JP2713257B2 - 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, and more particularly, to an optical head device for performing recording and reproduction on two different types of optical recording media.

[0002]

2. Description of the Related Art In recent years, standardization of digital video discs having a larger capacity than compact discs has been promoted. FIG. 18 shows a configuration diagram of an example of a conventional optical head device used for reproducing this digital video disk or compact disk. Referring to FIG.
Outgoing light from the mirror enters the half mirror 191, where about half is reflected, and the reflected light is further reflected by the collimator lens 1.
After the light is collimated in 4, the disk 17 is
It is condensed on the top, forms a spot, and is reflected.

[0003] The reflected light from the disk 17 is
6. The light is transmitted through the collimator lens 14 in a direction opposite to the direction of light incidence and enters the half mirror 191, where about half is transmitted, and the transmitted light is further applied to the photodetector 193 via the concave lens 192 to receive light. Is done. The photodetector 193 has a four-divided light receiving unit, and outputs a focus error signal to the half mirror 1.
A detection is performed by an astigmatism method using astigmatism generated at 91, and a track error signal is detected by a push-pull method. Further, the reproduced signal is detected from the sum of the output signals of the four divided light receiving units of the photodetector 193.

[0004]

In order to reproduce a large-capacity digital video disk, it is necessary to reduce the diameter of a condensed spot on the disk surface corresponding to a narrow track pitch. The diameter of the focused spot is inversely proportional to the numerical aperture of the objective lens 16 and proportional to the wavelength of light.
The numerical aperture of 6 should be as high as about 0.52 to 0.6, and the wavelength of the light emitted from the semiconductor laser 190 should be as short as about 635 nm to 655 nm.

On the other hand, in order to reproduce a compact disk, the standard for the inclination of the compact disk is loose, and it is necessary to suppress the occurrence of coma due to the inclination of the disk. Therefore, the numerical aperture of the objective lens 16 is about 0.45. And lower. In addition, in order to reproduce a write-once compact disc (CD-R) which is a kind of compact disc and uses an organic dye as a recording medium, the write-once compact disc has a 70% or more of only incident light near a wavelength of 785 nm. The wavelength of the light emitted from the semiconductor laser 190 must be about 785 nm because it is designed to obtain a high reflectance.

As described above, the two types of optical recording media, the digital video disk and the compact disk including the write-once type, differ in the wavelength of the semiconductor laser and the numerical aperture of the objective lens, which are optimum for reproducing each of them. In the conventional optical head device shown in (1), it is impossible to reproduce two types of optical recording media.

[0007] The present invention has been made in view of the above points,
An object of the present invention is to provide an optical head device capable of reproducing two types of optical recording media such as a digital video disk and a compact disk including a write-once type.

[0008]

In order to achieve the above object, the present invention provides a first light source for emitting a first light of a first wavelength and a second light source of a second wavelength different from the first wavelength. A second light source for emitting a second light; a first light from the first light source;
Multiplexed with the second light from the light source and guided to the optical recording medium, and multiplexed by the optical multiplexing / demultiplexing means for demultiplexing the reflected light from the optical recording medium. The first light is provided between an objective lens, an optical multiplexing / demultiplexing means, and an objective lens that transmits the reflected light to the optical recording medium and then reflects the reflected light on the optical recording medium, and transmits the reflected light. All light is transmitted,
An aperture limiting element for transmitting the incident light of the second wavelength only at the central portion of the light beam cross section, and a first light detection optical system for receiving the reflected light of the first wavelength demultiplexed by the optical multiplexing / demultiplexing means. ,
And a second photodetection optical system for receiving the reflected light of the second wavelength demultiplexed by the optical multiplexing / demultiplexing means.

The aperture limiting element according to the present invention comprises a wavelength filter film provided only outside a circular area having a diameter smaller than the effective diameter of the objective lens on the substrate, and a phase filter provided on the wavelength filter film. A first light having a first wavelength is almost completely transmitted outside the circular region, a second light having a second wavelength is almost completely reflected outside the circular region, and light incident into the circular region is formed. Is characterized in that both the first and second lights are completely transmitted.

Further, the aperture limiting element according to the present invention comprises a diffraction grating formed on the substrate only outside a circular region having a diameter smaller than the effective diameter of the objective lens, wherein the diffraction grating has a first wavelength. The first light is completely transmitted, the second light of the second wavelength is almost diffracted, and the light incident into the circular region is completely transmitted together with the first and second lights. I do.

Further, in the aperture limiting element according to the present invention, the diffraction grating and the wavelength filter film on the first substrate, and the phase compensation film on the second substrate each have a circular shape having a diameter smaller than the effective diameter of the objective lens. Only the outside of the region is sequentially laminated and formed, the space between the second substrate and the wavelength filter film is filled with an adhesive, and outside the circular region, the first light of the first wavelength is completely transmitted, The second light of the second wavelength is completely reflected and diffracted, and the light incident on the circular area is completely transmitted through both the first and second lights.

The optical head device of the present invention combines the first light from the first light source and the second light from the second light source and guides the combined light to the optical recording medium, while combining the light from the optical recording medium. An aperture limiting element is provided between the optical multiplexing / demultiplexing means for splitting the reflected light and the objective lens.
For the first light having the wavelength of the second light, all the incident light is transmitted, and for the second light having the second wavelength from the second light source, only the central portion of the light beam cross section of the incident light is transmitted. With this configuration, the objective lens can be used with an effective numerical aperture determined by the effective diameter of the objective lens and the focal length of the objective lens for the first light, and transmitted through the aperture limiting element for the second light. The objective lens can be used with an effective numerical aperture determined by the diameter of the cross section of the light beam to be formed and the focal length of the objective lens.

That is, in the present invention, since the effective numerical aperture of the objective lens is made different for the two wavelengths, the optimum wavelength and the numerical aperture of the objective lens for each of the two types of optical recording media are set. Can be selected.

[0014]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of an optical head device according to a first embodiment of the present invention. In the figure, a module 11 and a module 12 incorporate a semiconductor laser and a detection optical system for receiving light reflected from the disk 17. The wavelength of the semiconductor laser in the module 11 is 635 nm, and the wavelength of the semiconductor laser in the module 12 is 785 nm. The wavelength filter 13 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. Therefore, the emitted light from the semiconductor laser in the module 11 is
Is transmitted with almost no loss, and the emitted light from the semiconductor laser in the module 12 is reflected by the wavelength filter 13 with almost no loss.

The outgoing light from the semiconductor laser in the module 11 that has passed through the wavelength filter 13 with almost no loss is collimated by the collimator lens 14, and after passing through all aperture limiting elements 15, which will be described later, the objective lens 16 Is focused on the disk 17 to form a spot and reflected.
The reflected light from the disk 17 passes through the objective lens 16, the aperture limiting element 15, and the collimator lens 14 in the opposite direction, passes through the wavelength filter 13, and is received by the detection optical system in the module 11.

On the other hand, the outgoing light from the semiconductor laser in the module 12 reflected by the wavelength filter 13 with almost no loss is collimated by the collimator lens 14, and only the central portion of the light beam cross section passes through the aperture limiting element 15. Thereafter, the light is condensed on the disk 17 by the objective lens 16 to form a spot and is reflected. The reflected light from the disk 17 passes through the objective lens 16, the aperture limiting element 15, and the collimator lens 14 in the opposite direction, is reflected by the wavelength filter 13, and is received by the detection optical system in the module 12. The aperture limiting element 15 and the objective lens 16 are driven integrally by an actuator.

FIG. 2A is a plan view of the aperture limiting element 15 of FIG. 1, and FIG. 2B is a sectional view taken along the line II-II of FIG. As shown in FIGS. 7A and 7B, the aperture limiting element 15 has a substantially planar rectangular shape, and a wavelength filter film 22 and a phase compensation film 23 are laminated on, for example, a glass substrate 21 which is transparent to light. In this configuration, a circular groove 20 is formed in the center of the plate having the above structure. The diameter 2b of the circular groove 20 is smaller than the effective diameter 2a of the objective lens 16.

The wavelength filter film 22 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. Further, the phase compensation film 23
For a wavelength of 635 nm, the phase difference between the light passing through the wavelength filter film 22 and the phase compensation film 23 and the light passing through the air is 2π
[Rad. ]. In other words, the aperture limiting element 15 completely transmits light having a wavelength of 635 nm and completely reflects light having a wavelength of 785 nm in portions other than the circular groove 20 having a diameter of 2b. Light of 785 nm is completely transmitted.

The wavelength filter film 22 has a structure in which, for example, an odd number of high refractive index layers and low refractive index layers are alternately deposited on a glass substrate 21. In order to provide the above wavelength selection characteristics, when the refractive indices of the high refractive index layer and the low refractive index layer are n ₁ and n ₂ and the thicknesses are d ₁ and d ₂ , n ₁ · d ₁ = n ₂ · n. d ₂ = λ / 4 (λ =
785 [nm]). Ti as high refractive index layer
When O ₂ and SiO ₂ are used as the low refractive index layer, n ₁ = 2.
30, n ₂ = 1.46, so that d ₁ = 85 from the above equation.
[Nm], d ₂ = 134 [nm]. On the other hand, the phase compensation film 23 can be manufactured by, for example, depositing SiO ₂ on the wavelength filter film 22.

The second embodiment of the optical head device according to the present invention has a configuration in which the aperture limiting element 15 shown in FIG. 2 is replaced by the aperture limiting element 25 shown in FIG. 3 in the configuration diagram of FIG.
FIG. 3A shows an aperture limiting element 2 used in the second embodiment.
FIG. 3B is a plan view of FIG. 5, and FIG.
FIG. 3 shows a sectional view along the line. As shown in FIGS. 3A and 3B, the aperture limiting element 25 has a generally rectangular shape in a plane and a diffraction grating 29 on a glass substrate 28 which is transparent to light.
In this configuration, a circular groove 27 is formed in the center of the plate having the structure in which the groove is formed. The diameter 2b of the circular groove 27 is smaller than the effective diameter 2a of the objective lens 16.

