JPS63318185A - Distributed feedback semiconductor laser - Google Patents

Abstract

PURPOSE:To make an oscillating threshold current value lower and enable laser rays to be emitted efficiently in the direction perpendicular to a substrate by a method wherein a secondary corrugation is provided only in the region where a light distribution is large in intensity. CONSTITUTION:A first corrugation with a phase shift of lambda/4 is formed on the central part of a resonator on an InP substrate which serves also as a first clad layer 8 of a first conductivity type. A light wave path layer 6 consisting of n-InGaAsP, an active layer 5 composed of InGaAsP and a light wave path layer 4 consisting of p-InGaAsP are formed. An SiO2 insulating film 32 is formed onto the light wave path layer 4 and a secondary corrugation is formed only on the central part of the resonator through the SiO2 film 32 as a mask. A clad layer 3 consisting of p-InP is deposited on the light wave path 4. A mask of a SiO2 film is formed and the clad layer 3, the light wave path layers 4 and 6, and the active layer 5 are made to be left stripe-like. A buried layer 30 consisting of p-InP and a buried layer 31 composed of n-InP are grown. A p-side electrode 2 and an n-side electrode are provided, and then a laser ray extracting opening 33 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Industrial Application Field) The present invention relates to a distributed feedback semiconductor laser, and particularly to a surface emitting distributed feedback semiconductor laser.

(Prior Art) In optical communication systems using single-mode optical fibers aimed at large-capacity, long-distance transmission, pulse width broadening due to wavelength dispersion of the optical fibers poses a problem in terms of transmission bandwidth.

Therefore, a distributed feedback semiconductor laser has been proposed as a dynamic single mode (DSM) laser that oscillates in a longitudinal single mode spectrum even during high-speed modulation.

Further, as a light source for high-density optical information processing, a surface-emitting semiconductor laser has been proposed, which emits light in a direction perpendicular to a semiconductor board and can be integrated into a two-dimensional array.

Furthermore, a surface-emitting distributed feedback semiconductor laser has been proposed (IEICE-Technical Report, January 1987, 0QE
86-152). This semiconductor laser is constructed as shown in a perspective view in FIG. That is, active layers 13 and 2
It has a structure in which a waveguide layer 18 having the next corrugation 12 is sandwiched between a first cladding layer 14 and a second cladding layer 11. Further, a TJS structure is used as the main structure of the laser, and current is injected into the active layer 13 through the region 17 which has become p-type by diffusing zinc from the electrode 19. In operation, the waveguide 818 having the second-order collation performs distributed feedback oscillation of the second-order diffraction effect, and at the same time, the laser oscillation light is generated by the first-order diffraction effect of the waveguide layer 18 having the second-order collation. A part of the semiconductor substrate is taken out in a direction perpendicular to the semiconductor substrate.

(Problems to be Solved by the Invention) In the above-mentioned surface-emitting distributed feedback semiconductor laser, the feedback for laser oscillation is a second-order collagen whose coupling constant is smaller than that of a first-order collagen. rely on gaming. Therefore, it has a drawback that the oscillation threshold current value is higher than that of a distributed feedback type semiconductor laser having first-order collation.

Furthermore, since the coupling constant is small, laser light tends to leak in the direction of the resonance axis, and the efficiency of extracting light in the direction perpendicular to the semiconductor substrate is low.

[Structure of the Invention] (Means for Solving the Problems) The present invention has a waveguide layer having first-order collation in the direction of the resonance axis, and a light intensity distribution exists in the direction of the resonance axis. The present invention is a distributed feedback semiconductor laser characterized by having second-order collation only in a region where the light intensity distribution is strong.

(Function) In general, in a distributed feedback semiconductor laser, a phase shift is provided in the center of the resonator in the first-order corrugation in order to cause single-axis mode oscillation at the Bragg wavelength. In this case, if the product (L) of the coupling constant (L) of the waveguide layer with first-order collation and the resonator length (L) is large, the light intensity inside the co-irradiation device will be as shown in Figure 7. As shown, it is strong in the center of the resonator and weak near the end faces. This tendency becomes more pronounced as L increases.

Therefore, by providing a secondary collation in a region where the light intensity is strong, light can be efficiently extracted in a direction perpendicular to the semiconductor substrate.

In addition, since the coupling constant (N) of the waveguide layer having the first-order collagen is larger than the coupling constant (N) of the waveguide layer having the second-order collagen, the oscillation threshold current value can be kept low. In addition, since laser light is difficult to leak in the coaxial direction, it is possible to improve the efficiency of extracting light in the direction perpendicular to the semiconductor substrate.

(Example) The present invention will be described below by taking as an example a buried semiconductor laser using an InP/InGaASP semiconductor.

