JPS59152686A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To stabilize an oscillating mode at the high output operation time, to improve the differentiating efficiency and to stabilize to be adapted to environmental temperatures by continuously forming a coupling of an exciting region of a narrow waveguide width and a wide window region of a waveguide width in a coupling region that the waveguide width is varied in a tapered shape. CONSTITUTION:Window regions 22, 22' having a width Wg2, lengths Lw, Lw' are arranged at both ends of a laser oscillating region 21 having a width Wg1 and a length Le, and tapered couplers 23, 23' having lengths LT, LT' are coupled between the both regions 22, 22' and the region 21. The region 21 is limited in length at the laser oscillating region end faces 25, 25', and laser beams are emitted from the resonator end faces 24, 24'. An N type GaAs current blocking layer 32 for interrupting a current is accumulated on a P type GaAs substrate 31, and striped grooves are formed on the layer 32 and the substrate 31. A P type GaAlAs clad layer 33, a GaAs or GaAlAs active layer 34, a P type GaAlAs clad layer 35, and an N type GaAs cap layer 36 are sequentially laminated thereon. Thus, only the advantages of the VSIS laser of two types of active layer bent type and active layer flat type are utilized to complement the disadvantages, and a window laser can be readily manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a new structure of a semiconductor laser device having a window region that absorbs little laser light.

<Prior Art> It is well known that one of the factors that limits the lifespan of semiconductor lasers is the deterioration of the resonator end face, which serves as the light emitting surface. Further, when the semiconductor laser device is operated at high output, this cavity end face may be destroyed. At this time, the end face destruction output (hereinafter referred to as Pmax) was approximately 106 W/aCl in the conventional semiconductor laser. For example, WS lasers (Appl, Phys. , Lett, 1
5 May I 979P, 637) has been proposed. Alternatively, a structure in which the vicinity of the end face is buried with a material having a wider band gap than the active layer is also known.

However, in these types of semiconductor lasers, no optical waveguide is formed in the window region in a direction parallel to the junction. Therefore, since the laser light spreads and propagates in the window region, the amount of light reflected by the resonator reflection surface and returned to the laser oscillation region is reduced, which reduces the oscillation efficiency and increases the oscillation threshold current. It has its drawbacks. The propagation of light within a conventional semiconductor laser device is as shown in FIG. 1 when viewed from the top of the laser device. That is, a window region 2 is formed in the direction of the resonance resistant end of the strip-shaped laser oscillation operating region l.
, 2' are formed, and laser beams 4, 4' are output from the resonator end faces 3, 3'. In addition, the laser oscillation region end face 5,
5' is located inside the resonator end faces 3, 3', and the laser light travels from this position as shown by a propagation wavefront 6.

The focal point (beam waist) of the laser beam exists at the laser oscillation region end faces 5, 5' in the direction parallel to the junction, and at the resonator end faces 3, 3' in the direction perpendicular to the junction. This astigmatism becomes inconvenient when optical coupling is performed using a lens 4 or the like.

<Objective of the Invention> An object of the present invention is to provide a semiconductor laser device having a novel structure that overcomes the drawbacks of the conventional semiconductor laser device described above.

That is, an optical waveguide is also formed in the window region, and a tapered coupling region is provided between the excitation region (laser oscillation operating region) inside the cavity and the window region to couple the excitation region and the window region. ,
Causes laser oscillation. With such a configuration, the laser oscillation mode can be controlled in the window region, and the beam waist can be made to coincide with the end face. Furthermore, it is also possible to stabilize the mode of a semiconductor laser which is easily disturbed at high output. The present invention establishes such a semiconductor laser device.

<Embodiment> FIG. 2 is a diagram showing light propagation within a semiconductor laser device, which explains one embodiment of the present invention, as viewed from the top of the laser device.

A waveguide width Wg2 and each length Lw are located at both ends of the laser oscillation operating region 21 having a waveguide width Wgl and a length e.
, Lwl is arranged, with lengths LT, L between the side window region 22.22' and the working region 21.
T+ tapered joints 23, 23' are connected. The laser oscillation operating area 21 is the laser oscillation area end face 25, 25.
The propagation wavefront 26 of the zero laser beam whose length is limited by ' is as shown in the figure, and the laser beam is emitted from the resonator end faces 24, 24'.