The diffraction grating 29 is provided on the glass substrate
It is produced by depositing iO ₂ , etching the glass substrate 28, and integrally molding glass or plastic. Assuming that the thickness of the diffraction grating 29 is h, the refractive index is n, and the wavelength of the incident light is λ, the transmittance is cos ² (φ / 2) (where φ = 2π
(N-1) h / λ). Therefore, for example, the thickness h of the diffraction grating 29 is 4.14 μm, and the refractive index n is 1.46.
When the wavelength λ of the incident light is 635 nm, φ = 6
Since it is π, the transmittance is 100%, and when λ is 785 nm, φ is 4.85π, so the transmittance is 5.4%.

That is, the aperture limiting element 25 is
(A part other than the circular groove 27) is a wavelength 63
5 nm light is completely transmitted, and the light having a wavelength of 785 nm is almost diffracted.
Light of 5 nm and 785 nm is completely transmitted. The pattern of the diffraction grating 29 does not have to be linear but may be other shapes such as concentric circles.

The third embodiment of the optical head device according to the present invention has a configuration in which the aperture limiting element 15 shown in FIG. 2 is replaced by an aperture limiting element 31 shown in FIG. 4 in the configuration diagram of FIG.
FIG. 4A shows an aperture limiting element 3 used in the third embodiment.
1 and FIG. 4B is a sectional view taken along line IV-IV in FIG.

As shown in FIGS. 4 (a) and 4 (b), the aperture limiting element 31 has a substantially rectangular shape on a plane and a diffraction grating 35 and a wavelength filter film on a glass substrate 34 which is transparent to light. 36, a glass substrate 38 and a phase compensation film 39 at the center of the laminated plate,
In this configuration, a circular groove 33 is formed. This circular groove 3
The diameter 2b of 3 is smaller than the effective diameter 2a of the objective lens 16. The diffraction grating 35 and the wavelength filter film 36 are provided with a center hole having a diameter of 2b at the center.

The phase compensation film 39 is formed on a glass substrate 38, and the space between the wavelength filter film 36 and the glass substrate 38 is filled with an adhesive 37. Wavelength filter film 36
Transmits light with a wavelength of 635 nm almost completely, and a wavelength of 7
It has the property of reflecting light of 85 nm almost completely. Further, the phase compensation film 39 changes the phase difference between the light passing through the diffraction grating 35, the wavelength filter film 36, and the phase compensation film 39 and the light passing through the adhesive 37 and the air with respect to the wavelength of 635 nm by 2π.
[Rad. ].

The diffraction grating 35 has a structure in which S
It is produced by depositing iO ₂ , etching the glass substrate 34, integrally molding glass or plastic, or the like. For the transmitted light of the wavelength filter film 36, it does not work as a diffraction grating, and for the reflected light of the wavelength filter film 36, the thickness of the diffraction grating 35 is h, the refractive index is n, and the wavelength of the incident light is λ. Then, the reflectance is cos ² (φ / 2) (where φ = 4πnh /
λ). For example, h = 134 nm, n = 1.4
At 6, the reflectance is 0% for λ = 785 nm because φ = π.

That is, the aperture limiting element 31 completely transmits light having a wavelength of 635 nm in a portion around the circular groove 33 having a diameter of 2b (a portion other than the circular groove 33), and has a wavelength of 785.
nm light is completely reflected and diffracted, and a circular groove 33 having a diameter of 2b is formed.
Inside, the light having wavelengths of 635 nm and 785 nm is completely transmitted.

The wavelength filter film 36 is formed, for example, of the diffraction grating 3
5 can be manufactured by alternately depositing an odd number of high refractive index layers and low refractive index layers. To make the above function work, the refractive indices of the high refractive index layer and the low refractive index layer are n ₁ and n ₂ , and the thickness is ₁
, D ₂ , n ₁ · d ₁ = n ₂ · d ₂ = λ / 4 (λ = 78
5 [nm]). Ti as high refractive index layer
When O ₂ and SiO ₂ are used as the low refractive index layer, n ₁ = 2.
30, since n ₂ = 1.46, d ₁ = 85 [nm], d
₂ = 134 [nm].

On the other hand, the phase compensation film 39 can be produced by, for example, depositing SiO ₂ on a glass substrate 38. As the adhesive 37, a material having a refractive index substantially the same as that of the diffraction grating 35 is used. Further, the pattern of the diffraction grating 35 may be other shapes such as a concentric shape instead of a linear shape.

