JP2739596B2 - Distributed reflection semiconductor laser - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser used as a light source in an optical transmission system, and more particularly, to a tunable distributed reflection type semiconductor laser capable of changing its oscillation wavelength. .

[Conventional technology]

A wavelength tunable semiconductor laser capable of tunable oscillation wavelength has been actively studied as a local light source, which is an important component for coherent heterodyne detection in an optical transmission system. Among them, a distributed reflection type semiconductor laser (Dist
A ributed Bragg Reflector (hereinafter abbreviated as “DBR laser”) has been most studied since it can change the wavelength by passing an electric current through a light reflection region formed of a waveguide portion having a diffraction grating. The conventional problem of this laser is that the light coupling between the light emitting portion and the light reflection region is not large due to the use of evanescent coupling, and the light output is small. To solve this problem, a butt-joint shown in FIG.
A method of integrating the light emitting portion LE and the light reflection region LD by coupling is described in, for example, a literature (Electronics Letters, Vol. 24, No. 24, 1481-1482 by Y. Tohmori et al.).
(1988, p. 1988), and a high light output can be obtained by the technique. To manufacture this, a GaInAsP active layer 2 was formed on an n-type InP substrate 1 in FIG.
Must be grown on the entire surface, a part of the GaInAsP guide layer 3 needs to be selectively regrown on the removed portion. In FIG. 3, reference numeral 4 denotes a diffraction grating; 5, a p-type InP layer; 6, a p-type GaInAsP cap layer;
Is a p-type electrode, and 9 is an n-type electrode.

[Problems to be solved by the invention]

However, in FIG. 3, the regrown GaInAs
The quality of the P guide layer 3 is generally not so good, and since the P guide layer 3 contains many non-light emitting centers, the carrier lifetime is short. As a result, a current flows between the electrodes 8 and 9 and the GaInAsP
Even when the refractive index of the guide layer 3 was changed to change the oscillation wavelength, the change in the refractive index was small. Therefore, although the conventional DBR laser shown in FIG. 3 can provide high output, it has a disadvantage that the variable wavelength range is narrow.

The present invention has been made in view of such a point,
It is an object of the present invention to provide a DBR laser with a high quality guide layer and to provide a laser with a high optical output and a wide variable wavelength range.

[Means for solving the problem]

In order to achieve such an object, the present invention provides a wavelength-variable distributed-reflection semiconductor laser in which a light-emitting portion and a light-reflecting region are integrated by butt-coupling. A buffer layer having a band gap larger than that of the guide layer is provided.

[Action]

In the DBR laser according to the present invention, the quality of the guide layer is improved, and the life of the carrier can be extended and the amount of change in the refractive index can be increased.

〔Example〕

FIG. 1 is a configuration diagram illustrating an embodiment of a DBR laser according to the present invention, wherein 1 is an n-type InP substrate, and 2 is a wavelength of 1.55 μm.
m GaInAsP active layer, 3 a 1.3 μm wavelength GaInAsP guide layer, 4 a diffraction grating, 5 a p-type InP layer, 6 a p-type GaInAsP cap layer, 7, 8 a p-type electrode, 9 an n-type electrode, 10 is wavelength 1.1
A 5 μm GaInAsP buffer layer, LE is a light emitting portion, and LD is a light reflection region.

The outline of the fabrication of the DBR laser shown in FIG.
When growing the guide layer 3 in the light reflection region LD of the BR laser,
First, a buffer layer 10 having a larger band gap than the guide layer 3 is grown, and the guide layer 3 is grown thereon.

The DBR laser thus configured oscillates by passing a current II between the electrodes 7 and 9, and the oscillation wavelength can be made variable by passing a current I2 between the electrodes 8 and 9. FIG. 2 shows how the oscillation wavelength changes with respect to the current I2 for the conventional DBR laser shown in FIG. 3 and the DBR laser according to the present invention shown in FIG. In FIG. 2, a dotted line S1 indicates a conventional DB.
The characteristics of the R laser are shown, and the solid line S2 shows the characteristics of the DBR laser according to the present invention. As can be seen from FIG.
The oscillation wavelength of the DBR laser changes more greatly than the conventional DBR laser. This is because the quality of the guide layer 3 is improved, the lifetime of the carrier is increased, and the amount of change in the refractive index is increased.

〔The invention's effect〕

As described above, the present invention improves the quality of a guide layer in a distributed reflection type semiconductor laser using butt-coupling by providing a buffer layer having a band gap larger than the guide layer below the guide layer. As a result, the life of the carrier can be extended and the amount of change in the refractive index can be increased, so that a distributed reflection semiconductor laser having a large optical output and a wide variable wavelength range can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a distributed reflection semiconductor laser according to the present invention, and FIG. 2 compares the variation of the oscillation wavelength between the distributed reflection semiconductor laser of FIG. 1 and a conventional distributed reflection semiconductor laser. FIG. 3 is a configuration diagram showing a conventional distributed reflection type semiconductor laser. 1 ... n-type InP substrate, 2 ... GaInAsP active layer, 3 ... GaIn
AsP guide layer, 4 ... Diffraction grating, 5 ... P-type InP layer, 6 ...
... p-type GaInAsP cap layer, 7,8 ... p-type electrode, 9 ... n
Type electrode, 10: GaInAsP buffer layer, LE: Light emitting unit, LD
... Light reflection area.

Claims (1)

(57) [Claims] 1. A wavelength-variable distributed-reflection-type semiconductor laser in which a light-emitting portion and a light-reflecting region are integrated by butt-coupling. A distributed reflection type semiconductor laser comprising a buffer layer.