JPH01233411A - Quartz aspherical lens and optical pickup head using same as constituting element - Google Patents

Abstract

PURPOSE:To reduce the size, weight, and cost of the optical pickup head which uses ultraviolet light as source light by using the quartz aspherical lens as its element. CONSTITUTION:The quartz spherical lens which has one or two aspherical surfaces is used as one element. The quartz aspherical lens is manufactured by utilizing a gel-sol method. High purity by purification is easily obtained by this method because the raw material is liquid, and quartz having excellent transmissivity to ultraviolet rays is obtained. Further, a mold which has the aspherical lens shape is only prepared to easily obtain the aspherical lens. When the quartz aspherical lens manufactured as mentioned above is used, a pickup convergence optical system consisting of five quartz aspherical lenses is replaceable with one quartz aspherical lens 5 and the optical system is reduced in size and weight.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to an optical pickup that records and reproduces information using light and a lens that is a component thereof.

[Conventional technology]

High-density recording is an important issue in the field of optical memory, which uses light to record and reproduce information.

As a means to solve this problem, a proposal has been made to further shorten the light wavelength (=780 B m ) currently commonly used.

[Problem to be solved by the invention]

If we continue to shorten wavelengths, and the wavelengths used will be in the ultraviolet region, the B
Optical glasses such as Im-7 have lower transmittance, making it impossible to assemble an optical system.

Therefore, when using ultraviolet light as a light source, quartz is used as the glass material for lenses, etc. However, since quartz has an extremely high melting point of 1700° C., it has the disadvantage that it is not easy to process.

Attempts to make aspherical lenses currently used in OD player throat and cup heads out of quartz are difficult due to problems with the heat resistance of the mold. Therefore, as a quartz lens, a spherical lens that can be obtained through ordinary grinding and polishing processes can be considered. However, when attempting to construct an optical pickup head using spherical lenses, it is necessary to use multiple lenses to eliminate aberrations. Therefore, it has been difficult to provide a compact, lightweight, and inexpensive optical pickup head.The present invention has been made in view of the above points, and its purpose is to The purpose of the present invention is to provide a small, lightweight, and low-cost optical head that uses ultraviolet light as a light source.

[Means to solve the problem]

The quartz lens of the present invention is characterized by using one or two aspheric surfaces. Further, the optical pickup head of the present invention is characterized by having a quartz aspherical lens as a component.

[Effect]

The quartz aspheric lens is patented (patent application No. 62-204767)
By the method using the sol-gel method described in [
will be produced. According to this method, since the raw material is a liquid, high purity can be easily achieved through purification, and quartz having good transmittance in the ultraviolet region can be obtained. Further, an aspheric lens can be easily obtained by preparing a mold having an aspheric lens shape. By using the quartz aspherical lens manufactured in this way, the pickup focusing optical system (Fig. 1 (α)), which was conventionally composed of five quartz spherical lenses 2, can be replaced with a single quartz spherical lens. It can be replaced with an aspherical lens 5 (FIG. 1(b)), and the optical system can be made smaller and lighter. Furthermore, by using such a quartz optical element, for example, a He-Od laser (λ=525n) is used as a light source.
If m) is used, the recording density will be improved by about 4 to 5 times compared to the current semiconductor laser light source with λ=780 rzm.

〔Example〕

81(00,H,), 21.2 f, H,O1
5f, finely powdered silica 51 with an average particle size cL of 15μ was mixed and hydrolyzed to obtain a homogeneous sol. Add this sol to the second
The mixture was poured into a mold 6 having a convex lens shape with aspherical surfaces on both sides, the cross-sectional shape of which is shown in Figure (α), and gelatinized.

After gelation, the gel was taken out from the wholesaler 6 and dried at 60° C. for one week to obtain a porous silica gel. By sintering this porous silica gel in a sintering process at 1250° C., a quartz double-sided aspherical convex lens 7 was obtained. (Figure 2(b)
) This lens has a focal length liI! Gobaku, N people = 146.
It is a finite system lens with a wavefront aberration of 105λ. The quartz double-sided aspherical lens 7, the quartz λ/4 plate 8, the Gran-IF
ouscault Prism 9, He -Od V-The (
λ=5257'F'') e Signal detection system optical device 11. Using the photodetector 12, an optical pickup optical system shown in FIG. S was fabricated.

A laser beam is emitted from the H.-Od laser, and the disk 15 is
When I observed the focused spot above, the spot diameter was 14.
It was a μ book. Also, the width (
It was possible to detect a pit signal consisting of a group of bits with L2μ wind, depth (LO8μ), and length α45 to 1.5μ.

〔Effect of the invention〕

As explained above, according to the present invention, by using a quartz aspherical lens as a component in an optical pickup head optical system that uses ultraviolet light as a light source, the optical pickup head can be made smaller and lighter. This has the effect of making it possible to lower prices. Furthermore, since ultraviolet light is used as the light source, it has the effect of enabling higher-density recording than conventional pickups that use semiconductor lasers as the light source.

[Brief explanation of the drawing]

FIG. 1(α)(b) is a diagram explaining the action of the lens of the present invention, FIG. 2(α)(b) is a diagram explaining an embodiment of the quartz aspherical lens of the present invention, FIG. 1 is a diagram illustrating an embodiment of an optical pickup head of the present invention. 1... Laser 2... Quartz spherical lens 3... Light beam 4... Body 5. ......Quartz aspheric lens 6...
...Mold 7 having a double-sided aspherical convex lens shape...
...Quartz double-sided aspherical convex lens λ 8 ......Crystal/4 plates 9 ...Glan-Foucauet
Prism 11...Signal detection system optical device 12
...Photodetector 13 ...Data signal processing circuit 14 ...Error signal processing circuit 25 ...Disc or more Applicant Seiko Epson Co., Ltd. Agent Patent attorney Mogami (1 other person) Figure 1 (α2 Figure 2)

Claims (2)

[Claims] (1) A quartz aspherical lens characterized by using one or two aspherical surfaces. (2) An optical pickup head characterized in that the quartz lens described in item 1 is used as a component.