JPH02137385A - Semiconductor optical amplifier - Google Patents

Abstract

PURPOSE:To obtain this optical amplifier which can be manufactured easily, whose coupling efficiency with reference to a single-mode fiber is good and whose characteristic is excellent by a method wherein a window region is constituted of a material whose refractive index is nearly equal to an equivalent refractive index of an active region. CONSTITUTION:The following are provided: a stripe-shaped active region 15 filled with a semiconductor layer having a confinement effect with reference to a signal beam; a window region 16 which is connected to one end or both ends of the active region 15 and which is transparent with reference to the signal beam. In this case, the window region 16 is constituted of a material whose refractive index is nearly equal to an equivalent refractive index of the active region 15. Thereby, a reflection is not caused at a boundary part 19 of the active region and the window region; a prescribed value or lower is obtained as an average end-face reflectance of an optical amplifier; a prescribed interfiber optical amplification gain can be obtained with reference to an incident beam.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention suppresses the reflectance of the end face, thereby reducing fluctuations in signal gain with respect to fluctuations in wavelength of input light and reducing coupling loss with a single mode fiber. Concerning small semiconductor optical amplifiers.

[Conventional technology]

By using a semiconductor optical amplifier as a repeater in a long-distance transmission system, it is possible to reduce the size of the repeater and expand the regenerative repeating interval. Furthermore, by using the optical device as an amplifier immediately before the photodetector, the light reception level can be improved compared to the direct detection method. Furthermore, by using it as a loss compensator for an exchanger in optical switching, it has many advantages such as the ability to realize a multi-channel switching system without performing OE or EO conversion, so research and development is actively underway. . Conventional semiconductor optical amplifiers are of the resonant type, in which the semiconductor laser is biased below the threshold value, and the end face reflectance of both end faces of the semiconductor laser is reduced using means such as anti-reflection coating (AR co-coating), window end face structure, etc. It can be divided into suppressed traveling wave types. Traveling wave optical amplifiers are advantageous over resonant semiconductor optical amplifiers in that they have small gain fluctuations with respect to input light wavelength fluctuations and small gain saturation with respect to increases in input light intensity. However, in order to obtain a traveling wave semiconductor optical amplifier with such good characteristics, it is necessary to suppress the end face reflectance to 0.1% or less. However, it is extremely difficult to obtain desired end face reflectance with good reproducibility using only the conventionally used AR co-coating technology. Therefore, a semiconductor optical amplifier having a window end face structure is promising for suppressing the end face reflectance.

[Problem to be solved by the invention]

FIG. 2 shows a conventional semiconductor amplifier having a window end face structure manufactured by the present inventors. The basic structure is a double channel planar embedded heterostructure (DC-PBH structure), and has a figure-7 window end face. Hereinafter, before pointing out the problems, the element structure of a conventional semiconductor amplifier having a window end face structure will be explained along with the manufacturing process.

First, non-doped InGaA is placed on the top surface of the n-rnP substrate 1.
sP active layer 2, anti-meltback layer (AMB1'!>
3. I) -1nP cladding layer 4 by liquid phase epitaxy (LPE)
The thicknesses are 0.1 tl m and 0.01 tl m, respectively, by the method.
After successive crystal growth of μm and 1 μrn, [110
] direction, two grooves 12. with a depth of 1.5 μm and a width of 4 μm.
13 and a mesa stripe 14 having a width of 1.2 μm sandwiched therebetween. Further, in a portion corresponding to the window region 16, a groove 11 having a width of 4 μm and a depth of 1.5 μm is formed, which is continuous from the groove 12.13 and has no mesa stripe. The above mesa stripe formation and window region formation can be performed by one photolithography method. The length of the window region 16 is 30 μm. Next groove 11°12.1
A P-TnP current blocking layer 5, except for the upper part of the mesa stripe 14, is formed on the semiconductor multilayer crystal formed with
An n-InP current blocking layer 6, a p-1nl' buried layer 7 on the entire surface including the mesa stripe 14, and a P''-TnGaAsP contact layer 8 with a wavelength composition of 1.2 μm, each having a thickness of 1 μm at the flat part and 0. .5 μm, 6
Crystals were grown sequentially by the LPE method at ttm and 0.5 μm. Furthermore, on the contact layer 8 and the n-Inf' substrate 1
An electrode 9.10 made of Ti film is formed below. Finally, both end faces are coated with a thickness of 22 mm using the ECR plasma CVD method.
Anti-reflection coating film 17.1 by 00 people's 5iON
8, a semiconductor optical amplifier is completed. This conventional semiconductor optical amplifier with a window end face structure is suitable for buried growth.
nP is used, and the equipolarized refractive index of the active region and the refractive index of the window region are different. Therefore, the boundary 19 between the active region and the window region
There was a problem in that the end face reflectance could not be suppressed below the reflectance at . An object of the present invention is to provide a traveling wave semiconductor optical amplifier that is easy to manufacture, has good coupling efficiency with a single molded fiber, and has excellent characteristics.

[Means to solve the problem]

In order to solve the above problems, it is necessary to have a striped active region buried in a semiconductor layer that has a confinement effect for signal light, and connect it to one or both ends of this active region to allow signal light to be trapped. On the other hand, in a semiconductor optical amplifier having a transparent window region, the window region is made of a material having a refractive index approximately equal to the equipolarized refractive index of the active region.

〔Example〕

FIG. 1 shows a semiconductor optical amplifier having a window end face structure, which is an embodiment of the present invention. The manufacturing process is as follows.

First, non-doped InGa is placed on the top surface of the n-1nP substrate 1.
AsP active layer 2, anti-meltback layer (AMB layer),
After the p-1nP cladding layer 4 was successively grown to thicknesses of 0.1 μm, 0.01 μm, and 1 μm by liquid phase epitaxy (LPE), [110 ] direction, depth 1.5
Two grooves 12 and 13 each having a width of 4 μm and a mesa stripe 14 having a width of 1.2 μm sandwiched therebetween are formed.

Furthermore, in the portion corresponding to the window region 16, the groove 12.1
Continuing from 3, width 4 μm with no mesa stripe,
111 with a depth of 1.5 μm is formed. The length of the window region 16 is 30 μm. The equipolarized refractive index of the above active region is 3.2
4, but it has the same refractive index as I(lo, 9
1GaO・09^S0.2P0・8 (hereinafter InGa
AsP) is used for implant growth. That is, p -1nGaAsP current blocks 7120, n
-InGaAsP current blocking layer 21, p -1nGaAsP buried layer 22 on the entire surface, wavelength composition 1.
The p''-InGaAsP contact layer 8 of 2 μm has a thickness of 1 μm, 0.5 μm, 6 μm at the flat part, respectively.
Crystals were sequentially grown to 0.5 μm using the LPE method. Furthermore, T is formed on the contact layer 8 and below the n −1nP substrate 1
An electrode 9.10 made of i/Au is formed. Finally, anti-reflection coating films 17 and 18 made of 5iON with a thickness of 2200 mm are formed on both end faces by ECR plasma CVD. In the semiconductor optical amplifier manufactured in this way,
There was no reflection at the boundary 19 between the active region and the window region, and the average end face reflectance of the optical amplifier was 0.01% or less. Furthermore, for incident light with a wavelength of 1.55 μm and an intensity of -35 dBm, an inter-fiber optical amplification gain of 18 dEl was obtained when the injection current was 70 mA. Furthermore, at this time, as a result of sufficiently suppressing the end face reflectance, the incident light wavelength was reduced to 15 nm (more than the free spectral range for the Fabry-Perot mode).
The change in amplification factor during sweeping was very small, less than 1 dB.

In the above embodiment, an example was shown in which a DC-PBH structure was used, but other structures such as a BH tank structure may be used. In addition, the semiconductor material used is In
It is not limited to P-type. In particular, an example is shown in which InGaAsP is used as the constituent material of the window region, but other materials may be used as long as the material can make the refractive index equal to the equipolarized refractive index of the active region.

〔Effect of the invention〕

As explained above, the present invention solves the problem that, in a conventional semiconductor optical amplifier having a window end face structure, reflection at the boundary between the active region and the window region limits the effect of suppressing the average end face reflectance by the window end face structure. This problem has been solved, and the average reflectance in semiconductor optical amplifiers can be further suppressed. As a result, the characteristics of the semiconductor optical amplifier can be dramatically improved by suppressing gain fluctuations due to input light wavelength fluctuations and reducing gain saturation.

[Brief explanation of the drawing]

FIGS. 1 and 2 are structural diagrams of a traveling wave semiconductor optical amplifier having an end face window structure, which is an embodiment of the present invention and a conventional example, respectively. 1--- n -1nP substrate, 2... non-doped In
GaAsP active layer, 3... anti-meltback layer, 4
...p-1nP cladding layer, 5...p-InP
Current current bluff 2 layers...rh-1nP current blocking layer, 7...p-1oP embedded calendar, 8-P''-
1nGaAsP contact layer, 9.10--electrode, 11
, 12.13...Groove, 14...Mesa stripe, 1
5...Active region, 16...Window region, 17°18...
・Anti-reflective coating film, 19...Boundary between active region and window region, 20...p-InGaAsP current blocking layer, 21...n-1nGaAsP current blocking layer,
22-...p-1n6aAsF' buried layer (011- is In0091Ga0.09A!9.2
(represents PO08). Agent: Susumu Uchihara, patent attorney Figure 1

Claims (1)

[Claims] A semiconductor optical device having a striped active region embedded in a semiconductor layer that has a confinement effect on signal light, and a window region connected to one or both ends of the active region and transparent to the signal light. 1. A semiconductor optical amplifier characterized in that a window region is formed of a material having a refractive index substantially equal to the equivalent refractive index of an active region.