JPH0963141A - Optical pickup - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To increase the detection output and light emission of a photodetector due to a compact structure, simplification of manufacturing, improvement of reliability, and increase of the incident light amount of return light to the photodetector. To provide an optical pickup designed to reduce power consumption and power consumption of a unit. A light emitting unit, an objective lens for condensing a light beam emitted from the light emitting unit on a signal recording surface of a magneto-optical recording medium, and a light emitting unit are disposed between the light emitting unit and the objective lens. , A polarization hologram element 12 for separating the incident light into 0th order light and plus or minus 1st order light, and a 0th order light and plus or minus 1st order light of the return light beam separated by the polarization hologram element near the confocal point An optical pickup 10 including first and second photodetectors 23 and 24 that receive light at.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup, and more particularly to an optical pickup for recording and / or reproducing stored information on a magneto-optical disk recording medium such as a magneto-optical disk (MO).

[0002]

2. Description of the Related Art Conventionally, an optical pickup for recording / reproducing on / from such a magneto-optical disk is constructed as shown in FIG. In the figure, an optical pickup 1 is provided with a semiconductor laser element 2, a diffraction grating 3, a beam splitter 4, a collimator lens 5, an objective lens 6, a Wollaston prism 7, a multi-lens 8 and a photodetector 9, and each of these is provided. The optics are mounted individually.

According to the optical pickup 1 having such a configuration, the light beam emitted from the semiconductor laser element 2 is
After passing through the diffraction grating 3 and entering the beam splitter 4,
The beam splitter 4 separates the light beam emitted from the semiconductor laser element 2 and the return light beam from the magneto-optical disk MO. Here, the beam splitter 4 is generally composed of a pair of optical prisms and a reflecting surface 4a composed of a multilayer dielectric layer formed by vapor deposition, sputtering or the like between the pair of optical prisms.

The light beam of, for example, the P-polarized component from the semiconductor laser element 2 which is separated and transmitted by the beam splitter 4 enters a collimator lens 5, is converted into parallel light by the collimator lens 5, and then is incident on an objective lens 6. Incident. The objective lens 6 receives the incident light from the magneto-optical disk M.
While converging and irradiating on a certain point on the O signal recording surface,
It is adapted to be driven in the focus direction and the tracking direction by a driving means (not shown).

The return light beam containing the MO signal (magneto-optical signal) of the S-polarized component, which is reflected by the signal recording surface of the magneto-optical disk MO and whose polarization plane is rotated by the Kerr effect,
It again enters the beam splitter 4 via the objective lens 6 and the collimator lens 5. Here, the S-polarized component of the return light beam is reflected by the reflecting surface 4a of the beam splitter 4.

The S-polarized component reflected by the reflecting surface 4a of the beam splitter 4 is separated by the Wollaston prism 7 into a plurality of (for example, three) light beams, and each light beam is incident on the multi-lens 7. . Astigmatism is imparted to each light beam incident on the multi-lens 8 for detecting a focus error, and the optical path length of the return light beam to the photodetector 9 is shortened. The photodetector 9 has a light-receiving surface divided into a plurality of light-receiving portions in order to receive each light beam incident through the multilens 8. As a result, based on the detection signal from each light receiving unit of the photodetector 9, by the differential method or the like,
MO signals and error signals such as focus error signals and tracking error signals are detected.

[0007]

However, in the optical pickup 1 thus constructed, the return light beam from the magneto-optical disk MO is split by the beam splitter 4 and split by the Wollaston prism 7. By detecting each split beam,
The MO signal can be obtained. Since the Wollaston prism 7 is relatively expensive, the cost of the optical pickup 1 as a whole increases, and the Wollaston prism 7 limits the separation angle of the MO signal (magneto-optical signal). There was a problem that it became relatively large. Further, since the astigmatism and the coma aberration are inevitable in the division of the light beam by the Wollaston prism 7, distortion of the divided side beams becomes relatively large, and the divided beams overlap each other. There was a problem that it might end up.

Further, the diffraction grating 3, the beam splitter 4,
Since a large number of optical components such as the Wollaston prism 7 and the multi-lens 8 are individually assembled, the configuration of the entire apparatus becomes complicated, resulting in an increase in size and cost of the apparatus and an optical arrangement setting. However, there was a problem in terms of mass productivity.

Furthermore, in the above-mentioned conventional optical pickup 1, the return light beam from the magneto-optical disk MO is separated from the optical path toward the semiconductor laser element 2 which is the light source by the beam splitter 4, so the beam splitter 4 There is a problem in that the amount of light is reduced based on the reflectance of No. 1 and the amount of light incident on the photodetector 9 is reduced.

It is also conceivable to mount an optical element forming an optical pickup on a substrate and attach it to form an integrated light emitting / receiving element. However, if the light emitting part and the light receiving part are provided on different substrates, the light receiving efficiency decreases, and
Positioning for mounting each optical element is complicated, and strict alignment accuracy is required, resulting in high cost.

In view of the above points, the present invention can be constructed in a small size, simplifies manufacturing, improves reliability, and increases the amount of incident light returning to the photodetector. It is an object of the present invention to provide an optical pickup which is designed to increase the power consumption, reduce the power of the light emitting section, and reduce the power consumption.

[0012]

According to the present invention, the above object is to provide a light emitting portion for emitting a light beam and a light beam emitted from the light emitting portion for focusing on a signal recording surface of a magneto-optical recording medium. Is disposed between the light-emitting unit and the objective lens, and separates the light beam from the light-emitting unit into 0th-order light and plus / minus 1st-order light, and a magneto-optical recording medium. The return light beam from is regarded as ordinary light and extraordinary light, and a polarization hologram element for separating it into 0th order light and plus / minus 1st order light respectively, and a 0th order light of the return light beam separated by the polarization hologram element A first photodetector for receiving near the focal point and a second photodetector for receiving plus / minus primary light of the return light beam separated by the polarization hologram element near the confocal point, Optical pickup More, it is achieved.

According to the above structure, the light beam emitted from the light emitting portion is separated into three light beams, that is, the 0th order light and the plus / minus 1st order light by the polarization hologram element, and then the 0th order light is the objective lens. Is irradiated onto the signal recording surface of the magneto-optical recording medium via. The return light beam containing the magneto-optical signal, which is reflected by the signal recording surface of the magneto-optical recording medium and whose polarization plane is rotated by the Kerr effect, again enters the polarizing hologram element via the objective lens. Then, the return light beam is separated into three light beams, that is, the 0th order light and the plus / minus 1st order light by the polarization hologram element.

Therefore, the 0th-order light beam is incident on the first photodetector, and the plus / minus 1st-order light beam is incident on the second photodetector. Thus, the focusing error signal and the tracking error signal are detected based on each output signal of the divided light receiving surface on which the 0th order light of the first photodetector is incident, and the first photodetector and the second light are detected. A magneto-optical signal or a reproduction signal will be detected based on the detection signal of the detector.

The light emitting section and the first and second photodetectors are integrally formed on one substrate, and the light emitting section has a semiconductor laser having a horizontal resonator and a reflecting mirror. In the case where the photodetector is composed of a photodiode and at least a part of the light-receiving surface of the photodiode is arranged within the diffraction limit of return light, the light-emitting portion and the first and The second photodetector has a structure integrated on a common substrate. For this reason, the positioning accuracy due to the accuracy of the mask at the time of manufacturing can be obtained without the mutual positioning of the light emitting part and the photodetector at the time of assembly, and the optical pickup can be easily assembled. In addition, the assembly cost is reduced, the return light traveling toward the light emitting unit is directly incident on the first photodetector, and the first photodetector is disposed near the confocal point. As a result, the light receiving efficiency is improved.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS. still,
The embodiments described below are preferable specific examples of the present invention, and therefore, various technically preferable limitations are given,
The scope of the present invention is not limited to these embodiments unless otherwise specified in the following description.

FIG. 1 shows an embodiment of an optical pickup according to the present invention. In this case, the optical pickup 10 is a reciprocating transmission type optical pickup. In FIG. 1, an optical pickup 10 includes a light emitting / receiving element 11, a polarizing hologram element 12, and an objective lens 13.

The light emitting / receiving element 11 is integrally formed on one semiconductor substrate 20, as shown in the figure. That is,
The light emitting / receiving element 11 includes a semiconductor laser element 21 having a light emitting portion formed on the semiconductor substrate 20, and a reflecting mirror 22 formed so as to be inclined from the surface of the semiconductor substrate 20, and a photodetector. Is composed of a first photodetector 23 and a second photodetector 24 which are photodiodes formed on the semiconductor substrate 20. The semiconductor laser device 21 is a light emitting device utilizing recombination light emission of a semiconductor, and in the case shown in the figure, has a configuration having a horizontal resonator and is used as a light emitting portion. The light beam emitted in the horizontal direction from the semiconductor laser device 21 is guided to the reflecting mirror 22.

The reflecting mirror 22 has a tilt angle of, for example, 45 degrees, and by forming a reflecting film made of, for example, a metal film or a dielectric multilayer film on the inclined surface provided on the semiconductor substrate 20, It is configured. Thereby, the reflecting mirror 22 is adapted to totally reflect, for example, the S-polarized component of the light beam from the semiconductor laser element 21 upward in the drawing. As described above, the laser beam totally reflected upward is converged on the signal recording surface of the magneto-optical disk MO as the magneto-optical recording medium via the polarization hologram element 12 and the objective lens 13, and the magneto-optical disk MO is thus recorded. The laser light applied to the signal recording surface of P is subjected to the Kerr effect when reflected on the magneto-optical disk MO, and the polarization plane is rotated P
It becomes a component (a component including a magneto-optical signal). The return light from the magneto-optical disc MO containing the P component again passes through the objective lens 13 and the polarization hologram element 12, and the first photodetector 23 and the second photodetector 24 of the light receiving and emitting element 11 are returned.
To be incident on.

The polarizing hologram element 12 is constructed so as to transmit ordinary light and diffract extraordinary light.
Thereby, the polarization hologram element 12 separates the return light from the signal recording surface of the magneto-optical disc MO into 0th-order light and plus / minus 1st-order diffracted light.

As shown in FIG. 2, for example, the polarizing hologram element 12 is constructed as a birefringence diffraction grating type element, and includes a substrate 12a made of lithium niobate and an incident side of the substrate 12a, for example, benzoin. And a lattice 12b formed by a proton exchange method with an acid. As a result, in the region of the grating 12b, the refractive index for ordinary light is increased by about 0.13, and the refractive index for extraordinary light is decreased by about 0.04.

Further, in the polarization hologram element 12, a phase compensation film 12c made of a dielectric material having a thickness selected so as to cancel the phase difference received by the transmitting ordinary ray is provided on the grating 12b formed by the proton exchange. It is provided. Thereby, it is apparent that the extraordinary ray is observed so that the refractive index change due to the proton exchange occurs.

Here, the polarizing hologram element is manufactured as shown in FIG. That is, in FIG. 5, the polarizing hologram element 30 is formed by first coating a substrate 30a made of a uniaxial crystal such as lithium niobate with aluminum thin films 30b on both surfaces thereof. afterwards,
A resist film 30c is coated on one surface of the substrate 30a from above the aluminum thin film 30b. The resist film 30c is patterned by placing a grid pattern mask on the resist film 30c and exposing the resist film 30c. Then, by etching etc.
After patterning the aluminum thin film 30b, the resist film 30c is removed.

Then, the lattice-shaped portion from which the aluminum thin film 30b has been removed is subjected to proton exchange with, for example, benzoic acid to form a proton exchange layer 30d. Then, over the entire surface, niobate Nb ₂ O ₅
After the phase compensation film 30e made of a dielectric material such as is coated, the aluminum thin film 3 is lifted off.
0b is removed. Finally, over the entire surface, SiO
_Two layers 30f are formed by sputtering. As a result, the polarizing hologram element 30 is formed on one surface (upper surface) of the substrate 30a. It should be noted that the above manufacturing steps and constituent materials are just examples, and it is obvious that other steps and materials are used.

Thus, the polarizing hologram element 12 is
As shown in FIG. 2, with respect to the direction of the optical axis X, the incident light is split into normal light in a direction perpendicular to the normal light and extraordinary light in a direction parallel to the normal light. That is, in the incident return light beam, the ordinary light is transmitted as the 0th-order light and the extraordinary light is diffracted as the plus / minus 1st-order light, as shown in the figure. On the other hand, the first photodetector 23 and the second photodetector 24 described above are configured so that the 0th-order light and the plus / minus 1st-order light split by the polarization hologram element 12 can enter, respectively. It is arranged near the confocal point. The second photodetector 24 is located at the front side of the focus position for the −1st order light.
Further, it is arranged on the rear side of the focus position for + 1st order light.

Further, the polarization hologram element 12 is arranged so that its optical axis is inclined by 45 degrees with respect to the polarization direction of the incident light.

The objective lens 13 is a convex lens and focuses the light beam from the polarization hologram element 12 on a desired track on the recording surface of the magneto-optical disk MO which is rotationally driven.

The first photodetector 23 and the second photodetector 24 are formed separately as shown in FIG. That is, the first photodetector 23 is divided into four sensor parts a, b, c, d, and the second photodetector 24 is divided into three sensor parts e, f, g and h, respectively.
It is divided into i and j.

Then, the first and second photodetectors 23, 2
The detection signals of the sensor units a to j of No. 4 are amplified by head amplifiers in a processing circuit (not shown) and then output signals Sa, Sb, Sc, Sd, Se, Sf, S.
g, Sh, Si, Sj, and the arithmetic circuit calculates the magneto-optical (MO) signal, the focus error signal, and the tracking error signal, respectively. When the wavelength of the light beam from the semiconductor laser element 21 is λ and the numerical aperture of the objective lens 14 is NA, at least a part of the light receiving surface of the first photodetector 23 is the arrangement reference of this light receiving surface. The distance from the optical axis of the light beam that traverses the surface is provided at a position within 1.22λ / numerical aperture (NA), for example.

The optical pickup 10 according to the present embodiment is configured as described above, and the P-polarized light beam emitted from the semiconductor laser device 21 is reflected by the reflecting mirror 22 on the semiconductor substrate 20, and the polarization hologram is obtained. Element 12
Incident on. Here, the polarization hologram element 12 transmits ordinary light of incident light and diffracts only extraordinary light. That is, the ordinary component of the incident light beam is Io: (1-
X), the extraordinary light component Ie: X, and the diffraction efficiency for the extraordinary ray is (1-η), the light beam from the semiconductor laser element 21 passes through the polarization hologram element 12, as shown in FIG. Later, the zero-order light is the ordinary light component Io.
0: (1−X), extraordinary light component Ie0: X × η, and plus / minus primary light becomes ordinary light component Io1: 0 and extraordinary light component Ie1: X × (1−η) / 2.

In this case, the polarizing hologram element 12 is
Since it has a thin phase grating with a rectangular cross-sectional structure, its zero-order diffraction efficiency η is generally

[Equation 1] Where γ is the phase difference of the light transmitted through the two regions forming the grating. Therefore, the polarization hologram element 12
Ordinary component Io0 and extraordinary component Ie0 of the zero-order light transmitted through
Between them, a phase difference of γ will occur.

Thus, the polarization state of the 0th-order light transmitted through the polarization hologram element 12 becomes elliptically polarized light having an azimuth angle inclined by 45 degrees with respect to the incident polarization direction, as shown in FIG.
Here, the polarization hologram element 12 has an optical axis
Since it is tilted by -45 degrees with respect to the incident polarized light, the phase difference γ
Is

[Equation 2] It has become. Thereby, the polarization hologram element 12
The outgoing polarized light that has passed through does not cause a phase shift with respect to the incident polarized light. The 0th-order light beam divided by the polarization hologram element 12 in this way is the objective lens 13
Is focused on the signal recording surface of the magneto-optical disc MO.

The return light beam including the MO signal (magneto-optical signal) of the S-polarized component, which is reflected by the signal recording surface of the magneto-optical disk MO and whose polarization plane is rotated by the Kerr effect,
The light passes through the objective lens 13 and enters the polarizing hologram element 12 again. In this case, the polarizing hologram element 12
The return light beam incident on the polarization hologram element 12
Thus, the ordinary 0th-order light is transmitted and the extraordinary plus / minus 1st-order diffracted light is diffracted.

That is, the ordinary component of the incident light beam is Io
0: (1−X), extraordinary light component Ie0: X × η,
As shown in FIG. 7, the return light from the magneto-optical disk MO passes through the polarization hologram element 12, and its 0th-order light is an ordinary light component Io00: (1-X) and an extraordinary light component Ie0.
0: X × η ² , and the plus / minus primary light has an ordinary light component Io01: 0 and an extraordinary light component Ie01: X × (1-η).
・ It becomes η / 2. By the way, the polarizing hologram element 12
When the incident light on Io: 0.5 and Ie: 0.5 is set, the ordinary light component Io00: 0.5 and the extraordinary light component Ie00: 0.5 × η ^{2 of} the 0th-order light become positive. The ordinary light component Io01: 0 of the minus first-order light and the extraordinary light component Ie01:
0.25 × (1−η) · η, and the maximum value of Ie01 is given when η = 50%.

Further, since the 0th-order light has the reflecting mirror 22, the amount of light that can be detected by the first photodetector 23 with respect to the total incident light is 30%.
When the electrical amplification factor in the second photodetector 25 is A between the sum of the light amounts in the second photodetector 24 and the sum of the light amounts in the second photodetector 24,

(Equation 3) From this, A = 1.5 is determined. Thus, under the above conditions, the magneto-optical signal MO is as shown in FIG.

(Equation 4) Is detected by In addition, the tracking error signal TR
K is

(Equation 5) Is detected by

Further, the focus error signal FCS is
Since the polarization hologram element 12 has a lens effect, the + 1st-order light is focused on the front side of the photodetector, and the -1st-order light is focused on the rear side of the photodetector. ,

(Equation 6) Is detected by

Here, in the embodiment of FIG. 1, the semiconductor laser element 21 and the reflecting mirror 22 which are the above-mentioned light emitting parts,
Since the first and second photodetectors 23 and 24 are integrally formed on one semiconductor substrate 20, mutual positioning is not necessary, and the positioning accuracy due to the accuracy of the mask when manufacturing the semiconductor substrate 20 is improved. As a result, the optical pickup 10 can be easily assembled. In addition, the first and second photodetectors 23 and 24 are
Since the return light Lr traveling toward the light emitting portion is directly incident on the first photodetector 23 by being disposed within the diffraction limit of the return light by the first photodetector 23 Since the container 23 is arranged near the confocal point,
The light receiving efficiency can be improved.

In the above-mentioned embodiment, the polarization hologram element 12 is constructed as a birefringence diffraction grating type element, but the invention is not limited to this, and it may be constructed as a polarization hologram of another construction. Is clear. Further, in the above-described embodiment, the polarization hologram element 12 is configured to diffract the incident light only with respect to the extraordinary light, but is not limited to this, and diffracts the incident light only with respect to the ordinary light. Obviously, a polarizing hologram element having such a structure is also used.

[0039]

As described above, according to the present invention, it is possible to reduce the size of a photodetector because of its compact structure, simplification of manufacturing, improvement in reliability, and increase in the amount of incident light returning to the photodetector. It is possible to provide an optical pickup in which the detection output of the container is increased, the power of the light emitting unit is reduced, and the power consumption is reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an overall configuration of an embodiment of an optical pickup according to the present invention.

2 is a schematic perspective view showing a configuration example of a polarizing hologram element in the optical pickup of FIG. 1 and a polarization direction of an incident light beam.

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

4 is an enlarged plan view showing the configuration of each photodetector in the optical pickup of FIG.

5 is a cross-sectional view showing a diffraction state in the outward path of the polarization hologram element of FIG.

FIG. 6 is a diagram showing changes in the polarization state of a light beam by a polarizing hologram element.

7 is a cross-sectional view showing a diffracted state of multiple paths of the polarization hologram element of FIG.

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

[Explanation of symbols]

 10 Optical Pickup 11 Light Receiving / Emitting Element 12 Polarizing Hologram Element 13 Objective Lens 20 Semiconductor Substrate 21 Semiconductor Laser Element 22 Reflecting Mirror 23 First Photodetector 24 Second Photodetector

Claims (9)

[Claims] 1. A light emitting unit for emitting a light beam, an objective lens for irradiating the light beam emitted from the light emitting unit so as to focus the signal beam on a signal recording surface of a magneto-optical recording medium, the light emitting unit and the objective. It is arranged between the lens and the light beam from the light emitting portion to separate it into 0th order light and plus / minus 1st order light, and returns the returning light beam from the magneto-optical recording medium as ordinary light and extraordinary light, respectively. Next light and plus or minus 1
A polarization hologram element for separating the secondary light, a first photodetector for receiving the 0th order light of the return light beam separated by the polarization hologram element in the vicinity of the confocal point, and a polarization hologram element for separation And a second photodetector for receiving plus or minus primary light of the returned return light beam in the vicinity of the confocal point. 2. The polarizing hologram element according to claim 1, wherein the diffraction efficiency of the polarizing hologram element is selected so that the amount of plus / minus first-order diffracted light is maximized by the second photodetector. The optical pickup described. 3. The optical pickup according to claim 1, wherein the plus / minus first-order diffracted light of the return light from the polarizing hologram element has an arbitrary focal length. 4. The optical pickup according to claim 1, wherein the polarizing hologram element is formed such that its optical axis is inclined by an arbitrary angle with respect to the polarization direction of incident light. 5. The optical pickup according to claim 1, wherein the polarizing hologram element is formed such that its optical axis is inclined by 45 degrees with respect to the polarization direction of incident light. 6. The light emitting section and the first and second photodetectors are integrally formed on one substrate, and the light emitting section includes a semiconductor laser having a horizontal resonator and a reflecting mirror. And the first and second photodetectors are composed of photodiodes, and at least a part of the light-receiving surface of the photodiodes is arranged within the diffraction limit of return light. The optical pickup according to claim 1, wherein: 7. The optical pickup according to claim 1, wherein the first and second photodetectors are each divided into at least three parts. 8. The magneto-optical signal is detected from the sum of output signals of the first photodetector and the sum of output signals of the second photodetector. Optical pickup. 9. A tracking error signal is detected based on the output signals of the first photodetector or the first photodetector and the second photodetector, and the tracking error signal of the second photodetector is detected. 8. The focus error signal is detected based on the difference between the output signals.
An optical pickup according to item 1.