The wavelengths 635 nm and 785 of the aperture limiting elements 15, 25 and 31 shown in FIGS.
The effective numerical aperture for nm light is given by a / f and b / f, respectively, where f is the focal length of the objective lens 16. For example, f = 3 [mm], a = 1.56 [m]
m] and b = 1.35 [mm], a / f = 0.5
2, b / f = 0.45. Therefore, the wavelength of 635 nm
And a numerical aperture of 0.52 to reproduce a digital video disk, and a combination of a wavelength of 785 nm and a numerical aperture of 0.45 to reproduce a compact disk including a write-once type. The present invention can be applied not only to the read-only type and the write-once type, but also to a rewritable type phase change disk and a magneto-optical disk. Further, the aperture limiting elements 15, 25, and 31 can be integrated with the objective lens 16.

Next, the configuration of the wavelength filter used in the embodiment of the optical head device of the present invention will be described. FIG. 5 shows a configuration diagram of each example of the wavelength filter. The wavelength filter 13 shown in FIG. 5A is obtained by bonding two glass blocks 41 and 42 via a dielectric multilayer film 43. As shown in FIG. 5A, the incident light 44 having a wavelength of 635 nm is incident on the dielectric multilayer film 43 at an incident angle of 45 degrees, is transmitted almost completely, and goes straight. On the other hand, the incident light 45 having a wavelength of 785 nm enters the dielectric multilayer film 43 at an incident angle of 45 degrees, is almost completely reflected, and the traveling direction is bent by 90 degrees.

The wavelength filter 47 shown in FIG. 5 (b) is composed of three glass blocks 48, 49 and 50, the blocks 48 and 49 being bonded together via a dielectric multilayer film 51, and the blocks 49 and 50 being connected together. It is bonded through a dielectric multilayer film 52. As shown in FIG. 5B, the incident light 44 having a wavelength of 635 nm is incident on the dielectric multilayer film 52 through the block 50 at an incident angle of 22.5 degrees, is transmitted almost completely, and passes through the block 49. Go straight. On the other hand, the incident light 45 having a wavelength of 785 nm is incident on the dielectric multilayer film 51 through the block 49 at an incident angle of 22.5 degrees, as shown in FIG. Is incident on the dielectric multilayer film 52 at an incident angle of 22.5 degrees, and is also almost completely reflected here.
The light is emitted through the block 49 after being bent by 0 degrees. In general, the design of the wavelength filter is easier as the incident angle on the dielectric multilayer film is smaller.

The wavelength filter 1 shown in FIGS. 5A and 5B
Dielectric multilayer films 43, 51 and 52 used in 3, 47
Is designed to transmit the incident light 44 having a wavelength of 635 nm almost completely and reflect the incident light 45 having a wavelength of 785 nm almost completely. Can be designed to reflect almost completely. in this case,
The wavelength of the semiconductor laser in the module 11 of FIG.
nm, the wavelength of the semiconductor laser in the module 12 is 635
nm.

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, a polarization beam splitter can be used instead of the wavelength filter. For example, wavelengths of 635 nm and 785 nm
Is incident on the polarizing beam splitter as P-polarized light and S-polarized light, respectively, whereby the former is almost completely transmitted and the latter is almost completely reflected.

Next, a module in which the optical head device of the present invention is applied to a read-only optical disk device will be described. FIG. 6 shows a configuration diagram of an example of the module in this case. As shown in the drawing, this module has a package 56 containing a semiconductor laser 54 and a photodetector 55, and a window of the package 56 in the optical path of the laser light emitted from the semiconductor laser 54 with a spacer 59 interposed therebetween. Provided diffraction grating 57 and hologram optical element 58
It is composed of The diffraction grating 57 and the hologram optical element 58 have a structure in which a pattern is formed of SiO ₂ on a glass substrate, and function to transmit a part of incident light and diffract a part.

Next, the operation of this module will be described. The laser beam emitted from the semiconductor laser 54 goes straight and is divided by the diffraction grating 57 into three beams of transmitted light and ± first-order diffracted light. About 50% of element 58
To the disc (not shown). The three lights reflected by the disk are respectively hologram optical elements 58
, Where about 40% is diffracted as ± 1st-order diffracted light, transmitted through the diffraction grating 57 and received by the photodetector 55.

FIG. 7 shows an example of mounting of the semiconductor laser 54 on the photodetector 55 in the module of FIG. FIG. 7A shows a case where a glass mirror is used. The semiconductor laser 54 is provided on the photodetector 55 via a heat sink 61. Light emitted laterally from the semiconductor laser 54 is reflected by the inclined surface of the glass mirror 62 and goes upward in the figure.

FIG. 7B shows a case where a mirror formed by etching is used for the photodetector 55. The photodetector 55 has a concave portion 63 and an inclined mirror 64 formed by etching on the upper portion, and the semiconductor laser 54 is installed in the concave portion 63 formed by etching the photodetector 55. As a result, the light emitted laterally from the semiconductor laser 54 is reflected by the mirror 64 formed on the photodetector 55 by etching, and goes upward in the drawing.

