JP2004103614A - Optical amplifying element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical amplifier element which possesses a stable gain and is capable of suppressing a pattern effect. <P>SOLUTION: The optical amplifier element is composed of a semiconductor optical amplifiers 101 and 102, multi-mode interference 3 dB couplers 103 and 104, a DFB-LD 105, antireflection films 108 and 109, an input waveguide 110, oscillation optical waveguides 111 and 112, an output waveguide 113, and a substrate 114. A symmetrical Mach-Zehnder interference circuit 115 is composed of the SOAs 101 and 102 and the MMI couplers 103 and 104, and the oscillation wavelength of the DFB-LD 105 is set shorter than the band gap wavelength of the gain medium of the SOAs 101 and 102. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical amplification technique for amplifying an input signal light intensity of an arbitrary wavelength in a wavelength division multiplexing optical network.
[0002]
2. Description of the Related Art Conventionally, as an optical transmission system for transmitting optical signals of a plurality of different wavelengths, optical transmission using wavelength multiplexing, in which the optical signals of a plurality of different wavelengths are coupled to one optical fiber and transmitted. System (WDM system).
Further, the WDM system is rapidly being networked in order to enable not only one-to-one transmission but also optical transmission between a plurality of terminals such as one-to-many and many-to-many.
[0003]
In such a WDM system, an optical signal is a WDM multiplexing / demultiplexing circuit that multiplexes / branches according to a wavelength, a multiplexing / branching circuit that merges / branches all wavelengths collectively, and extracts or inserts a specific wavelength. Signal strength is degraded due to power loss caused by passing through an optical element such as an add-drop multiplexer (ADM). Therefore, the role of an optical amplifier that amplifies an optical signal transmitted through an optical fiber as light becomes important.
[0004]
When a conventional semiconductor optical amplifier (Semiconductor optica1 Amplifier, SOA) is used in a WDM system, the following problems have occurred. That is, in a WDM system, a wavelength-division multiplexed signal is incident, and the number of wavelength-division multiplexed signals is considered to change every time the signal passes through an ADM or the like. Now, it is assumed that a signal having the wavelength multiplex number m is incident on the SOA. The incident light intensity is P ₁ (dBm) in total of m waves, and the gain of the SOA at that time is G ₁ (dB). Here, if a signal is added by the ADM and the number of multiplexed wavelengths increases to n, then the incident light intensity becomes P ₂ (dBm) in total of n waves, and the saturation output P _{sat of the} SOA becomes P _sat <G ₁ saturated occurs if _{P 2,} SOA gain at that time becomes decreased _G 2 (dB).
In general, the relationship between the gain and the power of the input as described above is a relationship as shown in the following Patent Document 1 and Non-Patent Document 1.
[0005]
[Patent Document 1]
US Pat. No. 5,291,328 (FIG. 4)
[Non-patent document 1]
Journal of Lightwave Technology Vol. 16, No. 12 (1998) (p. 2228, FIG. 2)
[0006]
[Problems to be solved by the invention]
As described above, when the conventional SOA is used in the WDM system, there is a problem that the signal gain varies depending on the number of wavelength multiplexing. Further, in the state where the saturation occurs, not only the gain changes but also the waveform is deteriorated due to the pattern effect that the signal intensity changes according to the signal pattern.
[0007]
Accordingly, the present invention has been made in view of such unresolved problems of the conventional technology, and has as its object to provide an optical amplifying element that has no fluctuation in gain and suppresses a pattern effect. I have.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the optical amplifying device according to claim 1 of the present invention is an optical amplifying device for amplifying the light intensity of input signal light having an arbitrary wavelength,
Optical distribution means for distributing input signal light to a plurality of ports;
Amplifying means for amplifying the light intensity of the distributed input signal light,
Optical coupling means for merging output light from the amplifying means and branching to a plurality of output ports;
A laser oscillating means having a cavity for generating oscillation, which is formed independently of the amplifying means at any one of the plurality of branched output ports.
[0009]
This makes it possible to keep the gain constant and suppress the pattern effect.
According to a second aspect of the present invention, in the optical amplifying device according to the first aspect, the laser oscillation means is a Fabry-Perot type laser, a DFB (Distributed Feed-back) laser or a DBR (Distributed Bragg reflector) laser. It is characterized by.
[0010]
This makes it possible to keep the gain constant and suppress the pattern effect.
According to a third aspect of the present invention, in the optical amplifying device according to the first or second aspect, the oscillation wavelength of the laser oscillation means is set to be shorter than the band gap wavelength of the gain medium of the amplification means. Features.
This makes it possible to keep the gain constant and suppress the pattern effect.
[0011]
Further, the optical amplifying device according to claim 4 of the present invention includes a symmetric Mach-Zehnder interference circuit having an amplifying action formed on a substrate;
An input waveguide formed on an input side of a first arm of the symmetric Mach-Zehnder interference circuit;
An oscillation optical waveguide formed on the output side of the first arm and the input side of the second arm of the symmetric Mach-Zehnder interference circuit;
An output waveguide formed on the output side of the second arm of the symmetric Mach-Zehnder interference circuit;
A laser oscillation means having a cavity for generating oscillation, which is formed on the oscillation optical waveguide independently of the amplification means.
[0012]
This makes it possible to keep the gain constant and suppress the pattern effect.
According to a fifth aspect of the present invention, in the optical amplifying device according to the fourth aspect, the laser oscillation means is a Fabry-Perot laser, a DFB (Distributed Feed-back) laser, or a DBR (Distributed Bragg reflector) laser. It is characterized by.
[0013]
This makes it possible to keep the gain constant and suppress the pattern effect.
According to a sixth aspect of the present invention, in the optical amplifying device according to the fourth or fifth aspect, the oscillation wavelength of the laser oscillation means is set to a shorter wavelength than a band gap wavelength of a gain medium constituting the Mach-Zehnder circuit. It is characterized by doing.
This makes it possible to keep the gain constant and suppress the pattern effect.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 to 5 are views showing an embodiment of the optical amplifying device according to the present invention.
First, a first embodiment of the optical amplifier according to the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a first embodiment of the optical amplifying device according to the present invention.
[0015]
In the figure, 101 and 102 are semiconductor optical amplifiers (Semiconductor Optictor 1 Amplifier, SOA), 103 and 104 are multi-mode interference type 3 dB power plugs (Multi-mode Interference couplers, MMI couplers), 105 is a DFB-LD, and 106 and 107 are conductors. Waveguide end surfaces, 108 and 109 are antireflection films, 110 is an input waveguide, 111 and 112 are oscillation optical waveguides, 113 is an output waveguide, and 114 is a substrate. The SOAs 101 and 102 and the MMI couplers 103 and 104 form a symmetric Mach-Zehnder interference circuit 115.
[0016]
Hereinafter, the operation principle will be described. Approximately the same current is injected into the SOAs 101 and 102 connected to both arms of the symmetric Mach-Zehnder interference circuit 115, and both SOAs have a signal gain of 20 dB. At this time, since almost the same current is injected into both SOAs as described above, the symmetry of the Mach-Zehnder interference circuit 115 is preserved.
[0017]
Further, due to the properties of the symmetric Mach-Zehnder interference circuit 115, in the Mach-Zehnder interference circuit 115, light incident from the input waveguide 110 is emitted from the output waveguide 113, and light incident from the oscillation optical waveguide 111 is input to the input waveguide 112. Into an intersecting state in which the light is emitted.
The DFB-LD 105 connected to the oscillation optical waveguide 112 is controlled independently of the SOAs 101 and 102, and is set to oscillate regardless of the injection current of the SOAs 101 and 102.
[0018]
Here, the DFB-LD 105 is a distributed feedback (DFB type) semiconductor laser, and has a diffraction type resonator structure. That is, a periodic concavo-convex (functioning as a diffraction grating) structure is formed as a guide layer in a position adjacent to the active layer (which may be above or below), and light returned by the concavo-convex is oscillated. It is. In this structure, since the refractive index also changes periodically, the reflectivity increases due to Bragg reflection at the wavelength where the phase of the light reflected periodically matches, thereby causing laser oscillation.
[0019]
FIG. 2 is a diagram showing the relationship between the oscillation wavelength of the DFB-LD 105 and the gain spectra of the SOAs 101 and 102. In the present embodiment, the oscillation wavelength of the DFB-LD 105 is set to a shorter wavelength side than the band gap wavelength of the gain material of the SOAs 101 and 102, and therefore, as shown in FIG. _It is on the shorter wavelength side than _c . Here, the current of the DFB-LD 105 and SOA101,102, by adjusting the temperature, it is possible to gain SOA101,102 the oscillation wavelength as shown in FIG. 2 is set to the wavelength lambda ₀ to be zero. At this time, SOA101,102 the oscillation wavelength lambda ₀ of the DFB-LD 105 becomes a transparent state, the presence of the oscillation light does not affect the characteristics of SOA101,102.
[0020]
When the intensity of the input signal light 116 increases, the carrier density of the SOAs 101 and 102 decreases, and the gain spectrum becomes as shown by the dashed line in FIG. At this time, at the oscillation wavelength λ ₀ of the DFB-LD 105, the gains of the SOAs 101 and 102 become minus, that is, the SOAs 101 and 102 are in an absorption state. Therefore, the SOAs 101 and 102 absorb the oscillation light of the DFB-LD 105, and as a result, the carrier density increases and quickly recovers to the steady state shown by the solid line in FIG.
[0021]
On the other hand, when the input signal light intensity decreases, the carrier densities of the SOAs 101 and 102 increase, and the gain spectrum becomes as shown by the dotted line in FIG. At this time, at the oscillation wavelength λ ₀ of the DFB-LD 105, the gains of the SOAs 101 and 102 are positive, that is, the SOAs 101 and 102 are in an amplified state. Therefore, the SOAs 101 and 102 amplify the oscillation light of the DFB-LD 105, and as a result, the carrier density decreases and quickly recovers to the steady state shown by the solid line in FIG.
[0022]
As described above, even if the input signal strength changes, the carrier density of the SOAs 101 and 102 does not change, and the gain is kept constant. Therefore, even if the number of multiplexed wavelengths of the input signal changes, it is possible to minimize the fluctuation in gain and operate stably.
In the present embodiment, the oscillation light of the DFB-LD 105 incident from the input waveguide 112 is output from the oscillation optical waveguide 111 through the Mach-Zehnder interference circuit 115 due to the property of the symmetric Mach-Zehnder interference circuit 115. The oscillating light does not enter the input waveguide 110 and the output waveguide 113 of the signal light, and the signal light and the oscillating light are spatially separated. Therefore, an external filter for removing oscillation light is not required.
[0023]
Further, the structure of the SOAs 101 and 102 used in this embodiment is not particularly limited, and the effect described above can be expected by adopting this configuration for all normally used SOAs. That is, the SOA active layer can be applied to any material such as InGaAsP, GaAs, AlGaAs, InGaAs, and GaInNAs, and the active layer structure can be any of bulk, MQW, quantum wires, quantum dots, and SOA waveguides. Regarding the structure, a similar effect can be expected even when a pn buried structure, a ridge structure, a semi-insulating buried structure, a high-mesa structure, or the like is used regardless of the presence or absence of an SCH (separated confinement structure). The substrate is not limited to the n-type substrate, and it is needless to say that a similar effect can be obtained with a p-type or semi-green substrate.
[0024]
Further, in the above embodiment, an example is shown in which an MMI coupler is used as the 3 dB coupler, but the present invention is not limited to this, and a directional coupler may be used.
Further, in the above-described embodiment, an example is shown in which a DFB-LD is used as a laser oscillator. However, the laser cavity is not limited to the DFB-LD and is formed independently of the semiconductor amplifiers 101 and 102 serving as signal light amplifying means. If it does, a similar effect can be expected. For example, an active region where an active layer is present, a Bragg reflector at one end of the active region, and a DBR-LD that forms a cavity with a Bragg reflector or a reflective mirror at the opposite end, an active region and its active region. A similar effect can be expected even when a Fabry-Perot LD in which a cavity is formed by reflection mirrors existing at both ends is used. Regarding the spectrum of the oscillated light, it is not always necessary to perform single mode oscillation. Even when using an oscillation spectrum laser transmitter having a multipeak such as a Fabry-Perot LD, the short wavelength side of the oscillation spectrum is absorbed and the long wavelength side is amplified across λ ₀ , and the absorption and amplification are balanced in total. Since a steady state is achieved at this point, a similar effect can be expected.
[0025]
Further, a second embodiment of the optical amplifier according to the present invention will be described with reference to FIG. FIG. 3 is a diagram showing a second embodiment of the optical amplifying device according to the present invention.
In the figures, 301 and 302 are semiconductor optical amplifiers (SOAs), 303 and 304 are multimode interference type 3 dB power plugs (MMI couplers), 305 is a DFB-LD, 306 and 307 are waveguide end faces, and 308 and 309 are antireflection films. , 310 are input waveguides, 311 and 312 are oscillation optical waveguides, 313 is an output waveguide, 314 is a substrate, and 318 is a loop waveguide. The SOAs 301 and 302 and the MMI couplers 303 and 304 form a symmetric Mach-Zehnder interference circuit 315.
[0026]
The operation principle is the same as that of the first embodiment except that the oscillation light of wavelength λ ₀ output from the DFB-LD 305 enters the symmetric Mach-Zehnder interference circuit 315 from both the oscillation optical waveguides 311 and 312. The same is true.
Therefore, also in the case of the present embodiment, due to the property of the symmetric Mach-Zehnder interference circuit 315, the oscillation light of the DFB-LD 305 incident from the oscillation optical waveguide 312 passes through the Mach-Zehnder interference circuit 315 and is output from the oscillation optical waveguide 311. Also, the oscillating light of the DFB-LD 305 that enters from the oscillating optical waveguide 311 passes through the Mach-Zehnder interference circuit 315 and is output from the oscillating optical waveguide 312, so that the oscillating light is input to the input waveguide 310 and the output waveguide 313 of signal light. There is no mixing, and the signal light and the oscillation light are spatially separated. Therefore, an external filter for removing oscillation light is not required.
[0027]
Note that the structure of the SOA in this embodiment is not particularly limited similarly to the first embodiment, and the effect described above can be obtained by adopting this structure for all normally used SOAs. Can be expected. That is, the SOA active layer can be applied to any material such as InGaAsP, GaAs, AlGaAs, InGaAs, and GaInNAs, and the active layer structure can be any of bulk, MQW, quantum wires, quantum dots, and SOA waveguides. Regarding the structure, a similar effect can be expected even when a pn buried structure, a ridge structure, a semi-insulating buried structure, a high-mesa structure, or the like is used regardless of the presence or absence of an SCH (separated confinement structure). The substrate is not limited to the n-type substrate, and it is needless to say that a similar effect can be obtained with a p-type or semi-green substrate.
[0028]
The same effect can be expected by using a directional coupler as well as the MMI coupler as the 3 dB coupler.
Further, the same effect can be expected if the laser cavity is formed independently of the semiconductor amplifiers 301 and 302 as the signal light amplifying means, without being limited to the DFB-LD as the laser transmitter. For example, an active region where an active layer is present, a Bragg reflector at one end of the active region, and a DBR-LD that forms a cavity with a Bragg reflector or a reflective mirror at the opposite end, an active region and its active region. A similar effect can be expected even when a Fabry-Perot LD in which a cavity is formed by reflection mirrors existing at both ends is used. Further, the spectrum of the oscillated light does not necessarily have to be single mode oscillation.
[0029]
Furthermore, a third embodiment of the optical amplifying device according to the present invention will be described with reference to FIG. FIG. 4 is a diagram showing a third embodiment of the optical amplifier according to the present invention.
In the figure, 401 and 402 are semiconductor optical amplifiers (SOAs), 403, 404 and 419 are multimode interference type 3 dB power plugs (MMI couplers), 405 is a DFB-LD, 406 and 407 are waveguide end faces, and 408 and 409 are reflections. The prevention film, 410 is an input waveguide, 411, 412, and 418 are oscillation optical waveguides, 413 is an output waveguide, and 414 is a substrate. The SOAs 401 and 402 and the MMI couplers 403 and 404 form a symmetric Mach-Zehnder interference circuit 415.
[0030]
The operating principle is the same as that of FIG. 1 except that the oscillation light of wavelength λ ₀ output from the DFB-LD 415 is branched into two by the MMI 3 dB coupler 419 and enters the symmetric Mach-Zehnder interference circuit 415 from both the oscillation optical waveguides 411 and 412. This is exactly the same as the first embodiment shown in FIG. 1 and the second embodiment shown in FIG.
Therefore, also in the case of the present embodiment, due to the property of the symmetric Mach-Zehnder interference circuit 415, the oscillation light of the DFB-LD 405 incident from the oscillation optical waveguide 412 passes through the Mach-Zehnder interference circuit 415 and is output from the oscillation optical waveguide 411. Further, the oscillating light of the DFB-LD 405 that enters from the oscillating optical waveguide 411 passes through the Mach-Zehnder interference circuit 415 and is output from the oscillating optical waveguide 412, so that the oscillating light enters the input waveguide 410 and the output waveguide 413 of the signal light. There is no mixing, and the signal light and the oscillation light are spatially separated. Therefore, an external filter for removing oscillation light is not required.
[0031]
The structure of the SOA in this embodiment is not particularly limited as in the first embodiment and the second embodiment, and the structure is applied to all SOAs that are normally used. Thus, the effect as described above can be expected. That is, the SOA active layer can be applied to any material such as InGaAsP, GaAs, AlGaAs, InGaAs, and GaInNAs, and the active layer structure can be any of bulk, MQW, quantum wires, quantum dots, and SOA waveguides. Regarding the structure, a similar effect can be expected even when a pn buried structure, a ridge structure, a semi-insulating buried structure, a high-mesa structure, or the like is used regardless of the presence or absence of an SCH (separated confinement structure). The substrate is not limited to the n-type substrate, and it is needless to say that a similar effect can be obtained with a p-type or semi-green substrate.
[0032]
The same effect can be expected by using a directional coupler as well as the MMI coupler as the 3 dB coupler.
Further, the same effect can be expected if the laser cavity is formed independently of the semiconductor amplifiers 401 and 402 as the signal light amplifying means, without being limited to the DFB-LD as the laser transmitter. For example, an active region where an active layer is present, a Bragg reflector at one end of the active region, and a DBR-LD that forms a cavity with a Bragg reflector or a reflective mirror at the opposite end, an active region and its active region. A similar effect can be expected even when a Fabry-Perot LD in which a cavity is formed by reflection mirrors existing at both ends is used. Further, the spectrum of the oscillated light does not necessarily have to be single mode oscillation.
[0033]
Further, a fourth embodiment of the optical amplifier according to the present invention will be described with reference to FIG. FIG. 5 is a diagram showing a fourth embodiment of the optical amplifier according to the present invention.
In the fourth embodiment shown in FIG. 5, the MMI 3 dB coupler 419 in the third embodiment shown in FIG. 4 is replaced by a multimode interference (MMI) 1: 2 coupler 519.
[0034]
In the figure, 501 and 502 are semiconductor optical amplifiers (SOAs), 503 and 504 are multimode interference type 3 dB power plugs (MMI couplers), 505 is a DFB-LD, 506 and 507 are waveguide end faces, and 508 and 509 are antireflection films. Reference numeral 510 denotes an input waveguide, reference numerals 511, 512 and 518 denote oscillation optical waveguides, reference numeral 513 denotes an output waveguide, reference numeral 514 denotes a substrate, and reference numeral 519 denotes a multimode interference (MMI) 1: 2 coupler. The SOAs 501 and 502 and the MMI 3 dB couplers 503 and 504 form a symmetric Mach-Zehnder (Mach-Ze mder) interference circuit 515.
[0035]
The operating principle is exactly the same as that of the third embodiment shown in FIG. 4 except that the oscillation light of wavelength λ ₀ output from the DFB-LD 515 branches into two at the multimode interference type 1: 2 coupler 519. The same is true.
Note that the structure of the SOA in this embodiment is not particularly limited as in the first, second, and third embodiments described above. By adopting this configuration for the SOA, the effect as described above can be expected. That is, the SOA active layer can be applied to any material such as InGaAsP, GaAs, AlGaAs, InGaAs, and GaInNAs, and the active layer structure can be any of bulk, MQW, quantum wires, quantum dots, and SOA waveguides. Regarding the structure, a similar effect can be expected even when a pn buried structure, a ridge structure, a semi-insulating buried structure, a high-mesa structure, or the like is used regardless of the presence or absence of an SCH (separated confinement structure). The substrate is not limited to the n-type substrate, and it is needless to say that a similar effect can be obtained with a p-type or semi-green substrate.
[0036]
The same effect can be expected by using a directional coupler as well as the MMI coupler as the 3 dB coupler. Further, a similar effect can be expected even if a Y branch is used as the 1 × 2 coupler, without being limited to the MMI coupler.
Further, the same effect can be expected if the laser cavity is formed independently of the semiconductor amplifiers 301 and 302 as the signal light amplifying means, without being limited to the DFB-LD as the laser transmitter. For example, an active region where an active layer is present, a Bragg reflector at one end of the active region, and a DBR-LD that forms a cavity with a Bragg reflector or a reflective mirror at the opposite end, an active region and its active region. A similar effect can be expected even when a Fabry-Perot LD in which a cavity is formed by reflection mirrors existing at both ends is used. Further, the spectrum of the oscillated light does not necessarily have to be single mode oscillation.
[0037]
【The invention's effect】
As described above, according to the optical amplifying device of the present invention, it is possible to keep the gain constant even when the input signal intensity fluctuates, and to suppress the pattern effect even in the saturated state.
[Brief description of the drawings]
FIG. 1 is a diagram showing a first embodiment of the present invention.
FIG. 2 is a diagram showing a relationship between a gain spectrum of an SOA and an oscillation wavelength.
FIG. 3 is a diagram showing a second embodiment of the present invention.
FIG. 4 is a diagram showing a third embodiment of the present invention.
FIG. 5 is a diagram showing a fourth embodiment of the present invention.
[Explanation of symbols]
101, 102 SOA
103, 104 MMI 3 dB coupler 105 DFB-LD
106, 107 End faces 108, 109 Antireflection film 110 Input waveguide 111, 112 Oscillation optical waveguide 113 Output waveguide 114 Substrate 115 Symmetric Mach-Zehnder interference circuit 116 Input signal light 117 Output signal light 301, 302 SOA
303, 304 MMI 3 dB coupler 305 DFB-LD
306, 307 End faces 308, 309 Antireflection film 310 Input waveguides 311, 312 Oscillation optical waveguide 313 Output waveguide 314 Substrate 315 Symmetric Mach-Zehnder interference circuit 316 Input signal light 317 Output signal light 318 Loop waveguide 401, 402 SOA
403, 404 MMI 3dB coupler 405 DFB-LD
406, 407 End faces 408, 409 Antireflection film 410 Input waveguides 411, 412 Oscillating optical waveguide 413 Output waveguide 414 Substrate 415 Symmetric Mach-Zehnder interference circuit 416 Input signal light 417 Output signal light 418 Oscillating optical waveguide 419 MMI 3 dB coupler 501, 502 SOA
503, 504 MMI 3dB coupler 505 DFB-LD
506, 507 End faces 508, 509 Antireflection film 510 Input waveguide 511, 512 Oscillating optical waveguide 513 Output waveguide 514 Substrate 515 Symmetric Mach-Zehnder interference circuit 516 Input signal light 517 Output signal light 518 Oscillating optical waveguide 519 MMI 1: 2 coupler

Claims (6)

In an optical amplifying element for amplifying the light intensity of an input signal light having an arbitrary wavelength,
Optical distribution means for distributing input signal light to a plurality of ports;
Amplifying means for amplifying the light intensity of the distributed input signal light,
Optical coupling means for merging output light from the amplifying means and branching to a plurality of output ports;
An optical amplifying element comprising: a laser oscillation unit having a cavity for generating oscillation, which is formed independently of the amplification unit at any one of the plurality of branched output ports. 2. The optical amplifying device according to claim 1, wherein said laser oscillation means is a Fabry-Perot laser, a DFB (Distributed Feed-back) laser or a DBR (Distributed Bragg reflector) laser. 3. The optical amplifying device according to claim 1, wherein an oscillation wavelength of said laser oscillation means is shorter than a band gap wavelength of a gain medium of said amplification means. A symmetric Mach-Zehnder interferometer having an amplifying action formed on the substrate,
An input waveguide formed on an input side of a first arm of the symmetric Mach-Zehnder interference circuit;
An oscillation optical waveguide formed on the output side of the first arm and the input side of the second arm of the symmetric Mach-Zehnder interference circuit;
An output waveguide formed on the output side of the second arm of the symmetric Mach-Zehnder interference circuit;
An optical amplifying device, comprising: a laser oscillation unit having a cavity for generating oscillation, formed independently of the amplification unit on the oscillation optical waveguide. 5. The optical amplifying device according to claim 4, wherein said laser oscillation means is a Fabry-Perot type laser, a DFB (Distributed Feed-back) laser or a DBR (Distributed Bragg reflector) laser. 6. The optical amplifying device according to claim 4, wherein an oscillation wavelength of the laser oscillation means is shorter than a band gap wavelength of a gain medium constituting the Mach-Zehnder circuit.

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