JPS62130586A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To hardly affect influence of instability of external resonator by varying width of a stripe current implanting region parallel to an active layer along a cavity direction to obtain a longitudinal multimode oscillation, thereby suppressing a mode hopping noise. CONSTITUTION:An n-type GaAs current block layer 3, a p-type GaAlAs clad layer 4, a p-type GaAlAs active layer 5, an n-type GaAlAs clad layer 6, an n-type GaAs contact layer 7, and an electrode 8 are sequentially formed on a p-type GaAs substrate 2 added with an electrode 1 on its back surface, and a groove 9 in which a width is varied along a cavity direction is arranged between the layers 3. The groove 9 becomes a current implanting region, and a variation in the width of the groove 9 is formed by alternately disposing wide and narrow portions. Thus, the current implantation becomes irregular to obtain a peculiar longitudinal multimode oscillation with wide spectral width.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a semiconductor laser device that can be used in optical communication and original information processing equipment.Prior art Semiconductor laser devices are small and have low power consumption. It has become extremely important as a light source for optical communications, original disk memory, and even laser beam printers. When this semiconductor laser device is used, for example, as a light source for a source pickup of a source disk memory, an optical isolator must be used to prevent the reflected light from the laser source focused on the optical disk from returning into the semiconductor laser. This is because if there is light returned to the semiconductor laser device, the oscillation longitudinal mode of the laser fluctuates, often causing intensity noise at the laser source.

Fluctuations in the longitudinal mode of a laser are called mode hopping. In a video disc recording an analog signal, the noise generated due to mode hopping has a direct effect on the reproduced video signal, resulting in a reduction in image quality. Semiconductor laser device mode hopping due to return 9 yuan? The reason why this is likely to occur is that the gain spectrum width of the laser medium is wide, and the gain peak wavelength is
The reason is that it easily changes depending on the temperature and the source of return.

In addition, the reflectance of the resonator is as low as about 30%, and due to the presence of return light, it easily couples with the optical resonator formed outside the semiconductor laser device, and is affected by the unstable external resonator. , the oscillation state of the laser becomes unstable, which also causes noise.

What is the problem of the semiconductor laser device that the invention aims to solve? In order to use it as a low-noise light source, it is necessary to completely reproduce the original light source, but this is difficult in practice. In addition, promoting isolation measures will lead to higher equipment costs.

Therefore, the structure of the semiconductor laser device itself needs to be such that noise due to mode hopping does not occur even if there is a return source.

Means for Solving the Problems The semiconductor laser device of the present invention capable of solving the above problems has a structure in which the current injection region in a stripe shape changes continuously or discontinuously in the cavity direction KG. It has become.

Effect: According to this structure, the amount of current injected into the active region changes in response to the change in the width of the current injection region in the direction of the cavity, resulting in non-uniform emission intensity within the active region and self-excitation. Oscillation (self-pulsation) occurs, resulting in longitudinal multimode oscillation. Therefore, mode hopping noise can be suppressed. Furthermore, multimode oscillation also reduces the coherence of the laser beam, weakening the coupling with the external resonator, and making it less susceptible to the instability of the external resonator.

EXAMPLES A practical example of the present invention will be described below with reference to the drawings.

FIGS. 1A and 1B show the structure of a semiconductor laser device in an embodiment of the present invention. Figure 1 (A)
Its basic structure is a BTR3 type semiconductor laser (References:
The semiconductor laser device of the present invention, which has an internal stripe structure, is also described in FIG. (B) is a semiconductor laser whose basic structure is VSIS type (Reference: Yamamoto et al., IEICE Technical Report, '1101
．． FIG. 2 is a perspective view showing a semiconductor laser device of the present invention, also called an internal stripe type structure. As shown in the figure, the semiconductor laser device of the present invention has a p-type Ga
On the As substrate 2, an n-type GaAs current blocking layer 3, a p-type GhM S cladding layer 4, and a p-type GaAIAS active layer 6 are formed.
, an n-type GaAlAs cladding layer 6, an n-type GaAs contact layer 7, and a capacitor 8 are sequentially formed, and a groove 9 whose width changes along the cavity direction is located between the current blocking layer 3. , this groove portion 9 becomes a current injection region. The illustrated width of the groove portion 9 is varied by alternately locating wide portions and narrow portions.

By the way, the internal stripe c! of the BTRS laser, VSIS laser, etc. which is the basic structure of the semiconductor laser device of the present invention is ! With the structure, the current narrowed in the groove is efficiently injected into the active region 5 located directly above the groove by the current blocking layer 3Q, so that it is easy to lower the threshold voltage. Since the flux along the capacitance direction is constant, carrier injection becomes uniform, and in combination with the refractive index type waveguide structure, it has advantages such as excellent single-longitudinal mode properties.

In order to eliminate mode hopping due to returned light and suppress the generation of noise in these semiconductor laser devices, it is necessary to cause the semiconductor laser device to oscillate in a gold longitudinal multimode. In the multimode oscillation state, the fluctuations of individual longitudinal modes are large, but
This is because the overall strength fluctuation is small. Generally, a laser that oscillates in a single mode when there is no returned light becomes multimode when there is returned light. However, if the single mode property of the laser is too good, even if the returned light enters, it will not become sufficiently multimode, and very large noise will occur due to mode hopping in the transition stage from single mode to multimode. When using a semiconductor laser device for picking up an optical disk, the amount of returned light that becomes a problem is usually 0.1 to 1.0.
%, therefore, in an internal stripe type semiconductor laser device with too good single mode property, multimode is insufficient and it is not possible to achieve low noise.

Self-oscillation (self-pulsation) is one method for creating vertical multi-mode semiconductor lasers. A semiconductor laser device that undergoes self-pulsation emits pulse-like oscillation even though it is driven by direct current, resulting in unique longitudinal multimode oscillation with a wide spectrum width. In the present invention, in order to cause this self-pulsation, the @ of the groove portion 9 serving as the current injection region is changed in the capacitance direction to make the current injection non-uniform.

However, when the current injection is unconstrained, the loss inside the cavity increases, leading to problems such as an increase in the oscillation threshold and a decrease in external differential quantum efficiency. Therefore, it is preferable that the degree of non-uniformity of current injection be as low as possible. In consideration of the above reasons, the semiconductor laser device of the present invention illustrated in FIGS. 1 and 1B has a structure in which the groove width changes periodically.

FIGS. 2(A) to 2(D) are diagrams showing examples of patterns of the resist mask 1o formed on the current blocking layer 3 and combed (A), sawtooth (B), and wavy. (C) and Φ)
There are groove shapes such as, and all of them are capable of self-pulsation. The semiconductor laser device shown in FIGS. 1(A) and 1(B) has a groove portion serving as a current injection region formed using the comb-shaped resist mask shown in FIG. 21(A), and the manufacturing process thereof will be described below. I will explain about it.

FIGS. 3(A) to 3(C) are diagrams schematically showing the manufacturing process of the semiconductor laser device having the structure shown in FIG. 1(A). First, as shown in FIG. 3(A), an n-type GaAs current blocking layer 3 is formed in a mesa on a p-type GaAs substrate 2 having a mesa portion 11 with a width of 15 μm and a height of 2 μm provided parallel to the (011) direction. The upper portion of the portion 11 is grown to have a thickness of 1 μm. Next, comb-shaped resist masks 10 are placed on the current blocking layer 3 so as to face each other, as shown in FIG. 3(B). In addition, when arranging the resist mask 10, a relationship is established in which the comb-shaped portion is located above the mesa portion 1o.

Next, the portions not covered by this resist mask 10 are treated with an H2SO4-H2O2-based etchant of about 1.
By etching to a depth of 2 μm, the third [IN
As shown in (C), a groove portion 9 serving as a current injection region is formed, and the shape of this groove portion is such that wide portions and narrow portions are located alternately. The Gaps substrate 2 that has undergone the above treatment is subjected to crystal growth treatment again, and as shown in the fourth garden, a cladding layer 4, an active layer 5, and a cladding layer 6 are formed.
Then, contact layer 7 is formed to obtain a double heterostructure, and electrodes 1 and 8 are further formed to complete semiconductor laser fabrication. Note that the semiconductor laser device shown in FIGS. 4(B) and (C1) is connected to the line BB corresponding to the narrow portion of the groove 9 and the line C-corresponding to the wide portion of the groove 9. It is a sectional view taken along line C.

Incidentally, the cross-sectional shape of the groove portion 9 shown in FIG. 4(B) is V-shaped, and the current injected from this portion efficiently reaches the active layer 5. Therefore, the gain required for oscillation can be obtained at low current levels. On the other hand, since the cross-sectional shape of the groove shown in FIG. 4(C) is close to a U-shape, the current injected from this portion spreads widely. Therefore, the peak value of the gain is smaller than in the former case.

In this way, in the semiconductor laser device of the present invention, @? of the groove portion 9 serving as the current injection region. By making the changes periodically along the direction of the cavity, non-uniformity of the injected carriers is created and self-pulsation operation is made possible.

FIG. 5 shows a typical optical output of the semiconductor laser device of the present invention.
The current characteristics are shown by a solid line, and the current characteristics are shown by a normal BTRSTRS laser photoelectric current characteristic in which the groove width is uniform in the cavity. Comparing these characteristics, the semiconductor laser device of the present invention shows an increase in the oscillation threshold by about a factor of 10 compared to a conventional semiconductor laser device. This rise in the oscillation threshold is due to the current injection defect, which is based on the shape of the current injection region to enable self-pulsation operation, that is, the shape of the current injection region that changes along the cavity direction. This is caused by uniformity, and this does not significantly reduce the characteristics and does not cause any problems in actual operation.

FIG. 6 shows the oscillation vector of the semiconductor laser device of the present invention. The linewidth of the spectrum broadens, and adjacent modes overlap on the short wavelength side, indicating self-pulsation oscillation.

FIG. 7 is a diagram showing the entire relationship between the relative noise intensity and the amount of returned light, and the solid line indicates the relationship curve of the semiconductor laser device of the present invention. The broken line indicates the relationship for a single mode semiconductor laser device.

As is clear from the figure, the semiconductor laser device of the present invention is not affected by return light due to self-pulsation, and the noise level is extremely low.

In the embodiments described above, the width of the current injection region changes discontinuously along the cavity direction. It is also possible to have a shape that is curved so that it becomes narrow or a shape that is curved so that the center part resonates.

Effects of the Invention As described above, the present invention changes the width of the groove serving as the current injection region of an internal stripe laser semiconductor laser device along the cavity direction, thereby making the carriers injected into the active layer completely non-uniform. This makes it possible to cause self-pulsation and achieve low noise, and its practical effects are significant.

[Brief explanation of drawings]

1(A) and CB) are structural diagrams of a semiconductor laser device in an embodiment of the present invention, FIG. 2 is a plan view showing the shape of a resist mask pattern corresponding to the groove shape, and FIGS. 3 and 4. 5 is a perspective view showing the manufacturing process of the semiconductor laser device of the present invention and a sectional view of the completed semiconductor laser device, FIG. 5 is a characteristic diagram showing optical output-current characteristics, FIG. 6 is an oscillation spectrum diagram, and FIG. FIG. 3 is a characteristic diagram showing measurement results of relative noise intensity of laser light. DESCRIPTION OF SYMBOLS 1... Electrode, 2... P-type GaAs substrate, 3... N-type eaAs current blocking layer, 4...
...p-type GaAlAs cladding layer, 5...
p-type Ga and IAs active layer, 6...... aAI to n-type
As cladding layer, end...n-type GaAs contact layer, 8...electrode, 9...groove, 10
...Resist mask, 11...Mesa part. Figure 1 (A> (B) γ prisoner mark Figure 2 O rhenostoma included Figure 3 Figure 4 Figure 5 0 20 40 60 k) /DOj
-Kou (nshi A) Figure 6 Marujoblade 4ru W 7δ47δ0? 76L length (Figure 7 Light output 4W θ θ, θ/0.1/
People-Soviet Party (7,)

Claims (3)

[Claims] (1) A semiconductor laser device characterized in that the width of the striped current injection region parallel to the active layer changes continuously or discontinuously along the cavity direction. (2) The semiconductor laser device according to claim 1, wherein the width of the stripe-shaped current injection region is discontinuously changed by forming a wide portion and a narrow portion in series. (3) The semiconductor laser device according to claim 1 or 2, wherein the wide portion and the narrow portion are arranged in a periodic manner.