JP4448771B2 - Optical amplifier - Google Patents

Description

  The present invention relates to an optical amplifying apparatus suitable for use in a semiconductor optical amplifying apparatus capable of controlling the gain with respect to signal light by, for example, injection of control light.

With the dramatic increase in communication demand in recent years, the application range of high-capacity and high-speed photonic networks has expanded to the metro access systems familiar to subscribers. A photonic network applied to a metro access system has a flexible network configuration using an optical add drop multiplexer (OADM) or the like.
The optical amplifier used in such a network is capable of high-speed gain control with respect to fluctuations in the number of multiplexed wavelengths and fluctuations in the intensity of input light, and a function that always obtains a constant optical output. (Level control function) is required.

  As an optical amplifier having a level control function, for example, as shown in FIG. 4, a semiconductor optical amplifier (SOA) is provided in both arms 101 and 102 of a Mach-Zehnder interferometer 100 including 3 dB couplers 107 and 108, respectively. There has been proposed an optical amplifier having a configuration in which 103 and 104 are provided and a control SOA 105 is integrated outside the interferometer 100 (see, for example, Patent Document 1).

  In this optical amplifier, the signal light is amplified by the SOAs 103 and 104 disposed in both arms 101 and 102 of the Mach-Zehnder interferometer 100. Furthermore, an optical path of oscillation light (control light) is provided in the element so as to intersect the optical path of signal light, and an antireflection film (reflection) having a reflectance of about 0.1% as a feedback mechanism on the optical path of the oscillation light. Mirror) 106 and a gain medium such as SOA are arranged so that the oscillation light oscillates in the element. In addition, as a feedback mechanism, a diffraction grating, a loop waveguide, and the like are also disclosed. In this case, the SOAs 103 and 104 in the arms 101 and 102 also contribute to the laser oscillation of the oscillation light, and the gain with respect to the signal light is kept constant (clamped) at the gain (threshold gain) at the oscillation threshold of the oscillation light. . In this optical amplifier, the gain of the optical amplifier is controlled by changing the threshold gain of the SOAs 103 and 104 in both arms 101 and 102 by adjusting the gain of the control SOA 105 disposed outside the interferometer. I am doing so.

In particular, in Patent Document 1, oscillation starts when the gain of one-way oscillation light becomes the reciprocal of the end face residual reflectance, and the gain is clamped. When the residual reflectance of the antireflection film is 0.1%, the gain is clamped when the sum of the gains of the SOAs 103 and 104 in the arms 101 and 102 and the gain of the control SOA 105 reaches 30 dB. Therefore, for example, if the gain of the control SOA 105 is set to 10 dB, the gains of the SOAs 103 and 104 in the arms 101 and 102 are clamped to 20 dB. Therefore, by adjusting the gain of the control SOA 105, It is described that the gains of the SOAs 103 and 104 in 102 can be adjusted (see paragraph numbers 0046 and 0047, for example).
JP 2003-179289 A

By the way, an optical amplifier used in a photonic network is required to have a polarization-independent amplification characteristic whose gain does not change depending on the polarization state of signal light.
In the above-described conventionally proposed optical amplifier (see FIG. 4), a polarization-independent SOA is used for the SOA in the arm, thereby realizing a polarization-independent amplification characteristic for the signal light. it can.

In the above-described conventionally proposed optical amplifier (see FIG. 4), the SOA disposed in the arm and the control SOA disposed outside the interferor have a common active layer. It is normal. For this reason, the control SOA outside the interferometer also has polarization-independent amplification characteristics.
However, in the above-described conventionally proposed optical amplifier (see FIG. 4), the gain is set to a constant value by using oscillation, so that the injection current (control current) to the control SOA is changed. When gain control is performed, mode hopping occurs in the control light (oscillation light) in the oscillation state, and further, kinks occur due to this mode hopping. Thus, when a kink occurs during gain control, the gain (optical gain) of the optical amplifier does not change smoothly with respect to the control current, and continuous gain control becomes difficult. Also, the control circuit becomes complicated.

  By the way, as an optical amplifier having a level control function, for example, as shown in FIG. 5, SOAs 113 and 114 are provided in both arms 111 and 112 of a Mach-Zehnder interferometer 110 including 3 dB couplers 116 and 117, respectively. A configuration in which a DFB laser 115 is integrated as a control laser light source outside the device 110 has also been proposed (for example, see Japanese Patent Application No. 2004-508538). The end face of the optical amplifier is provided with an antireflection coating (reflectance <0.001%), and antireflection coating films 118 and 119 are formed.

  In this optical amplifier, signal light is amplified by SOAs 113 and 114 disposed in both arms 111 and 112 of the Mach-Zehnder interferometer 110. On the other hand, the control light emitted from the DFB laser 115 arranged outside the interferometer 110 is incident on both SOAs 113 and 114, amplified, and guided in the diagonal direction with the signal light in the element. ing. Then, by adjusting the power of the control light emitted from the DFB laser 115, the gain of the optical amplifier is controlled by the mutual gain modulation effect between the control light and the signal light.

  However, the optical amplifier having such a configuration has the same problem as the above-described optical amplifier (see FIG. 4). That is, even in an optical amplifier having such a configuration, it is usual that the DFB laser 115 has an active layer common to the SOAs 113 and 114. Therefore, the DFB laser 115 also has a polarization-independent amplification characteristic like the SOA. In this case, when gain control is performed by changing the injection current (control current) to the DFB laser 115 to adjust the power of the control light, mode hopping occurs in the control light in the oscillation state. As a result, kinks are generated [see FIG. 6]. Thus, when a kink occurs during gain control, the gain (optical gain) of the optical amplifier does not change smoothly with respect to the control current, and continuous gain control becomes difficult. Also, the control circuit becomes complicated.

  The present invention was devised in view of such a problem, and an object thereof is to provide an optical amplifying device capable of realizing continuous gain control while realizing polarization-independent amplification characteristics. To do.

For this reason, the optical amplifying device of the present invention includes a symmetric Mach-Zehnder interferometer including a pair of arms connecting the input side coupler, the output side coupler, and the input side coupler and the output side coupler, and a pair of arms. A first optical amplifier and a second optical amplifier that amplify signal light, an ASE light source that outputs ASE light as control light, and a symmetric Mach-Zehnder interferometer, respectively, that guides control light output from the ASE light source . and a control light waveguide, and an antireflection coating film provided on the end surface of the control light waveguide for the gain of the first and second optical amplifiers and G _1, the gain of the ASE light source and G ₂ , Where L is the optical loss in one way of the optical waveguide between the control light waveguide and the Mach-Zehnder interferometer where the control light is guided, and R is the reflectance of the non-reflective coating film, G ₁ + G ₂ <L + 10 * log (R ), The first and second optical amplifiers, the ASE light source, and the non-reflective coating film are configured.

  Therefore, according to the present invention, there is an advantage that continuous gain control can be realized while realizing polarization-independent amplification characteristics.

Hereinafter, an optical amplifying device according to an embodiment of the present invention will be described with reference to the drawings.
The optical amplifying device (optical amplifying element) according to the present embodiment prevents the control mode from causing polarization mode hopping by preventing laser oscillation of the control light in the entire element or in a part of the element. As a result, generation of kinks due to polarization mode hopping is prevented, and continuous gain control can be realized.
(First embodiment)
An optical amplifying device according to a first embodiment of the present invention will be described with reference to FIGS.

  The present optical amplifying device is a semiconductor optical amplifying device having a gain control function by injection of control light, and as shown in FIG. 1A, a symmetric Mach-Zehnder interferometer 1 and two semiconductor lights for amplifying signal light. Amplifiers (SOA; first and second optical amplifiers) 2 and 3, an ASE light source (ASE light source) 4 that outputs amplified spontaneous emission (ASE) amplified as control light, and an ASE light source The control light waveguide 5 for guiding the output control light (ASE light) is provided on the same semiconductor substrate 6.

In the present embodiment, in order not to oscillate the control light, both end faces (end faces on the signal light input side and signal light output side) 50A, 50B of the element 50 are both provided with a non-reflective coating. That is, as shown in FIG. 1A, non-reflective coating films 7 and 8 (reflectance R; for example, R <0.001%) are formed on both end faces 50A and 50B of the element 50, respectively. .
Here, as shown in FIG. 1A, the symmetric Mach-Zehnder interferometer 1 includes two 3 dB couplers 9 and 10 and a pair of arms 11 and 10 connected to these 3 dB couplers 9 and 10 and having the same optical path length. 12 and has a symmetrical structure. Of the two 3 dB couplers, the one provided on the signal light input side is called the input side 3 dB coupler (input side coupler) 9, and the one provided on the signal light output side is the output side 3 dB coupler (output side coupler). ) 10

  As shown in FIG. 1A, polarization-independent SOAs 2 and 3 are provided in the pair of arms 11 and 12, respectively. In other words, two SOAs 2 and 3 having polarization-independent characteristics are arranged inside the symmetric Mach-Zehnder interferometer 1. These SOAs 2 and 3 are configured to have the same length (same SOA length). Here, the SOAs 2 and 3 having the polarization-independent characteristics refer to those in which the gain difference ΔG (dB) between the polarizations is smaller than a predetermined value (for example, 2 dB) (for example, ΔG <2 dB; within several dB).

  Further, as shown in FIG. 1A, an input waveguide 13 for inputting signal light and an output waveguide 14 for outputting signal light are connected to the symmetric Mach-Zehnder interferometer 1, respectively. That is, the input waveguide 13 is connected to the input side 3 dB coupler 9 of the symmetric Mach-Zehnder interferometer 1, and the output waveguide 14 is connected to the output side 3 dB coupler 10 of the symmetric Mach-Zehnder interferometer 1. In the symmetric Mach-Zehnder interferometer 1, since the phase conditions are matched between the arms 11 and 12 (functionally symmetric), the signal light input from the input waveguide 13 is output at a symmetrical position. The signal is output from the waveguide 14.

  Furthermore, a control light waveguide 5 is connected to the symmetric Mach-Zehnder interferometer 1 as shown in FIG. As shown in FIG. 1A, the control light waveguide 5 includes a waveguide portion (input side portion) 5A connected to the input side 3 dB coupler 9 and a waveguide connected to the output side 3 dB coupler 10. Part (output side part) 5B. Then, the control light is input from the output side portion 5B. Here, the control light propagates in the opposite direction to the input light, and the path (optical path) through which the signal light propagates intersects the path (optical path) through which the control light propagates.

  Further, the input side portion 5A of the control light waveguide 5 reaches the end face 50A on the signal light input side of the element 50, and the output side portion 5B of the control light waveguide 5 is on the signal output side of the element 50. It reaches the end face 50B. As described above, since the antireflection coating films 7 and 8 are formed on the end faces 50A and 50B of the element 50, the antireflection coating is applied to both end faces of the control light waveguide 5 (5A and 5B). Films 7 and 8 are formed.

  The ASE light source 4 is provided in the waveguide portion 5B connected to the output side 3 dB coupler 10 of the control light waveguide 5. That is, the ASE light source 4 that does not have a reflection mechanism such as a diffraction grating, that is, does not use oscillation (laser oscillation) to output light, is disposed outside the symmetric Mach-Zehnder interferometer 1. Thus, by using the ASE light source 4 as the light source for control light, laser oscillation does not occur in a part of the element 50, and mode hopping peculiar to the laser oscillation phenomenon does not occur.

Here, the ASE light source 4 is provided as a light source for control light. However, the present invention is not limited to this, and any light source that does not use oscillation to output light may be used.
The control light emitted from the ASE light source 4 is ASE light having a broad wavelength spread. However, when the light enters the SOAs 2 and 3 in the arms 11 and 12, a mutual gain modulation effect is generated with the signal light. Therefore, if this mutual gain modulation effect is used, the gain of the signal light by the SOAs 2 and 3 can be suppressed.

Therefore, the gain control of the SOAs 2 and 3 can be performed by changing the light quantity of the ASE light incident on the SOAs 2 and 3 by controlling the injection current to the ASE light source 4 or the like.
By the way, in this embodiment, when the control light is guided through the optical path (the control light waveguide 5 and the symmetric Mach-Zehnder interferometer 1), the optical gain obtained by the control light on the optical path is received by the control light on the optical path. It is made smaller than the loss.

Specifically, in this embodiment, the gain of the SOAs 2 and 3 is G ₁ (dB), the gain of the ASE light source 4 is G ₂ (dB), and an optical waveguide (control light guide) is guided. The optical loss in one way of the waveguide 5 and the symmetric Mach-Zehnder interferometer 1; the optical path of the control light) is L (dB), the reflectance of the non-reflective coating films 7 and 8 is R, and G ₁ + G ₂ <L + 10 * log (R ) Is designed so that laser oscillation does not occur in the element 50 by designing the SOAs 2 and 3, the ASE light source 4, and the non-reflective coating films 7 and 8 that constitute the present optical amplifying apparatus. The ASE light source 4 constitutes a part of the optical path of the control light.

As described above, in the present embodiment, laser oscillation is prevented from occurring in the entire element 50, and as described above, the ASE light source 4 that does not use oscillation is used as the control light source. In some cases, laser oscillation does not occur, and mode hopping peculiar to the laser oscillation phenomenon is fundamentally eliminated.
Here, the composition wavelength of the gain medium used for the ASE light source 4 is preferably set to be longer than the composition wavelength of the gain medium used for the two SOAs 2 and 3. That is, it is preferable that the emission peak wavelength of the active layer of the ASE light source 4 is set longer than the emission peak wavelengths of the active layers of the two SOAs 2 and 3. Thereby, gain control efficiency can be improved.

  In order to lengthen the emission wavelength of the ASE light source 4 relative to the emission wavelength of the SOAs 2 and 3, the active layer of the SOAs 2 and 3 and the active layer of the ASE light source 4 can be grown simultaneously using, for example, a selective growth technique. It ’s fine. As described in the method for manufacturing an optical amplifier according to the second embodiment, which will be described later, the active layers of the SOAs 2 and 3 and the active layer of the ASE light source 4 can be separately formed by butt joint growth. The emission wavelength of the ASE light source 4 can be increased with respect to the emission wavelength.

Next, a method for manufacturing the optical amplifying device according to the present embodiment will be described with reference to FIGS. 1B and 1C as appropriate.
Here, FIG. 1B shows a cross-sectional structure of the SOAs 2, 3 and the ASE light source 4, and FIG. 1C shows a cross-sectional structure of the optical waveguide.
First, as shown in FIG. 1B, on an n-type InP substrate (n-InP substrate) 20, an n-InP cladding layer 21 (for example, a thickness of 1 μm or less), a lower SCH layer 22 (InGaAsP layer; light Guide layer; for example, emission wavelength 1.2 μm; thickness 100 nm, for example, strained bulk active layer 23 (InGaAs layer; for example, strain amount −0.24%; thickness 50 nm, for example), upper SCH layer 24 (InGaAsP layer; light guide) Layer; for example, emission wavelength of 1.2 μm; for example, thickness of 100 nm), p-InP cladding layer 25 (for example, thickness of 300 nm) is grown by, for example, metal organic chemical vapor deposition (MOVPE method), SOA2, 3 and ASE A laminated structure including an active layer constituting the light source 4 is formed.

Thus, in this embodiment, the two SOAs 2 and 3 and the ASE light source 4 have the same semiconductor stacked structure. That is, in this embodiment, the same structure as the SOAs 2 and 3 is used as the ASE light source 4.
Next, a SiO ₂ mask (dielectric mask) is formed only in the areas of the SOAs 2 and 3 and the ASE light source 4 [see FIG. 1A], and these areas are left until the n-InP cladding layer 21 is reached. (Ie, from the p-InP cladding layer 25 on the surface side to the lower SCH layer 22), for example, by wet etching.

  Next, in the removed region, as shown in FIG. 1C, the waveguide layer 26 (InGaAsP layer; for example, emission wavelength 1.3 μm; for example, thickness 200 nm), p-InP cladding layer 27 (for example, thickness 350 nm) Are grown in a butt joint by, for example, the MOVPE method, and the two arms 11 and 12 of the symmetrical Mach-Zehnder interferometer 1 and the control light waveguide 5 (5A, 5B) ), A laminated structure constituting the optical waveguide of the input waveguide 13 and the output waveguide 14 is formed.

Next, an SiO ₂ mask is formed in the regions of the SOAs 2 and 3 and the ASE light source 4 and the optical waveguide region. For example, an ICP-RIE (Inductively Coupled Plasma Reactive Ion Etching) method (inductively coupled plasma reactive ion etching method) is used. For example, a waveguide mesa structure having a height of 1.5 μm and a width of 1.5 μm is formed by dry etching such as [see FIGS. 1A to 1C].

Next, as shown in FIGS. 1B and 1C, on both sides of the mesa structure, a p-InP current blocking layer (first current blocking layer) 28, an n-InP current blocking layer (second current blocking layer). 29) is grown by, for example, the MOVPE method to form a current confinement structure.
Then, after removing the SiO ₂ mask, as shown in FIGS. 1B and 1C, a p-InP cladding layer 30 (for example, 3 μm in thickness) and an InGaAsP contact layer 31 (for example, an emission wavelength of 1.3 μm) are formed on the top. For example, a thickness of 100 nm) to complete the epitaxial growth.

Although not shown in the drawing, the InGaAsP contact layer 31 is removed from the wafer that has been epitaxially grown in this manner, leaving only the regions of the SOAs 2, 3 and the ASE light source 4, and the InGaAsP contact layer 31 in the regions of the SOAs 2, 3, and the ASE light source 4 is removed. Electrodes are formed on the front surface and the back surface of the n-InP substrate 1.
Further, after the cleavage, as shown in FIG. 1A, the non-reflective coating is applied to both end faces 50A and 50B of the element 50 to form the non-reflective coating films 7 and 8.

In the element 50 thus manufactured, as shown in FIG. 1A, signal light is input from the signal light input port to the input waveguide 13 and output from the signal light output port via the output waveguide 14. Will be.
Therefore, the optical amplifying apparatus according to the present embodiment has an advantage that continuous and stable gain control can be realized while realizing polarization-independent signal light amplification characteristics.

That is, according to the present optical amplifying device, since the polarization-independent SOAs 2 and 3 are provided on the arms 11 and 12 of the symmetric Mach-Zehnder interferometer 1, it is possible to realize polarization-independent signal light amplification characteristics. In addition, the control light source is the ASE light source 4, and the optical gain obtained by the ASE light as the control light on the optical path is set to be smaller than the optical loss that the control light receives on the optical path. Therefore, it is possible to prevent laser oscillation of the control light from occurring in the entire element or a part of the element, thereby preventing the occurrence of mode hopping, and thus the generation of kinks due to mode hopping. Can be prevented. As a result, it is possible to perform continuous gain control in which the optical gain (optical gain by SOA) smoothly changes with respect to the control current without degrading other characteristics of the optical amplifying device [ As shown in FIG. 2, a high-performance optical amplifying device can be realized. It is also possible to prevent the control circuit from becoming complicated.
(Second Embodiment)
Next, an optical amplifying device and a manufacturing method thereof according to a second embodiment of the present invention will be described with reference to FIG.

  The optical amplifying device according to this embodiment is different from the first embodiment in the structure of the ASE light source. That is, in the first embodiment described above, the active layer of the ASE light source has a strained bulk structure, which is the same as the structure of the SOA in the arm. In the present embodiment, as shown in FIG. The fourth active layer 32 is different from the structure of the SOAs 2 and 3 in the arms 11 and 12 in the MQW structure.

Other configurations are the same as those of the first embodiment described above. Also, in FIG. 3, the same components as those in the first embodiment (see FIG. 1) are denoted by the same reference numerals.
Next, a method for manufacturing the optical amplifying device according to the present embodiment will be described with reference to FIG. 3 as appropriate. FIG. 3 shows a cross-sectional structure of the ASE light source 4.
First, similarly to the first embodiment described above, an n-InP clad layer 21 (for example, a thickness of 1 μm or less), a lower SCH layer 22 (InGaAsP layer; light) on an n-type InP substrate (n-InP substrate) 20. Guide layer; for example, emission wavelength 1.2 μm; thickness 100 nm, for example, strained bulk active layer 23 (InGaAs layer; for example, strain amount −0.24%; thickness 50 nm, for example), upper SCH layer 24 (InGaAsP layer; light guide) Layers; for example, emission wavelength 1.2 μm; for example, thickness 100 nm), p-InP clad layer 25 (for example, thickness 300 nm) is grown by, for example, metal organic chemical vapor deposition (MOVPE method) to form SOAs 2 and 3 A laminated structure including the active layer to be formed is formed [see FIG.

Next, an SiO ₂ mask (dielectric mask) is formed only in the SOA 2 and 3 regions [see FIG. 1A], and these regions are left until the n-InP cladding layer 21 is reached (ie, the surface). Side p-InP cladding layer 25 to lower SCH layer 22), for example, by wet etching.
Next, in the region where the ASE light source 4 is formed [see FIG. 1A], as shown in FIG. 3, the lower SCH layer 22 (InGaAsP layer; light guide layer; for example, emission wavelength 1.2 μm; for example, thickness 100 nm) ), MQW active layer 32 (for example, emission wavelength 1.61 μm; for example, thickness 50 nm), upper SCH layer 24 (InGaAsP layer; for example, emission wavelength 1.2 μm; for example, thickness 100 nm), p-InP cladding layer 25 (for example, thickness) For example, by a MOVPE method to form a stacked structure including an active layer constituting the ASE light source 4.

Thereafter, the optical amplifying device according to the present embodiment is manufactured through the same manufacturing process as in the first embodiment.
Therefore, the optical amplifying device according to the present embodiment has the same operations and effects as those of the first embodiment described above.
In particular, in this embodiment, since the active layers of the SOAs 2 and 3 and the active layer of the ASE light source 4 can have different structures, the composition wavelength of the gain medium used in the ASE light source 4 is set to the two SOAs 2 and 3. It can be set longer than the composition wavelength of the gain medium used. That is, the emission peak wavelength of the active layer of the ASE light source 4 can be set longer than the emission peak wavelengths of the active layers of the two SOAs 2 and 3. Thereby, gain control efficiency can be improved.

In addition, when the active layers of the SOAs 2 and 3 and the active layer of the ASE light source 4 are grown simultaneously using, for example, a selective growth technique, the active layers of the SOAs 2 and 3 and the active layer of the ASE light source 4 have different structures. Therefore, the emission wavelength of the ASE light source 4 can be increased with respect to the emission wavelengths of the SOAs 2 and 3, and the gain control efficiency can be improved.
In addition, the manufacturing method of the optical amplifying device concerning each above-mentioned embodiment is only what showed an example, You may manufacture using another growth method and process. For example, a selective growth technique may be used. The layer structure of the optical amplifying device is merely an example, and other layer structures may be used. For example, in each of the above-described embodiments, the optical amplifying device is configured by an InGaAsP / InP-based material, but other materials such as an InAlGaAs / InP-based material may be used. Further, for example, a laminated structure having another configuration may be formed on a p-type substrate or a semi-insulating substrate.

In each of the above-described embodiments, the current confinement structure in the waveguide structures of the SOAs 2 and 3, the ASE light source 4, and the optical waveguide is a buried hetero structure (BH structure). However, the present invention is not limited to this. For example, a current confinement structure such as a high mesa structure, a ridge structure, or a semi-insulating buried hetero structure (SI-BH structure, SI-PBH structure) may be used.
In each of the above-described embodiments, the signal light and the control light are propagated in the opposite directions to the in-arm SOAs 2 and 3 in order to suppress an increase in the noise of the amplifier. For example, the signal light and the control light may be propagated in the same direction. In this case, a control light source may be provided in the input side portion 5A of the control light waveguide 5.

  In each of the above-described embodiments, a Mach-Zehnder interferometer having a symmetric structure having the same arm length and the same SOA length is used as the Mach-Zehnder interferometer. However, the present invention is not limited to this. For example, an asymmetric Mach-Zehnder interferometer having a pair of arms having different arm lengths may be used. Further, for example, Mach-Zehnder interferometers having an asymmetric structure in which the lengths of the SOAs 2 and 3 are different (having different SOA lengths) may be used. In this case, it is preferable to arrange a phase adjuster on one side or both sides of the arm. The phase adjuster can be integrated by forming electrodes so that a current can be injected into a part of the waveguide.

The present invention is not limited to the configurations described in the above-described embodiments and other columns, and various modifications can be made without departing from the spirit of the present invention.
(Appendix 1)
A Mach-Zehnder interferometer comprising an input side coupler, an output side coupler, and a pair of arms connecting the input side coupler and the output side coupler;
First and second optical amplifiers provided on the pair of arms, respectively, for amplifying signal light;
A light source for control light that outputs control light without using oscillation,
A control light waveguide connected to the Mach-Zehnder interferometer and for guiding control light output from the control light source;
An optical amplifying apparatus, characterized in that an optical gain obtained by control light when guided through the control light waveguide and the Mach-Zehnder interferometer is smaller than an optical loss received by the control light.

(Appendix 2)
2. The optical amplifying apparatus according to appendix 1, wherein the control light source is an ASE light source that outputs ASE light as control light.
(Appendix 3)
Note 1 or 2, wherein a composition wavelength of a gain medium used for the control light source is set to be longer than a composition wavelength of a gain medium used for the first and second optical amplifiers. 2. The optical amplifying device according to 2.

(Appendix 4)
The optical amplifier according to any one of appendices 1 to 3, wherein the optical amplifier is a polarization-independent optical amplifier.
(Appendix 5)
The optical amplifying device according to any one of appendices 1 to 4, further comprising a non-reflective coating film on an end face of the control light waveguide.

(Appendix 6)
The gain of the first and second optical amplifiers and G _1, the gain of the control light source and G _2, the optical loss is L in one way of the optical waveguide which control light is guided, the antireflection coating film 6. The optical amplifying device according to appendix 5, wherein the optical amplifier is configured to satisfy a relationship of G ₁ + G ₂ <L + 10 * log (R), where R is the reflectance of the light.

(Appendix 7)
The control light waveguide has a waveguide portion connected to the output-side coupler;
The optical amplification device according to any one of appendices 1 to 6, wherein the light source for control light is provided in the waveguide portion.
(Appendix 8)
The optical amplifying device according to any one of appendices 1 to 7, wherein the first and second optical amplifiers and the control light source have the same semiconductor stacked structure.

(Appendix 9)
The first and second optical amplifiers are configured to have an active layer having a strained bulk structure,
The optical amplification device according to any one of appendices 1 to 7, wherein the light source for control light is configured to have an active layer having a multiple quantum well structure.
(Appendix 10)
Additional notes 1 to 9, wherein the Mach-Zehnder interferometer, the control light waveguide, the first and second optical amplifiers, and the control light source are all provided on the same semiconductor substrate. The optical amplification device according to any one of the above.

(Appendix 11)
11. The optical amplifying device according to any one of appendices 1 to 10, wherein each of the input side coupler and the output side coupler is a 3 dB coupler.

BRIEF DESCRIPTION OF THE DRAWINGS (a)-(c) is a schematic diagram which shows the structure of the optical amplifier concerning 1st Embodiment of this invention, (a) is the top view, (b) is the structure of SOA and ASE light source FIG. 6C is a cross-sectional view showing the configuration of the optical waveguide. It is a figure for demonstrating the effect of the optical amplifier concerning 1st Embodiment of this invention, Comprising: It is a figure which shows the change of the optical gain with respect to a control current. It is typical sectional drawing which shows the structure of the ASE light source contained in the optical amplifier concerning 2nd Embodiment of this invention. It is a figure for demonstrating the structure of the conventional optical amplifier. It is a figure for demonstrating the structure of the conventional optical amplifier. It is a figure for demonstrating the subject of the conventional optical amplifier, Comprising: It is a figure which shows the change of the optical gain with respect to control current.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Symmetric Mach-Zehnder interferometer 2,3 Semiconductor optical amplifier (SOA; 1st and 2nd optical amplifier)
4 ASE light source (light source for control light)
5 Waveguide for control light 6 Semiconductor substrate 7, 8 Non-reflective coating 9 Input side 3 dB coupler (input side coupler)
10 Output side 3dB coupler (Output side coupler)
11, 12 Arm 13 Input waveguide 14 Output waveguide 20 n-type InP substrate (n-InP substrate)
21 n-InP cladding layer 22 Lower SCH layer (InGaAsP layer; light guide layer)
23 Strained bulk active layer (InGaAs layer)
24 Upper SCH layer 24 (InGaAsP layer; light guide layer)
25 p-InP clad layer 26 Waveguide layer (InGaAsP layer)
27 p-InP cladding layer 28 p-InP current blocking layer (first current blocking layer)
29 n-InP current blocking layer (second current blocking layer)
30 p-InP cladding layer 31 InGaAsP contact layer 32 MQW active layer 50 element 50A, 50B end face (end face on the signal light input side and signal light output side)

Claims (7)

A Mach-Zehnder interferometer comprising an input side coupler, an output side coupler, and a pair of arms connecting the input side coupler and the output side coupler;
First and second optical amplifiers provided on the pair of arms, respectively, for amplifying signal light;
An ASE light source that outputs ASE light as control light ;
A control light waveguide connected to the Mach-Zehnder interferometer for guiding control light output from the ASE light source ;
An antireflective coating film provided on the end face of the control light waveguide ;
The gain of the first and second optical amplifiers and G _1, wherein the gain of the ASE light source and G _2, the control light is guided, the optical waveguide of the Mach-Zehnder interferometer and the control light waveguide The first and second optical amplifiers and the ASE light source satisfy the relationship of G ₁ + G ₂ <L + 10 * log (R), where L is the light loss in one way and R is the reflectance of the non-reflective coating film. And an optical amplifying apparatus comprising the non-reflective coating film . Bandgap wavelength of the gain medium used for the control light source, characterized in that it is set to the long wavelength side than the bandgap wavelength of the gain medium used in the first and second optical amplifier, according to claim 1 The optical amplifying device described. It said optical amplifier, characterized in that it is a polarization-independent optical amplifier, the optical amplifier according to claim 1 or 2. The control light waveguide has a waveguide portion connected to the output-side coupler;
The control light source, characterized in that provided in the waveguide section, the optical amplifying device according to any one of claims 1-3. Wherein the first and second optical amplifier and said control light source is characterized in that it has a same semiconductor stacked structure, the optical amplifying device according to any one of claims 1-4. The first and second optical amplifiers are configured to have an active layer having a strained bulk structure,
It said control light source is characterized in that it is configured as having an active layer of multiple quantum well structure, the optical amplifying device according to any one of claims 1-4. The Mach-Zehnder interferometer, the control light waveguide, said first and second optical amplifiers, the control light source, characterized in that both are provided on the same semiconductor substrate, according to claim 1 to 6 The optical amplification device according to any one of the above.

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