JPS63119284A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To afford sufficient monitoring function even for the minute change of a laser oscillating wavelength by monitoring the oscillation conditions of a semiconductor laser by using a waveguide type branching filter which has wavelength selection and reflection functions and a photodetector. CONSTITUTION:The oscillated output light of a DFB laser is coupled to a light waveguide 3 which is directly coupled to an edge face. An InGaAsP layer of a composition which has a transparent band gap against laser light is used for the light waveguide. Part of the oscillated output light propagated in a light waveguide layer is diffracted by a grating 4 at an angle which satisfies Bragg condition. If the diffracted light of a steady state oscillation wavelength is entered in a photodetector 5, the diffracted light passes through a transparent characteristic buried region and is detected by the photo detector 5. If the oscillated wavelength of the laser is changed by an external factor, the Bragg condition by the grating 4 is changed and the incident condition to the photodetector is changed so the stabilizing of an absolute oscillation wavelength is contrived by monitoring each output of the photodetectors provided at an interval and by feeding the outputs of the photodetectors back to a control system.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a two-vane semiconductor laser used as a transmission component for optical communications or an optical integrated circuit element.

BACKGROUND OF THE INVENTION In recent years, as semiconductor laser manufacturing technology has improved, efforts have been made to put it into practical use in a wide range of fields such as optical information processing and optical communications. In particular, in the field of long-wavelength optical communications, the characteristics of InP-based DFB lasers have been significantly improved, and ultra-wavelength multiplexing transmission systems based on absolute stabilization of the oscillation wavelength are being studied. In this transmission method, the oscillation wavelength ranges from several to several tens of λ.
This method performs multiplex transmission in a very narrow wavelength band that is not affected by the wavelength dispersion of optical fibers by precisely controlling the spacing, and by using this method, the transmission capacity is increased several to tens of times compared to conventional methods. It is expected that this will be possible.

Problems to be Solved by the Invention However, semiconductor lasers generally have a problem in that their oscillation wavelength changes due to their structure. There are two major factors that can cause the oscillation wavelength to fluctuate:

11. Causes due to temperature changes 31.-- Semiconductor lasers obtain laser oscillation by injecting carriers into the active region and emitting and amplifying light by recombining the carriers. However, the conversion efficiency to light energy is 100
%, and a part of the injected carriers is also converted into thermal energy, causing a rise in the temperature of the active layer. As a result, the bandgap energy that influences the oscillation wavelength of the active layer changes, causing temperature drift of the oscillation wavelength. In the case of a 1.3 μm μm laser, the amount of change is about 5 A/deg for an FP laser, and about I A/deg for a DFB laser.

2. Due to changes in carrier concentration When a semiconductor laser is modulated at high speed, a phenomenon called chirping occurs. This is because carrier concentration changes in the active layer caused by direct modulation of light intensity change the effective refractive index of the active layer, and as a result, the effective refractive index of the active layer changes and the spectral width of the oscillation wavelength changes. This causes fluctuations in the center wavelength. As a light source for coherent communication, how to suppress this chirping and obtain stable laser light with a narrow spectral width has become a major issue, and various methods are being actively developed. In order to achieve absolute stabilization of the oscillation wavelength, a monolithic configuration is considered more promising than a hybrid configuration. Conventional lasers have a function to monitor the oscillation power but not the oscillation wavelength.For the reasons mentioned above, the oscillation There was a problem in terms of wavelength controllability. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a semiconductor laser device that can eliminate the above-mentioned drawbacks, that is, has a function of monitoring the oscillation wavelength.

Means for Solving the Problems In order to solve the above problems, the present invention includes a semiconductor laser formed on a substrate surface, an optical waveguide coupled to the semiconductor laser, and a wavelength It is equipped with a waveguide type optical demultiplexer having a selective reflection function and at least one or more light receiving elements installed at a predetermined position 51° from the waveguide type optical demultiplexer. integrated into and formed. Further, the semiconductor laser has a distributed feedback type or Bragg reflection type structure9, and a part of the laser oscillation light is diffracted by the waveguide type optical demultiplexer and detected by a light receiving element installed at a predetermined position. be done. The oscillation wavelength can be monitored by Bragg conditions.

Function The present invention uses a waveguide type optical demultiplexer in which a grating is formed on an optical waveguide as a narrowband optical filter.
1. With appropriate design, the filter can have a band width of 1 Å or less, and has a sufficient monitoring function even for minute changes in the laser oscillation wavelength.

