JP3198161B2 - Optical pickup device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device for a drive device for a magneto-optical disk or an optical disk.

[0002]

2. Description of the Related Art As an optical pickup device for a drive device for a magneto-optical disk or an optical disk , for example, as shown in FIG. 6, a laser beam emitted from a semiconductor laser 11 as a light source is converted into a parallel light beam by a collimating lens 12, and an objective lens is formed. The light source system 1 forms light spots on the recording medium 3 by condensing light from the light source 14, and the collimated lens 12 and the objective lens 14 collimate light beams formed by condensing reflected light from the light spots with the objective lens 14. Are directed in a direction different from the direction toward the light source 11 by the beam splitter 13 provided therebetween, and the polarization beam splitter 2 is placed in the optical path of the reflected light beam.
1. An optical pickup comprising: a condensing lens 22; a cylindrical lens 23; a quadrant photodetector 24; and a detection system 2 including a split optical detector 25 in the optical path split by the beam splitter 21. Devices are conventionally known.

FIG. 7 is a circuit diagram of a detection system of the optical pickup device. The quadrant photodetector 24 is composed of two straight lines 24a, 24b, 24c, 2
4d, and the two-segment photodetector 25 is
It is divided into two portions 25a and 25b by a straight line passing through the optical axis and extending in the track direction of the recording medium. The spot shape in the quadrant photodetector 24 becomes a circle as shown in the figure when the recording medium 3 is focused, and when the focal point is out of focus, the major axis is 45 degrees with respect to the quadrant due to astigmatism. It becomes an ellipse extending in the direction of °. When the spot of the laser beam is on the track, the light receiving amounts of the two portions 25a and 25b of the two-segment photodetector 25 are the same. Is generated.

Therefore, the circuit shown in FIG. 7 uses two parts 24a, 2a on the diagonal line of the four-divided photodetector 24.
A focus error signal is obtained from the difference between the sums of the respective light receiving outputs of 4c, 24b, and 24d.
5, a tracking error signal is obtained from the difference between the received light outputs of the two portions 25a and 25b, and the magneto-optical reproduction signal is obtained from the difference between the total received light output of the 4-split photodetector 24 and the total received light output of the 2-split photodetector 25. can get.

As shown in FIG. 6, the magneto-optical disk 3 is formed by laminating a perpendicular magnetic film 3b on a transparent substrate 3a.
It is advantageous to use the polycarbonates used for D and the like. However, since the polycarbonate has a large birefringence, the peripheral portion of the light beam guided to the detection system is elliptically polarized as shown in FIG. Disturbance due to elliptically polarized light or the like affects the focus error signal.

Also, disturbances such as optical axis shifts caused by the reflected light flux of the recording medium affect the tracking error signal detection.

Therefore, a pickup device capable of performing a stable servo control by reducing the influence of disturbance generated on the outer peripheral portion of the reflected light flux of the recording medium in the detection of the focus error signal and the tracking error signal of the optical pickup device. It is disclosed in Japanese Unexamined Patent Publication No. 2-236830.

FIG. 9 is a diagram showing the configuration, and the configuration of the light source system 1 is no different from the conventional pickup device shown in FIG. However, the detection system 4 differs from the conventional one in that the polarization beam splitter 41 is provided on the optical path of the reflected light beam split by the beam splitter 13, and the compound lens 42 is provided on the optical path of the P-polarized light passing therethrough. The five-divided photodetectors 43 are arranged, and the S-polarized light reflected by the polarization beam splitter 41 is received by a photodetector 44 having a single light receiving surface. As shown in FIG. 10, the compound lens 42 has a cylindrical lens 42a
Are formed. A long focal length lens portion 42b having a large radius of curvature is provided at a central portion facing the cylindrical lens 42a on the emission side surface, and a short focal length lens portion 42c having a small radius of curvature is formed at an outer peripheral portion thereof.

As shown in FIG. 11A, the light receiving surface of the five-divided photodetector 43 has a small circular portion 43e at the center.
Four generally square portions 43a, 43b, 4 around it
It is divided into five parts 3c and 43d.

When the light beam transmitted through the polarizing beam splitter 41 is incident on the compound lens 42, the outer peripheral portion of the light beam becomes a short focal length lens portion 4 of the compound lens 42 as shown in FIG.
2c, a small circular portion 43 at the center of the five-divided photodetector 42
e. The central portion of the light beam is provided with astigmatism by the cylindrical lens 42a of the compound lens 42 without giving any disturbance, and the four regions 43a, 43b, 4
The light is condensed on 3c and 43d, and according to the focus state, FIG.
1 (a), (b), and (c), as shown in S1, S
2. A spot having the shape of S3 is formed. When S2 is in focus,
S1 and S3 are examples of spot shapes when the focus is shifted from the in-focus position in the reflection direction.

Therefore, the circuits shown in FIG.
c and the sum of the respective light receiving outputs and the area 43 at the other diagonal position
The output of the difference between the sum of the respective light receiving outputs b and 43d is output as a focus error signal. The detection system 4 is adjusted so that the focus error signal becomes zero when the diameter of the beam irradiated on the recording medium 3 becomes minimum.

Also, two adjacent regions 43b, 43c and 43 of the four peripheral regions of the five-divided photodetector 43
The difference between the sums of the light receiving outputs a and 43d is output as a tracking error signal.

Further, the light receiving output of the photodetector 44 of the single light receiving section is subtracted from the sum of the light receiving outputs of the five regions of the five-split photodetector 43, and the magneto-optical reproduction signal is differentially detected.

However, in this example, a complex lens having a complicated shape is required in order to reduce the influence of disturbance generated on the outer periphery of the reflected light flux from the recording medium, and there is a problem that the cost is high.

[0015]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a recording system for detecting a tracking error signal using a simple optical element in a detection system of an optical pickup device of a magneto-optical disk or optical disk drive. Eliminates the effects of disturbances such as optical axis deviation caused by the reflected light beam from the lens, and in detecting a focus error signal,
An object of the present invention is to provide an optical pickup device that can reduce the influence of disturbance due to elliptically polarized light or the like generated by a light beam reflected from a recording medium.

[0016]

In order to solve the above-mentioned problems, an optical pickup device according to the present invention focuses light from a light source on a recording medium to form a minute spot, and uses the reflected light as an objective lens. A light beam which is condensed into a parallel light beam, directed by a beam splitter in a direction different from the direction toward the light source, receives the reflected light beam with a photodetector, and generates a servo signal based on the received light output. In the optical pickup device of the magnetic disk or optical disk drive device, in the optical path of the parallel reflected light flux separated by the beam splitter,
A two-divided photodetector having a circular opening at the center for receiving the outer peripheral portion of the reflected light beam and passing through the central portion, a polarizing beam splitter for separating the light passing through the circular opening, and separated by the polarizing beam splitter A light detector for detecting the reflected light and the transmitted light, respectively; a means for detecting a tracking error signal using an output of the two-divided light detector; and a light detector for detecting the reflected light and the transmitted light, respectively. It is characterized by comprising a means for detecting a focus error signal by using one output, and a means for detecting a reproduction signal by using both outputs of a photodetector for detecting the reflected light and the transmitted light.

[0017]

According to the above construction, the reflected light flux from the recording medium which travels in a direction different from the direction toward the light source by the beam splitter is divided into a peripheral portion where elliptically polarized light, which is a disturbance, is generated and an outer peripheral portion of the circular aperture of the two-divided photodetector. To reduce disturbance effects.
It is .

Therefore , a focus error signal is detected without being affected by disturbance, and a tracking error signal is detected from a difference between light receiving outputs of two areas outside a circular aperture of the two-segment photodetector.

One of the optical elements used in the detection system of the present invention
Examples thereof include a simple condenser lens, a cylindrical lens, a two-segment photodetector having a circular opening in a flat plate, and a four-segment photodetector conventionally used. The shape is incomparably simple as compared with the compound lens of the device proposed in the gazette, and the focus error signal and tracking error signal detection circuit is also simplified.

By changing the arrangement of the condenser lens and the cylindrical lens, the size of the apparatus can be reduced while achieving the same function and effect. The details will be made clear by the description of the embodiments which will be described in detail below with reference to the drawings.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the optical pickup device of the present invention. The optical pickup device is the same as the conventional device in that it comprises a light source 1 and a detection system 2, and the configuration of the light source system 1 is exactly the same as the conventional device described with reference to FIG. As the optical elements constituting the detection system, those having the same functions as conventional ones are used considerably. Therefore, members having the same function are denoted by the same reference numerals.

On the optical path in the detection system 2 for the reflected light flux from the recording medium 3 reflected by the beam splitter 13, a two-segment photodetector 46 having a circular opening at the center, a polarization beam splitter 41, a condenser lens 22, The cylindrical lens 23 and the quadrant photodetector 24 are arranged in this order, and a photodetector 44 having a single light receiving area is provided at a position where the light beam reflected by the polarization beam splitter 41 can be received.

Condensing lens 22, cylindrical lens 2
The point that the focus error signal detection system 45 is constituted by the three- and four-divided photodetectors 24 is the same as the conventional optical pickup device described with reference to FIG. As shown in FIG. 2, the light is blocked by the periphery of the circular opening 46a of the two-segment photodetector 46.
The focus error signal can be detected without being affected by disturbance. The tracking error signal is
Unlike the device proposed in the above-mentioned Japanese Patent Application Laid-Open No. 2-236830, the two regions 46b and 46 of the two-segment photodetector 46 which also functions as a member for blocking the outer periphery of the light beam without using the five-segment photodetector.
Since the detection can be performed from the difference between the light receiving signals c, the detection circuit configuration is simplified.

It should be noted that the magneto-optical reproduction signal is supplied to a four-division detector 24.
And the light receiving output of the photodetector 44.

A circuit for obtaining a focus error signal, a tracking error signal, and a magneto-optical reproduction signal from the outputs of the respective photodetectors can be easily analogized to the circuit of the conventional apparatus (FIG. 7), and is not shown. I do.

