JPH11186654A - Semiconductor optical amplifier and optical amplifier device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ultra-wide band semiconductor optical amplifier and optical amplifier device capable of simultaneously amplifying signal lights of two wavelengths of 1.3 and 1.5 μm for the optical communication. SOLUTION: This wide band semiconductor optical amplifier comprises an active regions in the form of a multiple quantum well structure where the thickness of one layer and energy gap of a quantum well are so formed as to be different from those of other layer. Non-reflective films 4, 5 are formed at both end faces of the active region 3, window regions at both end faces of the active region 3, and non-reflective film on its outside to further reduce the optical reflectivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier in the field of optical communication and optical measurement, and more particularly to a semiconductor optical amplifier and an optical amplifier having a wide band.

[0002]

2. Description of the Related Art As a conventional technique, a semiconductor optical amplifier is known. Among them, a traveling-wave optical amplifier having a wide wavelength band is described in Anritsu Technical No. 67 (Mar1
994), pages 22 to 27 will be described with reference to FIG.

In FIG. 6, reference numeral 21 denotes a substrate, 22 denotes a cladding layer, 23 denotes an active region, 25 denotes an end face obtained by a cleaved surface, 26 denotes an electrode, 27 denotes a window region, and 28 denotes a non-reflection coating.

[0004] An anti-reflection (AR) coat 28 of SiOx is applied to the cleaved end face 25 of FIG.
%. The window region 27 is provided so as to interrupt the active region in the vicinity of the end surfaces 25 on both sides. In the window region 27, light propagates while being diffused as a Gaussian beam. When returning to the active region 23, the spot size increases and the coupling effect to the original active region 23 decreases, so that the window region 27 has the effect of equivalently lowering the reflectivity of the end face 25 with respect to the active region 23. There is.

As described above, in this semiconductor optical amplifier, the active region 23 is formed by the plurality of quantum well layers and the barrier layers in contact with the quantum wells between the quantum well layers, and the window regions 27 are arranged at both ends. Further, a single-layer end face 25 of an anti-reflection film is formed on both outer sides thereof. And 1.54
An example of amplifying a wavelength of μm to 1.58 μm is disclosed.

[0006]

In optical communication, an optical amplifier is used for compensating the loss of an optical fiber or an optical component. However, in recent developments in optical communication, 1.3 μm and 1.55 μm signal lights are combined into one fiber. An experiment of an optical communication system for transmitting and receiving data on a computer has been conducted. In such an optical communication system, an ultra wideband optical amplifier capable of simultaneously amplifying from 1.3 μm to 1.55 μm is required. However, it is difficult to obtain an ultra-wide band semiconductor optical amplifier using the conventional technology.

[0007]

A semiconductor optical amplifier according to the present invention is formed such that the layer thickness of at least one layer and the energy gap of the quantum well are different from the layer pressure of the other layer and the energy gap of the quantum well. An active region 3 having a multiple quantum well structure and antireflection films 4 and 5 formed on both end surfaces of the active region.

Further, in the semiconductor optical amplifier according to the present invention, the multiple quantum well is formed such that the thickness of at least one layer and the energy gap of the quantum well are different from the thickness of the other layer and the energy gap of the quantum well. An active region 3 having a structure, window regions 7 formed at both ends of the active region, and antireflection films 4 and 5 formed on both outer end surfaces of the window region are provided.

An optical amplifier according to the present invention is a semiconductor optical amplifier comprising a semiconductor optical amplifier (11) and an optical isolator (10) arranged on the optical axis of the semiconductor optical amplifier. The semiconductor optical amplifier is the semiconductor optical amplifier according to claim 1.

Further, a semiconductor optical amplifier according to the present invention comprises a semiconductor optical amplifier (11) and an optical isolator (10) arranged on the optical axis of the semiconductor optical amplifier. The semiconductor optical amplifier is the semiconductor amplifier according to the second aspect.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a quantum well structure in the active region of a semiconductor optical amplifier is made a new structure, and furthermore, a structure is used which lowers the reflectivity at the end face over a wide band.