Embodiment Next, an embodiment of the present invention will be described with reference to the drawings. 1st
The figure shows one embodiment of the present invention, in which 1 is an InP substrate, 2 is an InP substrate, and 2 is an InP substrate.
is a BH tank structure InGaAsP/InPDFB laser,
3 is an optical waveguide with a three-dimensional confinement structure. 4 is a grating formed on the optical waveguide. 5
numeral 6 is a light-receiving element manufactured in an appropriate arrangement in a part of the embedded region of the DFB laser, numeral 6 is laser output light, and numeral 7 is laser light diffracted by the grating 4. The oscillation output light of the DFB laser is coupled to the optical waveguide 3 directly coupled to the end face.

As the composition of the optical waveguide, an InGaAsP layer having a composition that has a band gap that is transparent to laser light is usually used. A part of the oscillation output light propagating through the optical waveguide layer is diffracted by the grating 4 at an angle that satisfies the Bragg condition. The conditions at this time are determined by the laser oscillation wavelength: λ, the grating period: A, the incident angle to the grating 20, etc. Now, if the design is such that the diffracted light enters the light receiving element 5 for the oscillation wavelength in a steady state, the diffracted light will be detected by the light receiving element 5 after passing through the embedded region with transparent characteristics. It turns out.

When the oscillation wavelength of the laser changes due to external factors, the Bragg conditions due to the grating 4 change, and the conditions of incidence on the light receiving element change. By monitoring the output of each of the light-receiving elements arranged at a certain interval, it is possible to observe the shift of the oscillation wavelength from the steady state. Since the laser oscillation wavelength can be controlled externally by temperature or electric field, it is possible to stabilize the absolute oscillation wavelength by feeding back the output of the light receiving element to these control systems. become. Also, laser elements and optical waveguides.

Since the functional elements such as the demultiplexer and the light-receiving element are monolithically integrated, there is no need for alignment of optical elements, resulting in an extremely stable structure.

Although this example has been explained with a configuration using an InP-based material, it can also be applied to other materials, such as GaAs-based semiconductor materials or ferroelectric materials such as L i N b 03. It goes without saying that it can be done.

The present invention uses a waveguide type optical demultiplexer in which a grating is formed on the optical waveguide as a narrow band optical filter, and with appropriate design, the filter can have a band width of 1 Å or less, which is suitable for lasers. This provides a sufficient monitoring function even for minute changes in the oscillation wavelength. FIG. 2 shows a perspective view of a typical waveguide type duplexer. In the figure, 11 is a substrate, 12 is an optical waveguide layer, and 13 is a grating having a splitting effect formed on the optical waveguide layer.

Input light 14 coupled to the optical waveguide 12 is subjected to diffraction and deflected by the grating 13 in the waveguide. This relationship is expressed by the Bragg condition. As shown in FIG. 3, for light with an incident angle of 20 and a wavelength of λ in the medium, the diffraction grating 13 with a grating constant given by A-λ/2 sin θ satisfies the Bragg condition.
The incident light 15 is diffracted against the grating surface in the direction of the reflection angle θ and acts as a filter. At the same time, by installing a light receiving element that detects light in the traveling direction of the diffracted light, it can function as a light wave monitor.

Effects of the Invention As described above, according to the present invention, it is possible to realize a semiconductor laser device with extremely excellent characteristics as a light source for ultra-wavelength multiplexed transmission, and its practical effects are great. .

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the structure of a semiconductor laser device according to an embodiment of the present invention, FIG. 2 is a perspective view showing the structure of a waveguide type demultiplexer, and FIG. 3 is an explanatory diagram of Bragg diffraction conditions. 1... Board, 2... DFB laser, 3
...... Optical waveguide, 4... Grating, 5... Light receiving element, 6... Laser output light, 7... Laser light.

Claims (2)

[Claims] (1) a semiconductor laser formed on a substrate surface, an optical waveguide coupled to the semiconductor laser, and a waveguide-type optical demultiplexer formed on the optical waveguide and having a wavelength selective reflection function;
monolithically integrating at least one light receiving element installed at a predetermined position from the waveguide type optical demultiplexer;
A semiconductor laser device, wherein an oscillation state of the semiconductor laser is monitored using the waveguide type demultiplexer and the light receiving element. (2) The semiconductor laser device according to claim 1, wherein the semiconductor laser has a distributed feedback type or Bragg reflection type structure.