JPH04339330A - Optical head - Google Patents

Abstract

PURPOSE:To remove unnecessary diffracted light from a signal generation diffraction optical element and to reduce the size and the cost of an optical head by using a diffraction optical element having high diffraction efficiency and a diffraction optical element having low diffraction efficiency together. CONSTITUTION:Most of the outgoing light of a semiconductor laser 1 passes through a HOE3 and collected on a disk 5 by a HOE2. A part of the light diffracted by the HOE3 is directed to the HOE2 but not collected on the disk 5 because of high dependency of the HOE2 on an incident angle. The light which passed through the HOE3 without being diffracted by it and collected on the disk 5 passes through the HOE2 and HOE3 again as reflection light, but a part of it is diffracted by the HOE3 and led to a light receiving element 4 for focusing/tracking signal detection on a signal detector 10.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for recording and reproducing information on and from optical information recording media such as optical disks, magneto-optical disks, and optical cards.

0002

2. Description of the Related Art Hitherto, as this type of optical head, one disclosed in, for example, Japanese Unexamined Patent Publication No. 172538/1983 is known. As illustrated in FIGS. 6 and 7, this is a semiconductor laser 21, a diffraction grating 22 composed of diffraction gratings with different periods perpendicular to the dividing line, a converging lens 23, and a dividing line of the diffraction grating 22 whose direction is the dividing line. Two-split photodetectors 24 and 25 arranged in a direction that matches the direction of the line
It is composed of The diffraction grating 22 and the two-split photodetectors 24 and 25 are arranged at the positions shown in FIG. 7, and focusing and tracking are performed using the differential method and push-pull method, respectively, from the outputs of these photodetectors. I'm going.

[0003] As another example, for example, Japanese Patent Laid-Open No. 1983
The one disclosed in Japanese Patent No. 106933 is known. As illustrated in FIGS. 8 and 9, this includes a semiconductor laser 21, a reflection type diffraction grating 26, an objective lens 27, and a four-part photodetector 28. The four-split photodetector 28 is placed at the position shown in FIG.
Based on the positions of the two spots 29 and 30, the photocurrents from the photodetectors PD1, PD2, PD3, and PD4 on the four-part photodetector 28 are calculated to perform focusing, and tracking is performed using the push-pull method.

0004

[Problems to be Solved by the Invention] In these conventional optical heads, it is necessary to release unnecessary diffraction order light, that is, stray light, generated by the diffractive optical element, which causes a reduction in the S/N ratio during signal detection, out of the optical system. Measures have been taken, such as increasing the diffraction angle of the signal detection light, or arranging the diffractive optical element and the objective lens with a wide distance between them. For this reason,
Optical heads cannot be miniaturized, which is a factor that prevents product costs from being reduced.

The present invention has been made in view of the above-mentioned problems of the prior art, and its object is to provide an optical head that is smaller and cheaper.

[0006]

Means for Solving the Problems and Operations The principles and operations of the optical head according to the present invention will be explained based on FIGS. 1 and 2. An optical head according to the present invention includes a semiconductor laser, a light condensing means for irradiating an optical information recording medium with light emitted from the semiconductor laser as a spot, and a return light reflected by the optical information recording medium formed integrally with the light condensing means. In an optical head that includes an optical element that separates a part of the luminous flux from the optical path returning to the semiconductor laser, and a photodetector that receives the returned light separated by the optical element, a condensing means is used to reduce the influence of stray light. The first diffractive optical element is formed by combining the first diffractive optical element and the second diffractive optical element, and the first diffractive optical element is the second diffractive optical element.
It is characterized by higher incidence angle dependence than other diffractive optical elements.

As the diffractive optical element, for example, a blazed micro Fresnel lens is used, and FIG. "Fresnel lens with equal
, Kawasaki, Optics, Vol. 17, No. 4, p182 (1988)
). In the graph shown in FIG. 1, the horizontal axis is the angle of incidence on the blazed Fresnel lens, and the unit is minutes. The vertical axis is
These are intensity distributions of light spots at various incident angles formed by the present diffractive optical element, with the maximum intensity value at normal incidence being 100. At this time, the numerical aperture of the Fresnel lens is 0.
．． It is 2.

FIG. 2 shows the principle of the optical head according to the present invention. In the figure, 1 is a semiconductor laser, 2 is a first diffractive optical element with high diffraction efficiency for condensing light, and 3 is a focusing and tracking signal. A second diffractive optical element with low diffraction efficiency is used for generation, 4 is a photodetector for signal detection, and 5 is a disk. In this configuration, most of the light 6 emitted from the semiconductor laser 1 simply passes through the diffractive optical element 3 and is focused onto the surface of the disk 5 by the diffractive optical element 2. The return light reflected by the disk 5 returns while being condensed again by the diffractive optical element 2, and a part of it becomes diffracted light 7 by the diffractive optical element 3, and is guided to the signal detector 4, where it is used for focusing and tracking. Generate a signal.

A part of the emitted light 6 of the semiconductor laser 1 is actually diffracted by the diffractive optical element 3, and a plurality of unnecessary diffracted lights 8 are generated. In an optical head using a conventional objective lens, this diffracted light 8 becomes convergent light 9 and is focused on the surface of the disk 5, and returns to the optical system again, causing various noises. Since the optical head according to the present invention uses a diffractive optical element with high incidence angle dependence as shown in FIG.
The light is not focused on the disk 5. Therefore, the diffractive optical element 2
, 3 or the diffraction angle of the diffractive optical element 3 to be extremely large, the optical head can be made smaller.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below based on the embodiments shown in FIGS. 3 to 5. FIG. 3 shows a first embodiment of the present invention, and in the figure, 1 is a semiconductor laser, 4 is a light receiving element for signal detection, 10 is a signal detector, and 11 is a first laser beam with high diffraction efficiency for condensing light. 5 is a disk, which is an optical lens in which a diffractive optical element (hereinafter referred to as HOE) 2 and a second HOE 3 having low diffraction efficiency for signal generation are integrated.

In this configuration, most of the light emitted from the semiconductor laser 1 passes through the HOE 3 and is focused onto the disk 5 by the HOE 2. The light partially diffracted by the HOE 3 similarly heads toward the HOE 2, but is not focused onto the disk 5 because the HOE 2 is highly dependent on the incident angle. The light that passes through the HOE 3 without being diffracted and is focused on the disk 5 becomes return light and passes through the HOE 2 and HOE 3 again, but a part of it is diffracted by the HOE 3 and is focused on the signal detector 10. The light is guided to a light receiving element 4 for tracking signal detection. FIG. 4 shows an example of the arrangement of the light receiving element 4 for signal detection, in which the HOE 3 for signal light generation is divided into four pupils.
Four different spots are generated on the light receiving elements a to 4d. Tracking is performed by calculating the difference between the photocurrents from 4a and 4b, and push-pull focusing is performed by calculating the photocurrents from 4c and 4d. In addition, the information reproduction signal is 4a
and 4b's photocurrent output.

FIG. 5 shows a second embodiment of the present invention,
In the figure, 1 is a semiconductor laser, 4 is a light receiving element for signal detection,
10 is a signal detector, 12 is a first HOE 2 with high diffraction efficiency for condensing light and a second HOE 2 with low diffraction efficiency for signal generation.
HOE 3 is an integrated collimator lens, 13 is an objective lens, and 5 is a disk.

In this configuration, most of the light emitted from the semiconductor laser 1 passes through the HOE 3, becomes parallel light by the HOE 2, and is focused onto the disk 5 by the objective lens 13. Similarly, the light partially diffracted by HOE3 is
However, since the HOE 2 is highly dependent on the incident angle, it is not focused onto the disk 5. The light that passes through the HOE 3 without being diffracted and is focused on the disk 5 becomes return light and passes through the objective lens 13, HOE 2, and HOE 3 again. The light is guided to the focusing and tracking signal detection light receiving element 4 above. This embodiment has advantages such as the pattern spacing being increased during HOE production by using the HOE in the collimator lens portion, which has a smaller numerical aperture than the objective lens.

[0014]

[Effect of the invention] By using a diffractive optical element with high diffraction efficiency and a diffractive optical element with low diffraction efficiency, unnecessary diffracted light from the signal generation diffractive optical element can be removed, and the optical head can be made smaller. It is also extremely effective in reducing costs.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the incident angle dependence of a blazed micro Fresnel lens used in the present invention as a diffractive optical element.

FIG. 2 is a conceptual diagram showing the basic configuration of an optical head according to the present invention.

FIG. 3 is a diagram showing the configuration of a first embodiment of the present invention.

FIG. 4 is a layout diagram of light receiving elements on the signal detector in the first embodiment.

FIG. 5 is a diagram showing the configuration of a second embodiment of the present invention.

FIG. 6 is a diagram showing an example of a conventional optical head configuration.

FIG. 7 is a layout diagram of the diffraction grating and the two-split photodetector shown in FIG. 6;

FIG. 8 is a diagram showing another example of the configuration of a conventional optical head.

9 is a layout diagram of a photodetector on the four-part photodetector shown in FIG. 8. FIG.

[Explanation of symbols]

1 Semiconductor laser 2, 3 Diffractive optical element 4 Light receiving element for signal detection 5
Disk 6 Laser light 7,8 Diffracted light 9 Convergent light 10 Signal detector 11 Optical lens 12 Collimator lens 13 Objective lens

Claims (1)

[Claims] 1. A semiconductor laser, a condensing means for irradiating the light emitted from the semiconductor laser as a spot onto an optical information recording medium, and a return beam formed integrally with the condensing means and reflected by the optical information recording medium. In an optical head that includes an optical element that separates a part of the light flux from the optical path returning to the semiconductor laser, and a photodetector that receives the returned light separated by the optical element, the above-mentioned concentrator is used to reduce the influence of stray light. The optical means is formed by combining a first diffractive optical element and a second diffractive optical element, and the first diffractive optical element has higher incidence angle dependence than the second diffractive optical element. Features a light head.