JPS63160391A - Distributed feedback type semiconductor laser device - Google Patents

Abstract

PURPOSE:To make the whole system compact by causing a set at least out of the distributed reflectors to be variable ones where optical propagation constant is variable, thereby controlling optical propagation constant of the variable distributed reflactors by output difference signals of respective photodetectors that are coupled with two distributed reflectors. CONSTITUTION:A semiconductor laser oscillation part is composed of a gain region 10, variable distributed reflectors 13 and 14 where propagation constant is variable as well as a phase adjustment region 15. Moreover, an oscillation wavelength measuring part is composed of a Y-shaped multipoint type waveguide 16 connecting to the variable distributed reflector 14, a distributed reflector 18 having a sligntly longer Bragg wavelength than that connecting to the above waveguide, the distributed reflector 20 having a slightly shorter wavegude than the Bragg wavelength, and photodetectors 19 and 21 connecting to the distributed reflectors 18 and 20. The variable distributed reflectors 13 and 14 are controlled by output difference signals of the photodetectors 19 and 21 and in this way, oscillation wave lengths are controlled. Then, since the gain region 10 is controlled by the output sum signals of the phtodetectors 19 and 21, light output powers can be controlled.

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 distributed feedback semiconductor laser whose oscillation wavelength can be controlled.

(Prior Art) In optical communication systems that use single-mode optical fibers for long-distance, high-capacity transmission, pulse width broadening due to wavelength dispersion of optical fibers poses a problem in terms of transmission bandwidth.

For this reason, 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. In addition, a wavelength multiplexing method has been proposed as a method to enable even higher capacity transmission, and a heterodyne method has been proposed as an ultra-long distance transmission method, but in order to realize these methods, it is necessary to control and stabilize the oscillation wavelength.

Now, in order to control the oscillation wavelength of a semiconductor laser, conventionally,
Controlling the operating temperature has been a common method. However, temperature-based control has the drawback of slow response speed and being easily influenced by the environment in which it is used.

Therefore, a BIG-DBR type DSM laser with a black wavelength controller has been proposed as a light source whose oscillation wavelength can be electrically controlled (1986 Spring 1, Proceedings of the 33rd Joint Conference on Applied Physics, p. 8). ).

This light emitting device has an active layer having a gain and a variable distribution reflector that can control the black wavelength by changing the propagation constant of a waveguide coupled to the active layer. That is, as shown in a longitudinal cross-sectional view on the optical axis in FIG. 8, an active layer 0) having a gain near the black wavelength and variable distribution reflectors (2) on both sides of the active layer 0) capable of controlling the black wavelength are provided. The variable distribution reflector ■ is a semiconductor waveguide layer (
By injecting current and changing the carrier density, the refractive index of the medium changes due to the dispersion of interband absorption and plasma absorption, and the propagation constant of the waveguide changes, changing the black wavelength. Can be controlled. (2) is a Mi pole for electrically controlling the black wavelength of the variable distribution reflector (2). Further, (6) is an electrode that passes current through the active layer ω.

In this BIG-DBR type DSM semi-drifting laser with a black wavelength controller, one oscillation wavelength can be electrically controlled by injecting current into the variable distribution reflector electrode. It is suitable for wavelength multiplexing.

(Problem to be solved by the invention) However, since devices that are difficult to miniaturize, such as spectrometers and Fabry-Perot interferometers, are used to detect the oscillation wavelength of semiconductor lasers, the entire system is inevitably large. There were some drawbacks.

An object of the present invention is to provide a DBR type DSM type semi-contaminated laser with a black wavelength controller, which allows the entire system to be miniaturized.

[Structure of the invention]

(Means for Solving the Problems) According to the present invention, a distributed feedback type comprising a gain region and one or more distributed reflectors having a grating with respect to the traveling direction of light coupled to the gain region In the semiconductor laser, at least one of the distributed reflectors is a variable distributed reflector having a variable light propagation constant, and a first distributed reflector having a black wavelength longer than the black wavelength of the distributed reflector; a first photodetector coupled to the first distributed reflector; a second distributed reflector having a black wavelength shorter than the black wavelength of the distributed reflector; and a second distributed reflector coupled to the second distributed reflector. 2 photodetector.

The distributed reflector is provided with a region that optically couples the first distributed reflector and the second distributed reflector, and the distributed reflector has a variable distribution according to a difference signal between the outputs of the first photodetector and the second photodetector. A distributed feedback semiconductor laser device is provided that is characterized by controlling the propagation constant of light in a reflector.

(Function) With the above-described configuration, the output of the first photodetector and the output of the second photodetector both change in accordance with the oscillation wavelength. Furthermore, since the difference signal between these plane signals changes monotonically with respect to the oscillation wavelength, the oscillation wavelength can be measured using the difference signal.

Therefore, if the black wavelength of the variable distribution reflector is controlled by the difference signal between the outputs of the two photodetectors, the oscillation wavelength of the semiconductor laser can be controlled. That is, according to the present invention,
Wavelength measuring means can be integrated into the semiconductor laser.

A semiconductor laser device whose oscillation wavelength can be controlled can be configured compactly.

(Example) DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to drawings showing embodiments.

FIG. 1 shows a perspective view of a distributed feedback semiconductor laser device according to an embodiment of the present invention, with some semiconductor layers removed.

This embodiment is generally configured as follows. That is, it is composed of a semiconductor laser oscillation section and an oscillation wavelength measurement section. The semiconductor laser oscillation unit includes a gain region IO, a pair of variable distributed reflectors 13 and 14 having a grating in the direction of propagation of light coupled to the gain region IO and whose propagation constant is variable, and a gain region IO. 12 and a phase adjustment region 15 provided between the variable distribution reflector 13. Also,
The oscillation wavelength measuring section includes a Y-branch type waveguide 16 coupled to one variable distribution reflector 14, and a distributed reflector 18 having a black wavelength slightly longer than the black wavelength coupled to the Y-branch waveguide 16. , a distributed reflector 20 having a black wavelength slightly shorter than the black wavelength of the variable distributed reflector;
They are sensitive to light near the black wavelength and are composed of photodetectors 19.21 coupled to distributed reflectors 18.20, respectively. The difference signal of the output of the photodetector 19.21 is transmitted to the variable distribution reflector 13.14 via the wavelength control circuit 54.
By controlling the oscillation wavelength, the oscillation wavelength can be controlled. Further, the optical output can be controlled by controlling the gain region 10 via the optical output control circuit 56 based on the sum signal of the outputs of the photodetectors 19 and 21.

Hereinafter, a method of manufacturing the distributed feedback semiconductor laser device of this embodiment will be described with reference to FIGS. 2 to 6. In this embodiment, an InP-based buried semiconductor laser structure is adopted. First, on a substrate 22 made of n-InP, an active layer 24 made of GaInAsP, an absorption layer 26 for a detector, and a protective layer 22 made of GaInAsP or InP are placed.
Epitaxially grow M28. At this time, the active layer 24
Since the absorbing layer 26 for the detector can have the same composition, it can be grown simultaneously in a single growth process.The 0-order layer 26 is patterned with a photoresist and etched, leaving the active M24 and the absorbing layer 26 for the photodetector, 1i126. The epitaxial layer is removed to obtain the semiconductor substrate shown in FIG.

Next, variable distributed reflector 13.14, distributed reflector 18.2
Gratings 30, 32, 34 with a predetermined pitch are formed on the substrate 22 at positions relative to 0, as shown in FIG. The black wavelength of each distributed reflector 13, 14, 18, 20 is made different by changing the propagation constant depending on the width of the waveguide of the distributed reflector, as described later, so the pitch of all these gratings is the same. good.

Next, as shown in FIG. 4, InGaAsP is placed on the substrate 22.
A waveguide layer 36°I that is transparent to the oscillation wavelength and consists of
After forming a cladding layer 38 made of nP by sequentially epitaxially growing zero-order SiO□ by plasma CVD method,
A pattern 40 of SiO□ is formed by patterning and etching using photoresist. At that time, S, t
The pattern 40 of O is formed by etching in the first step to the width of the waveguide of the variable distributed reflector 13, 14, and the pattern 40 of the distributed reflector 18 is
In order to have an intermediate value of the radiation of the distributed reflector 20,
Determine [a, b, and c of the SiO□ stripe in each part. Next, using Sin and 40 as a mask, a cladding layer (38° waveguide) fJj36. Etching away the upper part of the substrate 22,
The mesa structure shown in FIG. 5 is obtained.

Next, a block layer 42 made of P-InP is placed on the substrate 22 so as to embed the mesa structure formed as described above.
- Block layers 44 made of InP are sequentially grown epitaxially. Then, electrode metal is further deposited. after that,
Variable distributed reflector 13.14° distributed reflector 1 shown in Figure 1
8.20. In order to electrically insulate and separate the Y-branch waveguide 16 and the detector 19 and 21, the boundaries of each region are etched until the substrate 22 is reached, excluding the vicinity of the waveguide. Remove.

As a result, the distributed feedback semiconductor laser device of the present invention shown in No. 8 is obtained. In addition, 46.47.48.49.
50 and 51 indicate electrodes in each region.

Now, in the above-mentioned distributed feedback semiconductor laser device, the variable distributed reflectors 13 and 14 are formed by the waveguide 36 made of semiconductor.
By injecting a current into the black wavelength, the refractive index of the medium changes due to interband absorption and dispersion of plasma absorption, and the propagation constant of the waveguide changes, which can be used to electrically change the black wavelength. . Also, in the one phase adjustment region 16, the phase can be controlled by changing the propagation constant of the waveguide 36 using the same principle.

The black wavelength of each distributed reflector can be set by the width of the waveguide. That is, by making the width of the waveguide of the distributed reflector 18 narrower than that of the distributed reflector 20 and making the respective propagation constants different, the distributed reflector 18 and the distributed reflector 2
The zero black wavelength can be made different. Furthermore, the black wavelength when no current is injected into the variable distributed reflectors 13 and 14 can be set to be between the black wavelengths of the distributed reflectors 18 and 20 by adjusting the width of the waveguide. I can do it. Note that the width of each of the four wave paths is determined in S10. above. determined by the pattern of

The resonator formed by the variable distributed reflectors 13 and 14 and the gain region IO has a relationship between wavelength and threshold current as shown by the solid line in FIG. 7a. Electrode 47 of phase adjustment region 15 for controlling phase
The current applied to the current is adjusted so that laser oscillation is performed at the lowest threshold current (point A). Furthermore, since the propagation constants of the variable distributed reflectors 13 and 14 can be electrically controlled in the same way, the relationship between the wavelength and threshold current shown by the broken line in the figure can be changed, and the black wavelength can be electrically controlled. As a result, the oscillation wavelength of the semiconductor laser can be electrically controlled.

Now, the laser light generated from the resonator passes through the Y-branched waveguide 1.
6 and passes through a distributed reflector 18.20. At this time, the distributed reflector 18 has a transmittance for the laser beam shown by a solid line in FIG. 7, and the distributed reflector 20 has a transmittance for the laser beam shown by a broken line in the figure. , the detectors 19 and 21 have wavelength sensitivities proportional to the oscillation wavelength of the laser as shown by the solid and broken lines in the figure, respectively.

Therefore, the difference signal between the detector 19 and the detector 21 is proportional to the oscillation wavelength of the laser near the black wavelength, and the sum signal is proportional to the optical output of the laser.

As described above, according to the semiconductor laser device of the present invention, a semiconductor laser in which a wavelength measuring means is integrated can be obtained. The difference signal between the two photodetectors is a signal proportional to the oscillation wavelength, and by controlling the current flowing through the semiconductor forming the waveguide of the variable distributed reflector 13 and 14, the semiconductor laser can easily oscillate. Wavelength can be controlled electrically. Furthermore, since optical output can also be detected, optical output control is easy.

In the above embodiments, an InP-based buried semiconductor laser device has been described, but the present invention is also applicable to other types of internal stripe semiconductor laser devices.

It can also be applied to semiconductor laser devices using other semiconductors such as GaAlAs. In addition, methods for shifting the black wavelength of the variable distributed reflector and the distributed reflector include a method of changing the black wavelength by equivalently changing the propagation constant of the waveguide by changing the thickness of the 38 waveguides, and a method of changing the black wavelength of the waveguide by changing the thickness of the waveguide. A method of changing the black wavelength by changing the propagation constant of the waveguide by changing the composition of the grating, a method of changing the black wavelength by directly changing the pitch of the grating, etc. can be used.

Furthermore, in the variable distribution reflector of the above embodiment, the semiconductor (
By injecting a current into a waveguide made of GaInAsP to change the carrier density, the refractive index of the medium changes due to the dispersion of interband absorption and plasma absorption, which changes the propagation constant of the waveguide. Although the wavelength is controlled, the refractive index of the waveguide may also be changed using the electro-optic effect.

Furthermore, although the above embodiments have been described using two variable distribution reflectors, one of the variable distribution reflectors is not necessarily required.

〔Effect of the invention〕

As described above, according to the semiconductor laser device of the present invention, the wavelength measuring means is integrated into the semiconductor laser element, and a system in which the oscillation wavelength can be easily controlled can be constructed compactly.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a distributed feedback semiconductor laser device according to an embodiment of the present invention, FIGS. FIG. 8, which is a diagram for explaining the operating principle of the present invention, shows a cross-sectional view of a conventional BIG-DBR type DSM type semiconductor laser with a black wavelength controller. 10... Gain region 13.14... Variable distributed reflector 15... Phase adjustment region 16... Y branch waveguide 18.20... Distributed reflector layer 19.21... Photo detection Device 46.47.48.49.50.51... Electrode 52... Subtractor 53... Adder 54.
... Wavelength control circuit 56 ... Optical output control circuit 58
・・・Phase control circuit agent Patent attorney Nori Chika Ken Yudo Ogo Norio Shiroishuu upstream (a) Figure 7 Figure 8

Claims (1)

[Scope of Claims] A distributed feedback semiconductor laser comprising a gain region and one or more distributed reflectors having a grating in the direction of propagation of light coupled to the gain region, comprising: a first distributed reflector, at least one of which is a variable distributed reflector having a variable light propagation constant, and which has a black wavelength longer than the block wavelength of the distributed reflector, coupled to the first distributed reflector; a second distributed reflector having a black wavelength shorter than a black wavelength of the distributed reflector; and a second photodetector coupled to the second distributed reflector; a region that optically couples the distributed reflector, the first distributed reflector, and the second distributed reflector; the difference in output between the first photodetector and the second photodetector; A distributed feedback semiconductor laser device, characterized in that a propagation constant of light of the variable distributed reflector is controlled by a signal.