JPS63224042A - Optical head - Google Patents

Abstract

PURPOSE:To arrange a light detecting means in the vicinity of a light source, and to reduce the size and the weight of the titled head by making both light beams, one led from the light source to an information storage medium, and the other led from the information storage medium to the light detecting means, pass along an approximately same optical path. CONSTITUTION:A light reflective cylindrical concave lens surface 16, the genera trix of which 45 deg.C inclined, is provided at the back surface of a deflecting beam splitting surface 6, and a head is constituted so that a laser beam L is transmitted through the deflecting beam splitting surface 6, and is reflected by the cylindrical concave lens surface 16. The laser beam L, led from a semi conductor laser beam 2 to the information storage medium 12, and the laser beam L, led from the information storage medium 12 to a photodetector 20, go forward on the approximately same path. Thus, the detector 20 can be arranged at the vicinity of the semiconductor laser 2, and the optical head can be miniaturized lightened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an optical head that reads at least information from an information storage medium using focused light.

(Prior Art) Generally, in an optical head used in an optical disk device, etc., a laser beam is emitted from a semiconductor laser, and this laser beam sequentially passes through a collimating lens, a polarizing beam splitter, and a quarter-wave plate. The light is focused by an objective lens onto an information storage medium having spiral or concentric tracks. This focused laser beam is reflected by the information storage medium, passes through the objective lens and the quarter-wave plate again, is returned to the polarizing beam splitter, and is reflected by the polarizing beam splitter. This reflected laser beam passes through a projection lens and is converted into an electrical signal by a photodetector. Thereby, the output from the photodetector is used to read information recorded on the information storage medium, detect defocus of the objective lens on the information storage medium, and detect track deviation on the information storage medium.

(Problem to be Solved by the Invention) However, in the above optical head, the laser beam returned from the information storage medium is guided in a direction different from that of the semiconductor laser by the polarizing beam splitter, so that the semiconductor laser and the photodetector are It is located in a remote location. This has the disadvantage that the optical head becomes larger and heavier, and the access time becomes longer.

The present invention has been made based on the above-mentioned circumstances, and an object thereof is to provide an optical head that can be made smaller and lighter, and furthermore, the access time can be shortened due to the weight reduction.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention reflects a light beam generated by a light beam generating means by a polarizing beam splitting surface, and A light beam is focused onto an information storage medium by a focusing means, and after being focused on the information storage medium by this focusing means, the light beam that is emitted from the information storage medium and passes through the focusing means again is used as a polarizing beam splitter. The plane of polarization of the light beam is rotated by a quarter-wave plate so that the plane of polarization is rotated by a quarter-wave plate, and the light beam that has been rotated and transmitted through the polarizing beam splitter is reflected by a light reflective cylindrical surface, and the reflected light beam is is detected by at least four divided light detection means for detecting at least defocus and track deviation.

(Operation) The light beam guided from the light source to the information storage medium and the light beam guided from the information storage medium to the photodetection means are made to travel on substantially the same optical path, thereby arranging the photodetection means near the light source. .

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

Reference numeral 2 in FIGS. 1 and 2 is a semiconductor laser (light source), and a laser beam L emitted from this semiconductor laser 2 is perpendicularly incident on one surface of the prism 4. A polarized beam splitting surface 6 is formed on the other surface of the prism 4, and approximately 100% of the incident laser beam L is reflected by the polarized beam splitting surface 6 and guided to a quarter wavelength plate 8. This guided laser beam L is 1
By passing through the /4 wavelength plate 8, it becomes circularly polarized light,
It is guided to the objective lens 10.

Here, ellipse correction is not performed on the cross-sectional intensity distribution of the laser beam L emitted from the semiconductor laser 2, and only the uniform portion of the intensity distribution near the center of the cross-sectional intensity distribution of the laser beam L is corrected. L is objective lens 10
The beam size of the laser beam L is made sufficiently larger than the aperture of the objective lens 10 so that the laser beam L passes through the aperture of the objective lens 10. In this case, although the utilization efficiency of the laser beam L decreases, the ellipse correction lens can be omitted.

A laser beam L guided to an objective lens 10 is directed to an information storage medium 12 having a track by this objective lens 10.
The light is focused on the top.

The laser beam L focused on the information storage medium 12 is
It is reflected on this information storage medium 12, and the objective lens 10
After passing through the quarter-wave plate 8, it is returned to the polarization beam splitting surface 6 of the prism 4.

Here, the laser beam L is converted into linearly polarized light whose photographing direction is rotated by 90 degrees compared to when it is reflected by the polarized beam splitting surface 6 by reciprocating through the quarter-wave plate 8. Therefore, the laser beam L returned to the polarized beam splitting surface 6 is transmitted through this polarized beam splitting surface 6.