FIG. 8A shows an interference fringe pattern of the diffraction grating 57 in the module of FIG. 6, and FIG. 8B shows an interference fringe pattern of the hologram optical element 58 in the module of FIG. The diffraction grating 57 has a pattern only in the region 66 near the center. The light emitted from the semiconductor laser 54 passes through the inside of the area 66, and the light reflected from the disc is
Pass outside 6.

FIG. 8 shows a hologram optical element 58.
As shown in (b), it 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. 9 shows the photodetector 55 in the module of FIG.
1 shows an example of the pattern of the light receiving section and the arrangement of the light spots on the light receiving section. In FIG. 9, a semiconductor laser 54 is provided at a position slightly below the center of the photodetector 55, and a mirror 70 for reflecting light emitted from the semiconductor laser 54 is provided. Further, in the figure, the installation position of the mirror 70 is interposed,
Light receiving sections 71, 72 and 73 are arranged on the left side, and light receiving sections 74, 75 and 76 are arranged on the right side. Furthermore,
The light receiving units 77 and 7 are located above the light receiving units 71 and 74, respectively.
8, light receiving units 79 and 80 are provided below the light receiving units 73 and 76, respectively. Light receiving units 71, 7
2 and 73, and the light receiving sections 74, 75, and 7
6 has the same light-receiving area as the light-receiving portions 77, 78, and 79.
And 80 are almost the same as the respective light receiving areas.

The + 1st-order diffracted light from the hologram optical element 58 on the return path of the transmitted light on the outward path of the diffraction grating 57 shown in FIG. 6 forms a light spot 81 on the three divided light receiving sections 71 to 73 shown in FIG. The -1st-order diffracted light of the hologram optical element 58 on the return path forms a light spot 82 on the light receiving sections 74 to 76 divided into three. Also, of the + 1st-order diffracted light on the outward path of the diffraction grating 57, the ± 1st-order diffracted light of the hologram optical element 58 on the return path forms light spots 83 and 84 on the light receiving portions 77 and 78, respectively. Of the -1st-order diffracted light, ± 1st-order diffracted light of the hologram optical element 58 on the return path is reflected on the light receiving portions 79 and 80 by the light spot 8 respectively.
5, 86 are formed.

The light receiving portions 71 to 73, 77 and 79 are located behind the light converging point, and the light receiving portions 74 to 76, 78 and 80 are located before the light converging point. When the levels of the electric signals obtained by the photoelectric conversion by the light receiving units 71 to 80 are respectively represented by V71 to V80, the focus error signal is represented by ｛(V71 + V73 +
V75)-(V72 + V74 + V76)}, and the track error signal is obtained by a known three-beam method.
It is obtained from the calculation of {(V77 + V78)-(V79 + V80)}. The playback signal of the disc is (V71 +
V72 + V73 + V74 + V75 + V76).

Next, a module will be described in which the optical head device of the present invention is applied to a write-once disk or a rewritable phase change disk optical head device. FIG. 10 shows a configuration diagram of an example of the module in this case. As shown in the figure, the module includes a semiconductor laser 90, a package 92 containing a photodetector 91, and a semiconductor laser 90.
And a quarter-wave plate 94 provided in the window of a package 92 in the optical path of the emitted laser light.

The polarization hologram optical element 93 is shown in FIG.
As shown in the figure, the structure is such that a pattern is formed by a proton exchange region 97 and a phase compensation film 98 on a lithium niobate substrate 96 having a birefringent property. Works to diffract.

Next, the operation of the module shown in FIG. 10 will be described. The light emitted from the semiconductor laser 90 is incident on the polarizing hologram optical element 93 as ordinary light and all passes therethrough. The polarized light is converted to circularly polarized light and travels to a disk (not shown). The reflected light from the disk is incident on the quarter-wave plate 94 and is converted from circularly polarized light into linearly polarized light. Then, the reflected light is incident on the polarizing hologram optical element 93 as extraordinary light. The light is diffracted and received by the photodetector 91. The mounting mode of the semiconductor laser 90 on the photodetector 91 is the same as that of FIG.

FIG. 12 shows an interference fringe pattern of the polarizing hologram optical element 93. As shown in the figure, the polarizing hologram optical element 93 has a configuration divided into four regions 101 to 104. The optical axis 105 of the polarizing hologram optical element 93 is set in a direction perpendicular to the polarization direction of the light emitted from the semiconductor laser 90.

FIG. 13 shows an example of the pattern of the light receiving portion of the photodetector 91 of the module shown in FIG. 10 and the arrangement of the light spots on the light receiving portion. 13, a semiconductor laser 90 is provided at a position slightly below the center of the photodetector 91, and
Mirror 10 for reflecting light emitted from semiconductor laser 90
7 are provided. Further, the light receiving units 109 and 11 which are divided into two parts on the left side in the figure with the installation position of the mirror 107 interposed therebetween.
0 is the light receiving unit 111 and 112 divided into two on the right side
Are arranged respectively. Further, the light receiving units 109 and 11
1, light receiving units 113 and 114 are provided on the upper side in the figure, and light receiving units 115 and 116 are provided on the lower side in the figure of the light receiving units 110 and 112, respectively.

The + 1st-order diffracted light from the region 101 of the polarizing hologram optical element 93 shown in FIGS. 10 and 12 forms a light spot 118 on the dividing line of the light receiving sections 109 and 110 divided into two as shown in FIG. The -1st-order diffracted light from the region 101 forms a light spot 122 on the light receiving section 116. The + 1st-order diffracted light from the region 102 in FIG. 12 of the polarizing hologram optical element 93 is 2 as shown in FIG.
A light spot 119 is formed on the division line between the divided light receiving units 111 and 112, and the −1st-order diffracted light from the region 102 forms a light spot 123 on the light receiving unit 115.

The ± 1st-order diffracted light from the region 103 of the polarizing hologram optical element 93 shown in FIG.
As shown in FIG. 12, light spots 120 and 124 are formed on the light receiving sections 113 and 116, respectively, and the area 1 shown in FIG.
The ± 1st-order diffracted lights from the light-receiving portions 114 and 115 respectively have light spots 121 and 12 on the light-receiving portions 114 and 115 as shown in FIG.
5 is formed.

When the levels of the electric signals obtained by photoelectric conversion by all of the light receiving units 109 to 116 are represented by V109 to V116, the focus error signal is obtained by the known Foucault method by ｛(V109 + V112).
− (V110 + V111)}, and the track error signal is obtained by the known push-pull method (V113 + V111).
−V114). The reproduction signal of the disc is obtained from the calculation of (V115 + V116).

Next, a module in which the optical head device of the present invention is applied to a rewritable magneto-optical disk optical head device will be described. FIG. 14 shows a configuration diagram of an example of the module in this case. As shown in the figure, the module includes a package 130 containing a semiconductor laser 126, a photodetector 127, microprisms 128 and 129.
A polarizing diffraction grating 131 provided in a window of a package 130 in an optical path of laser light emitted from a semiconductor laser 126 with a spacer 133 interposed therebetween, and a hologram optical element 13
2 is comprised. The polarizing diffraction grating 131 is shown in FIG.
It has the same structure as that of the polarizing hologram optical element 93 shown in FIG. 1, and has a function of transmitting part of ordinary light, diffracting part of incident light, and diffracting all extraordinary light.

Next, the operation of the module shown in FIG. 14 will be described. In FIG. 14, the laser light emitted from the semiconductor laser 126 makes the hologram optical element 132 approximately 80%
Is transmitted, and enters the polarizing diffraction grating 131 as ordinary light,
About 90% of the light passes through to the disk (not shown). On the other hand, 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 131 as ± first-order diffracted light. , -1st order diffracted light is received by the photodetector 127 via the microprism 129. About 90% of the ordinary light component is transmitted through the polarizing diffraction grating 131 and enters the hologram optical element 132. About ± 16th order diffracted light is diffracted by about 16% and received by the photodetector 127. The mounting mode of the semiconductor laser 126 on the photodetector 127 is the same as that of FIG.

FIG. 15A shows an interference fringe pattern of the polarizing diffraction grating 131 in the module shown in FIG. 14, and FIG.
Indicates patterns of interference fringes of the hologram optical element 132 in the module of FIG. Polarizing diffraction grating 13
One optical axis 135 is set in a direction perpendicular to the polarization direction of the light emitted from the semiconductor laser 126. The hologram optical element 132 has a pattern divided into four regions 136 to 139 only near the center as shown in FIG.

Of the reflected light from the disk, the transmitted light of the polarizing diffraction grating 131 passes through the regions 136 to 139, and the ± first-order diffracted light of the polarizing diffraction grating 131 is the territory 136.
~ 139 outside. The regions 136 and 137 of the hologram optical element 132 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. 16 shows the structure of the microprism 128 in the module shown in FIG. Micro prism 128
Are three glass blocks 141, 142 and 143
Among them, blocks 141 and 142 are formed by dielectric multilayer film 145.
And the blocks 142 and 143 are bonded together via a dielectric multilayer film 146.

According to the microprism 128 having this configuration, the P-polarized light component of the incident light 147 passes through the block 142, the dielectric multilayer 146, and the block 143 almost completely to become the transmitted light 148. On the other hand, the S-polarized light component of the incident light 147 is almost completely reflected twice by the dielectric multilayer films 146 and 145, and further passes through the block 142 to become reflected light 149. The configuration of the microprism 129 is the same as in FIG.

FIG. 17 shows an example of the pattern of the light receiving portion of the photodetector 127 in the module shown in FIG. 14 and the arrangement of the light spots on the light receiving portion. In FIG. 17, the photodetector 1
A semiconductor laser 126 is provided at a position slightly below the center of 27, and a mirror 150 for reflecting light emitted from the semiconductor laser 126 is provided. In the figure, light receiving units 151 and 152 are provided diagonally to the upper left, and light receiving units 153 and 154 are provided diagonally to the lower right.

The light receiving units 155, 156, and 15 are divided into three parts on the left side of the drawing with respect to the installation position of the mirror 150.
7, and a light receiving unit 158, 159, and 160 divided into three on the right side are arranged. Further, the light receiving unit 15
5 and 158, the light receiving sections 161 and 162
And light receiving units 163 and 164 are provided below the light receiving units 157 and 160 in the figure, respectively.

In this photodetector 127, the + 1st-order diffracted light from the polarizing diffraction grating 131 shown in FIG. 14 is separated into transmitted light and reflected light as shown in FIG. The transmitted light forms a light spot 171 on the light receiving unit 151 as shown in FIG. 17, and the reflected light forms a light spot 172 on the light receiving unit 152. The -1st-order diffracted light from the polarizing diffraction grating 131 is separated into transmitted light and reflected light by using the microprism 129 as an analyzer, and the transmitted light forms a light spot 173 on the light receiving section 153 as shown in FIG. The reflected light forms a light spot 174 on the light receiving section 154.

On the other hand, FIG.
The + 1st-order diffracted light from the regions 136 and 137 shown in FIG. 17B is divided into three light receiving portions 155 to 155 as shown in FIG.
Light spots 175 and 176 are formed on 57, respectively.
The -1st-order diffracted light from the regions 136 and 137 is applied to a light spot 1 on each of the three divided light receiving units 158 to 160.
77, 178 are formed. The light receiving units 155 to 157 are located behind the converging point, and the light receiving units 158 to 160 are located ahead of the converging point.

The hologram optical element 132 shown in FIG.
The ± 1st-order diffracted light from the region 138 shown in FIG.
As shown in FIG. 7, light spots 179 and 181 are formed on the light receiving sections 161 and 164, respectively. Further, the ± first-order diffracted lights from the region 139 of the hologram optical element 132 shown in FIG. 15B form light spots 180 and 182 on the light receiving portions 162 and 163, respectively, as shown in FIG.

When the levels of electric signals obtained by photoelectric conversion by all the light receiving sections 151 to 164 in the photodetector 127 are represented by V151 to V164, the focus error signal is obtained by a known spot size method. (V155 + V157 + V159)-(V1
56 + V158 + V160)}, and the track error signal is obtained by the known push-pull method by {(V1
61 + V164)-(V162 + V163)}. Also, the reproduction signal of the disc is Δ (V15
1 + V153)-(V152 + V154)}.

The embodiment of the optical head device of the present invention shown in FIG. 1 has a configuration using two modules 11 and 12 each having a built-in semiconductor laser and detection optical system for miniaturization. However, the present invention is not limited to this, and a configuration using two sets of blocks separately provided with a semiconductor laser and a detection optical system is also possible.

[0065]

As described above, according to the present invention,
For the first light, the objective lens can be used with an effective numerical aperture determined by the effective diameter of the objective lens and the focal length of the objective lens. For the second light, the cross section of the light beam transmitted through the aperture limiting element can be used. Since the objective lens can be used with an effective numerical aperture determined by the diameter and the focal length of the objective lens, the optimal wavelength and the numerical aperture of the objective lens can be selected for each of the two types of optical recording media. Therefore, both types of optical recording media, such as a digital video disk and a compact disk including a write-once type, can be reproduced with the optimum wavelength and the numerical aperture of the objective lens, respectively.

[Brief description of the drawings]

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

FIG. 2 is a plan view and a sectional view of an aperture limiting element used in the first embodiment of the optical head device according to the present invention.

FIG. 3 is a plan view and a cross-sectional view of an aperture limiting element used in a second embodiment of the optical head device according to the present invention.

FIG. 4 is a plan view and a cross-sectional view of an aperture limiting element used in a third embodiment of the optical head device according to the present invention.

FIG. 5 is a diagram showing a configuration of a wavelength filter used in an embodiment of the optical head device of the present invention.

FIG. 6 is a diagram showing a module configuration when the embodiment of FIG. 1 is applied to a read-only disc.

FIG. 7 is a diagram showing a mounting mode of a semiconductor laser on a photodetector in the module of FIG. 6;

8 is a diagram showing a pattern of interference fringes of a diffraction grating and a hologram optical element in the module of FIG. 6;

FIG. 9 is a diagram illustrating an example of 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. 6;

FIG. 10 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.

11 is a diagram showing a structure of an example of a polarizing hologram optical element in the module of FIG.

FIG. 12 is a diagram showing a pattern of interference fringes of a polarizing hologram optical element in the module of FIG. 10;

FIG. 13 is a diagram showing a pattern of a light receiving section of a photodetector and an arrangement of light spots on the light receiving section in the module of FIG.

FIG. 14 is a diagram showing a configuration of a module when the embodiment of the optical head device of the present invention is applied to a rewritable magneto-optical disk.

FIG. 15 is a diagram showing a pattern of interference fringes of a polarizing diffraction grating and a hologram optical element in the module of FIG. 14;

FIG. 16 is a diagram showing a configuration of a microprism in the module of FIG. 14;

FIG. 17 is a diagram showing a pattern of a light receiving section of a photodetector and an arrangement of light spots on the light receiving section in the module of FIG.

FIG. 18 is a diagram showing a configuration of an example of a conventional optical head device.

[Explanation of symbols]

11, 12 module 13, 47 wavelength filter 14 collimator lens 15, 25, 31 aperture limiting element 16 objective lens 17 disk 20, 27, 33 circular groove 21, 28, 34 substrate 22, 36 wavelength filter film 23, 39, 98 phase Compensation film 29, 35, 57 Diffraction grating 37 Adhesive 38 Glass substrate 41, 42, 48 to 50, 141 to 143 Block 43, 51, 52, 145, 146 Dielectric multilayer film 44, 45, 147 Incident light 54, 90 , 126 semiconductor lasers 55, 91, 127 photodetectors 56, 92, 130 packages 58, 132 hologram optical elements 59, 133 spacers 61 heat sinks 62, 64, 70, 107, 150 mirrors 63 recesses 66, 101-104, 136- 139 regions 71-80, 109-116 151-164 Light-receiving unit 81-86, 118-125, 171-182 Light spot 93 Polarizing hologram optical element 94 Quarter-wave plate 96 Lithium niobate substrate 97 Proton exchange area 105, 135 Optical axis 128, 129 Microprism 131 Polarizing diffraction grating 148 Transmitted light 149 Reflected light

Claims (6)

(57) [Claims] A first light source that emits a first light of a first wavelength; a second light source that emits a second light of a second wavelength different from the first wavelength; The first light from the first light source and the second light from the second light source are combined and guided to an optical recording medium;
An optical multiplexing / demultiplexing means for demultiplexing the reflected light from the optical recording medium; and condensing the light multiplexed by the optical multiplexing / demultiplexing means on the optical recording medium and then reflecting the light on the optical recording medium. An objective lens that transmits the reflected light; and an objective lens that is provided between the optical multiplexing / demultiplexing unit and the objective lens so that all the incident light of the first wavelength is transmitted and the incident light of the second wavelength is transmitted. Is an aperture limiting element that transmits only the central portion of the light beam cross section; a first light detection optical system that receives the reflected light of the first wavelength that is demultiplexed by the optical multiplexing / demultiplexing means; An optical head device comprising: a second light detection optical system that receives the reflected light of the second wavelength that has been split by the splitter. 2. A wavelength filter film provided only outside a circular area having a diameter smaller than an effective diameter of the objective lens on a substrate, and a phase filter provided on the wavelength filter film. A compensation film, outside the circular region, the first light of the first wavelength is almost completely transmitted, and the second light of the second wavelength is almost completely reflected,
2. The optical head device according to claim 1, wherein the light incident into the circular region is configured to completely transmit both the first and second lights. 3. The wavelength filter film according to claim 1, wherein a high refractive index layer having a thickness of d ₁ and a refractive index of n _{1 and} a low refractive index layer having a thickness of d ₂ and a refractive index of n ₂ are alternately formed in an odd number. A layer-deposited configuration, and
The optical head device according to claim 2, characterized in that a structure having a relationship that satisfies _{n 1 · d 1 = n 2} · d 2 = λ / 4 composed expression when the said second wavelength lambda. 4. The aperture limiting element comprises a diffraction grating formed on a substrate only outside a circular region having a diameter smaller than an effective diameter of the objective lens, wherein the diffraction grating has a wavelength of the first wavelength. The first light is completely transmitted, the second light of the second wavelength is almost diffracted, and the light incident into the circular region is completely transmitted together with the first and second lights. The optical head device according to claim 1, wherein: 5. The aperture limiting element according to claim 1, wherein the diffraction grating and the wavelength filter film are formed on a first substrate, and the phase compensation film is formed on a second substrate in a circular region having a diameter smaller than an effective diameter of the objective lens. Is sequentially formed only on the outside of the
The gap between the substrate and the wavelength filter film is filled with an adhesive, the first light of the first wavelength is completely transmitted outside the circular region, and the second light of the second wavelength is 2. The optical head device according to claim 1, wherein said optical head device is configured to completely reflect and diffract light, and to completely transmit light incident on said circular area together with said first and second lights. 6. The wavelength filter film, wherein a high refractive index layer having a thickness of d ₁ and a refractive index of n _{1 and} a low refractive index layer having a thickness of d ₂ and a refractive index of n ₂ are alternately formed. In this configuration, an odd number of layers are deposited on the diffraction grating, and the relationship satisfies the following formula: n ₁ · d ₁ = n ₂ · d ₂ = λ / 4 where λ is the second wavelength. The optical head device according to claim 5, wherein: