JPS63104393A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain a transverse mode stable even in a state of high-power beams, by serially disposing the first semiconductor laser element and the second semiconductor laser element with gains existing on the same wavelength band as in the first semiconductor so that their optical axes of waveguide paths are made identical with each other. CONSTITUTION:The first laser element 11 as a wavelength oscillatory region and the second laser element 12 as a beam power amplifying region are formed at fixed intervals on a one-sided surface of a P-Ga substrate 10, and a P side electrode 13 is formed on the other-sided surface. In the first laser element 11, a waveguide is formed of an active layer 16, which is interposed between the first clad layer 14 and the second clad layer 15 and in which gains to light vary with time, and resonators 17 and 18 are formed on both end surfaces of their clad layers. In the second laser element 12, resonator structure is formed so that its Q value is made smaller than that of the resonator structure formed in the first semiconductor laser element 11, and its gain exists on the approximately same wavelength band as in the first semiconductor laser device 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a semiconductor laser device used, for example, as a light source for optical information processing.

(Prior Art) Generally, when a semiconductor laser device is used as a light source for optical information processing, the laser light output from the semiconductor laser device is supplied to the information processing optical system, and at the same time, a part of the laser light is supplied to the information processing optical system. Some of the light is reflected by the fiber end of the optical system, a lens, a mirror, etc., and returns to the semiconductor laser device side again. By the way, this semiconductor laser device has a single wavelength of 3! ! In the case of continuous oscillation, when the laser light output from this semiconductor laser device and the above-mentioned reflected light are in a coherent state, reflection noise may be induced due to interaction.

Various techniques have been developed to prevent such reflection noise.

For example, there is a self-valsation type laser (ISSS type laser) (see Institute of Electronics and Communication Engineers - Technical Report, July 1984, 0QE84-57), in other words, this semiconductor laser device has an active layer at a frequency of about IGHz. This oscillates the carrier concentration within the active layer, thereby varying the gain and refractive index of the active layer. As a result, this semiconductor laser device undergoes self-oscillation (self-oscillation), and the oscillation wavelength fluctuates in the width of several nanoliters in the period of self-oscillation. Therefore, the laser beam output from the semiconductor laser device and the reflected light are less likely to be in a coherent state, and reflection noise is prevented from being induced.

In addition, as another example of a semiconductor laser device, JP-A-60-1
There is a semiconductor laser device disclosed in Japanese Patent No. 77693, whose structure is shown in FIG. It is arranged as follows. Then, by outputting spontaneous emission light with a wide spectrum width as an emission wavelength from the active layer 2a of the laser element 2, and injecting this light between the resonators 1b and 1c sandwiching the active layer 1a of the laser element 1, It oscillates with a spectrum as shown in Figure 8, thereby reducing reflection noise.

(Problems to be Solved by the Invention) By the way, in the above-mentioned self-balsation type semiconductor laser device, interactions such as saturable absorption, a weak refractive index guide structure as a waveguide for the structural mode, and spatial distribution of gain, etc. The lick that is used to generate and generate pulsation,
As the optical output increases, the transverse mode becomes more likely to be distorted, resulting in nonlinearity of the photo-current characteristics, distortion of the near-field image, etc. Therefore, there is a problem in terms of practicality in a high light output state.

In addition, in the semiconductor laser device shown in FIG. 7, the overall spectrum is wide as shown in FIG. 8, but the spectral width of each longitudinal mode is determined by the IC and the resonator 1b that sandwich the active layer 1a. Therefore, it has the disadvantage that reflection noise is larger than the above-mentioned self-balsation type semiconductor laser.

The present invention was made under these circumstances, and an object of the present invention is to provide a semiconductor laser device that has a stable transverse mode even in a high optical output state and generates very little reflection noise.

[Refinement of the Invention] (Means for Solving the Problems) That is, the semiconductor laser device of the present invention comprises a first semiconductor laser element having a resonator structure and whose oscillation frequency changes due to self-valsation; a second semiconductor laser element having a resonator structure with a Q value lower than the Q value of the resonator structure of the first semiconductor laser element and having a gain in substantially the same wavelength band as the first semiconductor laser element; The waveguide is characterized in that these waveguides are successively arranged so that their optical axes coincide.

(Function) In the semiconductor laser device of the present invention, the first semiconductor laser element has a resonator structure, and the oscillation frequency fluctuates due to self-valsation, and the optical axis of the first semiconductor laser element and the waveguide. The second semiconductor laser elements arranged consecutively so that the Q value of the first semiconductor laser element is lower than the Q value of the resonator structure of the first semiconductor laser element; Since it has a gain in almost the same wavelength band as the element, it has a stable transverse mode even in a high optical output state, and generates very little reflection noise.

(Example) Hereinafter, details of an example of the present invention will be described based on the drawings.

FIG. 1 is a diagram showing a semiconductor laser device according to an embodiment of the present invention. In the figure, reference numeral 10 denotes a substrate made of P-GaAs, and one surface of this substrate 10 has a first laser element 11 as a wavelength oscillation region and a second laser element 12 as an optical output amplification region. are formed with a predetermined gap, and a P-side electrode 13 is formed on the other surface.

The first laser element 11 has a first cladding JF! A waveguide is formed by sandwiching an active layer 16 whose gain for light changes over time between the active layer 14 and the second cladding layer 15, and has resonators 17 and 18 on both end faces thereof. That is, this first laser element 11 forms a wavelength oscillation region using self-valsation in which the oscillation wavelength changes over time. Incidentally, on the second cladding layer 15, an ohmic layer 19,'c, and a pole 20 are sequentially formed.

In addition, the second laser element 12 forms a waveguide in which an active layer 23 having a gain in the same wavelength band as the active layer 16 described above is sandwiched between a first cladding layer 21 and a second cladding layer 22. A high reflection film 24 is provided on the side facing the resonator 18 on both end faces, and a non-reflection film or a low reflection film (
25, which will be simply referred to as a low reflection film hereinafter.

The high reflection film 24 allows the light amplified by the second laser element 12 to pass back to the first laser element 1 as an optical wavelength vibration region.
1 and prevents wavelength oscillations from being suppressed. On the other hand, the low reflection 1-25 lowers the Q value of the resonator, making it easier to emit light. Furthermore, an ohmic R 26 and an electrode 27 are formed in this order on the second cladding layer 22. Furthermore, the above-mentioned active layer 23 is formed into a waveguide with a strong refractive index guide structure together with the first cladding layer 21 and the second cladding layer 22, so that the waveguide has a stable lateral direction even at high output in a plane perpendicular to the optical axis. It has a structure of an optical output amplification region that can maintain the mode. Furthermore, a semiconductor layer 28 that is transparent to the oscillation wavelength of the laser beam is provided between the active wi 16, the high reflection film 24, and the low reflection film 25, to prevent optical damage to the end of the active layer 16. It is said to be able to withstand high light output operation.

Then, the first laser element 11 as an optical wavelength vibration region
The light injected into the second laser element 12 as an optical output amplification region through the resonator 18 of
2 and is emitted from the low reflection film 25. that time,
Resonator 1 of the first laser element 11 as a wavelength vibration region
8 to the second laser element 1 as an optical output amplification region.
As shown in FIG. 2, the spectrum of the light injected into 5.2 is longitudinal multimode. Moreover, the width of each mode is wide. Since the resonator in the optical output amplification region has a low Q value, it is affected by the injected light, and the light emitted from the low reflection JI25 is in longitudinal multimode and , each mode has a wide spectrum and low coherency.

Furthermore, since the second laser element 12 serving as the optical output amplification region has a strong refractive index guide even during high carrier injection, the transverse mode is not distorted. Furthermore, since the active layer 23 is protected by the semiconductor layer 28, it will not be damaged even during high optical output.

According to this semiconductor laser device, therefore, it is possible to maintain stable characteristics even in a high optical output state without generating reflection noise.

Next, a more detailed explanation will be given based on a prototype example of an AlGaAs-based internal stripe type semiconductor laser device to which the present invention is applied.

First, as shown in FIG. 4, a current stopping layer 30 made of n-GaAs is formed on a substrate 29 made of P-GaAs by a crystal growth process, and then by patterning with a photoresist, a layer 30 that becomes a current path is formed. A substrate 29a having the same components as the substrate 29a is formed.

Then, as shown in FIGS. 5(a) to (C), on top of this,
The first clad W made of P-^lGaAs! i31,A
Active layer 32,33,34, n- made of lGaAs
Second cladding layer 35 made of AlGaAs, n-GaA
An ohmic layer 36 made of S is sequentially grown by liquid phase epitaxial growth.

As a result, the 5th line corresponds to lines a, b, and c in FIG.
A horizontal m1 plane is obtained, not shown in figures (a), (b), and (c).

Figure 5(a) shows W! in the wavelength vibration region. It has a concave cross section.

As shown in the figure, the shape of the current path 31a is the current blocking J
It has a T-shape with a protrusion toward Ff30, and current is concentrated in the active layer 32 directly above the center of this protrusion.
A saturable absorber is formed by providing a spatially steep carrier distribution within 2. In addition, the current blocking layer 30
The thickness tl of the upper first cladding layer 31 and the active layer 32 are both thick, and the equivalent refractive index difference in the lateral waveguide tv4 structure is small, so a pulsation accompanied by vibration of the wavelength of the oscillation wavelength is generated. .

FIG. 5(b) is a cross section of the optical output amplification region.

As shown in the figure, the current blocking layer 30 is formed by the first cladding layer 3.
The first cladding layer 31 has a convex portion having a width w2 and a height h2 toward the direction of
The thickness t2 of the active layer 33 and the thickness of the active layer 33 are small, and the waveguide is equivalently formed into a waveguide having a strong refractive index guide structure in the lateral direction.

Furthermore, since the active layer 33 has substantially the same composition as the active layer 32, it has an amplifying effect on light injected from the wavelength vibration region.

FIG. 5(C) is a cross section near the end of the optical output amplification region. As shown in the figure, the current blocking layer 30 has a height of ltMw3 (6w2) and a height hx (≧
h2), the thickness t3 of the first cladding layer 31 directly above the protrusion and the thickness of the active layer 134 are thinner than the optical output amplification region shown in FIG. 5(b), and the lateral direction is Since it has a stronger refractive index guide structure and the active layer 34 is thinner in the thickness direction, light strongly seeps into the cladding layer, making it difficult for end face breakage to occur even in a high light output state. Furthermore, since the growth rate of the active layer 311 is slower than that of other regions, the AlGaAs composition has a high He1 concentration. Therefore, there is no absorption effect for light in the wavelength oscillation region, and end face breakage is less likely to occur even in a high light output state.

After growing the semiconductor layer in this way, the P-side electrode 37 and the electrodes 38 and 39 are formed, and as shown in FIG. Form.

Then, using this pattern 40 as a mask, the semiconductor layer is removed by a reactive ion etching process to form a resonator.

After this, a high reflection film (not shown) is formed with a multi-R film of amorphous silicon and Al2O, and then a low reflection film (not shown) to reduce the reflectance is formed on the end face that emits the laser beam. It forms.

In addition, in this prototype example, the wavelength S dynamic region has a length of 250 μl.
, the optical output amplification region is 300 μl, and the gap between these is 3
It was set as μm. Also, the size of the convex portion on the current blocking R30 is w1 = 300 μll, w2 = 40 μrn, w3
=20. tzll, h2 = 0.4μll,
h 3 = 0.8 μl. Further, the reflectance of the high reflective film is 90%, and the reflectance of the low reflective film is 5%.

Although the above example describes an internal stripe type semiconductor laser device, the present invention can also be applied to semiconductor laser devices with other structures such as a buried type semiconductor laser device. Further, the above-mentioned examples include GaAs, G
Although the explanation was made using a8^S, Ga1nAsP
It can also be applied to devices using other semiconductors such as.

[Effects of the Invention] As explained above, according to the semiconductor laser device of the present invention, it is possible to obtain laser light that has a stable transverse mode even in a high optical output state and generates very little reflection noise. Become.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a semiconductor laser device according to an embodiment of the present invention, FIG. 2 is a spectrum of light emitted from the wavelength oscillation region of the device in FIG. 1, and FIG. 3 is a spectrum of light emitted from the device in FIG. 1. FIG. 4 is a partial perspective view of a prototype AlGaAs-based internal stripe type semiconductor laser device to which the present invention is applied; FIGS. 7 is a cross-sectional view of a conventional semiconductor laser device, and FIG. 8 is a diagram showing the light emitted from a conventional semiconductor laser device. It is a spectrum. 11...First laser element 12...
...Second laser element 16.28...
...Active layer 14.21...First cladding layer 15.2
2... Second cladding layer 17.19...
......Resonator surface 24......High reflection film 25......Low reflection, film Fig. 1 Fig. 2 Fig. 3 Fig. 4 (Q ) (b) (C) Figure 5 Figure 6

Claims (3)

[Claims] (1) A first semiconductor laser element having a resonator structure and whose oscillation frequency fluctuates due to self-valsation, and a resonator whose Q value is lower than the Q value due to the resonator structure of the first semiconductor laser element. a second semiconductor laser element having a structure and a gain in approximately the same wavelength band as the first semiconductor laser element; and a second semiconductor laser element having a gain in substantially the same wavelength band as the first semiconductor laser element, and are successively arranged so that the optical axes of these waveguides coincide. A semiconductor laser device characterized by: (2) Claim 1, characterized in that the reflectance of the resonator surface of the second semiconductor laser element on the side into which light is injected is higher than the reflectance of the resonator surface on the side that emits light. The semiconductor laser device described in . (3) The reflectance of the light emitting side of the resonator surface of the second semiconductor laser element is sufficiently low to the extent that this second semiconductor laser element cannot form a resonator structure. A semiconductor laser device according to claim 1, characterized in that: