JPH02260679A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To enable a laser device of this design to be easily manufactured by a method wherein a window region formed of a specific semiconductor compound layer is provided to the end face of an optical waveguide and is specified in length, whose peripheral part is formed into an arc surface of a condensing lens to improve the coupling efficiency of the window region with an optical fiber. CONSTITUTION:A GaInAsP active layer 22 serving as an optical waveguide 31, a P-InP clad layer 23, and a P-GaInAsP ohmic contact layer 24 are successively formed in lamination on an N-InP substrate 21 through a crystal growth method. The double hetero-structure section composed of layers 22-24 is etched up to the underside of the active layer 22 into an inverted mesa stripe, and an incident end face 32 and a projecting end face 33 side are also subjected to etching. Then, a P-InP buried layer 25 and an N-InP layer 26 are successively grown along the end face of the mesa stripe and the end faces 32 and 33 side to form a buried hetero-structure provided with a window region. The lengths of the layers 25 and 26 are made equal to or larger than 30mum, and both the end faces of the substrate 21, and the layers 25 and 26 are formed into a protrudent arc part 27.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a semiconductor laser device, and in particular, a semiconductor laser device that has high productivity, excellent coupling efficiency with an optical fiber, and is suitable as an amplifier in optical communication. This invention relates to a laser device.

(Prior Art) With the recent development of the optical communication field, the installation of optical fiber networks is also expanding. Therefore, there is an increasing demand for lower costs for installing optical fiber networks.

Incidentally, one of the items that occupies a large part of such installation costs is a repeater.

This repeater consists of a light receiving element, a light receiving element driving circuit, an amplifier,
It is composed of many parts such as a waveform shaping circuit, a light emitting element, a light emitting element drive circuit, etc., and requires a large amount of money due to the purchase cost of these parts, adjustment cost, testing cost to confirm reliability, etc. Therefore, there are expectations for the development of a semiconductor laser amplifier that can replace all of the above components with a single element.

FIG. 6 is a diagram showing an example of a conventional semiconductor laser amplifier, and is a conceptual diagram of the semiconductor laser amplifier viewed from the top of the device.

In the figure, reference numeral 1.2 indicates an anti-reflection film made of a single layer or multilayer dielectric material, and an entrance end surface 3 and an output end surface 4 are formed approximately in the center of these anti-reflection films. An optical waveguide 5 is embedded between the end faces 4. This optical waveguide 5 is buried in a current and optical confinement layer 6, and acts as an active layer that generates optical amplification gain by current injection from an electrode portion (not shown).

In such a semiconductor laser amplifier, light that enters the input end face 3 through the antireflection film 1 is amplified while being guided through the optical waveguide 5 and then output from the output end face 4 .

The semiconductor laser amplifier shown in FIG. 7 has the above structure of Ga1
The present invention is applied to an nAsP-based buried hetero type semiconductor laser oscillator, and is used as a semiconductor laser amplifier.

This laser element is constructed by fabricating a Ueno film using the same manufacturing process as a normal buried hetero semiconductor laser, forming an end face by cleavage, and then applying a single-layer or multi-layer dielectric anti-reflection coating. There is.

That is, on the n-1nP substrate 11, Ga1, which becomes an optical waveguide, is
nAsP active layer 12, p-InP cladding layer 13, p-
A Ga1nAsP atomic contact layer 14 is sequentially laminated by crystal growth. Then, etching is performed in a reverse mesa stripe shape to the bottom of the active layer 12, and crystal growth is performed sequentially along the sides of the mesa stripe to form a p-1nP buried layer 15 and an n-1nP buried layer 16 to form a current blocking layer. Thus, a so-called buried hetero (BH) structure is formed.

Thereafter, an n-side electrode 17 is formed on the upper surface of the element, and an n-side electrode 18 is formed on the lower surface of the element, both end surfaces are cleaved, and an antireflection film 19 is formed on the cleaved surfaces to complete the process.

In such a semiconductor laser amplifier, the effective energy reflectance of the input end face and the output end face is required to be 1% or less, and for better operation it should be 0.1% or less. is desired.

In order to achieve this energy reflectance with the anti-reflection film 19, it is necessary to use a dielectric material with a refractive index of 1 to 3 and set the accuracy of the refractive index to 0.1 or less and the film thickness for a given refractive index and film thickness. You have to match up to 10 people with accuracy. In general, the end face of a semiconductor laser is minute, measuring 100 .mu.m horizontally and 10 .mu.m vertically, 1 and there has been a problem in that it is extremely difficult to form an antireflection film that satisfies the above conditions with good reproducibility.

In addition, as another conventional device, as shown in FIGS. 8 and 9, the intersection angle between the optical waveguide 5, the input end surface 3, and the output end surface 4 is inclined from several degrees to 20 degrees relative to the vertical. Semiconductor laser amplifiers are also being considered in which the anti-reflection coating 1.2 is applied.

That is, the semiconductor laser amplifier shown in FIG. 8 is a semiconductor laser amplifier in which the optical waveguide 5 is formed obliquely with respect to the cleavage direction of the crystal, and is proposed by C. E. Zah et al. ElectronicsLett
ers Vol. 23, No. 19, pp. 990-991, 1987
Year).

Further, the semiconductor laser amplifier shown in FIG. 9 has an optical waveguide 5
is formed in the cleavage direction of the crystal, and the end faces 3.4 are formed obliquely by polishing or dry etching.

In both of the semiconductor laser amplifiers shown in FIGS. 8 and 9 above, the energy reflectance of the end facet 3.4 decreases, and even if the reflectance of the antireflection film 1.2 is on the order of several percent, , the effective reflectance is 0.1%.

In a semiconductor laser amplifier with such a structure, as the angle of inclination increases, the coupling efficiency with the optical fiber decreases.
There was a problem that sufficient gain could not be obtained as an optical amplifier. In addition, particularly in the structure shown in FIG. 7, since the axial direction of the crystal and the longitudinal direction of the optical waveguide 5 are misaligned, there is a problem that crystal growth is difficult and it is difficult to manufacture with good reproducibility.

10 and 11 are diagrams showing a conventional buried hetero type semiconductor laser amplifier with a so-called window region.
Figure 0 shows a plan view, and Figures 11 and 11 show a perspective cross section.

This buried hetero-type semiconductor laser amplifier has a buried layer 6 which serves as a current and light confinement layer made of a compound semiconductor having a larger forbidden band width and a higher refractive index than an active layer, and an optical waveguide 5.
Crystals are grown adjacent to the entrance end face 3 and exit end face 4 of
9a).

In such a buried hetero-type semiconductor laser amplifier, when the window region, that is, the length in the longitudinal direction of the optical waveguide 5 buried in the compound semiconductor 6 is set to 30 μ- or more, the theoretical effective energy reflectance is 0.6 μm. % or less. Furthermore, since the structure of this semiconductor laser element is similar to that of the buried hetero type semiconductor laser amplifier shown in FIG. 6,
The manufacturing process can be almost the same, and it has the advantage that low reflectance can be obtained relatively easily.

(Problem to be Solved by the Invention) However, in the above-mentioned buried hetero type semiconductor laser amplifier with a window region, as shown in FIG. Therefore, there was a problem in that the optical coupling rate with the optical fiber was reduced and sufficient gain could not be obtained as an optical amplifier.

In this way, in conventional semiconductor laser amplifiers, the manufacturing conditions for the refractive index and film thickness of the dielectric anti-reflection film are extremely strict, making it difficult to manufacture. Another problem is that when a semiconductor laser amplifier having a structure with a window region is used, the coupling rate with an optical fiber decreases, and a sufficient gain cannot be obtained as an optical amplifier.

The present invention has been made to solve the above-mentioned conventional problems, and aims to provide a semiconductor laser device that is easy to manufacture and has a high coupling efficiency with an optical fiber.

[Structure of the Invention] (Means for Solving the Problems) A semiconductor laser amplifier of the present invention includes a light-emitting crystal layer having an optical waveguide formed along an optical resonance direction, and at least one of both end faces of the optical waveguide. It has a light emitting or light incident end face formed on the end face, and a window region made of a semiconductor compound layer formed on at least one end side of the light emitting or light incident face of the optical waveguide, and the light emitting crystal layer is used as an electrode layer. In the semiconductor laser device, the window region is made of a compound semiconductor having a larger forbidden band width and a larger refractive index than the light emitting crystal layer, and the length of the window region in the direction of the optical waveguide is 30 μm or more. In addition, the outer edge of the window area is formed in the shape of an arcuate surface of a condensing lens.

(Function) The present invention provides a compound semiconductor having a larger forbidden band width and larger refractive index than the active layer by crystal growth on at least the end face of the optical waveguide in the light emitting crystal layer, with a length of 30 μm in the optical waveguide direction.
The outer edge of the compound semiconductor is formed into an arcuate surface of a condensing lens that condenses the light incident on the element or the light emitted from the element, and the outer edge of the compound semiconductor is By applying a single layer or multilayer dielectric film to the side surface to form an antireflection film, the coupling efficiency with the optical fiber increases and the gain as an optical amplifier increases.

In addition, the design conditions for the optical system at the same gain are relaxed,
It becomes possible to improve reliability.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment in which the present invention is applied to a Ga1nAsP-based buried hetero-type semiconductor amplifier.
FIG. 2 is a conceptual diagram of FIG. 1 viewed from the plane.

In the manufacturing of this embodiment, a wafer is manufactured using the same manufacturing process as a normal buried hetero type semiconductor laser, and after the end face is formed by cleavage, a single-layer or multi-layer dielectric anti-reflection film is applied.

That is, on the n-1nP substrate 21, G
a1nAsP active layer 22, p-1nP cladding layer 23,
A p-Ga1nAsP omic contact layer 24 is sequentially formed by crystal growth. Then, the double heterostructure consisting of the layers 22, 23, and 24 formed on the substrate 21 is etched to the bottom of the active layer 22 in the form of an inverted mesa stripe. The sides are also etched.

After this, p-1nP to create a current blocking layer
The buried layer 25 and the n-1nP buried layer 26 are sequentially crystal-grown along the side surfaces of the mesa fist stripes and the end surfaces 32 and 33, forming a so-called buried hetero (BH) structure with a window region.

The length of the compound semiconductor, that is, the buried layer 25.26, which is crystal-grown along the mesa stripe end face 32.33, that is, the length of the window region in the mesa stripe direction, is 30 μm or more, and the substrate 21 and the buried layer 25.26 are made to have a length of 30 μm or more. Both end surfaces of are formed into convex circular arc portions 27. Further, the compound semiconductor is formed of a member having a larger forbidden band width and a larger refractive index than the active layer 22.

The arcuate portion 27 can be easily formed, for example, by using a mask having a circular or elliptical shape and using a dry process such as ion milling or reactive ion etching.

Further, in the above embodiment, the arcuate portion 27 is formed up to the lower surface of the lnP substrate 21, but the arcuate portion 27 is not connected to the active layer 22.
It is sufficient to form up to about 50 μι in the vicinity, and dicing of individual chips on the wafer thus formed may be performed by cleaving, scribing, or the like.

The smaller the radius of curvature of the arcuate portion 27, the more the coupling efficiency with the optical fiber increases. For example, if the radius of curvature is set to 10 μm, the coupling efficiency increases by about twice.

Furthermore, as the active layer 22 that generates optical amplification gain,
x t-x using a Ga1nAsP crystal layer
yt-y The composition ratio of XsY is determined according to the wavelength of the light to be amplified. Further, as a compound semiconductor having a larger forbidden band width and refractive index than the active layer 22, n-type and n-type lnP crystal layers may be used.

After forming the arcuate portion 27 on the end face of the element in this manner, a p-side electrode 28 is formed on the upper face of the element, an n-side electrode 29 is formed on the lower face of the element, and an antireflection film 30 is formed on the end face to complete the process.

In the above embodiment, the double heterostructure including the Ga1nAsP active layer 22 is composed of only two types, an InP crystal layer and a Ga1nAsP crystal layer, but an InP buffer layer for reducing distortion of the crystal substrate, A GalnAsP layer having a transitional composition to prevent meltback of the active layer 22 may be formed between the active layer 22 and the InP layer 23.

In a buried hetero-type semiconductor laser amplifier with a window region having such a structure, a compound semiconductor having a larger forbidden band width and refractive index than the active layer 22 is formed adjacent to both end faces of the optical waveguide 31 to form the window region, and Since the length of the region is 30μ■, similar to the characteristics of a conventional buried hetero semiconductor laser amplifier with a window region, when using an antireflection film to reduce the effective energy reflectance to 0.1%, The reflective film formation conditions can be relaxed and production can be facilitated.

