JPH03137841A - Optical pickup device - Google Patents

Abstract

PURPOSE:To detect an error signal and a magnetooptic signal, and to improve their response characteristics and sensitivity by using only light beams obtained by splitting reflected light from a magnetooptic disk into two. CONSTITUTION:The surface G13a of a dual grating DG13 on the incidence side of the reflected light L from the magnetooptic disk is composed of concentric gratings which differ in pitch and the reverse surface G13b of the DG13 is composed of linear gratings which differ in pitch. Diffracted light Lb from the DG13 is guided to a photodetecting element Sb as converged light which has astigmatism by a polarization separating function and a unidirectional converging function in combination and a focus error signal is detected. Transmitted light La from the DG13 passes through the DG13 as it is and is guided to a photodetecting element Sa as it is. The element Sa consists of two divided photodetecting elements S1 and S2 and a track error signal is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical pickup device that records and reproduces information using a magneto-optical disk or the like.

(Prior Art) A magneto-optical signal in an optical pickup device that records and reproduces information using a magneto-optical disk or the like.

Devices that use gratings to detect focus error signals and track error signals are known (1).
st MICROOPTIC3C0NFERENCE
1987 P.

162-165).

An example of a conventional optical pickup device using this grating will be explained based on FIG. 4.

In FIG. 4, the light emitted from the semiconductor laser 1 is
After being collimated by a collimating lens 2, a beam shaping prism 3. The light passes through a polarizing beam splitter 4° and a mirror 5 (a prism in the illustrated example), is focused by an objective lens 6, and is irradiated onto a magneto-optical disk 7.

Thereby, the reflected light that has read the signal from the magneto-optical disk 7 is reflected by the polarizing beam splitter 4 through the objective lens 6 and the mirror 5, and is guided to the signal detection optical system 8.

The reflected light guided to the signal detection optical system 8 has its polarization direction rotated by 45 degrees by the 1/2λ plate 9, and becomes condensed light by the condensing lens 10, and is converted into HOE() Iologra.
When the light is incident on the optical element 11, it is separated into diffracted light and transmitted light by four different types of gratings formed on the surface of this HOEll.

At this time, the diffracted light is separated into four beams as shown in FIG.
．． s4. guided by,s,,s,.

On the other hand, the light that has passed through without being affected by HOE II is split into two orthogonal polarization components by passing through the polarizing prism 12, and the light receiving element S is split into two.
7. Each is guided by S.

In FIG. 5, each signal in the signal detection optical system 8 is determined by the magneto-optical signal being the output difference (87-S; 1) between the light-receiving element S7 and the light-receiving element S6; , and the output difference (S
S-8,) [: push-pull method].

The focus error signal is transmitted to the light receiving element S1 and the light receiving element S4.
The output difference between the sum of the outputs of the light-receiving element S2 and the sum of the light-receiving elements S3 and (S1+S,)-(Sl+83) [each detected by the double knife method.

6(a), (b), and (C) show that each light receiving element s1. s2. s3. s4. It shows how the spot shape of the diffracted light irradiated onto s, , s changes.

(Problems to be Solved by the Invention) In the case of the conventional optical pickup device shown in FIG. Since the detection is performed using different lights, the amount of light for each signal detection is reduced.

For this reason, this type of optical pickup device has a problem in that the detection range of each light-receiving element becomes narrow, and its response characteristics and sensitivity (control accuracy) deteriorate.

Furthermore, in this optical pickup device, the polarization angle of the diffracted light for extracting the focus error signal, the track error signal, and the magneto-optical signal becomes large.

Therefore, in this type of optical pickup device.

Since the light-receiving elements for detecting each of these signals are arranged at separate positions and the signal detection optical system 8 is enlarged, there is a natural limit to the miniaturization of the entire apparatus.

On the other hand, in order to eliminate the drawbacks of such conventional optical pickup devices, an optical pickup device using dual gratings was proposed earlier.

As shown in FIG. 7, this optical pickup device uses a semiconductor laser 1. Collimating lens 2. Beam shaping prism 3. The light passes through a polarizing beam splitter 4, is focused by an objective lens 6, and is irradiated onto a magneto-optical disk 7.

Thereby, the reflected light that has read the signal from the magneto-optical disk 7 is guided to the signal detection optical system 8 through the objective lens 6 and the polarizing beam printer 4.

The reflected light guided to the signal detection optical system 8 is focused by a condenser lens 1o and input to a dual grating 13, where it is separated into diffracted light and transmitted light.

Here, the tracking error signal and the focus error signal are detected using either the transmitted light or the diffracted light separated by the dual grating 13, respectively.

That is, in the illustrated example, each signal is detected by applying the astigmatism method using the 4-split prism 14 for the transmitted light, and applying the push-pull method using the 2-split prism 15 for the diffracted light. is being carried out.

Further, the detection of the magneto-optical signal is performed by detecting the difference in light intensity between the diffracted light and the transmitted light.

As is clear from FIG. 7, the optical pickup device using this dual grating 13 has a small polarization angle of the diffracted light for extracting the focus error signal, track error signal, and magneto-optical signal. The elements can be arranged relatively close together, making it easier to achieve miniaturization.

In addition, in this optical pickup device, detection of the magneto-optical signal is obtained by detecting the difference between the total amount of light of the light receiving element that detects the track error signal and the total amount of light of the light receiving element that detects the focus error signal. .

Therefore, in the optical pickup device using this dual grating 13, if the amount of light reflected from the magneto-optical disk 7 is the same as the amount of light reflected by the device, the total amount of light for detecting the magneto-optical signal is greater than that of the device described above. Therefore, the response characteristics and sensitivity (control accuracy) are improved compared to the above devices.

However, in the optical pickup device using this dual grating, as shown in FIG. After being guided, the light is focused by a condenser lens 10, and then enters a dual grating 13 where it is separated into diffracted light and transmitted light.

Therefore, in this optical pickup device, although each light receiving element can be arranged close to each other as described above, as a means for converging the diffracted light, the light receiving elements can be arranged independently as in the conventional device. Since the arranged condenser lens 10 is used, when setting the polarization angle of the diffracted light and the arrangement position of each light receiving element, etc., the specifications of the two parts, the condenser lens 10 and the dual grating 13, are required. Since this must be taken into account, there is a problem in that the degree of freedom in designing is naturally limited.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention records and reproduces information by irradiating light emitted from a laser light source onto an optical information recording medium, and also records and reproduces information on an optical information recording medium. In an optical pickup device that guides reflected light from a recording medium to a signal detection optical system and performs signal inspection such as a focus error signal and a track error signal, a side where the reflected light guided to the signal detection optical system is incident. A dual grating in which a front grating is formed and a back grating is formed opposite to the front grating has a polarization separation function, a unidirectional focusing function, and a bidirectional focusing function. A light receiving element for detecting each of the above signals is provided in each optical path of the transmitted light and the diffracted light obtained by dividing the light into two by this dual grating.

(Function) According to the present invention, the dual grating itself, which has gratings on both the front and back sides, has a polarization separation function, a unidirectional focusing function, and a bidirectional focusing function. The transmitted light and diffracted light are focused without using a focusing lens.

(Example) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

The purpose of the optical pickup device according to the present invention is to improve the sensitivity of the signal detection optical system and to simplify the size and size of the optical pickup device.

Therefore, in the following explanation, only the signal detection optical system embodying the present invention will be described, and the configuration and operation of other parts of the signal optical system will be illustrated with reference to the configuration of the conventional optical pickup device. etc. will be omitted.

First, the concept of the signal detection optical system in the optical pickup device of the present invention will be explained with reference to FIG.

This signal detection optical system 8 is configured such that the gratings on both the front and back surfaces of the dual grating 13 shown in FIG. 6 have a polarization separation function, a unidirectional focusing function, and a bidirectional focusing function.

That is, in FIG. 1(a), the magneto-optical disk 7 (
The surface grating 13a of the dual grating 13 on which the reflected light from the grating (see FIG. 7) is incident is composed of concentric gratings with different pitches.

On the other hand, the back grating 1 of the dual grating 13 is opposite to the front grating 13a.
3b is composed of linear gratings with different pitches.

Thereby, this dual grating 13 is configured such that its front surface grating 13a has a focusing function, and its back surface grating 13b has a unidirectional focusing function.

Therefore, the diffracted light Lb from the dual grating 13 has a bidirectional focusing function on its surface.

In other words, the sum of the polarization separation function and the unidirectional focusing function results in a focused light with astigmatism, which is transmitted to the light receiving element s.
be guided by b.

As shown in FIG. 1(b), the light receiving element sb is divided into four light receiving elements s3. s4. It is composed of four divided light receiving elements consisting of light receiving element S3 and light receiving element S.
A focus error signal is detected by the astigmatism method (S, +S, ) - (SS + S,) C, which is the output difference between the sum of the outputs of 4 and the sum of the light receiving elements S and S6.

On the other hand, the transmitted light La from the dual grating 13 passes through the dual grating 13 without being influenced by the front grating 13a and the back grating 13b, and is guided directly to the light receiving element Sa.

As shown in FIG. 1(b), the light receiving element Sa has a 2 minute mJ
The light receiving element S1. It is composed of a two-split light receiving element consisting of light receiving element S2, and detects a track error signal by the output difference (S, -82) [push-pull method] between light receiving element S1 and light receiving element S2.

FIG. 2(a) shows another embodiment of the present invention.

In the dual grating 13 in this embodiment, the front grating 13a is composed of linear gratings with different pitches, and the back grating 13a is composed of linear gratings with different pitches.
3b is composed of concentric gratings with different pitches.

As a result, the diffracted light Lb in this signal detection optical system 8
Due to the unidirectional focusing function of the front grating 13a, the light is focused in only one direction and is incident on the back grating 13b.

Therefore, this diffracted light Lb becomes a focused light with astigmatism due to the gratings 13a and 13b on the front and back sides, and the same effect as in the embodiment described above is achieved.

An example of the arrangement of the light receiving elements Sa and Sb in this embodiment is shown in FIG. 2(b).

FIG. 3(a) shows yet another embodiment of the present invention.

In the dual grating 13 in this embodiment, the front grating 13a is composed of concentric gratings with different pitches, the back grating 13b is composed of linear gratings with the same pitch, and the grating substrate 13c allows the diffracted light to be It is configured to have an astigmatism of Lb.

That is, while the astigmatism in each of the embodiments described above is determined by the degree of modulation of the pitch of the linearly formed grating, the astigmatism in this embodiment is controlled by the substrate thickness t of the grating substrate 13c. Ru.

An example of the arrangement of the light receiving elements Sa and Sb in this embodiment is shown in FIG. 3(b).

As described above, in the optical pickup device according to the present invention, the dual grating 13 itself, in which the gratings 13a and 13b are formed on both the front and back surfaces, has a polarization separation function, a unidirectional focusing function, and a bidirectional focusing function. Therefore, the transmitted light La obtained by this dual grating 13.

And the diffracted light Lb can be condensed without using the condensing lens 10.

Therefore, in this optical pickup device, the signal detection optical system 8 can be configured only with the dual grating 13, so that the configuration can be made smaller and simpler.

Further, in this optical pickup device, as shown in FIG. 1(b), FIG. 2(b), and FIG. 3(b), the shape and pitch of the front grating 13a and back grating 13b of the dual grating 13 are changed. By changing the distribution, the positional relationship between the light receiving elements Sa and Sb can be freely designed.

(Effects of the Invention) According to the present invention, the focus error signal, the track error signal, and the magneto-optical signal can be detected using only two beams, the transmitted light and the diffracted light, which are obtained by dividing the reflected light from the magneto-optical disk 7 into two. Since this is performed using light, the amount of light for each signal detection becomes large, and the response characteristics and sensitivity (control accuracy) can be improved.

Also, according to the invention, a focus error signal.

The polarization angle of the diffracted light for extracting the track error signal and the magneto-optical signal can be made small, and the light receiving elements that detect these signals can be placed close to each other, so the signal can be The detection optical system and the entire device can be downsized.

Furthermore, according to the present invention, there is no need to use an independently arranged condensing lens as in the conventional device as a means for converging the diffracted light, thereby increasing the degree of freedom in designing. can be improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the main parts of an embodiment of the present invention, FIG. 2 is a schematic diagram of the main parts of another embodiment of the invention, and FIG. 3 is a schematic diagram of the main parts of still another embodiment of the invention. FIG. 4 is a schematic perspective view of a conventional optical pickup device, FIG. 5 is a schematic perspective view of a signal detection optical system of the conventional optical pickup device, and FIG. 6 is a schematic perspective view of each light receiving element in the conventional signal detection optical system. A schematic diagram showing the arrangement, and FIG. 7 is a schematic diagram of another conventional optical pickup device. 1... Semiconductor laser, 2... Collimator lens, 3
... Beam shaping prism, 4... Polarizing beam splitter, 5... Mirror 6... Objective lens, 7...
Magneto-optical disk, 8...signal detection optical system, 9...1
/2λ plate, 13... dual grating, 13a
...Surface grating, 13b...Back surface grating, L...Reflected light, La...Transmitted light, Lb...
- Diffraction light, Sa, Sb... Light receiving element, 13c... Grating substrate, t... Grating substrate 13c
board thickness. (Kun%5 Zuko Ward (8) (C) (4) Begging Zuzu (4)

Claims (1)

[Claims] 1. Recording and reproducing information by irradiating light emitted from a laser light source onto an optical information recording medium, and guiding reflected light from the optical information recording medium to a signal detection optical system; In an optical pickup device that detects signals such as focus error signals and track error signals, a front surface grating is formed on the side where the reflected light guided to the signal detection optical system is incident, and a back side is formed on the side opposite to this. The gratings on both the front and back sides of the dual grating have a polarization separation function, unidirectional focusing function, and bidirectional focusing function, and the transmitted light obtained by dividing into two by this dual grating. and an optical pickup device comprising a light-receiving element for detecting each of the above signals in each optical path of the diffracted light. 2. The front grating of the above dual grating is a concentric grating with a different pitch and has a focusing function, and the back grating is a linear grating with a different pitch and has a unidirectional focusing function, so that the diffracted light of the dual grating 2. The optical pickup device according to claim 1, wherein the focused light has astigmatism. 3. The front surface grating of the dual grating has a focusing function with linear gratings with different pitches, the back grating has a focusing function with concentric gratings with different pitches, and the diffracted light of the dual grating has astigmatism. 2. The optical pickup device according to claim 1, wherein the optical pickup device becomes a focused light having . 4. The front surface grating of the above dual grating is a concentric grating with different pitches and has a focusing function, and the back surface grating is a linear grating with an equal pitch, and the diffracted light of the dual grating is focused by the parallel plate-shaped dual grating substrate. 2. The optical pickup device according to claim 1, wherein the focused light has point aberration.