Figure 3 (A) and (B) are x-x and Y-Y in Figure 2.
FIG. That is, FIG. 3(A) is a sectional view of the laser oscillation operating region 21, and FIG. 3(B) is a sectional view of the window region 22.22.
' is a sectional view of '.

H-G for blocking current on the p-GaAs substrate 31
An aAs current blocking layer 32 is deposited, and striped grooves are formed in the current blocking layer 32 and the GaAs substrate 31. On top of this, a p-GaAIAs cladding layer 83, a GaA3 or GaAlAs active layer 34,
n-GaAlAs cladding layer 35. N-GaAs cap layers 36 are sequentially laminated.

The structure shown in FIG. 3(A) is the same as that of a so-called active layer curved VSIS laser, and the structure shown in FIG. 3(B) is similar to that of a flat active layer VSIS laser. VSIS' (V-cha
nnneled 5ubstrate Inner 5t
Regarding lasers, please refer to the Technical Report (E
D-81-42.

1981, p. al), etc., is an internal stripe type laser having a light and carrier confinement structure in which a V-groove is formed in the substrate to form a current path. That is,
The current for laser oscillation is blocked by the n-GaAs layer 32, each having a width W. l.

Flows only to the channel portion of Wc2. These channel widths are W. They are formed so that l > Wc2, and under the same growth conditions, the active layer can be formed curved in the former case, and flat in the latter case. When the active layer is curved, a refractive index optical waveguide is formed, the width Wgl of which is the channel width W. becomes narrower than When the active layer 34 is flat, an optical waveguide is formed using the principle that the effective refractive index decreases due to light absorption into the n-GaAs layer 32 at both ends of the channel, and its width Wg2 is equal to the channel width W. Almost equal to 2.

The important event that led to the creation of the present invention is that when curved active layer V, S, IS lasers and VSIS lasers with flat active layer are individually fabricated under the same growth conditions, the curved active layer is always 100% faster. This means that it oscillates at a longer wavelength by ~200λ, ie, the band gap narrows by 21-42 meV. Furthermore, when the active layer is curved, the oscillation threshold current becomes smaller, but the transverse mode tends to become unstable, and when the active layer is made flat, the oscillation threshold current increases slightly, but the transverse mode becomes very stable. be. Therefore, if an optical waveguide having these two types of active layers is simultaneously formed and effectively coupled, laser oscillation will occur in the curved portion, and the laser light will simply pass through the flat portion. Therefore, by arranging the active layer so that the flat portions are located near both end faces, the oscillation threshold current Ith can be reduced and the transverse mode can also be stabilized.

Moreover, the output I with less end face deterioration or end face destruction durability
It is possible to fabricate a semiconductor laser with a large max. In other words, it is possible to make use of only the advantages of the two types of vsrs lasers described above and compensate for their disadvantages, and moreover, it is possible to easily manufacture a shaped laser.

An example of the manufacturing method of the present invention will be described below.

FIGS. 4(A), 4(B), 4(C), and 4(D) are manufacturing process diagrams illustrating one embodiment of the manufacturing method.

First, a p-type GaAs substrate (Zn doped, carrier concentration I
X I 019cm-8) 41 has an n-type GaAs layer (T
e-dope.

Carrier concentration 6X 1018cm -8) 42 to about 0
．． Liquid phase epitaxial growth is performed to a thickness of 611rn.

After that, as shown in FIG. 4(A) is formed on the surface of the n-type Cya A B layer 42.
A striped pattern of varying width as shown in is formed by conventional photolithography technology. The resist used was Shipley's AZ +350, and the dimensions of each part were Ll = 150 μm, L2 = 100 μm, L3 = 2.
A window is formed such that 0 μm, Wc+”6 μm, and wc2 = a μm. Through this window, the GaAs layer 42 is etched with a sulfuric acid-based etching solution.
The surface shapes in the Z2-Z2 direction are shown in Figure 4 (B
) (C).

Thereafter, a p-Gao, 5Alo, 5As cladding layer 8B, a p-Gao, 55A1o, 15As active layer 34. as shown in FIG. The n-Gao, 5A 10.5-A s Clarado layer 34 and the rl-GaA4 cap layer 36 have a flat area of 0.15 μm, o, and Ipm, respectively.

It was grown to 1.0 μm and 2 μm. However, the active layer thickness at the center of the curved portion of the active layer was 0.02 μm. The thickness of the wafer is reduced to approximately 100 mm by lapping the backside of the substrate.
μm, the surface of the n-GaAs cap layer 36 has A
u-Ge-Ni, and A on the back surface of the p-GaAs substrate 31.
An electrode layer is formed by depositing u-Zn and heating it to 450° C. to form an alloy. Next, after depositing Al on the back surface of the p-GaAs substrate 31, a pattern matching the pitch of the internal channels is formed as shown in FIGS. It is then interosseous in the center of the window region with length Ll, forming a resonator. Therefore, the window area is 50μ at each end of the device.
It will have a length of m.

This form of laser oscillates at l th = 30 mA,
The wavelength at that time was 7800λ. The end face breaking output Pmax was still about 100 mW. Moreover, 100rn
It oscillated in a stable transverse fundamental mode up to W.

Next, when the curved laser oscillation region of the active layer was used as a resonator between the bones, it oscillated in a higher-order transverse mode and the end face was destroyed at approximately 10 mW. Therefore, by the embodiment laser of the present invention,
This means that Pmax has improved about 10 times. Furthermore, when the end face is coated with At203, PmaX is approximately 200m
Improved to W. In addition, when manufacturing a laser with an oscillation wavelength of 8300λ, Pmax=20 without end face coating.
Pmax=400 mW with 0 mW'+end surface coating.

Here, if the coupling regions 23 and 23' are not provided, coupling will not be performed effectively and the differential efficiency will decrease (normal VSI
(approximately 1/2 that of an S laser), and there were still disadvantages such as the coupling efficiency fluctuating depending on the ambient temperature and the oscillation mode changing. When the coupling area was set to 20 μm or more, the differential efficiency was improved to a factor of 90 compared to normal VSIS, and stable oscillation was obtained even at ambient temperature.

When the above-mentioned morphological laser with an oscillation wavelength of 7800λ and Li0OA was operated continuously at an output of 30mW and 50°C, the following results were obtained.
Currently, there is no deterioration in any of them after 2500 hours.

The semiconductor laser of the present invention is the GaAlA semiconductor laser described in the above embodiment.
It is clear that the present invention is applicable not only to s-based lasers but also to InP-1nGaAsP-based and all other heterojunction lasers. Furthermore, the present invention is applicable not only to semiconductor lasers but also to mode converters for optical integrated circuits.

<Effects of the Invention> As described in detail above, according to the present invention, the excitation region that performs the laser oscillation operation and the window regions provided at both ends of the excitation region are connected by the tapered coupling region, and the width of the waveguide is reduced. Since the coupling between the narrow excitation region and the wide window region of the waveguide is performed continuously in the coupling region where the waveguide width changes in a tapered manner, the oscillation mode can be stabilized even during high-power operation.

It is also possible to improve the differential efficiency and stabilize against ambient temperature, and a highly reliable semiconductor laser device with good device characteristics can be obtained.

[Brief explanation of drawings]

FIG. 1 is a plan view illustrating the propagation of light in a conventional laser. FIG. 2 is a plan view illustrating light propagation in Form V, which shows one embodiment of the present invention. Figure 3 (A) and (B) are x-x and y-y in Figure 2, respectively.
FIG. FIGS. 4(A), 4(B), 4(C), and 4(D) are manufacturing process diagrams illustrating an embodiment of the manufacturing method of the present invention. 21...Laser oscillation operating area, 22.22'...Window area, 28.28'...Coupling area, 25.25'...
・Laser oscillation region end face, 3 ]-p-GaAs substrate, 8
2.-n-GaAs current blocking layer, 83.
-p-cladding layer, 3...active layer, 35...n-cladding layer, 36...n-cap layer.

Claims (1)

[Claims] 1. An excitation region having a curved active layer and a window region having a flat active layer at both ends of the resonator are provided in response to changes in the stripe width of the current confinement groove formed on the substrate, and the width of the excitation region and the window region is What is claimed is: 1. A semiconductor laser device, characterized in that the two waveguides are connected by a coupling region whose waveguide width changes in a tapered manner determined by the width of both waveguides.