JPH06120613A - Complex short resonator reflection semiconductor laser - Google Patents

Abstract

PURPOSE:To make the unimode oscillation possible without causing the expansion of the width of a spectrum line by arranging two resonators shorter in optical length than the length of light emitting regions and different form each other in optical length side by side, and equipping this device with a reflector for selecting the unimode required for laser oscillation. CONSTITUTION:Oscillation wavelength is put in a unimode by arranging the constitution such that there is invariably only one mode where all the wavelengths become the same, out of the inner longitudinal modes being each decided by the resonator A constituted of a light emitting region 12 and a phase control region 13 different in optical length from each other, the first resonator B in the region 15 deciding the oscillation wavelength, and the second resonator C. And, the position of the longitudinal mode is changed by changing the optical lengths of the resonators A, B, and C, and besides the position, too, where all modes accord with one another, is changed to change the oscillation wavelength. Moreover, the optical length of the resonator is changed, by heating each resonator, so as to change the refractive index of the wave guide paths so that it may not deteriorate the width of a spectrum line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser which is useful as a light source for coherent optical transmission and optical measurement and which can oscillate in a single mode and can shift wavelength in a wide band.

[0002]

2. Description of the Related Art The installation of main trunk optical fiber cables is progressing, and in the future, fiber cables will be introduced to each individual as a subscriber system. However, the conventional AM communication system requires a new communication system because the information transmission capacity is small. In order to deal with this, a coherent optical transmission system that treats light as a frequency has been devised, and an optical heterodyne system, which is one of the systems, is being developed. In this optical heterodyne system, the interference component obtained by multiplexing the signal light on the transmitting side and the local light on the receiving side is treated as a signal, so it is possible to simultaneously transfer a plurality of signal light with different frequencies with one fiber. Is. In order to put this system into practical use, the performance of the light source used is important, and the following performance is required as the required performance of the light source. That is, in order to increase the density of the information signal for the frequency band, the spectral line width of the signal light should be as narrow as possible,
In order to secure more channels with one light source, it is required to have a wavelength tunable function over a wide band, and to be able to perform frequency tuning of local light at a high speed enough to be tuned to signal light. Further, also in the optical measurement, similar performance of the light source is required from the viewpoint of resolution, measurement band, measurement speed.

As a main coherent light source, a distributed feedback laser in which a diffraction grating is provided in a light emitting region, a distributed Bragg reflection laser constituted by a light emitting region and a wavelength control region having a reflector with a diffraction grating, and light emission An example is an external diffraction grating reflector type laser having a region and an external diffraction grating reflector optically coupled to the region.

A three-electrode type distributed Bragg reflection laser shown in a sectional view in FIG. 4 has a light emitting region 12, a phase control region 13 and a Bragg reflection region 16 and a waveguide of the phase control region 13 or the Bragg reflection region 16. It is possible to change the refractive index by injecting carriers into, and it is possible to achieve frequency tuning of several nm at high speed. (Prior art 1)

Further, since the external diffraction grating reflector type laser whose sectional view is shown in FIG. 5 uses the external diffraction grating 18 to change the wavelength, it is possible to perform wideband frequency tuning with a narrow spectral line width. it can. (Prior art 2)

[0006]

The conventional wavelength tunable semiconductor laser described above has an excellent point. But,
The distributed Bragg reflection laser has a problem that the spectrum line width is widened due to fluctuations in carrier density that are inevitably generated with current injection. Further, in the distributed Bragg reflection laser, the Bragg wavelength (λB = 2 · n · Λ) is changed by changing the refractive index of the Bragg reflection region, but the maximum is 10 nm in the current technology. The external diffraction grating reflector type laser has the problems that continuous wavelength sweeping is difficult and the wavelength tuning speed is slow. A problem common to distributed Bragg reflection type lasers and external diffraction grating reflector type lasers is that it is difficult to form a diffraction grating accurately.

[0007]

Means for solving the above problem will be described below. That is, the problem of the conventional technique is solved by providing a wavelength tunable semiconductor laser capable of performing single-mode oscillation without sweeping the spectral line width and sweeping the entire band of the laser element at high speed and in a wide band. To be done. The means will be described below for each claim.

According to the first aspect of the present invention, a reflector for arranging two resonators having an optical length shorter than the light emitting region length and different optical lengths from each other to select a single mode required for laser oscillation is provided.

According to a second aspect of the present invention, there is provided means for changing the optical length of a region other than the light emitting region that determines the oscillation wavelength.

In the third aspect of the invention, the optical length is changed by heating the region that determines the oscillation wavelength.

[0011]

According to the invention of claim 1, a resonator A having a light emitting region 12 and a phase control region 13 having different optical lengths, a first resonator B in a region 15 for defining an oscillation wavelength, and a first resonator B Of the internal longitudinal modes determined by the two resonators C, the mode with the same wavelength is always 1
There was only one, and the oscillation wavelength was a single mode.