Furthermore, since the outer edge of the window area is formed into a convex circular arc part 27, the incident light is condensed by the lens effect of the circular arc part 27, and the coupling efficiency of the incident light increases. Although the emitted light 34 from the beam 33 spreads once in the window area, it is condensed again by the lens effect of the circular arc portion 27, so that it is possible to prevent the coupling efficiency from decreasing due to the spread of the beam.

In this way, in this embodiment, the coupling efficiency with the optical fiber increases, and the gain as an optical amplifier increases. Furthermore, since the design conditions for the optical system for the same gain are relaxed, reliability and productivity can be improved.

Incidentally, in the above-mentioned embodiments, an example in which the present invention is applied to a buried hetero-type semiconductor and a laser has been described, but the present invention can also be applied to other buried structures.

For example, as shown in FIG.
- After burying the active layer 22 with an InP layer 41 and forming a p-1nP layer 25 thereon for planarization,
p-Ga1nAsP contact! - It can also be applied to a semiconductor laser amplifier with a surface flattened buried heterostructure in which the layer 43 and the striped insulating film 42 are formed on the p-1nP layer 25.

In addition, as shown in FIG. 4, after growing the double heterostructure that serves as the base once, a groove is formed by etching, and then a crescent-shaped active layer 51 is buried in the second crystal growth. It can also be applied to a semiconductor laser amplifier with a buried crescent structure.

Furthermore, as shown in FIG. 5, prior to crystal growth, two channel-shaped grooves 61 that are close to each other are formed on the lnP substrate 21. The present invention can also be applied to a so-called double channel brainer buried heterostructure semiconductor laser amplifier in which the active layer 62 is buried in the region.

The present invention is of course applicable not only to semiconductor laser devices used as amplifiers as in the above embodiments, but also to general semiconductor laser oscillators.

[Effects of the Invention] As explained above, according to the present invention, manufacturing is easy;
Moreover, it is possible to realize a semiconductor laser device with high coupling efficiency with an optical fiber.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the configuration of an embodiment in which the present invention is applied to a buried heterostructure semiconductor laser amplifier, and FIG.
3 is a perspective view showing the configuration of an embodiment in which the present invention is applied to a surface flattened buried heterostructure semiconductor laser amplifier; FIG. 4 is a conceptual diagram of the semiconductor laser amplifier shown in FIG. FIG. 5 is a perspective view showing the configuration of an embodiment in which the present invention is applied to a semiconductor laser amplifier with a p-substrate buried crescent structure; FIG. Figure 6 is a conceptual diagram of a conventional semiconductor laser amplifier viewed from the top of the device, Figure 7 is a perspective view showing the configuration of a conventional semiconductor laser amplifier, and Figure 8 is an optical waveguide tilted from the crystal cleavage direction. Fig. 9 is a conceptual diagram of a conventional semiconductor laser amplifier formed as seen from the top surface of the device. Fig. 9 is a conceptual diagram of a conventional semiconductor laser amplifier formed with the optical waveguide end face tilted from the cleavage plane of the crystal, as seen from the top surface of the device. 11 is a conceptual diagram of a conventional semiconductor laser amplifier in which a window region is formed, viewed from the top surface of the element, and FIG. 11 is a perspective view showing the structure of a conventional semiconductor laser amplifier in which a window region is formed. 21......n-1nP substrate 22...
...Ga1nAsP active layer 23...
p-1nP cladding layer 24...p-Ga
1nAsP omic contact layer 25...
...p-1nP buried layer 26...n-1
nP buried layer 27...... Arc portion 28... P-side electrode 29... N-side electrode 30...・Anti-reflection film 31... Optical waveguide bow 2 Applicant: Toshiba Corporation

Claims (1)

[Scope of Claims] A light-emitting crystal layer having an optical waveguide formed along an optical resonance direction; a light output or input end face formed on at least one of both end faces of the optical waveguide; A semiconductor laser device having a window region made of a semiconductor compound layer formed on at least one end side of the light emitting or light incident end face, and the light emitting crystal layer being sandwiched between electrode layers, the window region is used as the light emitting crystal layer. It is made of a compound semiconductor having a larger forbidden band width and a larger refractive index than the crystal layer, and the length of this window region in the optical waveguide direction is 30°.
.mu.m or more, and the outer edge of the window region is formed in the shape of an arcuate surface of a condenser lens.