JPH0315831B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to improving the stability of oscillation axis mode characteristics in a semiconductor laser.

<Prior art> When a semiconductor laser is used as a light source for optical communication or optical information processing systems, it is stable and unaffected by ambient temperature, laser light output, or the feedback light of the laser light reflected from an external system. Oscillation is strongly required. This is because when the oscillation state of the semiconductor laser becomes unstable due to variations in the various parameters mentioned above, mode competition may occur due to interaction between the laser axis modes or between the laser axis mode and the external mode. This is because it generates noise and feedback-induced noise, and in optical transmission using fibers, it causes modal noise, which has a serious effect on reducing system performance. Therefore, various proposals and attempts have been made to stabilize the oscillation axis mode characteristics of this semiconductor laser.

Here are some examples: First,
There is a device that increases the reflectivity of both end faces of the laser resonator to prevent the return light from entering the semiconductor laser again, and also increases the internal light density of the laser oscillation part to suppress the non-oscillation axis mode. However, this method has the disadvantage that a large amount of output light cannot be extracted. Second
has a grating (diffraction grating) inside the waveguide.
Distributed feedback (DFB) lasers and Bragg reflection (DBR) lasers can be cited. These semiconductor lasers have strong wavelength selectivity by forming gratings inside the waveguide, so they have excellent axial mode stability against disturbances, but the manufacturing process is complicated and Manufacturing itself may be difficult depending on the material of the semiconductor laser. The third type is commonly called C ³ , which has a structure in which two semiconductor lasers or waveguides are juxtaposed across the cleavage plane.
(Cleaved Coupled Cavity) laser. This laser is stabilized by combining two laser axis modes, but the drawback in this case is that it is difficult to arrange the two lasers with good coupling, and the two laser injections are individually controlled to achieve a wide range of The point is that advanced technology is required to achieve axial mode stability in this region. Fourth, by forming one or more reflecting parts inside the waveguide of one semiconductor laser, the entire waveguide is divided into multiple parts, and the interference effect between axial modes in each divided waveguide is reduced. There is a device (interferometric laser) that stabilizes the axial mode by
It was proposed in IEEE Journal of Quantum Electronics, 1982, QE-18, No. 4, p. 610. This laser does not require special technology in the manufacturing process if the internal reflection section can be easily manufactured, and may also have excellent stability in the axial mode.

<Object of the Invention> The present invention relates to the optical waveguide structure of the above-mentioned interference laser, and provides a semiconductor laser in which a stable composite resonator is formed in the same substrate by a simple method and the stability of the oscillation axis mode is improved. The purpose is to provide equipment.

<Summary of the Invention> The composite cavity type semiconductor laser device of the present invention uses an active layer to compensate for the difference in effective refractive index based on the difference in light absorption by the substrate between the inside of a current-pinning channel formed on a substrate and the outside of the channel. In the refractive index waveguide structure built inside the substrate, there is a waveguide that is smoothly branched from at least one place, and at the end of the waveguide there is a channel formed on the substrate between the inside and outside of the substrate. This is an interference type semiconductor laser in which a resonator surface is formed by an effective refractive index difference based on a difference in light absorption, and this serves as an internal reflection section. With the above configuration, a plurality of laser resonators can be formed extremely easily and reliably within the same element substrate, and an interferometric semiconductor laser with a stable oscillation axis mode can be obtained.

<Example> FIG. 1 is a perspective view of the structure of a composite resonator type semiconductor laser device showing an example of the present invention. Also the second
The figure is a sectional view taken along line A-A' in FIG.
A current blocking layer 12 made of n-GaAs is deposited on a p-GaAs substrate 11, and from the surface of the current blocking layer 12,
A current path is opened by etching a V-shaped stripe groove that reaches the GaAs substrate 11. That is, the current blocking layer 12 is formed by the stripe grooves.
A striped structure is formed in which current flows only in the portions where is removed from the substrate 11. On top of this, p-Ga ₁ −
A cladding layer 13 made of yAlyAs, an active layer 14 made of p- (or n- or non-doped) Ga ₁ -xAlxAs, a cladding layer 15 made of n-Ga ₁ -yAlyAs, and a cap layer 16 made of n-GaAs are laminated to form an active layer. A double heterojunction type multilayer crystal structure for laser oscillation is provided with a refractive index distribution in 14. Also, the liquid crystal ratio is x=0.05, y=
Set to 0.3. The back surface of the GaAs substrate 11 has Au-
P-side electrode 17 obtained by vapor-depositing Zn and then heating alloying, and n-side electrode 1 obtained by vapor-depositing Au-Ge-Ni and heating-alloying on the cap layer 16.
8 are formed by vapor deposition. In the above structure, the stripe grooves include a main channel portion 19 consisting of a substantially linear groove connecting opposing end faces of the crystal, and a linear and curved groove that is smoothly bent and branched from the middle of the main channel portion 19. The sub-channel portion 22 consists of a groove. This branched groove, that is, the subchannel portion 22 does not extend to the end face of the crystal, but disappears midway.

The region of the active layer 14 directly above each groove serves as a waveguide for laser operation, and the end faces of each groove, that is, the cleavage planes at both ends of the main channel portion 19 and the terminal face of the sub-channel portion 22 serve as resonant surfaces. At this time, if the branched sub-channel section 22 is formed close to the main channel section 19, optical coupling occurs between the waveguides formed by the two grooves, and transverse modes are coupled. The Rukoto. As a result, a phase synchronization state is formed between the laser beams in the region where this optical coupling occurs. On the other hand, when the two waveguides are sufficiently separated, optical coupling between the waveguides cannot be obtained and their transverse modes are determined by individual grooves and are not influenced by each other.

As described above, the width of the main channel portion 19 and the width of the sub-channel portion 22 are determined by the presence or absence of optical coupling.
The transverse mode state of the two waveguides varies, but in either case, a resonator defined by the branched waveguide is formed inside. That is, at the terminal end of the sub-channel section 22, there is an effective refractive index difference (Δn) between the inside and outside of the groove based on light absorption of the substrate, and this (Δn) is calculated as the thickness d of the lower cladding layer outside the striped groove ( The flat part) is shown in FIG. 3. Assuming that the groove depth is 1 μm, d is 0.1 μm, and the thickness of the active layer 14 is 0.08 μm, a Δn of approximately 1×10 ^-2 will occur between the stripe groove and the other regions, and this effective refractive index will be The difference causes reflection of the laser beam and forms a resonant surface. That is, a first laser resonator 19' having a resonator length _l1 is constructed by the opposing resonant surfaces 20 and 21 and the waveguide corresponding to the stripe groove. Further, a second laser resonator 2 with a resonator length l ₂ has a waveguide within the active layer 14 corresponding to the sub-channel portion 22 of the branched striped groove.
2' is formed. This second laser resonator 2
2' shares one resonant surface with the resonant surface 20 of the first resonator 19', and also shares a waveguide with the first laser resonator 19' up to the position where the stripe groove branches from the resonant surface 20. are doing. Other resonance surface 2
3 is a plane where the end of the sub-channel portion 22 is located and is formed inside the crystal. As a result of the above, two l ₁ and l ₂
A resonator having a length of 100 nm is formed, and due to these interference effects, a semiconductor laser device having stable axial mode characteristics can be obtained. First laser cavity length l ₁ is 250μ
An interferometric laser with a second laser resonator length _l2 of 220 μm oscillates at an oscillation threshold current of 60 to 70 mA, and the temperature change in the axial mode starts from 22°C as shown in Figure 4.
It was stable without mode jump during temperatures up to 16°C up to 38°C.

When forming a channel on a substrate in this way,
By simply adding a channel section branched from a portion of the laser diode, it is possible to realize an interferometric semiconductor laser device with good reproducibility and excellent stabilization of the axial mode using a very simple manufacturing method.

The present invention is a technology that is generally applicable to semiconductor lasers with a structure in which a waveguide is formed by the difference in light absorption, and as shown in FIG. The invention can also be applied to manufacturable semiconductor laser devices, and the stripe grooves can have various shapes as shown in FIGS. 6A, B, and C.

The laser device structure shown in FIG. 5 includes an n-GaAlAs first cladding layer 52 on an n-GaAs substrate 51,
A GaAlAs active layer 53 and a p-GaAlAs second cladding layer 54 are epitaxially grown in sequence, an n-GaAs current blocking layer 55 is superimposed thereon, and striped grooves are formed to form a main channel portion and a sub-channel portion. In addition, p-GaAlAs third cladding layer 5
6 is stacked and the main and sub channel parts are buried and P-GaAs
It has a structure in which layer 57 is deposited. Note that a p-side electrode 58 is formed on the cap layer 57, and an n-side electrode 59 is formed on the GaAs substrate 51. The number of sub-channel parts branched from the main channel part is not limited to one, and the sub-channel parts may be arranged in parallel to the main channel part as a multi-branch structure of two or more.

Although the above embodiments have been described with reference to GaAs-GaAlAs-based semiconductor lasers, the present invention is applicable not only to GaAs-GaAlAs-based semiconductor lasers but also to semiconductor lasers constructed from Inp-InGaP-based and other materials.

<Effects of the Invention> As described in detail above, according to the present invention, it is possible to easily and reliably form an internal resonant surface, which has been a problem with conventional interference type laser devices. A semiconductor laser device can be provided.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of an interference laser according to the present invention. Figure 2 is A- in Figure 1.
It is an A′ cross-sectional view. FIG. 3 is an explanatory diagram showing the dependence of the effective refractive difference on the lower cladding layer thickness d. FIG. 4 is a characteristic diagram showing the temperature dependence of the oscillation wavelength (axial mode) of the interferometric laser shown in FIG. FIG. 5 is a sectional view of a semiconductor laser showing another embodiment of the present invention. FIG. 6 is a configuration diagram showing another groove structure (waveguide structure) of the channel portion according to the present invention. 11...p-GaAs substrate, 12...n-GaAs
Current blocking layer, 13... p-GaAlAs first cladding layer, 14... GaAlAs active layer, 15... n-
GaAlAs second cladding layer, 16... n-GaAs cap layer, 17... p-side electrode, 18... n-side electrode, 19... main channel section, 20, 21, 23...
...Resonance surface, 22...Subchannel section.

Claims (1)

[Scope of Claims] 1. A refractive index waveguide semiconductor laser device in which an effective refractive index difference based on light absorption is created between the inside and outside of a striped channel, which connects both opposing cleavage end faces. A first laser resonator that shares one end with a part of the first laser resonator, is branched in the middle and then disappears, and the other end face has an effective refractive index difference based on a difference in light absorption. and a second laser resonator formed in this manner, and the oscillation wavelength is determined by interference between the light from the first laser resonator and the light from the second laser resonator. An interference type semiconductor laser device characterized by: 2. The interference type semiconductor laser device according to claim 1, wherein the branch waveguide portions of the first laser resonator and the second laser resonator are not optically coupled to each other. 3. The interference type semiconductor laser device according to claim 1, wherein the branch waveguide portions of the first laser resonator and the second laser resonator are optically coupled to each other. 4. An interference type semiconductor laser device according to claim 1, 2, or 3, which has a large number of laser resonators branched in the middle.