According to a second aspect of the invention, the resonators A, B,
By changing the optical length of C, the position of the longitudinal mode of each resonator is changed, the position where all modes match is also changed, and the oscillation wavelength is changed.

According to the third aspect of the present invention, the optical length of each resonator is changed by heating each resonator so that the refractive index of the waveguide is changed. Does not deteriorate.

[0014]

EXAMPLES Examples of the present invention will be described below. Since a 1 μm band semiconductor laser has a gain band of about 100 nm, if the longitudinal mode can be selected in the range of 100 nm, wavelength shift (frequency tuning) is possible in the range of 100 nm.

First, an embodiment of the invention of claim 1 will be described.
According to the invention of claim 1, three types of resonators A, B, and C having lengths L1, L2, and L3 are formed in the semiconductor laser, and the internal longitudinal mode determined in each of the three types of resonators. Of these, only one mode with the same wavelength was used, and the oscillation wavelength was set to a single mode. This is explained in FIG. In the model, L1 represents the length of the resonator A composed of the light emitting region 12 and the phase control region 13. A portion other than the light emitting region 12 is a region 15 that determines the oscillation wavelength, a part of the region 15 that determines the oscillation wavelength is the phase control region 13, and the other portion is a reflection region 14. In the reflection region 14, the thick portion of the guide layer 3 is the first resonator B, and the resonator length thereof is L2. The thin portion of the guide layer 3 is the second resonator C, and its resonator length is L3. Where the thickness of the guide layer 3 is changed, a difference in refractive index occurs, and the first resonator B and the second resonator C serve as end faces that cause partial reflection. Resonator length L1
500 μm (light emitting region 300 μm, phase control region 20
0 μm), refractive index n1 is 3.25, wavelength λ0 is 1.55
.mu.m, the longitudinal mode spacing .DELTA..lambda.1 of resonator A is .DELTA..lambda.
From 1 = λ0 · λ0 / (2 · n1 · L1) 0.74 nm
Becomes Next, when the resonator length L2 is 50 μm and the refractive index n2 is 3.25, the longitudinal mode interval Δλ2 of the resonator B is 7.4 nm. Further, the resonator length L3 is 40 μm,
When the refractive index n3 is 3.20, the longitudinal mode interval Δλ3 of the resonator C is 9.4 nm. These three resonators A,
In B and C, there is always one place where the mode positions match, and oscillation occurs in the single longitudinal mode. Here, if the wavelength of the mode corresponding to the least common multiple of the values of the three longitudinal mode intervals is included in the gain region, multimode oscillation occurs, so that L1, L2, L3, n1, n2, and n3 are set. In this case, it is necessary to consider this.

Next, an embodiment of the invention of claim 2 will be described.
In the invention of claim 2, the optical lengths of the three resonators described above are changed to change the refractive index, and the positions of the longitudinal modes of the resonator A, the resonator B, and the resonator C are changed, It oscillates at a wavelength that matches the longitudinal mode. For example,
The refractive index change of 1% obtained by carrier injection is
Considering a resonator C having a resonator length of L3, Δλ
From 0 = λ0 · (Δn / n2), it corresponds to 15.5 nm, which exceeds the longitudinal mode interval of L2 of 7.4 nm. Therefore, any longitudinal mode of L2 or any longitudinal mode of L3 must be used. Only one will match. As a matter of course, the same applies to the L1 vertical mode. Here, by changing the refractive index of the phase control region 13, it is possible to sweep between the longitudinal modes in L1 and obtain a single wavelength in all bands.

This wavelength variable operation is shown in FIG. The vertical axis represents the position of the oscillation wavelength mode, and the horizontal axis represents the heater power.
In this embodiment, the refractive index is changed by heating the heater, but it is obvious that other means can be used.
The refractive index of the resonator C having the resonator length L3 is changed by heating with the lattice type heater 9 (represented by HLa in the drawing), and the wavelength of the longitudinal mode of L3 is shifted to thereby cause the resonator having the resonator length L2. The wavelengths of the longitudinal modes can be matched with each other, and a large wavelength shift occurs, and the heater 11b (HMc in the figure, which is a heating means provided on the waveguide 17 of the reflection region 14 is provided.
It is represented by. It was possible to shift the oscillation wavelength for each longitudinal mode of the resonator having the resonator length L1 by shifting the matched longitudinal mode of each resonator by heating with (1). Further, by changing the refractive index by a heater 11a (represented by HPc in the figure) provided on the waveguide 17 of the phase control region 13 to change the longitudinal mode of L1, the phase between the longitudinal modes is changed. The wavelength could be continuously shifted.

According to the third aspect of the invention, since the spectrum line width broadens when the refractive index is changed by carrier injection as in the conventional case, the refractive index is changed by local heating by the heater. However, the structure of the heater is designed by performing a thermal analysis simulation so that the heat of the heater is transmitted only to the guide layer and does not diffuse to the active layer.

