JP3541575B2 - Optical head device and composite anisotropic diffraction element used therefor - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical head device for a magneto-optical recording medium and a composite anisotropic diffraction element used for the same.
[0002]
[Prior art]
In an optical head device for a magneto-optical recording medium, the Kerr rotation angle (rotation angle of a polarization plane) of the magneto-optical recording medium is detected and used. As such an optical head device, one having a configuration as shown in FIG. 5 has been used.
[0003]
5, reference numeral 41 denotes a light source such as a semiconductor laser; 42, a simple diffraction grating; 43, a prism for separating beams; 44, a condenser lens; 45, a magneto-optical recording medium; 46, a Wollaston prism; Indicates a photodetector.
[0004]
In the optical head device of FIG. 5, light emitted from the light source 41 passes through the simple diffraction grating 42 and the prism 43, is condensed by the condenser lens 44, and reaches the magneto-optical recording medium 45. The return light reflected by the magneto-optical recording medium 45 is condensed again by the condenser lens 44, enters the prism 43, and is separated into two lights.
[0005]
One of the separated lights proceeds straight as it is, enters the simple diffraction grating 42 again, diffracts, and reaches the photodetectors 51 and 52. This diffracted light is used for detecting a focus error and a tracking error. The other of the separated light is reflected in the prism 43 and enters the Wollaston prism 46, where it is diffracted and reaches the photodetectors 53 to 55. This diffracted light is detected as a signal.
[0006]
[Problems to be solved by the invention]
However, such an optical head device has a problem that an expensive crystal material is used, the number of parts is large, adjustment is complicated, productivity is low, cost is high, and the shape is large. An object of the present invention is to provide an optical head device that solves these problems.
[0007]
[Means for Solving the Problems]
The present invention provides a light separation / diffraction element between a light source and a magneto-optical recording medium, separates return light from the magneto-optical recording medium into two or more lights by a light separation / diffraction element, and further diffracts the light. In the optical head device which is caused to reach the photodetector for drive control of the optical head device and the photodetector for signal detection, the light separation / diffraction element has a simple diffraction grating and a polarization diffraction grating. An optical head device characterized in that return light is diffracted by a simple diffraction grating, and + 1st-order and -1st-order diffracted lights are incident on and diffracted by polarization diffraction gratings having different polarization characteristics. I do.
[0008]
Also, its use of the substrate polarization grating of these is that an uneven inner surface of both the two substrates, the substrate one of the primary diffracted light is uneven in the incident side, the other first-order diffracted light emitted An optical head device which is a liquid crystal diffraction grating with liquid crystal encapsulated inside , and a simple diffraction grating is also formed on the outer surface of the light source side substrate of these light separation / diffraction elements. An optical head device adapted to generate the optical head.
[0009]
Further, at least one of the composite anisotropic diffraction elements having a polarization diffraction grating by interaction with an optically anisotropic material encapsulated therein using a substrate having an uneven inner surface, wherein the outer surface of at least one of the substrates has A diffraction grating is formed by unevenness, and one or more non-zero-order diffracted lights of the light diffracted by the outer diffraction grating are arranged so as to be incident on the inner polarization diffraction grating and diffracted again. And a composite anisotropic diffraction element characterized by the following.
[0010]
In addition, both of the two substrates use a substrate having irregularities on the inner surface. One of the first-order diffracted lights has irregularities on the incident side, and the other primary diffracted light has irregularities on the emission side. Provided is a composite anisotropic diffraction element arranged to be incident on a polarization diffraction grating.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, an optical separation diffraction element of the optical head device has a simple diffraction grating and the polarizing diffraction grating are diffracted return light by a simple diffraction grating, its +1 order and -1 order diffracted light, respectively Since the light is diffracted by being incident on polarization diffraction gratings having different polarization characteristics , the light separation / diffraction element can be manufactured in a small size and easily.
[0012]
As a reference, by providing a diffraction grating with irregularities on the inner and outer surfaces of the substrate and using a composite anisotropic diffraction element filled with an optically anisotropic material inside, it can be made extremely small, and that part can be adjusted after assembly Has the advantage that it becomes unnecessary.
[0013]
1 and 2 are sectional views of a specific example of the composite anisotropic diffraction element of the present invention. FIG. 1 shows a basic configuration, and FIG. 2 shows an example in which a fourth diffraction grating for generating three beams is provided. 1 and 2, reference numerals 1, 2, and 3 denote diffraction gratings, reference numerals 4 and 5 denote substrates, reference numeral 6 denotes a liquid crystal representative of an optically anisotropic material, reference numeral 10 denotes light from a light source such as a semiconductor laser, and reference numerals 11 to 16 Fig. 7 shows diffracted light of return light from a magneto-optical recording medium. Reference numeral 7 in FIG. 2 shows a diffraction grating for generating three beams.
[0014]
3 and 4 are schematic diagrams of specific examples of an optical head device using the composite anisotropic diffraction element of FIGS. 1 and 2. FIG. FIG. 3 corresponds to FIG. 1, and FIG. 4 corresponds to FIG. 3 and 4, reference numeral 21 denotes a light source such as a semiconductor laser, 22 denotes the composite anisotropic diffraction element of FIG. 1, 23 denotes a condenser lens, 24 denotes a magneto-optical recording medium, and 30 denotes a magneto-optical recording medium emitted from the light source. , 31 to 36 indicate photodetectors. In FIG. 4, reference numeral 25 denotes the composite anisotropic diffraction element shown in FIG. 2, and reference numeral 37 denotes light emitted from the light source and reaching the magneto-optical recording medium.
[0015]
In the present invention, the light separation / diffraction element of the optical head device has a simple diffraction grating and a polarization diffraction grating. The return light from the magneto-optical recording medium is diffracted by a simple diffraction grating, and the + 1st-order and -1st-order diffracted light are incident on polarization diffraction gratings having different polarization characteristics, and are diffracted. These two types of diffraction gratings are integrated.
[0016]
Specifically, on at least one side, a substrate having an uneven surface is used, and a polarization diffraction grating is used by the interaction with an optically anisotropic material enclosed therein, and a simple diffraction grating provided on the outer surface of the substrate is used. A composite anisotropic diffraction element is formed.
[0017]
The simple diffraction grating on the outer surface of the substrate may be formed in a stripe shape. For this purpose, it is preferable that the outer surface of the substrate is made uneven by etching, mechanical cutting, pressing, or the like to form a diffraction grating with good productivity. In this case, the substrate itself may be directly processed, or a transparent film having a specific refractive index may be formed on the substrate surface and then processed. In addition, the refractive index of the substrate itself can be partially changed to function as a diffraction grating. The simple diffraction grating on the outer surface is arranged on the magneto-optical recording medium side, and return light from the magneto-optical recording medium is diffracted by the simple diffraction grating.
[0018]
Of the light diffracted by the simple diffraction grating, the + 1st-order and -1st-order diffracted lights are made to enter polarization gratings having different polarization characteristics . This polarization diffraction grating diffracts light of a specific polarization direction by the interaction between the unevenness formed on the inner surface of the substrate and the optically anisotropic material enclosed therein for reference. The unevenness on the inner surface of the substrate may be formed in the same manner as the simple diffraction grating on the outer surface of the substrate.
[0019]
Polarization grating of the beam splitting diffraction element, form two polarization grating for diffracting the diffracted light both + 1-order and -1-order diffracted light. Preferably, the two polarization gratings have a difference in polarization dependence.
[0020]
Specifically, it is preferable that one has a polarization dependency such that one diffracts the P wave and the S wave goes straight, and the other diffracts the S wave and the P wave goes straight. For this reason, in the case of a polarization diffraction grating composed of the unevenness on the inner surface of the substrate and the optically anisotropic material, it is preferable that the surface of the two polarization diffraction gratings having the unevenness be the opposite substrate.
[0021]
In particular, since the relationship between the refractive index of the optically anisotropic material encapsulated therein and the unevenness of the substrate becomes important, it is necessary to adjust the refractive index of the unevenness. Therefore, if the substrate itself has a desired refractive index, it can be used as it is, but if the refractive index of the substrate itself is different from the desired refractive index, it is possible to form a transparent film having a desired refractive index on the substrate surface. preferable. This transparent film may be patterned by etching or the like, or may be formed directly into a desired pattern.
[0022]
Specifically, the refractive index of the uneven portion is made to match the ordinary light refractive index or the extraordinary light refractive index of the optically anisotropic material. A case in which liquid crystal is used as an optically anisotropic material and orientation processing is performed by rubbing in the longitudinal direction of the diffraction grating will be described.
[0023]
If the refractive index of the concave and convex portions is made to match the ordinary refractive index of the liquid crystal, the liquid crystal molecules are arranged in the longitudinal direction of the lattice, so that light having a polarization direction in a direction perpendicular to the longitudinal direction of the lattice is both refracted. Since the indices match, the light does not work as a diffraction grating and the light goes straight. On the other hand, light having a polarization direction in the longitudinal direction of the grating will act as a diffraction grating because the apparent refractive index of the liquid crystal becomes an extraordinary light refractive index and the two refractive indexes do not match, and the light is diffracted. .
[0024]
When the refractive index of the concave and convex portions is made to match the extraordinary light refractive index of the liquid crystal, since the liquid crystal molecules are arranged in the longitudinal direction of the lattice, light having a polarization direction perpendicular to the longitudinal direction of the lattice. Since the apparent refractive index of the liquid crystal becomes the ordinary light refractive index, the two refractive indexes do not match, and light is diffracted. On the other hand, light having a polarization direction in the longitudinal direction of the grating has the same refractive index, so that it does not work as a diffraction grating and the light goes straight.
[0025]
Therefore, by forming the concave and convex portions of the two diffraction gratings with materials that match the ordinary light refractive index and the extraordinary light refractive index, respectively, it is possible to have different polarization characteristics. Thereby, in the diffraction gratings 2 and 3, the P-wave component is diffracted on the one hand, and the S-wave component is diffracted on the other hand.
[0026]
As shown in FIG. 1, when forming an uneven portion on two substrates sandwiching a liquid crystal layer, if the alignment treatment is performed so that the liquid crystal is twisted by 90 °, both the uneven portions will have the ordinary light refractive index and the refractive index of the liquid crystal. The rates may match. This is because light passes through the liquid crystal layer and the polarization direction of the light is rotated by 90 ° and enters the diffraction grating in which the concave and convex portions are on the substrate 5 on the light source side. Is diffracted, while the S-wave component is diffracted.
[0027]
In the example of FIG. 1, the light diffracted by the diffraction grating 1, which is a simple diffraction grating, travels in at least two directions in addition to the zero-order light traveling straight. The light traveling to the left is diffracted by the diffraction grating 2 that is a polarization diffraction grating formed by the unevenness provided on the inner surface of the substrate 5 and the liquid crystal 6 that is an optically anisotropic material, and becomes light 11, 12, and 13. Reach the vessel. The light traveling to the right is diffracted by the diffraction grating 3 which is a polarization diffraction grating formed by the unevenness provided on the inner surface of the substrate 4 and the liquid crystal 6 which is an optically anisotropic material, and becomes light 14, 15, and 16 for light detection. Reach the vessel.
[0028]
Here, it is assumed that the light from the light source has a polarization direction inclined by 45 ° and includes both the P wave and the S wave components. The return light reflected by the magneto-optical recording medium has its polarization plane rotated by a certain angle. This return light is diffracted by the diffraction grating 1 which is a simple diffraction grating, and guided to two diffraction gratings 2 and 3.
[0029]
In the diffraction grating 2 on the left side, the 0th-order light 12 becomes substantially P-wave, and the -1st-order and + 1st-order lights 11 and 13 become almost S-waves. At 15, the light is substantially an S wave, and the −1 and +1 order lights 14 and 16 are substantially P waves. At this time, the polarization rotation angle on the magneto-optical recording medium can be read by calculating the difference between the sum of the S-waves of 11, 13 and 15 and the sum of the P-waves of 12, 14 and 16.
[0030]
As shown in FIG. 2, by providing the fourth diffraction grating 7 which is a simple diffraction grating on the outer surface of the substrate on the light source side, it can be used for generating three beams. The fourth diffraction grating 7 is usually set so that the directions of the stripes of the grating are orthogonal to the diffraction gratings 1, 2, and 3.
[0031]
In addition, by forming various curved gratings on the diffraction grating 1 or forming different curved gratings by dividing regions, the optical head device can have a function of detecting a focus error and a tracking error.
[0032]
As the substrate used for the composite anisotropic diffraction element, a substrate of ordinary glass, plastic, or the like can be used. If necessary, a transparent film having a desired refractive index is laminated and used. Further, if necessary, an alignment film of polyimide, a spacer for controlling a gap, an electrode, a sealing material, and the like are used for this.
[0033]
As an optically anisotropic material, liquid crystal is used as a typical material. Usually, a nematic liquid crystal having a positive dielectric anisotropy may be used. In the above description, the liquid crystal is described as using a liquid material, but a polymer liquid crystal can also be used. An anti-reflection coating may be formed to suppress unnecessary surface reflection, or the diffraction grating may be formed into a complicated shape to add an additional function.
[0034]
【Example】
On a glass substrate having a refractive index of 1.52 and a thickness of 2 mm (outer surface side), a SiO ₂ film is formed to a thickness of 0.6 μm by vapor deposition, and a pitch of 1.5 μm and a depth of 0 is formed by photolithography and dry etching. A diffraction grating 1 of 0.6 μm was formed. A pattern for focus error detection by an SSD (Spot Size Detection) method was formed on this diffraction grating.
[0035]
An SiON-based film having a refractive index of 1.79 and a thickness of 1.4 μm was formed by plasma CVD on a surface (the inner surface side) of the glass substrate opposite to the surface on which the diffraction grating was formed, at a position where + 1st-order light passes. The diffraction grating 3 having a pitch of 8 μm and a depth of 1.4 μm was formed by photolithography and dry etching.
[0036]
An SiON-based film having a refractive index of 1.52 and a thickness of 1.4 μm is provided at a position on the surface (inner side) of the second glass substrate having a thickness of 0.5 mm and a refractive index of 1.52 through which −1st-order light passes. Was formed by the plasma CVD method, and a diffraction grating 2 having a pitch of 8 μm and a depth of 1.4 μm was formed by photolithography and dry etching.
[0037]
An SiO ₂ film is formed by vapor deposition on a surface (outer surface side) of the second glass substrate opposite to the surface on which the diffraction grating is formed, at a position where the outward light from the semiconductor laser passes, and is subjected to photolithography and dry etching. A diffraction grating 4 having a pitch of 16 μm and a depth of 0.5 μm was formed.
[0038]
The two inner surfaces of the SiON-based films are made to face each other with the diffraction grating surfaces facing each other, the stripe directions are matched, and the −1st-order diffracted light is arranged to pass through the diffraction grating 2, and the peripheral portion is made of epoxy resin. Sealed. Thereafter, a liquid crystal having an ordinary light refractive index of 1.52 and an extraordinary light refractive index of 1.79 was injected, and the injection port was similarly sealed with an epoxy resin to prepare a liquid crystal element serving as a composite anisotropic diffraction element. Note that both substrates were provided with a polyimide thin film on the inner surface side and rubbed along the longitudinal direction of the lattice. For this reason, the twist angle of the liquid crystal was set to 0 °.
[0039]
As shown in FIG. 4, an optical head device was prepared using the above liquid crystal element, and the Kerr rotation angle of the magneto-optical disk was read.
[0040]
【The invention's effect】
In the present invention, an optical separation diffraction element of the optical head device has a simple diffraction grating and the polarizing diffraction grating are diffracted return light by a simple diffraction grating, its +1 order and -1 order diffracted light, respectively Since the light is diffracted by being incident on polarization diffraction gratings having different polarization characteristics , the light separation / diffraction element can be manufactured easily in a small size.
[0041]
In particular, by providing a diffraction grating with irregularities on the inner and outer surfaces of the substrate and using a composite anisotropic diffraction element filled with an optically anisotropic material typified by liquid crystal inside, the size can be extremely reduced, Since all the diffraction gratings are integrated, adjustment after assembly of the diffraction grating is not required.
[0042]
Furthermore, the use of such a light separating and diffractive element that does not require adjustment makes it possible to reduce the size of the optical head device itself, and the number of parts is small, so that the assembly is easy and the adjustment is easy, and the production is easy. Good nature. The present invention can be applied to various applications within a range that does not impair the effects of the present invention.
[Brief description of the drawings]
FIG. 1 is a sectional view of a specific example of a composite anisotropic diffraction element of the present invention.
FIG. 2 is a cross-sectional view of another specific example of the composite anisotropic diffraction element of the present invention.
FIG. 3 is a schematic diagram of a specific example of an optical head device using the composite anisotropic diffraction element of FIG.
FIG. 4 is a schematic diagram of a specific example of an optical head device using the composite anisotropic diffraction element of FIG. 2;
FIG. 5 is a schematic view of an example of a conventional optical head device.
[Explanation of symbols]
Diffraction grating: 1, 2, 3, 7
Substrate: 4, 5
Liquid crystal: 6
Light: 11-16

Claims (5)

An optical separation / diffraction element is provided between the light source and the magneto-optical recording medium, the return light from the magneto-optical recording medium is separated into two or more lights by the light separation / diffraction element, and the light is diffracted to form an optical head. In an optical head device that reaches a photodetector for drive control of the device and a photodetector for signal detection, the light separation / diffraction element has a simple diffraction grating and a polarization diffraction grating. An optical head device, wherein light is diffracted by a simple diffraction grating, and + 1st-order and -1st-order diffracted lights are incident on polarization diffraction gratings having different polarization characteristics and are diffracted. Both of the substrates having two polarization diffraction gratings have irregularities on the inner surface, and one of the primary diffracted light has irregularities on the incident side and the other primary diffracted light has irregularities on the emission side. , and the claim 1 Symbol placement of the optical head device is a liquid crystal diffraction grating in which liquid crystal is sealed therein. 3. The optical head device according to claim 2, wherein a simple diffraction grating is also formed on the outer surface of the substrate on the light source side of the light separating and diffractive element to generate three beams. In a composite anisotropic diffraction element having a polarization diffraction grating by interaction with an optically anisotropic material encapsulated therein, at least one of the substrates has an irregular surface on the inner surface, and at least one of the substrates has an irregular surface on the outer surface. A diffraction grating is formed, and one or more non-zero-order diffracted lights of the light diffracted by the outer diffraction grating are arranged to be incident on the inner surface polarization diffraction grating and diffracted again. Composite anisotropic diffraction element. Both substrates use substrates with irregularities on the inner surface. One of the first order diffracted light is a polarization grating having irregularities on the incident side, and the other is a diffractive grating having the first order diffracted light on the exit side. The composite anisotropic diffraction element according to claim 4, wherein the element is arranged so as to be incident on.

Images