JPH097217A - Optical pickup and optical element - Google Patents

Abstract

PURPOSE: To provide an optical pickup miniaturized in constitution with the cost reduced. CONSTITUTION: This optical element consists of a 1st diffraction element 30 for splitting incident light of linear polarization into 1st and 2nd components which are orthogonal to each other and a 2nd diffraction element 31 for splitting the light into 3rd and 4th components which are nearly transmitted through 1st order diffracted light of the 1st component emitted from the 1st diffraction element and are also orthogonal to 0-th order diffracted light of the 2nd component emitted from the 1st diffraction element. Then, the 1st diffraction element and the 2nd diffraction element constitute the optical element 25, so as to be polarization holograms disposed on both opposite sides of a substrate 30a of a hologram element respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup for recording and / or reproducing information signals on a magneto-optical disk.

[0002]

2. Description of the Related Art Conventionally, such an optical pickup is
It is configured as shown in FIG. That is, in FIG. 8, the optical pickup 1 includes a laser light source 3 such as a semiconductor laser device that emits a light beam toward a collimator lens 2 and a beam cross-sectional shape of the light beam converted by the collimator lens 2 into substantially parallel rays. And a beam cross-section shaping prism 5 for shaping the light beam toward the polarization beam splitter 4 and the polarization beam splitter 4
And the objective lens 8 for converging the reflected light of the reflective mirror 7 on the information recording surface of the magneto-optical disk 6.
And a signal detection system 9 sequentially arranged below the polarization beam splitter 4 along the optical axis.

Here, the signal detection system 9 causes return light, which is reflected by the polarization beam splitter 4 from the magneto-optical disk 6 to follow the optical system such as the objective lens 8 in sequence, below the polarization beam splitter 4. A polarization beam splitter 10 that reflects and transmits, and a half-wave plate 12 that emits the reflected light of the polarization beam splitter 10 toward a lens 11.
A polarization beam splitter 13 for decomposing the return light converted into convergent light by the lens 11 into components having different polarization planes, and light receiving elements 14 and 15 for receiving transmitted light and reflected light of the polarization beam splitter 13, respectively. A lens 16 for converting the transmitted light of the polarization beam splitter 10 into a convergent light, a cylindrical lens 17 for giving astigmatism to the emitted light of the lens 16, and a light receiving element 18 for receiving the emitted light of the cylindrical lens 17. Have

According to the optical pickup 1 having such a structure, the light beam emitted from the laser light source 3 is converted into parallel rays by the collimator lens 2, and then the beam cross-section shaping prism 5 shapes the beam cross-section. Is
After passing through the polarization beam splitter 4, the reflection mirror 7
Is reflected by. Further, this light beam is transmitted through the objective lens 8
By the action of the above, the light is converged on the information recording surface of the magneto-optical disk 6 which is rotationally driven.

When the return light beam reflected by the information recording surface of the magneto-optical disk 6 is reflected, a part thereof receives the Kerr effect corresponding to the magnetism and magnetism of the information recording surface, and is reflected by the reflection mirror 7. After being reflected, it enters the polarization beam splitter 4. In the polarization beam splitter 4, the return light beam whose polarization plane is rotated by the Kerr effect is reflected by the reflection surface of the polarization beam splitter 4 and emitted toward the polarization beam splitter 10. The light is emitted to the side and downward in FIG. The return light emitted to the side is the half-wave plate 1
The vibration direction is rotated by 2 and is converted into convergent light by the subsequent lens 11, which is then decomposed by the polarization beam splitter 13 into components whose polarization planes are orthogonal to each other. The decomposed components are
The light is received by the light receiving elements 14 and 15, respectively. As a result, the reproduction signal is detected by taking the difference in the amount of light between the light receiving elements 14 and 15.

Of the return light from the magneto-optical disk 6, the component whose polarization plane has not undergone Kerr rotation is emitted downward from the polarization beam splitter 10, converted into convergent light by the lens 16, and then the cylindrical light. Astigmatism is given by the lens 17, and the light is received by the light receiving element 18. As a result, the light receiving element 18 detects astigmatism to detect a focusing error, and the movement of the beam spot in the direction corresponding to the radial direction of the magneto-optical disk 6 is detected to detect a tracking error. It has become so.

[0007]

However, the optical pickup 1 thus constructed has the following problems. That is, this type of optical pickup 1
However, in order to detect the reproduction signal, expensive optical parts such as a half-wave plate and a polarization beam splitter are required, resulting in high cost. In addition, there is a problem in that the entire size becomes large by mounting these optical components. On the other hand, it is also known to use a Wollaston prism instead of the polarization beam splitter to detect the reproduced signal, but in this case as well, a special optical component called the Wollaston prism is required. However, there is a problem in that the cost increases and the overall size increases.

As one method for solving these problems, an optical pickup using a polarization hologram can be considered. That is, in the case of a polarization hologram, a grating is formed in a birefringent medium of which thickness is selected to give a predetermined phase difference to an ordinary ray and an extraordinary ray, whereby the 0th-order diffracted light is transmitted through the ordinary ray and the extraordinary ray. The optical elements are configured so that the ratios are 0 and 1 or 1 and 0, respectively. By using this polarization hologram, it is possible to separate two orthogonal polarization components into 0th-order diffracted light and plus / minus 1st-order diffracted light.

Furthermore, when an optical pickup is constructed using this polarization hologram, all the return light obtained from the magneto-optical disk is guided to this polarization hologram, and a reproduction signal or the like is generated from the diffraction light of this polarization hologram. When the signal is detected, the reproduced signal is detected by utilizing the return light without waste.

By the way, in a magneto-optical disk apparatus to which this type of optical pickup is applied, it is necessary to detect a tracking error and a focusing error. The tracking error and the focusing error need to be detected based on the change in the amount of the return light, regardless of the change in the polarization plane of the return light.

On the other hand, in the polarization hologram, since it is possible to separate the two orthogonal polarization components into the 0th-order diffracted light and the plus / minus 1st-order diffracted light, all of the returned light in the optical pickup. When this is guided to this polarization hologram and simply processed, after all, tracking error and focusing error are tracked,
There is a problem that it becomes difficult to separate from the return light a component whose light quantity changes regardless of the change of the polarization plane of the return light. Therefore, when a magneto-optical disk device is configured by an optical pickup to which such a polarization hologram is applied, after all, a method such as band separation is newly determined based on the light reception results of the 0th order diffracted light and the plus / minus 1st order diffracted light. It is necessary to detect the tracking error and the focusing error by using the SN of the reproduced signal.
There was a problem that the ratio deteriorates and the circuit configuration becomes complicated.

In view of the above points, the present invention provides an optical pickup and an optical element to be applied to this optical pickup or the like, which has a simple structure to improve the SN ratio of a reproduced signal. Has an aim.

[0013]

According to the present invention, the above object is to provide an optical pickup which irradiates a disc-shaped recording medium with a light beam and reproduces information recorded on the disc-shaped recording medium by utilizing the Kerr effect. In the optical path of return light from the disk-shaped recording medium, the return light is separated into first and second components orthogonal to each other, and the first component is converted into plus / minus first-order diffracted light. A first diffractive element that suppresses plus-minus first-order diffracted light and emits as zero-order diffracted light with respect to the second component, and decomposes and emits it, and suppresses and emits zero-order diffracted light; Is arranged on the optical path of the return light emitted from the diffractive element and substantially transmits the plus-minus first-order diffracted light of the first component, and the return light emitted as the zero-order diffracted light of the second component. , The orthogonal third and fourth components are separated, and the third component is decomposed into plus / minus first-order diffracted light and emitted, and the zero-order diffracted light is suppressed and emitted. Is plus or minus 1
A second diffractive element that suppresses the second-order diffracted light and emits it as the 0th-order diffracted light, a plus-minus first-order diffracted light of the first component that is emitted after substantially passing through the second diffractive element, and the second diffractive element. A light receiving element for receiving the plus / minus first-order diffracted light of the third component emitted after being decomposed by the diffraction element and the zero-order diffracted light of the fourth component emitted from the second diffraction element, respectively. In addition to the above, the first and second diffractive elements are polarization holograms respectively disposed on both one surface and the opposite surface of the substrate constituting the hologram element. This is achieved with an optical pickup.

[0014]

According to the above structure, the plus / minus first-order diffracted lights formed by the first and second diffractive elements are orthogonal components of the return light. Therefore, it is possible to detect the change of the polarization plane of the return light, and the 0th-order diffracted light of the second diffraction element is a component that does not depend on the change of the polarization plane.
As a result, tracking errors and the like are detected.

In particular, the first and second diffractive elements are composed of polarization holograms, and, for example, the ratio of the polarized component separation of the first diffractive element and the ratio of the polarized component separation of the second diffractive element are the same. By selecting the predetermined ratio, the components whose polarization planes are orthogonal to each other and the 0th-order diffracted light are easily generated.

By configuring the first and second diffractive elements on the opposite surfaces of the hologram element,
The overall configuration is simplified.

Further, by the optical element composed of such first and second diffractive elements, the incident light of linearly polarized light is changed into a component whose light quantity changes depending on the change of the polarization plane and a change of the polarization plane. Easily separated into independent components.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to FIGS. In addition, since the Examples described below are preferred specific examples of the present invention, various technically preferable limitations are given. However, the scope of the present invention particularly limits the present invention in the following description. The embodiment is not limited to these embodiments unless otherwise stated.

FIG. 2 shows an embodiment of an optical pickup of the magneto-optical disk device according to the present invention. In FIG. 2, an optical pickup 20 includes a laser light source 21 such as a semiconductor laser device that emits a linearly polarized light beam, and an objective lens that converges the light beam from the laser light source 21 onto an information recording surface of a magneto-optical disk 22. 23 and a laser beam source 21 and an objective lens 23, a return beam from the magneto-optical disk 22 enters through the objective lens 23, and is polarized by a beam splitter 24 which is bent sideways and emitted. A hologram element 25 adhered and held to the exit surface of the polarization beam splitter 24; a multi-lens 26 that gives astigmatism to the return light emitted from the hologram element 25; and a transmitted light of the multi-lens 26. The light receiving element 27 which receives light is included.

Here, the hologram element 25 is constructed as shown in FIG. That is, in FIG. 1, the hologram element 25 has a pair of polarizing holograms 30 and 31 formed on opposite surfaces of the substrate 30a. The surfaces on which the polarization holograms 30 and 31 are formed are, for example, the substrate 30a as described later.
A surface on which light is incident and a surface on which light is emitted.

The polarization holograms 30 and 31 realize the function of separating two orthogonal polarization components into different directions by a Wollaston prism often used in optical pickups. Here, the polarization holograms 30 and 31 are manufactured as shown in FIG.

That is, in FIG. 3, a substrate 30a made of a uniaxial crystal such as lithium niobate is coated with aluminum thin films 30b on both sides thereof (FIG. 3 (a)). Thereafter, one surface of the substrate 30a is coated with a resist film 30c from above the aluminum thin film 30b [FIG. 3 (b)]. The resist film 30c is patterned by placing a grid pattern mask on the resist film 30c and exposing the resist film 30c [FIG. 3 (c)]. Subsequently, the aluminum thin film 30b is patterned by etching or the like [FIG.
After (d)], the resist film 30c is removed.

Then, the lattice-shaped portion from which the aluminum thin film 30b has been removed is subjected to proton exchange with, for example, benzoic acid to form a proton exchange layer 30d [FIG. 3 (e)]. Then, after the phase compensation film 30e made of a dielectric such as niobate Nb2O5 is coated over the entire surface [FIG. 3 (f)], the aluminum thin film 30b is removed by lift-off [FIG.
(G)]. Finally, a SiO2 layer 30 is formed over the entire surface.
f is formed by sputtering. As a result, the polarization hologram 30 is formed on one surface (upper surface) of the substrate 30a [FIG. 3 (h)].

Similarly, a polarizing hologram 31 is formed on the other surface (lower surface) of the substrate 30a by the same process [FIG. 3 (i)]. It should be noted that the above manufacturing steps and constituent materials are just examples, and it is obvious that other steps and materials are used. The polarization holograms 30 and 31 thus formed on both surfaces of the substrate 30a are composed of a lattice formed by the proton exchange method.
As a result, the refractive index for ordinary rays increases by about 0.13 and the refractive index for extraordinary rays decreases by about 0.04 in this lattice region.

Further, the polarizing hologram 30 is selected so as to cancel the phase difference generated between the ordinary rays passing through the exchange region and the non-exchange region on the proton exchange lattice (proton exchange layer 30d). A phase compensating means such as a phase compensating film 30e having a predetermined thickness is provided. Thereby, it is apparent that the extraordinary ray is observed so that the refractive index change due to the proton exchange occurs. Therefore, the exchange region and the non-exchange region are periodically provided, and the proper phase compensation means is provided, so that the ordinary ray does not feel the difference in refractive index, and the extraordinary ray feels the difference in refractive index. Therefore, as shown in the upper part of FIG. 6, a diffraction grating that acts only on extraordinary rays is provided. At that time, if the extraordinary ray has a phase difference of π due to the exchange region and the non-exchange region, the extraordinary ray transmittance should be approximately 0% and the ordinary ray transmittance should be approximately 100%. You can

Further, as shown in FIG. 4, the polarization hologram 30 is formed such that the angle θ1 of the direction in which a plurality of grooves are continuous is 45 degrees with respect to the direction a of the crystal axis. As shown in FIG. 1, the continuous directions of are arranged so as to be the direction of the linearly polarized wave c of the return light. As a result, the polarization hologram 30 causes the return light emitted from the polarization beam splitter 24 to be 1 for the ordinary ray among the orthogonal components forming the return light.
It transmits as 0% 0th-order diffracted light, does not emit diffracted light other than 0th-order, and emits extraordinary rays, which are the remaining orthogonal components, as plus / minus 1st-order diffracted light and does not emit 0th-order diffracted light. It is like this.

On the other hand, the polarization hologram 31 is
Phase compensation such as a phase compensation film 30e having a thickness selected so as to cancel the phase difference generated between the extraordinary rays passing through the exchange region and the non-exchange region on the lattice (proton exchange layer) by the proton exchange. Means are provided.
As a result, it is apparent that the refractive index change due to the proton exchange occurs only for ordinary rays. Therefore, by providing the exchange region and the non-exchange region periodically and providing an appropriate phase compensating means, the extraordinary ray does not feel the difference in refractive index, and the ordinary ray feels the difference in refractive index. Therefore, as shown in the lower part of FIG. 6, a diffraction grating that acts only on ordinary rays is provided. At that time, if the ordinary ray has a phase difference of π due to the exchange region and the non-exchange region, the ordinary ray transmittance should be approximately 0% and the extraordinary ray transmittance should be approximately 100%. You can

Further, as shown in FIG. 5, the polarization hologram 31 is formed such that the angle θ2 in the direction in which a plurality of grooves are continuous is 45 degrees with respect to the direction a of the crystal axis. The grooves are arranged so that the continuous direction of the grooves is orthogonal to the continuous direction of the grooves of the polarization hologram 30. Thus, the polarization hologram 31 transmits the plus and minus first order diffracted light formed by the polarization hologram 30 by transmitting the ordinary ray and the extraordinary ray of the polarization hologram 30 as plus and minus first order diffracted light and zero order diffracted light, respectively. The polarization hologram 30 is transmitted as it is.
The 0th-order diffracted light formed in 1 is decomposed into plus / minus 1st-order diffracted light by the diffraction action and is emitted.

Thus, the 0th-order diffracted light cannot be emitted at all as the return light transmitted through the polarization holograms 30 and 31 of the hologram element 25. By the way, in the polarization hologram 30 described above, the phase difference between the light passing through the slit-shaped groove portion (the portion of the proton exchange layer 30d) and the portion other than the groove is 0 with respect to the ordinary ray, and with respect to the extraordinary ray. By shifting the phase difference between the light passing through the slit-shaped groove portion and the portion other than the groove from π to a predetermined phase between 0 and π, the extraordinary ray is divided into 0-order diffracted light and plus / minus 1st-order diffracted light. Will be decomposed at the ratio of.

The polarization hologram 31 described above is
The phase difference between the light passing through the slit-shaped groove part and the part other than the groove with respect to the extraordinary ray is 0, and the phase difference between the light passing through the slit-shaped groove part and the part other than the groove with respect to the ordinary ray Is displaced from π by a predetermined phase from 0 to π, the ordinary ray is decomposed into a 0th-order diffracted light and a plus / minus 1st-order diffracted light at a predetermined ratio. The displacement of the phase is performed by appropriately selecting the thickness of the phase compensation film 30e in the previous manufacturing process. Thus, the polarization hologram 30 of the hologram element 25,
The return light that passes through 31 will eventually have 0-th order diffracted light remaining at a predetermined ratio.

In this case, in the polarization hologram 30, the polarization beam splitter 24 of the polarization hologram 30 is used.
The extraordinary ray component of the return light emitted from is polarized by shifting the phase difference of the light transmitted through the slit-shaped groove portion and the portion other than the groove from π to a predetermined phase between 0 and π. The hologram 30 is decomposed into a 0th order diffracted light and a plus / minus 1st order diffracted light at a predetermined ratio. Similarly, the ordinary ray incident on the polarization hologram 31 is decomposed into 0-order diffracted light and plus / minus 1st-order diffracted light at a predetermined ratio by displacing the phase difference from π to a predetermined phase between 0 and π. Will be done.

That is, in the polarization hologram 30, the phase difference between the light passing through the slit-shaped grooves of the polarization holograms 30 and 31 and the parts other than the grooves is 0 for an ordinary ray and for an extraordinary ray. Is π, and the polarization hologram 31
In the case where π is an ordinary ray and 0 is an extraordinary ray, the return light is decomposed into the extraordinary ray of plus / minus first-order diffracted light and the ordinary ray of zero-order diffracted light by the polarization hologram 30. Then, in the polarization hologram 31, only the 0th-order diffracted light is decomposed into plus / minus 1st-order diffracted light. Therefore, the return light is decomposed into four components whose polarization planes are orthogonal to each other, whereas when the phase difference changes from π by a predetermined phase, the light is emitted from the polarization hologram 30. Both the 0th-order diffracted light and the plus / minus 1st-order diffracted light are diffracted by the polarization hologram 31, and eventually the return light is decomposed into 9 components as a whole and emitted as shown in FIG. become.

FIG. 7 shows spots formed on the light receiving element by the return light transmitted through the two polarization holograms 30 and 31 having the configuration shown in FIG. Here, the beams S11, S decomposed into the upper and lower parts of the 0th-order diffracted light M1 by the above effect.
In FIG. 13, one of the orthogonal components of the return light is decomposed in the polarization hologram 30. Since the polarization hologram 31 does not include a component to be decomposed, the light quantity is emitted without changing. On the other hand, in the beams S12 and S14 decomposed to the left and right of the 0th-order diffracted light M1, the other orthogonal component of the return light is decomposed in the polarization hologram 31, and at the time of this decomposition, The amount of light is reduced and the light is emitted.

Therefore, the beams S11, S13 and S12, S14 decomposed into the upper, lower, left and right are orthogonal components of the return light, and when the polarization plane of the return light changes, the light amount changes complementarily. . As a result, the optical pickup 20 detects the reproduction signal of the magneto-optical disk by calculating the sum of the light amounts of the beams S11, S13 and the beams S12, S14, and then taking the difference from these sums. It has become.

On the other hand, the 0th-order diffracted light M1 is a component obtained by decomposing the 0th-order diffracted light of polarization components separated at a predetermined ratio by the predetermined phase difference of the return light by the polarization hologram 31. At the time of this decomposition, it is considered that the polarization hologram 31 is a component separated from the beams S12 and S14 decomposed to the left and right at a predetermined ratio by the predetermined phase difference. Therefore, the 0th-order diffracted light M1 becomes a component that is held at a substantially constant light amount even if the polarization plane of the return light changes, and the optical pickup 20 detects a focus error or the like from the 0th-order diffracted light M1. It is like this.

Accordingly, in the above-mentioned embodiment,
The light receiving element 27 uses the 0th-order diffracted light M1 and the beam S.
11 to S14 are received. Here, this light receiving element 27
Is configured as shown in FIG. That is, in the light receiving element 27, five photodetectors are integrally formed on one semiconductor substrate so as to receive the 0th-order diffracted light M1 and the beams S11 to S14, respectively. Of these, the photodetector at the center is divided into four by dividing lines extending vertically and horizontally near the center, and each of the divided sensor elements 27 is divided.
Of the a, 27b, 27c, and 27d, the sensor elements 27a and 27d arranged in the vertical direction and the sensor elements 27b and 27.
With c, the sum signal of the output signals is obtained, and the difference signal between the sum signals is detected, so that the so-called push-pull method is applied to detect the tracking error signal.

Further, in this central photodetector, the return light given astigmatism is incident, and the sensor elements 27a and 27c and the sensor elements 27c and 27d arranged in the diagonal direction output signals respectively. The focus error signal is detected by applying the so-called astigmatism method by obtaining the sum signal of the above and detecting the difference signal between the sum signals.

On the other hand, among the other photodetectors, the photodetectors 27e and 27f arranged in the direction in which the diffracted light formed by the first diffraction grating 30 is continuous and the photodetectors 27e and 27f arranged in the direction orthogonal to this direction. The photodetectors 27g and 27h receive return light components whose polarization planes are orthogonal to each other to obtain sum signals, and a difference signal between the sum signals is obtained to detect a reproduction signal.

In a magneto-optical disk device to which this optical pickup is applied, a compact disk (CD)
When reproducing, the reproduction signal is obtained by summing the output signals of the sensor elements 27a to 27d.

According to the optical pickup 20 of the present embodiment, the light beam emitted from the laser light source 21 is transmitted through the polarization beam splitter 24 and then converged on the information recording surface of the magneto-optical disk 22 by the objective lens 23. . The return light reflected by the information recording surface of the magneto-optical disk 22 is
When reflected, it receives the Kerr effect according to the magnetization magnetism of the information recording surface, and changes beam splitter 2 through objective lens 23.
The light is reflected at 4, and is transmitted through the hologram element 25 formed on the emission surface and emitted.

When the return light passes through the hologram element 25, the first component whose polarization plane forms an angle of 45 degrees with respect to the polarization plane of the return light is the plus / minus first-order diffracted light by the polarization hologram 30. And the remaining second component is emitted as 0th-order diffracted light. The plus-minus first-order diffracted light of the first component is the following polarization hologram 31.
Is directly transmitted and emitted. On the contrary, the 0th-order diffracted light of the second component is
Decomposed into orthogonal third and fourth components containing the optic axis,
The third component is emitted as plus / minus first-order diffracted light, and the fourth component is emitted as zero-order diffracted light.

As a result, the return light is the hologram element 2
From FIG. 5, the orthogonal first-order plus / minus first-order diffracted light and the third plus-minus first-order diffracted light whose light quantities change complementarily in accordance with the change in the plane of polarization, and almost the same even when the plane of polarization changes The light is decomposed into the 0th-order diffracted light of the fourth component which is held at a constant light amount and is emitted.

The plus / minus first-order diffracted light of the first component and the plus / minus first-order diffracted light of the third component pass through the multi-lens 26 and are received by the sensor elements 27e, 27f and the sensor elements 27g, 27h. It As a result, the reproduction signal is detected by taking the difference between the sum signal of the output signals of the sensor elements 27e and 27f and the sum signal of the output signals of the sensor elements 27g and 27h. On the other hand, the zero-order diffracted light of the fourth component is received by the sensor elements 27a to 27d after being given astigmatism by the multilens 26. As a result, the sensor elements 27a arranged in the vertical direction,
The tracking error signal is detected by taking a difference between the sum signal of 27d and the sum signals of the sensor elements 27b and 27c, and at the same time, the sensor elements 27a and 27c arranged in the diagonal direction.
And the focus error signal is detected by taking the difference between the sum signal of the output signals of the sensor elements 27b and 27d.

Therefore, according to the optical pickup 20 of the present embodiment, even if all the returning light is incident on the polarization hologram, the component whose light quantity changes complementarily according to the change of the polarization plane and the polarization plane. By obtaining a component that is held at a substantially constant light amount even when is changed, the tracking error signal and the focus error signal can be detected with a simple configuration, and thus a low-cost optical pickup is provided. It will be. Further, the overall shape is reduced, and especially the thickness of the optical component is reduced, so that the overall thickness of the optical pickup is reduced and the SN ratio of the reproduction signal is further improved. Further, since it is possible to obtain the reproduction signal of the puncture disc now based on the sum of the output signals of the sensor elements 27a to 27d, the present invention is applied to an optical disc device capable of reproducing both a magneto-optical disc and a compact disc. By applying S
A reproduced signal having a good N ratio can be obtained, and the entire configuration is simplified.

In the above-mentioned embodiment, the first and second polarization holograms 30 and 31 are respectively formed on the opposite surfaces of the same substrate, that is, the entrance surface and the exit surface.
It may be replaced and formed on the emission surface and the incidence surface,
Further, the polarization hologram configured separately may be integrated with the substrate by adhesion or the like.

[0046]

As described above, according to the present invention, it is possible to provide an optical pickup and an optical element having a simple structure, a small size, and a reduced cost. .

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a hologram element according to the present invention.

FIG. 2 is a schematic diagram showing an overall configuration of an optical pickup incorporating the hologram element of FIG.

3A to 3D are process diagrams sequentially showing an example of a manufacturing process of the hologram element of FIG.

FIG. 4 is a front view showing a first polarization hologram of the hologram element of FIG. 1.

5 is a rear view showing a second polarizing hologram of the hologram element of FIG. 1. FIG.

FIG. 6 is a schematic diagram showing a polarization separation state of a polarization hologram of the hologram element of FIG.

7 is a schematic diagram showing a light receiving element in the optical pickup of FIG.

FIG. 8 is a schematic diagram showing a configuration of an example of a conventional optical pickup.

[Explanation of symbols]

 20 optical pickup 21 laser light source 22 magneto-optical disk 23 objective lens 24 polarization beam splitter 25 hologram element 26 multi-lens 27 light receiving element 30, 31 polarization hologram

Claims (5)

[Claims] 1. An optical pickup for irradiating a disc-shaped recording medium with a light beam and reproducing the information recorded on the disc-shaped recording medium by utilizing the Kerr effect, wherein the return light from the disc-shaped recording medium is on the optical path. And separates the return light into first and second components that are orthogonal to each other, and for the first component, plus or minus 1
A first diffractive element that decomposes and emits the 0th-order diffracted light, suppresses and emits the 0th-order diffracted light, and suppresses plus / minus 1st-order diffracted light of the second component and emits the 0th-order diffracted light. It is arranged on the optical path of the return light emitted from the first diffractive element, substantially transmits the plus / minus first-order diffracted light of the first component, and returns as the zero-order diffracted light of the second component. The light is split into orthogonal third and fourth components, plus or minus one for the third component.
A second diffractive element that decomposes and emits the 0th-order diffracted light and suppresses and emits the 0th-order diffracted light, and suppresses the plus / minus 1st-order diffracted light and emits as the 0th-order diffracted light for the fourth component; First-plus / minus first-order diffracted light of the first component, which is substantially transmitted through the second diffractive element and is emitted, and plus-minus first-order diffracted light of the third component, which is decomposed and emitted by the second diffractive element. And a light receiving element that receives the 0th-order diffracted light of the fourth component emitted from the second diffraction element, respectively, and the first and second diffraction elements form a hologram element. An optical pickup characterized in that it is a polarization hologram provided on each of the one surface of the substrate and the opposite surface thereof. 2. The direction of the crystal axis of the first diffractive element is tilted at an angle of 45 degrees with respect to the plane of polarization of the return light when not affected by the Kerr effect and is perpendicular to the optical axis. Is selected, and a continuous slit is formed in the continuous direction of the plus / minus first-order diffracted light of the first component, and the second diffraction element is a direction excluding the continuous direction of the slit of the first diffraction element. The optical pickup according to claim 1, wherein continuous slits are formed in the continuous direction at a pitch different from that of the first diffraction element. 3. The first diffractive element sets the phase difference of the light transmitted through the slit-shaped groove portion and the portion other than the groove with respect to the ordinary ray to 0, and defines the slit ordinary groove with respect to the extraordinary ray. The extraordinary ray is decomposed into a 0th-order diffracted light and a plus / minus 1st-order diffracted light at a predetermined ratio by displacing the phase difference of the light passing through the portion and the portion other than the groove from π to a predetermined phase between 0 and π. The optical pickup according to claim 1, wherein: 4. The second diffractive element sets the phase difference of the light transmitted through the slit-shaped groove portion and the portion other than the groove with respect to the extraordinary ray to 0, and defines the slit ordinary groove with respect to the ordinary ray. By shifting the phase difference of the light transmitted through the portion and the portion other than the groove from π to a predetermined phase between 0 and π, the ordinary ray becomes 0
The optical pickup according to claim 1, characterized in that it is decomposed into a first-order diffracted light and a plus-minus first-order diffracted light at a predetermined ratio. 5. The linearly polarized incident light is separated into first and second components which are orthogonal to each other, and the first component is:
It is decomposed into plus and minus first-order diffracted light and emitted, and 0
The first diffractive element that suppresses and emits the second-order diffracted light and suppresses the plus-minus first-order diffracted light and emits the second-order diffracted light as the 0th-order diffracted light; and the second diffracted light that is emitted from the first diffractive element. The first-order plus / minus first-order diffracted light is substantially transmitted, and the second-component zero-order diffracted light emitted from the first diffractive element is separated into orthogonal third and fourth components. The third component is decomposed into plus / minus first-order diffracted light and emitted, and the zero-order diffracted light is suppressed and emitted, and the fourth component suppresses plus / minus first-order diffracted light,
A second diffractive element that emits as 0th-order diffracted light is included, and the first diffractive element and the second diffractive element are provided on one surface of the substrate forming the hologram element and on the opposite surface thereof. , An optical element, which is a polarizing hologram respectively arranged.