JPH047017B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor laser device, and more particularly to a technique for improving the noise characteristics of a semiconductor laser device in which light is confined using a refractive index waveguide mechanism.

In addition to optical communication systems, semiconductor laser devices have recently come to be used as light sources for pickup systems, particularly in video disk devices and audio disk devices. However, when a semiconductor laser device is used as a pick-up light source, noise is generated in the semiconductor laser device when the reflected light from the laser beam reflected from the disk surface becomes return light and enters the semiconductor laser device. This has resulted in a reduction in the quality of the reproduced images from the video disk or the generation of abnormal sounds in the reproduced sound from the audio disk, posing a serious problem in practical use.

It is known that multi-mode elements generate less noise due to the incidence of reflected feedback light and are more stable than elements with a single longitudinal mode. It is easier to obtain a laser element with a single longitudinal mode by confining light with a refractive index waveguide mechanism, and a laser element with multiple longitudinal modes is easier to obtain by confining light with a gain waveguide mechanism.

However, the transverse mode of a laser element that confines light using a gain waveguide mechanism is unstable, and the transverse oscillation mode tends to fluctuate due to changes in the injection current, etc., and when used in optical systems such as pickups, the optical The axis changes, making it impossible to put it to practical use.

Therefore, the semiconductor laser device used as a pick-up light source is one that confines light using a refractive index waveguide mechanism.In addition, from the viewpoint of suppressing noise generation, the laser device is designed to have multiple longitudinal modes. It is necessary to configure the element. As is well known, the refractive index waveguide mechanism can be obtained by defining the active layer at a heterojunction interface and imparting a difference in the refractive index of light to the active layer so that the light is focused onto a striped micro region. However, in this structure, the degree of light convergence is high, and the longitudinal mode generally becomes a stable single mode.

The present invention provides a semiconductor laser device comprising a single longitudinal mode semiconductor laser element having a refractive index waveguide mechanism, and in which a laser beam is output from one end face of a resonator of the semiconductor laser element as a pick-up light source. A new and useful semiconductor that multiplies longitudinal modes and suppresses the generation of noise in the reflected feedback light by attaching to the semiconductor laser element an optical feedback system that returns and injects the laser light output from the other end face of the resonator of the element. The object of the present invention is to provide a laser device.

Hereinafter, the present invention will be explained in detail according to embodiments with reference to the drawings.

Figure 1 shows the oscillation spectrum of a laser device that confines light using a refractive index waveguide mechanism. This spectrum shows a single longitudinal mode.

FIG. 2 is a schematic diagram of a semiconductor laser device showing one embodiment of the present invention.

The laser beam output from one cavity end face of the laser element 1 having the spectral characteristics shown in FIG. rate 70%
The light is reflected by a reflecting mirror 3 having a reflecting surface, and then enters the laser element 1 via the condenser lens 2 again. The oscillation spectrum at this time is shown in FIG. FIG. 3 shows that the vertical mode is multiple. By returning laser light to the laser element using a fixed reflection mirror, a single longitudinal mode element can be made into a multi-mode element.

FIG. 4 is a schematic diagram of a semiconductor laser device showing another embodiment of the present invention.

Laser light output from one resonator end face of the laser element 1 is incident on a self-occurring lens 4. A reflective film 5 is formed on the self-occurring lens 4, and the laser light incident on the self-occurring lens 4 is reflected by the reflective film 5 and returned to the laser element 1.

FIG. 5 is a schematic configuration diagram of a semiconductor laser device showing still another embodiment of the present invention.

The laser beam output from one cavity end face of the laser element 1 is reflected by the concave mirror 6, and the laser beam is reflected by the concave mirror 6.
will be returned to.

A single longitudinal mode is multiplied by inputting the laser light outputted from one resonator end face of the laser element into the laser element as optically reflected feedback light. If the longitudinal mode becomes a multi-mode, as described above, even when signal light from a disk plate or the like of the output light is incident, noise generation will be reduced and stable information detection will be possible.

It is practical to use the laser light used to multiply the longitudinal modes that is output from the resonant end facet of the pair of resonant end faces of the laser element, which is not the resonant end face used as a light source for a pickup system, etc. .

Note that when the longitudinal modes of the semiconductor laser output light are multiplied, it may be possible to extract a part of the laser light output from one cavity end face and return it, and use the rest as the output light as a light source. This method requires a special optical system to stably return part of the laser beam and output the rest as the light source, which complicates the structure of the device. This is also unfavorable from the point of view of effectively utilizing the output laser light as a light source.

However, as in the present invention, when the laser beam output from a pair of resonant end faces of a laser element is fed back from the resonant end face that is not the resonant end face used as a light source for a pickup system, etc., the above-mentioned problem occurs. No problems arise, and from this point of view as well, the present invention can be said to be very practical.

As explained in detail above, the present invention provides a semiconductor laser device in which a laser beam is used as a light source such as a pickup from one end face of a resonator in which light is confined using a refractive index waveguide mechanism to stabilize transverse modes. By attaching to the semiconductor laser an optical feedback system that returns the laser light output from the other end surface of the resonator of the semiconductor laser element, the longitudinal mode is multiplied. Noise generated when the feedback light is incident on the laser element is suppressed, and stable operation can be achieved.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the oscillation spectrum of a laser element in which light is confined by a refractive index waveguide mechanism. FIG. 2 is a schematic configuration diagram of a semiconductor laser device showing one embodiment of the present invention. FIG. 3 is an explanatory diagram showing the oscillation spectrum of the semiconductor laser device shown in FIG. 2. FIGS. 4 and 5 are schematic configuration diagrams of semiconductor laser devices showing other embodiments of the present invention, respectively. 1... Laser element, 2... Condensing lens, 3...
Reflection mirror, 4... Self-cleaning lens, 5...
Reflective film, 6... concave mirror.

Claims (1)

[Scope of Claims] 1. A semiconductor laser device comprising a single longitudinal mode semiconductor laser element having a refractive index waveguide mechanism, in which laser light is output from one end face of a resonator of the semiconductor laser element as a pick-up light source, A semiconductor characterized in that an optical feedback system is attached to the semiconductor laser element to make the laser light outputted from the other end surface of the resonator of the semiconductor laser element return and enter the semiconductor laser element, and the longitudinal modes of the output light of the semiconductor laser element are multiplied. laser equipment.