JP2001344845A - Magneto-optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magneto-optical pickup device which suppress the influence of a wave front aberration even when an inexpensive material is used for a beam splitter. SOLUTION: The magneto-optical pickup device is provided with a light source, a condensing means to condense light rays on a magneto-optical recording medium, the beam splitter in which the joint surface of a first member and a second member acts as a polarized light separating plane, a photodetector, and a first diffraction element which guides light separated into the ordinary light and the extraordinary light by the beam splitter to the photodetector. The first diffraction element has a hologram pattern to compensate the wave front aberration generated by refraction on the joint surface of the first member and the second member.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magneto-optical pickup device for reproducing a magneto-optical disk.

[0002]

2. Description of the Related Art Magneto-optical disks are widely used as media for recording audio, video, document data, and the like, and various reproducing apparatuses for reproducing magneto-optical disks have been developed. The magneto-optical pickup device is a main component of a tip portion for extracting a signal from the magneto-optical disk in the magneto-optical disk reproducing device. Since this directly affects the size and weight of the entire magneto-optical disk reproducing device,
Higher performance has been strongly desired.

The present inventors have been conducting research and development of a magneto-optical pickup device aiming at miniaturization and high integration, and have already disclosed miniaturization and high integration in Japanese Patent Application No. 11-183204. We have proposed an optical pickup device. The configuration of this magneto-optical pickup device will be described with reference to FIGS. This magneto-optical pickup device includes a stem 301, a semiconductor laser 302 as a light source provided on the stem 301,
And a light transmissive substrate 304 mounted on the cap 303. The magneto-optical pickup device includes a half-wave plate 305 mounted on a light-transmitting substrate 304, and a half-wave plate 305.
A collimating lens 307 and an objective lens 308 for condensing a light beam emitted from the semiconductor laser 302 on a magneto-optical recording medium 309. Further, the magneto-optical pickup device includes a photodetector 310 disposed on the stem 301 and detecting reflected light from the magneto-optical recording medium 309 branched by the beam splitter 306. A first diffraction element 311 and a second diffraction element 312 are arranged on the light transmitting substrate 304.

[0004] The light beam emitted from the semiconductor laser 302 passes through the second diffraction element 312 to be transmitted light and ±
The light is separated into three light beams of the first-order diffracted light. After this, 1
The beam passes through the half-wave plate 305, is reflected by the first surface 313 and the second surface 314 of the beam splitter 306, passes through the collimator lens 307 and the objective lens 308,
The light is focused on the magneto-optical recording medium 309. The light beam reflected from the magneto-optical recording medium 309 is applied to the beam splitter 3
06 at the second surface 314, the refractive index of the first member and the second
The member is separated into ordinary light and extraordinary light at a refraction angle determined by the ratio of the ordinary light refractive index to the extraordinary light refractive index. Then, the first, located below the beam splitter 306,
, Where the light is further separated into transmitted light and diffracted light and condensed on the photodetector 310.

The beam splitter 306 is composed of a first member 315 made of an isotropic glass material and a second member 316 made of a birefringent material, and a boundary surface between the first member 315 and the second member 316. Is a polarization separation surface. The reflected light from the magneto-optical recording medium 309 is
The constituent materials of the beam splitter are selected as follows so that the wavefront aberration generated when the light is refracted at 4 is compensated. That is, the material setting is performed so that the average value of the ordinary light refractive index and the extraordinary light refractive index of the birefringent material constituting the second member 316 and the refractive index of the glass material of the first member 315 become substantially the same value. I do. For example, LF5 (n = 1.572), a product of SCHOTT, is used as the glass material of the first member 315.
With 2), 4 borated lithium as the birefringent material of the second member _{316 (n o = 1.605, n} e = 1.549)
Is used.

[0006] The first diffraction element 311 is divided into first to third regions. Further, the photodetector 310 is provided in FIG.
It has a structure as shown in FIG. First diffraction element 311
Are transmitted to the photodetectors 310e to 310h, respectively. The light diffracted in the first region of the first diffraction element 311 is on the boundary surface between the light detection unit 310c and the light detection unit 310d, and the light diffracted in the second region is in the light detection unit 310a. Is collected. Further, the light diffracted in the third region is collected on the light detection unit 310b.

The following information can be obtained from the intensity of the light detected by each of these light detection units. First, (a) a focus error signal based on the knife edge method can be obtained by calculating a difference between signals output from the light detection units 310c and 310d. Also, (b) the light detection unit 310
By calculating the difference between the signals output from g and 310h, a radial error signal based on the three-beam method can be obtained. Further, (c) the light detection units 310a and 310b
By calculating the difference between the signals output from, a so-called push-pull signal can be obtained. This push-pull signal is used to detect an address signal recorded meandering on the magneto-optical recording medium. The magneto-optical signal is obtained by calculating the difference between the signals output from the light detection units 310e and 310f.

According to the above-described magneto-optical pickup device, the light beam emitted from the semiconductor laser 302 is split into an extra light beam in the optical path to the magneto-optical recording medium 309, in addition to the polarizing prism and the second diffraction element 312. Does not pass through the element. Therefore, high light use efficiency can be ensured. In addition, since the magneto-optical signal, the focus, and the radial error signal are all detected by one common photodetector 310, the area of the photodetector can be reduced. Therefore, it is possible to further reduce the size and cost of the magneto-optical pickup device.

[0009]

However, in the above-mentioned magneto-optical pickup device, lithium tetraboride used as the birefringent material of the second member is expensive, and this lithium tetraboride is deliquescent. Therefore, it is necessary to use it after being protected by a moisture-proof film or the like. For this reason, the cost of the entire magneto-optical pickup device becomes high. Also, for example, in the second member,
If lithium niobate, which is an inexpensive and stable birefringent material, is used, an inexpensive pickup can be constructed. However, ordinary refractive index and an extraordinary refractive index of lithium niobate, respectively _{n o = 2.258, n e =} 2.17
8 is big. Since the refractive index of the glass material is at most about 2, the average value of the ordinary light refractive index and the extraordinary light refractive index of lithium niobate and the refractive index of the glass as the first member are different from those of the related art. The wavefront aberration cannot be compensated for by selecting them to be substantially equal. That is, neither the ordinary ray nor the extraordinary ray in the birefringent material can compensate for the wavefront aberration. Therefore, for example, lithium niobate and SF2 manufactured by SCHOTT, which is an inexpensive glass material, are used.
(N = 1.635), the following problem occurs. When the reflected light from the magneto-optical recording medium is refracted on the second surface, the refraction angle determined by the refractive index of glass and the ratio of the ordinary light refractive index and the extraordinary light refractive index of lithium niobate increases, and Wavefront aberration occurs in the reflected light. When the wavefront aberration occurs on the second surface 314, both the light transmitted through the first diffraction element 311 and the diffracted light similarly include the wavefront aberration. For this reason, as shown in FIG. 11, the positions of the focal points in the Y direction and the Z direction are shifted, and the condensed spot of the light beam on the photodetector is deformed as shown in FIG. This makes it difficult to design the beam arrangement, or when the focused spot protrudes from the photodetector due to assembly errors when assembling the magneto-optical pickup unit or expansion and contraction of unit components due to environmental changes. was there. As a result, a false signal is output from the photodetector, and the signal cannot be reproduced stably.

Accordingly, an object of the present invention is to provide a magneto-optical pickup device capable of stably detecting a signal even when an inexpensive material is selected for a beam splitter.

[0011]

A magneto-optical pickup device according to the present invention comprises a light source for generating a light beam, and a light condensing means for condensing the light beam emitted from the light source on a magneto-optical recording medium. I have. The magneto-optical pickup device is disposed between the light source and the light condensing means, and includes a first member made of an isotropic material and a second member made of an anisotropic material. The joining surface between the member and the second member has a beam splitter forming a polarization splitting surface. The magneto-optical pickup device is disposed between a photodetector for receiving the light reflected and guided by the magneto-optical recording medium, and a beam splitter and the photodetector. A first diffraction element for guiding to the detector. In this magneto-optical pickup device, the first diffractive element has a hologram pattern for compensating for a wavefront aberration generated by refraction at the joint surface.

By providing the first diffraction element with a hologram pattern for compensating the wavefront aberration generated by the refraction at the joining surface between the first member and the second member, it is possible to select an inexpensive beam splitter material. Even if it performs, a signal can be detected stably. That is, after performing stable signal detection, it is possible to reduce the cost of the second member, which has conventionally been particularly expensive.

In the magneto-optical pickup device according to the present invention, the hologram pattern is composed of a locus of the point H on the first diffraction element, which satisfies the relationship of (LH-PH) '= nλ. (Claim 2). Here, L: a point at which light passes through the first diffraction element and condenses, LH: an optical path length between points H and L, P: P is diffracted by the first diffraction element and condensed on the photodetector. Point, PH: optical path length between point P and point H, λ: wavelength of light beam, n: integer, (LH-P
H) ′: The optical path difference between the optical path length LH and the optical path length PH in a state where the wavefront aberration at the joint surface is folded into either the optical path length LH or the optical path length PH.

The above hologram pattern can be calculated using a computer, and the hologram pattern can be efficiently formed on a transparent substrate by photolithography and RIE (Reactive Ion Etching). As a result, a large cost reduction can be obtained as compared with the case where expensive lithium tetraboride is used for the second member.

The above-described magneto-optical pickup device of the present invention comprises:
Signal detection means for detecting a signal using only the diffracted light diffracted by the first diffraction element is provided (claim 3).

As described above, since the signal is detected using only the diffracted light, the condensing spot can be freely arranged by changing the design parameters of the first diffractive element. The arrangement of the photodetectors can be facilitated.

In the magneto-optical pickup device according to the present invention, the cross section of the first diffraction element is formed so as to have a sawtooth shape.

The sawtooth cross section of the first diffraction element increases the diffraction efficiency and increases the amount of light guided to the photodetector, thereby increasing the signal-to-noise ratio and stably reproducing the signal. can do.

In the magneto-optical pickup device according to the present invention, the second diffraction element may be provided on the optical path between the light source and the beam splitter. By disposing the second diffraction element, it is possible to output a stable tracking signal by the three-beam method. In the magneto-optical pickup device according to the present invention, the second member forming the beam splitter may be lithium niobate. In the present invention, there is no need to combine a glass material and a birefringent material forming the beam splitter so that the difference in refractive index between the first member and the second member is reduced. Therefore, for example, lithium niobate and SF2, a product of SCHOTT, are used.
Inexpensive material combinations such as can be selected.

In the magneto-optical pickup device of the present invention, a resin half-wave plate is disposed on both sides of the beam splitter (claim 5).

With the arrangement of the half-wave plate, the direction of polarization of the light beam emitted from the light source can be freely set, and compared with the case where a wave plate using a crystal such as quartz is arranged. Thus, an optical pickup can be configured at low cost.

In the magneto-optical pickup device according to the present invention, the light source and the photodetector are arranged in the same hermetically sealed package having a light-transmitting window.

By arranging the light source and the photodetector in the same hermetically sealed package, the relative position between the light source and the photodetector can be stably maintained for a long time, and a durable magneto-optical pickup device can be provided. It becomes possible to configure.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A magneto-optical pickup device according to an embodiment of the present invention will be described with reference to FIG.
The magneto-optical pickup device according to the present embodiment includes a stem 15, a light source 1 arranged on the stem 15 for generating a light beam, and a light beam emitted from the light source 1 condensed on a magneto-optical recording medium 10. A collimating lens 8 and an objective lens 9 are provided. The magneto-optical pickup device includes a first member 16 made of an isotropic material and a second member 17 made of an anisotropic material disposed between the light source 1 and the collimating lens 8. , A beam splitter 11 having a polarization separation surface formed on a surface 6 where the first member and the second member are bonded. The magneto-optical pickup device further includes 波長 wavelength plates 4 and 7 disposed on both the entrance side and the exit side of the beam splitter 11, and a photodetector 14 configured in the same package as the light source 1. And The magneto-optical pickup device has a first diffraction element 12 divided into three regions on which a hologram pattern for compensating a wavefront aberration generated by refraction on the surface 6 is formed. The first diffraction element diffracts the light reflected by the magneto-optical recording medium 10 and polarized and separated by the surface 6 and guides the diffracted light to the photodetector 14. At the time of this guidance, the above-mentioned wavefront aberration is compensated. Further, the photodetector 14 includes the first diffraction element 1
And signal detection means for detecting a signal using only the diffracted light diffracted by 2.

The first half-wave plate 4 disposed between the light source 1 and the beam splitter 11 is made of resin, and converts a p-polarized light beam emitted from the light source into s-polarized light.
The second half-wave plate 7 disposed between the beam splitter 11 and the collimating lens 8 is also made of resin, and converts the s-polarized light passing through the beam splitter into p-polarized light.
Convert to polarized light. The beam splitter 11 is disposed on an optical path from the light source 1 to the collimator lens 8 and has a polarization splitting surface 6 having a function of splitting light reflected from the magneto-optical recording medium 10. Further, the beam splitter 11 includes a first member 16 made of an isotropic optical material and a second member 17 made of an anisotropic optical material. The light beam emitted from the semiconductor laser 1 passes only through the first member 16 and reaches the collimating lens 8,
The light is focused on the magneto-optical recording medium 10 by the objective lens 9. The reflected light reflected by the magneto-optical recording medium 10 is:
The light passes through the first member 16, and is partially transmitted by the boundary surface 6 serving as a polarization splitting surface, and proceeds to the second member 17. Since the second member 17 is an anisotropic optical material, the reflected light from the magneto-optical recording medium is separated into two components, an ordinary light component 18 and an extraordinary light component 19, and the second component 17 has a different refraction angle. The light is refracted into the member and travels in different directions. Further, the ordinary light component and the extraordinary light component are combined with the second member 1.
7 and the half-wave plate 4, the first diffraction element 12
And is condensed on the photodetector 14.

The second diffractive element 2 is disposed on an optical path from the light source 1 to the beam splitter 11 on the light transmitting substrate 3 on which the first diffractive element 12 is disposed. Light source 1
Is emitted by the second diffraction element 2
It is divided into a total of three beams, two tracking beams and one signal recording / reproducing beam. Therefore, the light reflected from the magneto-optical recording medium 10 is transmitted to the first diffraction element 12
By the time, the ordinary light component and the extraordinary light component are generated for each of the three beams generated by the second diffraction element 2, and the three beams are separated into a total of six light beams.

The first diffraction element 12 is divided into three regions 12a, 12b and 12c as shown in FIG.
The diffraction element 12 has a hologram pattern for compensating for a wavefront aberration generated by refraction of the surface 6. The wavefront aberration is compensated by the first diffraction element 12 because:
The wavefront aberration is not compensated for only the light diffracted by the first diffraction element 12 and the light transmitted through the first diffraction element 12. Therefore, the light transmitted through the first diffraction element 12 becomes a large condensed spot on the photodetector 14. For this reason, the first diffraction element 12
Only the light diffracted by is used. For this reason, in FIG. 3, the light receiving portion for receiving the light transmitted through the first diffraction element, that is, the light receiving portions 310e to 310h in FIG. 10 are not formed. However, FIG.
Virtual light receiving units corresponding to the light receiving units 10e to 310h can be considered. The virtual point light source L is a point that converges on such a virtual light receiving unit.

The photodetector 14 shown in FIG.
It has a light receiving section divided into i. These light receiving parts
It is a light receiving unit that receives the diffracted light and corresponds to 310a to 310d in FIG. Of the signal recording / reproducing beams of light incident on the first area 12a of the first diffraction element 12,
The ordinary light component is guided on the boundary between 14f and 14g, and the extraordinary light component is guided on 14e. Further, the first diffraction element 12
The tracking beam of light that has entered the first region 12a is guided to 14h and 14i. First diffraction element 1
In the signal recording / reproducing beam of light incident on the second second region 12b, the ordinary light component is guided to 14d, and the extraordinary light component is guided to 14c. The tracking beam that has entered the second region 12b of the first diffraction element 12
h, 14i.

In the signal recording / reproducing beam of light incident on the third region 12c of the first diffraction element 12, the ordinary light component is guided to 14b, and the extraordinary light component is guided to 14a. The tracking beam that has entered the third region 12c of the first diffraction element 12 is guided to 14h and 14i. Therefore, a total of 18 condensed spots are formed on the photodetector 14. The output signals of the photodetectors 14a to 14i shown in FIG.
When i is set, each signal is obtained by the following calculation. (A)
By calculating (If-Ig), a focus error signal based on the knife edge method can be obtained. (B) By calculating (Ih-Ii), a radial error signal based on the three-beam method can be obtained.
(C) An address signal can be obtained by calculating (Ia + Ib)-(Ic + Id). further,
(D) (Ia + Ic + Ie)-(Ib + Id + If + I
By calculating g), a magneto-optical signal can be obtained.

Next, a method of designing the first diffraction element 12 using a generally well-known computer generated hologram will be described with reference to FIGS. The hologram pattern of the first diffraction element 12 has a position L of a virtual point light source.
Then, interference fringes on the light-transmitting substrate surface 3 of the divergent light from the two converging points P on the photodetector. As described above, the position of the virtual point light source is a point at which the light transmitted through the first diffraction element is collected, and the regions 310e to 310 in FIG.
h, and is a virtual point not provided in FIG. Although it is a virtual point, FIG.
This is a point that actually exists as shown by 10h, and simply means that the photodetector in FIG. 3 is not provided with a light receiving unit that receives the light. The condensing point P on the photodetector is a point where the light diffracted by the first diffraction element is condensed, and each region in FIG. 3 receives the diffracted light. When it is not necessary to compensate for the wavefront aberration, a set of points H on the first diffraction element 12 where the optical path length difference from the two points L and P is an integral multiple of the wavelength is equal to the hologram pattern of the first diffraction element. Become. That is, a curve connecting H that satisfies the relationship represented by LH-PH = nλ becomes the pattern of the first diffraction element 12. Here, n represents an integer and λ represents a wavelength.

To manufacture the first diffractive element 12 for compensating the wavefront aberration generated by the refraction on the surface 6 determined by the refractive index ratio between the first member 16 and the second member 17, the following steps are required. A hologram pattern is formed in the following manner.
The point at which the light transmitted through the first diffraction element converges on the virtual photodetector is defined as a virtual light source L, and the divergent light emitted from this light source has the opposite wavefront of the light beam including the wavefront aberration. The above calculation may be performed by superimposing information. That is, assuming that the length obtained by folding the wavefront aberration into the optical path length LH is (LH) ′, a trajectory of H is formed to satisfy (LH) ′ − PH = nλ to create a hologram pattern. Alternatively, as shown in the flowchart of FIG. 8, an optical path length (P) in which the information on the wavefront aberration is superimposed on the optical path length from the focal point P to H.
As H) ′, a locus of H satisfying LH− (PH) ′ = nλ may be obtained. As described above, (LH-PH) '
= Nλ indicates that either of the two is performed.

In the above hologram pattern, the first
When the cross section of the diffraction element 12 is rectangular, the diffraction efficiency is about 40
% Can only be obtained. However, by making the cross-sectional shape a saw-tooth shape as shown in FIG. 5, a diffraction efficiency of 100% is obtained, and the signal quality is improved.

The second diffraction element 2 may be omitted in order to improve the optical coupling efficiency of the optical path from the light source 1 to the magneto-optical recording medium 10. In this case, the tracking error signal detection uses the push-pull method instead of the three-beam method. Since only the signal recording / reproducing beam applied to the magneto-optical recording medium is used, the number of condensed spots on the photodetector 14 is six in total, and the light receiving portion on the photodetector 14 has a shape as shown in FIG. It will be. First diffraction element 12
Of the light incident on the first region 12a, the ordinary light component is guided to the division line between the light detection units 140a and 140b, and the extraordinary light component is guided to the light detection unit 140e. Second area 12b
Out of the light incident on the photodetector 140c,
The extraordinary light component is guided to the light detection unit 140f. Third
Of the light incident on the region 12c, the ordinary light component is guided to the light detection unit 140d, and the extraordinary light component is guided to 140g. Assuming that the output signals of the light detectors 140a to 140g are Ia to Ig, respectively, by calculating (Ia-Ib), a focus error signal based on the knife edge method can be obtained. Also, (Ic + If) −
By calculating (Id + Ig), a radial error signal and an address signal based on the push-pull method can be obtained. Also, (Ia + Ig + Ic + Id)-(I
By calculating (e + If + Ig), a magneto-optical signal can be detected.

[0034]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A description will be given of specific examples of materials constituting a beam splitter. First member 1 of beam splitter 11
6 and the second member 17 are, for example, SCHOTT
A company's products SF2 (n = 1.635), and lithium niobate _{(n o = 2.258, n e} = 2.178) is made from. In this case, the refractive index of the first member 16 and the average refractive index of the ordinary light refractive index and the extraordinary light refractive index of the second member 17 are significantly different. It is greatly refracted, and astigmatism and coma occur. However, the first diffraction element 12 disposed between the surface 6 and the photodetector 14 has a hologram pattern formed so as to cancel or reduce the wavefront aberration generated by refraction on the surface 6. . For this reason, on the photodetector 14, a point-like condensed spot is obtained as shown in FIG. As described above, by providing the first diffraction element 12 with a wavefront aberration compensating structure, the beam shape on the photodetector 14 can be made into a small point as shown in FIG. As a result, the beam arrangement and design on the photodetector 14 are facilitated, and the condensed spot protrudes from the photodetector 14 due to errors in assembling the pickup unit and expansion and contraction of unit components due to environmental changes. Is gone.

On the other hand, as a comparative example, consider a case where the first diffraction element 12 does not have a structure for compensating the wavefront aberration generated on the surface 6. The first member 16 and the second member 17 of the beam splitter 11 are, for example, SF2 (n = 1.63), which is a product of SCHOTT, respectively.
5), and lithium niobate (n _o = 2.258, n _e
= 2.178). In this case, since the refractive index of the first member 16 and the average refractive index of the ordinary light and the extraordinary light of the second member 17 are significantly different, the ordinary light and the extraordinary light are largely refracted on the surface 6 in the + y-axis direction. Aberration and coma occur. For this reason, as shown in FIG. 12, on the photodetector 14, a large condensed spot becomes wider than the width of the photodetector 14. As a result, it becomes difficult to arrange and design the beam on the photodetector 14, and a condensed spot can protrude from the photodetector 14 due to errors in assembling the pickup unit and expansion and contraction of unit components due to environmental changes. There is.

Although the embodiments of the present invention have been described above, the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is limited to these embodiments. It is not something to be done. The scope of the present invention is shown by the description of the claims, and further includes all modifications within the meaning and scope equivalent to the description of the claims.

[0037]

As described above, by compensating the wavefront aberration generated by the refraction at the joint surface between the first member and the second member by the first diffraction element, the condensed spot on the photodetector can be formed. It is smaller than the case without compensation. Therefore, the possibility of the condensed spot protruding from the photodetector due to unit assembly errors or aging changes is reduced, and a magneto-optical pickup device capable of stably detecting a signal without increasing the number of parts. Can be provided.

Further, since the signal is detected using only the diffracted light, the converging spot can be freely arranged by changing the design parameters of the first diffraction element, and the photodetector at the time of designing the optical pickup can be obtained. Can be easily arranged.

Further, by making the cross section of the first diffraction element into a saw-tooth shape, the diffraction efficiency can be increased and the signal-to-noise ratio can be increased by increasing the amount of light guided to the photodetector.

Further, between the light source and the beam splitter,
By disposing the second diffraction element, it is possible to output a stable tracking signal by the three-beam method.

Further, since it is not necessary to combine the glass material and the birefringent material constituting the beam splitter so that the difference in the refractive index becomes small, for example, lithium niobate and SF2 which is a product of SCHOTT are used. An inexpensive combination of materials can be selected.

Also, by using a half-wave plate made of resin, the polarization direction of the light beam emitted from the light source can be freely set, and a wave plate using a crystal such as quartz can be used. An inexpensive optical pickup can be provided as compared with the case where the optical pickup is arranged.

[Brief description of the drawings]

FIG. 1 is a side view showing a configuration of a magneto-optical pickup device according to an embodiment of the present invention.

FIG. 2 is an external view of a first diffraction element of the magneto-optical pickup device according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of a photodetector of the magneto-optical pickup device according to the embodiment of the present invention.

FIG. 4 is a schematic diagram showing a method for manufacturing a first diffraction element of the magneto-optical pickup device according to the embodiment of the present invention using a computer generated hologram;

FIG. 5 is a sectional view of a first diffraction element of the magneto-optical pickup device according to the embodiment of the present invention.

FIG. 6 is a diagram illustrating an example of a photodetector of the magneto-optical pickup device according to the embodiment of the present invention.

FIG. 7 is a design flowchart of a computer generated hologram having no aberration compensation function.

FIG. 8 is a design flowchart of a computer generated hologram having an aberration compensation function.

FIG. 9 is a side view of a conventional magneto-optical pickup device.

FIG. 10 is a top view of a photodetector of a conventional magneto-optical pickup device.

FIG. 11 is a diagram showing a condensing state of a conventional magneto-optical pickup device.

FIG. 12 is a diagram showing a condensed spot on a photodetector of a conventional magneto-optical pickup device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Light source, 2nd diffraction element, 3 light-transmitting substrate, 4
1/2 wavelength plate, 5 semiconductor slope, 6 joining surface between first member and second member, 7 1/2 wavelength plate, 8 collimating lens, 9 objective lens, 10 magneto-optical recording medium,
Reference Signs List 11 beam splitter, 12 first diffraction element, 13
Cap, 14 Photodetector, 15 Stem, 16 First
A member of 17, a second member, 18 an ordinary light component of reflected light,
19 Extraordinary light component of reflected light.

Claims (6)

[Claims] A light source for generating a light beam; a light condensing means for condensing the light beam emitted from the light source on a magneto-optical recording medium; and a light source disposed between the light source and the light condensing means; A beam splitter including a first member made of an isotropic material and a second member made of an anisotropic material, wherein a joining surface between the first member and the second member forms a polarization separation surface. And a photodetector that reflects the magneto-optical recording medium and receives the guided light; and a photodetector that is disposed between the beam splitter and the photodetector, and transmits light from the beam splitter to the photodetector. First to guide
A magneto-optical pickup device, wherein the first diffraction element includes a hologram pattern for compensating a wavefront aberration generated by refraction at the bonding surface. 2. The light according to claim 1, wherein the hologram pattern is a locus of a point H on the first diffraction element that satisfies a relationship of (LH-PH) ′ = nλ. Magnetic pickup device. Here, L: a point at which light passes through the first diffraction element and condenses, LH: an optical path length between points H and L, P: P is diffracted by the first diffraction element and condensed on the photodetector. Point, PH: optical path length between point P and point H, λ: wavelength of light beam, n: integer, (LH-PH) ′: optical path length L
H is the optical path difference between the optical path length PH and the optical path length PH in a state where the wavefront aberration at the joint surface is folded. 3. A signal detecting means for detecting a signal using only the diffracted light diffracted by the first diffraction element,
The magneto-optical pickup device according to claim 1. 4. The magneto-optical pickup device according to claim 1, wherein a cross section of the first diffraction element is formed so as to have a sawtooth shape. 5. The magneto-optical pickup device according to claim 1, wherein a half-wave plate made of resin is arranged on both surfaces of said beam splitter. 6. The magneto-optical pickup device according to claim 1, wherein the light source and the photodetector are arranged in a hermetically sealed package having a translucent window.