JP2005236254A - Semiconductor optical amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor optical amplifier capable of suppressing gain variations due to input luminous intensity without causing oscillation light mixed in the guide direction of signal light. <P>SOLUTION: Stimulation is caused in a direction orthogonal to the guide direction of the signal light by embedding n-GaInAsP current block layers 504 to both sides of a GaInAsP active layer 502 formed on an n-InP substrate 501 and forming n-InP embedded layers 510 arranged in a direction orthogonal to the GaInAsP active layers 502 at a prescribed interval to the n-GaInAsP current block layers 504. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a semiconductor optical amplifier, and in particular, is suitable for application to an optical transmission system using wavelength division multiplexing (WDM).

2. Description of the Related Art Conventionally, as an optical transmission system that transmits a plurality of optical signals having different wavelengths, there is an optical transmission system (WDM system) that uses wavelength multiplexing to transmit a plurality of optical signals having different wavelengths by combining them with one optical fiber. .
In this WDM system, a WDM multiplexing / demultiplexing circuit that merges and branches optical signals according to wavelength, a multiplexing / branching circuit that merges and branches light of all wavelengths at once, and an add / drop that extracts or inserts a specific wavelength An optical element such as a multiplexer (Add-drop multiplexer, ADM) is used, and the signal strength is deteriorated due to an intensity loss caused when an optical signal passes through these optical elements.

For this reason, in a WDM system, an optical amplifying element that amplifies an optical signal transmitted through an optical fiber as light is indispensable.
7A is a cross-sectional view of a conventional semiconductor optical amplifier cut along the optical waveguide direction, FIG. 7B is a cross-sectional view taken along the line AA ′ of FIG. As an example of a conventional semiconductor optical amplifier (SOA), a structure using an n-InP substrate 101 is shown.

In FIG. 7, a GaInAsP active layer 102 that is a gain medium is formed in a stripe shape on an n-InP substrate 101, and the GaInAsP active layer 102 is embedded by a p-InP layer 103 and an n-InP layer 104. .
A p-InP layer 105 is formed on the GaInAsP active layer 102 and the n-InP layer 104, and a p-GaInAs contact layer 106 is formed on the p-InP layer 105. A p-side electrode 107 is formed on the p-GaInAs contact layer 106, and an n-side electrode 108 is formed on the back surface of the n-InP substrate 101.

FIG. 8 is a diagram showing saturation characteristics of the semiconductor optical amplifier of FIG.
In FIG. 8, when the input light intensity is small, the gain is almost constant even when the input light intensity increases. However, when the input light intensity exceeds a certain value, the gain decreases rapidly. Here, in the WDM system, a wavelength multiplexed signal is incident as an optical signal, and the number of wavelength multiplexed signals varies every time it passes through an add drop multiplexer or the like.

It is assumed that an optical signal having a wavelength multiplexing number m is incident on the semiconductor optical amplifier. In this case, when the incident light intensity of the semiconductor optical amplifier is P ₁ (dBm) in the total of m waves, the gain of the semiconductor optical amplifier is G ₁ (dBm).
Here, it is assumed that an optical signal is added by the add / drop multiplexer and the wavelength multiplexing number is increased to n. In this case, when the incident light intensity of the semiconductor optical amplifier is P ₂ (dBm) in total for n waves, the gain of the semiconductor optical amplifier is G ₂ (dB).

  As described above, when the semiconductor optical amplifier of FIG. 4 is used in a WDM system, the incident light intensity varies depending on the number of wavelength multiplexing, and thus the gain of the optical signal varies. For this reason, in the conventional optical amplifier, as disclosed in Patent Document 1, in order to prevent the gain of the optical signal from fluctuating due to the number of wavelength multiplexing, the gain is set to a certain value by using the oscillation action. Some used a clamping method.

9A is a cross-sectional view of a conventional semiconductor optical amplifier cut along the optical waveguide direction, and FIG. 9B is a cross-sectional view taken along the line CC ′ of FIG. 9A.
In FIG. 9, a GaInAsP active layer 202 that is a gain medium is formed in a stripe shape on an n-InP substrate 201, and the GaInAsP active layer 202 is embedded by a p-InP layer 203 and an n-InP layer 204. .

  Here, a GaInAsP isolation and confinement (SCH) layer 209 is formed on the lower surface of the GaInAsP active layer 202, and a GaInAsP isolation and confinement (SCH) layer 210 is formed on the upper surface of the GaInAsP active layer 202. A grating is formed on the layer 210. A p-InP layer 205 is formed on the GaInAsP separation confinement layer 210 and the n-InP layer 204, and a p-GaInAs contact layer 206 is formed on the p-InP layer 205. A p-side electrode 207 is formed on the p-GaInAs contact layer 206, and an n-side electrode 208 is formed on the back surface of the n-InP substrate 201.

In the semiconductor optical amplifier of FIG. 9, since an optical signal is reflected by the grating formed in the GaInAsP separation confinement layer 210, positive feedback is applied and oscillation can be performed like a DFB laser. However, the coupling coefficient of the grating is smaller than that of a normal DFB laser, and the oscillation threshold is high.
In the laser oscillation state of the semiconductor optical amplifier of FIG. 9, the carrier density in the gain medium is clamped to a constant value. However, since the oscillation threshold is high, the carrier density is clamped to a value higher than that of a normal DFB laser. .

For this reason, in the DFB type semiconductor optical amplifier having the grating of FIG. 8, as long as oscillation occurs, the carrier density of the gain medium (GaInAsP active layer 202) is constant, and the gain is proportional to the carrier density of the gain medium. The gain can be clamped to a constant value.
Therefore, in the oscillation state described above, even if the current value injected into the semiconductor optical amplifier is increased, the gain of the semiconductor optical amplifier can be kept constant only by increasing the light intensity of the oscillation light. When the input signal light intensity increases, the oscillation light intensity decreases and the total light intensity inside the semiconductor optical amplifier is kept constant, so that the carrier density of the semiconductor optical amplifier may vary. Therefore, the gain of the semiconductor optical amplifier can be kept constant.

FIG. 10 is a diagram showing saturation characteristics of the semiconductor optical amplifier of FIG.
10, in the semiconductor optical amplifier of FIG. 9, even if the input light intensity of signal light incident from the outside fluctuates, the gain is maintained at a constant value Go. That is, even when the wavelength multiplexing number of the signal light is changed from m to n and the total input power is changed from P ₁ to P ₂ , the gain is a constant value of Go.
Further, in the semiconductor optical amplifier of FIG. 9, the gain decreases only when the intensity of incident light from the outside further increases and the oscillation is suppressed. On the contrary, as long as oscillation occurs in the semiconductor optical amplifier of FIG. 9, the gain can be kept constant regardless of the incident light intensity or the number of multiplexed wavelengths of the incident signal.

