JPS63149850A - Magneto-optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To perform the magneto-optical recording and reproducing by arranging the transparent substrate placing a pair of grid couplers whose grids are crossed at a specific angle between the lenses located between a laser light source and magneto-optical disk, a pair of nonreciprocal discoid double refraction plates, a diffracted light waveguide and an optical detector. CONSTITUTION:The light of a laser 22 is passed through a lens 23, receiving the rotary polarization via a pair of transparent substrates 29, 33, waveguides 30, 34, diffraction grid couplers 24, 26 and nonreciprocal discoid double refraction plates 25, 27 and projected on a magneto-optical disk 21. In this case, the magnetizing direction of the magnetic body of the disk is selected by an electromagnet 20 in the case of a writing and erasing. At the time of reproducing the reflection light of the disk varies at + or - theta for the magnetizing direction. The polarized plane is rotated by a refraction plate 27 and the diffracted light is combined with a waveguide path 34 by the grid coupler 26. The transmitting light of the coupler 26 is also combined with the waveguide path 30 by the coupler 24 and taken off by lenses 35, 32. Then reproducing is performed by using the output of detectors 36, 32 by keeping S=e-(a+b+c+ d)=0, by focusing with F=(a+d)-(b+c)=0 and the tracking is performed by T=(a+b)-(c+d)=0.

Description

[Detailed description of the invention] Technical field The present invention relates to a magneto-optical information recording and reproducing device.

Prior Art Conventionally, a pickup for this type of magneto-optical memory has been constructed as shown in FIG. First, a laser beam emitted from a semiconductor laser 1 is made into parallel light by a collimator lens 2, passes through a half mirror 3, and then is condensed onto a magneto-optical disk 5 by a condenser lens 4. Here,
During recording, an electromagnet 6 facing the magneto-optical disk 5
Magnetic recording is performed on the light irradiated portion. When reading, the reflected light from the magneto-optical disk 5 enters the half mirror 3 as light with a rotated polarization plane, is reflected by the reflective surface 3a, and is then polarized by the λ/2 plate 7. The angle is adjusted and the beam is converted by a convex lens 8 and a concave lens 9.

Thereafter, the light enters the polarizing beam splitter 10 and is split into two lights with different polarization directions. First, on the one hand, the signal enters the photodetector 11 and is converted into a tracking error signal ΔT by the push-pull method using the operational amplifier 12. On the other hand, it is configured so that it enters the photodetector 14 via the cylindrical lens 13 and obtains a focus error signal ΔF using the astigmatism method. Further, a recording signal is obtained by detecting polarization rotation information from a differential signal ΔS from these photodetectors 11.14 via a differential amplifier 15.16.

However, in such a conventional optical pickup structure of a magneto-optical memory, the entire optical pickup is composed only of bulk type optical elements. Therefore, it is large, heavy, and complicated.

As a result, high-speed access is not possible. Furthermore, there are many adjustment points during assembly, and changes over time are likely to occur.

Furthermore, since a half mirror is used in the optical system, the light utilization efficiency is also reduced.

Purpose The present invention has been made in view of the above points, and it is possible to reduce the size and weight of an optical pickup, achieve system miniaturization and high-speed access, and further improve assembly by integrating elements. The object of the present invention is to provide a magneto-optical information recording/reproducing device which can facilitate adjustment, improve mechanical stability, and also has good light utilization efficiency.

Structure In order to achieve the above object, the present invention includes a magneto-optical disk for recording magneto-optical information, a laser light source, and a lens optical system that focuses laser light from the laser light source onto the magneto-optical disk. A grating that is disposed between the laser light source and the lens optical system and transmits the laser light from the laser light source toward the magneto-optical disk and diffracts the reflected light from the magneto-optical disk has a predetermined intersection angle. a pair of grating couplers set to , a pair of non-reciprocal homocentric refracting plates that rotate the plane of polarization of incident light to these grating couplers, a waveguide layer that guides the diffracted light by the grating couplers, and a waveguide layer that guides the diffracted light by the grating couplers; A photodetector for detecting optical information guided by a waveguide layer; a substrate having at least a portion of the transparent portion for integrally forming the grating coupler, the waveguide layer, and the photodetector; , differentially processing the detection signals from these photodetectors to obtain a magneto-optical signal of the magneto-optical disk;
The present invention is characterized in that it includes a differential calculation means for reading a focus error signal and a tracking error signal, and an actuator for focusing control and tracking control.

Hereinafter, a first embodiment of the present invention will be described based on FIGS. 1 to 12. First, an optical pickup according to the present embodiment, which does not include a half mirror or a polarizing beam splitter, is provided between a magneto-optical disk 21 equipped with an electromagnet 20 and a semiconductor laser 22 as a laser light source that emits laser light. .

This light pickup includes a collimating lens 23 and a first grating coupler 24 in order from the semiconductor laser 22 side.
, a first non-reciprocal circular birefringent plate 25, a second grating coupler 26, a second non-reciprocal circular birefringent plate 27, and a condenser lens 28.

Although the collimating lens 23 and the condensing lens 228 are shown here as ordinary convex lenses, a single lens or a combination of an aspherical lens, a grating lens, a Fresnel lens, a distributed refractive index lens, etc. may be used as appropriate.

The first grating coupler 24 is provided on a waveguide layer 30 formed on a transparent substrate 29 made of glass, a dielectric material, or the like. Here, a waveguide lens 31 and a photodetector 32 are provided on the waveguide M30 along with the first grating coupler 24. This is the same on the second grating coupler 26 side that is paired with the first grating coupler 24, and the waveguide lens beam splitter 35 and the waveguide Ji34 are formed on a transparent substrate 33 made of glass or the like. It is provided together with the photodetector 36.

Here, a pair of first and second grating couplers 24.2
Reference numeral 6 is a relief type blazed grating arranged in straight lines at regular intervals, and when viewed from above, two grating couplers 24.2 are shown in a developed view in FIG.
6 are arranged so as to intersect with each other at a certain intersection angle, for example, α=45°. In addition to surface relief type gratings 24 and 26, volume phase type gratings may also be used, but gratings with high diffraction efficiency are preferable. Further, as a manufacturing method, a method using a resist and etching using an electron beam or interference exposure, a mold method, or the like may be used as appropriate.

On the other hand, the waveguide layers 30 and 34 are both transparent substrates 29 and 33.
It is made of a transparent material with a refractive index higher than that of . for example,
High refractive index glass, Nb, 03, Ta205, Si, N
, etc., by vacuum evaporation method, sputtering method, CV
It is formed by laminating using the D method, the ECR method, or the like. In addition, methods for increasing the refractive index by using organic substances such as polymers, ion exchange, impurity diffusion, etc. may be used. The waveguide lens 31 and the waveguide lens beam splitter 35 are made of a material with a higher refractive index than the waveguides M30 and M34, such as T i O, for example.

The photodetector 32 is formed by forming a photodiode such as α-3L on the waveguide layer 30 by vacuum evaporation, sputtering, CVD, ECR, or the like.

The photodetector 36 side is also made of photodiodes, etc., and consists of four detectors 36a to 36d.

Furthermore, the pair of first and second non-reciprocal circularly birefringent plates 25.2
Reference numeral 7 uses, for example, a Faraday rotator, and is configured to produce a Faraday effect by applying a magnetic field using donut-shaped magnets 37 and 38. The Faraday rotator may be made of dielectric, magnetic, glass, or other materials. In particular, in the case of magnetic materials, YIG (Y, Fe, 011), GdB i IG (G
d, -xB 1xFe501°) A material with a large figure of merit, such as a crystal, is preferred. In this case, the polarization plane rotation angle is
It can be adjusted by the thickness of the magnetic material in the optical axis direction and the strength of the applied magnetic field. In addition, any material that exhibits non-reciprocal circular phase refraction may be used.

The detection outputs from the detectors 36a to 36d are manually input in pairs to differential amplifiers 39a to 39d, respectively. The configuration is such that the outputs from the differential amplifiers 39a and 39b are manually input to the differential amplifier 40a to obtain a tracking error signal ΔT. Also, the outputs from the differential amplifiers 39c and 39d are output from the differential amplifier 40b.
The focusing error signal ΔF is obtained by inputting the focusing error signal ΔF. Furthermore, a differential amplifier 39a.

The differential amplifier 4 receives the output signal from the differential amplifier 40c, which receives the signal from the differential amplifier 39b, and the detection signal from the photodetector 32, and outputs a differential output ΔS as a magneto-optical signal.
1 is provided. These differential amplifiers 39a to 3
9d, 40a to 4oc, and 41 constitute differential calculation means.

In such a configuration, the operation of the optical pickup according to this embodiment will be explained in detail with reference to FIGS. 1, 2, and 3. Here, FIG. 3 shows the polarization direction when laser light passes through each element shown in FIG. 1. First, the laser beam emitted from the semiconductor laser 22 passes through the collimating lens 23 , passes through the transparent substrate 29 , the waveguide layer 30 and the first grating coupler 24 , and enters the first non-reciprocal circularly birefringent plate 25 . incident. FIG. 3(a) shows the polarization direction of the light emitted from the semiconductor laser 22,
FIG. 2B shows the angle of polarized light incident on the first grating coupler 24. At this time, it is necessary to set the polarization direction of the light emitted from the semiconductor laser 22 perpendicular to the grating direction of the first grating coupler 24, as shown in FIG. 2(b). Then, the polarization direction is rotated about the optical axis by the first non-reciprocal circular birefringent plate 25, as shown in FIG. 2(c). This polarization rotation angle is determined by the first and second grating couplers 24. 26 is equal to α=45° in the case of FIG. 2, and the rotation direction of the polarized light is also perpendicular to the grating direction of the second grating coupler 26 in FIG. It is necessary to set it to . According to such a configuration of condition settings, when the emitted light from the semiconductor laser 22 passes through the 1°2 grating coupler 24.26, the amount of light coupled to the waveguide layer 30.34 is minimized, and the detection system can reduce noise. The light exiting the first non-reciprocal circularly birefringent plate 25 is transmitted to the transparent substrate 33.
, after passing through the waveguide [34 and the second grating coupler 26, the plane of polarization is further rotated by the second non-reciprocal circularly birefringent plate 27, as shown in FIG. 3(e). Here,
This rotation angle can be arbitrarily selected within a certain range as described later, but here, for example, 22.5 degrees.
is set to . Thereafter, the light is irradiated onto the magneto-optical disk 21 by the condenser lens 28 with the polarization direction shown in FIG. At this time, during writing or erasing, the magnetization direction of the magnetic material on the magneto-optical disk 21 is selected by the electromagnet 20.

On the other hand, under such light irradiation conditions, during reading, first, as shown in FIG. changes by a small angle ±Δθ corresponding to the magnetization direction of the disk.

After such reflected light is collimated again by the condensing lens 28, the plane of polarization is further rotated by 22.5° by the second non-reciprocal circular birefringent plate 27, as shown in FIG. . Then, the second grating coupler 26 is attached to the same figure (
i) is incident in the polarization direction as shown by the solid arrow.

Here, we will consider the polarization characteristics of the high diffraction efficiency grating, which is a grating coupler. For example, in a relief type grating, as shown in FIG. 4, the angle between the linearly polarized light incident on the grating 42 and the grating direction is θ. At this time, diffraction efficiency [%] and transmittance [%]
The θ dependence of ) exhibits characteristics as shown in FIG. That is,
When the polarization plane of the incident light coincides with the grating direction, the diffraction efficiency becomes maximum and the transmittance becomes minimum. Conversely, when the plane of polarization of the incident light is perpendicular to the grating direction, the diffraction efficiency is at its lowest and the transmittance is at its highest. Now, if the diffraction efficiency is 11 and the transmittance is 12, these are approximately I, = C, co s"0 + C2 I, "C, sin" θ0 C4 (however, 01 to C4 are constants) change in relationship.

Since the second grating coupler 26 also has such characteristics, when linearly polarized light in the ↓ polarization direction shown in FIG. 3(i) enters the second grating coupler 26, Assuming that the length of the solid arrow indicates the intensity of the incident light, the light with the intensity of the dashed arrow corresponding to the component in the lattice direction is corrected in the T direction perpendicular to the lattice. At this time, when the incident polarization plane rotates counterclockwise, the intensity of the diffracted light increases, and when the plane of incident polarization rotates clockwise, the intensity of the diffracted light decreases.

In any case, the diffracted light by the second grating coupler 26 is coupled into the waveguide layer 34. Further, the intensity of the light transmitted through the second grating coupler 26 has a characteristic opposite to the intensity of the diffracted light with respect to rotation of the plane of polarization. And the second
The light that has passed through the grating coupler 26 again is shown in Figure 3 (
As shown in j), the optical surface is further rotated by 45° by the first non-reciprocal circularly birefringent plate 25. As a result, the same figure (
The light enters the first grating coupler 24 in the polarization direction shown in k). Here, the diffracted light intensity is shown in Figure 3 (k).
This corresponds to the size of the broken line vector in the middle, and is diffracted in the J direction perpendicular to the grating and coupled into the waveguide layer 30. In FIG. 3(k), when the incident polarization plane is rotated counterclockwise, the intensity of the diffracted light becomes weaker, and when it is rotated clockwise, the intensity becomes stronger.

As a result, when comparing the diffracted light intensities of the second and first grating couplers 26°24, it is found that when the polarization direction of the reflected light from the magneto-optical disk 21 is rotated by ±Δθ, one of the diffracted lights becomes stronger depending on the direction of rotation. The other diffracted light becomes weaker. Therefore, the rotation direction of polarized light can be detected by taking the difference between both diffracted lights.

Therefore, first, the light diffracted by the second grating coupler 26 is guided through the waveguide layer 34 and split into two by the waveguide lens beam splitter 35.
a, 36b and an intermediate position of the detectors 36c, 36d. Further, the light diffracted by the first grating coupler 24 is guided through the waveguide layer 30 and focused onto the photodetector 32 by the waveguide lens 31. here,
Now, let the outputs of the detectors 36a to 36d be a-d, and the output of the photodetector 32 be e. Then, the differential output Δ5 of the diffracted light of the second and first grating couplers 26.24=e−
(a + c + d), and by adjusting the electric circuit constants, etc., so that ΔS = O at this time, so that the polarization direction when the polarization plane of the reflected light from the magneto-optical disk 21 does not rotate is the reference. Set it. According to this, from FIG. 3, if the plane of polarization of the reflected light from the magneto-optical disk 21 rotates clockwise from the reference direction, ΔS>o, and if it rotates counterclockwise, ΔS×o. As a result, the magneto-optical disk 21
Since the sign of ΔS changes in response to the above signal, the written information can be reproduced.

Next, the detection operation of a focus error signal (focus error signal) will be explained. When the magneto-optical disk 21 is at the reference position, the reflected light from the magneto-optical disk 21 becomes a substantially parallel beam of light when passing through the second grating coupler 26.

At this time, as shown in FIG.
a, '36b and the center between the detectors 36c and 36d, and their outputs have a relationship of a=b, c+=d. Therefore, the focus error signal ΔF is ΔF=(a
+d)-(b+c), ΔF=O. but,
When the magneto-optical disk 21 approaches the focal point, the reflected light becomes a slightly diverging beam as shown in FIG. 6(a). Therefore, the outputs become a) b, c) d, and the focus error signal ΔF becomes ΔF)O.

On the other hand, when the magneto-optical disk 21 moves further away from the focal point, the reflected light becomes a slightly convergent beam as shown in FIG. 6(b). Therefore, the output becomes a<b, c<d, and the focus error signal ΔF becomes ΔF(O. Therefore, the focus error direction can be determined by the positive or negative of the focus error signal ΔF, so this focus error signal ΔF becomes O. Autofocusing control becomes possible by moving the condensing lens 28 in the optical axis direction using an actuator (not shown).In this case, not only the condensing lens 28 but also
The entire waveguide including other waveguide elements may be moved and displaced. Alternatively, the entire structure including the semiconductor laser 22 and collimating lens 23 may be moved and displaced.

Next, a method of detecting the tracking error signal ΔT will be explained. First, it is assumed that the tracks on the magneto-optical disk 21 are provided in a direction perpendicular to the grating direction of the second grating coupler 26 shown in FIG.

Then, the tracking error signal ΔT is ΔT=(a+
b) - (c+d), when the focal position is on the track, the intensities of both light beams separated by the waveguide lens beam splitter 35 are equal, ΔT, -0.

However, if the focal position deviates from the track, the intensities of both light beams will no longer be equal due to diffraction, and ΔT>O or ΔT<O. Therefore, the direction of tracking deviation is known, and ΔT=
By displacing and moving the condensing lens 28 in a direction perpendicular to the track using an actuator (not shown) so that the angle becomes O, auto-tracking becomes possible. In this case, as in the focusing control, not only the condensing lens 28 but also the waveguide element portion or the semiconductor laser 22 and the collimating lens 23 may be displaced and moved.

By the way, the intersection angle of the first and second grating couplers 24°26 in the grating direction will be discussed. In the above explanation, this intersection angle was explained in the case of 45', but in general terms, if this intersection angle is α, this intersection angle α can be arbitrarily selected and set within the range of O' and α<90''. For example, FIG. 7 shows the polarization operation when the intersection angle α is set to 22.5'.As shown in FIG. 7(b), the polarization plane of the linearly polarized light from the semiconductor laser 22 is The angle of rotation of the first non-reciprocal circularly birefringent plate 25 is set to be incident in a direction perpendicular to the lattice direction of the coupler 24.As shown in FIG. 5
is set equal to °. As a result, the polarization plane of the light incident on the second grating coupler 26 becomes perpendicular to the grating direction, as shown in FIG. 2D. and,
When the rotation angle of the second non-reciprocal circularly birefringent plate 27 is set to 33.75° as shown in FIG.
j) As shown in (k), it can be seen that the sign of the differential output ΔS changes depending on the rotation direction of the polarization plane of the reflected light from the magneto-optical disk 21. This makes it possible to detect signal playback.

Think more generally. First, the intersection angle α is O such that α≦π/
Case 4 will be explained with reference to FIGS. 8 and 9. In this case, the polarization direction of the reflected light from the magneto-optical disk 21 becomes as shown in FIG. 8(f) based on the polarization direction of the incident light on the first grating coupler 24 shown in FIG. 8(a). It is assumed that the beam is rotated by an angle β and then enters the second grating coupler 26. At this time, the rotation angle of the second non-reciprocal circularly birefringent plate 27 is (β-α)/2. or,
The rotation angle of the first non-reciprocal circularly birefringent plate 25 is the same as the intersection angle α. Under such conditions, the magneto-optical disk 21
In order to obtain the signal recorded in the differential output ΔS, the angle β is limited. FIG. 9 shows the possible range of this angle β with diagonal lines. That is, under the condition that the intersection angle α is O<α≦π/4, the angle β is O≦β<α, (π/2)−α×β(π/2)10α, π−α ku β ku π
It can be arbitrarily set to 10α, (3π/2)−α×β×(3π/2)10, or 2π−α×β≦2π. Of these, the diffraction efficiency to the second grating coupler 26 is particularly high (π/2) -
α×β×(π/2)+α or (3π/2)−α×β×(
It is preferable to set the angle β around 3π/2)+α.

Among these, especially when β-factor is set to π/2 or β-3π/2, the maximum detected rotation angle ±Δθmax becomes the largest under the condition that the intersection angle α=constant.

Next, the case where the crossing angle α is π/4≦α×π/2 is the 10th
This will be explained with reference to the figures and FIG. In this case as well, the polarization direction of the reflected light from the magneto-optical disk 21 is
), the polarization direction of the light incident on the first grating coupler 24 is used as a reference, and the light is rotated by an angle β as shown in FIG. Other than this, the illustrated symbols and the like are the same as those in FIG. 8. FIG. 11 shows the possible range of the angle β with diagonal lines. That is, under the condition that the intersection angle α is π/4≦α and π/2, the angle β
is O≦β×(π/2)−〇, α×β×π−α, (π/2)+α×β×(3π/2)−〇, π+α×β×2π−α, (3π/2 )+α and β≦2π. Among these, the diffraction efficiency to the second grating coupler 26 is particularly high.
It is best to set the angle β in the range α or π + α × β × 2π − α. Among these, especially β=π/2 or β-3
If π/2 is used, the maximum detected rotation angle ±ΔθmaX will be the largest under the condition that the crossing angle α=constant.

Based on these study results, the maximum detected rotation angle ±Δθm for the intersection angle α, which can range from 0 to π/2, is determined.
FIG. 12 shows ax.

According to this characteristic diagram, the maximum detected rotation angle ±Δe max is maximum when the intersection angle α=45° (=π/4). Next, the first and second non-reciprocal circularly birefringent plates 25.2
7 usually causes some absorption loss, so it is advantageous to make the thickness as thin as possible in terms of effective use of light. For this purpose, the total rotation angle of the polarization plane should be as small as possible before the light from the semiconductor laser 22 is reflected by the magneto-optical disk 21, diffracted by the grating couplers 26 and 24, and coupled into the waveguide layer 34, 30. It can be said to be good. Here, the total rotation angle is α+(β-ization)/2+(β-ization)/
2+α=α+β. From this, the intersection angle α is the 12th
Setting the maximum detection rotation angle Δθmax in the figure to a small value within the allowable range and setting the angle β=π/2 is the most suitable combination for reducing the loss. Furthermore, regarding the diffraction efficiency of the grating couplers 24 and 26, the maximum diffraction efficiency of each is expressed as η1. Let η2 be the reflected light from the magneto-optical disk 21. Then, the maximum diffracted light intensity of each grating coupler 24.26 is η11°, (1-η1
)η2■. bawl. Therefore, in order to make both intensities as close as possible and to increase the light utilization efficiency, it is preferable to set the efficiency η to #50% and to make the efficiency η2 as high as possible.

Next, a second embodiment of the present invention will be described with reference to FIG. 13. Portions that are the same as or correspond to those shown in the above embodiments are indicated using the same reference numerals (the same applies to the following embodiments). In this embodiment, the collimating lens 23 is omitted and the lens system is made up of only the condensing lens 28. According to this embodiment, since only one lens is required, the device can be made smaller and lighter, and the configuration can be simplified. However, compared to the previous embodiment, the condenser lens 28 requires greater power.

Further, a third embodiment of the present invention will be explained with reference to FIG.

In this embodiment, the first and second grating couplers 24, 26
(Waveguide layer 30.34) is formed on an opaque substrate 42.43. Here, these opaque substrates 42
．． Openings 42a and 43a are formed in the opening 43 as a light-transmitting section for transmitting the laser light from the semiconductor laser 22 to the magneto-optical disk 21 side. More specifically, these opaque substrates 42 and 43 are made of a semiconductor substrate such as Si, and the openings 42a and 43a are formed by dry or wet etching, polishing, ion sealing, or the like. Further, transparent buffer layers 44 and 45 are formed on these opaque substrates 42 and 43, respectively.

The refractive index of these buffer layers 44, 45 must be lower than the refractive index of the waveguide layer 30, 34 formed thereon.

The buffer layers 44, 45 and the waveguide layers 30, 34 are formed by laminating transparent materials using a vacuum evaporation method, a sputtering method, a CVD method, an ECR method, or the like. Alternatively, it may be formed using an organic material such as a polymer, ion exchange, impurity diffusion, or the like. Furthermore, when an opaque substrate 42.43 is used as in this embodiment, a photodetector 32.36 can also be formed in this substrate 42.43. 46.47
are electrodes for these photodetectors 32 and 36, and are formed by vacuum evaporation, sputtering, or the like.

Next, a fourth embodiment of the present invention will be described with reference to FIG. 15. In this example, regarding two transparent substrates 29°33,
These are omitted, and one first non-reciprocal circularly birefringent plate 25 is used for both purposes. Further, in this embodiment, a collimating lens 48 and a condensing lens 49 made of a blazed Fresnel lens are used in place of the collimating lens 23 and condensing lens 28 which are ordinary convex lenses. Even in this example, the waveguide [30°34
The first non-reciprocal birefringent plate 25 on which the grating couplers 24 and 26 are formed is made of a dielectric or magnetic material having a Faraday effect, and requires a core magnet 37.

According to this embodiment, each member and element except the semiconductor laser 22 can be integrated around the first non-reciprocal circularly birefringent plate 25, making the structure simpler.

Further, the weight can be further reduced, the access time can be shortened, and the reliability can be improved.

In the case of this embodiment, as shown in FIG. 16, the transparent substrate 33 and the first non-reciprocal circular birefringence plate 25 may be integrated as a substrate. More specifically, the first non-reciprocal circularly birefringent plate 25 can be laminated on the transparent substrate 33 by a crystal growth method such as a liquid phase or vapor phase, a CVD method, a sputtering method, a vacuum evaporation method, a coating method, or the like. can. According to this, the configuration is almost the same as that shown in Fig. 15, but a transparent substrate such as a normal dielectric crystal or a semiconductor can be used as the substrate base, and there are no conditions or freedom in selecting the materials used. You can expand your horizons. Here, the waveguide layer 30.34
It is necessary that the refractive index of the transparent substrate 33 and the first non-reciprocal circular birefringence plate 25 be higher than that of the transparent substrate 33 and the first non-reciprocal circularly birefringent plate 25. Waveguide layer 30
．． If 34 alone does not satisfy this condition, 14th
Waveguide layer 30.34 and plate 25.33 as in the case of the figure etc.
A buffer layer having a lower refractive index than the waveguide layers 30 and 34 may be provided between the waveguide layers 30 and 34.

Further, a fifth embodiment of the present invention will be explained with reference to FIG. 17.

In this embodiment, a waveguide Fresnel lens beam splitter 50 is used in place of the waveguide lens beam splitter 35, and a waveguide Fresnel lens 5 is used in place of the waveguide l-nons 31.
1 is used. These beam splitter 50 and lens 51 can be fabricated by techniques such as patterning of a high refractive index material, diffusion, ion exchange, etc. to increase the refractive index.

Furthermore, a sixth embodiment of the present invention will be explained with reference to FIG. In this embodiment, the first and second grating couplers 24.2
By using a curvature lattice shape instead of a straight lattice shape as the lattice shape of No. 6, a light condensing effect is also provided. According to this, the waveguide lens 31 can be made unnecessary on the first grating coupler 24 side. Further, on the second grating coupler 26 side, a waveguide beam splitter 52 may be sufficient instead of the waveguide lens beam splitter 35. However, if the grating curvature of these grating couplers 24 and 26 is made too large, it will have a negative effect on the optimum angle and efficiency as a pickup, so it is preferable to set the curvature as small as possible.

In any of the embodiments or modifications, the first grating coupler 24 (including the substrate, waveguide layer, etc.)
The vertical positional relationship between the second grating coupler 26 and the second grating coupler 26 (including the substrate, waveguide layer, etc.) may be reversed.

Effects As described above, in the present invention, the optical pickup uses a pair of grating couplers and a pair of non-reciprocal circular phase refracting plates, and the photodetector can be mounted on the same substrate with the waveguide layer etc., making it lightweight.・Can be made more compact,
Access time can be shortened, and since the same substrate can be used, it is also possible to form one piece using photolithography, etc., simplifying assembly and adjustment work, and furthermore, it is possible to reduce the amount of laser light from the laser light source. Not only can the light be efficiently focused on the magneto-optical disk, but also the reflected light from the magneto-optical disk can be efficiently diffracted and guided to the photodetector, resulting in highly efficient use of light and improved optical detection. This also reduces the amount of noise light that enters the device, allowing for better reading with a good S/N ratio.

[Brief explanation of the drawing]

FIG. 1 is a side view conceptually showing a first embodiment of the present invention;
Figure 2 is a plan view showing a part of it in an exploded view, Figure 3 is an explanatory diagram showing the polarization operation, Figure 4 is an explanatory diagram of the grating, and Figure 5 is the dependence of transmittance and diffraction efficiency on angle O. Fig. 6 is a plan view showing the state when a focusing error signal is generated, Fig. 7 is an explanatory diagram showing the polarization operation when the crossing angle is varied, and Fig. 8 is a diagram showing the polarization operation when the crossing angle is changed within a predetermined range. An explanatory diagram showing the polarization operation in a general case where the polarization operation is different, FIG. 9 is a coordinate diagram showing the possible range of the angle β at that time, and FIG.
The figure is an explanatory diagram showing the polarization operation in a general case where the crossing angle is varied within a predetermined range. Figure 11 is a coordinate diagram showing the possible range of the angle β at that time. Figure 12 is the crossing angle α - maximum detected rotation. 13 is a side view conceptually showing the second embodiment of the present invention, FIG. 14 is a side view conceptually showing the third embodiment of the present invention, 15th The figure is a side view conceptually showing the fourth embodiment of the present invention, FIG. 16 is a side view conceptually showing a modification thereof, Country 17 is a plan view showing the fifth embodiment of the present invention, FIG. 18 is a plan view showing a sixth embodiment of the present invention, and FIG. 19 is a side view showing a conventional example. 21... magneto-optical disk, 22... semiconductor laser (laser light source), 24... grating coupler, 25...
... Non-reciprocal circular phase refracting plate, 26... Grating coupler, 27... Non-reciprocal circular phase refracting plate, 28... Condensing lens (lens optical system), 29... Transparent substrate (substrate) ,
30... Waveguide layer, 32... Photodetector, 33...
Transparent substrate (substrate), 34... Waveguide layer, 36... Photodetector, 39a to 39d, 40a to 40c, 41-Differential amplifier (differential calculation means), 42.43... Opaque substrate (substrate), 42a, 43a...opening (transparent part), 4
9...Condensing lens (lens optical system) applicant
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'+7 71 ■ Figure υ Procedural Amendments Imported February 2, 1986

Claims (1)

[Claims] A magneto-optical disk for recording magneto-optical information, a laser light source, a lens optical system for focusing laser light from the laser light source onto the magneto-optical disk, and between the laser light source and the lens optical system. a pair of grating couplers arranged to transmit laser light from the laser light source toward the magneto-optical disk and diffract reflected light from the magneto-optical disk, the grating directions of which are set at a predetermined crossing angle; a pair of non-reciprocal circularly birefringent plates that rotate the plane of polarization of light incident on the grating coupler; a waveguide layer that guides the diffracted light by the grating coupler; and a waveguide layer that guides the light diffracted by the grating coupler. A photodetector that detects optical information, a substrate having at least a part of the light-transmitting part for integrally forming the grating coupler, the waveguide layer, and the photodetector; It is characterized by comprising differential calculation means for differentially processing detection signals to read magneto-optical signals, focus error signals and tracking error signals of the magneto-optical disk, and actuators for focusing control and tracking control. A magneto-optical information recording and reproducing device.