JPH0281335A - Optical pickup - Google Patents

Abstract

PURPOSE:To extremely miniaturize and lighten the title pickup by forming a diffraction grating for diffracting a beam to detect the modulation signal, automatic focus detection signal, and tracking detection signal in a focused spot forming lens to a medium in multiple layers. CONSTITUTION:The beam from a laser light source 1 is sent to an objective lens 2, and focused to read the recording pit 3. The reflected beam is returned to the objective lens 2 along with the automatic focus, tracking, and information signals. A diffraction grating 4 (hologram) is stamped on the surface of the objective lens 2 to diffract the return light, hence zeroth- and + or -first-order diffracted light are formed, and the light is sent to an automatic focus detector 5 and a tracking detector 6. Since the diffraction grating is stamped on the front or rear of both sides of the objective lens 2 in this way, a beam splitter can be dispensed with, the optical pickup is remarkably lightened, and the cost can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a recording/reproducing pickup optical system for an optical disc that records information as a row of pits and reproduces the information by shining a light spot on the information.

[Conventional technology]

Conventionally, the optical system of an optical disk pickup consists of a light source, collimator, beam splitter, focus lens, autofocus and tracking detection optical system, etc., and each component is assembled into a single body. . This has many drawbacks, such as a large number of assembly steps, no reduction in cost, increased weight, and the time it takes to access between tracks. Additionally, related devices of this type include:
For example, Hitachi Hyoron, Vol. 65, No. 10 (1981)
(October) Pages 23 to 38, etc.

(Problems to be Solved by the Invention) The purpose of the present invention is to eliminate the above-mentioned drawbacks, significantly reduce the number of parts, simplify the assembly process, reduce costs, and significantly reduce the weight of the entire reproduction optical system. The objective is to realize high-performance optical pickups for audio, video, data recording/playback, and erasable types.

[Means to solve the problem]

The above object is achieved by applying the multiple recording property of holography. That is, the basic components of an optical pickup include a semiconductor laser light source and an objective lens that focuses the beam from the light source onto the recording medium.
The other parts are considered to be attached to these parts. Then, in order to detect modulation signals, automatic focus detection, and tracking signals, a beam splitter that serves to take out the reflected beam from the medium is made into a hologram.

This is imprinted on the objective lens as a transmission phase hologram (diffraction grating).

Furthermore, the modulation signal, autofocus and tracking signal detectors are hybridized beside the semiconductor laser and housed in one package.

By doing the above, the optical pickup components can be reduced to two components: an objective lens with a beam splitter engraved thereon, and an element that integrates a detector and a light source, and the above objective can be achieved. .

[Effect] FIG. 1 provides a detailed explanation of the invention.

The beam from the laser light source 1 reaches the objective lens 2 and is focused to read the recording pit 3. The reflected beam is
It returns to the objective lens 2 again, including autofocus, tracking, and information signals. A diffraction grating (hologram) 4 is engraved on the surface of the objective lens 2, which diffracts the returned light to generate 0th-order and ±1st-order diffracted light, respectively, and an automatic focus detector 5. and a tracking signal detector 6.

In this way, by imprinting a diffraction grating on the front or back surface or both of the objective lens 2, a beam splitter is no longer necessary, and the optical pickup is reduced to two components: the objective lens and the photoelectric conversion section. Significant weight and cost reductions will be realized.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

That is, FIG. 2 is a front view of the objective lens explained in FIG. 1. This diffraction grating is formed as follows. That is, as shown in FIG. 3, a beam from a coherent laser light source 8 is split into three beams by a beam splitter 9.

Each beam is focused by lenses 10 to 12,
The diverging light is divided into the aforementioned aspherical plastic or glass lens 2.
The above is a method of forming a holographic diffraction grating, in which interference fringes formed on the back surface 7 or the photosensitive material coated on the front surface are recorded. There is also a method of determining the interference fringes formed by theoretical calculations, and then imprinting and transferring the determined pattern onto a mold for an aspherical plastic lens.

Needless to say, the latter method will be used for mass production.

FIG. 4 shows the explanation. That is, mold 1
A diffraction grating pattern 14 determined by numerical calculation is formed on one side of the plastic material 15 by embossing 16. At this time, the curvature of the mold is an aspherical surface.

Single lens provides high NA1, for example 0.4 or more.

The lens 17 is as follows.

Furthermore, to give an example of an autofocus (AF) system,
As shown in FIG. 5, the front light detector for AF is divided into 52 or 4 parts, and the front and rear differentials using the edge 18 are used.
Automatic focus detection based on the difference in light amount between the divided detectors, or a method of detecting astigmatism caused by the cylinder lens 19 and the diagonal plate 20 using a four-divided detector, etc., are used.

On the other hand, regarding tracking, a method of detecting a change in light amount caused by a tracking deviation of a diffraction pattern by a pre-group pre-crimped on a disk;
Alternatively, it may be prewritten on the disc. It becomes possible to apply a method using a row of pre-pits for sample servo.

[Effects of the Invention] As described above, according to the present invention, it is possible to reduce a pickup for recording and reproducing an optical disc to two component parts: an objective lens section and a photoelectric conversion section.
Ultra-compact pickup.

Or it can be made lighter. In addition, adjustment becomes easy, and a significant cost reduction can be expected.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, FIG. 2 is a front view of the objective lens 2, FIG. 3 is a diagram showing a method of forming a diffraction grating by a holographic method, and FIG. 4 is a diagram showing the present invention. FIG. 5, which is a diagram showing the manufacturing process of the engraved lens according to the invention, is an explanatory diagram of the automatic focusing method. DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 2... Engraved aspherical plastic lens, 3... Optical disc, 4... Diffraction grating, 5... Automatic focus detector, 6... Tracking detector, 7 ...Diffraction grating, 8...Semiconductor laser, 9...
・Beam splitter, 10-12...lens, 13.
14...Mold, 15...Plastic or glass,
18...Edge, 19...Cylinder lens. 11-Y--NoN

Claims (1)

[Claims] 1. An optical pickup that records and reproduces information on a medium as a row of pits, which is equipped with means for guiding a modulated beam through the recording medium, and is equipped with a means for guiding a modulated beam through the recording medium, and a means for guiding the modulated beam and an automatic focus detection signal. An optical pickup characterized in that a diffraction grating for deflecting a beam for detecting a tracking detection signal is multiplexed on a lens for generating a focusing spot on a medium.