(Manufacturing Method) The manufacturing method of the embodiment of the invention of claim 3 will be briefly described below. FIG. 1A is a top view of the element, and FIG. 1B is a cross-sectional view of the element taken along a line. An active layer 2 of 1.55 μm band is grown to a thickness of 0.1 μm on an InP substrate 1, the active layer 2 other than the light emitting region 12 is removed, and a 1.3 μm band guide layer 3 of 0.2 μm is formed.
Grow m thick. The guide layer 3 at the portion L3 is etched to a thickness of 0.05 μm so that L2 = 50 μm and L3 = 40 μm are repeated on the portion of the guide layer 3 which becomes the reflection region 14. After that, the clad layer 5 is grown, and mesa etching is performed so that the waveguide 17 having a width of about 1.5 μm is formed, and buried growth is performed while also serving as current confinement and light confinement.

Up to this point, the growth process has been described. Next, the step of forming electrodes and a heater as a heating means will be described. First, electrodes 6 and 7 for injecting a current are formed on the substrate 1 side and the growth side of the light emitting region 12. Next, the insulating film 8 of SiO 2 is deposited on the region 15 that defines the oscillation wavelength, that is, the growth-side surfaces of the phase control region 13 and the reflection region 14. On top of that, a lattice type heater 9 of Au thin film which is a heating means is patterned so as to coincide with the location of L3 which was previously etched (indicated by hatching in the figure), and the electrode pad 9a of the heater 9 of Au, An insulating film 10 of SiO 2 is deposited again except for the portion where 9b is provided. Finally, in order to heat the phase control region 13, an Au heater 11a which is a heating means is provided above the waveguide 17 of the phase control region 13, and an Au heater 11b which is a heating means is provided above the waveguide of the reflection region 14. Patterning (shown by the solid line in the figure).

In the above-mentioned embodiment, the region 15 for determining the oscillation wavelength is provided on one side of the light emitting region 12, but it is obvious that the same effect can be obtained by providing it on both sides. Also, the first
Although the resonator B and the second resonator C are alternately provided, a structure in which the first resonator is continuous and the second resonator C is provided after that is naturally conceivable. Furthermore, the length of the resonator is not limited to the eigenvalue, and it is possible to form a reflective end face by changing the width of the waveguide or by providing a refractive index difference with the temperature distribution. The same operation is possible not only with a waveguide but also with a gain or absorption. Furthermore, it is all necessary to configure the waveguide with a plurality of guide layers, to have a quantum well structure, to use an optical material other than InP-based material for the element, and to use a temperature control element such as Peltier to control the refractive index. It is included in the embodiments of the present invention. In addition, the wavelength-defining region can also be applied to broadband switches.

[0022]

According to the invention of claim 1, single mode oscillation is possible without forming a diffraction grating. According to the invention of claim 2, it is possible to oscillate in a single mode and change the wavelength in the entire gain band of the element. According to the invention of claim 3, in the invention of claim 2, the operation of low threshold value, high efficiency and long life is enabled without deterioration of the spectrum line width.

[0023]

[Brief description of drawings]

FIG. 1 is a top view and a sectional view of an embodiment of the invention of claim 3;

FIG. 2 is a diagram for explaining the principle of the invention of claim 1;

FIG. 3 is a diagram showing characteristics of an embodiment of the invention of claim 2;

FIG. 4 is a sectional view of a conventional distributed Bragg reflection type laser.

FIG. 5 is a cross-sectional view of a conventional external diffraction grating laser.

[Explanation of symbols]

 1 Substrate 2 Active Layer 3 Guide Layer 5 Clad Layer 6 Electrode 7 Electrode 8 Insulating Film 9 Lattice Type Heater 10 Insulating Film 11a Heater 11b Heater 12 Light Emitting Area 13 Phase Control Area 14 Reflecting Area 15 Area for Defining Oscillation Wavelength 16 Bragg Reflecting Area 17 Waveguide 18 Diffraction grating A Resonator B First resonator C Second resonator.

Claims (3)

[Claims] 1. A compound short cavity reflection type semiconductor laser comprising a light emitting region (12) and a region (15) for defining an oscillation wavelength on the same substrate, wherein the end face is at least partially reflective. A first resonator (B), one end of which is optically connected to the light emitting region and has a first optical length shorter than the length of the light emitting region.
And; defined by at least a partially reflective end face, one end face of which is optically connected to the other end face of the first resonator and has a second optical length shorter than the light emitting region length. A compound short-cavity reflective semiconductor laser having a second resonator (C) in a region that defines the oscillation wavelength. 2. The compound short-cavity reflective semiconductor laser according to claim 1, further comprising means for changing an optical length of a region that determines an oscillation wavelength. 3. The compound short cavity reflection type semiconductor laser according to claim 2, wherein a heating means is used as a means for changing the optical length.