JPS6010686A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To oscillate a semiconductor laser device in a low noise with a stable light output by enhancing the reflectivity of two resonator ends higher than that of the end of a semiconductor crystal material itself. CONSTITUTION:The reflectivity of a light in an oscillating wavelength of two resonator ends are enhanced larger than that of a semiconductor crystal itself of a laser medium, and smaller than that of 100 percent. Since the reflectivity of the resonator end is high in such a structure, the ratio of the returning light of the light itself into the resonator is decreased, and since the reflectivity is high, the light energy stored therein is hardly affected by the influence of the light incident from the exterior, thereby obtaining stable oscillated state. Further, since the reflectivity of the both ends is smaller than 100%, the lights can be produced from both side ends.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor laser device used as a light source for optical information processing.

Conventional configurations and their problems Semiconductor lasers have many features such as being small, highly efficient, and can be directly modulated by drive current.In recent years, semiconductor lasers have been used as light sources for optical communications and optical information processing. It has come to be used as a.

In order to use it for these purposes, it is necessary that fluctuations in optical output, that is, optical intensity noise, be small.

Page 2 In particular, it is important to have little light intensity noise when the own light is reflected and returned when coupled with an optical system.

Conventional semiconductor lasers, such as the one shown in FIG.
A groove 11 is provided in the A s substrate 1, and n - Ga is formed on this groove 11.
1y A 7 y As (y SaO-4) layer 2
, n Ga1゜AI As (x=○~0.2) active layer 3 r p Ga 1yAll As (y=0.4
) In the semiconductor laser equipped with layer 4, the crystal cleavage is used for the resonator end face, and this end face is usually left unattached or coated with a dielectric film such as SiO2 or A12o3 at λ/ 2n (n is the refractive index of the material λ
is the thickness of the laser (laser oscillation wavelength). In addition, 5 is an n-GaAs layer, and 6 is T i / P t /
Au electrode, 7 is Au-Ge-N i electrode, 51 is Zn
This is a diffusion area. The current-optical output characteristics and current-noise characteristics of such a semiconductor laser are as shown in FIG. Furthermore, when the optical output is kept constant at 3 mW and the own light returns by about 0.1 to 5% by reflection, the temperature dependence of the signal-to-noise intensity ratio is as shown in Figure 3.
Page Ru. In these figures, the noise frequency is 2 to 12III, and the noise bandwidth is 300kt (measured at There wasn't.

OBJECTS OF THE INVENTION In view of the above drawbacks, the present invention provides a semiconductor laser that can oscillate with low noise even in the presence of return light.

Structure of the Invention In order to achieve this object, the semiconductor laser of the present invention has a reflectance of light at the oscillation wavelength of the two cavity end faces that is higher than the reflectance of the semiconductor crystal itself as a laser medium, and has a reflectance of 1o.
It consists of making the reflectance smaller than ○%.

With this configuration, the reflectance of the resonator end face is high, so the proportion of the return light of the own light returning to the inside of the resonator is small. Under the influence of incident light
, a stable oscillation state can be obtained. Furthermore, since the reflectance of both end faces is smaller than 100%, light can be extracted from both end faces, and one can be used as a light output for a monitor. Changes in light output can be detected, It is also possible to stabilize the optical output by applying negative feedback. This configuration realizes low-noise operation with little variation in optical output.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 4 shows the structure of a semiconductor laser in an embodiment of the present invention. In Figure 4, 8 is Twin Ridge 5ub, which the present inventors have already proposed.
A straight (T RS ) type semiconductor laser,
FIG. 5 shows an xy cross-sectional view parallel to the cavity end face of the same laser.

Reference numeral 9 denotes a Si3N4 film having a thickness of λ/4n (λ is the oscillation wavelength of the laser, and nl is the refractive index of Si3N4 at λ). 10 is amorphous St (hereinafter a-S i TH
The film thickness is λ/4n2 (n2 is a at λ).
- refractive index of Si) or more.

The operation of the semiconductor laser configured as described above on page 5 will be described below. In the TR8 type semiconductor laser, two ridges provided on the substrate absorb light, stabilize the oscillation transverse mode of the laser, and realize fundamental transverse mode oscillation. This is to increase the reflectance of light by repeated reflection interference of the Si3N4/a-9t film attached to the end face of the resonator.In this example, a laser with an oscillation wavelength of 7800A is used, so the reflectance is in the range of 70 to 80. ing.

FIG. 6 shows the current-optical output characteristics and current-light characteristics of the semiconductor laser of this example. 7th
The figure shows that in the semiconductor laser of this example, the optical output emitted from one end face is 3 mW, the other optical output proportional to this is detected, negative feedback is applied, and the operating current is controlled to 3 mW.
Optical output signal-to-noise intensity ratio when the optical output is constant (
, S/N).

Such optical output control reduces the light reflectance of the resonator end face to 1.
This is because it is made smaller than 0.00% so that light output can be extracted from both end faces.

As can be seen from these results on page 6, the semiconductor laser according to the present invention has a power efficiency of 10 to 30 dB compared to the conventional semiconductor laser.
noise reduction has been achieved.

Effects of the Invention As described above, in the semiconductor laser of the present invention, the reflectance of the two cavity end faces is higher than the reflectance of the end face of the semiconductor crystal material itself, and is smaller than the reflectance of 10%. As a result, it is possible to oscillate with stable optical output and operate with low noise, and its industrial value is significant.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a conventional semiconductor laser, FIG. 2 is a diagram showing current-optical output characteristics and current-noise intensity characteristics of a conventional semiconductor laser, and FIG. 3 is a diagram showing S/N of a conventional semiconductor laser.
FIG. 4 is a perspective view of a semiconductor laser device according to an embodiment of the present invention, FIG. 5 is an x-y sectional view of the same semiconductor laser device, and FIG. 6 is a diagram showing the temperature dependence of N. Figure 7 is a diagram showing the current-optical output characteristics and current-noise characteristics of the semiconductor laser device of the example, and Figure 7 is a diagram showing the results of measuring the temperature dependence of S/N in the same semiconductor laser device on page 7. It is. 1------ n-GaAs layer, 2... n-
Ga1-yAlyAS layer, 3-=-n-Ga1, Al
xAs layer, 4・-・-p-Ga1-yAlyAS layer, 6-=-・n-GaAs, 6-・-T i /
Pt/Au electric chair, 7 m-Au-Ge-Ni electrode, 8.
...TR3 type semiconductor laser, 9...Si
3N4.1o...Si, 11...groove,
51...Zn diffusion region. Name of agent: Patent attorney Toshi Nakao
Figure O / 1 Figure 2 Q 50 100 Atonement Hi';

Claims (1)

[Claims] The reflectance of light at the oscillation wavelength of the two resonator end faces is higher than the reflectance of the surface of the semiconductor crystal material itself, which is the laser medium, and is also lower than 100% reflectance. Semiconductor laser equipment.