JPH01146141A - Optical element - Google Patents

Abstract

PURPOSE:To minimize the internal stress due to the change of temperature and humidity to prevent the degradation in optical characteristic by providing a constricted part in a part of an optical element which is integrally molded with a synthetic resin. CONSTITUTION:In case of a hologram element 1, for instance, a synthetic resin superior in light transmittance like a polyacrylic ester resin or a polycarbonate resin is used as the synthetic resin constituting the optical element 1. An optical action part area 11 is provided in the center and junction parts 13 used for junction and fixing to metals 8 or the like are provided in both ends, and grooves having constricted sections are constituted between the optical action part 11 and junction parts 13 to form stress absorbing parts 12. A stress absorbing parts 12 having constricted sections function as a kind of dumper which absorbs the internal stress due to the change of volume of the fixed optical element 1 itself. Thus, the degradation in optical characteristic due to the change of volume of the synthetic resin optical element 1 itself is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to an optical element. More specifically, the present invention relates to a synthetic resin integrally molded optical element for separating, condensing, reflecting, etc. a light beam. The optical element of the present invention is useful, for example, as a hologram element which is an optical element in an optical pickup optical system used in an optical information recording/reproducing apparatus or the like.

(b) Conventional technology Recently, so-called compact disc players, video disc players, optical disc filling systems,
2. Description of the Related Art Optical information recording/reproducing devices such as CDROMs are being actively developed and improved.

In such an optical information recording/reproducing apparatus, reducing the size and weight of the optical pickup is an important issue.

Regarding this point, a proposal has been made to use a diffraction grating in place of the conventional splitter prism etc. for detecting focus errors and tracking errors of the light beam in the optical system of the optical pickup (Japanese Patent Application Laid-open No. 112246/1982). These are also called hologram elements.

Using such a hologram element in an optical system for optical pickup is advantageous not only in terms of its size and weight reduction, but also in terms of focus and tracking control. As this hologram element, a so-called glass hologram element in which a light diffraction part is provided on a glass plate is known, but efforts have been made to further reduce the weight and number of parts, and to improve the processability of the element itself. It is considered more advantageous to use a synthetic resin board of high quality.

(c) Problems to be Solved by the Invention Since the above hologram element is inserted into the optical path of the optical pickup, it must be fixed and mounted by bonding with adhesive to the metal wall material or members that constitute the optical pickup optical path. There is.

However, when the hologram element made of the synthetic resin described above is fixedly attached in this way, there is a large difference in linear expansion coefficient from that of metal, so when the environmental temperature changes, the bonding member absorbs the volume change of the hologram element. There is a problem in that internal stress is generated in the element and the optical characteristics are impaired.

Further, there is a problem in that a similar phenomenon occurs when the hologram element absorbs water due to an increase in humidity.

Such problems have occurred not only in the above-mentioned hologram element but also in various optical elements integrally molded with synthetic resin.

This invention was made under such circumstances,
In particular, the purpose is to prevent deterioration of optical properties due to volume changes of the synthetic resin optical element itself.

(d) Means for Solving the Problems Thus, according to the present invention, an optically active part capable of separating, condensing, reflecting, etc. a light beam is set in a synthetic resin molded body,
There is provided an optical element characterized in that a stress absorbing portion having a constricted cross section is provided between a joint portion of the molded body with another member and the optically acting portion.

This invention is configured to minimize internal stress caused by changes in temperature and humidity and prevent deterioration of optical properties by providing a constricted part in a part of an optical element integrally molded with synthetic resin. It is.

The optical element in this invention includes not only a hologram element, but also a lens element, a prism element, a reflecting mirror element, etc., and has at least an optical function part capable of separating, condensing, and reflecting a light beam, and is made of synthetic resin. It is sufficient if it is integrally molded.

Various synthetic resins can be used to construct optical elements, but for example, in the case of hologram elements, it is best to use synthetic resins with excellent light transmittance, such as polyacrylic acid ester resins and polycarbonate resins. Are suitable. A hologram can be created by forming a light diffraction section by forming a predetermined grating groove at a predetermined position on one surface of such a synthetic resin plate by machining or by forming a film of a hologram recording material such as a silver salt photosensitive material or dichromate gelatin. Devices can be manufactured.

In the optical element of the present invention, the stress absorbing portion having a constricted cross section is provided between the optically acting portion and the joining portion. Optical elements usually have an optically active region in the center and joints at both ends that are used for bonding and fixing with metal, etc. Therefore, grooves each having a constricted cross section are formed between the optically working region and the joints. It is preferable that the stress absorbing portion be formed by using the stress absorbing portion. Note that such a constriction can be easily produced by cutting, but it may also be directly produced using a corresponding mold when molding the synthetic resin substrate.

(E) Function The stress absorbing portion having a constricted cross section acts as a kind of damper that absorbs internal stress generated by volume changes that may occur in the fixed optical element itself.

(f) Example The present invention will be explained below with reference to the drawings.

FIG. 1A is a configuration explanatory diagram showing an optical pickup device using a hologram element 1 which is an embodiment of the optical element of the present invention. In the figure, the optical pickup device is composed of an aluminum cylinder 5 in which a condenser lens 2 and a hologram element 1 are arranged and fixed in order in the direction away from an optical disk 3 as a recording medium, and a semiconductor laser 6 is mounted at the center near the bottom of the aluminum cylinder 5. A photodetector 7 is arranged near the semiconductor laser 6. In addition, depending on the case, between the condensing lens 2 and the hologram element 1 or between the hologram element 1
A collimating lens 4 may be inserted between the laser diode 6 and the semiconductor laser 6 as shown in FIG. 1B.

A schematic enlarged sectional view of the hologram element 1 is shown in FIG. 2, an enlarged view of the main part is shown in FIG. 3, and a perspective view is shown in FIG. 4.

As shown in these figures, the hologram element 1 has a diffraction section 11 (diameter 3 mm) composed of a large number of grating grooves in the center of one side.
: A plate-like body made of acrylic resin (PMMA) (thickness: 1.5 m, length: 6 mm, width: 4 mm)
, both ends 13 serving as a joint part and the diffraction part 11
groove-shaped constricted portions 1 whose plate thickness rapidly decreases between them.
2 is provided. Here, the dimensions H and L of the constricted portion 12 are each 0.5 mm, and the taper angle α is approximately 9.
It is assumed to be 0°. In this embodiment, the hologram element 1 is bonded and fixed to lane-shaped bonding members 8 provided on both walls of the unsealed interior via both end portions 13 using an adhesive.

Since the hologram element 1 is bonded and fixed to a metal bonding member 8 and integrally molded with a synthetic resin material, internal stress is likely to occur due to changes in volume caused by changes in temperature and humidity. The stress concentrates on the weaker constricted portion 12 and is absorbed there. Therefore, deterioration of optical properties is prevented or suppressed without this stress affecting the diffraction section.

Note that the appropriate shape and dimensions of the constricted stress absorbing portion are not particularly limited to the cross-sectional shape of the constricted portion 12, as they depend on the material and overall shape of the target optical element, as well as the usage environment. .

At least, it is sufficient that a portion where the thickness rapidly decreases is provided at rl between the optically active portion and the bonding portion of the optical element.

(G) Effects of the Invention According to the optical element of the present invention, deterioration of optical properties that may occur due to volume changes can be prevented. Therefore,
It has excellent environmental resistance and can be expected to have new uses that have not existed before.

[Brief explanation of the drawing]

1A and 1B are configuration explanatory diagrams illustrating an optical pickup device constructed using a hologram element, which is an embodiment of the optical element of the present invention, and the second section is a schematic cross-sectional view of the hologram element, and the second section is a schematic cross-sectional view of the hologram element. Figure 3 is an enlarged view of the main part of Figure 2, and Figure 4 is an enlarged view of the main part of Figure 2.
The figure also shows a perspective view of the hologram element. 1...Hologram element, 11...Diffraction part, 12...Narrow part, 13...
・Both ends. Figure 1 AIM1rZIB 13 1J

Claims (1)

[Claims] 1. An optically active part that can separate, focus, reflect, etc. a light beam is set on a synthetic resin molded body, and there is a cross-sectional narrowing between the joint part with other parts of the molded body and the optically active part. An optical element characterized by being provided with a stress absorbing portion having a shape.