JPS63229638A - Optical recorded information reader - Google Patents

Abstract

PURPOSE:To obtain a device superior in wavelength characteristic, noise characteristic, or the like by providing a non-reflection coating on one resonator end face of a semiconductor laser and reflecting and diffracting the emitted light from this end face on the principal surface of an optical recording medium to feed back the light to the semiconductor laser and projecting the emitted light from the other resonator end face to a photodetector. CONSTITUTION:A coating 2 of low reflectivity is provided on one resonator end face of a semiconductor laser 1, and the light emitted from this coated resonator end face is reflected on the principal surface of an optical recording medium 3 and is fed back to the semiconductor laser again. The light emitted from the other resonator end face is projected to a photodetector 6 for reception. Consequently, the incident light to the photodetector 6 is changed in accordance with the presence/absence and the condition of feedback of the reflected light from a disk 3. Thus, the intensity of light is read by the photodetector arranged in the vicinity of the exit end and the operation level of the semiconductor laser is adjusted to improve S/N of the photodetector output.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an apparatus for reading information signals from an optical recording medium such as an optical disk in the field of optical information processing.

Conventional technology A method for reading information recorded on the surface of an optical recording medium such as an optical disk is to focus a semiconductor laser beam onto the surface of the optical recording medium, and use a light receiving element to identify the amount of reflected light or diffracted light. It was done by doing. In such a conventional system, it was inevitable that a portion of the light reflected or diffracted by the surface of a medium such as an optical disk would return to the original semiconductor laser.

Problems to be Solved by the Invention In this way, when the own laser light is fed back from the optical disk surface to the semiconductor laser, the oscillation characteristics of the semiconductor laser become unstable and the noise level increases. However, there have been problems with the inaccuracy of the read information. Countermeasures have been taken to create a multi-vertical mode by superimposing high frequencies, but no fundamental solution has yet been found.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention actively utilizes the return light from the main surface of the optical recording medium, and uses an external This is intended to be a resonator type laser configuration.

A low-reflection coating is applied to one side of the resonator end face of the semiconductor laser, and the light emitted from the coated resonator end face is reflected by the main surface of the optical recording medium, returns to the semiconductor laser again, and is transmitted to the other resonator end face. The arrangement is such that the light emitted from the end face is irradiated onto the receiving light receiving element.

Function: This type of signal readout system utilizes the effect that when the semiconductor laser's own light is fed back, the semiconductor laser's characteristics (light intensity, threshold value, resistance, etc.) change. This can typically be read as light intensity with a light receiving element placed near the output end. In addition, by adjusting the operating level of the semiconductor laser,
It is possible to dramatically improve the S/N ratio of the light receiving element output.

EXAMPLE An example of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a semiconductor laser, 2 is a non-reflective coating film, 3 is an optical disk, 4 is a collimating or condensing lens, 5 is a reflecting mirror, 6 is a photodetector, and 7 is a laser driving device. Note that the film 2 may be a low-reflection coating film, and this case is also considered to be non-reflective. Light emitted from one end face of the laser 1 is reflected from the surface of the disk 3 and returned to the laser 1. The light emitted from the other resonator end face of the laser 1 enters the light receiving element 6. The light incident on the light receiving element 6 changes depending on whether or not the reflected light from the disk 3 returns and the situation. A semiconductor laser 1 having one end surface coated with a non-reflection coating usually has a higher oscillation threshold current than a normal one.

This is due to the increase in mirror loss in semiconductor lasers. On the other hand, information is written on the surface of the optical disk 3 so that the reflectance changes with respect to the light irradiated to read the information. If the laser, optical disk surface, etc. are constructed as shown in Fig. 1, a laser can be constructed by considering the optical disk surface as an external resonator surface, and at the same time, the reflectance of the external resonator surface is It varies greatly depending on the information recorded in the . These conditions are shown in FIG. When the amount of light reflected from the disk surface is large, the optical output-current characteristic of the semiconductor laser 1 becomes as shown in A, and the optical output becomes larger at an appropriate operating current value, and the signal read by the photodetector 6 becomes sharper. On the other hand, when the amount of light reflected from the disk surface is small, the optical output-current characteristic of the semiconductor laser 1 is as shown in B, and the optical output at the same operating current value ID is 'small', and the signal read out by the photodetector 6 is becomes smaller. By configuring the optical disk surface as one resonator surface of the external cavity laser, information on the optical disk surface can be transmitted to the photodetector 6.
It becomes possible to read out as an electrical signal from.

Although a semiconductor laser coated with an anti-reflection coating was used in the embodiment, the same effect can be obtained even when the reflectance is on the order of several inches.

Effects of the Invention As described above, according to the present invention, it is possible to stably read out information on an optical recording medium such as an optical disk through an optical signal with an extremely simple configuration, and it is extremely useful in practice.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an optical recording information reading device according to an embodiment of the present invention, and FIG. 2 is an output characteristic diagram of the device. 1...Semiconductor laser, 2...Non-reflection coat pattern, 3...Optical disk, 4...Optical lens, 5...Reflection mirror , 6...
Photodetector, a... Laser drive circuit.

Claims (1)

[Claims] One cavity end face of the semiconductor laser is coated with a non-reflection coating, and the light emitted from the cavity end face is reflected or diffracted by the main surface of the optical recording medium and returned to the semiconductor laser again. An optical recording information reading device arranged so that light emitted from the light receiving element is irradiated with the light emitted from the light receiving element.