JPS5894142A - Optical head - Google Patents

Abstract

PURPOSE:To obtain a titled head which is suitable for mass production and has good characteristics, by irradiating a laser beam from a light source by an off- axis grating lens and converging its reflected light by another off-axis grating lens. CONSTITUTION:A laser beam irradiated from a semiconductor laser 11 is converged by an off-axis grating lens 13 and is irradiated on optical type recording medium 12 as a spot having a small diameter, and a reflected light from this recording medium 12 is converged by another off-axis grating lens 15 and is made incident to a light detector 14.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an optical head used for signal reproduction of disc-shaped recording media such as video discs and digital audio discs.

Technical Background of the Invention and Problems There have been various types of optical heads using semiconductor lasers as light sources, but their basic forms are shown in FIGS. In the method shown in the figure, a laser beam emitted from a semiconductor laser 1 becomes a parallel beam from a collimation lens 2#c, is converged by an objective lens 3, and is recorded as a minute spot with a diameter of about 11 am.

The medium 4 is irradiated. The reflected light from the recording medium 5 travels backward along the same optical path and returns to the semiconductor laser 1#c, and a reproduced signal is obtained by the photodetector 5 disposed on the opposite side.

The configuration of this method seems to be simpler than heads of other methods, but in order to obtain the focus error signal and the tracking error signal, it is necessary to use the Faupring method, and a drive means for this is required. On the other hand, the method shown in FIG.
The light is reflected by the light beam and guided to the photodetector 4 to obtain a reproduced signal.

At this time, it is necessary to insert a beam conversion element 8 such as a cylindrical lens or a prism between the beam splitter 6 and the photodetector 5 in order to obtain a focus error signal.

Therefore, this method has many drawbacks: it requires a large number of parts, has a large space factor, is complicated to manufacture and adjust, is expensive, and is prone to deviations due to aging.

What is common to the systems shown in Figures 1 and 2 is that the collimating lens 2 and the objective lens are heavy and expensive, and the driving devices for the focusing servo and tracking servo are large and consume a lot of power. increase Further, there are also drawbacks such as difficulty in obtaining sufficient frequency characteristics up to high frequencies.

2. Purpose of csaA This invention eliminates the above drawbacks, has a relatively simple structure,
It is an object of the present invention to provide an optical head that is easy to manufacture and adjust, is therefore suitable for mass production, and has poor characteristics.

Summary of the Invention The present invention provides a first ophthalmic gelating lens disposed between a light source made of a semiconductor laser and an optical recording medium, and a photodetector for receiving reflected light between the optical recording medium and the optical recording medium. A second ophaxis gelating lens is provided.

The laser beam from the light source is focused by the first off-axis gelating lens and irradiated onto the optical recording medium, and the reflected light from the recording medium is focused by the second off-axis gelating lens and sent to the photodetector. is reached, thereby producing a reproduced output.

Effects of the Invention The optical head having such a structure has the advantage that the structure is simplified because it does not require the Four Spring method 7 or the beam converting element 8 as in the case of the optical head shown in FIG. Furthermore, since the ophaxis gelating lens can be easily obtained through a process applying semiconductor microfabrication technology such as LSI, manufacturing and adjustment are easy, and the book can be made suitable for mass production. Further, the optical head obtained by the present invention can have good characteristics.

EMBODIMENT OF THE INVENTION An embodiment of the present invention will be explained below with reference to the drawings. A first ophthalmic gelating lens 13 is disposed in the middle of the optical path leading to the recording medium 12.

A second ophthalmic gelating lens 1 is provided to guide the reflected light from the optical recording medium 12 to the photodetector 14.
5 is disposed at a position symmetrical to the first ophaxis gelating lens 13. In addition.

As the photodetector 14, one having a light receiving surface divided into four parts is used.

The reflected light from the recording medium 12 is focused by the second off-axis gelating lens 13 and irradiated onto the optical recording medium 12 as a small diameter spot. and enters the photodetector 141.

At this time, since the photodetector 14 has a light-receiving surface divided into four parts, the focus error signal is output as the output of a differential amplifier connected to the output end of the photodetector 14 using the -beam method. , and the tracking error signal is pushed,
Each can be easily obtained as the output of a differential amplifier connected to the output terminal iζ of the photodetector 14 using the pull method.

The ophaxis gelating lens used in the optical head of the present invention is made of 'i1 consonant resist, for example, PMM.
For direct mass production using an electron beam on a glass plate coated with A,
Electron beam direct - painting method! A star mask is manufactured, and mass production can be carried out using the electron beam exposure method based on the star mask or the ultraviolet exposure method using an ultraviolet resist, as in the case of L8I.

This is a significant reduction in the cost of making using holographic technology.

Furthermore, the oscillation wavelength of semiconductor lasers is currently limited to near-infrared wavelengths of around 800 mm, and it is considered difficult to shorten the wavelength. An advantage of the present invention is that there are no sensitive sensitizers in this wavelength range, which makes it difficult to fabricate hologram lenses, but it is possible to fabricate axial-dating lenses.

Note that interference with the first-order light can be avoided by using an ophaxis gelating lens as in the present invention for the chromatic tube of zero-order light produced due to low diffraction efficiency.

FIG. 4 shows an embodiment in which the present invention is further embodied and a first off-axis gelating lens 13 and a second off-axis gelating lens 15 are integrally formed on a single glass plate 16. be.

In FIG. 4, 17 is a base body, and this base body 17 output device 1
4 is covered with a cap 18, and the opening of the first ophaxis gelating lens 13 and the second
A glass plate 16 on which an ophaxis gelating lens 15 is formed is attached also as a lid. Note that 19 in Figure 1 indicates a terminal.

By integrally forming the two offaxis gelating lenses in this way and attaching them with good mutual positional relationship, the adjustment of the offaxis gelating lenses 13 and 15 attached to the cap 14 can be performed with rotational speed within the image. Further, by devising the cover means for the base body 17 and the cap 18, such adjustment can be made unnecessary.

In the case of the embodiment shown in FIG. 4, the entire optical head can be packed into the size of a can package for semiconductor devices (for example, TO-5), so its weight should be 1 g or less. Can be done.

Furthermore, since the Offaxis Greiten lens itself is used as a window to seal the container, it is possible to have a structure with no waste.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but can be implemented with various modifications without changing the gist.

For example, in the above embodiment, by adding a cylindrical effect to the second ophthalmic gelating lens, the astigmatism method can be used to detect the focus error signal and the tracking error signal. The lens at this time can of course be obtained in one pattern, and its shape can also be easily obtained by calculation.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of an example of a conventional optical herad, 82
FIG. 3 is a schematic diagram of another example of the conventional optical head, FIG. 3 is a schematic diagram of one embodiment of the present invention, and FIG. 4 is a schematic diagram of another embodiment of the present invention. It is. 5... Photodetector 6... Beam splitter -- λ/4 plate 8... Beam conversion element 11
-・Disgraceful residence-S 12...Optical recording medium 1
3...-first ophthalmoscope reducing lens 14
. . . Photodetector 15 . . . Second ophthalmoscope reducing lens 1
6...Glass plate 17...Base 18...Cap 19...Terminal Figure 1 Front 2 Figures

Claims (1)

[Claims] A light source made of a Cυ semiconductor laser, an off-axis gelating lens II that converges and irradiates a laser beam from the light source onto an optical recording medium, and a second off-axis gelating lens that converges the reflected light from the recording medium. 1. An optical head comprising: a second off-axis gelating lens; and a photodetector that receives light converged by the second off-axis gelating lens and generates an output. (2) First Ofaxis gelating lens and Raku 2
2. The optical head according to claim 1, wherein the ophaxis gelating lenses are formed on the same plate. (3) Claim 1 or 2, characterized in that the light source and the photodetector are contained in a can package, and the first and second ophaxis gelating lenses are used as a lid and sealed. Optical head described in section. (4) The optical head according to any one of claims 1 to 3, characterized in that a cylindrical action is added to the second off-accurate Q-segregation lens.