JPH01124279A - Distributed feedback laser - Google Patents

Abstract

PURPOSE:To execute a distributed feedback operation of a beam without being influenced by a shape of a diffraction grating by a method wherein, because the diffraction grating of a semiinsulating thin film is formed and a region where an injected electric current flows is limited regularly, the diffraction grating by a change in a composition is not formed. CONSTITUTION:An Fe-doped semiinsulating InGaAsP layer 22 is grown on an n-InP substrate 21; a resist 23 is coated and a diffraction grating pattern 23 is formed; after that, an etching operation reaching the n-InP substrate 21 is executed; a semiinsulating InGaAsP diffraction grating 24 is formed. The resist 23 is removed; after that, an n-InGaAsP guide layer 25, an undoped InGaAsP active layer 26, a p-InP clad layer 27 and a p-InGaAsP cap layer 28 are grown; an n-type electrode 29 and a p-type electrode 30 are evaporated. An electric current injected from the side of the n-type substrate 21 reaches the active layer 26 after a current path 31 has been modulated by the diffraction grating 24; a refractive index corresponding to a cycle of the diffraction grating is distributed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to a distributed feedback laser (DFB) with a built-in diffraction grating.
(laser).

2. Description of the Related Art Recently, DFB lasers that oscillate in a single axis mode in the 1.3 μm and 1.6 μm bands have come to be used as light sources for large-capacity, long-distance optical transmission or coherent communications. This DFB laser has a known structure as shown in FIG. 2, for example. In a DFB laser, a laser beam that propagates through a waveguide layer is wavelength-selected using a diffraction grating and returned to the laser, thereby causing a laser that normally oscillates in a multi-axis mode to oscillate in a single-axis mode. For the vertical transverse mode that propagates around the active layer, a diffraction grating with convexes and convexes having different crystal compositions appears as a reflector with different refractive indexes. For this purpose, a diffraction grating with a height difference of 1000 Å or more must be formed near the optical waveguide layer or the active layer.

Problems to be Solved by the Invention However, the above configuration requires a growth method that prevents the uneven shape of the diffraction grating from disappearing during crystal growth. Therefore, there was a problem in that it was necessary to devise a method for protecting the diffraction grating, such as by performing low-temperature growth.

The present invention provides a semiconductor laser which has a simple structure and is effective in solving the above problems.

Means for Solving the Problems In view of the above, the present invention provides, in place of the uneven diffraction grating,
A semi-insulating shrimp layer is provided, a diffraction grating is formed on it as in the conventional manufacturing method, and the current flow is restricted by the period of the diffraction grating, thereby creating a step shape in which the crystal composition is changed as in the conventional method. This is a DFB laser that does not require

Operation According to the present invention, the flow of the injected current is modulated by the diffraction grating of the semi-insulating thin film periodically left on the substrate with the above-described configuration. For this reason, the carrier density injected into the active layer is also modulated, resulting in periodic changes in the refractive index due to the plasma effect. The plasma effect is a phenomenon in which the higher the carrier density, the lower the refractive index. In the laser oscillation state, the injected carrier density is n=1~2×10α, so the refractive index is 10−6~1o due to this plasma effect.
This is a decrease of about -2 compared to the region where no current is injected. As a result, it is possible to obtain an effect equivalent to that of a conventional DFB laser having a concavo-convex shape, which has a change in crystal composition and a change in refractive index.

Embodiment FIG. 1 shows a structural diagram of a DFB laser in an embodiment of the present invention. In the figure, 10 is an n-InP substrate, 11 is an Fe-doped semi-insulating InGaAsP diffraction grating, 12 is an n-InGaAsP guide layer,
13 is an undoped InGaAsP active layer, 14 is a p-I
An nP cladding layer and 15 a p-InGaAsP cap layer.

The method of manufacturing and operation of the semi-insulating InGaAsP diffraction grating 11 of the DFB laser of this embodiment configured as described above will be explained with reference to FIG. In Figure 2, n-I
F is deposited on the nP substrate 21 by liquid phase growth or vapor phase growth.
The semi-insulating InGaAsP layer 22 doped with e is 0.0.
Grow approximately 1 to 0.2 μm.

C^) After that, a resist 25 is applied and a diffraction grating pattern 2 is formed by a two-beam interference exposure method using a conventional laser light source.
3 is formed and then etched until reaching the n-InP substrate 21 to form a (k)-n diffraction grating 24 of semi-insulating InGaAsP. After removing the resist 25, the n-I nGaAsP guide layer 25 and the undoped In
GaAsP active layer 26, p-InP cladding layer 27.1
)--InGaAsP cap layer 28 is grown. An n-type electrode 29 and an n-type electrode 3o are deposited to form an element structure. The laser structure may be a C-PBH structure as shown in FIG. In FIG. 3a, the current injected from the n-type substrate side 21 reaches the active layer 26, where the current path 31 is modulated by the semi-insulating InGaAsP diffraction grating 24 as shown by the arrows. As a result, a refractive index distribution corresponding to the period of the diffraction grating as shown in Figure 3 is created.
It can exhibit the same effect as a conventional diffraction grating in which the refractive index is changed by changing the composition.

In the example, the semi-insulating diffraction grating and the guide layer were made of InGaAsP, but semi-insulating InP and n-
It may also be an InP cladding layer. However, the semi-insulating grating and the layer above it are InP-InP or InGaAsP.
- It is necessary to use a combination of InGaAsP.

As described in detail, according to the present invention, since a diffraction grating is not formed due to compositional changes, distributed feedback of light can be performed without being influenced by the shape of the diffraction grating. big.

[Brief explanation of the drawing]

Figure 1 is a structural diagram of a DFB laser according to an embodiment of the present invention, and Figures 2a and b are semi-insulating InGaAsP lasers in the same embodiment.
An explanatory diagram of a method for manufacturing a diffraction grating, FIG. 3a. b is an explanatory diagram of the operation. 10...n-InP substrate, 11...F
e Doped InGaAsP diffraction grating, 12-・-・-
n-InGaAsP guide layer, 13... Undoped InGaAsP active layer, 14 =---n, -I
nGaAs P7 bottom/L' dopak layer, 15
......p-InP cladding layer, 16...
p-InGaAsP cap layer, 21...-n
-InP substrate, 22...Semi-insulating InGaAs
P, 23...Resist, 24...Semi-insulating InGaAsP diffraction grating, 25...Nie I
nGaAsP diffraction grating, 26...undoped I
nGaAsP active layer, 27...-P-InP cladding layer, 28...p-I n Ga A
s P cap layer, 29・old・・n type electrode, 3o・・
...N-type electrode.

Claims (1)

[Claims] A distributed feedback laser characterized by regularly restricting the region through which an injection current flows by forming a semi-insulating thin film diffraction grating.