JP2825540B2 - Surface-emitting type semiconductor laser device with combined outputs - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The invention described herein is based on the NASA contract NAS 1
During the course of conducting research under -17441, the provisions of Section 305 of the 1958 National Aerospace Act (72 Stat. 435; 4
2 USC2457).

This application is a pending application no. 0712 filed on August 9, 1988;
This is a partial continuation of No. 30,105.

FIELD OF THE INVENTION The present invention relates to surface emitting lasers, and more particularly to means for locking the phase and combining the outputs of a pair of said lasers.

[Prior Art] A surface emitting laser has a light emitting surface (diffraction grating region).
It is an advantage over edge-emitting lasers in that it has a lower power density due to its larger output, and thus more power is generated without the thermal effects leading to failure.
In addition, the active area of a surface-emitting laser is made longer than that of a Fabry-Perot (FP) cavity laser in order to obtain more gain without the use of a spurious frequency by using a diffraction grating. Can be done. In order to obtain higher output, surface emitting lasers
Optical waveguides and gratings, or Opti published April 1988
cs Letters, Volume 13, No. 4, P312-314, NW Carlson et al., `` Dynamically Stable 0 ° Phase Mod
e Operation of A Grating-surface-emitting Diode-la
The outputs can be combined using a distributed Bragg reflection structure (DBR) as shown in FIG.

[Problems to be Solved by the Invention] However, in the above-described device, the phase lock of a large number of lasers is caused by a large main beam width,
It is not enough to prevent incoherent light beams with high amplitude and wide beam width side lobes (side lobes) and the generation of spurious frequencies. IEEE Journal of Quantum Electronics, Volume Q published in July 1975
E-11, No.7, P451 ~ 457 `` Grating-
Coupled Double-Hetero-Structure AlGaAs Diode Laser
From "s" it is known to arrange two lasers in the longitudinal direction, but the output is limited to only one pair.

Accordingly, it is desirable to obtain high power from a surface emitting laser having good phase locked and coherent output light beams.

Means for Solving the Problems A surface-emitting type semiconductor laser device having an output coupled thereto according to the present invention is a surface-emitting type semiconductor laser device for emitting an output optical signal perpendicular to a main surface of the laser device. A substrate having first and second opposed major surfaces; first contact means on the first major surface of the substrate; longitudinally spaced apart from each other; A first region defining a central region, each of which is located on the second major surface of the substrate and is laterally arranged;
And a second laser region; an optical medium that spreads over the central region and the first and second laser regions and through which light generated by the first and second laser regions propagates; and a cap that overlies the optical medium. A layer and a second contact means, and a cap layer extending over the central region in optical communication with the second contact means and the optical medium to delimit the major surface of the laser device. A single optical diffraction grating surface formed by etching, wherein the first and second laser regions are disposed longitudinally opposite the diffraction grating surface, the diffraction grating surface being disposed in the optical medium; Diffraction for propagating and phase-locking and combining light generated in the first and second laser regions and for directing the output optical signal perpendicular to the major surface of the laser device. It has a grating period.

FIG. 1 shows a doping level of about 10 ¹⁸ cm ⁻³ and a thickness of about 10
N-type contact layer (electrode) such as sintered Ni / Ge / Au formed under a substrate 12 of 0 μm and N-conducting, for example GaAs
1 shows a device generally indicated by reference numeral 10, including 11. At the top center of the substrate 12 is a 1 μm deep channel 13 (described in detail below) so that the laser (described below) is of the channeled substrate planar (CSP) type. Overlying the substrate 12 is an N-conducting N-type cladding layer 14. N-type cladding layer 14 also acts as a barrier to holes. On the N-type cladding layer 14, about 500
There is an active layer 16 that is between Å and 2000 Å, preferably about 800 厚 thick. The active layer 16 is not intentionally doped,
In general, Al _Z Ga _1-z As where 0 ≦ z ≦ 0.13 is included. Barrier layer
Numeral 18 acts as a barrier to electrons, overlies active layer 16 and has a thickness of about 200-1000 ° and is intentionally undoped. The active layer 16 and the barrier layer 18 are usually
During manufacture, it is somewhat doped from each adjacent layer. A waveguide layer 20 of LOC (Large Optical Cavity) or optical medium is provided on the barrier layer 18 and generally includes Al _Y Ga _1-Y As. Here, Y is 0.15 ≦ Y
≦ 0.4, including Al _y Ga _1-y As with a thickness of about 0.25 μm to 1 μm and an N-type doping concentration of about 5 × 10 ¹⁷ cm ⁻³ . Waveguide layer
In the center of the upper surface of 20, there is a diffraction grating surface 22, the amplitude of which from the highest value to the lowest value of the grating surface waveform is 1000.
Å, and the waveform interval is λ / _ne (λ is the wavelength of the generated light, _ne is the effective refractive index for the guided mode).

Profile of the waveform, by periodic structure of the lambda / n _e is, for example, the width of the top of the grooves using a V-shaped groove such that about half of the spacing between the grooves, lambda / n _e
(Hereinafter referred to as λ / _ne component). The P-type cladding layer 24 includes segments 24a and 24a provided on the ends of the waveguide layer 20, respectively.
4b, which is P-conducting-type doped. The N-type cladding layer 14, the barrier layer 18, and the P-type cladding layer 24 are generally made of Al _x Ga _1-x
As (0.3 ≦ x ≦ 0.8). Cladding layers 14 and 24 generally have a thickness of about 1 μm and a doping level of about 5 × 10 ¹⁷ cm ⁻³ . Cap layer 26 has segments 26a and 26b overlaid on segments 24a and 24b, respectively, of the P-type cladding layer, and generally has a size of about 10 ¹⁸ cm ^-3 to 10
GaAs with a doping level of ¹⁹ cm ^-3 and doped P-type with a thickness of about 0.5 μm. The P-type contact layer 28 is composed of segments 28a and 28b provided on the cap layer segments 26a and 26b, respectively. In general, a layer Ti / Pt / Including Au. On either side of this structure are appropriately cleaved end facet reflective surface layers 30a and 30b with a dielectric stack of, for example, alternating SiO ₂ and Al ₂ O ₃ . Generally, about three pairs of layers (six layers) are used, each having a thickness of about one quarter wavelength, as shown in U.S. Pat. No. 4,092,659.

The longitudinally arranged DH-LOC lasers 32a and 32b are formed by the structure described above, each preferably having a length L1 of about 200 μm. Diffraction grating length L2 is preferably about 300μ
m. Therefore, the laser or laser regions 32a, 32b
Is the diffraction grating surface relative to the diffraction grating 22 that extends over the central region between the laser regions 32a and 32b.
They are spaced apart on the opposite side of 22. As shown in FIG. 2, the device 11 has a width W of about 300 μm. Substrate 12
The top of the channel 13 at the top of is shown by dashed lines 34a and 34b, and is preferably about 4 μm to 8 μm wide, but the bottom of the channel 13 shown by dashed lines 36a and 36b is narrower. The sidewalls between them (reference numbers 38a and 38b) form an angle of about 57 ° with respect to the top of the substrate 12.

This embodiment can be carried out by a liquid phase epitaxial method using well-known appropriate reagents and dopants. The channel 13 is formed by etching the substrate 12 along the surface 111A by using a Karos solution at 20 ° C. In this case, the Karos solution is 5: 1 by volume.
1 is a mixture of H ₂ SO ₄ / H ₂ O ₂ / H ₂ O. Similarly, each segment of the P-type cladding layer 24, the cap layer 26 and the P-type electrode layer 28 comprises a layer 24, a portion of lasers 32a and 32b,
It is formed by etching the central portions of layers 24, 26 and 28 while masking the edges of 26 and 28. An anisotropic etchant such as a 1: 1: 8 Karos solution is used.

In operation, a positive voltage is applied to the P-type contact layer 28,
In addition, a negative voltage is applied to the N-type contact layer 11. P-type contact layer 28
Holes are injected into the active layer 16 and the cladding layer 14 provides a barrier to prevent the holes from moving further downward. Similarly, electrons are injected from the N-type contact layer 11 into the active layer 16 and the barrier layer 18 provides a barrier for electrons from moving further upwards. When the injected electrons reach a threshold current value, a population inversion occurs, which causes stimulated emission of photons. The photons generated by both laser regions 32a and 32b are present in waveguide 20, and a first portion of the photons incident on the surface of the diffraction grating is coupled to the λ / _ne component of the diffraction grating by an arrow. As shown at 34, the light is emitted perpendicular to the waveguide 20.

The second part of the photons incident on the diffraction grating surface 22 is caused by the action of the λ / _ne component of the diffraction grating surface 22 so that the laser region 32a
And back during 32b, which increases optical feedback and enhances laser action. Since the intensity of the reflected light depends on the wavelength of the light generated by each laser device, the feedback required for oscillation exists only in a specific period. Therefore, the light generated by the laser regions 32a and 32b is wavelength locked. The remainder of the photons incident on the diffraction grating surface 22 caused by each of the laser regions 32a and 32b is sent by the optical medium 20 to the other laser regions 32b, 32a, respectively,
Thereby, the two laser regions are phase-locked together.
Since both laser regions 32a and 32b share the same device, the light generated by both laser regions is locked in both wavelength and phase and is emitted through the grating surface and perpendicular to the grating surface.

Since only two laser regions 32a and 32b are used, the waveguide 20 is relatively short, and thus has low losses, so that the phase and wavelength locks of the two lasers 32a and 32b are more, It is larger than when a laser as described above is used. Also,
Thereby, the mode in the longitudinal direction of the laser 32 is stabilized, and the emission wavelength becomes single as compared with the case where the Fabry-Perot resonator laser has a plurality of modes. Furthermore, more light output is possible than when a single laser is used.

FIG. 3 shows a second embodiment of the quantum well type (QW type) laser regions 32a and 32b. FIG. 3 shows the laser region 3
2a is the same as the laser region 32b, so only one is shown. Elements in FIG. 3 that correspond to elements in FIG. 1 have been given corresponding reference numerals. Cladding layers 14 and 24
Is the thickness of 2.5μm from about 0.5 [mu] m, and an appropriate conductivity type dopant is doped to about 10 ¹⁷ cm ³ to doping level of ^{5 × 10 18 cm -3, Al} X Ga 1-X As (0.4 ≦ x
≤ 1). The central portion of the cladding layer 24 includes a distributed Bragg reflection structure (DBR) 22 at about a valley of the DBR 22.
It is 1000 mm thick. The undoped confinement layers 36 and 40 are approximately 500 to 4000 mm thick, Al _X Ga _{1 -X} As (0.1
5 ≦ x ≦ 0.60), and may be a graded type or a non-graded type.

The undoped quantum well layer 38 comprises Al _X Ga _1-X As (0 ≦ x ≦ 1) with a thickness of about 10 ° to 400 °.

In general, the threshold current of the quantum well type embodiment shown in FIG. 3 is low, the amount of change in the threshold current decreases with temperature, and the differential quantum efficiency increases as compared with the DH-LOC laser.

FIG. 4 shows an apparatus according to an embodiment of the present invention for obtaining more light output compared to using only a pair of lasers, while maintaining phase and wavelength coherency. In this embodiment, the substrate 12 has a second surface, like the reflection surface layers 30a and 30b and the diffraction grating surface 22.
It extends in the lateral direction compared to the figure. Diffraction grating surface 22
Thereby, it includes only one integrated means to phase lock and combine the total laser power to achieve high coherency. For illustration, the CSP-LOC laser region 32a
And only channel 13 of 32b is shown. Each of the five channels 13 extends below only a pair of corresponding longitudinally arranged lasers, as in FIG. Thus, there are a total of ten lasers in the apparatus of FIG. Also,
The channels 13a, 13b, 13c, 13d and 13e are generally laterally arranged with respect to each other with a center-to-center spacing of about 4 to 10 μm. Thus, the optical mode in the lateral direction of the laser (parallel to the joint plane) is connected, and consequently
Phase and wavelength coupling and coherency occur for the entire row. The entire row thereby provides a single wavelength light output from the grating surface 22 perpendicular to the substrate 12. Depending on the efficiency of L1 and the grating surface 22, it is possible to increase the light output by a factor of 10 to 50 compared to a single laser. The QW laser shown in FIG. 3 can be used in place of the DH-LOC laser in FIG.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a double heterostructure LOC (DH-LOC) laser used in a first embodiment of the present invention, FIG. 2 is a top view of FIG. 1, and FIG. FIG. 4 is a cross-sectional side view of a quantum well (QW) laser used in a second embodiment of the present invention; FIG. 4 is a top view of the embodiment of the present invention showing a plurality of laterally adjacent lasers; . 10 device, 11 N-type contact layer, 12 substrate, 13 channel, 14 N-cladding layer, 16 active layer, 18
Barrier layer, 20 waveguide layer, 22 diffraction grating surface, 24
P-type cladding layer, 24a, 24b ... segment, 26 ... cap layer, 26a, 26b ... segment, 28 ... P-type contact layer, 2
8a, 28b: Segment, 30a, 30b: Reflective surface layer, 32a, 32b
…… Laser area, 34a, 34b …… Top of channel, 36a, 36b
…… the bottom of the channel, 38a, 38b …… the side wall.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/18

Claims (3)

(57) [Claims] 1. A surface-emitting type semiconductor laser device for emitting an output optical signal perpendicular to a main surface of a laser device, comprising: a substrate having first and second opposed main surfaces; First contact means on a first major surface, spaced longitudinally from each other to define a central area therebetween, each of which is disposed on the second major surface of the substrate; The first is located and the sides are arranged in a row
And a second laser region; an optical medium that spreads over the central region and the first and second laser regions and through which light generated by the first and second laser regions propagates; and a cap that overlies the optical medium. A layer and second contact means, and a single optical grating surface extending over the central region in optical communication with the optical medium to form the major surface of the laser device. The first and second laser regions are disposed on opposite sides of a diffraction grating surface in a longitudinal direction, and the diffraction grating surface includes light propagating to the optical medium and light generated in the first and second laser regions. A surface emitting semiconductor laser device having a period of a diffraction grating for phase-locking and combining and emitting the output optical signal perpendicular to the main surface of the laser device. Second laser regions, respectively, first the substrate 2
A plurality of laterally aligned phase-locked lasers disposed on a major surface of the laser, the plurality of lasers being spaced apart from each other in the longitudinal first and second laser regions. Corresponding lasers located in the longitudinal direction
A surface-emitting type semiconductor laser device having outputs coupled to each other in a row. 2. The apparatus of claim 1, wherein each of said lasers comprises a LOC laser of a double heterojunction type. 3. The apparatus of claim 1, wherein each of said lasers comprises a quantum well laser.