JPH0554421A - Optical pickup - Google Patents

Abstract

PURPOSE:To get rid of occurrence factors of electrical offset of an error detecting system for an optical pickup. CONSTITUTION:Among internal surfaces of a case 15 which houses the optical device of the optical pickup, the part from which excess light goes out is provided with a tapered part 17 of more than 45 deg., and the excess light going out of a polarizing beam splitter 3 is run away to the outside of the case 15. Painting the tapered part provides more effects. Excess light is prevented from coming into an optical system again as stray light, so accurate measurement is permitted.

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 optically reproducing, recording / reproducing, or recording / reproducing / erasing various information on a disc-shaped recording medium.

[0002]

2. Description of the Related Art FIG. 2 is a diagram showing an example of the configuration of a conventional apparatus. (A) is a front view, (b) is a plan sectional view taken along the line BB of (a), and (c) is the left side. Each view is shown.

A light beam emitted from the semiconductor laser 1 is collimated by a collimator lens 2 and then enters a polarization beam splitter 3. At this time, if the polarization characteristics of the polarization beam splitter and the arrangement of the semiconductor laser 1 are properly selected,
60% of the incident light flux is transmitted by the cemented surface, and the remaining 40% is reflected. The transmitted light flux is reflected by the rectangular prism 4, enters the objective lens 14, and is condensed on a disc-shaped recording medium (not shown). The objective lens 14 is supported and driven by an objective lens driving device 16.

After that, the light beam reflected by the disk-shaped recording medium passes through the objective lens 14 and the right-angle prism 4 and again enters the polarization beam splitter 3, the P-polarized component is transmitted, and the S-polarized component is reflected and polarized. It enters the beam splitter 5. By appropriately selecting the polarization characteristics of the polarization beam splitter 5, 70% of the incident light flux is reflected by the joint surface and enters the polarization beam splitter 12.
By appropriately selecting the polarization characteristic of the polarization beam splitter 12, the P-polarized component of the incident light beam is transmitted to the light receiving element 13.
The S-polarized component is captured by the light receiving element 11, and the reproduced signal of the recorded information is detected by the differential output of the light receiving elements 13 and 12.

On the other hand, the remaining 30% of the light flux that has passed through the joint surface of the polarization beam splitter 5 passes through the λ / 4 plate 6 and becomes circularly polarized light, which is then incident on the concave mirror half mirror 7.
% Of the transmitted light is captured by the light receiving element 8, and the track error signal is detected. The remaining 50% of the reflected light flux passes through the λ / 4 plate 6 again while being condensed and enters the polarization beam splitter 5, but this time, the azimuth angle of polarization with respect to the light flux after exiting the polarization beam splitter 3 is increased. Since it becomes S-polarized light having an angle of 90 ° and enters the polarization beam splitter 5, 100% of the entire light flux is reflected by the cemented surface, and a focus error signal is generated by the knife edge method composed of the knife edge 9 and the light receiving element 10. Was being detected.

[0006]

In the above-mentioned conventional apparatus, the polarization characteristic of the polarization beam splitter 3 is set to P-polarized light in order to reduce the return light to the semiconductor laser 1 as much as possible.
Although 0% is transmitted and 40% is reflected, the light amount of 60% of the light flux emitted from the semiconductor laser 1 is not used for this reason. The problem here is that, as shown in FIG. 2 (b), after 60% of the surplus light is reflected by the polarization beam splitter 3, it is returned to the polarization beam splitter by the internal reflection of the case 15. It is incident. Specifically, this surplus light reaches the polarization beam splitter 7 of the error detection system, becomes stray light, and causes a DC electric offset in the focus detection system and the track detection system. Further, this offset can be electrically corrected when the reproducing power of the semiconductor laser 1 is constant, such as when the apparatus is in the reproducing state. Therefore, when the reproducing state is changed to the recording state, the emission power of the semiconductor laser 1 is changed. Since it is added, accurate offset correction becomes impossible, and accurate focusing control and tracking control of the objective lens 14 cannot be performed.

[0007]

In order to solve the above problems, the present invention provides a semiconductor laser as a light source, a collimating lens for collimating a light beam emitted from the semiconductor laser,
A first polarization beam splitter arranged in front of the semiconductor laser, a right-angle prism arranged in front of the first polarization beam splitter, and an objective lens for condensing a light beam emitted from the right-angle prism on a disc-shaped recording medium. And an objective lens driving device for driving the objective lens, a second polarizing beam splitter arranged in front of the emission surface of the S polarization component of the first polarizing beam splitter, and a second polarizing beam splitter. λ / 4 plate, concave mirror half mirror bonded to λ / 4 plate, and S of second polarization beam splitter
A third polarizing beam splitter arranged in front of one of the exit surfaces of the polarization components, a knife edge arranged in front of the other, and at least 2 arranged in front of the knife edge.
A first light receiving element which is divided or more, a concave mirror half mirror,
A second light receiving element that is arranged in front of the concave mirror half mirror and is at least divided into two or more, first and second light receiving elements that are arranged in front of each of the exit surfaces of the second polarization beam splitter, and these By providing a case accommodating the optical element and a taper portion of at least 45 ° or more in front of the S-polarized component of the first polarization beam splitter of the case, it is possible to prevent excess light from returning to the optical system again. is there.

In the above, by applying a black coating to the tapered portion, it becomes more effective.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

1A and 1B are views showing the configuration of an embodiment of the present invention. FIG. 1A is a front view, FIG. 1B is a plan sectional view taken along the line AA in FIG. 1A, and FIG. Each view is shown.

A light beam emitted from the semiconductor laser 1 is collimated by a collimator lens 2 and then incident on a polarization beam splitter 3 arranged in front. At this time, the polarization beam splitter 3 transmits 60% of P polarized light and 1% of S polarized light.
Since the polarization characteristic is provided so that the light is reflected by 100%, and the light flux after being emitted from the collimator lens 2 is arranged so as to correspond to the P-polarized light, 60% of the light amount is transmitted through the polarization beam splitter 3 and the right angle prism. 40% of the light is reflected and travels in the direction of the case 15.

100% of the light incident on the prism 4 is reflected, enters the objective lens 14, and is focused on a disc-shaped recording medium (not shown) under focusing control and tracking control.

The light beam reflected by the disk-shaped recording medium again passes through the objective lens 14 and is reflected by the right-angle prism 4 and is re-incident on the polarization beam splitter 3 and P
The polarization component is transmitted and the S polarization component is reflected and enters the polarization beam splitter 5. Since the polarization beam splitter 5 has such a polarization characteristic that 30% of P-polarized light is transmitted and 100% of S-polarized light is reflected, 70% of the light beam incident on the polarization beam splitter 5 has a polarization characteristic of the polarization beam splitter 5. The light is reflected by the cemented surface and enters the front polarization beam splitter 12. Since the polarization beam splitter 12 has polarization characteristics such that 50% of P-polarized light is transmitted and 100% of S-polarized light is reflected, the P-polarized component of the light beam incident on the polarization beam splitter 12 is transmitted to the light receiving element 13 and S-polarized light. The component is captured by the light receiving element 11, and the reproduced signal of the recorded information is detected by the differential output of the light receiving elements 12 and 13.

The remaining 30% of the light flux that has passed through the joint surface of the polarization beam splitter 5 passes through the λ / 4 plate 6 in front of it, becomes circularly polarized light, and enters the concave mirror half mirror 7. 50% of the light flux incident on the concave mirror half mirror 7 is transmitted and is caught by the light receiving elements 8 of at least two divisions in the front, and the track error signal is detected. The remaining 50% of the reflected light flux is λ again while being condensed.
The light passes through the / 4 plate 6 and enters the polarization beam splitter 5, but this time it becomes S-polarized light having an azimuth angle of 90 ° with respect to the light beam after exiting the polarization beam splitter 3, and enters the polarization beam splitter 5. Therefore, 100% of the total luminous flux is reflected by the cemented surface, 50% of the luminous flux is shielded by the knife edge 9 arranged in front, and the remaining luminous flux is incident on the light receiving element 10 of at least two divisions. The focus error signal is detected by the knife edge method including the light receiving element 10.

On the other hand, the remaining 40% of the amount of light reflected by the polarization beam splitter 3 toward the case 15 is reflected laterally by the taper portion 17 having a 45 ° taper attached to the inner wall of the case, and is reflected outside the case 15 of the pickup. It will be escaped and will not enter the optical system again and become stray light. In this embodiment, since the tapered portion 17 is painted black, the amount of light reflected by the tapered portion 17 and emitted to the outside of the case 15 is reduced.

[0016]

As described above, according to the present invention, the taper portion is provided on the inner surface of the case of the pickup, and the black coating is further applied to allow the excess light to escape to the outside of the pickup, so that the inside of the optical system can be prevented. There is an effect that it can be prevented from being incident as stray light again.

This also has the effect of eliminating the factor that causes a DC offset in the focus detection system and the track detection system.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention, (a)
Is a front view, (b) is a plan sectional view taken along line AA of (a),
(c) represents the left side view.

FIG. 2 is a diagram showing a configuration of an example of a conventional device, (a) is a front view, (b) is a plan sectional view taken along line BB of (a),
(c) represents the left side view.

[Explanation of symbols]

 1 Semiconductor Laser 2 Collimator Lens 3, 5 Polarizing Beam Splitter 4 Right Angle Prism 6 λ / 4 Plate 7 Concave Mirror Half Mirror 8, 10, 11 Photoreceptor 9 Knife Edge 12 Polarizing Beam Splitter 13 Photoreceptor 14 Objective Lens 15 Case 16 Objective Lens Drive Device 17 Tapered part

Claims (2)

[Claims] 1. A device for reproducing, recording / reproducing, or recording / reproducing / erasing various information on a disc-shaped recording medium, wherein a semiconductor laser as a light source and a light beam emitted from the semiconductor laser are collimated light. Collimating lens, a first polarization beam splitter arranged in front of the semiconductor laser, a right-angle prism arranged in front of the first polarization beam splitter, and a light beam emitted from the right-angle prism in the disk shape. An objective lens for focusing light on the recording medium,
An objective lens driving device for driving this objective lens, and a second polarization beam splitter arranged in front of one of the exit surfaces of the S polarization component of the first polarization beam splitter,
A 4 / λ plate joined to the second polarization beam splitter, a concave mirror half mirror joined to the 4 / λ plate, and one of the exit faces of the S polarization components of the second polarization beam splitter in front of A third polarization beam splitter arranged, a knife edge arranged in front of the other, and a first splitting section arranged in front of the knife edge of at least two or more.
Light receiving element, a second light receiving element of at least two divisions arranged in front of the concave mirror half mirror, and first and second portions arranged in front of each emission surface of the second polarization beam splitter. An optical pickup comprising a light receiving element and a case accommodating these optical elements, at least 45 ° in front of the other emission surface of the S-polarized component of the first polarization beam splitter of the case. An optical pickup having the above tapered portion. 2. The optical pickup according to claim 1, wherein the taper portion of the case is painted black.