A light reflecting member 14 is superimposed on the polarizing beam splitting surface 6 of the prism 4. The light reflecting member 14 has a light reflecting cylindrical concave lens surface 16 formed on the opposite side from the polarizing beam splitting surface 6 . Furthermore, the generatrix 18 of this cylindrical concave lens surface 16 forms an angle of approximately 45 degrees with respect to the plane defined by the optical axis extending from the objective lens 10 and the optical axis extending from the light emitting point of the semiconductor laser 2 on the polarizing beam splitting surface 6. The light reflecting member 14
is superimposed on the polarizing beam splitting surface 6.

Laser beam L transmitted through polarized beam splitting surface 6
is reflected by the light reflective cylindrical concave lens surface 16,
As a result, the cross-sectional shape of the laser beam L is expanded in only 11 directions and converted into an elliptical shape. The laser beam L that has been changed to have an elliptical cross-sectional shape passes through the polarizing beam splitting surface 6 again and is irradiated onto a photodetector 20 placed near the semiconductor laser 2 .

This photodetector 20 is divided into four photodetection cells 22...
It is arranged near the semiconductor laser 2. The photodetector 20 detects defocus using the so-called astigmatism method, detects track deviation using the so-called push-pull method,
and information detection is performed. In addition, this optical head is
The objective lens 10 is maintained in focus and directed toward a predetermined track by moving the entire object vertically and horizontally in accordance with the defocus detection result and the track deviation detection result.

Further, as shown in FIGS. 2 and 3, the semiconductor laser 2 and the photodetector 2o are supported by a semiconductor element mounting frame 23. Optical components other than the semiconductor laser 2 and the photodetector 20 are housed in an optical component mounting frame 24. The semiconductor element mounting frame 23 is fixed to the optical component mounting frame 24 with screws 26.degree. 26. In general, the joint between the semiconductor element mounting frame 23 and the optical component mounting frame 24 is sealed with a hermetic seal 28 in order to protect the environmental resistance of the semiconductor element.

According to the above configuration, the light reflective cylindrical concave lens surface 16 whose generatrix is inclined by 45 degrees is provided on the back surface of the polarizing beam splitting surface 6, and the laser beam L is transmitted through the polarizing beam splitting surface 6, and the laser beam L is transmitted through the polarizing beam splitting surface 6. Since it has a reflective configuration, one photodetector 20 can detect defocus using the astigmatism method, track deviation detection using the push-pull method, and information detection. The laser beam L guided from the information storage medium 12 to the photodetector 20
The photodetector 20 can be placed near the semiconductor laser 2 because the laser beam L guided to the semiconductor laser 2 travels on substantially the same optical path. Therefore, the optical head can be made smaller and lighter, and the access time can be shortened due to the weight reduction.

[Effects of the Invention] As explained above, according to the present invention, the light beam guided from the light source to the information storage medium and the light beam guided from the information storage medium to the photodetection means are made to travel on substantially the same optical path. As a result, the photodetector can be placed near the light source, thereby achieving excellent effects such as reduction in size and weight, and shortening of access time due to the reduction in weight.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention; FIG. 1 is a perspective view of the optical head excluding the mounting frame, FIG. 2 is a sectional view of the optical head, and FIG. 3 is a cross-sectional view of the optical head. FIG. 2 is a front view showing a semiconductor laser and a photodetector supported by a semiconductor element mount frame. 2...Light beam generating means (semiconductor laser), 6...
・Polarizing beam split surface, 8...1/4 wavelength plate, 1
0... Focusing means (objective lens), 12... Information storage medium, 16... Light reflective cylindrical surface, 20...
- Light detection means (photodetector). Applicant's agent Patent attorney Takehiko Suzue Figure 2 Collection Figure 3

Claims (2)

[Claims] (1) A light beam generating means for generating a light beam, a polarizing beam splitting surface for reflecting the light beam generated by the light beam generating means, and a light beam reflected by the polarizing beam splitting surface onto an information storage medium. a light beam condensing means for condensing light onto an information storage medium, and a light beam that is emitted from the information storage medium and passes through the condensing means again after being condensed onto an information storage medium by the condensation means and passes through the polarization beam splitter. a quarter-wave plate for rotating the polarization plane of the light beam; a light-reflecting cylindrical surface for reflecting the light beam whose polarization plane has been rotated by the quarter-wave plate and transmitted through the polarizing beam splitter; 1. An optical head comprising at least four divided light detection means for detecting a light beam reflected by a cylindrical surface and detecting at least defocus and track deviation. (2) The generatrix of the cylindrical surface forms an angle of approximately 45 degrees with respect to a plane defined by the optical axis extending from the light condensing means and the optical axis extending from the light source on the polarizing beam splitting surface. An optical head according to claim 1, characterized in that: