JPH03104022A - Optical head - Google Patents

Abstract

PURPOSE:To reduce the number of parts and to make an optical head small in size and light in weight by providing two-divided concave mirrors equipped with various focal distances. CONSTITUTION:Light emitted from a semiconductor laser 1 is condensed through a collimator lens 2, beam splitter 5 and objective lens 4 to an optical recording medium 3. After the reflected light from the medium 3 is splitted by the splitter 5, the optical path of the light is bent at 90 deg. by two-divided concave mirrors 9 equipped with the various focal distances and the light is condensed to a photodetector 7 set up in a center between the two focal positions of the mirrors 9. It is preferable to provide a moving means 12 to move the mirrors 9 so that a spot can be formed at the photodetection center of the detector 7, and it is also preferable to use a reflection type hologram lens, which is divided into two and equipped with the various focal distances, instead of the mirrors 9.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical head for an optical disc.

2. Description of the Related Art In recent years, with the spread of compact discs and the development of optical recording media such as optical discs, magneto-optical discs, and optical cards, optical heads for use in playback devices 1 or recording/playback devices have been actively developed.

Furthermore, various improvements have been made to methods for positioning and adjusting optical components, which are important in manufacturing optical heads.

A conventional optical head will be described below with reference to the drawings.

FIG. 4 is a configuration diagram of a conventional optical head, in which 1 is a semiconductor laser, 2 is a collimating lens for converting the diverging light emitted from the semiconductor laser 1 into a thousand lines of light, 3 is an optical recording medium, and 4 is a An objective lens for condensing light onto the optical recording medium 3; 5 a beam splitter for separating a part of the reflected light from the optical recording medium 3; 6 a beam reflected by the beam splitter 6; 8 is a detection lens for condensing the light, 8 is a 4-split photodetector for detecting the optical information 1 or the focus error signal of the optical recording medium 3, and 8 is a 90-degree optical path.
It is a two-divided stepped mirror that is deflected and focused on the photodetector 7.

Problems to be Solved by the Invention However, in the above conventional configuration, the adjustment of the detection lens and the
The adjustment button of the divided stepped mirror 8 and the photodetector must be adjusted respectively. Another problem is that the number of parts is large and it takes up a large amount of space.

The present invention solves the above-mentioned conventional problems, and aims to provide a smaller and lighter optical head.

Means for Solving the Problems To achieve this object, an optical head of the present invention includes a focusing semiconductor laser, an objective lens for condensing light emitted from the semiconductor laser onto an optical recording medium, and the semiconductor laser. and a beam splitter provided between the objective lens; a concave mirror divided into two parts with different focal lengths and provided in a direction in which the reflected light from the optical recording medium is separated by the beam splitter; It consists of a photodetector installed approximately at the midpoint between the two focal points.

Effect: With the above configuration, the number of parts can be reduced, and a smaller and lighter optical head can be provided.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of an optical head in a first embodiment of the present invention, in which 1 is a semiconductor laser, 2 is a collimating lens, 3 is an optical recording medium, 4 is an objective lens, 5 is a beam splitter, and 7 is an optical head. The configuration of the detector is similar to that of the conventional example. Reference numeral 9 denotes a two-divided concave mirror, each of which has a different focal length, bends the light emitted from the beam splitter 6 by 90 degrees, and connects two spots on the photodetector T. The photodetector 7 is connected to the second part of the concave mirror 9. A moving means is installed at the center of the focal point position and further adjusts the concave roller 9 along the curved surface 11 so as to connect the spot to the center of the light receiving surface of the photodetector 7, as shown in FIG. I have 12.

FIG. 2 shows the state of the spot on the photodetector T when the button is pressed in the first embodiment of the present invention. 71L, completed b, 70, 7
d is a light receiving element included in the photodetector 7, respectively. Figure 2a shows the case where the objective lens 4 moves away from the disk 3, Figure 2b shows the case at the focal position, and Figure 2C shows the case where the objective lens 4 moves away from the disk 3.
indicates the case where the objective lens 4 moves in a direction approaching the disk 3, and shows that the differential output changes in each case.

Next, a second embodiment of the present invention will be described with reference to the drawings.

FIG. 3 is a configuration diagram of an optical head showing a second embodiment of the present invention. The difference from the first embodiment in the figure is that a two-divided reflective hologram lens 13 with different focal lengths is provided in place of the two-divided concave mirror 9.

According to the first and second embodiments, instead of the conventional detection lens having a condensing function and the stepped mirror divided into two, two
Since the divided concave mirror 9 or the two-divided reflective hologram lens 13 is used, the number of parts can be reduced and a compact optical head can be provided.

Effects of the Invention The present invention can reduce the number of parts by providing a two-part concave mirror assembly having two focal lengths or a two-part reflection hologram lens. Furthermore, by providing a moving means for moving the concave mirror on a curved surface so as to connect the spot to the center of the light-receiving surface of the photodetector, the shift of the spot on the photodetector due to adjustment is reduced.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an optical head according to a first embodiment of the present invention, FIG. 2 is an explanatory diagram of a focus detection system of an optical head according to the present invention, and FIG. FIG. 4 is a diagram showing the configuration of a photodetector of an optical head according to the prior art.

Claims (3)

[Claims] (1) A semiconductor laser, an objective lens for condensing light emitted from the semiconductor laser onto an optical recording medium, a beam splitter provided between the semiconductor laser and the objective lens, and a beam splitter for condensing light emitted from the semiconductor laser onto an optical recording medium. an optical system consisting of a concave mirror divided into two parts having different focal lengths and provided in a direction in which the reflected light of the mirror is separated by the beam splitter, and a photodetector provided at a substantially midpoint position between the two focal points of the concave mirror. head. (2) The optical head according to claim 1, further comprising a moving means for moving the concave mirror so as to connect the spot to the light receiving center of the photodetector. (3) The optical head according to claim 1, wherein instead of the two-divided concave mirror, a two-divided reflective hologram lens having different focal lengths is used.