The semiconductor laser of this embodiment is constructed as shown in FIG. 1 as a longitudinal sectional view on the optical axis in the direction of the resonator, and FIG. 2 as a perspective view. That is, a first cladding layer 8 of a first conductivity type; a first waveguide layer 6 of a first conductivity type having first-order collagen 7;
an active layer 5 having a gain for the Bragg wavelength corresponding to the first-order collagen; a second waveguide layer 4 of the second conductivity type having the second-order collagen 1 in the center; It has a structure in which second cladding layers 3 are laminated. Each of these laminated layers is then formed into a stripe, with the first layer on both sides.
, embedded with the second embedding Jfi30.31.

In the figure, 2.9 is an electrode 1, and the electrode 2 has a light extraction port 33.

Next, a method of manufacturing this semiconductor laser will be explained.

First, as shown in FIG. 3, a first-order collage 7 with a phase shift 35 of λ/4 is formed at the center of the vibrator on an InP plate that also serves as the first cladding layer 8 of the first conductivity type. do.

Next, as shown in FIG. 4, using the liquid phase growth method, n-I
Waveguide layer 6 made of nGaASP and having a thickness of 0.2 utn
．． Made of InGaAsP, thickness 0.11J! n active layer5. A waveguide layer 4 made of p-InGaAsP and having a thickness of 0.21 ttn is formed. At this time, the waveguide layer 6 includes the first
The shape of the collagen 7 formed on the cladding layer 8 is reflected.

Next, using the plasma CVD method, a layer with a thickness of 062 mm is deposited on the waveguide layer 4.
A rabbit 5i02 insulator IIu32 is formed, and then the 8102 film in the central region of the resonator is removed by a photoresist process. Next, using the SiO2 film as a mask, a secondary collage is formed only in the center of the resonator, resulting in a structure 1q shown in FIG.

After peeling off the 5iO21, a liquid phase growth method is used to grow the cladding layer 3 of p-■n'P with a thickness of two stages on the waveguide layer 4, as shown in FIG.

After this attack, a SiO2 film is again formed using the plasma CVD method, and a photoresist process leaves Si021W4 in a stripe shape with a width of 5 mm. This striped 5
Using the i02 film as a mask, chemical etching is performed to remove the cladding layer 3, waveguide layer 4.8, and active layer 5 so as to leave them in a striped pattern.

After this, using a liquid phase growth method, 1) a filling 1530 made of -InP. Buried layer 3 made of n-1nP
1 to fill both sides of the striped region.

Further, an n-side electrode 2 and an n-side electrode 9 are formed, and a part of the n-side electrode 2 is removed by a photoresist process to form a laser beam extraction port 33. Through the above steps, the surface emitting distributed feedback semiconductor laser of this embodiment shown in FIG. 2 is obtained.

In the above-described embodiment, the first-order collagen 7 and the second-order collagen 1 were created in different waveguide layers 3.4, respectively, but as shown in FIG. Both the collagen 7 and the secondary collagen 1 may be formed in a region with high light intensity.

Furthermore, in the embodiment shown in FIG.
A waveguide layer 6 may be provided in which a waveguide layer 6 and a second-order collagen 1 are formed.

Further, in the above-described embodiments, an InP-based semiconductor laser was used, but the present invention can also be practiced using other semiconductors such as GaAsW. In addition, the λ/4 phase shift formed in the central part of the first-order collagen can be achieved by changing the width of the waveguide layer in the central part instead of shifting the phase of the collagen used in the above embodiment. The propagation constant may be changed to equivalently shift the phase.

[Effects of the Invention] According to the present invention, it is possible to create a surface-emitting distributed feedback semiconductor laser that has a low oscillation threshold current value and efficiently emits light in the direction perpendicular to the semiconductor substrate.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view of a surface emitting distributed feedback semiconductor laser of the present invention, FIG. 2 is a perspective view of a semiconductor laser device of the present invention, and FIGS. 3 to 5 are a vertical sectional view of a surface emitting distributed feedback semiconductor laser of the present invention. FIG. 8 is a diagram showing the electric field distribution inside the resonator of a semiconductor laser to explain the manufacturing process of the laser. FIG. 8 is a perspective view of a conventional TJS type surface emitting distribution feedback semiconductor laser. 1...Second-order collagen, 2...Electrode, 3...
・Second cladding layer, 4...Second waveguide layer, 5...Active layer, 6...First waveguide layer, 7...First-order collagen, 8...Second cladding Layer, 9... Electrode, 10... Ohmic layer, 11... Second cladding layer, 30... Buried layer, 31... Buried layer, 32... Light extraction port.

Claims (1)

[Claims] In a distributed feedback semiconductor laser that has a waveguide layer that has first-order corrugation in the direction of the resonance axis and has a light intensity distribution in the direction of the resonance axis, second-order collocation occurs only in a region where the light intensity distribution is strong. A distributed feedback semiconductor laser comprising: