JPH0474319A - Optical pickup - Google Patents

Abstract

PURPOSE:To make the device small in size and light in weight, and to shorten the adjustment time of a focus detecting system by constituting the focus detecting system by performing partial masking to two emitting faces of a polarization beam splitter, and also, joining a split prism. CONSTITUTION:The emitting face of a polarization beam splitter 4 becomes two sectors from a circular luminous flux because two triangular parts 17 in the vertical direction in four triangular parts divided into four by two pieces of diagonal lines are subjected to sand grinding and black coating, and they are made incident on a split prism 14. Two sector luminous fluxes which are made incident on the split prism 14 are subjected to horizontal shift by two wedge prisms of its arbitrary angle of the split prism and emitted, and caught by a photodetector 16 being in front thereof. In such a way, the device can be made small in size and light in weight, and the adjustment time of a focus detecting system can be shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Fields] The present invention is a method for optically recording various information on a disk-shaped recording medium.
This invention relates to an optical pickup for a device that only performs playback.

[Prior Art] Conventionally, this type of device has a configuration as shown in FIGS. 7 and 8, in which a light beam emitted from a semiconductor laser 1 is made into parallel light by a collimating lens 2, and then the parallel beam is disposed in front. The light enters the beam shaping prism 3, becomes a circular light beam expanded by about 2.5 times in a direction parallel to the PN junction surface of the semiconductor laser 1, and enters the polarizing beam splitter 4. At this time, the polarizing beam splitter 4 is arranged so that the light beam emitted from the collimating lens enters as S-polarized light, so that the light beam incident on the polarizing beam splitter 4 is 100% due to the junction surface coated with the dielectric multilayer film. reflected, λ
After passing through the /4 plate 5, it becomes circularly polarized light and is focused onto a disc-shaped recording medium 7 by an objective lens 6.

After this, the light beam reflected by the disc-shaped recording medium 7 passes through the objective lens 6 again, passes through the λ/4 plate 5, and becomes a linearly polarized light whose azimuth angle is 90' with the light beam emitted from the semiconductor laser 1. The light enters the polarizing beam splitter 4 again. At this time, this light beam enters the polarizing beam splitter 4 as P-polarized light, so it is 100% transmitted, passes through the λ/4 plate 5, becomes circularly polarized light, is reflected while being condensed by the concave mirror 8, and is reflected again as a λ/4 light beam. After passing through the plate 5, it becomes S-polarized light, which is then 100% reflected by the junction surface coated with the dielectric multilayer film of the polarizing beam splitter 4, and enters the beam splitter 9.

50% of the luminous flux incident on the beam splitter 9 is transmitted in a direction parallel to the optical axis of the collimating lens 2, and the remaining 50% is transmitted in a direction parallel to the optical axis of the collimating lens 2.
% is reflected in the direction perpendicular to it, and the beam splitter 9
A further 50% of the light beam emitted in a direction parallel to the optical axis of the collimating lens 2 is blocked by the knife 10 in front, captured by the light receiving element 12, and focusing control is performed by its differential output, and the remaining part is collimated. The light beam emitted in the direction perpendicular to the optical axis of the lens 2 is captured by the light receiving element 11, and tracking control and reproduction signal detection are performed.

[Problems to be Solved by the Invention] Since the conventional configuration device described above employs a single knife method for focus detection, the knife 10 must be adjusted in a plane perpendicular to the optical axis of the collimating lens. Not only is this necessary, but it also takes a considerable amount of time to adjust. In addition, if an offset occurs in the differential output of the light receiving element 12 due to an external shock or environmental change, there is little margin for electrical correction.
The light receiving element 12 must be adjusted again.

Furthermore, as a configuration of the optical system, a beam shaping prism 3,
Since the polarizing beam splitter 4 and the beam splitter 9 are linearly joined, the overall shape of the device becomes large.

[Means for Solving the Problems] The optical pickup of the present invention is an apparatus that only optically records and reproduces various information on a disc-shaped recording medium.
A semiconductor laser as a light source, a collimator lens that converts the light beam emitted from the semiconductor laser into parallel light, and a collimator lens arranged in front of the output surface of the collimator lens to make the light beam emitted from the collimator lens parallel to the PN junction surface of the semiconductor laser. A beam shaping prism that expands in any direction at any magnification,
A λ/4 plate is bonded to each of the two output surfaces in a direction orthogonal to the optical axis of the collimating lens, and a concave half mirror is bonded to one of the λ/4 plates, and the optical axis of the collimating lens is Of the parts divided into four by the two diagonal lines on the exit plane parallel to , the two triangular parts parallel to the beam expansion direction of the beam shaping prism are sanded surfaces and are coated with black paint for light absorption. a polarizing beam splitter, a split prism joined to the partially black-painted surface of the polarizing beam splitter, and a first light receiving element having at least four divisions arranged in front of the split prism; A second light receiving element divided into at least four parts is arranged in front of the concave half mirror.

[Example code] Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a diagram of the same embodiment viewed from the far field in a direction parallel to the optical axis of the objective lens 6.

The light beam emitted from the semiconductor laser 1 is made into parallel light by the collimating lens 2, and then enters the beam shaping prism 3 placed in front, where it is transformed by about 2.5 times in the direction parallel to the PN junction surface of the semiconductor laser 1. The light is expanded and becomes a circular light beam that enters the polarizing beam splitter 4. At this time, the polarizing beam splitter 4 transmits 100% of the P-polarized light and 100% of the S-polarized light with respect to the light beam emitted from the semiconductor laser 1.
In this case, the polarizing beam splitter 4 is arranged so that the light beam after exiting the collimating lens 2 enters as S-polarized light, so the light beam incident on the polarizing beam splitter 4 is The light is 100% reflected by the junction surface coated with the dielectric multilayer film, becomes circularly polarized light after passing through the λ/4 plate 5, and is focused onto the disc-shaped recording medium 7 by the objective lens 6.

After this, the light beam reflected by the disc-shaped recording medium 7 passes through the objective lens 6 and the λ/4 plate 5 again, and becomes linearly polarized light with an azimuth angle of 90° with the light beam emitted from the semiconductor laser 1, and becomes a polarized beam again. In order to enter the splitter 4,
This time, it passes through the bonded surface coated with the dielectric multilayer film,
It passes through the λ/4 plate 5 and becomes circularly polarized light, which becomes a concave mirror half mirror.
13.

50% of the light beam incident on the concave half mirror 13 is transmitted while being focused, and is captured by the light receiving element 15 disposed in front. FIG. 4 shows the light beam incident on the light receiving element 15, and E, F, G, and H in the figure represent four light receiving surfaces, respectively. Track detection is performed by differential output of (H-F), and playback signal detection is performed by (E+F+G+
Detected by the output of H).

The remaining 50% of the light incident on the concave mirror half mirror 13 is reflected while being focused by the concave mirror, and is reflected by the λ/4 plate 5.
The light passes through the beam and becomes S-polarized light again, so it is reflected by the junction surface coated with the dielectric multilayer film of the polarizing beam splitter 4.
The beam enters the split prism 14 as shown in FIG. 6, but at this time, the exit surface of the polarizing beam splitter 4
As shown in the figure, among the four triangular parts divided by the two diagonals, two vertical triangular parts 1
Since the light beam 7 has been sand-treated and painted black, the circular light beam becomes two fan-shaped lights and enters the split prism 14 .

The two fan-shaped light beams incident on the split prism 14 are laterally shifted by the two wedge prisms at arbitrary angles of the split prism, and then emitted and captured by the light receiving element 16 in front.

FIG. 5 shows two fan-shaped light beams incident on the light-receiving element 16, and A, B, C, and D in the figure represent four light-receiving surfaces, respectively. Focus detection employs a double knife method, and is performed by differential outputs such as (A+D)-(B+C), for example.

[Effects of the Invention] As explained above, according to the present invention, the two exit surfaces of the polarizing beam splitter are partially masked and a split prism is joined to form a focus detection system, thereby reducing the size of the device. This has the advantage of being lightweight, reducing the adjustment time of the focus detection system, and easily increasing the margin for offset correction of the focus detection system against environmental changes.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, FIG. 2 is a diagram of the embodiment of FIG. 1 viewed from the far field in a direction parallel to the optical axis of the objective lens 6, and FIG. 3 is the same diagram. A diagram for explaining the masking part of the polarizing beam splitter of the example,
FIG. 4 is a diagram for explaining the light receiving state of the light receiving element of the track detection system of the same embodiment, and FIG. 5 is a diagram for explaining the light receiving state of the light receiving element of the focus and detection system of the same embodiment. Figure 6 is a diagram for explaining the split prism used in the same example, Figure 7 is a diagram showing a conventional example, and Figure 8 is a view of the conventional example from the far field in a direction parallel to the optical axis of the objective lens. FIG. 1... Semiconductor laser, 2... Collimator lens, 3
... Beam shaping prism, 4... Polarizing beam splitter, 5... λ/4 plate, 6... Objective lens, 7...
- Disc-shaped recording medium, 8... Concave mirror, 9... Beam splitter, 10... Knife, 11, 12, 15. IF
5... Light receiving element, 13... Concave mirror half mirror 14
... Split prism, 17... Masking part for light absorption.

Claims (1)

[Claims] A device that only optically records and reproduces various information on a disk-shaped recording medium includes a semiconductor laser as a light source, a collimator lens that converts the light beam emitted from the semiconductor laser into parallel light, and a front side of the exit surface of the collimator lens. a beam shaping prism disposed in the collimating lens, which expands the luminous flux emitted from the collimating lens by an arbitrary magnification in a direction parallel to the PN junction surface of the semiconductor laser; λ/4 plates are bonded to each, and a concave mirror half mirror is bonded to one of the λ/4 plates, and the output surface parallel to the optical axis of the collimating lens is divided into four parts by two diagonal lines. Among them, two triangular parts parallel to the beam expansion direction of the beam shaping prism are sand-striped surfaces, and the polarizing beam splitter is painted black for light absorption, and the part of the polarizing beam splitter is painted black. a split prism bonded to a surface subjected to a process, a first light-receiving element having at least four divisions arranged in front of the split prism, and a second light-receiving element having at least four divisions arranged in front of the concave mirror half mirror. An optical pickup characterized by arranging.