JPH087313A - Optical head - Google Patents

Abstract

PURPOSE:To stably record/reproduce data even when temperature change by making thermal expansion coefficients of a lens holder material fixing a collective lens and an optical head base material fixing a photodetecting element different from each other when placing the materials. CONSTITUTION:A material for a lens holder 2 fixing a collective lens 1 and a photodetecting element 4 are fixed. A thermal expansion coefficient of the material is made different from that of a material for an optical head base 3. Supporting that the thermal expansion coefficient of the material for the lens holder 2 is A1, the thermal expansion coefficient of the material for the optical head base 3 is A2, a distance from a fixed position of the lens holder 2 to the collective lens 1 is X1, and a distance from the fixed position of the lens holder 2 to the photodetecting element 4 is X2, A1XX1=A2XX2 is satisfied. Since a distance between the optical part 2 and 3 can be kept constant inn a wide temperature range in this manner, data can be recorded/reproduced stably even when temperatures change.

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 writing and reading information on a recording medium such as an optical disc or a magneto-optical disc by using an optical spot.

[0002]

2. Description of the Related Art Various optical parts such as lenses and prisms are used in an optical system of an optical head. These optical parts are adhered and fixed to a base by an adhesive.
Optical head In order to stably exhibit the performance of the optical head, it is necessary to minimize the positional displacement and the collapse due to the adhesion of the optical components. Therefore, various proposals have been made conventionally.

In Japanese Laid-Open Patent Publication No. 59-223956, the optical base and the substrate for the light receiving element are made to have the same coefficient of thermal expansion so that the condensing position does not shift on the light receiving element due to temperature change. It is disclosed. Also,
In Japanese Patent Laid-Open Nos. 63-39148 and 63-52340, when an objective lens actuator made of a different material is mounted on the optical base, a cushioning material is sandwiched between the optical base and the actuator to suppress distortion of the optical base and the actuator. It is disclosed.

Further, in Japanese Patent Laid-Open No. 63-148435, it is disclosed that the material of the optical base is selected to be equal to the coefficient of thermal expansion of the optical component to suppress the deviation of the relative position and angle of the optical component due to temperature change. Has been done. Further, Japanese Patent Application Laid-Open No. 63-269323 discloses that a part of the optical component is used for adhesion so that expansion and contraction of the optical base does not affect the optical component. .

[0005]

However, in all of the above techniques, the purpose is to suppress the distortion of the optical base that occurs due to temperature change when dissimilar materials are attached to the optical base, and the distance relationship between the optical components. Has no effect on changes in. Therefore, in the case of these disclosed technologies, there is not much problem when parallel light passes between optical components, but defocusing and collimation failure occur between elements such as a condenser lens and a collimator lens that generate focused light. .

An object of the present invention is to provide an optical head that solves these problems.

[0007]

In order to solve the above problems, the present invention provides an optical head in which an optical base for mounting a light receiving element and a holder for a condenser lens are made of materials having different thermal expansion coefficients. Configured.

[0008]

Since the present invention is configured as described above, even if the ambient temperature of the optical head changes and the distance between the mounting position of the lens holder and the light receiving element changes, the relative distance between the condenser lens and the light receiving element also changes. Can be suppressed.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a partial sectional view of an optical head showing an embodiment of the present invention.

The condenser lens 1 is fixed to the condenser lens holder 2 and then screwed to the optical base 3. The light receiving element 4 is bonded to the optical base 3 via the substrate.

Here, X1 = 20 mm, X2 = 50 m
m, the material of the condenser lens holder 2 is glass fiber reinforced plastic (coefficient of thermal expansion 60 × 10 ¹⁰ ) and the material of the optical base is aluminum (coefficient of thermal expansion 24 × 10 ⁻⁶ ).
In FIG. 2, which is the conventional method, the working distance is X.
= 30 mm, X = 30.00 with a temperature rise of 10 degrees.
It becomes 7 mm, and a 7 micron defocus occurs. In this method, X1 = 20.112 mm, X2 = 50.12
mm, the working distance is X3 = X2-X
No change at 1 = 30 mm.

Here, the combination of materials is not limited to aluminum and plastic. The selection of X1 and X2 may be a value that allows the change of the working distance to be within the allowable value within the predetermined temperature range. Although the relationship between the condenser lens 1 and the light receiving element 4 is dealt with here, the same can be said for the relationship between the laser diode and the collimator lens. The method of fixing the lens holder is not limited to screwing.

[0013]

As described above, according to the configuration and method of the present invention, the distance between optical components can be kept constant in a wide temperature range, and stable recording / reproducing can be performed even if the temperature changes. .

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of an optical head showing an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of a conventional optical head.

[Explanation of reference numerals] 1 condenser lens 2 condenser lens holder 3 optical base 4 light receiving element

Claims (2)

[Claims] 1. An optical head, characterized in that a lens holder material for fixing a condenser lens and an optical head base material for fixing a light receiving element are made to have different thermal expansion coefficients from each other, and both are attached. 2. The coefficient of thermal expansion of the lens holder material is A
1. The coefficient of thermal expansion of the optical head base material is A2, and the distance from the fixed position of the lens holder to the light receiving element is X.
1. When the distance from the fixed position of the lens holder to the light receiving element is X2, it is set such that A1 * X1 = A2 * X2.