JPH11353728A - Magneto-optical head - Google Patents

Abstract

(57) Abstract: Two polarizing polarizing gratings are arranged orthogonally and used as a polarization separating element of a magneto-optical head to split reflected light from a magneto-optical disk to a photodetector. By also serving as a branching element, a coaxial optical system in which the optical axis from the semiconductor laser to the magneto-optical disk and the optical axis of the detection light are substantially common, and the semiconductor laser and the photodetector are integrated into one package. According to the present invention, polarization separation is performed using a polarizing diffraction grating that can be manufactured by an exposure and development process using a photomask, has excellent mass productivity, is easy to be miniaturized, and can freely design its separation ratio and separation angle. At the same time, a servo signal such as a defocus signal or a tracking error signal is detected, and a magneto-optical head using a coaxial optical system in which a semiconductor laser light source is arranged on the optical axis of the 0-order light at the center of ± 1st-order diffracted light can be provided. This makes it easy to realize a magneto-optical head that is small in size, has a small number of components, and is easy to mass-produce.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to miniaturization of a magneto-optical head for recording and reproducing a magneto-optical disk.

[0002]

2. Description of the Related Art Conventionally, a polarization separating element generally used in a magneto-optical head is formed by laminating a dielectric multilayer film on a slope of a polarizing prism 11 as shown in FIG. As a result, almost 100% of P-polarized light (linearly polarized light component oscillating in a plane perpendicular to the boundary surface) is transmitted to the bonded boundary surface, and almost 100% of S-polarized light (linearly polarized light component oscillating in the boundary surface) is reflected. be able to. In order to detect the polarization rotation in the magneto-optical disk by using this, the linear polarization direction of the reflected light is inclined by 45 ° with respect to the separation direction so that the transmitted light and the reflected light have substantially the same amount of light on average. A signal is reproduced by detecting a change in the balance between the transmitted light and the reflected light due to the rotation of the polarization from the difference in the detected light amounts.

As another conventional method, Japanese Patent Publication No.
There is a magneto-optical head constructed as in Japanese Patent Publication No. 6-77351 using the special Wollaston prism 21 described in U.S. Pat. This prism is formed by laminating a birefringent material in a specific principal axis direction, and has a configuration as shown in FIG. That is, there is light at the center in the same polarization state as the incident light beam, and light of two orthogonal polarization components is branched on both sides. If this is used, three light detectors 2
Since 2, 23, and 24 can be configured on one surface, the optical head can be reduced in size by forming one package. in this case,
It is possible to detect a magneto-optical signal from the light on both sides and detect a servo signal such as a defocus signal or a tracking signal from the light at the center.

[0004] Although not a polarization separation element of a magneto-optical head, a polarization separation element using a grating is known in National Technical Report Vol. 41 No. 6 (1995) 62.
Pages 2 to 628 (National Technical Report, Vol.
41, No. 6 (1995) 622-628). This is schematically configured as shown in FIG. Incident light that is incident on the polarizing diffraction grating 31 and is polarized in a specific direction is transmitted without generating diffracted light, converted into circularly polarized light by the λ / 4 plate 32, reflected by the reflecting object 33, and again. λ
The light passes through the ４ plate 32 and becomes linearly polarized light in a direction orthogonal to the direction of incidence, and enters the polarizing diffraction grating 31. In this case, the light is diffracted almost 100% to generate ± 1st-order diffracted light. Such an effect is obtained by the polarizing diffraction grating 3.
This is because a birefringent optical crystal such as lithium niobate is used as a material for forming the element 1 and the phase difference at which the grating acts on two orthogonal linearly polarized lights is different. In this case, the polarizing diffraction grating 31 can also be used as a polarization splitting element that separates the linearly polarized light in the polarization direction at the time of incidence into 0th-order light and the linearly polarized light in the direction orthogonal thereto as ± 1st-order diffraction light. Although an optical crystal is required, since it is a diffraction grating, this polarization separation element can be manufactured by an exposure and development process using a photomask, has excellent mass productivity, is easy to miniaturize, and can freely design its separation ratio and separation angle. There are advantages.

[0005]

Conventionally, a polarization separation element as shown in FIG. 1 which is generally used for a magneto-optical head requires two detection surfaces 12 and 13, so that the size of the magneto-optical head is small. Not suitable for conversion.

Another conventional method is disclosed in Japanese Patent Publication No. 1952/1992.
The special Wollaston prism 21 described in FIG. 2 described in FIG. 2 has a three-dimensional shape. In introducing very small size, the thickness of itself can still be a problem. For further miniaturization, the semiconductor laser and the photodetector should be packaged in the same package, and a coaxial optical system in which the optical path of light incident on the disc and the optical path of the reflected light going to the photodetector are almost common will be constructed. In this case, there are problems that the separation ratio of light quantity and the separation angle are limited to specific values, and that unnecessary polarized light separated on the outward path is reflected by the disk and mixed into the signal light on the return path. Further, in practice, it is necessary to detect a defocus signal and a tracking error signal even when a coaxial optical system is formed. For this purpose, the detector must be a split detector. However, since the Wollaston prism has only two separated beams other than at the center, it must be shared with a magneto-optical signal. However, this tends to cause noise mixing and a reduction in resolution.

The National Technical Report Vol. 41, No. 6 (1995), pp. 622 to 62 shown in FIG.
Page 8 (National Technical Report, Vol. 41, No. 6 (1
995) 622-628), a polarization splitting element using a grating, when trying to use this for magneto-optical signal detection, one of two orthogonal polarization components is the sum of two photodetector outputs, The other is a signal from one photodetector,
Symmetry such as shot noise due to the photodetector and thermal noise of the amplifier at the subsequent stage is lost, and the common-mode rejection ratio and the signal-to-noise ratio are reduced. In addition, it is difficult to integrate a photodetector for detecting a servo signal, and it is impossible to arrange a coaxial optical system in which a semiconductor laser light source is arranged on the central optical axis.

In view of these problems, an object of the present invention is to use a polarizing diffraction grating which can be manufactured by an exposure and development process, has excellent mass productivity, is easy to be miniaturized, and can freely design its separation ratio and separation angle. Magneto-optical head with a coaxial optical system that performs polarization separation and simultaneously detects servo signals such as defocus signals and tracking error signals, and arranges a semiconductor laser light source on the optical axis of the 0th order light at the center of ± 1st order diffracted light It is to provide.

[0009]

In order to solve the above-mentioned problems, a semiconductor laser, an optical system for condensing the light on a magneto-optical disk, and a light reflected from the magneto-optical disk are branched to a photodetector. In a magneto-optical head including a light splitting element, a polarization splitting element that splits the split light into two orthogonal linearly polarized lights, and a photodetector that independently detects the split light, the polarization splitting element is Two polarizing diffraction gratings that diffract only a specific linearly polarized light component and transmit a linearly polarized light component orthogonal to the specific linearly polarized light component are superimposed so that the gratings are substantially orthogonal. As a result, these two polarizing diffraction gratings can independently diffract two orthogonal linearly polarized light components, and polarization separation and detection with good symmetry of the two polarized light components can be performed.

A semiconductor laser, an optical system for condensing the light on a magneto-optical disk, and a polarization splitting element for splitting reflected light from the magneto-optical disk to a photodetector and splitting the light into two orthogonal linearly polarized lights. And in a magneto-optical head composed of photodetectors that independently detect the separated light, the polarization splitting element diffracts only a specific linearly polarized light component and transmits two linearly polarized light components orthogonal to it. The polarizing diffraction grating is arranged so that the gratings are substantially orthogonal to each other, and the photodetector is integrated in the same package as the semiconductor laser. This makes it possible to realize a coaxial detection optical system in which the optical axis from the semiconductor laser to the magneto-optical disk and the optical axis of the zero-order light of the detection light are common, which is effective for miniaturization of the optical head.

In the above-described magneto-optical head,
The two sets of. ±.
Of the first-order diffracted light, a magneto-optical signal is detected from any two received light signals having different polarizations, and one or both of a defocus signal and a tracking error signal are detected from the other two. As a result, it is possible to detect the servo signal at the same time while preventing noise and the like from being mixed in the magneto-optical signal.

At this time, the grating shape of the polarizing diffraction grating is a curve. In this way, the diffraction grating can have a lens function with respect to the diffracted light, and unnecessary diffraction light generated when light traveling from the semiconductor laser toward the magneto-optical disk is transmitted through the diffraction grating can be converted into light. By defocusing on the magnetic disk, it is possible to eliminate the influence of noise added to the detection signal.

There are four photodetectors for receiving two sets of ± 1st-order diffracted lights having different polarizations. Two adjacent photodetectors are light-receiving regions without division lines, and the other two adjacent light-detection regions are division lines. It is a certain photodetector. As a result, the magneto-optical signal and the servo signal can be detected independently, and the addition operation is not required for the magneto-optical signal, so that noise can be prevented from being mixed.

In these magneto-optical heads, the transmittance of one-way zero-order light of the polarizing diffraction grating is set to 50% or more and 70% or less. It is necessary to perform recording on the magneto-optical disk, and it is necessary to secure an efficiency of about 30% of the amount of light reaching the magneto-optical disk with respect to the amount of light emitted from the semiconductor laser.
Since the coupling efficiency from the semiconductor laser to the lens is about 50 to 60%, the transmittance of the zero-order light of the diffraction grating is also 50 to 60%.
60% or more is required. However, if it is too high, the amplitude of the detected magneto-optical signal will be small. A magneto-optical signal by a sufficiently large magneto-optical mark is represented by T (1−T) sin 2θ where T is the transmittance of the 0th-order light of the polarizing diffraction grating.
(Θ is the polarization rotation angle of the magneto-optical disk). In the conventional magneto-optical head, since the coefficient of sin 2θ is about 0.2 to 0.25, the transmittance T is 7
It must be suppressed to 0% or less.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 shows an embodiment of the polarizing diffraction grating according to the present invention. Polarizing diffraction gratings 41 and 42 that diffract only linearly polarized light in a direction perpendicular to the grating are made to act on two linearly polarized lights incident from the right side in the drawing so as to be orthogonal to each other. Then, the polarization diffraction grating 41 first generates diffracted light only in the polarization component orthogonal to the grating, and the linear polarization component parallel to the grating is not subjected to any diffraction action. Next, the polarizing diffraction grating 4
By arranging the same polarizing diffraction grating 42 perpendicular to the polarizing grating 1 as described above, the polarized light diffracted by the polarizing diffraction grating 41 becomes a polarization component parallel to the grating in the polarizing diffraction grating 42, so that there is no diffraction effect. Transmit without receiving. On the other hand, the polarized light component transmitted without being diffracted by the polarizing diffraction grating 41 is diffracted by the polarizing diffraction grating 42 because it becomes a polarized light component orthogonal to the grating. In this way, five light rays including the zero-order light are generated after passing through the two polarizing diffraction gratings. Of these, two diffracted lights facing each other are linearly polarized lights having the same polarization direction, and adjacent diffracted lights are orthogonally linearly polarized lights. Therefore, it can be seen that the incident light is polarized and separated.

FIG. 5 is a diagram showing the polarization state of the diffracted light by the polarization diffraction grating 51 in which the polarization diffraction gratings 41 and 42 of FIG. 4 are superimposed. As a result, two diffracted lights opposing each other are linearly polarized lights having the same polarization direction, and adjacent diffracted lights have a total of four diffracted lights having orthogonal linearly polarized lights, and a total of five rays including the zero-order light are generated. .

FIG. 6 is a diagram for explaining the principle of the polarizing diffraction grating. Here, lithium niobate (LiNbO)
Here is an example using ₃ ). The lithium niobate substrate 61 has a main axis 68 of refractive index anisotropy in the direction of the plane of the paper, and forms a proton exchange region 62 there in accordance with the grating pattern. Further, a dielectric film 63 is formed according to the grating pattern. At this time, the phase difference φo between the grating pattern and the ordinary rays 64 and 65 incident therebetween and the phase difference φe between the extraordinary rays 66 and 67 can be expressed as follows.

[0019]

(Equation 1)

Here, each phase difference is set to an appropriate design value in consideration of diffraction efficiency, and is solved as a simultaneous linear equation in which the thickness Td of the dielectric film and the depth Tp of the proton exchange region are unknown. ,

[0021]

(Equation 2)

The polarization grating which gives a desired phase difference independently between the ordinary ray and the extraordinary ray can be designed. For example, the wavelength λ is set to 0.41 μm, CeO ₂ is used for the dielectric layer, the refractive index nd is set to 2.2, φo = 0 °, φe =
Tp = 0.64 μm, Td = 90 °
The thickness may be 0.021 μm.

A method for producing a refractive index change region by proton exchange is described in, for example, Hiroshi Nishihara, “Optical Integrated Circuit,” Ohmsha (Showa 6).
0, 1st edition) pp. 167 to 170, and for the method of forming a lattice pattern by proton exchange, see Ibid., 2
Page 08. According to this, benzoic acid (C ₆
By heating the H ₆ COOH) as a liquid state at a temperature between the melting point 121 ° C of boiling point 250 ° C, when immersing the lithium niobate therein occur exchange of lithium ions and hydrogen ions, the crystal A high refractive index layer is formed on the surface.
In order to form a lattice, C
A mask is formed with r, Ti, or the like. In the case of Ti, after sputtering Ti on the lithium niobate crystal, the lattice is patterned by a photoresist, and T
A mask can be formed by opening a window in the i-film. After that, proton exchange is performed, the Ti film is removed, and annealing is performed to form a lattice.

Various other materials can be used to form the polarizing diffraction grating. For example, Japanese Journal of Applied Physics, 3
6, 1997, pages 589 to 590 (Jpn.
J. Appl. Phys. , 36 (1997) pp. 5
89-590) show that a polarizing diffraction grating can also be formed by forming a grid-like electrode on a liquid crystal polymer material and applying an ultraviolet voltage while applying an AC voltage. In this case, when the voltage is applied, the liquid crystal molecules are aligned in accordance with the electric field, so that the ordinary refractive index acts regardless of the polarized light, so that the liquid crystal molecules are isotropic. Therefore, when the voltage is not applied, the liquid crystal molecules are initialized by a method called rubbing. Since the liquid crystal molecules are oriented in the in-plane direction, the ordinary refractive index and the extraordinary refractive index act depending on the polarization direction. Therefore, in this method, when compared with a polarizing diffraction grating obtained by proton exchange of lithium niobate, the difference Δno in the ordinary refractive index between the grating and the region other than the grating is always 0, and the difference Δne in the extraordinary refractive index is always the ordinary refractive index. It corresponds to the difference between the refractive index and the extraordinary refractive index. Therefore, in the case of a polarization diffraction grating using a liquid crystal polymer, only one stage of the liquid crystal polymer grating can be used so that no grating acts on ordinary light. In other words, while the polarizing diffraction grating formed by proton exchange of lithium niobate is composed of a two-stage lattice consisting of a proton exchange region and an isotropic dielectric, there is an advantage that only one liquid crystal lattice is required.

Examples of isotropic materials usually used for forming thin films are, for example, Terutsu Kose and other editors, "Optical Engineering Handbook"
It is described on page 175 of Asakura Shoten (first edition, 1986). For example, various materials such as SiO ₂ , LiF, ZnS, and MgO can be used according to the refractive index.

Regarding anisotropic materials, Hiroshi Nishihara, “Optical Integrated Circuit” Ohmsha (1st edition of 1985), pp. 139-142.
According to the page, for example, lithium niobate (ne
= 2.2, no = 2.286), titanium oxide (ne = 2.865, no = 2.583), lead molybdate (ne = 2.262, no = 2.386), tantalum acid Lithium (ne = 2.176, no = 2.18
0), barium titanate (ne = 2.41, no = 2.
36), zinc oxide (ne = 1.999, no = 2.01)
5) and the like.

FIG. 7 shows an embodiment of a magneto-optical head using the polarizing diffraction grating of the present invention. The linearly polarized light from the semiconductor laser 71 passes through the beam splitter 72, is converted into parallel light by the collimator lens 73, is reflected by the rising mirror 74, and is collected on the magneto-optical disk 77 by the objective lens 76 mounted on the lens actuator 75. Be lighted. Then, depending on the presence or absence of the magneto-optical domain, the polarization direction rotates in the opposite direction, and the recorded information is conveyed. The reflected light returns to the objective lens 7 again.
6. After passing through the rising mirror 74 and the collimating lens 73, the light is reflected by the beam splitter and enters the polarizing diffraction grating 78 according to the present invention. Then, each of the linearly polarized light components in the directions at + 45 ° and −45 ° with respect to the incident linearly polarized light direction is diffracted as ± 1st-order diffracted light. Further, the remaining light passes through the polarizing diffraction grating 78 as it is as the zero-order light. Thereafter, astigmatism is given by a cylindrical lens 79 for detecting astigmatism defocus, and the photodetector 7
The light is collected at 10. The photodetector 710 includes a quadrant detection area 711 at the center and a magneto-optical signal detection area 71 around the detection area 711.
2, 715, tracking error signal light detection area 71
3, 714, 0-order light at center, ± 1 at period
Next-order diffracted light is detected. When recording information on the magneto-optical disk 77, the magneto-optical disk is magnetized uniformly in one direction in advance, and a magnetic field opposite to the initial magnetization direction is applied by the electromagnetic coil 716. The recording domain is formed by locally increasing the temperature from the Curie temperature of the recording film by the intensity-modulated semiconductor laser light. Magnetic field modulation recording in which the magnetization direction by an electromagnetic coil is modulated by recording information while recording is performed while irradiating the medium with a focused spot having a constant intensity so that the medium has a Curie point temperature or higher may be used. Of course, a method in which light or a magnetic field is pulse-modulated and recorded may be used.

FIG. 8 is a diagram for explaining a method of detecting a signal from the photodetector 710. First, a defocus error signal is detected from the central four-divided light detection area 711. As the defocus error signal, the differential amplifier 82 detects the differential signal of the sum of the signal outputs of the four divided diagonal regions. This is fed back to the lens actuator 75 of FIG. 7 to perform closed loop control. Further, a tracking error signal can be obtained by detecting the differential signal of the sum of the two regions on both sides of the two-divided photodetectors 713 and 714 by the differential amplifier 83.
This is called a push-pull method, and is a method for detecting an imbalance in a diffraction pattern due to a guide groove on a magneto-optical disk. This tracking error signal is also shown in FIG.
Is fed back to the lens actuator 75 to perform closed loop control. However, the lens actuator 7 shown in FIG.
Reference numeral 5 denotes a two-dimensional actuator having drive axes in two directions, that is, the optical axis direction and the disk radial direction. The ± 1st-order diffracted light having orthogonal polarization components by the polarizing diffraction grating 78 according to the present invention is detected by the two light receiving regions 712 and 713 on both sides of the four-divided light detection region 711, and the output differential signal is output. Is detected by the differential amplifier 81 to obtain a magneto-optical signal.

FIG. 9 shows a second embodiment of the magneto-optical head according to the present invention. The linearly polarized light emitted from the semiconductor laser at the center of the module 91 in which the semiconductor laser and the photodetector are integrally mounted is transmitted through the refraction type polarizing diffraction grating 92 according to the present invention, and is turned on by the rising mirror 93. Is reflected and focused on a magneto-optical disk 96 by a finite objective lens 95 mounted on a lens actuator 94.
At this time, unnecessary diffracted light is generated even on the outward path by the refraction-type polarizing diffraction grating 92. However, since the grating is curved and has a lens function, the focal position of the diffracted light can be largely shifted from the 0th-order light, and The light hardly returns to the photodetector and therefore has virtually no effect. This is a serious problem in a three-beam Wollaston prism having no lens action. The light reflected by the recording film of the magneto-optical disk 96 rotates the polarization directions of the linearly polarized light in opposite directions depending on the presence or absence of a recording magnetic domain, and conveys recorded information. Then, the light again enters the refraction type polarizing diffraction grating 92 through the finite system objective lens 95 and the rising mirror 93. And 0
The next light returns to the semiconductor laser as it is, but is + 45 ° with respect to the polarization direction of the original linearly polarized light emitted from the semiconductor laser.
The linearly polarized light components in the direction of −45 ° are each diffracted into ± 1st-order diffracted light, and the semiconductor laser photodetector integrated module 9
1 are detected by the respective light receiving units. Here, since the refraction-type polarizing diffraction grating 92 has a refracting power, the + 1st-order diffracted light is focused before the detection surface for each polarized light, and the -1st-order diffracted light is light conjugate to the refracted light. Therefore, irradiation is performed so that the focal point is located deeper than the detection surface. Thus, the detection of defocus by the beam size method can be performed simultaneously with the detection of the tracking signal by the push-pull method. Also, a magneto-optical signal can be obtained from the difference between the detected light amounts of the respective polarized lights. Note that, similarly to the linear grating already described, the refraction-type polarization diffraction grating 92 is configured such that one of the same two refraction-type polarization diffraction gratings that act only on linearly polarized light in one direction is rotated by approximately 90 degrees and bonded together. It has become.

FIG. 10 shows a second example of the magneto-optical head shown in FIG.
FIG. 7 is a diagram for explaining a signal detection method in the embodiment of FIG. A semiconductor laser 101 is provided at the center of the semiconductor laser photodetector integrated module 91. The semiconductor laser 101 is preferably of a surface emitting type, but a conventional general semiconductor laser chip having a Fabry-Perot resonator structure and a 45 ° reflecting mirror may be mounted in a hybrid manner. A light receiving area for detecting the diffracted light by the polarizing diffraction grating is provided around the semiconductor laser 101. First, a difference between the outputs from the magneto-optical signal detection areas 102 and 103 on the left and upper sides in the figure is calculated by the differential amplifier 81 to obtain a magneto-optical signal. The right and lower sides of the semiconductor laser 101 are the servo signal detection areas. First, a tracking error signal is obtained by calculating the sum and difference from the tracking signal detection light receiving regions 104, 105, 106, and 107 by the differential amplifier 83. Defocus signal detection light receiving area 108, 1
09, 1010, and 1011.
To obtain a defocus error signal.

FIG. 11 is a view for explaining the direction of the diffracted light when the light leaving the semiconductor laser 101 and traveling toward the magneto-optical disk 96 is diffracted by the polarization diffraction grating 92 in the embodiment of FIG. Since the polarization diffraction grating 92 has a lens function as described above, the diffracted light is applied to the magneto-optical disk 9.
6 is largely out of focus. Therefore, the reflected light is further defocused, and hardly affects the amount of light received by the detectors 102 and 105.

On the other hand, the three-beam Wollaston prism 21
A problem in the case of realizing the configuration of the embodiment shown in FIG. 9 by using FIG. 9 will be described with reference to FIG. Since the three-beam Wollaston prism 21 does not have a lens function, when a part of the light exiting the semiconductor laser 101 and traveling toward the magneto-optical disk 96 is separated, the light is focused on the disk similarly to the main beam at the center. tie. Therefore, since the reflected light returns along the same optical path as the outward path, it overlaps with the optical path of the polarized and separated light of the main beam as shown in FIG.
At 105, a part of the light is received. This acts as noise on the reproduced signal, causing signal quality to deteriorate.

FIG. 13 shows an embodiment in which the magneto-optical head according to the present invention is formed by using a development exposure process using a photomask, which is common in a semiconductor manufacturing process.

First, gallium nitride or the like is stacked on a substrate 134 of sapphire crystal or the like, and a surface emitting laser 131 and photodetectors 132 and 133 are formed. Further, a refraction type liquid crystal polymer polarization diffraction grating 13
11 and 1312 are formed in two stages. Then, a condensing grating 136 made of a dielectric film is formed on the back surface of the condensing grating 136 to form an objective lens. Then, the surface emitting laser substrate and the polarizing diffraction grating substrate are integrated with the transparent substrate 138 using a transparent resin adhesive. In the magneto-optical head manufactured in this manner, the light from the surface emitting semiconductor laser 131 is first transmitted through the polarizing diffraction grating and is transparent by the focusing grating objective lens 136 in the same manner as in the embodiment of FIG. The light is focused on the bottom surface of the substrate 138. The magneto-optical head itself has a magneto-optical disk 13 having a magneto-optical recording film on its surface.
9 is arranged close to a distance of about 1/4 or less of the light wavelength by a general flying slider or the like on a magnetic disk or the like at the present time. As an evanescent wave, it can contribute to reading of recorded information on the magneto-optical disk 139. Therefore, the transparent substrate 138 and the magneto-optical disk 139
A signal can be reproduced with a condensed spot in the transparent substrate 138 while an air layer is interposed between them. This method is based on analogy with a method of improving resolution called general immersion in a microscope, and is based on solid immersion (Solid Immersion).
n) in recent years.

The reflected light obtained by reading the information of the recording magnetic domain of the magneto-optical disk 139 as the polarization rotation is
The ± 1st-order diffracted light diffracted by the refraction-type polarizing diffraction grating 1313 is guided to the photodetectors 132 and 133. As described above, these diffracted lights are linearly polarized light components in directions of +45 and −45 ° with respect to the polarization direction of the emitted light of the semiconductor laser, respectively. It is possible to get a signal.

Further, by using the light receiving area pattern described with reference to FIG. 10 also in this embodiment, it is possible to obtain a defocus signal and a tracking error signal. In this embodiment, since the entire head can be made small by the alignment using a photomask and the exposure and development process, the entire magneto-optical head of this embodiment can be mounted on an actuator. Then, the tracking error signal is fed back to this actuator to perform closed loop control. On the other hand, although a defocus signal can be obtained, defocus control becomes unnecessary by controlling the height of the magneto-optical head by the flying slider. However, when the polarizing diffraction grating is formed into a linear pattern,
In addition to generating unnecessary condensed spots due to diffraction on the outward path, there is a problem that the reflected light is mixed into the photodetector. Therefore, it is desirable that the polarizing diffraction grating also has a refraction type curved pattern.

[0037]

According to the present invention, polarization separation can be performed using a polarizing diffraction grating that can be manufactured by an exposure and development process using a photomask, has excellent mass productivity, is easy to be miniaturized, and can freely design its separation ratio and separation angle. At the same time, a servo signal such as a defocus signal or a tracking error signal is detected, and a magneto-optical head using a coaxial optical system in which a semiconductor laser light source is arranged on the optical axis of the 0-order light at the center of ± 1st-order diffracted light can be provided. . This makes it easy to realize a magneto-optical head that is small in size, has a small number of components, and is easy to mass-produce.

[Brief description of the drawings]

FIG. 1 shows a conventional example of polarization separation by a polarizing prism.

FIG. 2 shows a conventional example of polarization separation by a Wollaston prism.

FIG. 3 shows a conventional example of a polarizing diffraction grating.

FIG. 4 shows an embodiment of a polarizing diffraction grating according to the present invention.

FIG. 5 shows an embodiment in which two polarizing diffraction gratings are superimposed orthogonally.

FIG. 6 is a diagram illustrating the principle of a polarizing diffraction grating.

FIG. 7 shows an embodiment of a magneto-optical head according to the present invention.

FIG. 8 is a diagram for explaining a signal detection method for a magneto-optical head according to the present invention.

FIG. 9 shows a second embodiment of the magneto-optical head according to the present invention.

FIG. 10 is a diagram for explaining a signal detection method of a second embodiment of the magneto-optical head according to the present invention.

FIG. 11 is a diagram showing that there is no influence of outward diffracted light when a curved diffraction grating according to the present invention is used.

FIG. 12 is a diagram illustrating a problem when the embodiment of FIG. 9 is realized using a three-beam Wollaston prism.

FIG. 13 shows a third embodiment of the magneto-optical head according to the present invention.

[Explanation of symbols]

11 ° polarizing prism, 12, 13 ° detecting surface, 21 °
{Wollaston prism, 22, 23, 24} Photodetector, 31} Polarizing diffraction grating, 32} λ / 4 plate, 3
3 ‥‥ reflective object, 41, 42 ‥‥ polarizing diffraction grating, 51
{Superimposed polarizing diffraction grating, 61} lithium niobate substrate, 62} proton exchange region, 63} dielectric film, 64, 65} ordinary ray, 66, 67} extraordinary ray,
68 ° refractive index anisotropic principal axis, 71 ° semiconductor laser, 7
2 ‥‥ beam splitter, 73 ‥‥ collimating lens,
74 ° rising mirror, 75 ° lens actuator, 76 ° objective lens, 77 ° magneto-optical disk, 7
8 ° polarizing diffraction grating, 79 ° cylindrical lens, 710 split photodetector, 711 quad split detection area, 712, 714 photomagnetic signal photodetector, 71
3,715 ‥‥ 2 split photodetector for tracking error signal detection, 716 ‥‥ electromagnetic coil, 81,82,83 ‥‥ differential amplifier, 91 ‥‥ semiconductor laser photodetector integrated module, 92 ‥‥ refractive polarization Diffractive grating, 93 ° rising mirror, 94 ° lens actuator, 95 ° finite objective lens, 96 ° magneto-optical disk, 97 ° electromagnetic coil, 101 ° semiconductor laser, 102, 103 °
Photodetection area for magneto-optical signal, 104, 105, 106, 1
07 ‥‥ tracking signal detection area, 108, 109,
1010, 1011 ° defocus signal detection area, 131
ガ Gallium nitride surface emitting semiconductor laser, 132, 133
{Gallium nitride photodetector, 134} Sapphire crystal substrate, 136} Condensing grating objective lens, 13
8 {transparent substrate, 139} recording film exposed type magneto-optical disk, 1310 {glass substrate, 1311, 1312}
Refractive polarizing diffraction grating made of liquid crystal polymer, 1313 °
Polarization separation element made of liquid crystal polymer.

Claims (6)

[Claims] A semiconductor laser, an optical system for condensing the light on a magneto-optical disk, an optical splitting element for splitting reflected light from the magneto-optical disk to a photodetector, and the split light orthogonal to the optical detector. A magneto-optical head composed of a polarization separation element that separates into two linearly polarized lights and a photodetector that independently detects the separated light, wherein the polarization separation element diffracts only a specific linear polarization component, A magneto-optical head comprising two polarizing diffraction gratings that transmit a linearly polarized light component perpendicular to the diffraction grating and are superposed so that the gratings are substantially orthogonal to each other. 2. A semiconductor laser, an optical system for condensing the light on a magneto-optical disk, and a polarization splitter for splitting a reflected light from the magneto-optical disk to a photodetector and splitting the reflected light into two orthogonal linearly polarized lights. An element and a magneto-optical head composed of photodetectors that independently detect the separated light, wherein the polarization splitting element diffracts only a specific linearly polarized light component,
This is achieved by arranging two polarizing diffraction gratings that transmit a linearly polarized light component orthogonal to it so as to be superimposed so that the gratings are substantially orthogonal to each other. The photodetector is integrated with the semiconductor laser in the same package. A magneto-optical head. 3. The magneto-optical head according to claim 1, wherein, of the two sets of ± 1st-order diffracted lights whose polarization directions are orthogonal to each other by said polarizing diffraction grating, light is output from any two light receiving signals having different polarizations. A magneto-optical head which detects a magnetic signal and detects one or both of a defocus signal and a tracking error signal from the other two signals. 4. The magneto-optical head according to claim 3, wherein
A magneto-optical head, wherein the grating of the polarizing diffraction grating is a curve. 5. The magneto-optical head according to claim 3, wherein
There are four photodetectors for receiving two sets of ± 1st-order diffracted lights having different polarizations, two adjacent photodetectors without a dividing line, and the other two adjacent photodetectors with a dividing line. A magneto-optical head, characterized in that: 6. A magneto-optical head according to claim 2, wherein the transmittance of the one-way zero-order light of the polarizing diffraction grating is 50%.
A magneto-optical head characterized by being at least 70%.