JPH0863778A - Optical pickup - Google Patents

Abstract

PURPOSE: To stably provide a tracking error signal by integrally attaching a polarization hologram being a separated optical system to an objective lens and allowing a 1st-order light beam of a return light beam separated with the polarization hologram to be made incident on a light receiving surface without spot deviation. CONSTITUTION: The return beam from a recording surface of an optical disk 15 is made incident on the polarization hologram 13 through the objective lens 12 again. The return beam is separated into three beams of a zero-order beam and 1st-order beams Le1, Le2 by the polarization hologram 13 with respect to a diffraction pattern in the radial direction shown by an oblique line, and respective beams are made incident on a light receiving part of a laser coupler 11 and the corresponding light receiving surface S1, S2 of a photodetector 14. Thus, by performing arithmetic operation based on a detection signal from the light receiving part of the coupler 11, the tracking error signal is generated. Then, since the hologram 13 is attached to the objective lens 12 integrally, no spot deviation of the first-order beams from the hologram 13 occur on the light receiving surfaces S1, S2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup for recording and / or reproducing on an optical disc.

[0002]

2. Description of the Related Art Conventionally, an optical pickup for recording and / or reproducing information on such an optical disc is basically a light source for emitting a light beam and an optical disc for emitting the light beam emitted from the light source. It is composed of an objective lens for irradiating the recording surface of the disk so as to focus it, and a light receiving section for receiving the returning light beam from the recording surface of the disk. Further, according to the configuration, a separating optical system such as a half mirror and a beam splitter for separating the light beam from the light source unit and the returning light from the recording surface of the optical disc, and a collimator for collimating the light beam from the light source. An optical element such as a lens or a condenser lens for condensing the return light beam on the light receiving portion is added.

According to the optical pickup having such a configuration, the light beam emitted from the light source section of the laser coupler is imaged at a certain point on the recording surface of the optical disc through the objective lens. As a result, the return light beam from the recording surface of the optical disc again enters the light receiving surface of the photodetector via the objective lens. Then, signals such as an optical disk read signal, a focus error signal, and a tracking error signal are generated based on the detection signals from the respective light receiving surfaces of the photodetector.

[0004]

However, in the optical pickup constructed as described above, when the so-called 1-beam push-pull method is adopted for tracking error detection, the objective lens is driven in the radial direction of the optical disk. If so, the spot on the photodetector moves, so that spot deviation easily occurs due to the offset. Therefore, it is necessary to provide a correction means for suppressing the spot deviation, and the electric circuit for processing the detection signal of the photodetector becomes complicated,
There was a problem of high cost.

Further, in the case of obtaining address information from a wobble signal, for example, in a CDR disk or MD disk, since the wobble signal is detected by push-pull operation, access by moving the objective lens in the radial direction is performed. Sometimes, the spot movement on the photodetector causes a difference in the divided areas of the photodetector, and the S / N of the wobble signal is lowered, so that an accurate wobble signal cannot be obtained.

In view of the above points, the present invention provides an optical pickup which has a simple structure and is capable of obtaining a stable tracking error signal or wobble signal by eliminating the spot shift on the photodetector. Is intended.

[0007]

According to the present invention, there is provided a light source section for emitting a light beam, and a light beam emitted from the light source section for irradiating a recording surface of an optical disk so as to focus the light beam. Objective lens, a light receiving section for receiving a return light beam from the recording surface of the disc, and a polarized light disposed in the optical path between the objective lens and the light source and integrally attached to the objective lens. This is achieved by an optical pickup including a sex hologram and a photodetector that receives the primary light separated by the polarization hologram.

In the optical pickup according to the present invention, preferably, the tracking error signal is detected by the photodetector based on the primary light separated by the polarization hologram.

In the optical pickup according to the present invention, the wobble signal is preferably detected by the photodetector based on the primary light separated by the polarization hologram.

[0010]

According to the above construction, the polarization hologram which is the separation optical system is integrally attached to the objective lens. Therefore, even when the objective lens is driven in the radial direction of the optical disc at the time of access, the primary light of the return light beam separated by the polarization hologram is incident on the light receiving surface of the photodetector without causing spot deviation. Will be done. Thus, when the tracking error signal or the wobble signal is detected by the primary light incident on the photodetector from the polarization hologram, the stable tracking error signal or the wobble signal is obtained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to FIGS. In addition, since the Examples described below are preferred specific examples of the present invention, various technically preferable limitations are given. However, the scope of the present invention particularly limits the present invention in the following description. The embodiment is not limited to these embodiments unless otherwise stated.

