JP2001185806A - Wavelength switching semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength switching semiconductor laser capable of suitably selecting and using two oscillation wavelengths by switching modes of both sides of a stop band by using a gain coupling DFB. SOLUTION: The semiconductor laser has a structure for obtaining a distributed feedback by providing periodic recesses and protrusions on an active layer. In the laser, a clad layer is formed on the active layer. Two or more electrodes are formed in the direction of a resonator on the clad layer. Thus, an oscillation mode of the long wavelength side and the short wavelength side of the stop band can be selected by changing the current injection amount of any electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser, and more particularly to a semiconductor laser oscillating in a single mode.
The present invention relates to a semiconductor laser that can be used by switching between two oscillation wavelengths.

[0002]

2. Description of the Related Art Conventionally, a so-called variable wavelength laser which shifts the oscillation wavelength of a single mode laser by a carrier effect or a thermal effect has been often used as a variable wavelength semiconductor laser.

[0003]

In the case of the thermal effect, a relatively large variable width (several nm) can be obtained, but the response is slow. On the other hand, the response due to the carrier effect is fast, but the variable width is very small (1-2 nm) in the simple structure as shown in FIG.
There is a problem that the SR (Side Mode Suppression Ratio: the suppression ratio of the sub mode to the main mode) cannot be made large.

In order to obtain a large variable width, TTG (Tunabl
e Twin Guide) laser and SSG (Super Structure)
Grating) A rather complicated manufacturing process structure such as a laser is required. These increase the wavelength change amount with respect to the control current in order to expand the wavelength variable width. Therefore,
To switch to a specific wavelength and fix it, the control current must be precisely controlled.

In short, in the past, the refractive index of a waveguide was changed by a thermal effect or a carrier effect in order to change the wavelength, but there were the above-mentioned limitations. In particular, in the case of a DFB (Distributed Feedback) structure, when a uniform diffraction grating is used, there are two modes on both sides of the stop band, and there is no selectivity of these modes, so that there is a problem that mode competition occurs to cause instability. High SMSR
It is also difficult to get.

[0006] A high SMS that eliminates the conflict between these two modes
A gain-coupling DFB has been proposed and demonstrated as a method of obtaining R, but has not been discussed so far from the viewpoint of changing the oscillation wavelength.

SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem and to use a gain coupling DFB to switch between modes on both sides of a stop band and to appropriately select and use two oscillation wavelengths. It is to provide a semiconductor laser.

[0008]

In order to achieve the above object, according to the present invention, there is provided a semiconductor laser having a structure in which an active layer is provided with periodic unevenness to obtain a distributed feedback. A cladding layer is formed, and two or more electrodes are formed on the cladding layer in the resonator direction. By changing the current injection amount of any one of the electrodes, the stop band on the long wavelength side and the short wavelength side is stopped. The oscillation mode is configured to be selectable.

According to such a configuration, the switching of the oscillation wavelength is performed on the long wavelength side and the short wavelength side of the stop band.
The two wavelength intervals are determined by the structure and are stable. Moreover, a wavelength interval of several nm can be obtained. Such a laser is suitable for use as a light source for a wavelength division multiplexing (WDM) network.

In this case, the periodic irregularities of the active layer may be formed on either the upper surface or the lower surface of the active layer. In this case, the composition of the layer around the active layer is selected such that the equivalent refractive index is increased corresponding to the convex or concave portions of the periodic unevenness of the active layer.

According to a fourth aspect of the present invention, a pattern supply layer is formed on the lower surface of the active layer with periodic irregularities formed on the lower surface of the active layer with a low refractive layer interposed therebetween. The layer may have a configuration in which periodic irregularities complementary to the periodic irregularities of the active layer are formed. With such a configuration, it is possible to switch the oscillation wavelength as in the first to third aspects.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional structural view showing one embodiment of a wavelength switching semiconductor laser according to the present invention. The figure simply shows a cross-sectional structure along a stripe. An active layer 2 and a clad layer 3 are stacked on a clad layer 1, and periodic unevenness is provided on an upper surface of the active layer 2 to provide distributed feedback. It is formed in a structure to obtain. In this case, the composition of the layer around the active layer is selected so that the equivalent refractive index becomes higher in accordance with the projections of the unevenness. The composition of the layer around the active layer can be selected so that the equivalent refractive index becomes higher corresponding to the concave and convex portions.

A common electrode 6 is attached to the lower surface of the cladding layer 1.
Two separate electrodes 4, 5 are attached.

In such a configuration, when a current is injected into both the electrodes 4 and 5, the gain has a periodicity corresponding to the unevenness of the active layer 2 (the gain at a thick portion is high) and the gain coupling DF
Acts as a B laser.

Here, when the unevenness of the active layer 2 is filled with a layer having a lower refractive index than the active layer like the cladding layer 3, the distribution of the gain and the distribution of the refractive index become as shown in FIG. In phase, the longer wavelength side of the stop band oscillates preferentially, as seen in the spectrum of FIG.

