JPH0555689A - Distributed reflection type semiconductor laser with wavelength control function - Google Patents

Abstract

(57) [Abstract] [Purpose] To expand the wavelength tunable range of distributed Bragg reflector semiconductor lasers. In a distributed reflection semiconductor laser in which an active layer region and an inactive layer region are optically coupled to each other and integrated, a well layer made of a material having a lattice constant larger than that of a substrate is used in the inactive layer region. Also has a multiple quantum well structure in which a plurality of layers sandwiched between barrier layers made of a material having a large band gap and substantially the same lattice constant as the substrate are laminated, that is, a strained multiple quantum well structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distributed reflection type semiconductor laser having a wavelength control function capable of changing the oscillation wavelength, which is important as a light source for optical transmission.

[0002]

2. Description of the Related Art A semiconductor laser whose oscillation wavelength can be changed and whose spectral line width is narrow has been actively studied as a light source for coherent communication. Among them, distributed reflection semiconductor lasers (Distributed Br)
The agg Reflector Laser (hereinafter referred to as a DBR laser) can change the oscillation wavelength by injecting a current into a wavelength control region including a waveguide having a diffraction grating and a phase adjusting region including a waveguide having no diffraction grating. Yes, and the most research done. An example of a DBR laser realized by butt-coupling an active layer region and a non-active layer region is shown in FIG. 5 (for example, Electronics paper by Tomori et al.
ers) 24, 24, 1481-1482, 198.
See 8 years). In FIG. 5, 1 is an n-type P substrate, 2 is Ga
InAsP active layer, 3 GaInAsP guide layer, 4 diffraction grating, 5 p-type InP clad layer, 6 GaInA
sP cap layer, 7 and 8 are p-type electrodes, and 9 is an n-type electrode. 20 is an active region and 21 is an inactive region. In this example, the active layer region and the non-active layer region are butt-coupled to each other, so that the light coupling loss is reduced and the output characteristics are improved.

[0003]

In coherent communication, a light source having a wide variable wavelength width is required. However, in the conventional DBR laser, GaI is formed in the inactive layer region.
Since the nAsP guide layer was used, even if an electric current is passed through the wavelength control region to change the refractive index of the GaInAsP guide layer and change the oscillation wavelength, the GaInAs
Since the change in the refractive index of the P guide layer was small, there was a drawback that the variable wavelength range was narrow.

The present invention has been made in view of the above points, and an object of the present invention is to provide a DB having a wide wavelength variable width.
To provide an R laser.

[0005]

In order to achieve the above object, a distributed Bragg reflector semiconductor laser according to the present invention comprises an active waveguide layer formed in a predetermined region on a semiconductor substrate, the active waveguide layer and an optical waveguide layer. A tunable distributed reflection type semiconductor laser in which a diffraction grating is provided on at least a part of the surface of the inactive waveguide layer, However, a quantum well layer made of a material having a lattice constant larger than that of the substrate material and a barrier layer made of a material having a band gap larger than that of the quantum well layer and having substantially the same lattice constant as the substrate are alternately formed. It is characterized by having a laminated multiple quantum well structure.

[0006]

In the present invention, in the integrated DBR laser in which the active layer region and the non-active layer region are optically coupled, the non-active layer region is formed by a well layer made of a material having a lattice constant larger than that of the substrate. A multiple quantum well structure (hereinafter referred to as a strained multiple quantum well structure) in which a plurality of layers having a band gap larger than that and being sandwiched between barrier layers made of a material having substantially the same lattice constant as that of the substrate are laminated is used. In the strained multiple quantum transfer structure, since the well layer has strain, the effective mass of heavy holes decreases, and the amount of change in the refractive index due to the plasma effect increases. Therefore, in the DBR laser according to the present invention, the strained multiple quantum well is used as the inactive layer, so that the amount of change in the refractive index due to the plasma effect is increased and the variable wavelength width can be increased.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings.

Embodiment I FIG. 1 is a schematic sectional view illustrating a first embodiment of the DBR laser according to the present invention.

In FIG. 1, 1 is an n-type InP substrate, 2 is a GaInAsP active layer having a bandgap wavelength of 1.55 μm, 10 is a strained multiple quantum well structure guide layer, 4 is a diffraction grating, 5 is a p-type InP cladding layer, 6 is n-type GaInAs
P-cap layers, 7 and 8 are p-type electrodes, and 9 is an n-type electrode.

FIG. 2 is an enlarged view of the strained multiple quantum well structure guide layer 10 in FIG.

In FIG. 2, 11 is Ga _0.17 In _0.83 A
s _0.6 P _0.4 well layer, 12 is Ga _0.17 In _0.83 As _0.37
P _0.63 barrier layer, 13 is Ga _0.17 In _0.83 As _0.37 P _0.63
The light confinement layer is shown. The thickness of each layer is, for example, 30 Å for the well layer 11, 100 Å for the barrier layer 12, and about 1000 Å for the optical confinement layer 13. Since only the lattice constant of the well layer 11 is larger than the lattice constant of the substrate, the well layer has compressive strain. The optical bandgap wavelength of the strained multiple quantum well structure guide layer is 1.3 μm.

Next, a method for manufacturing the DBR laser according to the present invention shown in FIG. 1 will be briefly described. A GaInAsP active layer 2 was laminated on the entire surface of the n-type InP substrate 1 by using a metal organic vapor phase epitaxial growth method or the like, and then an unnecessary portion of the GaInAsP active layer was removed by using a SiO ₂ or SiN _x mask, and then removed. The strained multiple quantum well structure guide layer 10 is laminated on the portion. After removing the SiO ₂ or SiN _x mask, unevenness is formed on the surface of the guide layer 10 by resist patterning and etching to form a diffraction grating 4, and then a p-type InP clad layer is laminated. Then, dry etching or the like is used to control the lateral mode, and the film is processed into a narrow stripe shape with a width of 1.5 μm, for example, and a p-type InP clad layer is further deposited to fill the active layer 2 and the guide layer 10. Then, the p-type electrodes 7 and 8 and the n-type electrode 9 are vapor-deposited, and the GaInAsP cap layer 6 and a part of the p-type InP clad layer are chemically etched to separate the electrodes 7 and 8 from each other. Etc. to remove.

In the DBR laser having such a configuration, laser oscillation is caused by passing a current I ₁ between the electrodes 7 and 9, and oscillation wavelength is changed by passing a current I ₂ between the electrodes 8 and 9. The change in the oscillation wavelength with respect to the current I ₂ is shown in FIG. 3 for the conventional DBR laser and the DBR laser according to the present invention. In FIG. 3, the dotted line S1 is the conventional DBR.
The characteristics of the 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. 3, the oscillation wavelength of the DBR laser according to the present invention changes more greatly than that of the conventional DBR laser.

Example II In Example I described above, a DBR laser having a structure in which an active waveguide layer and an inactive waveguide layer are butt-coupled has been described, but the present invention is also applicable to DBR lasers having other structures. Is applicable. For example, also in the DBR laser having the structure shown in FIG. 4, the wavelength sweep width can be expanded by using the strained multiple quantum well structure for the inactive waveguide layer.

In FIG. 4, 1 is an n-type InP substrate, 2 is a GaInAsP active layer having a bandgap wavelength of 1.55 μm, 10 is a strained multiple quantum well structure guide layer, 4 is a diffraction grating, 5 is a p-type InP clad layer, 6 is n-type GaInAs
P-cap layers, 7 and 8 are p-type electrodes, and 9 is an n-type electrode. 20 is an active region and 21 is an inactive region.

The difference between the DBR laser shown in FIG. 1 and the DBR laser shown in FIG. 4 is that the active waveguide layer 2 and the inactive waveguide layer 10 are butt-coupled to each other in the DBR laser of FIG. On the other hand, the DBR laser of FIG. 4 has a structure in which the active layer 2 is partially laminated on the inactive waveguide layer. In the DBR laser shown in FIG. 4, the optical coupling efficiency between the active layer region 20 and the non-active layer region 21 becomes low, so that the DB shown in FIG.
Although the output characteristics are inferior to those of the R laser, there is an advantage that the production is easy because the non-active waveguide layer and the active waveguide layer can be laminated in a continuous series of steps. Regarding the wavelength sweep characteristics, the DBR laser shown in FIG. 1 and the DBR laser shown in FIG. 2 exhibit the same characteristics, and the application of the present invention provides the same operation as that of the first embodiment.

In the above-described embodiments, the DBR laser having the inactive layer region having the diffraction grating on both sides of the active layer region has been described. However, the DBR laser having the inactive layer region only on one side of the active layer region, The present invention is also applicable to a DBR laser in which a region without a diffraction grating is provided in a part of the inactive region.

Further, regarding a DBR laser having a multiple quantum well structure or a strained multiple quantum well structure in the active waveguide layer,
It goes without saying that the present invention is applicable.

[0019]

As described above, according to the present invention,
In the distributed Bragg reflector semiconductor laser, the use of the strained multiple quantum well structure in the inactive layer has an excellent effect of widening the wavelength tunable width.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a first embodiment of a distributed Bragg reflector semiconductor laser according to the present invention.

FIG. 2 is an enlarged view for explaining the strained quantum well structure of FIG. 1 in detail.

FIG. 3 is a graph showing the amount of change in the oscillation wavelength of the distributed Bragg reflector semiconductor laser of FIG. 1 and the conventional distributed Bragg reflector semiconductor laser in comparison.

FIG. 4 is a schematic sectional view showing a second embodiment of the distributed Bragg reflector semiconductor laser according to the present invention.

FIG. 5 is a schematic cross-sectional view showing a conventional distributed Bragg reflector semiconductor laser.

[Explanation of symbols]

 1 n-type InP substrate 2 GaInAsP active layer 3 GaInAsP guide layer 4 diffraction grating 5 p-type InP clad layer 6 n-type GaInAsP cap layer 7, 8 p-type electrode 9 n-type electrode 10 strained multiple quantum well structure guide layer 11 GaInAsP well layer 12 GaInAsP barrier layer 13 GaInAsP optical confinement layer 20 Active region 21 Inactive region

Claims (1)

[Claims] 1. A surface of the inactive waveguide layer, comprising: an active waveguide layer formed in a predetermined region on a semiconductor substrate; and an inactive waveguide layer optically coupled to the active waveguide layer. In the wavelength tunable distributed reflection type semiconductor laser in which at least a part of is provided with a diffraction grating, the inactive waveguide layer comprises a quantum well layer made of a material having a larger lattice constant than a substrate material and the quantum well layer. Also has a distributed band reflection type semiconductor laser with a wavelength control function, which has a large band gap, and has a multiple quantum well structure in which a substrate and barrier layers made of a material having substantially the same lattice constant are alternately laminated. ..