JP2004139728A - Optical head device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical head device which has a large ratio of a light quantity used for detecting an information signal recorded in a disk and a track error signal according to a phase difference method to the quantity of the light reflected from the disk, and can obtain high SN ratios concerning these signals. <P>SOLUTION: The light reflected from the disk 6 is diffracted by a hologram optical element 7 and is received by a photo-detector 9. A focus error signal is detected from the negative primary diffracted light of the hologram optical element 7, and the track error signal by the phase difference method, a track error signal by a push-pull method, and the information signal recorded in the disk 6 are detected from the positive primary diffracted light of the hologram optical element 7. A diffraction efficiency of the positive primary diffracted light is higher than that of the negative primary diffracted light. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an optical head device for performing recording and reproduction on an optical recording medium, and in particular, an optical head device capable of detecting both a track error signal by a phase difference method and a track error signal by a push-pull method. It is about.

For a read-only optical recording medium such as a DVD-ROM, a phase difference method is generally used as a method for detecting a track error signal. On the other hand, for a rewritable optical recording medium such as a DVD-RAM, a push-pull method is generally used as a method for detecting a track error signal. Therefore, in order to support both a read-only optical recording medium and a rewritable optical recording medium with a single optical head device, both a track error signal by the phase difference method and a track error signal by the push-pull method are used. It is necessary to detect. The Foucault method (or double knife edge method), the astigmatism method, and the spot size method are generally used as a method for detecting the focus error signal, but the Foucault method is compared with the astigmatic method and the spot size method. It is characterized in that the noise of the focus error signal when crossing the track is small. Patent Documents 1 and 2 can detect both a track error signal by a phase difference method and a track error signal by a push-pull method, and can detect a focus error signal by a Foucault method. An optical head device is disclosed.
FIG. 18 shows a configuration of a first conventional optical head device disclosed in Patent Document 1. As shown in FIG. The light emitted from the semiconductor laser 1 is collimated by the collimator lens 2, enters the polarization beam splitter 3 as P-polarized light, transmits almost 100%, and is converted from linearly polarized light to circularly polarized light by the で wavelength plate 4. The light is focused on the disk 6 by the objective lens 5. The reflected light from the disk 6 passes through the objective lens 5 in the opposite direction, is converted from circularly polarized light into linearly polarized light by the quarter-wave plate 4, enters the polarizing beam splitter 3 as S-polarized light, and is almost 100% reflected. The light is diffracted by the hologram optical element 158, passes through the lens 8, and is received by the photodetector 159.
FIG. 19 is a plan view of the hologram optical element 158. The hologram optical element 158 is divided into four regions 160 to 163 by two dividing lines parallel to the radial direction and the tangential direction of the disk 6.
FIG. 20 shows a pattern of the photodetector 159 and a light spot on the photodetector 159. The light detector 159 has light receiving units 164 to 171. The + 1st-order diffracted light from the region 160 of the hologram optical element 158 forms a light spot 173 on the boundary between the light receiving unit 164 and the light receiving unit 165, and the -1st-order diffracted light forms a light spot 178 on the light receiving unit 170. The + 1st-order diffracted light from the region 161 of the hologram optical element 158 forms a light spot 172 outside the light receiving portion, and the -1st-order diffracted light forms a light spot 179 on the light receiving portion 171. The + 1st-order diffracted light from the region 162 of the hologram optical element 158 forms a light spot 174 on the boundary between the light receiving section 166 and the light receiving section 167, and the -1st-order diffracted light forms a light spot 177 on the light receiving section 169. The + 1st-order diffracted light from the region 163 of the hologram optical element 158 forms a light spot 175 outside the light receiving portion, and the -1st-order diffracted light forms a light spot 176 on the light receiving portion 168. When the outputs from the light receiving units 164 to 171 are represented by V164 to V171, the focus error signal by the Foucault method is obtained from the calculation of (V164 + V167)-(V165 + V166). The track error signal by the phase difference method is obtained from the phase difference between V168 + V170 and V169 + V171. The track error signal by the push-pull method is obtained from the calculation of (V168 + V171)-(V169 + V170). The information signal recorded on the disk 6 is obtained from the calculation of V168 + V169 + V170 + V171 or V164 + V165 + V166 + V167 + V168 + V169 + V170 + V171.
FIG. 21 shows a configuration of a module 180 which is a main part of a second conventional optical head device disclosed in Patent Document 2. A semiconductor laser 181 and a photodetector 182 are installed inside the module 180, and a hologram optical element 183 is installed in a window of the module 180. Light emitted from the semiconductor laser 181 partially passes through the hologram optical element 183 and travels toward the disk. The light reflected from the disk is partially diffracted by the hologram optical element 183 and received by the photodetector 182.
FIG. 22 is a plan view of the hologram optical element 183. The hologram optical element 183 is divided into four regions 184 to 187 by two dividing lines parallel to the radial direction and the tangential direction of the disk.
FIG. 23 shows a pattern of the photodetector 182 and a light spot on the photodetector 182. The light detector 182 includes light receiving units 188 to 193. The + 1st-order diffracted light from the region 184 of the hologram optical element 183 forms a light spot 195 on the boundary between the light receiving unit 189 and the light receiving unit 190. The + 1st-order diffracted light from the region 185 of the hologram optical element 183 forms a light spot 194 on the light receiving section 188. The + 1st-order diffracted light from the region 186 of the hologram optical element 183 forms a light spot 197 on the light receiving section 193. The + 1st-order diffracted light from the region 187 of the hologram optical element 183 forms a light spot 196 on the boundary between the light receiving unit 191 and the light receiving unit 192. When the outputs from the light receiving units 188 to 193 are respectively represented by V188 to V193, the focus error signal by the Foucault method is obtained from the calculation of (V189 + V192)-(V190 + V191). The track error signal by the phase difference method is obtained from the phase difference between V189 + V190 + V191 + V192 and V188 + V193. The track error signal by the push-pull method is obtained from the calculation of (V189 + V190 + V193)-(V188 + V191 + V192). The information signal recorded on the disc is obtained from the calculation of V188 + V189 + V190 + V191 + V192 + V193.
FIG. 24 is a cross-sectional view of the hologram optical element 183. The hologram optical element 183 has a configuration in which a dielectric film 198 is formed on the glass substrate 14. Outgoing light from the semiconductor laser 181 enters the hologram optical element 183 as incident light 199, passes through as transmitted light 200, and travels toward the disk. The reflected light from the disk enters the hologram optical element 183 as incident light 201, is diffracted as + 1st-order diffracted light 202, and is received by the photodetector 182. By making the cross-sectional shape of the dielectric film 198 into a sawtooth shape, the diffraction efficiency of the + 1st-order diffracted light is increased and almost no -1st-order diffracted light is generated.

JP-A-10-143878 JP-A-10-143883

In the first conventional optical head device, the information signal recorded on the disk 6 is obtained from the calculation of V168 + V169 + V170 + V171 or V164 + V165 + V166 + V167 + V168 + V169 + V170 + V171. In the latter case, the light spot 173 formed on the boundary between the light receiving unit 164 and the light receiving unit 165 and the light spot 174 formed on the boundary between the light receiving unit 166 and the light receiving unit 167 are used for detecting an information signal. . However, since the frequency characteristics of the photodetector on the boundary line are lower than those on the light receiving section, the light spot formed on the boundary line does not substantially contribute to the detection of the information signal, which is a high-frequency signal. Therefore, only the case where the information signal recorded on the disk 6 is obtained from the calculation of V168 + V169 + V170 + V171 will be considered.
Since both the information signal recorded on the disk 6 and the track error signal by the phase difference method are high frequency signals, a high S / N is required. In order to obtain a high S / N, it is necessary to increase the ratio A of the light amount used for detecting these signals to the light amount of the reflected light from the disk 6 as much as possible. Since the cross-sectional shape of the hologram optical element 158 is rectangular, the diffraction efficiency of the + 1st-order diffracted light is equal to the diffraction efficiency of the -1st-order diffracted light. In this case, the maximum value of the diffraction efficiency of the ± 1st-order diffracted light is about 40.5%. That is, the maximum value of A is 0.405. This value is not necessarily large enough.
In the second conventional optical head device, the information signal recorded on the disc is obtained from the calculation of V188 + V189 + V190 + V191 + V192 + V193. In this case, the light spot 195 formed on the boundary between the light receiving unit 189 and the light receiving unit 190 and the light spot 196 formed on the boundary between the light receiving unit 191 and the light receiving unit 192 are used for detecting information signals. However, since the frequency characteristics of the photodetector on the boundary line are lower than those on the light receiving section, the light spot formed on the boundary line does not substantially contribute to the detection of the information signal, which is a high-frequency signal. That is, this is equivalent to detecting an information signal using only the light spot 194 and the light spot 197 corresponding to half of the cross section of the reflected light from the disk, and therefore the resolution of the information signal and the crosstalk between adjacent tracks are poor. However, the information signal cannot be detected correctly. Further, since the focus error signal is detected using only the light spot 195 and the light spot 196 corresponding to half of the cross section of the reflected light from the disk, the noise of the focus error signal when crossing the track is large, Detection cannot be performed correctly.
The hologram optical element 183 in the second conventional optical head device is used instead of the hologram optical element 158 in the first conventional optical head device, a focus error signal is detected from the -1st-order diffracted light, and the phase difference is detected from the + 1st-order diffracted light. It is also conceivable to detect a track error signal by the push-pull method, a track error signal by the push-pull method, and an information signal recorded on the disk 6. However, in this case, since the diffraction efficiency of the + 1st-order diffracted light is high, the value of A can be increased. However, since almost no -1st-order diffracted light is generated, the focus error signal is actually detected. You can't do that.
An object of the present invention is to solve the above-mentioned problems in a conventional optical head device and to be used for detection of an information signal recorded on a disk and a track error signal by a phase difference method with respect to the amount of reflected light from the disk. An object of the present invention is to provide an optical head device in which a ratio A of light amounts is large and a high S / N is obtained for these signals.