Next, when the injection current to the electrode 5 is reduced or reverse biased, the active layer 2 has an absorption below the electrode 5. Since the absorption becomes larger at the place where the unevenness is thicker, the distribution of the absorption and the distribution of the refractive index are in the same phase, that is, when viewed as the distribution of the gain and the distribution of the refractive index, the distribution becomes opposite as shown in FIG. As can be seen from the spectrum of FIG. 3B, the short wavelength side of the stop band easily oscillates.

That is, the oscillation is maintained on the electrode 4 side and the electrode 5
If a current value is applied so that the active layer on the side does not absorb light, oscillation can be performed on the longer wavelength side of the stop band.
If the non-injection side or the reverse bias is used, the oscillation can be performed on the short wavelength side of the stop band, and thus the oscillation wavelength can be switched.

FIG. 4 shows another embodiment of the present invention in which the layer structure around the uneven active layer is changed. Cladding layer 7 and active layer 1
The portion where the pattern supply layer 8 and the low refractive index layer 9 are formed between 0 is different from the structure of FIG.

In this case, irregularities are provided (processed) on the lower surface of the active layer 10, and a pattern supply layer 8 is provided thereunder with a low refractive index layer 9 interposed therebetween. The pattern supply layer 8
This is a layer having an intermediate refractive index, and unevenness complementary to that of the active layer 10 is formed on the upper surface thereof. Thereby, the active layer 1
The relationship between the unevenness of 0 and the refractive index can be reversed from that in the above embodiment.

In this embodiment, when current is injected into both electrodes, the distributions of the gain and the refractive index become opposite phases (FIG. 3A).
(See FIG. 3 (b))
If one electrode is not injected with current or reverse biased, the longer wavelength side of the stop band oscillates (see FIG. 2).
(B)).

In the embodiment described above, the switching of the oscillation wavelength is performed on the long wavelength side and the short wavelength side of the stop band, so that the interval between the two wavelengths is determined by the structure and is stable. You can also get
Further, since the gain coupling property is used, a high SMSR is obtained in each mode, and the mode is strong against return light.

It should be noted that the foregoing description has been directed to specific preferred embodiments for the purpose of illustration and illustration of the invention. Therefore, the present invention is not limited to the above-described embodiments, and includes many more modifications without departing from the spirit thereof.
This includes deformation. For example, the number of electrodes attached to the upper surface of the cladding layer 3 or 11 is not limited to two, and two or more electrodes may be formed.

[0023]

As described above, according to the present invention,
Since the switching of the oscillation wavelength is performed on the long wavelength side and the short wavelength side of the stop band, the two wavelength intervals are determined by the structure and are stable, and there is an effect that a wavelength interval of several nm can be obtained. Further, since the gain coupling property is used, a high SMSR is obtained in each mode, and there is an effect that the mode is strong against return light.

The same wavelength tuning as that of the conventional two-electrode DFB can be performed by a thermal effect or a carrier effect, and it can be used in combination with a wavelength switch between modes.

The semiconductor laser of the present invention is suitable for use as a light source for a wavelength division multiplexing (WDM) network.

[Brief description of the drawings]

FIG. 1 is a sectional structural view showing one embodiment of a wavelength switching semiconductor laser according to the present invention.

FIG. 2 is an explanatory diagram for explaining an operation.

FIG. 3 is another explanatory diagram for explaining the operation.

FIG. 4 is another embodiment of the present invention.

FIG. 5 is a structural diagram showing an example of a conventional semiconductor laser having a simple structure.

[Explanation of symbols]

 1,7 clad layer 2,10 active layer 3,11 clad layer 4,5,12,13 electrode 6,14 common electrode 8 pattern supply layer 9 low refractive index layer

Claims (4)

[Claims] 1. A semiconductor laser having a structure in which periodic unevenness is provided in an active layer to obtain distributed feedback, wherein a cladding layer is formed on the active layer, and two or more electrodes are formed on the cladding layer in a resonator direction. The wavelength switching semiconductor laser is characterized in that the oscillation mode on the long wavelength side and the short wavelength side of the stop band can be selected by changing the current injection amount of any one of the electrodes. 2. The wavelength switching semiconductor laser according to claim 1, wherein said active layer is formed by processing periodic irregularities on an upper surface or a lower surface of said active layer. 3. The composition of a layer around the active layer is selected so that the equivalent refractive index becomes higher corresponding to the convex or concave portion of the periodic unevenness of the active layer. Or the wavelength switching semiconductor laser according to 2. 4. The periodic unevenness of the active layer is processed on a lower surface of the active layer, and a pattern supply layer is formed on a lower surface of the active layer with a low refractive layer interposed therebetween. 4. The wavelength switching semiconductor laser according to claim 1, wherein periodic irregularities complementary to the irregularities are formed.