JPH065982A - Semiconductor laser element - Google Patents

Abstract

(57) [Abstract] [Purpose] A semiconductor laser device having a structure in which the lasing wavelength can be easily changed without requiring strict process accuracy. [Structure] A main waveguide 21 having a channel waveguide structure is formed on a semiconductor substrate, and at least two sub-waveguides 22 and 23 are formed on the main waveguide 21. Waveguides 21, 22, 2
An optical coupler 10 for branching / coupling light waves is formed between the three, and the coupler 10 performs guided light field distribution wavefront division in the horizontal direction. The oscillation wavelength from the end face 14 of the main waveguide 21 can be controlled by selecting the electrodes 11, 12 and 13 that inject current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device used as a light source for optical communication or optical signal transmission of optical equipment.

[0002]

2. Description of the Related Art Conventionally, as a semiconductor laser constituted by a plurality of waveguides coupled through an optical coupler, a composite resonator laser including a Y-branch type optical coupler 100 as shown in FIG. 7 is known (I H.A. Fattah
et al. "Semiconductor Int
erferometric Laser "Appl.Ph
ys. Lett. 41, 2, pp. 112-114 (J
Uly 1982)).

Further, an interference type laser including X-branch type optical couplers 110a and 110b as shown in FIGS. 8A and 8B is also known. (J. Salzman et al.
"Cross Coupled Cavity Sem
iconductor Laser "Appl.Phy
s. Lett. 52, 10, pp. 767-769 (M
arch 1988)). Here, R1 to R4 are resonance planes, and L1 to L4 are resonator lengths, respectively.

[0004]

However, the above-mentioned conventional example has the following drawbacks. First, when a Y-branch type optical coupler as shown in FIG.
Since a large branch angle of 00 cannot be obtained, the element length becomes as large as 1 mm or more, and integration with other optical devices becomes particularly difficult. Further, in the case of the example including the X branch as shown in FIG. 8, there are problems such as high process accuracy such as position accuracy and depth accuracy required for the X branch parts 110a and 110b, and poor yield and reproducibility. . That is, for the field distribution of the light wave propagating in the optical waveguide, the X branch portions 110a, 11
Since the form of branching and merging is determined depending on how 0b is formed, strict process accuracy is required.

Therefore, in view of the above problems, it is an object of the present invention to provide a semiconductor laser device having an optical coupler having a structure that does not require strict process accuracy.

[0006]

In the semiconductor laser device of the present invention which achieves the above object, at least two waveguides are connected to a channel waveguide structure formed on a semiconductor substrate, and an optical wave is generated between the waveguides. Is equipped with an optical coupler for performing the coupling, and the coupler portion is configured so as to perform the wavefront division of the guided light field distribution in the horizontal direction.

That is, according to the semiconductor laser device of the present invention, a channel waveguide structure formed on a semiconductor substrate has a structure for performing laser amplification of a light wave and a reflector for reflecting the light wave at one end of the waveguide. At least two sub-waveguides each having a main waveguide that outputs the formed light wave, a structure that performs laser amplification of the light wave, and a reflector that reflects the light wave at one waveguide end are formed. An optical coupler for coupling light waves is provided at an intersection between the sub-waveguides and the main waveguide that are connected to each other, and the coupler section couples light waves between the horizontal waveguides. And an optical coupler section for performing the guided light field distribution wavefront division in the horizontal direction.

More specifically, the crossing portion is T-shaped or cross-shaped, the coupler portion is formed with a portion having a different reflectance in a part of the channel waveguide structure, and the light wave is reflected. The reflector for performing is a reflector having a cleaved surface of the semiconductor substrate or a periodic structure, or at least two laser beams of different wavelengths can be obtained by selecting a waveguide for laser amplification of the light wave of the waveguide. Or the semiconductor laser device is configured as a compound resonator laser.

[0009]

1 is a top view showing a semiconductor laser according to a first embodiment of the present invention, and FIG. 2 is a sectional view taken along the line AA 'in FIG.
FIG. 3 is a sectional view taken along line BB ′ of FIG. In FIG. 1, 1
0 is an etching groove that serves as a horizontal wavefront splitting type coupler,
Reference numerals 11, 12, 13 denote electrodes for injecting current, 14, 1
5 and 16 are cleavage planes formed on the end faces of the element,
Reference numeral 21 is a main waveguide, and 22 and 23 are sub-waveguides connected to the main waveguide 21, respectively.

First, the process procedure of the first embodiment will be described. On the n ⁺ GaAs substrate 1, the molecular beam growth method (MB
According to E), the n-type AlGaAs layer 2 serving as the first cladding layer, the GaAs layer 3 serving as the active layer, the p-type AlGaAs layer 4 serving as the second cladding layer, and the p ⁺ -type GaA serving as the cap layer.
An epitaxial film made of the s layer 5 is sequentially grown. A buffer layer made of GaAs may be formed on the interface with the substrate 1 if necessary. The film thickness of the first and second clad layers 2 and 4 was 1 μm, and the film thickness of the active layer 3 was about 0.1 μm. Next, a width of 3 is formed on the upper portion by photolithography.
μm desired pattern (waveguides 21, 22, shown in FIG.
23 pattern), and a ridge portion was formed by reactive ion beam etching (RIBE) to form a stripe structure for lateral confinement (see FIGS. 2 and 3). The waveguide pattern shown in FIG. 1 has a tapered shape at the crossing portion, but this is to smooth the waveguiding of the light wave.

Next, an insulating film 6 made of SiN is formed on the substrate 1 on which the ridge portion is formed by a plasma CVD method, and a pattern of a current injection window is formed by a photolithography method. Then, the SiN insulating film 6 only in the portion exposed by the pattern was etched by RIBE to form a current injection window (see three shaded portions in FIG. 1). After that, Cr-Au ohmic electrodes 11, 12, and 13 are formed as an upper electrode by a vacuum evaporation method, and G
After shaving the aAs substrate 1 by lapping to a thickness of 100 μm, AuGe-Au is used as an n-type ohmic electrode 7.
Electrodes were deposited on the back surface of substrate 1. Then, heat treatment was performed to obtain ohmic contact with the p-type and n-type electrodes 11, 12, 13, and 7.

Further, from the center of the branching / multiplexing portion of the ridge waveguides 21, 22, 23, φ in the waveguide direction of the light wave in the horizontal direction.
A triangular etching groove 10 having an end face reaching the bottom of the active layer 3 in the vertical direction at an angle of = 45 ° is formed by RIB.
A 45 ° mirror, that is, a total reflection mirror, was formed bidirectionally by forming it by the E method.

The operation will now be described. Electrode 11,
When a current is injected into 12, the light wave propagates through the optical coupler 10 through the L-shaped optical path as shown by 17 (a), and the cleavage planes 14 and 16 serve as the resonance planes of the Fabry-Perot resonator. Laser oscillation. The oscillation wavelength λ _{1 at} this time is represented by λ ₁ = 2n _eff · l ₁ / (m + 1) (n _eff : equivalent refractive index, m: integer). l ₁ is the length of the L-shaped optical path 17 (a).

On the other hand, when a current is injected into the electrode 11 and the electrode 13, the light wave propagates through the optical coupler 10 through the L-shaped optical path having a length l ₂ as shown in 17 (b), and the cleavage plane 14 is formed. Laser is oscillated using the cleavage plane 15 as a Fabry-Perot resonator. The oscillation wavelength λ _{2 at} this time is represented by λ ₂ = 2n _eff · l ₂ / (m + 1) (n _eff : transmission refractive index, m: integer). Therefore, if the resonator lengths l ₁ and l ₂ or the structure of the semiconductor laser shown in FIGS. 2 and 3 is set so that desired oscillation wavelengths λ ₁ and λ ₂ can be obtained, an electrode for injecting current is selected. This makes it possible to obtain laser lights having two different wavelengths λ ₁ and λ ₂ . When current is injected into all electrodes, it functions as a compound resonator laser.

In the branching / multiplexing element according to the present embodiment, the coupler section 10 forms a wavefront splitting type branch coupler in the horizontal direction (extending direction of the substrate 1 on which the channel waveguide structure is formed). End face 10 of etching groove 10
The processing depth of a and 10b may be any depth as long as etching is performed beyond the active layer 3, and strict precision depth control is unnecessary. In the present embodiment, the etching groove 10 is provided at the step portion, but there is no problem because the depth control is not required to be strict as described above. In this embodiment, the ridge type waveguide is described as the channel waveguide, but a refractive index type waveguide or the like can be similarly used.

FIG. 4 is a plan view showing a second embodiment of the present invention. FIG. 5 is a sectional view taken along the line AA ′ of FIG. Figure 4
1, 40 is an optical coupler having the same structure as the optical coupler 10 of FIG. 1, 41, 42 and 43 are electrodes for injecting a current, 44 is a cleavage plane formed on the upper end surface of the device, and 35 is
Is the main waveguide, and 36 and 37 are the main waveguides 35, respectively.
Sub-waveguides 45 and 46 connected to the sub-waveguides 45 and 46 are distributed Bragg reflectors formed in the sub-waveguides 36 and 37, respectively. Further, in FIG. 5, 51, 52, 53, 5
4, 55, 56 and 57 are layers 1, 2, 3 of FIG. 3, respectively.
It corresponds to 4, 5, 6 and the electrode 7.

Next, the operation will be described. Electrodes 41, 4
When a current is injected into 2, the light wave is
7 (a) propagates through an L-shaped optical path and laser oscillation is performed using the cleavage plane 44 and the distributed Bragg reflector 45 as reflectors. The oscillation wavelength lambda ₁ at this time is determined by the grating period lambda ₁ of the distributed Bragg reflector _{45, λ 1 = n eff ·} Λ 1: represented by (n _eff the effective refractive index). On the other hand, when a current is injected into the electrode 41 and the electrode 43, the light wave propagates through the optical coupler 40 through the inverted L-shaped optical path as shown by 47 (b), and the cleavage surface 44 and the distributed Bragg reflector 46 are transmitted. Laser oscillation as a reflector. The oscillation wavelength λ _{2 at} this time is determined by the distributed Bragg reflector 4
It is determined by the lattice constant λ _{2 of} 6 and is represented by λ ₂ = n _eff · Λ ₂ (n _eff : equivalent refractive index). Therefore, by setting the structure of the desired oscillation wavelength lambda _1, as the lambda ₂ is obtained distributed Bragg reflector 45, 46, two wavelengths lambda ₁ differ by selecting an electrode for injecting current, lambda ₂ The laser light can be easily obtained. Further, when the current is injected into all the electrodes, it is possible to simultaneously oscillate laser lights having _two wavelengths λ ₁ and λ ₂ .
In the structure like this embodiment, since the distributed Bragg reflector is used as the reflector, it is possible to obtain the laser light oscillated in the single mode.

FIG. 6 is a plan view showing a third embodiment of the present invention. In this example, the optical coupler has a C-shaped groove 60 (a) at the intersection of the optical waveguides 58 and 59 intersecting in a cross shape.
By forming 60 (b), the light wave is branched / combined. Such fine grooves 60 (a), 60 (b)
The focused ion beam (F
IB) etching, reactive ion beam (RIB
Fine processing technology such as etching by E) can be applied. The optical coupler units 60 (a), 60 in this embodiment
The parts other than (b) can be realized with the same configuration as the second embodiment. That is, 61, 62, 63 and 64 are electrodes for injecting current, 65 is a cleavage plane formed on the upper end surface of the device, 35 is a main waveguide, and 66, 67 and 68 are respective waveguides 59. , 58 of the distributed Bragg reflector. In the configuration shown in this embodiment, in addition to the same function as that of the second embodiment of the present invention (optical paths 69 (a), 69 (b))
By injecting a current into the electrodes 61 and 64, laser light having an oscillation wavelength λ ₃ determined by the structure of the distributed Bragg reflector 68 can be obtained (optical path 69 (c)).
). The layer structure is also substantially the same as in FIG.

In the first to third embodiments, the active region is formed with the double hetero (DH) structure, but the present invention is not limited to this, and the single quantum well (SQW) structure and the multiple quantum well are provided. (MQW) structure etc. may be sufficient.

In the first to third embodiments, the channel waveguide is formed by the ridge wave structure. However, the buried hetero stripe (BH) structure, the channel substrate planar stripe (CPS) structure, and the current light confinement are confined. A refractive index guided laser having a structure in which an absorption layer is provided near the active layer may be used. The present invention is also effective for a gain waveguide type laser such as a stripe electrode type or a proton bombard type. Further, if the ridge structure is cut down to the bottom of the active layer, the patterning at the time of forming the ridge structure is changed without newly forming an etching groove as shown in FIG. 1 to form the groove shape as shown in FIG. (V shape) may be formed on the side wall of the ridge structure. Furthermore, as the semiconductor material, in addition to GaAs / AlGaAs, InP / InG
A material of aAsP type or AlGaInP type may be used.

[0021]

As described above, in the semiconductor laser device according to the present invention, at least two waveguides are connected,
Since the structure is provided with an optical coupler for dividing the guided light field distribution wavefront in the horizontal direction for coupling light waves between the waveguides, it is possible to easily change the oscillation wavelength by selecting an electrode for injecting a current. be able to. Further, since the optical coupler is configured to perform at least horizontal wavefront division, the manufacturing accuracy in the depth direction is reduced, and it is possible to manufacture only with the horizontal positional accuracy.

[Brief description of drawings]

FIG. 1 is a plan view showing a first embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA ′ of FIG.

FIG. 3 is a sectional view taken along line BB ′ of FIG.

FIG. 4 is a plan view showing a second embodiment of the present invention.

5 is a cross-sectional view taken along the line AA ′ of FIG.

FIG. 6 is a plan view showing a third embodiment of the present invention.

FIG. 7 is a diagram showing a conventional example.

FIG. 8 is a diagram showing a conventional example.

[Explanation of symbols]

1,51 substrate 2,4,52,54 clad layer 3,53 active layer 5,55 cap layer 6,56 insulating film 7,11,12,13,41,42,43,57,6
1, 62, 63, 64 electrode 10, 40, 60 (a), 60 (b) coupler 45, 46, 66, 67, 68 distributed Bragg reflector 14, 15, 16, 44, 65 cleaved surface 21,22 , 23, 35, 36, 37, 58, 59 Waveguide 45, 46, 66, 67, 68 Distributed Bragg reflector 14, 15, 16, 44, 65 Cleaved surface

Claims (8)

[Claims] 1. A light emitting device having a channel waveguide structure formed on a semiconductor substrate, wherein a structure for performing laser amplification of a light wave and a reflector for reflecting the light wave at one end of the waveguide are formed to output a light wave. And at least two sub-waveguides each having a structure for performing laser amplification of a light wave and a reflector for reflecting a light wave formed at one end of the waveguide are connected, and the sub-waveguide is formed. An optical coupler for coupling light waves is provided at the intersection between the main waveguides, and the coupler portion has an optical coupler portion for coupling light waves between the waveguides in the horizontal direction, A semiconductor laser device, characterized in that the coupler section is configured to perform a guided light field distribution wavefront division in a horizontal direction. 2. The semiconductor laser device according to claim 1, wherein the intersecting portion is T-shaped. 3. The semiconductor laser device according to claim 1, wherein the intersecting portion has a cross shape. 4. The semiconductor laser device according to claim 1, wherein the coupler portion is formed by forming a portion having a different reflectance in a part of a channel waveguide structure. 5. The semiconductor laser device according to claim 1, wherein the reflector for reflecting the light wave is a reflector having a cleavage plane of a semiconductor substrate. 6. The semiconductor laser device according to claim 1, wherein the reflector for reflecting the light wave is a reflector having a periodic structure of a semiconductor substrate. 7. The semiconductor laser device according to claim 1, wherein it is possible to obtain laser light of at least two different wavelengths by selecting a waveguide that performs laser amplification of a light wave of the waveguide. . 8. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is configured as a compound resonator laser.