FIG. 1 shows an embodiment of an optical pickup according to the present invention. The optical pickup 10 comprises a laser coupler 11, an objective lens 12, a polarizing hologram 13 as a separating optical system, and a photodetector 14. .

The laser coupler 11 is composed of a light source section and a light receiving section. The light source section is, for example, a semiconductor laser element, and the light receiving section is, for example, a light receiving element.

Here, a semiconductor laser device (not shown)
Is a light emitting device utilizing recombination light emission of a semiconductor and is used as a light source. In addition, the light receiving element (not shown)
For example, a photodiode, a phototransistor, or the like, which outputs an output signal corresponding to the amount of received light.

The objective lens 12 rotatably drives the optical beam from the light source section of the laser coupler 11 on the optical disk 1.
An image is formed on a desired track on the recording surface of No. 5.

The light beam applied to the recording surface of the optical disk 15 passes through the polarization hologram 13 again via the objective lens 12 as a return light beam.

Here, the polarization hologram 13 is composed of, for example, a substrate made of lithium niobate and a lattice formed by the proton exchange method on the incident side of this substrate, and in the region of this lattice, It has different refractive indexes for ordinary light and extraordinary light. Further, as shown in FIG. 2, the polarization hologram 13 has two regions H1 and H2 which are divided into two in the radial direction of the optical disc along a line along the optical axis. In this case, the polarization hologram 13 is set so that the hologram surface 13a is the upper surface. The separation direction of the hologram surface 13a is set to the radial direction. As a result, the primary lights Le1 and Le2 from the respective regions H1 and H2 of the polarization hologram 13 are imaged so as to form spots on the points P1 and P2 of the photodetector 14 (see FIG. 1).

Further, the polarization hologram 13 is integrally attached to the aperture stop 12a of the objective lens 12. As a result, when the objective lens 12 is driven in the radial direction of the optical disc 15 by the biaxial actuator 16 during access, the polarization hologram 13
Will move integrally with the objective lens 12. still,
The polarization hologram 13 need only be integrally attached to the objective lens 12, and may be fixed not only to the aperture stop of the objective lens 12 but also to other parts such as the objective lens holder.

Thus, when the return light beam passes through the polarization hologram 13 as shown in FIG.
In each of the regions H1 and H2 of the polarization hologram 13, the 0th-order light I0 that is the ordinary light and the 1st-order lights Le1 and Le2 that are the extraordinary lights are separated in the radial direction.
In addition, the polarization hologram 13 is adapted to directly transmit the light incident from below in FIG.

As a result, the 0th-order light is emitted from the laser coupler 1.
It proceeds to 1 and enters the light receiving portion. that time,
A micro-prism (not shown) provided in the laser coupler 11 divides it into three parts to obtain a focusing error signal.

As shown in FIG. 3, the photodetector 14 has two beams, which are separated in the radial direction by the areas H1 and H2 of the polarization hologram 13, respectively.
That is, for the primary lights Le1 and Le2, the image formation points P
It is configured to have light-receiving surfaces S1 and S2 centered at 1 and P2.

The optical pickup 10 according to this embodiment is configured as described above, and the light beam emitted from the light source section of the laser coupler 11 passes through the polarization hologram 13 and passes through the objective lens 12 to An image is formed at a certain point on the recording surface of the optical disc 15.

The return light beam from the recording surface of the optical disk 15 enters the polarization hologram 13 again via the objective lens 12. Here, the return light beam is related to the diffraction pattern in the radial direction shown by diagonal lines in FIG.
Are separated into three light beams, and the respective light beams are incident on the light receiving portion of the laser coupler 11 and the corresponding light receiving surfaces S1 and S2 of the photodetector 14, respectively.

As a result, the light receiving portions S1 and S2 of the photodetector 14 output the output signals I1 and I2, respectively.

Therefore, the read signal of the optical disk 15 and the focus error signal are obtained by performing the calculation based on the detection signal of the light receiving section of the laser coupler 11, and the output signals of the respective light receiving sections S1 and S2 of the photo detector 14 are obtained. A tracking error signal is generated based on I1 and I2. That is, the tracking error signal TRK
Is

[Equation 1] Will be given with a push-pull signal.

Since the polarization hologram 13 is integrally attached to the objective lens 12,
In the light receiving portions S1 and S2 of the photodetector 14, the primary light of the polarization hologram 13 does not cause spot deviation.

4 and 5 show another embodiment of the optical pickup of the present invention. In this example,
Compared to the optical pickup 10 shown in FIGS. 1 to 3, the configuration is different in that a polarization hologram 20 and a photodetector 21 are arranged instead of the polarization hologram 13 and the photodetector 14, and another configuration. Is the same as the optical pickup 10 of FIG.

In this case, the polarization hologram 20 is divided into four regions H1, H2, H by dividing the radial hologram 20 in the radial direction and the tangential direction.
3, H4. Corresponding to this, the photodetector 21 similarly has four light receiving portions S1, S2, S3.
Equipped with S4.

According to this structure, the returning light beam from the recording surface of the optical disk 15 enters the polarization hologram 20 again via the objective lens 12. Here, the return light beam is transmitted by the polarization hologram 20 to the 0th order light and the 1st order light.
The next light beams Le1, Le2, Le3, and Le4 are separated into five light beams, and each light beam is laser coupler 11 respectively.
Of the photodetector and the corresponding photodetector S of the photodetector 14
It is incident on 1, S2, S3 and S4.

As a result, the light receiving portions S1, S2, S3 and S4 of the photo detector 14 output the output signals I1 and I1, respectively.
I2, I3 and I4 are output.

Therefore, the read signal of the optical disk 15 and the focus error signal are obtained by performing the calculation based on the detection signal of the light receiving portion of the laser coupler 11, and the light receiving portions S1, S2 of the photodetector 14 are obtained.
A tracking error signal is generated based on the output signals I1, I2, I3, I4 of S3, S4. That is, the tracking error signal TRK is

[Equation 2] Will be given by a push-pull signal according to the DPD method.

In the above-mentioned embodiment, as the polarization hologram, a hologram having a characteristic of transmitting ordinary light and diffracting extraordinary light is used. However, the present invention is not limited to this. Obviously, polarizing holograms having the property of transmitting light are also used.

As described above, in the above embodiment, the polarization hologram which is the separation optical system is integrally attached to the objective lens. Therefore, even when the objective lens is driven in the radial direction of the optical disc at the time of access, the primary light of the return light beam separated by the polarization hologram is incident on the light receiving surface of the photodetector without causing spot deviation. Will be done.

Thus, when the tracking error signal or the wobble signal is detected by the primary light incident on the photodetector from the polarization hologram, the stable tracking error signal or the wobble signal is obtained. In this case, since the spot deviation does not occur, an electric circuit for correcting the spot deviation is unnecessary, so that the overall configuration of the optical pickup is simplified and the cost is reduced.

In the above embodiment, the primary light separated by the polarization holograms 13 and 20 is detected by the photodetectors 14 and 21 to generate the tracking error signal, but the invention is not limited to this. Obviously, for example, a wobble signal may be generated.

Further, in the above embodiment, the laser coupler in which a part of the light source and the light receiving portion are formed on the same substrate is used. However, the present invention is not limited to this, and can be applied to all optical pickups that perform push-pull type tracking control with one beam.

[0037]

As described above, according to the present invention, it is possible to obtain a stable tracking error signal or wobble signal by eliminating the spot shift on the photodetector with a simple structure. Pick-up will be provided.

[Brief description of drawings]

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

FIG. 2 is a plan view of a two-part polarization hologram in the optical pickup of FIG.

3 is a plan view of a photodetector in the optical pickup of FIG.

FIG. 4 is a plan view of a four-division polarization hologram in another embodiment of the optical pickup according to the present invention.

5 is a plan view of a photodetector in the optical pickup of FIG.

[Explanation of symbols]

 10 Optical Pickup 11 Laser Coupler 12 Objective Lens 13 Polarizing Hologram 14 Photodetector 20 Polarizing Hologram 21 Photodetector

Claims (3)

[Claims] 1. A light source section for emitting a light beam, an objective lens for irradiating the light beam emitted from the light source section so as to focus on a recording surface of an optical disk, and return light from the recording surface of the disk. A light receiving section for receiving a beam, a polarizing hologram arranged in an optical path between the objective lens and a light source and integrally attached to the objective lens, and a primary separated by the polarizing hologram. An optical pickup comprising a photodetector for receiving light. 2. The optical pickup according to claim 1, wherein a tracking error signal is detected by a photodetector based on the primary light separated by the polarization hologram. 3. The optical pickup according to claim 1, wherein a wobble signal is detected by a photodetector based on the primary light separated by the polarization hologram.