate
The hologram optical element has a surface aberration,
For the + 1st order diffracted light or -1st order diffracted light of the
The light emitted from the objective lens is a light source to which the emitted light is guided.
Spherical aberration generated when transmitting through the substrate of the recording medium and the objective
Has spherical aberration that cancels the sum of the spherical aberration of the lens
An optical head apparatus characterized in that it. 2. The hologram optical element according to claim 1, wherein the interference fringe pattern on the substrate is formed only in a region having a diameter smaller than an effective diameter of the objective lens.
The optical head device as described in the above. 3. The hologram optical element according to claim 1, wherein the interference fringe pattern on the substrate is formed in a region having substantially the same diameter as the effective diameter of the objective lens, and the hologram optical element is provided on a substrate surface opposite to the surface on which the interference fringe pattern is formed. 2. The optical head device according to claim 1, wherein the phase compensation film and the wavelength filter film are formed only outside a region having a diameter smaller than an effective diameter of the objective lens. 4. The optical head device according to claim 1, wherein the hologram optical element has a concentric interference fringe pattern and the cross-sectional shape of the interference fringe pattern is stepped. Wherein said optical multiplexing means, a function of demultiplexing the reflected light from the optical recording medium of the emitted light of the reflected light and the second semiconductor laser from the optical recording medium of the emitted light of the first semiconductor laser The light detection unit has a separate light receiving element that reflects the reflected light of the light emitted from the first semiconductor laser from the optical recording medium and the reflected light of the emitted light of the second semiconductor laser from the optical recording medium. 2. The optical head device according to claim 1, wherein the optical head device detects the light. Wherein said optical multiplexing means, one of the semiconductor laser of emitting light and is transmitted through the light reflected from the optical recording medium, reflected from the other one of the semiconductor laser of emitting light and the optical recording medium The optical head device according to claim 5 , wherein the optical head device reflects light. 7. The optical multiplexing means is constituted by a polarization beam splitter, and the outgoing light of one of the semiconductor lasers enters the optical multiplexing means as S-polarized light and the outgoing light of one of the other semiconductor lasers becomes P-polarized light. The optical head device according to claim 5, wherein 8. The same light receiving element as claimed in claim 1, wherein the light detecting section reflects the reflected light of the emitted light of the first semiconductor laser from the optical recording medium and the reflected light of the emitted light of the second semiconductor laser from the optical recording medium. 2. The optical head device according to claim 1, wherein the optical head device detects the light. 9. The optical multiplexing means transmits the outgoing light from one of the semiconductor lasers as P-polarized light, and converts the reflected light of the outgoing light from one of the semiconductor lasers from the optical recording medium into S-polarized light. claims, characterized in that the reflected, and reflects the light emitted and the other of the semiconductor laser as
9. The optical head device according to 8 .