The optical head device according to claim 1, wherein the light source, an objective lens for condensing light emitted from the light source on an optical recording medium, and the light provided between the light source and the objective lens. First light separating means for separating the optical path of the reflected light from the recording medium from the optical path of the emitted light from the light source, and further reflecting the reflected light from the optical recording medium passing through the first light separating means into a first group. A second light separating unit that separates the first group of light and a second group of light, and an optical head device having a photodetector that receives the first group of light and the second group of light. The light amount of the light is larger than the light amount of the second group of light, the track error signal by the phase difference method, the track error signal by the push-pull method, and the information recorded on the optical recording medium from the light of the first group. Signal, and focus error by the Foucault method from the second group of light. Detecting the signal, the second light separating means is a hologram optical element, the first group of light is + 1st-order diffracted light of the hologram optical element, and the second group of light is a hologram optical element. It is a -1st-order diffracted light.
Thus, when the reflected light from the disc is divided into the first group of light and the second group of light, the light amount of the first group of light is greater than the light amount of the second group of light, Is large, and a high S / N can be obtained with respect to the information signal recorded on the disk and the track error signal by the phase difference method.

An optical head device according to a second aspect of the present invention relates to the optical head device according to the first aspect, wherein the hologram optical element has four regions defined by two division lines parallel to a radial direction and a tangential direction of the optical recording medium. The four regions are characterized in that the directions of the gratings or the pitches of the gratings are different from each other.

An optical head device according to a third aspect of the present invention is the optical head device according to any one of the first and second aspects, wherein the phase distribution of the grating in the hologram optical element is a four-level step-like shape, and the two adjacent two When the phase difference of light passing through the level is φ, and the widths of the first to fourth stage gratings are p / 2−w, w, p / 2−w, w, φ is approximately π / 2. In addition, the range of w / p is characterized by 0 <w / p <0.25 or 0.25 <w / p <0.5.

The optical head device according to claim 4, wherein the light source, an objective lens for condensing light emitted from the light source on an optical recording medium, and the light provided between the light source and the objective lens. First light separating means for separating the optical path of the reflected light from the recording medium from the optical path of the emitted light from the light source, and further reflecting the reflected light from the optical recording medium passing through the first light separating means into a first group. A second light separating unit that separates the first group of light and a second group of light, and an optical head device having a photodetector that receives the first group of light and the second group of light. The light amount of the light is larger than the light amount of the second group of light, the track error signal by the phase difference method, the track error signal by the push-pull method, and the information recorded on the optical recording medium from the light of the first group. Signal and focus by the Foucault method from the second group of light. Detecting a difference signal, wherein the first light separating means and the second light separating means are an integrated polarizing hologram optical element, and the polarizing hologram optical element transmits light emitted from the light source; And diffracts the reflected light from the optical recording medium, and the first group of light is + 1st-order diffracted light of the polarizing hologram optical element, and the second group of light is the light of the polarizing hologram optical element. It is a -1st-order diffracted light.

An optical head device according to a fifth aspect of the present invention is the optical head device according to the fourth aspect, wherein the polarizing hologram optical element is formed by two division lines parallel to a radial direction and a tangential direction of the optical recording medium. The four regions are characterized in that the directions of the lattices or the pitches of the lattices are different from each other.

An optical head device according to a sixth aspect of the present invention is the optical head device according to any one of the fourth and fifth aspects, wherein the phase distribution of the grating in the polarizing hologram optical element has a step shape of four levels, The phase differences of the extraordinary light passing through two adjacent levels are φo, φe, and the widths of the first to fourth gratings are p / 2-w, w, p / 2-w, w, respectively. At this time, φo is approximately 0, φe is approximately π / 2, and the range of w / p is 0 <w / p <0.25 or 0.25 <w / p <0.5, and Light emitted from a light source is incident on the polarizing hologram optical element as ordinary light, and reflected light from the optical recording medium is incident on the polarizing hologram optical element as extraordinary light.

An optical head device according to a seventh aspect of the present invention is the optical head device according to any one of the fourth and fifth aspects, wherein the phase distribution of the grating in the polarizing hologram optical element is a four-level stepped shape, The phase differences of the extraordinary light passing through two adjacent levels are φo, φe, and the widths of the first to fourth gratings are p / 2-w, w, p / 2-w, w, respectively. At this time, φo is approximately π / 2, φe is approximately 0, and the range of w / p is 0 <w / p <0.25 or 0.25 <w / p <0.5, and Light emitted from a light source is incident on the polarizing hologram optical element as extraordinary light, and reflected light from the optical recording medium is incident on the polarizing hologram optical element as ordinary light.

9. The optical head device according to claim 8, wherein the light source, an objective lens for condensing light emitted from the light source on an optical recording medium, and the light provided between the light source and the objective lens. First light separating means for separating the optical path of the reflected light from the recording medium from the optical path of the emitted light from the light source, and further reflecting the reflected light from the optical recording medium passing through the first light separating means into a first group. A second light separating unit that separates the first group of light and a second group of light, and an optical head device having a photodetector that receives the first group of light and the second group of light. The light amount of the light is larger than the light amount of the second group of light, the track error signal by the phase difference method, the track error signal by the push-pull method, and the information recorded on the optical recording medium from the light of the first group. Signal and focus by the Foucault method from the second group of light. Detecting a difference signal, wherein the second light separating means is a Wollaston prism, wherein the first group of light is one of two refracted lights of the Wollaston prism, and the second group of light is Is the other of the two refracted lights of the Wollaston prism.

The optical head device according to claim 9 of the present invention relates to the optical head device according to claim 8, wherein the Wollaston prism is a first prism positioned on the incident side of the reflected light from the optical recording medium and the optical recording medium. The optical axis of the first prism is inclined by θ with respect to a direction parallel to the polarization direction of the reflected light from the optical recording medium. The optical axis of the second prism is inclined by θ with respect to the direction perpendicular to the polarization direction of the reflected light from the optical recording medium, and the first group of light is transmitted from the optical recording medium. Of the reflected light, the first prism is extraordinary light, the second prism is refracted light that becomes ordinary light, and the second group of light is reflected light from the optical recording medium in the first prism. Joko, the second pre It is refracted light that becomes extraordinary light in the mechanism, and the range of θ is −45 ° <θ <0 ° or 0 ° <θ <45 °.

The optical head device according to claim 10, wherein the Wollaston prism is a first prism located on an incident side of the reflected light from the optical recording medium, and the optical recording medium is the optical recording medium. The optical axis of the first prism is inclined by θ with respect to a direction parallel to the polarization direction of the reflected light from the optical recording medium. The optical axis of the second prism is inclined by θ with respect to the direction perpendicular to the polarization direction of the reflected light from the optical recording medium, and the first group of light is transmitted from the optical recording medium. The reflected light is ordinary light in the first prism, refracted light that becomes abnormal light in the second prism, and the second group of light is reflected light from the optical recording medium in the first prism. Extraordinary light, said second The prism is a refracted light that becomes ordinary light in the prism, and the range of θ is −90 ° <θ <−45 ° or 45 ° <θ <90 °.

An optical head device according to an eleventh aspect of the present invention is the optical head device according to any one of the eighth to the tenth aspects, wherein the wollaston prism is disposed between the Wollaston prism and the photodetector or the first light separation unit and the wollaston. A four-segment prism for refracting reflected light from the optical recording medium is provided between the ton prisms, and the four-segment prisms are two parallel to a radial direction and a tangential direction of the optical recording medium. It is divided into four regions by dividing lines, and the four regions are characterized in that the directions of inclination of the exit surface with respect to the entrance surface or the angles formed by the exit surface and the entrance surface are different from each other.

An optical head device according to a twelfth aspect of the present invention is directed to the optical head device according to any one of the eighth to tenth aspects, wherein the wollaston prism is disposed between the Wollaston prism and the photodetector or the first light separating means and the wollaston. A hologram optical element for diffracting reflected light from the optical recording medium as + 1st-order diffracted light is provided between the ton prisms, and the hologram optical element is parallel to a radial direction and a tangential direction of the optical recording medium. It is divided into four regions by two dividing lines, and the four regions are characterized by different grating directions, grating pitches, or grating phase distributions.

An optical head device according to a thirteenth aspect of the present invention is the optical head device according to the twelfth aspect, wherein the phase distribution of the grating in the hologram optical element is N-stepped (N is an integer of 3 or more), and is adjacent to each other. When the phase difference between the light transmitted through the two levels is φ and the widths of the first to Nth gratings are all p / N, φ is approximately 2π / N.

As described above, according to the optical head device of the present invention, when the reflected light from the disk is divided into the first group of light and the second group of light, the amount of the first group of light becomes Since it is larger than the light amount of the two groups of light, the value of the light amount ratio A is large, and a high S / N can be obtained for the information signal recorded on the disk and the track error signal by the phase difference method.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a first embodiment of the optical head device of the present invention. The light emitted from the semiconductor laser 1 is collimated by the collimator lens 2, enters the polarization beam splitter 3 as P-polarized light, transmits almost 100%, and is converted from linearly polarized light to circularly polarized light by the で wavelength plate 4. The light is focused on the disk 6 by the objective lens 5. The reflected light from the disk 6 passes through the objective lens 5 in the opposite direction, is converted from circularly polarized light into linearly polarized light by the quarter-wave plate 4, enters the polarizing beam splitter 3 as S-polarized light, and is almost 100% reflected. The light is diffracted by the hologram optical element 7, transmitted through the lens 8, and received by the photodetector 9.

FIG. 2 is a plan view of the hologram optical element 7. The hologram optical element 7 is divided into four regions 10 to 13 by two dividing lines parallel to the radial direction and the tangential direction of the disk 6. The direction of the lattice is parallel to the tangential direction of the disk 6 in any of the regions 10 to 13. Further, the pitch of the lattice becomes wider in the order of the region 10, the region 11, the region 12, and the region 13.

FIG. 3 is a sectional view of the hologram optical element 7. The hologram optical element 7 has a configuration in which a dielectric film 15 is formed on a glass substrate 14. The reflected light from the disk 6 enters the hologram optical element 7 as incident light 16, is diffracted as −1st-order diffracted light 17 and + 1st-order diffracted light 18, and is received by the photodetector 9. The cross-sectional shape of the dielectric film 15 is a four-level stepped shape. The height differences between two adjacent levels are all equal. Assuming that the phase difference between the light passing through two adjacent levels is φ, and the widths of the first to fourth gratings are p / 2-w, w, p / 2-w, and w, respectively, the -1st-order diffracted light And the diffraction efficiency η + 1 of the + 1st-order diffracted light are given by equations (1) and (2), respectively.
η-1 = (2 / π2) (1-cos2φ) {1-sin (2πw / p) sinφ} (1)
η + 1 = (2 / π2) (1-cos2φ) {1 + sin (2πw / p) sinφ} (2)
If φ = π / 2 and w / p = 0.135 or w / p = 0.365, η-1 = 0.10 and η + 1 = 0.71. Therefore, a focus error signal is detected from the -1st-order diffracted light 17, and a track error signal by the phase difference method, a track error signal by the push-pull method, and an information signal recorded on the disk 6 are detected from the + 1st-order diffracted light 18. Then, the value of A becomes 0.71, which is larger than the value of the first conventional optical head device. The range of w / p satisfying η-1 <η + 1 and η-1 ≠ 0 is 0 <w / p <0.25 or 0.25 <w / p <0.5.

Assuming that the difference between the heights of two adjacent levels of the dielectric film 15 is h / 4, the refractive index of the dielectric film 15 is n, and the wavelength of the incident light 16 is λ, φ is given by Expression (3).
φ = (2π / λ) (n−1) h / 4 (3)
In the case of λ = 660 nm, n = 1.46 when SiO 2 is used as the dielectric film 15. Therefore, in order to set φ = π / 2, h = 1.43 μm may be used.

FIG. 4 shows a pattern of the photodetector 9 and a light spot on the photodetector 9. The light detector 9 has a light receiving section 19 to a light receiving section 26. The -1st-order diffracted light from the area 10 of the hologram optical element 7 forms a light spot 27 on the boundary between the light receiving section 19 and the light receiving section 20, and the + 1st-order diffracted light forms a light spot 34 on the light receiving section 26. The -1st-order diffracted light from the area 11 of the hologram optical element 7 forms a light spot 28 on the boundary between the light receiving section 19 and the light receiving section 20, and the + 1st-order diffracted light forms a light spot 33 on the light receiving section 25. The -1st-order diffracted light from the area 12 of the hologram optical element 7 forms a light spot 29 on the boundary between the light receiving section 21 and the light receiving section 22, and the + 1st-order diffracted light forms a light spot 32 on the light receiving section 24. The -1st-order diffracted light from the area 13 of the hologram optical element 7 forms a light spot 30 on the boundary between the light receiving sections 21 and 22, and the + 1st-order diffracted light forms a light spot 31 on the light receiving section 23. When the outputs from the light receiving units 19 to 26 are respectively represented by V19 to V26, the focus error signal by the Foucault method is obtained from the calculation of (V19 + V22)-(V20 + V21). The track error signal by the phase difference method is obtained from the phase difference between V23 + V26 and V24 + V25. The track error signal by the push-pull method is obtained from the calculation of (V23 + V25)-(V24 + V26). The information signal recorded on the disk 6 is obtained from the calculation of V23 + V24 + V25 + V26.

A description will be given of a second embodiment of the optical head device according to the present invention. In the second embodiment of the optical head device of the present invention, the hologram optical element 7 and the photodetector 9 in the first embodiment of the optical head device of the present invention shown in FIG. This is a configuration in which the photodetector 48 is replaced.

FIG. 5 is a plan view of the hologram optical element 35. FIG. The hologram optical element 35 is divided into four regions 36 to 39 by two dividing lines parallel to the radial direction and the tangential direction of the disk 6. The direction of the lattice is inclined at a predetermined angle in the negative direction with respect to the tangential direction of the disk 6 in the regions 36 and 37, and in the positive direction with respect to the tangential direction of the disk 6 in the regions 38 and 39. It is inclined by a predetermined angle. The pitch of the grating is equal in the region 36 and the region 39 and in the region 37 and the region 38, and is wider in the latter than in the former.

FIG. 6 is a sectional view of the hologram optical element 35. FIG. 6A is a cross-sectional view of a region 36 and a region 37, and FIG. 6B is a cross-sectional view of a region 38 and a region 39. In FIG. 6A, the hologram optical element 35 has a configuration in which a dielectric film 40 is formed on a glass substrate 14. The reflected light from the disk 6 enters the hologram optical element 35 as incident light 42, is diffracted as −1st-order diffracted light 43 and + 1st-order diffracted light 44, and is received by the photodetector 48. On the other hand, in FIG. 6B, the hologram optical element 35 has a configuration in which a dielectric film 41 is formed on a glass substrate 14. The reflected light from the disk 6 enters the hologram optical element 35 as incident light 45, is diffracted as −1st-order diffracted light 46 and + 1st-order diffracted light 47, and is received by a photodetector 48. The cross-sectional shapes of the dielectric film 40 and the dielectric film 41 are the same as the cross-sectional shape of the dielectric film 15 in the hologram optical element 7 shown in FIG. Accordingly, a focus error signal is detected from the -1st-order diffracted light 43 and the -1st-order diffracted light 46, and a track error signal by the phase difference method, a track error signal by the push-pull method, and the disc 6 are detected from the + 1st-order diffracted light 44 and the + 1st-order diffracted light 47. If the configuration is such that the information signal recorded in the first optical head device is detected, the value of A becomes 0.71, which is larger than the value of the conventional first optical head device.

FIG. 7 shows a pattern of the photodetector 48 and a light spot on the photodetector 48. The light detector 48 has a light receiving section 49 to a light receiving section 56. The -1st-order diffracted light from the region 36 of the hologram optical element 35 forms a light spot 57 on the boundary between the light receiving section 49 and the light receiving section 50, and the + 1st-order diffracted light forms a light spot 64 on the light receiving section 56. The -1st-order diffracted light from the region 37 of the hologram optical element 35 forms a light spot 58 on the boundary between the light receiving section 49 and the light receiving section 50, and the + 1st-order diffracted light forms a light spot 63 on the light receiving section 55. The -1st-order diffracted light from the region 38 of the hologram optical element 35 forms a light spot 59 on the boundary between the light receiving sections 51 and 52, and the + 1st-order diffracted light forms a light spot 62 on the light receiving section 54. The -1st-order diffracted light from the region 39 of the hologram optical element 35 forms a light spot 60 on the boundary between the light receiving unit 51 and the light receiving unit 52, and the + 1st-order diffracted light forms a light spot 61 on the light receiving unit 53. When the outputs from the light receiving units 49 to 56 are represented by V49 to V56, the focus error signal by the Foucault method is obtained from the calculation of (V49 + V52)-(V50 + V51). The track error signal by the phase difference method is obtained from the phase difference between V53 + V56 and V54 + V55. The track error signal by the push-pull method is obtained from the calculation of (V53 + V55)-(V54 + V56). The information signal recorded on the disk 6 is obtained from the calculation of V53 + V54 + V55 + V56.

FIG. 8 shows a third embodiment of the optical head device of the present invention. A semiconductor laser 66 and a photodetector 67 are provided inside the module 65. The light emitted from the semiconductor laser 66 is collimated by the collimator lens 2, transmitted almost completely through the polarizing hologram optical element 68, converted from linearly polarized light into circularly polarized light by the 波長 wavelength plate 4, and converted by the objective lens 5. The light is focused on the disk 6. The reflected light from the disk 6 passes through the objective lens 5 in the opposite direction, is converted from circularly polarized light into linearly polarized light by the quarter-wave plate 4, is almost completely diffracted by the polarizing hologram optical element 68, and passes through the collimator lens 2. The light passes through and is received by the photodetector 67.

The plan view of the polarizing hologram optical element 68 is the same as the plan view of the hologram optical element 7 shown in FIG. The polarizing hologram optical element 68 is divided into four regions 10 to 13 by two dividing lines parallel to the radial direction and the tangential direction of the disk 6. The direction of the lattice is parallel to the tangential direction of the disk 6 in any of the regions 10 to 13. Further, the pitch of the lattice becomes wider in the order of the region 10, the region 11, the region 12, and the region 13.

FIG. 9 is a sectional view of the polarizing hologram optical element 68. The polarizing hologram optical element 68 has a structure in which a proton exchange region 70 is formed in a lithium niobate substrate 69 having birefringence, and a dielectric film 71 is formed on the substrate. The light emitted from the semiconductor laser 66 is incident on the polarizing hologram optical element 68 as incident light 72, is transmitted as transmitted light 73, and travels toward the disk 6. The reflected light from the disk 6 enters the polarizing hologram optical element 68 as incident light 74, is diffracted as −1st-order diffracted light 75 and + 1st-order diffracted light 76, and is received by the photodetector 67. The cross-sectional shape of the proton exchange region 70 and the dielectric film 71 is a four-level stepped shape. The difference in depth between two adjacent levels in the proton exchange region 70 is all equal, and the difference in height between two adjacent levels in the dielectric film 71 is all equal. The phase differences between the ordinary light and the extraordinary light passing through two adjacent levels are φo and φe, and the widths of the first to fourth gratings are p / 2-w, w, p / 2-w, and w, respectively. Then, the transmittances ηo0 and ηe0 for ordinary light and extraordinary light, the diffraction efficiencies ηo-1 and ηe-1 of −1st-order diffracted light for ordinary light and extraordinary light, and the diffraction efficiencies ηo + 1 and ηe of + 1st-order diffracted light for ordinary light and extraordinary light +1 is given by the equations (4) to (9).
ηo0 = (1/2) (1 + cos2φo)
× {1-4w / p (1-2w / p) (1-cosφo)} (4)
ηe0 = (1/2) (1 + cos2φe)
× {1-4w / p (1-2w / p) (1-cosφe)} (5)
ηo-1 = (2 / π2) (1-cos2φo) {1-sin (2πw / p) sinφo} (6)
ηe-1 = (2 / π2) (1-cos2φe) {1-sin (2πw / p) sinφe} (7)
ηo + 1 = (2 / π2) (1-cos2φo) {1 + sin (2πw / p) sinφo} (8)
ηe + 1 = (2 / π2) (1-cos2φe) {1 + sin (2πw / p) sinφe} (9)
If φo = 0, φe = π / 2, w / p = 0.135 or w / p = 0.365, ηo0 = 1, ηo-1 = 0, ηo + 1 = 0, ηe0 = 0, ηe-1 = 0.10, ηe + 1 = 0.71. That is, when the light emitted from the semiconductor laser 66 is made incident on the polarizing hologram optical element 68 as ordinary light, 100% of the light is transmitted as transmitted light, and the reflected light from the disk 6 is made incident on the polarizing hologram optical element 68 as extraordinary light. Then, 10% is diffracted as -1st-order diffracted light and 71% is diffracted as + 1st-order diffracted light. Therefore, a focus error signal is detected from the -1st-order diffracted light 17, and a track error signal by the phase difference method, a track error signal by the push-pull method, and an information signal recorded on the disk 6 are detected from the + 1st-order diffracted light 18. Then, the value of A becomes 0.71, which is larger than the value of the first conventional optical head device. The range of w / p satisfying ηe-1 <ηe + 1 and ηe-1 ≠ 0 is 0 <w / p <0.25 or 0.25 <w / p <0.5.

The difference between the depths of two adjacent levels of the proton exchange region 70 is d / 4, the difference between the heights of two adjacent levels of the dielectric film 71 is h / 4, and the refractive index for ordinary light and extraordinary light due to proton exchange. Assuming that the changes are Δno and Δne, the refractive index of the dielectric film 71 is n, and the wavelengths of the incident light 72 and the incident light 74 are λ, φo and φe are given by equations (10) and (11), respectively.

φo = (2π / λ) {Δnode / 4 + (n−1) h / 4} (10)
φe = (2π / λ) {Δned / 4 + (n−1) h / 4} (11)
When λ = 660 nm, Δno = −0.04 and Δne = 0.12, and when Nb2O5 is used as the dielectric film 71, n = 2.2. Therefore, φo = 0 and φe = π / 2. For this purpose, it suffices that d = 4.13 μm and h = 138 nm.

FIG. 10 shows a pattern of the photodetector 67 and a light spot on the photodetector 67. A semiconductor laser 66 and a mirror 77 are provided on the photodetector 67, and the photodetector 67 has light receiving units 78 to 85. Light emitted from the semiconductor laser 66 is reflected by the mirror 77 and travels toward the disk 6. The -1st-order diffracted light from the region 10 of the polarizing hologram optical element 68 forms a light spot 86 on the boundary between the light receiving section 78 and the light receiving section 79, and the + 1st-order diffracted light forms a light spot 93 on the light receiving section 85. The −1st-order diffracted light from the region 11 of the polarizing hologram optical element 68 forms a light spot 87 on the boundary between the light receiving section 78 and the light receiving section 79, and the + 1st-order diffracted light forms a light spot 92 on the light receiving section 84. The −1st-order diffracted light from the region 12 of the polarizing hologram optical element 68 forms a light spot 88 on the boundary between the light receiving unit 80 and the light receiving unit 81, and the + 1st-order diffracted light forms a light spot 91 on the light receiving unit 83. The -1st-order diffracted light from the region 13 of the polarizing hologram optical element 68 forms a light spot 89 on the boundary between the light receiving section 80 and the light receiving section 81, and the + 1st-order diffracted light forms a light spot 90 on the light receiving section 82. When the outputs from the light receiving units 78 to 85 are represented by V78 to V85, respectively, the focus error signal by the Foucault method is obtained from the calculation of (V78 + V81)-(V79 + V80). The track error signal by the phase difference method is obtained from the phase difference between V82 + V85 and V83 + V84. The track error signal by the push-pull method is obtained from the calculation of (V82 + V84)-(V83 + V85). The information signal recorded on the disk 6 is obtained from the calculation of V82 + V83 + V84 + V85.

A fourth embodiment of the optical head device according to the present invention will be described. In the fourth embodiment of the optical head device according to the present invention, the polarization hologram optical element 68 and the photodetector 67 in the third embodiment of the optical head device according to the present invention shown in FIG. This is a configuration in which the optical element 94 and the photodetector 109 are replaced.

The plan view of the polarizing hologram optical element 94 is the same as the plan view of the hologram optical element 35 shown in FIG. The polarizing hologram optical element 94 is divided into four regions 36 to 39 by two dividing lines parallel to the radial direction and the tangential direction of the disk 6. The direction of the lattice is inclined at a predetermined angle in the negative direction with respect to the tangential direction of the disk 6 in the regions 36 and 37, and in the positive direction with respect to the tangential direction of the disk 6 in the regions 38 and 39. It is inclined by a predetermined angle. The pitch of the grating is equal in the region 36 and the region 39 and in the region 37 and the region 38, and is wider in the latter than in the former.

FIG. 11 is a sectional view of the polarizing hologram optical element 94. FIG. 11A is a cross-sectional view of a region 36 and a region 37, and FIG. 11B is a cross-sectional view of a region 38 and a region 39. In FIG. 11A, the polarizing hologram optical element 94 has a structure in which a proton exchange region 95 is formed in a lithium niobate substrate 69 having birefringence, and a dielectric film 96 is formed on the substrate. . The outgoing light from the semiconductor laser 66 enters the polarizing hologram optical element 94 as incident light 99, transmits as transmitted light 100, and travels to the disk 6. The reflected light from the disk 6 enters the polarizing hologram optical element 94 as incident light 101, is diffracted as -1st-order diffracted light 102 and + 1st-order diffracted light 103, and is received by the photodetector 109. On the other hand, in FIG. 11B, the polarizing hologram optical element 94 has a structure in which a proton exchange region 97 is formed in a lithium niobate substrate 69 having birefringence, and a dielectric film 98 is formed on the substrate. It is. The outgoing light from the semiconductor laser 66 enters the polarizing hologram optical element 94 as incident light 104, transmits as transmitted light 105, and travels to the disk 6. The reflected light from the disk 6 enters the polarizing hologram optical element 94 as incident light 106, is diffracted as −1st-order diffracted light 107 and + 1st-order diffracted light 108, and is received by the photodetector 109. The cross-sectional shapes of the proton exchange region 95 and the proton exchange region 97 are the same as the cross-sectional shape of the proton exchange region 70 in the polarizing hologram optical element 68 shown in FIG. 9, and the cross-sectional shapes of the dielectric films 96 and 98 are the same. The cross-sectional shape of the dielectric film 71 in the polarization hologram optical element 68 shown in FIG. That is, when the light emitted from the semiconductor laser 66 is made incident on the polarizing hologram optical element 94 as ordinary light, 100% of the light is transmitted as transmitted light, and the reflected light from the disk 6 is incident on the polarizing hologram optical element 94 as extraordinary light. Then, 10% is diffracted as -1st-order diffracted light and 71% is diffracted as + 1st-order diffracted light. Accordingly, a focus error signal is detected from the -1st-order diffracted light 102 and the -1st-order diffracted light 107, and a track error signal by the phase difference method, a track error signal by the push-pull method, and the disc 6 If the configuration is such that the information signal recorded in the first optical head device is detected, the value of A becomes 0.71, which is larger than the value of the conventional first optical head device.

FIG. 12 shows a pattern of the photodetector 109 and a light spot on the photodetector 109. A semiconductor laser 66 and a mirror 77 are provided on the photodetector 109, and the photodetector 109 has light receiving units 110 to 117. Light emitted from the semiconductor laser 66 is reflected by the mirror 77 and travels toward the disk 6. The -1st-order diffracted light from the region 36 of the polarizing hologram optical element 94 forms a light spot 118 on the boundary between the light receiving unit 110 and the light receiving unit 111, and the + 1st-order diffracted light forms a light spot 125 on the light receiving unit 117. The −1st-order diffracted light from the region 37 of the polarizing hologram optical element 94 forms a light spot 119 on the boundary between the light receiving unit 110 and the light receiving unit 111, and the + 1st-order diffracted light forms a light spot 124 on the light receiving unit 116. The -1st-order diffracted light from the region 38 of the polarizing hologram optical element 94 forms a light spot 120 on the boundary between the light receiving section 112 and the light receiving section 113, and the + 1st-order diffracted light forms a light spot 123 on the light receiving section 115. The −1st-order diffracted light from the region 39 of the polarizing hologram optical element 94 forms a light spot 121 on the boundary between the light receiving unit 112 and the light receiving unit 113, and the + 1st-order diffracted light forms a light spot 122 on the light receiving unit 114. If the outputs from the light receiving units 110 to 117 are represented by V110 to V117, respectively, the focus error signal by the Foucault method is obtained from the calculation of (V110 + V113)-(V111 + V112). The track error signal by the phase difference method is obtained from the phase difference between V114 + V117 and V115 + V116. The track error signal by the push-pull method is obtained from the calculation of (V114 + V116)-(V115 + V117). The information signal recorded on the disk 6 is obtained from the calculation of V114 + V115 + V116 + V117.

In the third and fourth embodiments of the optical head device of the present invention, the polarization hologram optical element 68 and the polarization hologram optical element 94 determine the phase difference between light passing through two adjacent levels with respect to ordinary light and extraordinary light. When φo and φe, φo = 0 and φe = π / 2, and the light emitted from the semiconductor laser 66 is made to enter the polarizing hologram optical element 68 or the polarizing hologram optical element 94 as ordinary light, and Is reflected as extraordinary light on the polarizing hologram optical element 68 or the polarizing hologram optical element 94. On the other hand, when the phase difference between the ordinary light and the extraordinary light passing through two adjacent levels with respect to the ordinary light and the extraordinary light in the polarizing hologram optical element 68 and the polarizing hologram 94 is φo and φe, φo = π / 2 and φe = 0. And the light emitted from the semiconductor laser 66 is made incident on the polarizing hologram optical element 68 or the polarizing hologram optical element 94 as extraordinary light, and the reflected light from the disk 6 is reflected on the polarizing hologram optical element 68 or the polarizing hologram. A configuration in which the light is incident on the optical element 94 as ordinary light is also possible.

FIG. 13 shows a fifth embodiment of the optical head device according to the present invention. The light emitted from the semiconductor laser 1 is collimated by the collimator lens 2, enters the polarization beam splitter 3 as P-polarized light, transmits almost 100%, and is converted from linearly polarized light to circularly polarized light by the で wavelength plate 4. The light is focused on the disk 6 by the objective lens 5. The reflected light from the disk 6 passes through the objective lens 5 in the opposite direction, is converted from circularly polarized light into linearly polarized light by the quarter-wave plate 4, enters the polarizing beam splitter 3 as S-polarized light, and is almost 100% reflected. The light is refracted by the Wollaston prism 126 and the quadrant prism 127, passes through the lens 8, and is received by the photodetector 9.

FIG. 14 shows the configuration of the Wollaston prism 126. FIG. 14A is a side view, and FIG. 14B is a plan view. The Wollaston prism 126 has a configuration in which a prism 128 and a prism 129 made of lithium niobate having a birefringent property are bonded. The reflected light from the disk 6 enters the Wollaston prism 126 as incident light 130, is refracted as refracted light 131 and refracted light 132, and travels to the four-prism 127. The polarization direction of the incident light 130 with respect to the bonding surface of the prism 128 and the prism 129 is S-polarized light. The optical axis 133 of the prism 128 is inclined by θ with respect to the S polarization direction, and the optical axis 134 of the prism 129 is inclined by θ with respect to the P polarization direction. Since the refractive index of lithium niobate for ordinary light is greater than the refractive index for extraordinary light, a component of the incident light 130 that becomes ordinary light in the prism 128 and a component that becomes extraordinary light in the prism 129 becomes refracted light 131, The component that becomes ordinary light in the prism 129 becomes the refracted light 132. At this time, the ratio of the intensity of the refracted light 131 and the intensity of the refracted light 132 to the intensity of the incident light 130 is given by sin2θ and cos2θ, respectively. If θ = −22 ° or θ = 22 °, sin2θ = 0.14 and cos2θ = 0.86. The range of θ satisfying sin2θ <cos2θ and sin2θ ≠ 0 is −45 ° <θ <0 ° or 0 ° <θ <45 °.

FIG. 15 shows the configuration of the four-segment prism 127. 15A and 15B are cross-sectional views, and FIG. 15C is a plan view. The four-divided prism 127 is made of plastic, and is divided into four regions 135 to 138 by two dividing lines parallel to the radial direction and the tangential direction of the disk 6. FIG. 15A is a sectional view of a region 135 and a region 136, and FIG. 15B is a sectional view of a region 137 and a region 138. The exit surface is inclined with respect to the entrance surface in the + direction around the tangential direction of the disk 6 in the region 135 and the region 136, and in the-direction around the tangential direction of the disk 6 in the region 137 and the region 138. are doing. The angle between the exit surface and the entrance surface is equal in the region 135 and the region 138, and is equal in the region 136 and the region 137, and is larger in the former than in the latter. In FIG. 15A, the refracted light from the Wollaston prism 126 is incident on the regions 135 and 136 of the four-piece prism 127 as the incident light 139 and the incident light 141, respectively, and is refracted as the refracted light 140 and the refracted light 142, respectively. Then, the light is received by the photodetector 9. On the other hand, in FIG. 15B, the refracted light from the Wollaston prism 126 is incident on the regions 137 and 138 of the quadrant prism 127 as the incident light 143 and the incident light 145, respectively. Each is refracted and received by the photodetector 9.

Accordingly, a focus error signal is detected from the light refracted as the refracted light 131 by the Wollaston prism 126 and refracted as the refracted light 140, the refracted light 142, the refracted light 144, and the refracted light 146 by the four-split prism 127. , A refracted light 132, a refracted light 142, a refracted light 144, and a refracted light 146 refracted from the refracted light as a refracted light 132, a track error signal by a phase difference method, a track error signal by a push-pull method, and If the information signal recorded on the disk 6 is detected, the value of A becomes 0.86, which is larger than the value of the first conventional optical head device.

パ The pattern of the photodetector 9 and the light spot on the photodetector 9 are as shown in FIG. Of the light refracted as the refracted light 131 by the Wollaston prism 126, the light refracted as the refracted light 140 in the region 135 of the four-divided prism 127 forms the light spot 27 on the boundary between the light receiving unit 19 and the light receiving unit 20. The light refracted as the refracted light 142 in the region 136 of the split prism 127 forms the light spot 28 on the boundary line between the light receiving portion 19 and the light receiving portion 20, and the light refracted as the refracted light 144 in the region 137 of the four split prism 127 is received. A light spot 29 is formed on the boundary line between the unit 21 and the light receiving unit 22, and the light refracted as the refracted light 146 in the area 138 of the four-divided prism 127 forms a light spot 30 on the boundary line between the light receiving unit 21 and the light receiving unit 22. . Of the light refracted as the refracted light 132 by the Wollaston prism 126, the light refracted as the refracted light 140 by the region 135 of the four-divided prism 127 forms the light spot 31 on the light receiving portion 23, and the region 136 of the four-divided prism 127 The light refracted as the refracted light 142 forms the light spot 32 on the light receiving portion 24, and the light refracted as the refracted light 144 in the region 137 of the four-divided prism 127 forms the light spot 33 on the light receiving portion 25. The light refracted as the refracted light 146 in the area 138 of the split prism 127 forms a light spot 34 on the light receiving section 26. The focus error signal according to the Foucault method, the track error signal according to the phase difference method, the track error signal according to the push-pull method, and the information signal recorded on the disk 6 are calculated and calculated according to the first embodiment of the optical head device of the present invention. Obtained from the same operation.

The fifth embodiment of the optical head device according to the present invention has a configuration in which the four-divided prism 127 is provided between the Wollaston prism 126 and the lens 8. On the other hand, a configuration in which the four-divided prism 127 is provided between the polarization beam splitter 3 and the Wollaston prism 126 is also possible.

A sixth embodiment of the optical head device according to the present invention will be described. The sixth embodiment of the optical head device of the present invention has a configuration in which the hologram optical element 147 replaces the four-divided prism 127 in the fifth embodiment of the optical head device of the present invention shown in FIG. The light reflected from the disk 6 is refracted by the Wollaston prism 126, diffracted by the hologram optical element 147, and received by the photodetector 9.

FIG. 16 is a plan view of the hologram optical element 147. The hologram optical element 147 is divided into four regions 148 to 151 by two dividing lines parallel to the radial direction and the tangential direction of the disk 6. The direction of the lattice is parallel to the tangential direction of the disk 6 in any of the regions 148 to 151. The pitch of the grating is equal in the region 148 and the region 151 and in the region 149 and the region 150, and is wider in the latter than in the former.

FIG. 17 is a sectional view of the hologram optical element 147. FIG. 17A is a cross-sectional view of a region 148 and a region 149, and FIG. 17B is a cross-sectional view of a region 150 and a region 151. In FIG. 17A, the hologram optical element 147 has a configuration in which a dielectric film 152 is formed on a glass substrate 14. Refracted light from the Wollaston prism 126 is incident on the hologram optical element 147 as incident light 154, is diffracted as + 1st-order diffracted light 155, and is received by the photodetector 9. On the other hand, in FIG. 17B, the hologram optical element 147 has a configuration in which a dielectric film 153 is formed on a glass substrate 14. The refracted light from the Wollaston prism 126 enters the hologram optical element 147 as incident light 156, is diffracted as + 1st-order diffracted light 157, and is received by the photodetector 9. The cross-sectional shape of the dielectric film 152 and the dielectric film 153 is an 8-level stepped shape. The height differences between two adjacent levels are all equal. Assuming that the phase difference between the light passing through two adjacent levels is φ, and the widths of the gratings in the first to eighth stages are all p / 8, the diffraction efficiency η + 1 of the + 1st-order diffracted light is given by equation (12). Can be
η + 1 = (4 / π2) (1-1 / √2) {1 + cos (φ−π / 4)}
× {1 + cos (2φ−π / 2)} 1 + cos (4φ−π)}
… (12)
If φ = π / 4, η + 1 = 0.95.

Accordingly, a focus error signal is detected from the light refracted as refracted light 131 by the Wollaston prism 126 and diffracted by the hologram optical element 147 as the + 1st-order diffracted light 155 and + 1st-order diffracted light 157, and is refracted as the refracted light 132 by the Wollaston prism 126. A track error signal by the phase difference method, a track error signal by the push-pull method, and an information signal recorded on the disk 6 are detected from the light refracted and diffracted by the hologram optical element 147 as the + 1st-order diffracted light 155 and the + 1st-order diffracted light 157. With this configuration, the value of A becomes 0.86 × 0.95 = 0.82, which is larger than the value of the first conventional optical head device.

The height difference between two adjacent levels of the dielectric film 152 and the dielectric film 153 is h / 8, the refractive index of the dielectric film 152 and the dielectric film 153 is n, the wavelength of the incident light 154 and the wavelength of the incident light 156 are Assuming λ, φ is given by equation (13).
φ = (2π / λ) (n−1) h / 8 (13)
In the case of λ = 660 nm, n = 1.46 when SiO 2 is used for the dielectric film 152 and the dielectric film 153. Therefore, in order to set φ = π / 4, h = 1.43 μm may be used.

パ The pattern of the photodetector 9 and the light spot on the photodetector 9 are as shown in FIG. Of the light refracted as the refracted light 131 by the Wollaston prism 126, the light diffracted as the + 1st-order diffracted light 155 in the region 148 of the hologram optical element 147 forms a light spot 27 on the boundary between the light receiving portion 19 and the light receiving portion 20. The light diffracted as the + 1st-order diffracted light 155 in the region 149 of the hologram optical element 147 forms a light spot 28 on the boundary between the light receiving section 19 and the light receiving section 20, and as the + 1st-order diffracted light 157 in the area 150 of the hologram optical element 147. The diffracted light forms a light spot 29 on the boundary between the light receiving unit 21 and the light receiving unit 22, and the light diffracted as + 1st-order diffracted light 157 in the region 151 of the hologram optical element 147 is the boundary between the light receiving unit 21 and the light receiving unit 22. A light spot 30 is formed on the line. Of the light refracted as the refracted light 132 by the Wollaston prism 126, the light diffracted as the + 1st-order diffracted light 155 in the region 148 of the hologram optical element 147 forms the light spot 31 on the light receiving section 23, The light diffracted as the + 1st-order diffracted light 155 in the area 149 forms a light spot 32 on the light receiving section 24, and the light diffracted as the + 1st-order diffracted light 157 in the area 150 of the hologram optical element 147 is placed on the light receiving section 25. The light diffracted as + 1st-order diffracted light 157 in the region 151 of the hologram optical element 147 forms a light spot 34 on the light receiving section 26. The focus error signal according to the Foucault method, the track error signal according to the phase difference method, the track error signal according to the push-pull method, and the information signal recorded on the disk 6 are calculated and calculated according to the first embodiment of the optical head device of the present invention. Obtained from the same operation.

In the sixth embodiment of the optical head device according to the present invention, the hologram optical element 147 is provided between the Wollaston prism 126 and the lens 8. On the other hand, a configuration in which the hologram optical element 147 is provided between the polarization beam splitter 3 and the Wollaston prism 126 is also possible.

In the sixth embodiment of the optical head device according to the present invention, the phase distribution of the grating in the hologram optical element 147 is a staircase having eight levels, and the phase difference of light passing through two adjacent levels is φ, one step. When the widths of the grids in the first to eighth stages are all p / 8, φ = π / 4. On the other hand, in general, the phase distribution of the grating in the hologram optical element 147 is N-stepped (N is an integer of 3 or more), and the phase difference between light transmitted through two adjacent levels is φ, When the widths of the gratings in the 〜th to Nth stages are all p / N, a configuration where φ = 2π / N is also possible.

In the fifth and sixth embodiments of the optical head device of the present invention, the optical axis 133 of the prism 128 is inclined by θ with respect to the S polarization direction, and the optical axis 134 of the prism 129 is inclined with respect to the P polarization direction. Of the incident light 130, the focus error signal is detected from the refracted light 131, which is a component that becomes an extraordinary light in the prism 128 and the extraordinary light in the prism 129, and the extraordinary light in the prism 128 and the ordinary light in the prism 129. A track error signal by the phase difference method, a track error signal by the push-pull method, and an information signal recorded on the disk 6 are detected from the refracted light 132 as a component, and the range of θ is −45 ° <θ < 0 ° or 0 ° <θ <45 °. At this time, the ratio of the intensity of the refracted light 131 and the intensity of the refracted light 132 to the intensity of the incident light 130 is given by sin2θ and cos2θ, respectively, where sin2θ <cos2θ and sin2θ ≠ 0. On the other hand, the optical axis 133 of the prism 128 is inclined by θ with respect to the S polarization direction, the optical axis 134 of the prism 129 is inclined by θ with respect to the P polarization direction, and A focus error signal is detected from the refracted light 132, which is a component that becomes an extraordinary light in the prism 128 and an ordinary light in the prism 129, and a track is detected by the phase difference method from the refracted light 131, which is an ordinary light in the prism 128 and an extraordinary light in the prism 129. An error signal, a track error signal by the push-pull method, and an information signal recorded on the disk 6 are detected, and the range of θ is −90 ° <θ <−45 ° or 45 ° <θ <90 °. It is. At this time, the ratio of the intensity of the refracted light 131 and the intensity of the refracted light 132 to the intensity of the incident light 130 is given by sin2θ and cos2θ, respectively, where sin2θ> cos2θ and sin2θ ≠ 0.

In the optical head device described above, the reflected light from the disk is divided into a first group of light and a second group of light, and a track error signal by the phase difference method and a track by the push-pull method are obtained from the first group of light. An error signal and an information signal recorded on the disc are detected, and a focus error signal is detected from the second group of light. The light amount of the first group of light is larger than the light amount of the second group of light.
The effect of this optical head device is that the ratio A of the light amount used for detecting the track error signal by the information signal recorded on the disk and the phase difference method to the light amount of the reflected light from the disk is large, and the S signal for these signals is high. / N is obtained. The reason is that the amount of the first group of light is large.

FIG. 1 is a diagram illustrating a first embodiment of an optical head device according to the present invention. FIG. 2 is a plan view of a hologram optical element according to the first embodiment of the optical head device of the present invention. FIG. 2 is a cross-sectional view of a hologram optical element according to the first embodiment of the optical head device of the present invention. FIG. 3 is a diagram showing a pattern of a photodetector and a light spot on the photodetector in the first embodiment of the optical head device of the present invention. FIG. 9 is a plan view of a hologram optical element according to a second embodiment of the optical head device of the present invention. FIG. 9 is a cross-sectional view of a hologram optical element according to a second embodiment of the optical head device of the present invention. It is a figure showing a pattern of a light detector and a light spot on a light detector in a 2nd embodiment of an optical head device of the present invention. FIG. 11 is a diagram illustrating a third embodiment of the optical head device according to the present invention. It is sectional drawing of the polarization hologram optical element in the 3rd Embodiment of the optical head device of this invention. It is a figure showing a pattern of a light detector and a light spot on a light detector in a 3rd embodiment of an optical head device of the present invention. It is a sectional view of a polarization hologram optical element in a 4th embodiment of an optical head device of the present invention. It is a figure showing a pattern of a light detector and a light spot on a light detector in a 4th embodiment of an optical head device of the present invention. It is a figure showing a 5th embodiment of an optical head device of the present invention. It is a figure showing the composition of the Wollaston prism in a 5th embodiment of the optical head device of the present invention. It is a figure showing composition of a 4 division prism in a 5th embodiment of an optical head device of the present invention. It is a top view of the hologram optical element in a 6th embodiment of the optical head device of the present invention. It is sectional drawing of the hologram optical element in the 6th Embodiment of the optical head device of this invention. FIG. 9 is a diagram illustrating a configuration of a first conventional optical head device. FIG. 11 is a plan view of a hologram optical element in a first conventional optical head device. It is a figure which shows the pattern of the photodetector in the 1st conventional optical head device, and the light spot on a photodetector. FIG. 11 is a diagram illustrating a configuration of a module that is a main part of a second conventional optical head device. It is a top view of the hologram optical element in the conventional 2nd optical head device. It is a figure which shows the pattern of the photodetector in the 2nd conventional optical head device, and the light spot on a photodetector. It is sectional drawing of the hologram optical element in the conventional 2nd optical head device.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Collimator lens 3 Polarization beam splitter 4 1/4 wavelength plate 5 Objective lens 6 Disk 7 Hologram optical element 8 Lens 9 Photodetector 10, 11, 12, 13 Area 14 Glass substrate 15 Dielectric film 16 Incident light 17 -1 order diffracted light 18 +1 order diffracted light 19, 20, 21, 22, 23, 24, 25, 26 Light receiving unit 27, 28, 29, 30, 31, 32, 33, 34 Light spot 35 Hologram optical element 36, 37 38, 39 regions 40, 41 dielectric film 42 incident light 43 -1st-order diffracted light 44 + 1st-order diffracted light 45 incident light 46 -1st-order diffracted light 47 + 1st-order diffracted light 48 photodetector 49, 50, 51, 52, 53, 54, 55, 56 Light receiving unit 57, 58, 59, 60, 61, 62, 63, 64 Light spot 65 Module 66 Semiconductor laser User 67 Photodetector 68 Polarizing hologram optical element 69 Lithium niobate substrate 70 Proton exchange region 71 Dielectric film 72 Incident light 73 Transmitted light 74 Incident light 75 -1st-order diffracted light 76 + 1st-order diffracted light 77 Mirror 78, 79, 80 , 81, 82, 83, 84, 85 Light receiving unit 86, 87, 88, 89, 90, 91, 92, 93 Light spot 94 Polarizing hologram optical element 95 Proton exchange area 96 Dielectric film 97 Proton exchange area 98 Dielectric Film 99 Incident light 100 Transmitted light 101 Incident light 102 -1st-order diffracted light 103 + 1st-order diffracted light 104 Incident light 105 Transmitted light 106 Incident light 107 -1st-order diffracted light 108 + 1st-order diffracted light 109 Photodetector 110, 111, 112, 113, 114 , 115, 116, 117 Light receiving sections 118, 119, 120, 121 , 122, 123, 124, 125 Light spot 126 Wollaston prism 127 Quadrant prism 128, 129 Prism 130 Incident light 131, 132 Refracted light 133, 134 Optical axis 135, 136, 137, 138 Area 139 Incident light 140 Refracted light 141 Incident light 142 Refracted light 143 Incident light 144 Refracted light 145 Incident light 146 Refracted light 147 Hologram optical element 148, 149, 150, 151 Area 152, 153 Dielectric film 154 Incident light 155 + 1st-order diffracted light 156 Incident light 157 + 1st-order diffracted light 158 Hologram optical element 159 Photodetector 160, 161, 162, 163 Area 164, 165, 166, 167, 168, 169, 170, 171 Light receiving section 172, 173, 174, 175, 176, 177, 178, 1 9 light spot 180 module 181 semiconductor laser 182 photodetector 183 hologram optical element 184, 185, 186, 187 area 188, 189, 190, 191, 192, 193 light receiving section 194, 195, 196, 197 light spot 198 dielectric film 199 Incident light 200 Transmitted light 201 Incident light 202 + 1st-order diffracted light

Claims (13)

A light source, an objective lens for condensing outgoing light from the light source on an optical recording medium, and an optical path of reflected light from the optical recording medium provided between the light source and the objective lens. First light separating means for separating the light from the optical path of the emitted light, and second light separating means for further separating the reflected light from the optical recording medium passing through the first light separating means into a first group of light and a second group of light. An optical head device having a photodetector that receives the first group of light and the second group of light,
The light amount of the first group of light is larger than the light amount of the second group of light, and the first group of light has a track error signal by a phase difference method, a track error signal by a push-pull method, and the optical recording medium. Detect the information signal recorded in, to detect a focus error signal by Foucault method from the second group of light,
The second light separating means is a hologram optical element, the first group of light is a + 1st-order diffracted light of the hologram optical element, and the second group of light is a -1st-order diffracted light of the hologram optical element. An optical head device, comprising: The hologram optical element is divided into four regions by two division lines parallel to a radial direction and a tangential direction of the optical recording medium, and the four regions are different in a grating direction or a grating pitch from each other. The optical head device according to claim 1, wherein: The phase distribution of the grating in the hologram optical element has a step shape of four levels, and the phase difference between the light passing through two adjacent levels is φ, and the width of the first to fourth gratings is p / 2−2. When w, w, p / 2−w, w, φ is approximately π / 2, and the range of w / p is 0 <w / p <0.25 or 0.25 <w / p <0. 3. The optical head device according to claim 1 or 2, wherein A light source, an objective lens for condensing outgoing light from the light source on an optical recording medium, and an optical path of reflected light from the optical recording medium provided between the light source and the objective lens. First light separating means for separating the light from the optical path of the emitted light, and second light separating means for further separating the reflected light from the optical recording medium passing through the first light separating means into a first group of light and a second group of light. An optical head device having a photodetector that receives the first group of light and the second group of light,
The light amount of the first group of light is larger than the light amount of the second group of light, and the first group of light has a track error signal by a phase difference method, a track error signal by a push-pull method, and the optical recording medium. Detect the information signal recorded in, to detect a focus error signal by Foucault method from the second group of light,
The first light separating means and the second light separating means are an integrated polarizing hologram optical element, and the polarizing hologram optical element transmits light emitted from the light source and the optical recording medium. Diffracted reflected light from the, and the first group of light is the + 1st-order diffracted light of the polarizing hologram optical element,
The optical head device, wherein the second group of light is -1st-order diffracted light of the polarizing hologram optical element. The polarizing hologram optical element is divided into four regions by two dividing lines parallel to a radial direction and a tangential direction of the optical recording medium, and the four regions have a grating direction or a grating pitch. The optical head device according to claim 4, wherein the optical head devices are different from each other. The phase distribution of the grating in the polarizing hologram optical element is a stepped shape of four levels, and the phase difference between the ordinary light and the extraordinary light transmitted through two adjacent levels is φo, φe, the first to fourth stages. When the widths of the lattices are p / 2-w, w, p / 2-w, and w, respectively, φo is approximately 0, φe is approximately π / 2, and the range of w / p is 0 <w / p. <0.25 or 0.25 <w / p <0.5, and the light emitted from the light source is made incident on the polarizing hologram optical element as ordinary light, and the reflected light from the optical recording medium is emitted from the optical recording medium. 6. The optical head device according to claim 4, wherein the light is incident on the polarizing hologram optical element as extraordinary light. The phase distribution of the grating in the polarizing hologram optical element is a stepped shape of four levels, and the phase difference between the ordinary light and the extraordinary light transmitted through two adjacent levels is φo, φe, the first to fourth stages. Assuming that the width of the lattice is p / 2-w, w, p / 2-w, w, φo is approximately π / 2 and φe is approximately 0, and the range of w / p is 0 <w / p. <0.25 or 0.25 <w / p <0.5, and the light emitted from the light source is made to enter the polarizing hologram optical element as extraordinary light, and the reflected light from the optical recording medium is emitted. 6. The optical head device according to claim 4, wherein ordinary light is incident on the polarizing hologram optical element. A light source, an objective lens for condensing outgoing light from the light source on an optical recording medium, and an optical path of reflected light from the optical recording medium provided between the light source and the objective lens. First light separating means for separating the light from the optical path of the emitted light, and second light separating means for further separating the reflected light from the optical recording medium passing through the first light separating means into a first group of light and a second group of light. An optical head device having a photodetector that receives the first group of light and the second group of light,
The light amount of the first group of light is larger than the light amount of the second group of light, and the first group of light has a track error signal by a phase difference method, a track error signal by a push-pull method, and the optical recording medium. Detect the information signal recorded in, to detect a focus error signal by Foucault method from the second group of light,
The second light separating means is a Wollaston prism, the first group of light is one of two refracted lights of the Wollaston prism, and the second group of light is a light of the Wollaston prism. An optical head device, which is the other of the two refracted lights. The Wollaston prism is composed of a first prism located on an incident side of reflected light from the optical recording medium and a second prism located on an exit side of reflected light from the optical recording medium, and the first prism The optical axis of the prism is inclined by θ with respect to a direction parallel to the polarization direction of the reflected light from the optical recording medium, and the optical axis of the second prism is the polarization direction of the reflected light from the optical recording medium. And the first group of light becomes extraordinary light in the first prism and ordinary light in the second prism among the reflected light from the optical recording medium. The second group of light is refracted light, the second group of light is ordinary light in the first prism of the reflected light from the optical recording medium, is refracted light that becomes abnormal light in the second prism, and the θ Range is -45 ° <θ The optical head device according to claim 8, wherein <0 ° or 0 ° <θ <45 °. The Wollaston prism is composed of a first prism located on the incident side of the reflected light from the optical recording medium and a second prism located on the exit side of the reflected light from the optical recording medium. The optical axis of the prism is inclined by θ with respect to a direction parallel to the polarization direction of the reflected light from the optical recording medium, and the optical axis of the second prism is the polarization direction of the reflected light from the optical recording medium. And the first group of light becomes ordinary light in the first prism and extraordinary light in the second prism among the reflected light from the optical recording medium. Is a refracted light, the second group of light is an extraordinary light in the first prism out of the reflected light from the optical recording medium, a refracted light that becomes ordinary light in the second prism, and the θ Range is -90 <Θ <-45 ° or 45 ° <θ <optical head apparatus according to claim 8, wherein the is 90 °. Between the Wollaston prism and the photodetector or between the first light separation means and the Wollaston prism, a quadrant prism that refracts reflected light from the optical recording medium is provided, and The four-divided prism is divided into four regions by two dividing lines parallel to a radial direction and a tangential direction of the optical recording medium, and the four regions are formed in a direction in which the exit surface is inclined with respect to the entrance surface or The optical head device according to any one of claims 8 to 10, wherein an angle between the light emitting surface and the light incident surface is different from each other. Between the Wollaston prism and the photodetector or between the first light separating means and the Wollaston prism, a hologram optical element for diffracting reflected light from the optical recording medium as + 1st-order diffracted light is provided. And the hologram optical element is divided into four regions by two dividing lines parallel to a radial direction and a tangential direction of the optical recording medium, and the four regions are arranged in a direction of a grating, a direction of a grating, 11. The optical head device according to claim 8, wherein the pitch or the phase distribution of the grating is different from each other. The phase distribution of the grating in the hologram optical element is N-stepped (N is an integer of 3 or more), and the phase difference between light transmitted through two adjacent levels is φ, the first to Nth gratings. 13. The optical head device according to claim 12, wherein when all widths are p / N, φ is approximately 2π / N.

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