JPH05266502A - Optical head for optical disk device - Google Patents

Abstract

PURPOSE:To provide an optical head changing the optical path of a detective beam without increasing the number of parts and reducing the outside dimension of an optical disk device in the direction of the thickness. CONSTITUTION:A laser beam 11 outgoing from a laser diode 1 passes through a linear diffraction grating 2 and whose optical path is changed in the direction of the optical disk 5 regarding the surface of a parallel flat plate glass 23 as a first reflection surface 23A and the laser beam is converged by a convex lens 4 and projected on the information storage surface 5P of the optical disk as a minute beam spot 12. The parallel flat plate glass 23 is provided with a second reflection surface 23B on the surface opposing to the first reflection surface and a diffracted beam reflected by the information storage surface 5P is reflected by the second reflection surface. Thus, the detective beam 25 added with astigmatism is outgone in a direction parallel to the optical axis of the laser beam 11 while holding a prescribed interval (d) and a quadripartite photodiode pair 6 is arranged on a position where the luminous flux distribution of the detective beam becomes a circle at the time of focusing.

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 an optical disk device, such as a portable disk player, which is particularly required to be compact, lightweight and inexpensive.

[0002]

2. Description of the Related Art An optical head of a portable disk player focuses laser light emitted by a laser diode on an information storage surface (pit surface) of an optical disk and reflects it on the pit surface. The diffracted light is converted into an electric signal by a photo diode to read recorded information and detect a focus error. To reduce the weight and cost of the optical system, the number of parts of the optical system is reduced. Are being miniaturized.

FIG. 2 is a schematic diagram showing a simplified conventional optical head, which passes through a laser light 11 linear diffraction grating radiated and diverged from a laser diode 1. ,
The surface of the parallel plate glass 3 having an inclination of 45 ° with respect to the optical axis 11A of the laser light 11 is used as the first reflecting surface 3A to change the direction of 90 °, and a convex lens (also called an objective lens) 4
The information storage surface (hereinafter referred to as a pit surface) 5P of the optical disk 5 which is focused by the optical disk 11 and is arranged in a direction orthogonal to the optical axis 11B.
It is projected as a minute light spot 12 on the upper side. The convex lens 4 is supported by an optical axis adjusting mechanism 9 driven by a servo mechanism (not shown) to perform focusing control on the pit surface 5P and tracking control for moving and positioning the light spot 12 on the information track. Be seen.

On the other hand, the diffracted light reflected by the pit surface 5P and containing the information such as the information storage state and the focused state is transmitted through the parallel flat plate glass 3 to become the detection light 15 to which the astigmatism is added, thereby becoming a photodiode. -It is incident on the terminal 6 and is converted into an electric signal. Here, when the photo diode 6 is a 4-division photo diode pair and the light spot 12 is focused on the pit surface 5P, the cross-sectional shape of the luminous flux distribution of the detection light 15 around the optical axis 15A becomes circular. If it is arranged at the position, the stored information on the pit surface can be read from the sum of the output electric signals of the respective divided photodiodes 6A, 6B, 6C and 6D. Also, the focus position of the small light spot 12 is the pit surface 5.
When deviated from P, the luminous flux distribution of the detection light 15 on the photo diode 6 becomes an ellipse orthogonal to each other with the optical axis 15A as the center, depending on the distance of the focal point to the pit surface. Therefore, if the photo diode 6 is divided into four parts by straight lines that are offset by 45 ° with respect to the major axis directions of the ellipses orthogonal to each other, the optical axis 1
Since there is a difference between the sum (6A + 6C) and (6B + 6D) of the output electric signals of the pair of divided photodiodes that are symmetric with respect to 5A, the difference between these signals is used as the focus error signal for the servo signal.
By driving the Po mechanism, focusing control by the so-called astigmatism method can be performed.

[0005]

In the simplified conventional optical head described above, the light composed of the laser diode 1, the linear diffraction grating 2, the parallel plate glass 3 and the convex lens 4 is used. The projection system does not include a collimating lens or a beam shaping lens for collimating the laser light 11 or a beam splitter for branching the detection light from the projection system, and the detection is performed. Since the system is composed of only the photo diode 6 and does not include optical parts, the number of optical parts of the optical head is significantly reduced as compared with the conventional optical head including the above-mentioned optical parts, and the optical disk device and the optical disk pre-recorder. Yar
Can be made lighter and less expensive. On the other hand, of the external dimensions of the optical disc player, the dimensions of the two long sides are determined by the size of the optical disc. Therefore, miniaturization reduces the short two sides (thickness) to flatten the external dimensions and increase the volume. The challenge is to reduce

However, in the conventional optical head, since the optical axis 15A of the detection light 15 in the detection system is perpendicular to the information storage surface 5P of the optical disk 5, the photodiode
There is a drawback that the distance between the disk 6 and the optical disk 5 becomes long, which hinders the reduction of the dimension of the optical disk player in the thickness direction. Further, if the detection light 15 is configured to be changed by 90 ° in the direction perpendicular to the paper surface in FIG. 2, it is expected that the dimension of the optical disc player in the thickness direction can be reduced and downsized. Since it is necessary to add an optical component for changing the angle by 90 °, there arises a problem that the reduction in weight and the reduction in price are hindered.

An object of the present invention is to obtain an optical head which can change the optical path of the detection light without increasing the number of parts and can reduce the outer dimensions of the optical disk device in its thickness direction.

[0008]

In order to solve the above-mentioned problems, according to the present invention, an emission laser of a laser diode is used.
The light is passed through a linear diffraction grating to change the optical path toward the optical disc with the surface of the parallel plate glass as the first reflecting surface.
In a projection system in which a laser beam is focused by a convex lens arranged on the optical path and projected as a minute light spot on the information storage surface of the optical disk, the parallel flat glass faces the first reflection surface. A second reflecting surface on the surface of the optical disc, and diffracted light reflected by the information storage surface of the optical disc is reflected by the second reflecting surface to detect the detection light with astigmatism. It is assumed that the laser diode is formed so as to be emitted in a direction parallel to the optical axis of the emitted laser light of the laser diode at a predetermined interval.

It is also assumed that a photo diode is provided at a position where the luminous flux distribution of the detection light becomes circular when a minute light spot is focused on the information recording surface of the optical disk by the convex lens. Furthermore, the photodiode is divided into four photodiodes.
It is assumed that the focus error of the convex lens is detected based on the astigmatism of the reflected light.

[0010]

In the structure of the present invention, the parallel flat plate glass for changing the optical path of the laser light from the laser diode in the optical disc direction is provided with the second reflecting surface facing the first reflecting surface. The diffracted light reflected by the information storage surface of the optical disk is reflected by the second reflecting surface to detect the detection light to which astigmatism is given, with respect to the optical axis of the laser beam. The optical path of the detection light that was perpendicular to the conventional optical disc can be changed by a simple structure change such that the second reflection surface is provided on the parallel flat glass by arranging the light beams to be emitted in the parallel direction while maintaining the interval. Can be changed by 90 ° in the direction parallel to the laser light, and a flat optical head with a volume smaller than that of parallel flat glass can be obtained, so the optical head can be made thinner without increasing the number of optical components. The function to do is obtained.

Further, when the microlens spot is focused on the information recording surface of the optical disk by the convex lens, the photodiode may be provided at a position where the luminous flux distribution of the detection light becomes circular. -The space between the laser light and the detection light can be integrated by arranging them close to the diode, and the space between them can be reduced to a minimum.
By effectively using the space as a rational component placement space, a function of facilitating flattening of the outer dimensions of the optical head and the optical disk device that houses the optical head can be obtained. Furthermore, by making the photo diode a 4-division photo diode pair, the miniaturized optical head can be provided with the function of detecting the focus error signal based on the astigmatism method.

[0012]

EXAMPLES The present invention will be described below based on examples. FIG. 1 is a schematic diagram schematically showing an optical head of an optical disk device according to an embodiment of the present invention. The same components as those of the conventional technique are designated by the same reference numerals, and a duplicate description will be omitted. In the figure, the parallel plate glass 23 is
A second reflecting surface 23B coated with a reflecting film is formed on the surface of the parallel flat plate glass having the first reflecting surface 23A facing the first reflecting surface. The laser light 11 emitted from the laser diode 1 and diverging passes through the linear diffraction grating 2 and has an inclination of 45 ° with respect to the optical axis 11A of the laser beam 11. An optical disk in which the surface of the parallel plate glass 23 is used as a first reflecting surface 23A, the direction of which is changed by 90 °, is converged by a convex lens (also referred to as an objective lens) 4, and the light incident surface is orthogonal to its optical axis 11B. 5P pit surface 5P
It is projected as a minute light spot 12 on the upper side.

The diffracted light which is reflected by the pit surface 5P and contains information such as the information storage state and the focused state is transmitted through the convex lens 4 and the first reflecting surface 23A of the parallel flat plate glass 23, and the second The light is reflected by the reflecting surface 23B and again emitted as the detection light 25 from the first reflecting surface. At this time, the optical axis 2 of the detection light 25 to which the astigmatism is added by the parallel plate back surface mirror -23
5A shows the amount of light that the light obliquely travels back and forth in the parallel plate glass.
The laser beam 11 will move in parallel with the laser beam 11,
The astigmatic ray bundle is parallel to the optical axis 11A of the light 11 while maintaining a predetermined distance d determined by the refractive index and thickness of the parallel plate glass. Therefore, by controlling the focus of the convex lens 4, a small light spot 12 is formed on the information storage surface 5P of the optical disc 5.
When the focal point is in focus, the four-division photodiode pair 6 is provided at a position where the luminous flux distribution of the detection light 25 becomes circular, so that the detection light 25 can be converted into an electric signal to read information, and the astigmatism can be obtained. The focus error signal can be detected based on the method.

In the optical head of the optical disk device configured as described above, the detection light which has been perpendicular to the optical disk surface in the past is changed by a simple structure change such that the second reflecting surface is formed on the back surface of the parallel plate glass. Since the optical path of 15 can be changed by 90 ° to the detection light 25 parallel to the laser light 11 without increasing the number of components, the space distance required between the parallel flat plate glass 3 and the photo diode 6 in the past is unnecessary. Therefore, the spectroscopic head can be flattened to reduce the size of the optical disc player. Further, the four-divided photodiode pair 6 is arranged close to the laser diode 1 to integrate the optical paths of the laser light 11 and the detection light 25, and the space thereof can be reduced to a minimum. By effectively using the reduced space as a rational component arrangement space, it is possible to obtain an advantage that the outer dimensions of the optical head and the optical disk device that houses the optical head can be reasonably thinned.

[0015]

As described above, according to the present invention, the parallel plate glass for changing the optical path of the laser light from the laser diode in the optical disc direction is provided with the second flat plate facing the first reflecting surface. A reflecting surface is provided so that the diffracted light reflected by the information storage surface of the optical disk is reflected by the second reflecting surface. As a result, it is possible to achieve the function of changing the optical path of the detection light in the direction perpendicular to the optical disk surface by 90 ° in the direction parallel to the laser light without increasing the number of parts, and thereby flattening the optical head. Therefore, it is possible to provide a thinned optical disk device, especially an optical disk player. Also, a four-division photodiode pair is set as a laser diode.
Since the laser beam and the optical path of the detection light are integrated by arranging them in close proximity to the terminal 1 and the space thereof can be reduced to a minimum,
By effectively utilizing the reduced space as a rational space for arranging parts, it is possible to obtain an advantage that the outer dimensions of the optical head and the optical disk device accommodating the space can be reasonably thinned.

[Brief description of drawings]

FIG. 1 is a configuration diagram schematically showing an optical head of an optical disk device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram schematically showing a simplified conventional optical head.

[Explanation of symbols]

 1 Laser Diode 2 Linear Diffraction Grating 3 Parallel Flat Glass 3A First Reflecting Surface 4 Convex Lens (Objective Lens) 5 Optical Disk 5P Information Storage Surface (Pit Surface) 6 Photodiode (4 Division Photodiode Pair) ) 9 optical axis adjusting mechanism 11 laser light (light emitted from laser diode) 11A optical axis of laser light 12 microscopic light spot (focus point) 15 detection light 15A optical axis of detection light 23 Parallel Flat Glass (with Second Reflecting Surface) 23A First Reflecting Surface 23B Second Reflecting Surface 25 Detection Light 25A Optical Axis of Detection Light

Claims (3)

[Claims] 1. The laser light emitted from a laser diode is passed through a linear diffraction grating to change the optical path in the optical disc direction with the surface of a parallel plate glass as the first reflecting surface, and is distributed on this optical path. A projection system for converging laser light by a convex lens which is projected and projecting it as a minute light spot on the information storage surface of the optical disk, wherein the parallel flat glass plate has a second surface on a surface facing the first reflection surface. Of the laser light, the diffracted light reflected by the information storage surface of the optical disk is reflected by the second reflective surface to detect the astigmatism. An optical head of an optical disk device, characterized in that it is formed so as to be emitted in a direction parallel to the optical axis of the emission laser light while maintaining a predetermined interval. 2. A photodiode is provided at a position where the luminous flux distribution of the detection light becomes circular when a minute light spot is focused on the information recording surface of the optical disk by the convex lens. Optical head for optical disk drive. 3. The optical disk apparatus according to claim 2, wherein the photo diode is composed of a 4-division photo diode pair, and is formed so as to detect the focus error of the convex lens based on the astigmatism of the reflected light. Light head.