In the quantum well structure, the amplification wavelength range is determined by the thickness of the well layer and the energy gap of the well layer (the energy difference between the first levels of electrons and holes; the same applies hereinafter). Generally, when the energy gap is reduced or the thickness of the well layer is increased, the amplification wavelength region shifts to the longer wavelength side, and when the energy gap is increased or the well layer thickness is reduced, the amplification wavelength region shifts to the shorter wavelength side. Therefore, if a plurality of types of quantum wells having different energy gaps and well layer thicknesses are formed, the amplification band is synthesized and expanded. Here, since the well layer thickness is related to the optical gain coefficient, the optimum numerical value is determined by numerical calculation so that the band is wide and flat in the determination.

Furthermore, in order to obtain a traveling-wave semiconductor optical amplifier having a stable amplification function, it is necessary to reduce the end face reflectance to 1% or less over the band concerned and to prevent reflection from the far end. It is difficult to obtain such a low reflectance in the very wide amplification band of the present invention with a conventional single-layer antireflection film. Need to be formed. The multi-layer antireflection film is described in "Polarization-
independent antireflectio
n coatings for semiconduct
to optical amplifiers "El
electronics Letters, Vo1.24
pp61-62, etc., and applied to the present invention. In order to obtain a lower reflectivity, a window structure (window region) or an isolator, which is a known technique, was used.

Further, the semiconductor optical amplifier is applied, and an optical amplifier is provided with an optical isolator on the optical axis.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS.

In FIG. 1, 1 is a substrate, 2 is a cladding layer, 3 is an active region, 4 is a second non-reflective film, 5 is a first non-reflective film, and 6 is an electrode. The first non-reflective film 5 and the second non-reflective film 4 form an end face.

As an example, when an amplification wavelength band is set in a wavelength range of 1.2 μm to 1.6 μm, the substrate 1 is made of n-InP,
The cladding layer 2 is p-InP, the quantum well layer in the active region 3 and the barrier layer are InGaAsP. FIG. 2 shows a schematic view of an example of the band structure. FIG. 2 is a schematic diagram for easy understanding, and the well layer thickness and the energy gap do not accurately represent actual values.
In this example, the well layer is composed of four types of well layers having different thicknesses and energy gaps. A well layer with a low energy gap was arranged on the substrate 1 side so that injected carriers due to a current applied to the electrode 6 from the outside were effectively supplied to each well layer. When the amplification wavelength range is from 1.2 μm to 1.6 μm, the energy gap of each well layer (A [e in FIG. 2)
V], B [eV], C [eV], D [eV]) and the well layer thickness (denoted as a, b, c, d in FIG. 2) are 0.75 eV to 0.89 eV, respectively. , 0.004 to 0.018 μm. Further, the composition of each layer was determined as a lattice matching state in which stable production and characteristics are easily obtained from these values. The multiple quantum well structure composed of the different well layers is grown by a general MOVPE (metal organic chemical vapor deposition) method, and the active region 3 is buried.
Is polished to a thickness of about 100 μm to form an electrode 6. The substrate 1 is cleaved into chips, wiring for supplying a current to the chips is performed, and finally, antireflection films 4 and 5 (end faces) are vapor-deposited on the light incident surface and the light exit surface. The anti-reflection films 4 and 5 may be made of SiOx or the like, and a plurality of films having different compositions and thicknesses are formed. In the present embodiment, the first non-reflective film 5 and the second non-reflective film 4 are shown, and other layers are not shown. The wavelength band characteristic of the semiconductor optical amplifier obtained in this manner is as shown by the solid line in FIG. 3, which is much wider than the conventional wavelength band characteristic indicated by the dotted line. The anti-reflection films 4 and 5 may be formed by vapor deposition while gradually changing the composition in the light traveling direction.

A second embodiment will be described with reference to FIG.

FIG. 4 is obtained by adding a window area 7 to the configuration of FIG. That is, after the active region 3 is grown in the same manufacturing procedure as in the first embodiment, window regions 7 are formed at both ends on the optical axis of the active region 3 in order to obtain a lower end face reflectance than in the first embodiment. Provide. The window region 7 is formed by etching after growth and embedding a material having the same composition as that of the clad layer 2 in the etched region. This window area 7
In this case, the light propagates while being diffused as a Gaussian beam without being confined, so that the light reflected at the end face 4.5 becomes larger than the spot size of the light that is incident upon returning to the active region 3. . For this reason, the reflected light has a lower coupling efficiency to the original active region 3, and the window region 7 has an effect of equivalently lowering the end face reflectance with respect to the active region 3. The window region 7 has an effect of lowering the reflectance as the length is longer, but the window region 7 is set to about 30 μm because the coupling efficiency may decrease or interference light with the electrode 6 may be generated.

Next, a third embodiment and a fourth embodiment will be described with reference to FIG.

In FIG. 5, 8 is an optical fiber, 9 is a coupling lens, 10 is an isolator, and 11 is a semiconductor optical amplifier according to the first embodiment or the second embodiment.

In the third embodiment, the semiconductor optical amplifier obtained in the first embodiment is used as the semiconductor optical amplifier 11, and the coupling lens 9, the optical isolator 10, and the input and output are provided on the optical axis. The optical fiber 8 is arranged. The coupling lens 9 enhances the efficiency of the optical coupling between the input / output optical fiber 8 and the optical isolator 10 and the optical coupling between the optical isolator 10 and the semiconductor optical amplifier 11, but can be omitted because it is not an essential component. By the operation of the optical isolator 10, the return light from the optical component receiving the output light of the optical isolator is removed, and the optical amplifier operates stably.

The fourth embodiment uses the semiconductor amplifier obtained in the second embodiment as the semiconductor optical amplifier 11.
Other configurations are the same as those of the third embodiment, and provide the same effects as those of the third embodiment.

In the above embodiments, the antireflection films 4 and 5 have a refractive index closer to the value of the adjacent active region 3 or window region 7 on the inside, and closer to the refractive index of the air toward the outside. Here, the reflectance is 1% or less, and the lower the better, the better.

[0025]

As described above, in the semiconductor optical amplifier of the present invention, the amplification band is greatly expanded by the semiconductor device using different multiple quantum wells, and the problem of reflection caused by the expansion of the amplification band is also reduced. The problem can be solved by using a multilayer antireflection film, a window region (window structure), an optical isolator, and the like. As a result, an unprecedented ultra-wideband semiconductor optical amplifier and optical amplifier were realized.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating an example of a band structure according to the present invention.

FIG. 3 is a diagram showing wavelength characteristics of a semiconductor optical amplifier obtained by the present invention.

FIG. 4 is a schematic diagram showing a second embodiment of the present invention.

FIG. 5 is a schematic diagram showing a third embodiment of the present invention.

FIG. 6 is a schematic diagram showing a conventional semiconductor optical amplifier having a window region.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Cladding layer 3 Active region 4 Second non-reflection film 5 First non-reflection film 6 Electrode 7 Window region 8 Optical fiber 9 Coupling lens 10 Optical isolator 11 Semiconductor optical amplifier according to the first or second embodiment 21 Substrate

Claims (4)

[Claims] An active region having a multiple quantum well structure formed such that the layer thickness of at least one layer and the energy gap of the quantum well are different from the layer thickness of the other layer and the energy gap of the quantum well; A semiconductor optical amplifier comprising anti-reflection films (4) and (5) formed on both end surfaces of the active region. 2. An active region (3) having a multiple quantum well structure formed such that the layer thickness of at least one layer and the energy gap of the quantum well are different from the layer thickness of the other layer and the energy gap of the quantum well. A semiconductor optical amplifier, comprising: a window region (7) formed at both ends of the active region; and antireflection films (4) and (5) formed on both outer end surfaces of the window region. 3. A semiconductor optical amplifier (11), and an optical isolator (10) arranged on an optical axis of the semiconductor optical amplifier.
A semiconductor optical amplifier comprising: the semiconductor optical amplifier according to claim 1, wherein the semiconductor optical amplifier is the semiconductor optical amplifier according to claim 1. 4. A semiconductor optical amplifier (11), and an optical isolator (10) arranged on an optical axis of the semiconductor optical amplifier.
3. A semiconductor optical amplifier comprising: a semiconductor optical amplifier according to claim 2;