JPH01183186A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To decrease a reduction in an optical output due to temperature rise and to obtain the output having a predetermined intensity at the time of driving a pulse by increasing the end face reflectivity for outputting a laser beam to be mainly used as compared with that of the other end face. CONSTITUTION:The reflectivity of a front end face for outputting a laser beam to be mainly used is increased over that of a rear end face. Accordingly, optical output P current I characteristic for the light emitted from the front end face becomes as shown in fig. a, and optical output P - current I characteristic for the light emitted from the rear end face becomes as shown in Fig. b. Generally, the light emitted from the front end face having high reflectivity becomes lower in efficiency than that from the rear end face. Accordingly, even if the temperature of an active layer is raised by the conduction of a pulse driving current I of a semiconductor laser, a reduction in the optical output P can be reduced as designated by an arrow due to its low efficiency. thus, the variation in the optical output can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser suitable as a light source for a printer, for example.

[Conventional technology]

A laser beam printer drives a semiconductor laser (hereinafter abbreviated as LD) with a pulse current, and prints with a light output corresponding to the drive current waveform. As LD, the third
The Fabbri-Bello type shown in the figure is common.

The LD chip 1 shown in FIG. 3 has two resonator end faces 2.
When GaAs is used as the material, both end surfaces 2 and 2a have a reflectance of 32%. As shown in FIG. 4, this LD chip 1 is assembled into a heat dissipation block 4, further assembled into a stem 6 in which a light receiving element 5 for controlling the light output of the LD is incorporated, and a window glass 7 is assembled.
A semiconductor laser device is obtained by attaching the attached cap 8.

In this semiconductor laser, the emitted light 3 from the front end surface 2 of the LD serves as a light source for the printer, and the intensity is controlled by the emitted light 3a from the rear end surface 2a which is incident on the light receiving element 5 for controlling light output.

By the way, when a pulse drive current I as shown in FIG. 5(a) is passed through a normal LD, it is desirable to obtain an optical output p with a waveform corresponding to the drive current waveform.
As shown in Figure (b), due to the thermal characteristics of the LD, the optical output P decreases ΔP at the final pulse stage t2 compared to the optical output PF at the initial pulse stage t1. As shown in FIG. 6, this is due to the fact that the optical output P-I characteristic of the LD tends to fluctuate significantly depending on the temperature, and the operating current . Even if the temperature is kept constant, as the temperature rises, it will shift as shown by the arrow in the figure. That is, when the LD is energized by the drive current, the L
As the temperature of the active layer of D increases, as shown in Fig. 6, the optical output P-current characteristic changes, and even if the pulse current is constant, the optical output at the final stage t2 of the pulse is lower than that at the initial stage t1. A decrease in P will occur.

[Problem to be solved by the invention]

In the conventional LD as described above, as shown in FIG.
Since the optical output P decreases, there is a problem in that when used as a light source for a printer, printing results in shading.

The present invention has been made to solve these problems, and an object of the present invention is to provide a semiconductor laser that can reduce the decrease in optical output due to temperature rise and provide a constant intensity of optical output during pulse driving.

[Means to solve the problem]

In the semiconductor laser according to the present invention, the reflectance of the end face on the side from which laser light is mainly used is higher than the reflectance of the other end face.

(Function) In this invention, the output efficiency from the end face on the side from which laser light is taken out is reduced, and the slope of the optical output-current characteristic of the laser light emitted from this end face becomes gentle.

〔Example〕

FIG. 1 is a side view showing an embodiment of the semiconductor laser of the present invention.

In this figure, the same symbols as in FIG. 3 indicate the same parts, 9a is a λ/4 thick AuzO3 film, 9b is a λ/2 thick A
J22o, film 10, is a λ/4 thick Si film (where λ is the oscillation wavelength), and is formed by electron beam evaporation or sputter evaporation.

Next, the operation will be explained.

In this embodiment, the front end surface 2 includes an AfL2o3 film 9a with a thickness of λ/4 and a Si film 10. A dielectric film consisting of three layers of An2o3 film 9a is formed, and AJ120 with a thickness of λ/2 is formed on the rear end surface 2a.
An s film 9b is formed. In this way, λ with different refractive index n
When a multilayer film of /4 thickness (nA203=1.6.ns+=4) is formed, the reflectance increases, and the reflectance at the front end surface 2 is about 60%. On the other hand, AJ with λ/2 thickness
The reflectance at the rear end surface 2a on which the 22O3 film 9b is formed does not change and remains at 32%. The AJ120s films 9a and 9b also function as protective films for both end surfaces 2 and 2a.

In this way, when the reflectance of the front end surface 2 from which the laser beam mainly used is made higher than that of the rear end surface 2a, the front end surface 2
As shown in FIG. 2(a), the optical output P-current characteristic for the emitted light 3 from the rear end surface 2a is as shown in FIG.
The optical output P-current characteristic for the current is shown in FIG. 2(b).

Generally, Pth is the optical output at the oscillation threshold Ith,
Operating current I. When the optical output at , is expressed as POI, the output light 3 from the front end surface 2 with high reflectance has an efficiency η
is lower than the output light 3a from the rear end surface 2a.

That is, even if the temperature of the active layer rises due to the application of the pulse drive current I of the LD, since the efficiency η is low, the decrease in the optical output P can be reduced as indicated by the arrow in FIG. 2.

Therefore, if used as a light source for a laser beam printer, for example, no shading will occur in printing. In the above embodiment, the case where the reflectance of the front end surface 2 is 60% and the reflectance of the rear end surface 2a is 32% is explained, but the effect of this invention is to reduce the efficiency of the emitted light 3 from the front end surface 2. It goes without saying that the reflectance is not limited to the above-mentioned reflectance.

(Effects of the Invention) As explained above, in this invention, the reflectance of the end face on the side from which the laser beam mainly used is made higher than the reflectance of the other end face, so that there is less reduction in optical output during pulse driving, and the printer This has the effect of making it suitable as a light source for devices that cannot tolerate fluctuations in optical output.

[Brief explanation of the drawing]

FIG. 1 is a side view showing an embodiment of the semiconductor laser of the present invention, FIG. 2 is a diagram for explaining optical output-current characteristics, FIG. 3 is a diagram showing a semiconductor laser chip, and FIG. 4 is a diagram showing the semiconductor laser chip. FIG. 5 is a diagram showing the structure of a laser; FIG. 5 is a diagram for explaining the decrease in optical output in a conventional semiconductor laser; FIG. 6 is a diagram for explaining the optical output-current characteristic of a conventional semiconductor laser. In the figure, 1 is the LD chip, 2.2a is the end face of the resonator, 3.3a is the emitted light, 9a and 9b are IQ203 films, 10
is an St film. Note that the same reference numerals in each figure indicate the same or corresponding parts. Agent Masuo Oiwa (2 others) Figure 3 Figure 4 - Y Inn, 7a Figure 5 a 3a 5 Figure 6 - Temperature rise

Claims (1)

[Claims] A Fabry-Perot semiconductor laser having two opposing cavity end faces, characterized in that the end face reflectance on the side from which laser light is mainly used is higher than the reflectance on the other end face.