JPS61287042A - Optical image pickup device - Google Patents

Abstract

PURPOSE:To miniaturize an optical image pickup device forming a knife edge in common use with a reflection film to the side face of a polarized prism and using the reflection film so as to fold the optical path of a focus error signal detection optical system. CONSTITUTION:The knife edge is formed with a thin film in common use for a reflection film 7 in a focus error signal detection optical system using the knife edge, the reflection film 7 is formed directly to a 1/4 wavelength plate 6 sticked to a polarized prism 3 and the reflection film 7 folds the optical path of the focus error signal detection optical system. Thus, the length of the focus error signal detection optical system is reduced. Further, the knife edge which has been constituted conventionally by a metallic plate is formed by the reflection film 7 to attain light weight.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention always and accurately positions the laser spot of an optical pickup that optically detects information recorded on an optical disc on the recorded information surface of the optical disc. The present invention relates to an optical pickup device.

``Prior Art'' A conventional optical pickup device of this type is shown in FIG. In the recorded disc, B is a semiconductor laser that generates a laser for reading information on optical disc A, C is a polarizing prism, D is a quarter-wave plate, and E is a device that directs the above laser onto the recorded information surface of optical disc A. This is an objective lens that focuses light into a predetermined spot size.

Next, a focus error signal detection optical system disposed on the right side of the polarizing prism C is composed of a knife F made of a metal plate and a photodetector G such as a photodiode. The photodetector G is placed at the focal position of the detection system (the position where the spot size is minimum), and the knife F is placed between the polarizing prism C and the photodetector G.

Next, two effects will be explained. First, the P-polarized light emitted from the semiconductor laser B is transmitted through the polarizing film of the polarizing prism C, and is changed from linearly polarized light to circularly polarized light by a quarter-wave plate.

This circularly polarized laser beam is focused by an objective lens E onto the signal surface of the optical disk A at a predetermined spot size. The reflected light on the signal surface of the optical disk is circularly polarized light whose rotation direction is opposite to that at the time of incidence, and by passing through the 174-wavelength plate again, linearly polarized light whose polarization direction is rotated by 90" from that at the time of incidence ( The light becomes S-polarized light, and is reflected by the polarizing film surface of the polarizing prism C toward the focus error signal detection optical system.

In the focus error signal detection optical system, the knife F generates a focus error signal on the photodetector G by blocking 1/2 of the light beam around the optical axis of the detection system as the optical disk A moves up and down. let Then, based on this focus error signal, the optical pickup is always performed on the optical disc A.
Control so that it is held in the correct position.

"Problems to be Solved by the Invention" However, in the conventional optical pickup device, the focus error signal detection optical system is constructed using the Knifezi method.
The detection optical system has a long protruding shape in the direction perpendicular to the incident optical axis, which has the drawback of making it difficult to miniaturize the optical pickup.

The present invention has been made in order to solve the above-mentioned drawbacks, and a knife is formed on the side surface of a polarizing prism to also serve as a reflective film, and this reflective film is used to reduce the focus error signal. The object of the present invention is to provide a miniaturized optical pickup device by bending the optical path of a detection optical system.

"Structure of the Invention" The present invention will be described below based on embodiments of the drawings. 1st
The figure is a schematic configuration diagram of an optical pickup device according to the present invention, and FIG. 2 is an enlarged exploded perspective view of the main parts.

In the drawing, l is an optical disk on which information is optically recorded, 2 is a semiconductor laser that generates a laser for reading information on the optical disk, 3 is a polarizing prism, and 4 is the optical disk of the polarizing prism 3! A quarter wavelength plate 5 disposed on the side is an objective lens that focuses the laser beam onto the information surface of the optical disc 1 to a predetermined spot size.

Next, regarding the focus detection optical system, 6 is a 174-wave plate directly glued to the right side of the polarizing prism 3, and 7 is a thin film formed in the lower half area of the quarter-wave plate 6. It is a knife and a reflective film. This knife cum reflection 1
III7 (hereinafter abbreviated as reflective film) is formed by depositing or sputtering a thin metal film such as an aluminum film. Reference numeral 8 denotes a photodetector such as a two-split optical sensor for detecting focus error, which is bonded to the left side surface of the polarizing prism 3. Reference numeral 9 denotes a photodetector, such as a two-split optical sensor for tracking error detection, which is bonded on top of the reflective film 7 formed on the right side of the polarizing prism 3. ``Action of the Invention'' Next, the operation of the above embodiment will be explained. do.

First, P-polarized light emitted from the semiconductor laser 2 passes through the polarizing film of the polarizing prism 3, and is converted from linearly polarized light to circularly polarized light by the 1/4 wavelength plate 4. This circularly polarized light is focused onto the signal surface of the optical disc 1 by the objective lens 5.
Next, the reflected light reflected from the signal surface of the optical disc l is
It is converted into circularly polarized light with the rotation direction opposite to that at the time of incidence. This circularly polarized light passes through the 1/4 wavelength plate 4 again, and this time becomes linearly polarized light (S-polarized light) with the polarization direction rotated by 90 degrees, and is reflected by the polarizing film of the optical prism 3. Introduced into the focus detection optical system.

The light entering the focus error signal detection optical system is 1/4
By passing through the wavelength plate 6, it is converted into circularly polarized light again, and by the reflective film 7 formed in the lower half area of the 174 wavelength plate 6, the upper half of the light beam is transmitted and the lower half is reflected. The light becomes circularly polarized light with a rotation opposite to that of the incident light due to reflection by the zero-reflection film 7, which can bend the optical path, and then passes through the quarter-wave plate 6 again, so that the polarization direction is rotated by 90'' compared to the time of incidence. (Linearly polarized light) The light becomes P-polarized light, can pass through the polarizing film of the polarizing prism 3, and reaches the photodetector 8 of the two-split optical sensor for detecting focus error.

On the other hand, tracking error detection uses light passing through the upper half area of the polarizing prism 3 that is not reflected.
Detection is performed by a two-part photodetector 9 for tracking error detection.

"Other Embodiments" FIGS. 3 to 5 show other embodiments of the optical pickup device according to the present invention. In this embodiment, a thin micro Fresnel lens 10 is used in place of the objective lens 5 of the above embodiment, and is placed on the 174 wavelength plate 4 glued to the optical disk l side of the polarizing prism 3. has been done. The micro Fresnel lens IO is also called a Fresnel zone plate, grating lens, computer hologram, Fresnel ring, etc., and is published in Proceedings of the Institute of Electronics and Communication Engineers 19.
October 1981 VOL, J84-C, No, 10 f1
Pages 52-657, Proceedings of the Institute of Electrical Communication Engineers, January 1883 VOL.

J88-C, No. 1, pages 85 to 81 for details.

Reference numeral 10a denotes a lens pattern formed on the micro Fresnel lens 10, and the drawing shows an efficiency-improving type lens pattern having concentric circles in plan view and a sawtooth (blazed type) cross-sectional shape. This lens pattern 10a is formed of ultraviolet curing resin (photopolymer), photoresist, electron beam resist, etc., and has a thickness of several meters.

11 is a lens substrate, and this lens substrate 11 is similar to the above 1/
It is bonded onto the four-wavelength plate 4 via a spacer 12, and the above-mentioned micro Fresnel lens 10 is attached to the back surface of the lens substrate 11. Here, lens substrate 1
1 is glass or plastic acid, thickness is 0.3~1
．． 0wm is used.

Further, the spacer 12 is formed of a metal plate or a plastic sheet, and the thickness of the spacer 12 is set to be slightly thicker than the thickness of the lens pattern loa.
An air layer 13 is formed between the lens pattern 10a and the quarter-wave plate 4 to increase the difference in refractive index with the lens pattern 10a.

In addition, in the drawing, the micro Fresnel lens 10 is used to protect the lens pattern loa surface.

The micro Fresnel lens 10 is placed facing the polarizing prism 3 side, but it may also be placed facing the optical disk 1 side. In this case, the micro Fresnel lens 10 is directly glued onto the 1/4 wavelength plate 4, and the spacer 12 is unnecessary. , the air layer 13 has a lens pattern lo
It can be formed on the upper part of a.

Note that a thin plate-like hologram lens may be used instead of the micro Fresnel lens 10, and other points are the same as in the above embodiment.

In this embodiment, since the thin micro Fresnel lens 10 is used in place of the objective lens 5, the distance from the polarizing prism 3 to the optical disc l can be significantly shortened. Therefore, the size of the optical pickup in the optical axis direction can be reduced.

``Effects of the Invention'' As described above, the present invention provides a focus error signal detection optical system using a knife of an optical pickup device that optically reads information recorded on an optical disc l, in which the knife also serves as the reflective film 7. the reflection s7 is formed directly on the quarter-wave plate 6 bonded to the polarizing prism 3,
Since the optical path of the focus error signal detection optical system is bent by this reflective film 7, the focus error signal detection optical system can be shortened.

Further, by using the reflective film 7 for the knife edge, which was conventionally made of a metal plate, it is possible to reduce the weight.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an optical pickup device according to the present invention, and FIG. 2 is an exploded perspective view of the main parts. FIG. 3 is a schematic configuration diagram showing another embodiment of the optical pickup device, FIG. 4 is an enlarged longitudinal sectional view of the same essential part, FIG. 5 is a partially exploded perspective view of the same essential part, and FIG. The figure shows a schematic configuration diagram of a conventional optical pickup device. l... Optical disk, 2... Semiconductor laser. 3...Polarizing prism. 4.6...l/4 wavelength plate, 5...objective lens, 7...reflection film, 8...photodetector. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Δ

Claims (2)

[Claims] (1) In a focus error signal detection optical system using a knife edge of an optical pickup device that optically reads information recorded on an optical disk, the knife edge is a thin film that also serves as a reflective film, and the reflective film is used as a polarizing prism. glued 1
1. An optical pickup device, characterized in that it is formed directly on a /4 wavelength plate, and the optical path of a focus error signal detection optical system is bent by this reflective film. (2) A patent claim characterized in that a thin plate-shaped lens such as a Fresnel lens or a hologram lens is used as the objective lens, and the lens is bonded to a quarter wavelength plate of an incident optical path that is bonded to a polarizing prism. The optical pickup device according to item 1 of the range.