In Patent Document 2, gain regions are inserted into two arm waveguides of a symmetric Mach-Zehnder interferometer, light reflecting means is provided at an input port serving as a cross port of the symmetric Mach-Zehnder interferometer. An optical amplifying device in which a laser resonator is constituted by a reflecting means is disclosed. In this optical amplifying device, signal light is input from the port to which the light reflecting means is connected. The input signal light is amplified in the gain region where the signal gain is clamped to the laser oscillation threshold state. The amplified signal light is separated from the laser oscillation light and output from different ports.
JP-A-7-106714 JP 2000-12978 A

However, when the DFB type semiconductor optical amplifier of FIG. 9 is used, the oscillation light is mixed in the same optical path as the signal light, so that there is a problem that a wavelength filter for removing the mixed oscillation light is necessary.
Furthermore, since the DFB semiconductor optical amplifier of FIG. 9 has a very strong oscillation light intensity, if the incident signal intensity is small, the oscillation light can be emitted with the same intensity as the signal light even when a normal wavelength filter is used. There was a problem of remaining.
Further, the method disclosed in Patent Document 2 has a problem that it is necessary to provide an optical waveguide or the like for separating amplified signal light and laser oscillation light, which increases the element size.
Accordingly, an object of the present invention is to provide a semiconductor optical amplifier capable of suppressing gain fluctuations due to input light intensity without mixing oscillating light in the waveguide direction of signal light.

In order to solve the above-described problem, according to a semiconductor optical amplifier according to claim 1, an optical waveguide that is formed on a substrate and that amplifies signal light is disposed so as to intersect the optical waveguide, and is disposed on the substrate. And a resonance part that oscillates in a horizontal direction.
As a result, the gain of the optical waveguide can be clamped by the oscillating action at the resonance portion while allowing the oscillation light to be guided in a direction different from the direction in which the signal light is guided. For this reason, it is possible to amplify the input signal light in the gain medium whose gain is clamped by oscillation while preventing the oscillation light from being mixed into the amplified light emitted from the optical waveguide. As a result, it is possible to eliminate the need for a wavelength filter or an optical waveguide for separating the signal light and the oscillation light, and it is possible to suppress a gain variation due to the input light intensity while suppressing an increase in element size.

According to another aspect of the semiconductor optical amplifier of the present invention, the optical waveguide is formed on the substrate and amplifies the signal light, and is arranged so as to intersect the optical waveguide, and oscillates in a direction horizontal to the substrate. And an active region formed on the substrate and arranged in parallel with the optical waveguide.
Accordingly, it is possible to control the threshold current density of oscillation generated in the resonance portion while allowing the oscillation light to be guided in a direction different from the waveguide direction of the signal light. Therefore, it is possible to control the carrier density of the optical waveguide while causing oscillation in the resonance part, and it is possible to clamp the gain of the optical waveguide while allowing the gain of the optical waveguide to be controlled. Therefore, it is possible to amplify the input signal light to a desired value within the gain medium whose gain is clamped by oscillation while preventing the oscillation light from being mixed into the amplified light emitted from the optical waveguide. . As a result, while making it possible to adjust the gain, it is possible to suppress fluctuations in gain due to the input light intensity, and it is possible to suppress an increase in element size, thereby suppressing an increase in the size of the wavelength multiplexing optical transmission system. It becomes possible to do.

According to another aspect of the semiconductor optical amplifier of the present invention, the active region is separated into a plurality of regions where current can be injected independently.
As a result, the gain can be varied according to the portion of the optical waveguide, and fine gain adjustment can be performed.
According to another aspect of the semiconductor optical amplifier of the present invention, the separated regions have different volumes.
This makes it possible to vary the current value injected into the active region according to the portion of the optical waveguide, and fine gain adjustment can be performed by injecting current into the active region.

According to another aspect of the semiconductor optical amplifier of the present invention, the active region includes an absorption region configured to prevent current from being injected into an end portion along the optical waveguide direction of the signal light. .
As a result, it is possible to prevent the active region from oscillating in a direction parallel to the waveguide direction of the signal light before oscillating in the direction orthogonal to the waveguide direction of the signal light to be originally oscillated. It is possible to effectively assist the gain in the direction orthogonal to the waveguide direction.

According to another aspect of the semiconductor optical amplifier of the present invention, the resonating unit includes current blocking layers disposed on both sides of the optical waveguide.
As a result, it is possible to cause oscillation in a direction perpendicular to the waveguide direction of the signal light while allowing the current injected into the optical waveguide to be blocked by the current blocking layer. For this reason, it is possible to clamp the gain of the optical waveguide while efficiently injecting current into the optical waveguide, and to prevent the oscillation light from being mixed into the amplified light emitted from the optical waveguide. It is possible to keep the gain of the semiconductor optical amplifier constant while suppressing the increase in element size.

According to another aspect of the semiconductor optical amplifier of the present invention, the current blocking layer has a laminated structure in which a layer having a high refractive index is sandwiched between layers having a low refractive index.
Thereby, it becomes possible to form a slab waveguide in a direction orthogonal to the waveguide direction of the signal light, and to suppress a waveguide loss in a direction orthogonal to the waveguide direction of the signal light. Therefore, it is possible to easily cause oscillation in the direction orthogonal to the waveguide direction of the signal light while preventing the oscillation light from being mixed into the amplified light emitted from the optical waveguide, thereby increasing the element size. The gain of the semiconductor optical amplifier can be kept constant while suppressing.

The semiconductor optical amplifier according to claim 8, wherein the optical waveguide includes an active layer formed on the substrate and a clad layer formed on the active layer, and is provided in the current blocking layer. The band gap of the high refractive index layer is larger than the band gap of the active layer.
This makes it possible to suppress the absorption loss when light is guided through the current blocking layer, compared with the case where light is guided through the active layer, and the absorption loss in the direction orthogonal to the signal light guiding direction. Can be suppressed. Therefore, it is possible to easily cause oscillation in the direction orthogonal to the waveguide direction of the signal light while preventing the oscillation light from being mixed into the amplified light emitted from the optical waveguide, thereby increasing the element size. While suppressing, it becomes possible to keep the gain of the semiconductor optical amplifier constant, and it is possible to suppress an increase in element size.

According to another aspect of the semiconductor optical amplifier of the present invention, the current blocking layer includes a diffraction grating that reflects light in a direction orthogonal to the optical waveguide.
This makes it possible to reflect light in a direction orthogonal to the waveguide direction of the signal light without forming a highly reflective film on the resonance part after the element is cut out, while suppressing complication of the manufacturing process. Oscillation can be caused in a direction orthogonal to the light guiding direction.

According to another aspect of the semiconductor optical amplifier of the present invention, the diffraction grating includes a buried layer that is arranged in a direction orthogonal to the optical waveguide and has a refractive index different from that of the current blocking layer having a high refractive index. It is characterized by.
As a result, a diffraction grating can be formed in the current blocking layer by using photolithography technology and etching processing technology, and the gain of the semiconductor optical amplifier can be kept constant while suppressing the complexity of the manufacturing process. It becomes possible, and an increase in element size can be suppressed.

The semiconductor optical amplifier according to claim 11 is formed on an optical waveguide formed on a substrate and provided with an active layer for amplifying signal light, and an active layer continuing from the optical waveguide, And a diffraction grating that reflects light so as to be orthogonal to the waveguide.
Thereby, a gain can be given to the region where the diffraction grating is formed, and oscillation can be easily caused in a direction different from the waveguide direction of the signal light. For this reason, even when the signal light intensity fluctuates due to changes in the number of multiplexed signal lights, the carrier density of the active layer can be kept constant, and the gain of the semiconductor optical amplifier can be clamped to a constant value. It becomes possible.

According to another aspect of the semiconductor optical amplifier of the present invention, an optical waveguide formed on the substrate for amplifying signal light, an active region formed on the substrate and arranged in parallel with the optical waveguide, And a diffraction grating which is formed in the active region and reflects light so as to intersect the optical waveguide.
Thereby, a gain can be given to the region where the diffraction grating is formed, and oscillation can be easily caused in a direction different from the waveguide direction of the signal light. For this reason, even when the signal light intensity fluctuates due to changes in the number of multiplexed signal lights, the carrier density of the active layer can be kept constant, and the gain of the semiconductor optical amplifier can be clamped to a constant value. It becomes possible.

The semiconductor optical amplifier according to claim 13 further includes a current blocking layer formed on the substrate and separating the optical waveguide and the active region.
Thereby, current injection into the optical waveguide and current injection into the active region where the diffraction grating is formed can be controlled separately. Therefore, the carrier density of the optical waveguide can be controlled with high accuracy, and the gain control of the signal light can be performed with high accuracy.
The semiconductor optical amplifier according to claim 14 is characterized in that a coupling coefficient of the diffraction grating is 100 cm ⁻¹ or more.
Thereby, the reflectance of the diffraction grating can be increased, and even when the width of the optical waveguide is narrow, it is possible to cause oscillation in a direction orthogonal to the waveguide direction of the signal light.

  As described above, according to the present invention, by arranging the resonance portion so as to intersect the optical waveguide, it is possible to prevent the oscillation light from being mixed into the amplified light emitted from the optical waveguide, and to gain by the oscillation. It is possible to amplify the input signal light within the gain medium in which is clamped. For this reason, a wavelength filter or an optical waveguide for separating the signal light and the oscillation light can be dispensed with, and the gain fluctuation due to the input light intensity can be suppressed while suppressing an increase in the element size.

Hereinafter, a semiconductor optical amplifier according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a perspective view showing a schematic configuration of the semiconductor optical amplifier according to the first embodiment of the present invention.
In FIG. 1, a GaInAsP active layer 502 is formed in a stripe shape on an n-InP substrate 501. Both sides of the GaInAsP active layer 502 are embedded with a p-InP current blocking layer 503 and an n-GaInAsP current blocking layer 504 that are sequentially stacked on the n-InP substrate 501. The band gap wavelength of the n-GaInAsP current blocking layer 504 is shorter than the band gap wavelength of the GaInAsP active layer 502, that is, the band gap of the n-GaInAsP current blocking layer 504 is larger than the band gap of the GaInAsP active layer 502. It is preferable to set so.

Here, by forming the GaInAsP active layer 502 between the n-InP substrate 501 and the p-InP cladding layer 505, an optical waveguide for amplifying signal light can be configured. Further, by embedding both sides of the GaInAsP active layer 502 with the p-InP current blocking layer 503 and the n-GaInAsP current blocking layer 504, a buried heterostructure can be formed.
Here, the n-GaInAsP current blocking layer 504 is formed with a diffraction grating that reflects light in a direction orthogonal to the GaInAsP active layer 502. In other words, the n-GaInAsP current blocking layer 504 is formed with n-InP buried layers 510 arranged at predetermined intervals in a direction orthogonal to the GaInAsP active layer 502.

  A p-InP clad layer 505 is formed on the GaInAsP active layer 502 and the n-GaInAsP current blocking layer 504, and a p-GaInAs contact layer 506 is formed on the p-InP clad layer 505. A p-side electrode 507 is formed on the p-GaInAs contact layer 506, and an n-side electrode 508 is formed on the back surface of the n-InP substrate 501. Here, the p-side electrode 507 is patterned corresponding to the shape of the GaInAsP active layer 502, and a bonding pad 507 a is connected to the p-side electrode 507. An insulating film 509 such as a silicon oxide film is formed on the p-GaInAs contact layer 506 so that the p-side electrode 507 and the bonding pad 507a are exposed. Further, antireflection films (AR coating) are applied to both end faces of the optical waveguide provided with the GaInAsP active layer 502.

  In the case where the GaInAsP active layer 502, the p-InP current blocking layer 503, the n-GaInAsP current blocking layer 504, the p-InP cladding layer 505, and the p-GaInAs contact layer 506 are formed on the n-InP substrate 501, for example, Epitaxial growth such as MBE (Molecular Beam Epitaxy), MOCVD (Metal Organic Chemical Vapor Deposition), or ALCVD (Atomic Layer Chemical Vapor Deposition) can be used.

  Then, by applying a voltage to the p-side electrode 507, current can be injected into the GaInAsP active layer 502 while constricting the current in the n-GaInAsP current blocking layer 504. When a current is injected into the GaInAsP active layer 502, the GaInAsP active layer 502 can emit light. The light generated in the GaInAsP active layer 502 is reflected by the n-GaInAsP current blocking layers 504 on both sides of the GaInAsP active layer 502, and can cause laser oscillation in a direction orthogonal to the GaInAsP active layer 502. . When laser oscillation occurs in a direction perpendicular to the GaInAsP active layer 502, the carrier density of the GaInAsP active layer 502 can be kept constant even when the signal light intensity incident on the GaInAsP active layer 502 varies, The gain of the semiconductor optical amplifier can be clamped to a constant value.

When the signal light is incident on the GaInAsP active layer 502, the signal light is amplified while being guided through the GaInAsP active layer 502, and the amplified light can be emitted from the side opposite to the signal light incident surface.
As a result, the gain of the GaInAsP active layer 502 can be clamped while enabling oscillation in a direction different from the direction in which the signal light is guided. Therefore, it is possible to amplify the input signal light in the GaInAsP active layer 502 whose gain is clamped while preventing oscillation light from being mixed into the amplified light emitted from the GaInAsP active layer 502. As a result, it is possible to eliminate the need for a wavelength filter or an optical waveguide for separating the signal light and the oscillation light, and it is possible to suppress a gain variation due to the input light intensity while suppressing an increase in element size.

  Here, the n-GaInAsP current blocking layer 504 has a higher refractive index than the p-InP current blocking layer 503 and the p-InP cladding layer 505. Therefore, by sandwiching the n-GaInAsP current blocking layer 504 between the p-InP current blocking layer 503 and the p-InP cladding layer 505, the n-GaInAsP current blocking layer 504 is used as a core layer, and the p-InP current blocking layer is formed. Slab waveguides having the layer 503 and the p-InP clad layer 505 as clad layers can be formed on both sides of the GaInAsP active layer 502.

For this reason, it becomes possible to suppress the waveguide loss in the n-GaInAsP current blocking layer 504, and to reduce the waveguide loss in the direction orthogonal to the waveguide direction of the signal light. Oscillation can be easily caused in a direction orthogonal to the direction.
Further, by setting the band gap of the n-GaInAsP current blocking layer 504 to be larger than the band gap of the GaInAsP active layer 502, absorption loss when light is guided through the n-GaInAsP current blocking layer 504 is suppressed. It becomes possible. For this reason, the absorption loss in the direction orthogonal to the signal light guiding direction can be suppressed, and oscillation can be easily caused in the direction orthogonal to the signal light guiding direction.

  Further, by providing a diffraction grating that reflects light in a direction orthogonal to the waveguide direction of signal light in the n-GaInAsP current blocking layer 504, a highly reflective film is formed in the n-GaInAsP current blocking layer 504 after the element is cut out. Therefore, the light can be reflected in the direction orthogonal to the signal light guiding direction, and the oscillation can be caused in the direction orthogonal to the signal light guiding direction while suppressing the complexity of the manufacturing process. It becomes possible.

  Here, n-InP buried layers 510 arranged at a predetermined interval in a direction orthogonal to the GaInAsP active layer 502 are formed in the n-GaInAsP current blocking layer 504, so that the n-InP buried layer 510 is formed using photolithography technology and etching processing technology. It becomes possible to form a diffraction grating in the -GaInAsP current blocking layer 504, and to oscillate in a direction perpendicular to the waveguide direction of the signal light while suppressing complication of the manufacturing process.

  When oscillation is performed in the direction orthogonal to the signal light guiding direction, if the width of the GaInAsP active layer 502 is narrow, the gain in the direction orthogonal to the signal light guiding direction decreases, and the signal light Oscillation in the direction orthogonal to the waveguide direction is less likely to occur. For this reason, it is necessary to increase the reflectance of the diffraction grating formed in the n-GaInAsP current blocking layer 504, and the difference in refractive index between the concave portion and the convex portion of the diffraction grating is increased or the depth of the diffraction grating is increased. Is preferred.

FIG. 2 is a diagram showing the relationship of the reflectance with respect to the normalized coupling coefficient of the semiconductor optical amplifier of FIG. FIG. 2 shows the Bragg wavelength reflectivity R at which the reflectivity is highest with respect to the normalized coupling coefficient, assuming that the diffraction grating is lossless. However, the normalized coupling coefficient represents the product of the coupling coefficient κ and the diffraction grating length L.
In FIG. 2, when the normalized coupling coefficient of the diffraction grating is about 1.0, a reflectance R of about 58% can be obtained. Further, if the normalized coupling coefficient of the diffraction grating is about 1.5, a reflectance R of 80% or more can be obtained. Furthermore, when a reflectance R of 90% or more is required, the normalized coupling coefficient of the diffraction grating may be set to about 1.8. When the reflectance R is 99% or more, the normalized coupling coefficient of the diffraction grating needs to be 3 or more.

On the other hand, in the configuration of FIG. 1, the resonance direction is a direction orthogonal to the waveguide direction of the signal light, so that almost half of the lateral width of the device is the diffraction grating length L. The calculation result in FIG. 2 is based on the assumption that there is no loss. However, since there is a loss in an actual device, the reflectance is lower than the calculation result. Accordingly, the diffraction grating length L is preferably shorter. For example, when the diffraction grating length L is 150 μm and the reflectance R is 80% or more, that is, when the normalized coupling coefficient is about 1.5, a coupling coefficient of 100 cm ⁻¹ or more is required. Further, when it is desired to set the diffraction grating length L to 150 μm and the reflectance R to be 99% or more, that is, when the normalized coupling coefficient is 3, a coupling coefficient of 200 cm ⁻¹ is required.

  The shape of the GaInAsP active layer 502 may be a bulk, MQW (multiple quantum well), quantum wire, quantum dot, or the like, and a separate confinement heterostructure (SCH) or the like in order to set the upper and lower confinement to a desired value. A gradient refractive index confinement structure (GRIN-SCH) in which the refractive index is gradually changed may be used. Further, the material is not limited to the combination of InP and GaInAsP, and other semiconductor materials such as GaAs, AlGaAs, GaInAs, GaInNAs, and AlGaAsP may be used.

However, since the absorption increases when the forbidden band width becomes smaller than the energy of the oscillation light, the forbidden band width of the semiconductor material used instead of the p-InP current blocking layer 503 and the n-GaInAsP current blocking layer 504 is GaInAsP activity. It is preferably larger than the forbidden band width of the semiconductor material used instead of the layer 502. Further, the refractive index of the semiconductor material used instead of the n-InP buried layer 510 needs to be different from the refractive index of the surrounding material.
In the above-described embodiments, the method of linearly forming the optical waveguide for amplifying the signal light has been described. However, a resonator structure may be formed on both sides of the bent waveguide.

FIG. 3 is a cross-sectional view showing another configuration example of the current blocking layer of the semiconductor optical amplifier of FIG.
In FIG. 3A, a p-InP current blocking layer a2 and an n-GaInAsP current blocking layer a3 are sequentially stacked on an n-InP substrate a1. In the n-GaInAsP current blocking layer a3, n-InP buried layers a11 arranged at a predetermined interval are formed. A p-InP contact layer a4 is formed on the n-GaInAsP current blocking layer a3 in which the n-InP buried layer a11 is buried. Note that a GaInAsP current blocking layer may be used instead of the p-InP current blocking layer a2.

  In FIG. 3B, a p-InP current blocking layer b2 and an n-GaInAsP current blocking layer b3 are sequentially stacked on the n-InP substrate b1. In the n-GaInAsP current blocking layer b3, n-InP buried layers b11 arranged at a predetermined interval are formed. A p-InP contact layer b4 is formed on the n-GaInAsP current blocking layer b3 in which the n-InP buried layer b11 is embedded. Note that a GaInAsP current blocking layer may be used instead of the p-InP current blocking layer b2.

An n-GaInAsP layer b3 ′ is inserted between the n-GaInAsP current blocking layer b3 and the p-InP contact layer b4. Thereby, the position and coupling coefficient of the diffraction grating can be easily adjusted, and the reflectance in the direction orthogonal to the waveguide direction of the signal light can be adjusted while suppressing the complexity of the manufacturing process. Note that a p-GaInAsP layer may be used instead of the n-GaInAsP layer b3 ′.
In addition, an n-InP layer may be used instead of the n-GaInAsP layer b3 ′, which makes it possible to easily adjust the current block characteristics. Note that a stacked structure of an n-GaInAsP layer and an n-InP layer may be used instead of the n-GaInAsP layer b3 ′.

  In FIG. 3C, a p-InP current blocking layer c2 and an n-GaInAsP current blocking layer c3 are sequentially stacked on the n-InP substrate c1. In the n-GaInAsP current blocking layer c3, n-InP buried layers c11 arranged at a predetermined interval are formed. A p-InP contact layer c4 is formed on the n-GaInAsP current blocking layer c3 in which the n-InP buried layer c11 is buried. Note that a GaInAsP current blocking layer may be used instead of the p-InP current blocking layer c2.

Also, a p-GaInAsP layer c2 ′ is inserted between the p-InP current blocking layer c2 and the n-GaInAsP current blocking layer c3. Thereby, the position and coupling coefficient of the diffraction grating can be easily adjusted, and the reflectance in the direction orthogonal to the waveguide direction of the signal light can be adjusted while suppressing the complexity of the manufacturing process.
In addition, an n-InP layer may be used instead of the p-GaInAsP layer c2 ′, thereby making it possible to easily adjust the current block characteristics. Note that the n-GaInAsP layer b3 ′ in FIG. 3B may be further inserted between the n-GaInAsP current blocking layer c3 and the p-InP contact layer c4 in FIG.

FIG. 4 is a perspective view showing a schematic configuration of a semiconductor optical amplifier according to the second embodiment of the present invention.
In FIG. 4, a GaInAsP active layer 802 is formed in a stripe shape on a n-InP substrate 801, and a GaInAsP active layer 811 arranged in parallel with the GaInAsP active layer 802 is formed. The sides of the GaInAsP active layers 802 and 811 are buried with a p-InP current blocking layer 803 and an n-GaInAsP current blocking layer 804 that are sequentially stacked on the n-InP substrate 801. Note that the band gap wavelength of the n-GaInAsP current blocking layer 804 is shorter than the band gap wavelength of the GaInAsP active layers 802 and 811, that is, the band gap of the n-GaInAsP current blocking layer 804 is the band gap of the GaInAsP active layers 802 and 811. It is preferable to set it to be larger.

  Here, by forming the GaInAsP active layer 802 between the n-InP substrate 801 and the p-InP cladding layer 805, an optical waveguide for amplifying signal light can be configured. Further, by embedding both sides of the GaInAsP active layer 802 with the p-InP current blocking layer 803 and the n-GaInAsP current blocking layer 804, a buried heterostructure can be configured.

  Here, in the n-GaInAsP current blocking layer 804 separated from each other via both the GaInAsP active layers 802 and 811, a diffraction grating that reflects light in a direction orthogonal to the GaInAsP active layer 802 is formed. That is, n-InP buried layers 810 arranged in a direction perpendicular to the GaInAsP active layer 802 are formed in the n-GaInAsP current blocking layer 804 separated from each other via both the GaInAsP active layers 802 and 811. Has been.

  A p-InP cladding layer 805 is formed on the GaInAsP active layers 802 and 811 and the n-GaInAsP current blocking layer 804, and p-GaInAs contact layers 806a and 806b are formed on the p-InP cladding layer 805. Has been. Here, the p-GaInAs contact layer 806 a is patterned corresponding to the shape of the GaInAsP active layer 802. Further, the p-GaInAs contact layer 806b is patterned corresponding to the shape of the GaInAsP active layer 811 so as not to reach the end of the GaInAsP active layer 811.

A signal optical waveguide electrode 807 is formed on the p-GaInAs contact layer 806a, and a bonding pad 807a is connected to the signal optical waveguide electrode 807. Further, a gain assisting region electrode 812 is formed on the p-GaInAs contact layer 806b, and a bonding pad 812a is connected to the gain assisting region electrode 812. An n-side electrode 808 is formed on the back surface of the n-InP substrate 801.
Further, an insulating film 809 such as a silicon oxide film is formed on the p-InP clad layer 805 so that the signal optical waveguide electrode 807, the gain auxiliary region electrode 812, and the bonding pads 807a and 812a are exposed. Further, antireflection films (AR coating) are applied to both end faces of the optical waveguide provided with the GaInAsP active layers 802 and 811.

  Then, by applying a voltage to the signal optical waveguide electrode 807, current can be injected into the GaInAsP active layer 802 while confining the current in the n-GaInAsP current blocking layer 804. When a current is injected into the GaInAsP active layer 802, the GaInAsP active layer 802 can emit light. The light generated in the GaInAsP active layer 802 is reflected by the n-GaInAsP current blocking layers 804 on both sides of the GaInAsP active layer 802, and can cause laser oscillation in a direction orthogonal to the GaInAsP active layer 802. .

  In addition, by applying a voltage to the gain assisting region electrode 812, current can be injected into the GaInAsP active layer 811 while confining the current in the n-GaInAsP current blocking layer 804. Then, by injecting current into the GaInAsP active layer 811, it becomes possible to control the threshold current density of oscillation generated in the direction orthogonal to the GaInAsP active layer 802, and to control the carrier density of the GaInAsP active layer 802. Can do.

When laser oscillation occurs in a direction perpendicular to the GaInAsP active layer 802, the carrier density of the GaInAsP active layer 802 can be kept constant even when the signal light intensity incident on the GaInAsP active layer 802 varies, The gain of the semiconductor optical amplifier can be clamped to a constant value.
When the signal light is incident on the GaInAsP active layer 802, the signal light is amplified while being guided through the GaInAsP active layer 802, and the amplified light can be emitted from the side opposite to the signal light incident surface.

  As a result, the gain of the GaInAsP active layer 802 can be clamped and the gain of the GaInAsP active layer 802 can be controlled while allowing the oscillation light to be guided in a direction different from the waveguide direction of the signal light. It becomes possible. Therefore, the input signal light is amplified to a desired value in the GaInAsP active layer 802 whose gain is clamped by oscillation while preventing the oscillation light from being mixed into the amplified light emitted from the GaInAsP active layer 802. Is possible. As a result, it is possible to suppress the gain fluctuation due to the input light intensity while making it possible to adjust the gain of the semiconductor optical amplifier. Even when the semiconductor optical amplifier is used in the wavelength multiplexing optical transmission system, the gain depends on the number of wavelength multiplexing. It is possible to prevent the gain fluctuation of the optical signal.

  Further, by disposing the p-GaInAs contact layer 806b and the signal optical waveguide electrode 807 so as not to reach the end of the GaInAsP active layer 811, an absorption region can be provided at the end of the GaInAsP active layer 811. For this reason, it is possible to prevent the GaInAsP active layer 811 from oscillating in a direction parallel to the waveguide direction of the signal light before oscillation occurs in a direction orthogonal to the waveguide direction of the signal light to be originally oscillated. It can be prevented that the gain becomes constant and the gain in the direction orthogonal to the waveguide direction of the signal light cannot be effectively obtained.

  The GaInAsP active layer 811 may be separated into a plurality of regions where current can be injected independently, or the volumes of the separated GaInAsP active layer 811 may be different. This makes it possible to vary the current value injected into the GaInAsP active layer 811 according to the site of the GaInAsP active layer 811 and to perform subtle gain adjustment by injecting current into the GaInAsP active layer 811. it can.

  In the embodiment of FIG. 4, the method of forming the GaInAsP active layer 802 and the GaInAsP active layer 811 using the same layer structure has been described, but the GaInAsP active layer 802 and the GaInAsP active layer 811 are not necessarily the same layer structure. However, the materials of the GaInAsP active layer 802 and the GaInAsP active layer 811 may be different from each other. In the embodiment of FIG. 4, the method for preventing the n-InP buried layer 810 from being formed between the GaInAsP active layers 802 and 811 has been described. However, the n-InP buried layer between the GaInAsP active layers 802 and 811 is described. 810 may be formed.

FIG. 5 is a perspective view showing a schematic configuration of a semiconductor optical amplifier according to the third embodiment of the present invention.
In FIG. 5, a GaInAsP active layer 902 is stacked on an n-InP substrate 901, and the GaInAsP active layer 902 has a GaInAsP active layer 902 that remains in a stripe shape in the light guiding direction. A buried layer 910 is buried. Here, the n-InP buried layer 910 is periodically arranged in a direction orthogonal to the light guiding direction, and constitutes a diffraction grating that reflects light in the direction orthogonal to the light guiding direction. A p-InP cladding layer 905 is formed on the GaInAsP active layer 902 in which the n-InP buried layer 910 is buried. Here, by forming the GaInAsP active layer 902 between the n-InP substrate 901 and the p-InP clad layer 905, an optical waveguide for amplifying signal light can be configured. Further, by embedding the n-InP buried layer 910 in the GaInAsP active layer 902, a diffraction grating that reflects light in a direction orthogonal to the light guiding direction is formed, and then a gain is formed in the region where the diffraction grating is formed. Can be given. The length of the diffraction grating region having gain is set so that light is reflected and oscillated by diffraction gratings on both sides sandwiching the stripe waveguide formed in the GaInAsP active layer 802, and one side having gain is oscillated. It can be set not to oscillate only in the diffraction grating region.

  On the p-InP cladding layer 905, p-GaInAs contact layers 906a and 906b are formed. Here, the p-GaInAs contact layer 906a is patterned corresponding to the stripe waveguide formed in the GaInAsP active layer 902. The p-GaInAs contact layer 906b is patterned corresponding to the diffraction grating region in which the n-InP buried layer 910 is disposed so as not to reach the input / output end of the semiconductor optical amplifier. Here, by arranging the p-GaInAs contact layer 906b so as not to reach the input / output end of the semiconductor optical amplifier, oscillation in a direction parallel to the stripe waveguide can be suppressed.

  A signal optical waveguide electrode 907 is formed on the p-GaInAs contact layer 906a, and diffraction grating region electrodes 912 and 913 are formed on the p-GaInAs contact layer 906b. An n-side electrode 908 is formed on the back surface of the n-InP substrate 901. In addition, an insulating film 909 such as a silicon oxide film is formed on the p-InP cladding layer 905 so that the signal optical waveguide electrode 907 and the diffraction grating region electrodes 912 and 913 are exposed. In addition, an antireflection film (AR coating) is applied to both end faces of the optical waveguide provided with the GaInAsP active layer 902.

  A current can be injected into the GaInAsP active layer 902 by applying a voltage to the signal optical waveguide electrode 907. When a current is injected into the GaInAsP active layer 902, the GaInAsP active layer 902 can emit light. The light generated in the GaInAsP active layer 902 is reflected by the n-InP buried layers 910 on both sides of the stripe waveguide formed in the GaInAsP active layer 902, and laser oscillation occurs in a direction perpendicular to the stripe waveguide. Can be awakened.

At this time, by applying a voltage to the diffraction grating region electrodes 912 and 913, current can be injected into the GaInAsP active layer 902 in which the n-InP buried layer 910 is buried. Thereby, a gain can be given to the diffraction grating region in which the n-InP buried layer 910 is buried, and laser oscillation can be easily caused in a direction orthogonal to the stripe waveguide.
When laser oscillation occurs in a direction orthogonal to the stripe waveguide formed in the GaInAsP active layer 902, the carrier density of the GaInAsP active layer 902 is increased even when the signal light intensity incident on the GaInAsP active layer 902 varies. It can be kept constant, and the gain of the semiconductor optical amplifier can be clamped to a constant value.

  When the signal light is incident on the GaInAsP active layer 902, the signal light is amplified while being guided through the GaInAsP active layer 902, and the amplified light can be emitted from the side opposite to the signal light incident surface. Here, the n-InP buried layer 910 having a refractive index smaller than that of the GaInAsP active layer 902 is periodically buried in the GaInAsP active layer 902, whereby diffraction gratings are formed on both sides of the stripe waveguide. For this reason, even when the GaInAsP active layer 902 continuing from the stripe waveguide is used as the gain region of the diffraction grating region, the average refractive index of the diffraction grating region can be reduced compared to the stripe waveguide, and the stripe waveguide The signal light can be guided efficiently.

  Further, by dividing the signal optical waveguide electrode 907 and the diffraction grating region electrodes 912 and 913, the current distribution ratio to the signal optical waveguide electrode 907 and the diffraction grating region electrodes 912 and 913 can be changed. This makes it possible to control the oscillation threshold current density in the direction orthogonal to the stripe waveguide, to change the carrier density of the stripe waveguide, and to change the gain of the signal light. . The signal optical waveguide electrode 907 and the diffraction grating region electrodes 912 and 913 are not necessarily arranged separately, and the signal optical waveguide electrode 907 and the diffraction grating region electrodes 912 and 913 may be shared. In the third embodiment described above, the method of separating the p-GaInAs contact layers 906a and 906b in order to limit the current injection region has been described. However, the p-InP cladding layer 905 is etched to a predetermined depth. Thus, the separation resistance between the stripe waveguide and the diffraction grating region may be further increased.

FIG. 6 is a perspective view showing a schematic configuration of a semiconductor optical amplifier according to the fourth embodiment of the present invention.
In FIG. 6, a GaInAsP active layer 1002 is stacked on an n-InP substrate 1001, and the GaInAsP active layer 1002 has a GaInAsP active layer 1002 left in a stripe shape in the light guiding direction. A buried layer 1010 is buried. Here, the n-InP buried layer 1010 is periodically arranged in a direction orthogonal to the light guiding direction, and constitutes a diffraction grating that reflects light in the direction orthogonal to the light guiding direction. A p-InP current block sequentially stacked on the n-InP substrate 1001 is formed between the stripe waveguide formed in the GaInAsP active layer 1002 and the diffraction grating region where the n-InP buried layer 1010 is disposed. A layer 1003 and an n-GaInAsP current blocking layer 1004 are formed.

  A p-InP cladding layer 1005 is formed on the GaInAsP active layer 1002 and the n-GaInAsP current blocking layer 1004 in which the n-InP buried layer 1010 is buried. Here, by forming the GaInAsP active layer 1002 between the n-InP substrate 1001 and the p-InP cladding layer 1005, an optical waveguide for amplifying signal light can be configured. Further, by embedding the n-InP buried layer 1010 in the GaInAsP active layer 1002, a diffraction grating that reflects light in a direction orthogonal to the light guiding direction is formed, and then gain is obtained in the region where the diffraction grating is formed. Can be given.

  On the p-InP cladding layer 1005, p-GaInAs contact layers 1006a and 1006b are formed. Here, the p-GaInAs contact layer 1006 a is patterned corresponding to the stripe waveguide formed in the GaInAsP active layer 1002. The p-GaInAs contact layer 1006b is patterned corresponding to the diffraction grating region in which the n-InP buried layer 1010 is disposed so as not to reach the input / output end of the semiconductor optical amplifier. Here, by arranging the p-GaInAs contact layer 1006b so as not to reach the input and output ends of the semiconductor optical amplifier, oscillation in a direction parallel to the stripe waveguide can be suppressed.

  A signal optical waveguide electrode 1007 is formed on the p-GaInAs contact layer 1006a, and diffraction grating region electrodes 1012 and 1013 are formed on the p-GaInAs contact layer 1006b. An n-side electrode 1008 is formed on the back surface of the n-InP substrate 1001. An insulating film 1009 such as a silicon oxide film is formed on the p-InP clad layer 1005 so that the signal optical waveguide electrode 1007 and the diffraction grating region electrodes 1012 and 1013 are exposed. In addition, an antireflection film (AR coating) is applied to both end faces of the optical waveguide provided with the GaInAsP active layer 1002.

  By applying a voltage to the signal optical waveguide electrode 1007, current can be injected into the GaInAsP active layer 1002 while constricting the current in the n-GaInAsP current blocking layer 1004. When a current is injected into the GaInAsP active 1002, the GaInAsP active layer 1002 can emit light. The light generated in the GaInAsP active layer 1002 is reflected by the n-InP buried layers 1010 on both sides of the stripe waveguide formed in the GaInAsP active layer 1002, and laser oscillation is performed in a direction perpendicular to the stripe waveguide. Can be awakened.

  At this time, by applying a voltage to the diffraction grating region electrodes 1012, 1013, current can be injected into the GaInAsP active layer 1002 in which the n-InP buried layer 1010 is buried. Accordingly, gain can be given to the diffraction grating region in which the n-InP buried layer 1010 is buried, and laser oscillation can be easily caused in a direction perpendicular to the stripe waveguide.

When laser oscillation occurs in a direction perpendicular to the stripe waveguide formed in the GaInAsP active layer 1002, the carrier density of the GaInAsP active layer 1002 is increased even when the signal light intensity incident on the GaInAsP active layer 1002 varies. It can be kept constant, and the gain of the semiconductor optical amplifier can be clamped to a constant value.
When signal light is incident on the GaInAsP active layer 1002, the signal light is amplified while being guided through the GaInAsP active layer 1002, and the amplified light can be emitted from the side opposite to the signal light incident surface.

  Here, the p-InP current blocking layer 1003 and the n-GaInAsP current blocking layer 1004 are disposed between the stripe waveguide formed in the GaInAsP active layer 1002 and the diffraction grating region where the n-InP buried layer 1010 is disposed. By forming, current injection into the stripe waveguide and current injection into the active region where the diffraction grating is formed can be controlled separately. Therefore, the carrier density of the stripe waveguide can be controlled with high accuracy, and the gain control of the signal light can be performed with high accuracy.

  Further, by sandwiching the n-GaInAsP current blocking layer 1004 between the p-InP current blocking layer 1003 and the n-InP substrate 1001, a layer having a higher refractive index can be sandwiched by a layer having a lower refractive index than GaInAsP. Light can be efficiently guided in a direction orthogonal to the stripe waveguide formed in the active layer 1002. However, when the stripe waveguide formed in the GaInAsP active layer 1002 and the diffraction grating region where the n-InP buried layer 1010 is disposed are close to each other, a waveguide structure is not necessarily formed in a direction orthogonal to the stripe waveguide. do not have to. For this reason, instead of using the p-InP current blocking layer 1003 and the n-GaInAsP current blocking layer 1004 sequentially stacked on the n-InP substrate 1001, for example, a semi-insulating InP layer doped with Fe is used. May be.

  Note that diffraction gratings may be formed in the p-InP current blocking layer 1003 and the n-GaInAsP current blocking layer 1004 in order to increase the reflectance in the direction orthogonal to the stripe waveguide. In the above-described fourth embodiment, the method of giving gain to both diffraction gratings on both sides of the stripe waveguide has been described. However, by forming one diffraction grating in the GaInAsP active layer 1002, one diffraction grating is formed. It is also possible to provide a gain only for the first and the other diffraction grating in the current blocking layer.

  The semiconductor optical amplifier described above can be applied to applications such as optical transmission processing systems using light such as optical communication, optical switching, and optical information processing, and in particular, prevents fluctuations in gain of an optical signal due to the number of multiplexed wavelengths. This makes it possible to suppress an increase in the size of the wavelength division multiplexing optical transmission system.

1 is a perspective view showing a schematic configuration of a semiconductor optical amplifier according to a first embodiment of the present invention. It is a figure which shows the relationship of the reflectance with respect to the normalization coupling coefficient of the semiconductor optical amplifier of FIG. FIG. 6 is a cross-sectional view showing another configuration example of the current blocking layer of the semiconductor optical amplifier in FIG. 1. It is a perspective view which shows schematic structure of the semiconductor optical amplifier which concerns on 2nd Embodiment of this invention. It is a perspective view which shows schematic structure of the semiconductor optical amplifier which concerns on 3rd Embodiment of this invention. It is a perspective view which shows schematic structure of the semiconductor optical amplifier which concerns on 4th Embodiment of this invention. 7A is a cross-sectional view of a conventional semiconductor optical amplifier cut along the optical waveguide direction, and FIG. 7B is a cross-sectional view taken along the line AA ′ of FIG. 7A. It is a figure which shows the saturation characteristic of the semiconductor optical amplifier of FIG. 9A is a cross-sectional view of a conventional semiconductor optical amplifier cut along the optical waveguide direction, and FIG. 9B is a cross-sectional view taken along the line CC ′ of FIG. 9A. It is a figure which shows the saturation characteristic of the semiconductor optical amplifier of FIG.

Explanation of symbols

501, a1, b1, c1, 801, 901, 1001 n-InP substrate 502, 802, 811, 902, 1002, 1011 GaInAsP active layer 503, 803, 1003 p-InP current blocking layer 504, 804, 1004 n-GaInAsP Current blocking layer 505, 805, 905, 1005 p-InP cladding layer 506, 806a, 806b, 906a, 906b, 1006a, 1006b p-GaInAs contact layer 507, 907, 1007 Upper surface electrode 507a, 807a, 812a Bonding pad 508, 808 , 908, 1008 Back electrode 509, 809, 909, 1009 Insulating film 510, a11, b11, c11, 810, 910, 1010 n-InP buried layer a2, b2, c2 p-InP layer a , B3, b3', c3 n-GaInAsP layer C2 'p-GaInAsP layer a4, b4, c4 p-InP contact layer 807 signal waveguide electrodes 812 gain auxiliary area electrode 912,913,1012,1013 diffraction grating region electrode

Claims (14)

An optical waveguide formed on the substrate for amplifying signal light;
A semiconductor optical amplifier comprising: a resonance unit that is disposed so as to intersect with the optical waveguide and that oscillates in a direction horizontal to the substrate. An optical waveguide formed on the substrate for amplifying signal light;
A resonance part that is arranged to intersect the optical waveguide and oscillates in a direction horizontal to the substrate;
A semiconductor optical amplifier comprising an active region formed on the substrate and arranged in parallel with the optical waveguide.   3. The semiconductor optical amplifier according to claim 2, wherein the active region is divided into a plurality of regions into which current can be injected independently.   4. The semiconductor optical amplifier according to claim 3, wherein the separated regions have different volumes.   5. The semiconductor light according to claim 2, wherein the active region includes an absorption region configured to prevent current from being injected into an end portion along the optical waveguide direction of the signal light. amplifier.   The semiconductor optical amplifier according to claim 1, wherein the resonating unit includes current blocking layers disposed on both sides of the optical waveguide.   7. The semiconductor optical amplifier according to claim 6, wherein the current blocking layer has a laminated structure in which a layer having a high refractive index is sandwiched between layers having a low refractive index. The optical waveguide is
An active layer formed on the substrate;
A clad layer formed on the active layer,
8. The semiconductor optical amplifier according to claim 7, wherein a band gap of the high refractive index layer provided in the current blocking layer is larger than a band gap of the active layer.   9. The semiconductor optical amplifier according to claim 6, wherein the current blocking layer includes a diffraction grating that reflects light in a direction orthogonal to the optical waveguide.   10. The semiconductor optical amplifier according to claim 9, wherein the diffraction grating includes a buried layer that is arranged in a direction orthogonal to the optical waveguide and has a refractive index different from that of the current blocking layer having a high refractive index. An optical waveguide formed on a substrate and provided with an active layer for amplifying signal light;
A semiconductor optical amplifier comprising a diffraction grating formed in an active layer continuing from the optical waveguide and reflecting light so as to be orthogonal to the optical waveguide. An optical waveguide formed on the substrate for amplifying signal light;
An active region formed on the substrate and disposed in parallel with the optical waveguide;
A semiconductor optical amplifier, comprising: a diffraction grating formed in the active region and reflecting light so as to intersect the optical waveguide.   13. The semiconductor optical amplifier according to claim 12, further comprising a current blocking layer formed on the substrate and separating the optical waveguide and the active region. The semiconductor optical amplifier according to claim 9, wherein a coupling coefficient of the diffraction grating is 100 cm ⁻¹ or more.

Images