JPH02201742A - Optical pickup - Google Patents

Abstract

PURPOSE:To substitute one focus detecting system with the other focus detecting system even when offset is generated in the other focus detecting system, and to correctly detect the focus by providing a holder, in which the directions of the dividing lines of respective photodetectors are arranged so as to be orthogonal in the two focus detecting systems. CONSTITUTION:Two luminous fluxes which have not been shaded by a knife 11a are received by front photodetectors 12a and 12b. The dividing line of the photodetector 12a is arranged so as to correspond to an edge shading it in the parallel direction to the optical axis of a plano-convex lens 8 of the knife 11a, and the dividing line of the photodetector 12b is arranged so as to correspond to an edge shading it in the vertical direction of the optical axis, and the elements are integrally held by a holder 13. Consequently the two focus detecting systems can be formed by respective differential outputs. Thus even when the offset is generated in either one of the focus detecting systems, the correct detection is attained by the remaining detecting system.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup for optically recording and reproducing various information on a disc-shaped recording medium.

[Conventional technology]

Conventionally, this type of device has the configuration shown in FIG.

The light beam emitted from the semiconductor laser 21 passes through the collimating lens 2
After being made into parallel light by 2, the light enters a polarizing beam splitter 23 placed in front. At this time, the beam splitter 23 is arranged so that the light beam emitted from the collimating lens 22 enters as P-polarized light, so that the light beam incident on the beam splitter 23 is 100% transmitted and reflected by the total reflection mirror 24, and is λ/ After passing through the fourth plate 25, it becomes circularly polarized light and is sent to the disc-shaped recording medium 2 by the objective lens 26.
The light is focused on 7.

Next, the light beam reflected by the disk-shaped recording medium 27 passes through the objective lens 26 again and passes through the λ/4 plate 25,
The light becomes linearly polarized light having an azimuth angle of 90° with the light beam emitted from the semiconductor laser 21, is reflected by the total reflection mirror 24, and enters the polarizing beam splitter 23 again. At this time, this light beam enters the splitter 23 as S-polarized light and is reflected by the junction surface coated with the dielectric multilayer film, and is reflected by the beam splitter 29 to which the plano-convex lens 28 is joined.
While being focused, 50% of the light is transmitted and captured by the light receiving element 30 placed in front of the light, which performs tracking control and high frequency signal (hereinafter referred to as RF multiplied signal detection).
The remaining 50% of the light incident on the beam fritter 29 is reflected in a direction perpendicular to the optical axis of the plano-convex lens 28 by the joint surface coated with a dielectric multilayer film, and is reflected perpendicularly to the optical axis by a knife 31 in front of the plano-convex lens 28. Further 50% of the light is blocked within the plane, and is captured by the light receiving element 32, and focus control is performed by differential output.

[Problem to be solved by the invention]

In the conventional configuration device described above, focus control is performed using a knife-edge method from the beam splitter 29 to the plano-convex lens 28.
The light beam emitted in the direction perpendicular to the optical axis is blocked by 50% in the plane perpendicular to the optical axis by the knife 31, and the dividing line is the edge of the knife 31 using the light receiving element 32 which is divided into two or more parts. Control is performed using the differential output to capture the parallel objects, but if an offset occurs in the differential output of the light receiving element 32 due to an external impact, etc., not only will focus control become impossible, but the focus detection function will also be disabled. In order to recover, the light receiving element 32 must be adjusted again.

[Means to solve the problem]

In order to solve the above problems, the present invention uses a polarization splitting means to enable the adoption of a two-line focus detection system based on the knife method, and the two knifes are installed in directions orthogonal to each other.

〔Example〕

Next, an embodiment of the present invention will be described with reference to FIGS. 1, 2, 3, and 4. After the light beam emitted from the semiconductor laser 1 is made into parallel light by the collimating lens 2,
The light enters a polarizing beam splitter 3 placed in front.

At this time, the splitter 3 is arranged so that the light beam after exiting the collimating lens 2 enters as P-polarized light, so the light beam incident on the splitter 3 is 100% transmitted and reflected by the total reflection mirror 4, and is reflected by the λ/4 plate. After passing through 5, the light becomes circularly polarized light and is focused onto a disc-shaped recording medium 7 by an objective lens 6.

Next, the light beam reflected by the disk-shaped recording medium 7 passes through the objective lens 6 again and passes through the λ/4 plate 5, and becomes linearly polarized light whose azimuth angle with the light beam after emission from the semiconductor laser 1 is 90°. Then, it is reflected by the total reflection mirror 4 and enters the polarizing beam splitter 3 again, so it is reflected by the junction surface coated with the dielectric multilayer film, enters the beam splitter 9 to which the plano-convex lens 8 is joined, and is converged at 50. %
is transmitted and captured by the light receiving element 10 placed in front of it, and tracking control and RF signal detection are performed.

The remaining 50% of the light incident on the beam splitter 9 is reflected by the dielectric multilayer coated junction surface in a direction perpendicular to the optical axis of the plano-convex lens 8 and enters the Savart plate 14. At this time, the Savart plate 14 is arranged so that the optical axes 16 of the two birefringent bodies are joined in opposite directions and are incident obliquely to the optical axis 16, so that the first birefringent The light beam that enters the body becomes two polarized lights that are perpendicular to each other. The light beam corresponding to the ordinary ray continues as it is, but the light beam corresponding to the extraordinary ray does not follow Snell's law and travels to the second birefringent body. However, since the optical axis 16 is arranged in the opposite direction to the first birefringent body, the light beam that was an extraordinary ray in the first birefringent body becomes an ordinary ray, and the light that was an ordinary ray becomes an extraordinary ray. Since the light beam becomes a light beam and travels obliquely, as a result, it is emitted from the Savart plate 14 as two completely parallel condensed light beams.

Next, one of the two light beams emitted from the Savart plate 14 is perpendicular to the optical axis of the plano-convex lens 8, and the other is parallel to the optical axis by a knife 11 as shown in FIG. The light is blocked by 50% in each plane. At this time, as shown in FIG. 2, the knife lla is dropped into the casing 15, which is provided with a V-shaped groove that can block 50% of light in the direction perpendicular to the optical axis of the plano-convex lens 8.
It is only necessary to adjust a in the direction parallel to the optical axis of the plano-convex lens 8.

The two beams of light that are not blocked by the knife lla are received by the front light receiving elements 12a and 12b, respectively, but as shown in FIG. The light-receiving element 12b is held integrally by the holder 13 so that its dividing line coincides with the edge that blocks light in the direction perpendicular to the optical axis of the plano-convex lens 8. , two focus detection systems are formed by the respective differential outputs. As a result, even if the holder 13 moves in a direction perpendicular to the optical axis of the plano-convex lens 8 due to an external impact, causing an offset in the light receiving element 12a, no offset occurs in the light receiving element 12b; Even if the holder 13 moves in a direction parallel to the optical axis of the plano-convex lens 8 and an offset occurs in the light receiving element 12b, no offset occurs in the light receiving element 12a. therefore,
Even if an offset occurs in one of the focus detection systems, accurate detection is possible by using the other focus detection system.

〔Effect of the invention〕

As described above, according to the present invention, in two focus detection systems, by having holders arranged such that the directions of the dividing lines of the respective light receiving elements are orthogonal,
Even if an offset occurs in one of the focus detection systems due to an external impact or the like, accurate detection can be achieved by replacing it with the other focus detection system.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a diagram for explaining the shape of a casing used in an embodiment of the present invention, and Fig. 3 is a diagram showing an embodiment of the present invention.
The figure is a diagram for explaining the shape of a knife used in an embodiment of the present invention, Figure 4 is a diagram for explaining a holder for a light receiving element used in an embodiment of the present invention, and Figure 5 is a diagram for explaining a conventional device. FIG. 1...Semiconductor laser, 2...Collimating lens, 3...Polarizing beam splitter, 4...
...Total reflection mirror ....λ/4 plate, 6.
...Objective lens, 7...Disc-shaped recording medium, 8...Plano-convex lens, 9...Beam splitter, 10.12a, 12b... ...light receiving element, 11. lla...knife, 13...
Holder, 14...Savart plate, 15...
・Housing, 16...Optical axis. Agent Patent Attorney Susumu Uchihara Anojozono $4buchi

Claims (2)

[Claims] (1) Used in an optical information recording device that optically records/reproduces various information on a disc-shaped recording medium, or only reproduces it, and detects the out-of-focus of a light spot on the disc-shaped recording medium by a knife-edge method. In an optical pickup for detecting out-of-focus, the light beam for detecting the focus shift is divided into two light beams by polarization splitting, and each of these divided light beams is divided into two light beams using a knife edge method using a knife edge in a direction orthogonal to each other. An optical pickup characterized in that it has a means for detecting with a light receiving element. (2) The optical pickup according to claim 1, wherein the polarization division is performed by a Savart plate using a birefringent crystal.