JPS58175148A - Optical pickup device - Google Patents

Abstract

PURPOSE:To detect a high-quality signal from a disc, by returning a specific quantity or more of the light of a semiconductor laser to reduce the noise accompanied with the change of the longitudinal mode of the laser. CONSTITUTION:About >=10% quantity of emitted light of a laser 1 is fed back. Since the noise is reduced rapidly by this feedback, a half mirror (reflection factor 20%) 15 having a reflective face vertical to the optical axis is provided in a parallel luminous flux 13 at the rear of a coupling lens 2 to feed back lights 14 to the semiconductor laser 1 stably (optical feedback quantity 20%).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pickup device using a semiconductor laser.

In optical pickups used for signal generation of optical discs, etc., the laser beam emitted from the conductor is narrowed down to a minute spot (K) on the disc signal surface using an optical lens, etc., and then modulated by the DZF signal. A photodetector converts the reflected light into an electrical signal and reproduces the information sound.

The configuration of this Nadeno Hikari big amplifier is shown in Figure 1.

The light beam of the semiconductor laser 1 is made into a parallel light beam by a coupling lens 2, and focused onto the signal surface of a disk 6 by an objective lens 5 along a polarizing prism 5 and a 1/4 wavelength 14Y.

The reflected light passes through an objective lens 5, a 1/4 wavelength plate 4, is reflected by a polarizing prism 5, and is converted into an electrical signal by a photodetector 7. Since this type of optical system uses a polarizing prism 5 and a quarter-wavelength plate 4, the reflected light does not return to the semiconductor laser in principle. Due to anisotropy (birefringence), etc., a small amount of light returns to the semiconductor laser 1, and it is impossible to reduce the amount of feedback light to V$&C. In this case, especially in a single mode laser diode with a longitudinal mode such as a refractive index guide structure, due to this small amount of feedback light, the longitudinal mode changes and the optical output changes.In the case of signal regeneration, this optical output fluctuation is caused by noise. Moreover, it has been difficult to detect a signal better than that from a disk.

SUMMARY OF THE INVENTION An object of the present invention is to provide an original pick amplifier device in which the drawbacks of optical output fluctuation noise described above are reduced.

Conventional single-mode lasers have been designed to reduce noise caused by feedback light by preventing light from returning to the semiconductor laser as much as possible (Reference: Nikkei Mechanical 12/21*1
ν81%).

The applicant used various semiconductor lasers in the optical system shown in Figure 1, and as a result of investigating the relationship between the level of this feedback noise and the amount of feedback in detail, we found that the noise becomes large at a certain amount of feedback, but above a certain amount. In fact, I discovered it. This will be explained below.

FIG. 2 shows the relationship between the amount of reflected feedback light and the noise level of a single mode laser. This is an example in which a C sp type laser is used and coupled with a numerical aperture of AA=Q and 15. Here, an optical system that controls the amount of light emitted from the semiconductor laser is not used. This is because the light emitting pattern of the semiconductor laser is an elliptical shape, and the light intensity distribution at the aperture of the objective lens is uniform and a small spot can be formed. Therefore, it is common for about 10 to 50 of the amount of emitted light to pass through the optical system, although it varies depending on the laser light emission pattern.

Hereinafter, the amount of feedback is defined as the amount of light passing through this optical system, %:1oo.

As can be seen from this second factor, the noise decreases rapidly when the return rate exceeds about 10%. Also, please return to the laser at least 2096.
The noise is almost reduced to a level where there is no problem.

This is thought to be due to the deterioration of the copy lens, such as when the single mode laser becomes multi-like when it is fed back beyond a certain level.

An embodiment of the present invention utilizing the phenomenon described above will be explained with reference to FIGS. 3-1 and 4.

FIG. 5 shows the structure of an embodiment of the present invention! i. A half mirror (reflectance of 20 cm) 15 with a reflective surface perpendicular to the optical axis is installed in the parallel light beam after the coupling lens 2, and provides stable optical feedback to the semiconductor laser 1. (Light return amount 2
0chi) can be performed.

Figure @4 is a configuration diagram of another embodiment of the present invention, in which the m-party prism 5
A half-mirror reflective coating 15' is applied to Kjtm@ without the addition of zero-incidence optical components, and there is an advantage that stable light feedback to the semiconductor laser 1 (light return amount 20-) can be performed.

As described above, in this embodiment, stable reduction of laser noise was achieved by optical feedback.

As described above, in the present invention, by returning part of the optical sound of the semiconductor laser, the noise level accompanying the change in the longitudinal mode of the laser is reduced, making it possible to detect a signal sound of higher quality than that of a disk.

Furthermore, it is clear that the effects of the present invention can be obtained without adding any optical components by providing a half-mirror coating with appropriate feedback i on the incident light surface and outgoing light surface of the polarizing prism.

[Brief explanation of the drawing]

Figure 1 is a basic configuration diagram of an optical pickup, and Figure 2 is the relationship between the amount of laser feedback light and noise! FIG. 6 is a block diagram showing one embodiment of the present invention, and No. 41 is a block diagram showing another embodiment of the present invention. 1... Semiconductor laser 2... Coupling lens 6
...Polarizing prism 4...1/4 wavelength rice 5...Objective lens 6...Disc 7...Photodetector 1
5...Laser light 14...Laser return party 15...Norf mirror 15'...Half mirror - Reflective coat representative patent attorney thin 1) Li Shinsai 1 figure 2 figure shi - The 尤n'1 Fffr crawl -! (Genzai 3 Diagram"?+ffi

Claims (1)

[Claims] t The light beam of the semiconductor laser is focused onto a disk by an objective lens through a coupling lens and a light deflection element, and the reflected light from the disk is picked up by a photodetector via the light deflection element. In an optical pickup device,
A translucent light return material having a surface perpendicular to the optical axis is provided between the coupling lens and the objective lens, and a light amount corresponding to 10% or more of the light amount narrowed down by the objective lens is always returned to the semiconductor laser. Optical pickup device with 1% mold. 2. The optical return material comprises a half-mirror reflection coat provided on the incident light surface side of the optical deflection element.
The optical pickup device described in Section 1.