JPH0964480A - Semiconductor light amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate optical axis adjustment for introducing light to a gain region and obtain a stable amplifier of high gain by providing a converging means for introducing light from the outside to a gain region. SOLUTION: A semiconductor light amplifier comprises a gain region 1, a semiconductor layer 2, a coating 3 deposited on an amplifier edge face for transmitting light close to a hundred percent and a converging means 7 for introducing light 5 from the outside to a gain region 1. The converging means 7 consists of a transparent medium whose reflectance is high than that of the gain region 1 and is formed in a wedge shape, and an edge part thereof is formed to coincide with an amplifier end part position and a bottom surface is arranged to be brought into contact with an upper part of the gain region 1 as a boundary surface with the gain region 1. Light 5 from an outside which is entered into the slope is entered to a boundary surface with the gain region 1 at a critical angle or less. Thereby, light proceeds along the boundary surface without receiving total reflection, and is injected to the gain region 1, amplified and projected from an amplifier to an outside as output light 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor optical amplifier, and more particularly to a traveling wave type semiconductor laser optical amplifier used as a light source for optical communication, optical applied measurement, and optical information processing.

[0002]

12 (a) and 12 (b) are a perspective view and a cross-sectional view showing the structure of a general semiconductor optical amplifier. In the figure, 1 is a gain region of a semiconductor optical amplifier (hereinafter, referred to as an amplifier unless otherwise specified) that gives a gain to light 5 from the outside, 2 is a semiconductor layer of the amplifier, and 3 is a reflectance of an end portion of the amplifier as much as possible. By showing a coating for reducing the size, external light 5 passes through the gain region 1 in the amplifier,
It is amplified with a predetermined gain.

[0003]

However, in the conventional semiconductor optical amplifier, the size of the gain region 1 into which the light 5 from the outside is incident is about 1 μm in the vertical direction and the entrance is small, so that the light is almost parallel to the gain region 1. It is difficult to adjust the optical axis because it is incident on the laser beam, and it is difficult to obtain stable amplified light with high gain.

The present invention has been made to solve the above-mentioned problems, and the optical axis for guiding the light to the gain region can be easily adjusted, and stable amplified light with high gain can be obtained. The purpose is to obtain a semiconductor optical amplifier.

[0005]

A semiconductor optical amplifier according to the present invention is a semiconductor optical amplifier having a gain region that amplifies and outputs light incident from the outside, and guides light from the outside to the gain region. It is characterized in that it is provided with a light collecting means.

Further, the condensing means is made of a medium having a refractive index larger than that of the gain region and has a wedge shape for guiding the light from the outside incident from the slope to the gain region. is there.

Further, the light condensing means has a bottom surface which is in contact with the gain region so as to be disposed above the gain region, and serves as a boundary face with the gain region, and external light incident on the slope is bounded with the gain region. It is characterized in that it is incident on the surface at a critical angle or less.

Further, in the light collecting means, the side face is brought into contact with the entrance of the gain region of the amplifier end face and the upper part thereof, and the light from the outside incident on the slope is formed at a critical angle with the boundary face with the gain region. It is characterized in that it is made incident below.

Further, a total reflection coating film is applied to the non-output side end portion of the amplifier, a coating film having a predetermined reflectance is applied to the output side end portion, and the resonance is formed outside the amplifier by the coating film. The temperature controller is further provided for adjusting the length of the vessel so that the light incident on the gain region resonates.

Further, the light condensing means further comprises a waveguide which is in contact with the entrance of the gain region of the amplifier end face and is provided along the extension line of the gain region, and has a refractive index higher than that of the waveguide. The bottom of each of the waveguides is brought into contact with the bottom to sandwich the waveguide, and the side of the gain region is brought into contact with each of the amplifier end faces of the upper and lower portions of the gain region, so that light from outside incident on the respective slopes can be received. It is characterized in that a pair of wedge-shaped media which are incident at a critical angle or less are provided on the boundary surface with the gain region.

Further, the waveguide is characterized in that the gain region is extended from the end of the amplifier to the outside.

Further, the light condensing means is characterized in that it is a tapered light guide which has an entrance opening widened and guides light incident from the outside to the gain region.

Further, the above-mentioned light guide is characterized in that the widened incident port is provided inside the amplifier so as to coincide with the end of the amplifier.

Further, the above-mentioned light guide is characterized in that it is provided at a position outside the front of the amplifier end.

Further, the condensing means is a reflection type diffraction grating for condensing the light incident from the outside into the gain region.

Further, the condensing means is a condensing mirror for condensing the light incident from the outside into the gain region.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. The semiconductor optical amplifier according to the present invention will be described below with reference to the drawings. 1A and 1B are a perspective view and a cross-sectional view showing a schematic configuration of the semiconductor optical amplifier according to the first embodiment. As shown in FIG. 1, the semiconductor optical amplifier according to the first embodiment has a gain region 1, a semiconductor layer 2, and a coating 3 (reflectance 0%) provided on the end face of the amplifier for transmitting light close to 100%. And a condensing means 7 for guiding the light 5 from the outside to the gain region 1.

Here, the condensing means 7 is made of a transparent medium having a refractive index higher than that of the gain region 1, and has a wedge shape.
The top surface is aligned with the position of the end of the amplifier, and the bottom surface is in contact with the gain area 1 so as to be disposed above the gain area 1 to form a boundary surface with the gain area 1. By making the light incident on the boundary surface with 1 at a critical angle or less, the light propagates along the boundary surface without being totally reflected, enters the gain region 1, is amplified, and is emitted as output light 6 from the amplifier to the outside. It is done like this.

As shown in FIG. 2, the tip angle (apex angle) ψ of the top of the wedge-shaped light converging means 7 is set in a range satisfying the following conditions. Now, let each of the refractive indices of air, the condensing means 7 and the gain region 1 be n ₁ , n ₂ and n _3, and make the incident angle between the normal to the slope of the condensing means 7 and the light 5 from the outside. And refraction angles θ ₁ and θ ₂ , and ξ is an angle formed by a light 5 from the outside and a surface parallel to the boundary surface between the gain region 1 and the bottom surface of the light condensing means 7. The incident angles and refraction angles formed by the normal to the boundary surface with the bottom surface and the light refracted by the condensing means 7 are θ ₃ and θ ₄ , and the boundary surface between the gain area 1 and the bottom surface of the condensing means 7 and the gain area 1 The angle formed by the light refracted by is φ.

Here, with respect to the plane of the gain region 1, an angle ξ,
In order to collect incident light having an angle θ ₁ on the normal to the slope of the wedge-shaped light collecting means 7 in the gain region 1, n ₁ sin θ ₁ = n ₂ sin θ ₂ (1) n ₂ is obtained from Snell's law. sin θ ₃ = n ₃ sin θ ₄ (2) Equations (1) and (2) are satisfied, and π / 2 = θ ₁ + ξ + ψ (3) π / 2 = φ + θ ₄ (4) ψ = θ ₃₋ θ ₂ (5) ξ> φ (6) As a range of the angle ψ, ψ _min <ψ <ψ _max (7) The range of the angle ψ may be set so as to satisfy the formula (7).

Therefore, the external light 5 incident from the left side of FIG. 1B has a higher refractive index than the gain region 1 and has a wedge shape, and guides the light incident from the slope to the gain region 1. Since the light is incident on the boundary surface with the gain region 1 at a critical angle or less by the optical means 7, the light propagates along the boundary surface and is incident on the gain region 1 for amplification, and the output light 6 is output from the amplifier to the outside. Is emitted as.

Further, conventionally, the light is guided to the gain region 1 by a lens, a spherical fiber or the like. In the gain region 1, the horizontal direction is several μm or more, while the vertical direction is 1.
Although it was very narrow as μm and it was difficult to collect the light, since the light is made incident on the gain region 1 through the wedge-shaped light collecting means 7, the light collecting region on the slope becomes large and the light is collected in the vertical direction. Light is generated and it becomes easy to collect light.

That is, the light 5 from the outside that has entered the medium having a large refractive index enters the interface with the gain region 1 at a critical angle or less and travels along the interface without undergoing total reflection. The light incident on the gain region 1 is amplified and output. In order to allow the light 5 from the outside to enter a medium having a large refractive index at an angle equal to or less than that for realizing the critical angle,
Even if the incident angle is large, the light can be made to enter the gain region 1 almost in parallel, and there is a margin in the incident angle. Further, since the light is made incident along the boundary surface with the gain region 1, the region where light is to be condensed is large. Since the incident light can be narrowed down to the medium surface having a large refractive index, the light can be condensed and the optical axis can be easily adjusted, and the amplified light with high gain and stable can be obtained.

Embodiment 2. Next, FIG. 3 shows a second embodiment.
FIG. 3 is a schematic configuration diagram showing a semiconductor optical amplifier according to the present invention. The semiconductor optical amplifier according to the second embodiment shown in FIG. 3 has almost the same configuration as that of the first embodiment shown in FIG. 1, but the installation position of the wedge-shaped condensing means 7 is different. That is, in FIG. 3, the wedge-shaped light converging means 7 has its apex aligned with the front and outer sides of the amplifier end position and its side surface in contact with the entrance of the gain region 1 of the amplifier end and the upper part thereof,
The external light 5 incident on the slope is incident on the boundary surface with the gain region 1 at a critical angle or less.

Therefore, by using the wedge-shaped light converging means 7 according to the second embodiment, the light 5 from the outside can be made to travel along the bottom surface of the wedge, and the gain region 1 at the exit portion thereof. Since the light 5 from the outside can be easily incident, the light 5 from the outside is incident on the gain region 1 and amplified.

Embodiment 3 FIG. Next, FIG. 4 shows a third embodiment.
FIG. 3 is a schematic configuration diagram showing a semiconductor optical amplifier according to the present invention. The semiconductor optical amplifier according to the third embodiment shown in FIG. 4 serves as a light condensing means and is in contact with the entrance of the gain region 1 on the end face of the amplifier and is provided with the waveguide 8 provided along the extension line of the gain region 1. And having a refractive index higher than that of the waveguide 8 and contacting the bottoms of the upper and lower portions of the waveguide 8 to sandwich the waveguide 8 and to the amplifier end faces of the upper and lower portions of the gain region 1, respectively. A pair of wedge-shaped light converging means 7a, 7b are provided, which are in contact with each other at their side surfaces, and make light incident from the outside, which is incident on the inclined surface, enter the boundary surface with the gain region 1 at a critical angle or less.

Therefore, according to the third embodiment, the wedge-shaped focusing means 7a and 7 having a high refractive index are provided at the entrance of the gain region 1.
By attaching a light collector having a structure in which a low refractive index waveguide 8 is sandwiched by b, light having the same function as a lens can be collected, and the light 5 from the outside can be near the bottom surfaces of the wedge-shaped light collecting means 7a and 7b. The light can be advanced substantially parallel to the gain region 1 and guided to the entrance of the gain region 1, the adjustment function like a lens can be canceled, light can be condensed easily, and stable amplified light with high gain can be obtained.

Fourth Embodiment Next, FIG. 5 shows a fourth embodiment.
FIG. 3 is a schematic configuration diagram showing a semiconductor optical amplifier according to the present invention. In the semiconductor optical amplifier according to the fourth embodiment shown in FIG.
The third embodiment differs from the third embodiment shown in FIG. 2 in that the gain region 1 is extended from the end of the amplifier to the outside and the extended portion 1a is replaced with the waveguide 8.

Therefore, according to the fourth embodiment, the gain region 1 is sandwiched by the wedge-shaped condensing means 7a and 7b having a higher refractive index than the gain region 1 above and below the gain region 1. Light 5 from the outside can be made incident from the upper and lower parts of the gain region 1, and the light can be collected easily.
Stable amplified light with high gain can be obtained.

Embodiment 5 Next, FIG. 6 shows a fifth embodiment.
FIG. 3 is a schematic configuration diagram showing a semiconductor optical amplifier according to the present invention. The semiconductor optical amplifier according to the fifth embodiment shown in FIG. 6 is provided with a tapered light guide 9 as a light converging means, which has an entrance opening expanded and guides light 5 incident from the outside to the gain region 1. Tena,
The light guide 9 is provided inside the amplifier so that the expanded entrance is aligned with the end of the amplifier.

Therefore, according to the fifth embodiment, by providing the tapered light guide 9 having the entrance opening expanded to guide the light 5 incident from the outside to the gain region 1, the light from the outside is prevented. Since a large area for collecting light can be taken, the light can be collected easily, and the light entrance of the light guide 9 is matched with the end of the amplifier to be incorporated in the amplifier to form an integrated element. Can be easier.

Embodiment 6 FIG. Next, FIG. 7 shows a sixth embodiment.
FIG. 3 is a schematic configuration diagram showing a semiconductor optical amplifier according to the present invention. In the semiconductor optical amplifier according to the sixth embodiment shown in FIG.
The fifth embodiment differs from the fifth embodiment shown in FIG. 7 in that the light guide 9 is provided at a position outside the front end of the amplifier.

Therefore, according to the sixth embodiment, since the light guide 9 is provided on the outside to guide the light 5 from the outside to the gain region 1 and amplify the light, the integrated device shown in FIG. Also makes its production easier.

Embodiment 7 Next, FIG. 8 shows a seventh embodiment.
FIG. 3 is a schematic configuration diagram showing a semiconductor optical amplifier according to the present invention. In the semiconductor optical amplifier according to the seventh embodiment shown in FIG. 8, in comparison with the semiconductor optical amplifier according to the first embodiment shown in FIG.
The non-output side end portion of the amplifier is provided with the total reflection coating film 10, the output side end portion is provided with the coating film 11 having a predetermined reflectance, and is attached to the outside of the amplifier and is constituted by the coating films 10 and 11 described above. The temperature controller 12 is further provided to adjust the length of the resonator so that the light incident on the gain region 1 resonates.

From the left side of FIG. 8, the light 5 from the outside which is incident on the wedge-shaped condensing means 7 having a higher refractive index than the gain region 1 is:
Since the light enters the interface with the gain region 1 at a critical angle or less, the light travels along the interface and enters the gain region 1. At this time, the temperature of the amplifier is changed by using the temperature controller 12 attached to the outside of the amplifier, and the length of the resonator formed by the coating films 10 and 11 causes the light incident on the gain region 1 to resonate. By making adjustments in this way, a standing wave is created and laser oscillation is generated. By doing so, it corresponds to the amplification of the light from the outside, and even if the intensity of the incident light is weak, oscillation is possible.

That is, according to the seventh embodiment, the FP
(Fabry-Perot) Resonator type semiconductor optical amplifier is configured, and in each of the above-described embodiments, a traveling wave type semiconductor optical amplifier is configured, and light from the outside is transmitted through the gain region 1 only once. On the other hand, the light is repeatedly amplified in the gain region 1. Then, at that time, if the resonator length is not a half-wavelength, the light is extinguished by interference, but if it is a half-wavelength, the light becomes strong due to resonance. Therefore, in order to cause the resonance by doubling the resonator length by half wavelength, the temperature of the semiconductor optical amplifier is adjusted by the temperature controller 12 to control the resonator length, so that the resonator length is multiplied by half wavelength of light. ,
A high amplification factor can be obtained.

Embodiment 8 FIG. Next, FIG. 9 shows an eighth embodiment.
FIG. 3 is a schematic configuration diagram showing a semiconductor optical amplifier according to the present invention. In the semiconductor optical amplifier according to the eighth embodiment shown in FIG. 9, the semiconductor optical amplifier according to the second embodiment shown in FIG.
That is, the side surface of the wedge-shaped condensing means 7 is brought into contact with the entrance of the gain region 1 of the amplifier end face and the upper part thereof, and external light 5 incident on the slope is bounded with the gain region 1. For a semiconductor optical amplifier which is designed to be incident at a critical angle or less, a total reflection coating film 10 is applied to the non-output side end of the amplifier, and a coating film 11 having a predetermined reflectance is applied to the output side end. In addition, a temperature controller 12 which is attached to the outside of the amplifier and adjusts the length of the resonator constituted by the coating films 10 and 11 so that the light incident on the gain region 1 resonates is further provided.

Therefore, according to the eighth embodiment, similarly to the second embodiment, the light 5 from the outside can be made to travel along the wedge-shaped bottom surface, and the gain region 1 at the exit portion thereof can be made incident. The light can be focused on the mouth, and similarly to the seventh embodiment, a resonator type semiconductor optical amplifier is configured to repeatedly amplify light in the gain region 1. At that time, the temperature of the semiconductor optical amplifier is adjusted by the temperature controller 12 to control the resonator length, so that the resonator length can be half the wavelength of light and a high amplification factor can be obtained.

Embodiment 9 Next, FIG. 10 is a schematic configuration diagram showing a semiconductor optical amplifier according to the ninth embodiment. FIG.
In the semiconductor optical amplifier according to the ninth embodiment shown in FIG. 0, the reflection type diffraction grating 13 is used as the light collecting means to collect the light 5 incident from the outside in the gain region 1.

Therefore, the light 5 from the outside is condensed by the reflection type diffraction grating 13 having a condensing function, guided to the gain region 1 and amplified to become the output light 6. At that time, by using the reflection type diffraction grating 13 having a condensing function as the condensing means, its handling becomes easy, and the focal length can be adjusted by changing the inter-grating interval.
The focal point can be changed.

Embodiment 10 FIG. Next, FIG. 11 is a schematic configuration diagram showing a semiconductor optical amplifier according to the tenth embodiment.
In the semiconductor optical amplifier according to the tenth embodiment shown in FIG. 11, a light collecting mirror 14 is used as a light collecting means to collect the light 5 incident from the outside in the gain region 1.

Therefore, the light 5 from the outside is condensed by the condenser mirror 14 having a condensing function, guided to the gain region 1 and amplified to become the output light 6. At that time, by using the condensing mirror 14 having a condensing function as the condensing means, it is easy to handle, and the focal length can be adjusted by changing the curvature of the mirror. Can be changed.

As described above, according to the present invention, since the light condensing means for guiding the light from the outside to the gain region is provided, the optical axis adjustment for guiding the light to the gain region becomes easy and the gain is high. Stable amplified light can be obtained.

Since the light collecting means is made of a medium having a refractive index higher than that of the gain region and has a wedge shape,
Light from the outside may be condensed on a wedge-shaped slope having a larger area than the entrance of the gain region, and the region to be condensed can be enlarged and can be condensed in the vertical direction, facilitating the condensing. Further, even if the incident angle is large, the light can be made to enter the gain region almost in parallel, a margin can be created in the incident angle, and the incident light can be narrowed down to the medium surface having a large refractive index. Adjustment becomes easy, and stable, amplified light with high gain can be obtained.

Further, as a wedge-shaped condensing means, the bottom surface is contacted so as to be disposed above the gain region to form a boundary surface with the gain region, and light from the outside which is incident on the slope is brought into the gain region. By making the light incident on the boundary surface at a critical angle or less, the light travels along the boundary surface and is incident on the gain region without undergoing total internal reflection, so the bottom surface serves as the boundary surface and the gain region extends along the boundary surface. Since the light is made incident, the area where the light should be collected can be made large, and the light can be collected easily.

Further, as a wedge-shaped light collecting means, the side surface is brought into contact with the entrance of the gain region of the amplifier end face and the upper part thereof, and the light from the outside incident on the slope is brought to the boundary surface with the gain region. Since it is configured to be incident at a critical angle or less, it is possible to allow light from the outside to travel along the bottom surface of the wedge shape and to focus it on the gain region at the exit portion, so that the incidence of light from the outside It will be easy.

Further, a total reflection coating film is applied to the non-output side end portion of the amplifier, a coating film of a predetermined reflectance is applied to the output side end portion, and the resonance is formed by the coating film attached outside the amplifier. By further providing a temperature controller that adjusts the length of the resonator so that the light incident on the gain region resonates, a resonator-type semiconductor optical amplifier can be configured, and light can be repeatedly amplified within the gain region. In addition, the temperature of the semiconductor optical amplifier is adjusted by the temperature controller to control the resonator length, so that the resonator length can be half the wavelength of light and a high amplification factor can be obtained.

Further, the light collecting means is provided with a waveguide which is in contact with the entrance of the gain region of the amplifier end face and is provided along the extension line of the gain region, and has a refractive index higher than that of the waveguide. The bottom of each of the waveguides is brought into contact with the bottom to sandwich the waveguide, and the side of the gain region is brought into contact with each of the amplifier end faces of the upper and lower portions of the gain region, so that light from outside incident on the respective slopes can be received. Since a pair of wedge-shaped light converging means for making incident light at a critical angle or less are provided at the boundary surface with the gain region, a pair of high-refractive-index wedge-shaped light converging means are provided at the entrance of the gain region to form a waveguide having a low refractive index. By attaching a condenser with a configuration sandwiching between the two, it is possible to collect light with the same function as a lens, and allow external light to travel in parallel with the gain region near the bottom surface of the pair of wedge-shaped light converging means, thereby gain region Lens to the entrance of Can be adjusted function is canceled, such as,
Focusing becomes easy, and stable amplified light with high gain can be obtained.

Further, by extending the gain region to the outside from the end of the amplifier and replacing the extended portion with the above-mentioned waveguide, a pair of wedge-shaped focusing beams having a higher refractive index than the gain region in the upper and lower parts of the gain region. With the configuration in which the gain region is sandwiched by means, light from the outside can be made incident from the upper and lower parts of the gain region, light can be easily condensed, and stable amplified light with high gain can be obtained.

Further, the light collecting means is provided with a tapered light guide having an entrance opening expanded to guide the light incident from the outside to the gain region, so that the light from the outside should be condensed. Since a large area can be obtained, it is easy to collect light.

Further, the light guide is incorporated into the amplifier by aligning the widened entrance of the light guide with the end of the amplifier, so that an integrated device can be produced and its handling is easy. Can be one.

Further, by providing an optical guide at a position outside the front of the amplifier end and guiding light from the outside to the gain region and amplifying it, the manufacture becomes easier than the case of forming an integral type element.

Further, by using a reflection type diffraction grating having a light collecting function as the light collecting means, it is easy to handle, and the focal length can be adjusted by changing the inter-grating interval. The light spot can be changed.

Furthermore, by using a condensing mirror having a condensing function as the condensing means, it is easy to handle, and the focal length can be adjusted by changing the curvature of the mirror. You can change the points.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an outline of a semiconductor optical amplifier according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining a setting range of a tip angle (vertical angle) ψ of the top of the wedge-shaped light converging unit in FIG.

FIG. 3 is a configuration diagram showing an outline of a semiconductor optical amplifier according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram showing an outline of a semiconductor optical amplifier according to a third embodiment of the present invention.

FIG. 5 is a configuration diagram showing an outline of a semiconductor optical amplifier according to a fourth embodiment of the present invention.

FIG. 6 is a configuration diagram showing an outline of a semiconductor optical amplifier according to a fifth embodiment of the present invention.

FIG. 7 is a configuration diagram showing an outline of a semiconductor optical amplifier according to a sixth embodiment of the present invention.

FIG. 8 is a configuration diagram showing an outline of a semiconductor optical amplifier according to a seventh embodiment of the present invention.

FIG. 9 is a configuration diagram showing an outline of a semiconductor optical amplifier according to an eighth embodiment of the present invention.

FIG. 10 is a configuration diagram showing an outline of a semiconductor optical amplifier according to a ninth embodiment of the present invention.

FIG. 11 is a configuration diagram showing an outline of a semiconductor optical amplifier according to a tenth embodiment of the present invention.

FIG. 12 is a schematic diagram showing a schematic configuration of a semiconductor optical amplifier according to a conventional example.

[Explanation of symbols]

1 gain region, 1a extension of gain region, 5 external light for amplification, 6 amplified output light, 7, 7a,
7b wedge-shaped light condensing means, 8 waveguide, 9 light guide, 10 total reflection coating film, 11 coating film having predetermined reflectance, 12 temperature controller, 1
3 reflection type diffraction grating, 14 condensing mirror.

Claims (12)

[Claims] 1. A semiconductor optical amplifier having a gain region for amplifying and outputting light incident from the outside, the semiconductor light amplifier comprising a condensing means for guiding the light from the outside to the gain region. amplifier. 2. The light condensing means is made of a medium having a refractive index larger than that of the gain region, and has a wedge shape for guiding light from the outside incident from a slope to the gain region. 1. The semiconductor optical amplifier according to 1. 3. The light condensing means has a bottom surface which is in contact with the gain region so as to be disposed above the gain region, and serves as a boundary face with the gain region, and external light incident on the slope is bounded with the gain region. 3. The semiconductor optical amplifier according to claim 2, wherein the light is incident on the surface at a critical angle or less. 4. The light converging means has a side surface in contact with an entrance of a gain region of an amplifier end face and an upper part thereof, so that light incident from the outside on a slanted surface has a critical angle at a boundary face with the gain region. 3. The semiconductor optical amplifier according to claim 2, wherein the light is made incident below. 5. A resonance formed by applying a total reflection coating film to a non-output side end portion of an amplifier and a coating film having a predetermined reflectance to an output side end portion and being attached to the outside of the amplifier and formed by the coating film. 5. The semiconductor optical amplifier according to claim 1, further comprising a temperature controller that adjusts the length of the container so that the light incident on the gain region resonates. 6. The condensing means further comprises a waveguide which is in contact with an entrance of a gain region of an amplifier end face and is provided along an extension line of the gain region, and has a refractive index higher than that of the waveguide. The waveguide has upper and lower portions in contact with the bottom portions so as to sandwich the waveguide and has side surfaces in contact with the upper and lower amplifier end surfaces of the gain region, respectively. 3. The semiconductor optical amplifier according to claim 2, further comprising a pair of wedge-shaped media which are incident on the boundary surface with the gain region at a critical angle or less. 7. The waveguide as defined in claim 6, wherein the gain region is extended from the end of the amplifier to the outside.
The semiconductor optical amplifier described. 8. The semiconductor light according to claim 1, wherein the light converging means is a tapered light guide having an entrance opening expanded to guide light incident from the outside to the gain region. amplifier. 9. The semiconductor optical amplifier according to claim 8, wherein the light guide is provided inside the amplifier with the widened incident opening aligned with the end of the amplifier. 10. The semiconductor optical amplifier according to claim 8, wherein the light guide is provided at a position outside and outside the end of the amplifier. 11. The semiconductor optical amplifier according to claim 1, wherein the condensing means is a reflection type diffraction grating that condenses light incident from the outside into the gain region. 12. The semiconductor optical amplifier according to claim 1, wherein the condensing means is a condensing mirror for condensing light incident from the outside into the gain region.