FIG. 3 is a diagram showing a configuration of a detection system 2 according to another embodiment of the optical pickup device of the present invention. In this embodiment, the condenser lens 22 is used as the beam splitter 13 of the light source system 1.
And the two-segment photodetector 46. At the position of the two-segment photodetector 46, the reflected light beam is contracted by the action of the condenser lens 22, so that the light receiving area of the two-segment photodetector 46 having a circular aperture and the cylindrical lens 23 of the focus error signal detection system 45 And quadrant detector 24
Can be reduced. As a result, the weight of the optical pickup device can be reduced.

In the detection system of still another embodiment of the optical pickup device shown in FIG. 4, the condenser lens 22 is fitted in a central circular opening of the two-part photodetector 46 . According to this configuration, the diameter of the reflected light beam at the position of the two-segment photodetector 46 is not different from that of the configuration of FIG. 1, but the cylindrical lens 23 and the four-segment photodetector 24 of the focus error signal detection system 45 The size of the detection system 2 can be reduced as in the embodiment of FIG.

In the detection system of another embodiment of the optical pickup device shown in FIG. 5, the condensing lens 22 is provided between the beam splitter of the light source system and the two-segment photodetector 46 in FIG. 19, except that the cylindrical lens 23 is fitted in the circular opening of the two-divided photodetector 46. As a result, the focus error signal detection system 45 can be almost integrated with the two-segment detector 46, and the size of the detection system 2 can be further reduced.

[0030]

As described above, according to the present invention, the focus error is eliminated by using an optical element having a simple shape to remove the influence of disturbance such as elliptically polarized light generated around the reflected light flux of the recording medium. A servo signal such as a signal or a tracking error signal is obtained, and stable servo control can be performed at low cost.

According to the second, third and fourth aspects of the present invention, the size of the optical pickup device can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of an optical pickup device according to an embodiment of the present invention.

FIG. 2 is a perspective view of the two-piece detector.

FIG. 3 is a cross-sectional view illustrating a configuration of a detection system according to another embodiment of the present invention.

FIG. 4 is a sectional view showing a configuration of a detection system according to still another embodiment of the present invention.

FIG. 5 is a sectional view showing a configuration of a detection system according to still another embodiment of the present invention.

FIG. 6 is a cross-sectional view illustrating an example of a configuration of a conventional optical pickup device.

FIG. 7 is a circuit diagram of the detection system.

FIG. 8 is an explanatory diagram illustrating a problem when a material having a large birefringence is used for a substrate of a recording medium.

FIG. 9 is a cross-sectional view showing an example of a configuration of a known optical pickup device for solving the above problem.

FIG. 10 is a cross-sectional view showing a configuration of a compound lens used in the optical pickup device.

FIG. 11 shows the light receiving surface of a five-segment photodetector used in the optical pickup device, and (a), (b),
FIG. 3C is a plan view showing a spot shape that changes depending on a focus state.

FIG. 12 is an explanatory diagram for explaining the operation of the compound lens of the optical pickup device.

FIG. 13 is a circuit diagram of a detection system of the optical pickup device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source system 2 Detection system 3 Recording medium 3a Transparent substrate 12 Collimating lens 13 Polarizing beam splitter 14 Objective lens 22 Condensing lens 23 Cylindrical lens 24 Quadrant photodetector 41 Polarization beam splitter 44 Photodetector 46 2-part detector 46a Round Opening

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G11B ^7/ 09-7/22 G11B 11/00-11/105

Claims (4)

(57) [Claims] 1. A light spot from a light source is condensed on a recording medium to form a minute spot, and the reflected light is condensed by an objective lens into a parallel light flux, and a direction different from the direction toward the light source by a beam splitter. In the optical pickup device of a magneto-optical disk or optical disk drive device configured to receive the reflected light beam with a photodetector and generate a servo signal based on the received light output, the parallel light beam separated by the beam splitter In the optical path of the reflected light beam, a two-segment photodetector having a circular opening at the center for receiving the outer peripheral portion of the reflected light beam and passing through the central portion, a polarizing beam splitter for separating the light passing through the circular opening, A photodetector for detecting the reflected light and the transmitted light separated by the beam splitter; and providing a tracking error signal using an output of the two-divided photodetector. Output means, a means for detecting a focus error signal using one output of a photodetector for detecting the reflected light and the transmitted light, and a photodetector for detecting the reflected light and the transmitted light, respectively. Means for detecting a reproduced signal using an output. 2. The optical pickup according to claim 1, further comprising a condensing lens for condensing the parallel reflected light flux between the beam splitter and the two-segment photodetector. apparatus. 3. The optical pickup device according to claim 1, wherein a condensing lens for condensing the parallel reflected light beam is fitted in a circular opening at the center of the two-divided photodetector. 4. A condensing lens for converging the parallel reflected light beam is provided between the beam splitter and the two-divided photodetector, and a cylindrical opening is provided at a center circular opening of the two-divided photodetector. The optical pickup device according to claim 1, wherein a lens is fitted.