JP2010166317A - Optical signal amplification device - Google Patents

Abstract

An optical signal amplifying device in which oscillation due to optical resonance does not occur and an optical signal amplifying operation is stable is provided.
A first semiconductor optical amplifier 14 to which an input signal light Iin having a first wavelength λ1 is input, a first ambient light not including the first wavelength λ1, and a control light Ic having a first wavelength λ1 are input. A second semiconductor optical amplifier 16, a first Bragg reflection grating 20 that reflects the first ambient light output from the first semiconductor optical amplifier 14 and inputs the first ambient light to the second semiconductor optical amplifier 16; And a second Bragg reflection grating 24 that reflects the second ambient light output from the semiconductor optical amplifier 16 and re-inputs the second ambient light to the second semiconductor optical amplifier 16 for negative feedback amplification. In the amplifying apparatus 10, since the first Bragg reflection grating 20 and the second Bragg reflection grating 24 have reflection wavelength bands that do not substantially overlap each other, oscillation or optical resonance between them is suppressed. Optical signal amplification operation Is obtained.
[Selection] Figure 1

Description

  The present invention relates to an optical signal amplifying apparatus for amplifying an optical signal with low distortion and a high degree of modulation.

  In the field where electrical signals are converted into optical signals, amplified and transmitted, the converted optical signals are larger than electrical signals based on the conversion characteristics of electrical / optical conversion elements such as semiconductor lasers and light emitting diodes. It is known to distort. In particular, when a pulsed electric signal is input to the semiconductor laser, the optical signal intensity rapidly increases at the rise of the pulse of the output optical signal, and an optical signal waveform overshooting like a beard is obtained. Generally, when these optical signal waveforms are amplified by an optical amplifier, the distortion is amplified and transmitted, and a technique for optically reducing the distortion has not been obtained. Further, in the electronics field, negative feedback amplification control is an important technique for constructing a low distortion amplifier, but no equivalent technique has been obtained for an optical amplifier. Further, in the electronics field, there are three-terminal amplifiers having a signal amplifying action like transistors, but they have not been obtained in the field of optoelectronics.

  On the other hand, the present inventor utilizes the mutual gain modulation phenomenon of the semiconductor optical amplifier (SOA), and the ambient light (centered on λ1) after passing through the semiconductor optical amplifier with respect to the input signal light of the predetermined wavelength λ1. It was shown that the input signal light can be amplified with low distortion by feeding back the light in the wavelength band other than λ1) to the input side and named the negative feedback optical amplification effect (Non-patent Reference 1). This effect is that the ambient light exhibits intensity reversal with respect to the input signal light by XGM (mutual gain modulation), so that the gain of the semiconductor optical amplifier is modulated according to the input signal light by feeding back this ambient light. A negative feedback light amplification effect is obtained, optical signal distortion is optically reduced, and a high degree of modulation is obtained.

`` Negative feedback optical amplification effect based on cross-gain modulation in semiconductor aptical amplifiers '' (Applied Physics Letters, Volume 88, published 8 March 2006)

  By the way, the present inventor has conceived a three-terminal type optical amplifying device that makes use of the above-described conventional negative feedback light amplification effect and does not require a structure for holding an optical component and can be configured in a small and inexpensive device. Although this optical amplifying device is not known, (a) when input signal light having a first wavelength is input, the light intensity amplification characteristic of ambient light having the first wavelength is changed according to the intensity of the input signal light. (B) a first semiconductor optical amplifier that outputs a modulated and amplified light, and a first ambient light that does not include the first wavelength and is inverted with respect to the intensity of the input signal light; When the second input signal light of two wavelengths is input, the light intensity amplification characteristics of the light other than the second wavelength are modulated according to the intensity of the second input signal light, and the second input signal light is amplified. A second semiconductor optical amplifier that outputs an output light and a second ambient light that does not include the second wavelength, the intensity of which is inverted with respect to the intensity of the second input signal light; and (c) an output from the first semiconductor optical amplifier. A first wavelength selection element for selecting the first ambient light from the received light and inputting it to the second semiconductor optical amplifier; and (d) the second semiconductor Of the light output from the optical amplifier to reflect the second ambient light, and a second wavelength selection element to the negative feedback amplifier to re-enter the second ambient light into the second semiconductor optical amplifier, it is intended to include.

  However, according to the optical signal amplifier, the first Bragg reflection grating that reflects the first ambient light output from the first semiconductor optical amplifier has reflection wavelength bands on both sides of the first wavelength, and negative feedback amplification. Because the second Bragg reflection grating that reflects the second ambient light output from the second semiconductor optical amplifier for re-input also has reflection wavelength bands on both sides of the first wavelength band, the first Bragg reflection Since the reflection wavelength band of the grating and the reflection wavelength band of the second Bragg reflection grating have portions that overlap each other, oscillation due to optical resonance may occur and the optical signal amplification operation may become unstable. .

  The present invention has been made against the background described above, and an object of the present invention is to provide an optical signal amplifying apparatus in which oscillation due to optical resonance does not occur and the optical signal amplifying operation is stable.

  The present inventor has conducted various studies against the background described above, and as a result, the reflection wavelength band of the first Bragg reflection grating that reflects the first ambient light output from the first semiconductor optical amplifier, and the negative feedback amplification. If the reflection wavelength band of the second Bragg reflection grating that is reflected in order to re-input the second ambient light output from the second semiconductor optical amplifier does not overlap with each other, an optical signal amplification operation using negative feedback amplification Was found to be stable. The present invention has been made based on such findings.

  That is, the invention according to claim 1 for achieving the above object is as follows. (A) When input signal light having a first wavelength is input, the ambient light having the first wavelength is changed according to the intensity of the input signal light. A first semiconductor optical amplifier that modulates light intensity amplification characteristics and amplifies the input signal light and outputs first ambient light that does not include the first wavelength and is inverted with respect to the intensity of the input signal light; (B) When the second input signal light having the second wavelength is input, the light intensity amplification characteristic of the light other than the second wavelength is modulated according to the intensity of the second input signal light, and the second input A second semiconductor optical amplifier that outputs an output light obtained by amplifying the signal light and a second ambient light not including the second wavelength, the intensity of which is inverted with respect to the intensity of the second input signal light, and (c) the first First wavelength selection for selecting the first ambient light from the light output from the semiconductor optical amplifier and inputting it to the second semiconductor optical amplifier And d) reflecting the second ambient light out of the light output from the second semiconductor optical amplifier and re-inputting the second ambient light to the second semiconductor optical amplifier for negative feedback amplification. (E) a control light having a wavelength different from that of the first ambient light is input to the second semiconductor optical amplifier as the second input signal light, and thus has the same wavelength as the control light. (F) The first wavelength selection element and the second wavelength selection element have reflection wavelength bands that do not overlap each other.

  The invention according to claim 2 is the invention according to claim 1, wherein (g) a common fiber portion and a pair of first branch fiber portion and second branch fiber portion branched from one end of the common fiber portion are provided. The first branch fiber portion receives light output from the first semiconductor optical amplifier, the common fiber portion receives the control light, and the second branch fiber portion inputs the second semiconductor optical amplifier. And (h) an output optical fiber that guides light output from the second semiconductor optical amplifier, and (i) the first wavelength selection element includes the common fiber portion. A reflection wavelength band that reflects the first partial ambient light belonging to one of the wavelength bands sandwiching the first wavelength among the first ambient light output from the first semiconductor optical amplifier. The first partial ambient light is converted into the second semiconductor light. (J) The second wavelength selection element is provided in the output optical fiber, and is output from the second semiconductor optical amplifier. Of the ambient light, it has a reflection wavelength band for reflecting the second partial ambient light belonging to the other wavelength band of the wavelength bands sandwiching the first wavelength, and the second partial ambient light is sent to the second semiconductor optical amplifier. It is composed of a second Bragg reflection grating to be re-input.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein (k) a first input optical fiber that guides the input signal light to the first semiconductor optical amplifier; and (l) the first optical fiber. The first partial ambient light that is provided in the input optical fiber and that belongs to one of the wavelength bands sandwiching the first wavelength among the first ambient light output from the first semiconductor optical amplifier is reflected. And a third Bragg reflection grating for negatively amplifying the first partial ambient light by re-inputting the first partial ambient light to the first semiconductor optical amplifier.

  The invention according to claim 4 is the invention according to claim 1 or 2, wherein (m) when the input signal light having the first wavelength is input, the first wavelength is determined according to the intensity of the input signal light. Modulating the light intensity amplification characteristics of the ambient light, and amplifying the input signal light and the third ambient light around the first wavelength inverted in intensity with respect to the intensity of the input signal light A third semiconductor optical amplifier that outputs to the optical amplifier is included.

  The invention according to claim 5 is the invention according to claim 4, wherein (n) the output light of the first wavelength that is the amplified light of the input signal light from the third semiconductor optical amplifier is reflected. A common fiber portion provided with a fourth Bragg reflection grating, and a pair of the first branch fiber portion and the second branch fiber portion branched from one end of the common fiber portion; The output light of the first wavelength from the third semiconductor optical amplifier is input, and the output light of the first wavelength reflected by the fourth Bragg reflection grating is passed through the second branch fiber part, and the first semiconductor light A second optical coupler to be input to the amplifier is included.

  The invention according to claim 6 is the invention according to claim 4 or 5, wherein (o) a second input optical fiber that guides the input signal light to the third semiconductor optical amplifier; and (p) the second optical fiber. Provided in the input optical fiber, and reflects the fifth partial ambient light belonging to one of the wavelength bands sandwiching the first wavelength among the third ambient light output from the third semiconductor optical amplifier. A fifth Bragg reflection grating having a reflection wavelength band and re-inputting the fifth partial ambient light to the third semiconductor optical amplifier for negative feedback amplification.

  The invention according to claim 7 is the invention according to claim 5, wherein (q) the first semiconductor optical amplifier is connected to an end of the second branch of the second optical coupler on the first semiconductor optical amplifier side. A sixth Bragg reflection grating having a reflection wavelength band for reflecting, to the first semiconductor optical amplifier, first partial ambient light belonging to one of a pair of wavelength bands sandwiching the first wavelength among the first ambient light of It is characterized by providing.

  The invention according to claim 8 is the invention according to claim 5, wherein (r) the first Bragg reflection grating is input from the other end of the common fiber portion of the second optical coupler and the first semiconductor. A bias light having a third wavelength different from the first wavelength amplified by an optical amplifier is used as the other of the wavelength bands sandwiching the first wavelength among the first ambient light output from the first semiconductor optical amplifier. The first partial ambient light belonging to the wavelength band is reflected to the second semiconductor optical amplifier.

  The invention according to claim 9 is the invention according to any one of claims 2 to 8, wherein (s) the first Bragg reflection grating is a reflection wavelength band wider than a reflection wavelength band of the second Bragg reflection grating. It is characterized by having.

  The invention according to claim 10 is the invention according to any one of claims 2 to 9, wherein (t) the optical fiber constituting the first optical coupler and the output optical fiber are polarization plane independent light. It is characterized by comprising a fiber.

  The invention according to claim 11 is the invention according to any one of claims 2, 5 to 9, wherein (u) the optical fiber constituting the first and second optical couplers and / or the first or second. The input optical fiber and / or the output optical fiber is composed of a polarization plane-independent optical fiber.

  The invention according to claim 12 is the invention according to any one of claims 1 to 11, wherein (v) the wavelength of the control light is the first wavelength.

  According to the optical signal amplifying device of the first aspect of the present invention, (a) when input signal light of the first wavelength is input, the light intensity of the ambient light of the first wavelength according to the intensity of the input signal light A first semiconductor optical amplifier that modulates amplification characteristics and outputs the light that has amplified the input signal light and the first ambient light that does not include the first wavelength that is inverted in intensity with respect to the intensity of the input signal light; b) When the second input signal light having the second wavelength is input, the light intensity amplification characteristic of the light other than the second wavelength is modulated according to the intensity of the second input signal light, and the second input signal light A second semiconductor optical amplifier that outputs an output light obtained by amplifying the light and a second ambient light not including the second wavelength, the intensity of which is inverted with respect to the intensity of the second input signal light, and (c) the first semiconductor light. A first wavelength selection element that selects the first ambient light from the light output from the amplifier and inputs the first ambient light to the second semiconductor optical amplifier; (d) A second wavelength selection element that reflects the second ambient light out of the light output from the second semiconductor optical amplifier, and re-inputs the second ambient light to the second semiconductor optical amplifier to perform negative feedback amplification. And (e) outputting control light having a wavelength different from that of the first ambient light as the second input signal light to the second semiconductor optical amplifier, thereby outputting the output light having the same wavelength as the control light. (F) Since the first wavelength selection element and the second wavelength selection element have reflection wavelength bands that do not overlap each other, oscillation or optical resonance between them is suppressed. A stable optical signal amplification operation can be obtained.

  According to the invention of claim 2, (g) the common fiber portion, and a pair of first branch fiber portion and second branch fiber portion branched from one end of the common fiber portion, The light output from the first semiconductor optical amplifier is input to the branch fiber portion, the control light is input to the common fiber portion, and the first light is input from the second branch fiber portion to the second semiconductor optical amplifier. An optical coupler; and (h) an output optical fiber that guides light output from the second semiconductor optical amplifier. (I) the first wavelength selection element is provided in the common fiber portion; A reflection wavelength band for reflecting the first partial ambient light belonging to one of the wavelength bands sandwiching the first wavelength of the first ambient light output from the one semiconductor optical amplifier; A first for inputting ambient light to the second semiconductor optical amplifier. (J) The second wavelength selection element is provided in the output optical fiber, and the first ambient light output from the second semiconductor optical amplifier is provided in the output optical fiber. A second Bragg reflection having a reflection wavelength band for reflecting the second partial ambient light belonging to the other one of the wavelength bands sandwiching the wavelength, and re-inputting the second partial ambient light to the second semiconductor optical amplifier Since it is composed of a grating, oscillation or optical resonance between the first Bragg reflection grating and the second Bragg reflection grating is suppressed, and a stable optical signal amplification operation can be obtained. Further, since the first Bragg reflection grating is provided in the control light input optical fiber and the second Bragg reflection grating is provided in the output optical fiber, it is easier than in the case where it is provided in the branch portion of the optical coupler. Moreover, since it is formed stably, a stable and highly accurate reflection wavelength band can be obtained.

  According to the invention of claim 3, (k) a first input optical fiber for guiding the input signal light to the first semiconductor optical amplifier, and (l) provided in the first input optical fiber, A reflection wavelength band that reflects the first partial ambient light belonging to one of the wavelength bands sandwiching the first wavelength among the first ambient light output from the first semiconductor optical amplifier; A third Bragg reflection grating that re-inputs the first partial ambient light to the first semiconductor optical amplifier to negatively amplify the first partial optical light, so that an S / N ratio is obtained by negatively amplifying the first semiconductor optical amplifier. High and stable optical signal amplification of the input signal light can be obtained.

  According to the invention of claim 4, (m) when the input signal light of the first wavelength is input, the light intensity amplification characteristic of the ambient light of the first wavelength according to the intensity of the input signal light A third semiconductor that modulates the input signal light and outputs the third ambient light around the first wavelength, the intensity of which is inverted with respect to the intensity of the input signal light, to the first semiconductor optical amplifier Since the optical amplifier is included, the input signal light intensity input to the first semiconductor optical amplifier is increased, and the optical signal amplification accompanied by the negative feedback amplification is obtained by the input signal light having a relatively small intensity.

  According to the invention of claim 5, (n) a fourth Bragg reflection grating for reflecting the output light of the first wavelength, which is the amplified light of the input signal light from the third semiconductor optical amplifier, A common fiber portion provided, and a pair of the first branch fiber portion and the second branch fiber portion branched from one end of the common fiber portion, and the third semiconductor optical amplifier is connected to the first branch fiber portion. Second output light of the first wavelength is input, and the output light of the first wavelength reflected by the fourth Bragg reflection grating is input to the first semiconductor optical amplifier via the second branch fiber portion. Since the optical coupler is included, the input signal light intensity input to the first semiconductor optical amplifier is increased, and the optical signal amplification with negative feedback amplification is obtained by the input signal light having a relatively small intensity. In addition, since the fourth Bragg reflection grating is provided in the common fiber portion, it is easily and stably formed as compared with the case where it is provided in the branch portion of the optical coupler, so that a stable and highly accurate reflection wavelength band can be obtained. .

  According to the invention of claim 6, (o) a second input optical fiber for guiding the input signal light to the third semiconductor optical amplifier, and (p) the second input optical fiber, A reflection wavelength band for reflecting the fifth partial ambient light belonging to one of the wavelength bands sandwiching the first wavelength among the third ambient light output from the third semiconductor optical amplifier; A fifth Bragg reflection grating that re-inputs the fifth partial ambient light to the third semiconductor optical amplifier and amplifies it by negative feedback, so that stable input signal light can be generated by the negative feedback amplification action of the third semiconductor optical amplifier. Amplification is obtained.

  According to the invention of claim 7, (q) the first ambient light from the first semiconductor optical amplifier is connected to the end of the second branching portion of the second optical coupler on the first semiconductor optical amplifier side. A first Bragg reflection grating having a reflection wavelength band for reflecting the first partial ambient light belonging to one of the pair of wavelength bands sandwiching the first wavelength to the first semiconductor optical amplifier is provided. Negative feedback amplification can be generated in the semiconductor optical amplifier.

  According to an eighth aspect of the present invention, (r) the first Bragg reflection grating is input from the other end of the common fiber portion of the second optical coupler and amplified by the first semiconductor optical amplifier. A bias light having a third wavelength different from the first wavelength is a first wavelength belonging to the other of the wavelength bands sandwiching the first wavelength in the first ambient light output from the first semiconductor optical amplifier. Since the reflected light is reflected to the second semiconductor optical amplifier together with the partial ambient light, the cross-gain modulated bias light and the control light are superimposed and supplied to the second semiconductor optical amplifier. A strong optical signal amplification output is obtained.

  According to the invention of claim 9, (s) since the first Bragg reflection grating has a reflection wavelength band wider than the reflection wavelength band of the second Bragg reflection grating, the first semiconductor There is an advantage that the ratio of the ambient light output from the optical amplifier 14 to the second semiconductor optical amplifier 16 is increased and the inverted input signal is reliably transmitted to the second semiconductor optical amplifier 16.

  According to the invention of claim 10, (t) the optical fiber constituting the first optical coupler and the output optical fiber are composed of polarization plane-independent optical fibers. An optical signal amplification output stable with respect to temperature can be obtained.

  According to an eleventh aspect of the invention, (u) an optical fiber or / and the first or second input optical fiber or / and output optical fiber constituting the first and second optical couplers are: Since it is composed of a polarization-independent optical fiber, an optical signal amplification output that is stable with respect to vibration and temperature can be obtained.

  According to the invention of claim 12, (v) since the wavelength of the control light is the first wavelength, output light of the first wavelength can be obtained.

It is the schematic explaining the principal part structure of the optical signal amplifier of one Example of this invention. FIG. 2 is a perspective view for explaining a semiconductor chip constituting a semiconductor optical amplifier in the embodiment of FIG. 1. In the Example of FIG. 1, it is a figure which expands and demonstrates the principal part of a 1st Bragg reflection grating. FIG. 2 is a diagram showing a power spectrum of output light Iout when the first wavelength λ1 is 1551 nm in the embodiment of FIG. 1. In the embodiment of FIG. 1, the reflection wavelength band of the first Bragg reflection grating is indicated by a solid line, and the reflection wavelength band of the second Bragg reflection grating is indicated by a broken line. FIG. 2 is a diagram showing input signal light used in the operation of the optical signal amplifying device in the embodiment of FIG. 1. It is a figure which shows the control light used in the Example of FIG. 1 at the time of the action | operation of an optical signal amplifier. FIG. 8 is a diagram illustrating output signals when the input signal light illustrated in FIG. 6 and the control light illustrated in FIG. 7 are respectively input in the embodiment of FIG. 1. It is a figure explaining the principal part structure of the optical signal amplifier in the other Example of this invention, Comprising: It is a figure equivalent to FIG. It is a figure explaining the principal part structure of the optical signal amplifier in the other Example of this invention, Comprising: It is a figure equivalent to FIG. In the Example of FIG. 10, it is a figure which shows the reflection wavelength band of a 4th Bragg reflection grating. It is a figure explaining the principal part structure of the optical signal amplifier in the other Example of this invention, Comprising: It is a figure equivalent to FIG. In the Example of FIG. 12, it is a figure which shows the reflection wavelength range of a 5th Bragg reflection grating. It is a figure explaining the principal part structure of the optical signal amplifier in the other Example of this invention, Comprising: It is a figure equivalent to FIG. It is a figure explaining the principal part structure of the optical signal amplifier in the other Example of this invention, Comprising: It is a figure equivalent to FIG.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the drawings used for the following description, the dimensional ratios of the respective parts are not necessarily drawn accurately.

  FIG. 1 is a diagram showing a configuration of an optical signal amplifying apparatus 10 according to an embodiment of the present invention. In FIG. 1, an optical signal amplifying apparatus 10 includes a first input optical fiber 12, a first semiconductor optical amplifier 14, a second semiconductor optical amplifier 16, a first optical coupler 18, a first Bragg reflection grating 20, and an output optical fiber. 22, a second Bragg reflection grating 24, and the like, and output light Iout obtained by modulating the input signal light Iin having the first wavelength λ1 using the control light Ic. FIG. 4 is a spectrum illustrating the power (intensity) of the output light Iout when the first wavelength λ1 is 1551 nm.

  The first semiconductor optical amplifier 14 is composed of, for example, a chip-like element shown in FIG. 2, and includes a semiconductor substrate 14a composed of a compound semiconductor, such as indium phosphorus InP, and an III-V group epitaxially grown thereon. An optical waveguide 14b made of a mixed crystal semiconductor and formed with a predetermined width by photolithography and having a relatively high refractive index, and a pn junction constituting a part of the multilayer film in the optical waveguide 14b. , An active layer 14c composed of any one of bulk, multiple quantum well, strained superlattice, and quantum dot, an upper electrode 14e fixed to the upper surface of the optical waveguide 14b, and a lower electrode fixed to the lower surface of the semiconductor substrate 14a 14f. In a state where an injection current flows between the upper electrode 14e and the lower electrode 14f, when the input signal light Iin having a predetermined wavelength λ1 is incident and propagated through the optical waveguide 14b, the active layer 14c is passed. The light is amplified by the induced radiation action and output. At the same time, the first ambient light having an ambient wavelength other than the wavelength λ1 centered on the wavelength λ1 and the intensity increasing or decreasing (intensity inversion) in inverse proportion to the intensity modulation of the input signal light L1 by the so-called mutual gain modulation action. (Spontaneously generated light) is generated and output.

  Similar to the first semiconductor optical amplifier 14 shown in FIG. 2, the second semiconductor optical amplifier 16 includes a semiconductor substrate 16a made of a compound semiconductor such as indium phosphorus (InP), and a III-V epitaxially grown thereon. An optical waveguide 16b made of a mixed crystal semiconductor and formed of a multilayer film having a relatively high refractive index formed to a predetermined width by photolithography, and a pn junction constituting a part of the multilayer film in the optical waveguide 16b. The active layer 16c composed of any one of a bulk, a multiple quantum well, a strained superlattice, and a quantum dot, an upper electrode 16e fixed to the upper surface of the optical waveguide 16b, and a lower portion fixed to the lower surface of the semiconductor substrate 16a Electrode 16f. In the state in which an injection current flows between the upper electrode 16e and the lower electrode 16f, the active layer 16c is in the process in which the control light Ic having the predetermined wavelength λ1 and the first ambient light are incident and propagated in the optical waveguide 16b. The output light Iout having the wavelength λ1 that is modulated by the control light Ic by the so-called mutual gain modulation function, and the first wavelength λ1. Second ambient light (naturally generated light) that has an ambient wavelength other than the first wavelength λ1 and whose intensity increases or decreases (intensity inversion) in inverse proportion to the intensity modulation of the output light Iout is generated. Is also output.

  The first input optical fiber 12 is a well-known clad or cell-hook type optical fiber having polarization independence for transmitting light while preserving the polarization plane of light, and is output from a signal source (not shown). The input signal light Iin having the first wavelength λ 1 is guided and incident on the first semiconductor optical amplifier 14. A front spherical lens 12z is formed on the end surface of the first input optical fiber 12 on the first semiconductor optical amplifier 14 side, and is optically coupled to the input side of the first semiconductor optical amplifier 14.

  The first optical coupler 18 is composed of a polarization-independent optical fiber, and includes a common fiber portion 18c and a branch fiber portion that is directed to a pair of first semiconductor optical amplifiers 14 branched from one end of the common fiber portion 18c. 18a and a branch fiber portion 18b directed to the second semiconductor optical amplifier 16, and control light Ic of the first wavelength λ1 from the common fiber portion 18c and first ambient light reflected by the first Bragg reflection grating 20 are, for example, A large amount is distributed to the second semiconductor optical amplifier 16 side at a branching ratio of 1: 5. The first optical coupler 18 is configured, for example, by melting and stretching the ends of a pair of optical fibers. Tip spherical lenses 18az and 18bz are formed on the tip surfaces of the pair of branch fiber portions 18a and 18b, respectively, and are connected to the output side of the first semiconductor optical amplifier 14 and the input side of the second semiconductor optical amplifier 16, respectively. Optically coupled.

The first Bragg reflection grating 20 is provided in the common fiber portion 18c that is a predetermined distance away from the branch point of the first optical coupler 18 or an optical fiber coupled thereto. For example, as shown in FIG. 3, the first Bragg reflection grating 20 includes a substantially cylindrical core 30 made of quartz SiO ₂ to which germanium Ge is added, and a refractive index lower than that of the core 30 and its outer periphery. In the optical fiber (common fiber portion 18c) formed by the clad 32 made of substantially cylindrical quartz SiO ₂ covering the surface, the core 20 is caused by a light-induced refractive index change due to ultraviolet irradiation using a phase mask or the like. Typically, a periodic refractive index change of about 10,000 to 20,000 layers is constituted by an optical fiber grating formed in the light propagation direction in one or more groups in the propagation direction of the core 20. The refractive index change may have an equal period, but it may be one in which the period is sequentially changed in a chirp shape. The first Bragg reflection grating 20 has a characteristic of selectively reflecting light having a wavelength corresponding to the period of the refractive index and the effective refractive index. For example, if the first wavelength λ1 is 1551 nm, In order to reflect one side and transmit the other side with respect to the first wavelength λ1 of the first ambient light not including the first first wavelength λ1 as the center, the wavelength band of the first ambient light Among them, it has a reflection characteristic of reflecting a wavelength band on one side with respect to the first wavelength λ1, for example, a reflection wavelength bandwidth of at least about 5 nm or more, for example, about 8.5 nm, reflecting light on the shorter wavelength side than the first wavelength λ1. And functions as a wavelength selective filter. The solid line in FIG. 5 is a diagram illustrating the reflection wavelength band of the Bragg reflection grating 20. As the reflection wavelength bandwidth of the first Bragg reflection grating 20 is wider, the effect of reliably transmitting the inverted input signal to the second semiconductor optical amplifier 16 is obtained.

  The output optical fiber 22 is composed of a polarization-independent optical fiber, and receives the output light Iout output from the second semiconductor optical amplifier 16 and guides it to a predetermined position (not shown). A tip lens 22z is also formed on the end surface of the output optical fiber 22 on the second semiconductor optical amplifier 16 side, and is optically coupled to the output side of the second semiconductor optical amplifier 16.

  The second Bragg reflection grating 24 is provided at the end of the output optical fiber 22 on the second semiconductor optical amplifier 16 side. Similar to the first Bragg reflection grating 20, the second Bragg reflection grating 24 is composed of an optical fiber grating formed by providing multiple layers of refractive index changes in the light propagation direction. The second Bragg reflection grating 24 outputs the second ambient light having an ambient wavelength other than the first wavelength λ1 centered on the first wavelength λ1 output from the second semiconductor optical amplifier 16 to the second semiconductor optical amplifier 16. By making the light incident again, negative feedback amplification is generated in the second semiconductor optical amplifier 16 to increase the modulation factor and the S / N ratio. The second Bragg reflection grating 24 reflects the second ambient light and prevents the first Bragg reflection grating 20 from generating resonance (oscillation) with the first Bragg reflection grating 20. The reflection wavelength bands are different from each other so that the frequency bands do not overlap. For example, as shown by the solid line in FIG. 5, when the reflection wavelength band of the first Bragg reflection grating 20 has a reflection wavelength band that reflects light on the short wavelength side with respect to the first wavelength λ1, the second Bragg reflection grating is used. 24 has a reflection wavelength band for reflecting light on the long wavelength side with respect to the first wavelength λ1, as indicated by a broken line in FIG. The reflection wavelength band of the second Bragg reflection grating 24 is preferably about 5 nm. If it is too wide, the negative feedback amplification effect increases and the intensity of the output light Iout decreases. If it is too narrow, the negative feedback amplification effect decreases and the modulation degree cannot be sufficiently obtained.

  An experimental result of the optical signal amplification operation of the optical signal amplification device 10 performed by the present inventor will be described with reference to FIGS. 6, 7, and 8. When the input signal light Iin having the first wavelength λ1 shown in FIG. 6 is input to the first semiconductor optical amplifier 14 through the first input optical fiber 12, the first semiconductor optical amplifier 14 has the first wavelength λ1. While the input signal light Iin is amplified, first ambient light other than the first wavelength λ1 whose intensity is inverted is generated, and each is combined and output. In the first Bragg reflection grating 20 provided in the common fiber portion 18c of the first optical coupler 18, the amplified light having the first wavelength λ1 of the output light passes but the first of the first ambient light. Partial ambient light having a wavelength shorter than the wavelength λ1 is reflected. Therefore, the partial ambient light on the short wavelength side is incident on the second semiconductor optical amplifier 16 together with the control light Ic having the first wavelength λ1 input to the common fiber portion 18c of the first optical coupler 18 shown in FIG. The

  In the second semiconductor optical amplifier 16, when the control light Ic having the first wavelength λ1 and the partial ambient light on the short wavelength side, which is light other than the first wavelength λ1, are input, the control light Ic having the first wavelength λ1 is input. Outputs the output light Iout of the first wavelength λ1 that has been amplified and subjected to the modulation of the partial ambient light by the mutual gain modulation. Two ambient lights are also output. FIG. 8 shows the output light Iout. In FIG. 8, the waveform of the output light Iout indicated by the broken line, the one-dot chain line, the two-dot chain line, and the three-dot chain line corresponds to the waveform indicated by the broken line, the one-dot chain line, the two-dot chain line, and the three-dot chain line of the control light Ic. Yes. From this, the input signal light Iin is modulated by the control light Ic and the output light Iout is output through the output optical fiber 22, so that the optical signal amplifying apparatus 10 uses the same light as the transistor 3 It has terminal control characteristics, that is, functions as an optical three-terminal control device.

  Since the second Bragg reflection grating 24 provided on the second semiconductor optical amplifier 16 side of the output optical fiber 22 has a reflection wavelength band indicated by a broken line in FIG. 5, the output light Iout of the first wavelength λ1 is generated. Of the second ambient light, part of the second ambient light having a wavelength longer than the first wavelength λ 1 is reflected and re-input to the second semiconductor optical amplifier 16. Operate feedback amplification. By this negative feedback amplification operation, the modulation degree of the output light Iout is increased, and the noise is reduced and the S / N ratio is increased. In FIG. 8, the fact that the intensity of the lower peak value of the output light Iout, that is, the minimum extreme value (local minimum) is close to the zero value (baseline) indicates such an effect.

  As described above, in this embodiment, when the input signal light Iin having the first wavelength λ1 is input, the light intensity amplification characteristic of the ambient light having the first wavelength λ1 is modulated according to the intensity of the input signal light Iin. A first semiconductor optical amplifier 14 that outputs the amplified light of the input signal light Iin and the first ambient light that does not include the first wavelength λ1 whose intensity is inverted with respect to the intensity of the input signal light Iin; When the first ambient light not including the first wavelength λ1 is input, the light intensity amplification characteristic of light other than the wavelength of the first ambient light is modulated according to the intensity of the first ambient light, and the first ambient light Output light Iout having the light amplified and wavelength-converted to the wavelength λ1 of the control light Ic and second ambient light that does not include the wavelength λ1 of the control light Ic that is inverted in intensity with respect to the intensity of the output light Iout Second semiconductor optical amplifier 16 and control light input optical fiber (common fiber portion 18 c) branching the control light Ic of the first wavelength λ1 input through the first optical coupler 18 and the first semiconductor optical amplifier 14 to be input to the first semiconductor optical amplifier 14 and the second semiconductor optical amplifier 16, respectively. A first Bragg reflection grating 20 that reflects the output first ambient light and inputs the first ambient light to the second semiconductor optical amplifier 16, and an output for guiding the light output from the second semiconductor optical amplifier 16 The second Bragg reflection grating 24 that reflects the second ambient light output from the optical fiber 22 and the second semiconductor optical amplifier 16 and re-inputs the second ambient light to the second semiconductor optical amplifier 16 to perform negative feedback amplification. , And the optical signal amplifying apparatus 10 that outputs the output light Iout having the first wavelength λ1 transmitted through the second Bragg reflection grating 24, the first Bragg reflection grating 20 and the second Bragg reflection grating 24 are substantially Since it has a reflection wavelength band that does not overlap each other, the oscillation or optical resonance between them is suppressed, stable optical signal amplifying operation is obtained.

  Further, according to the present embodiment, the first Bragg reflection grating 20 is provided in the control light input optical fiber (common fiber portion 18c), and the first ambient light output from the first semiconductor optical amplifier 14 is the first one. Having a reflection wavelength band for reflecting the first partial ambient light belonging to one of the pair of wavelength bands sandwiching one wavelength λ1, and inputting the first partial ambient light to the second semiconductor optical amplifier 16 The second Bragg reflection grating 24 is provided in the output optical fiber 22 and is the other wavelength in the wavelength band sandwiching the first wavelength λ 1 of the second ambient light output from the second semiconductor optical amplifier 16. The second Bragg reflection grating 20 and the second Bragg reflection grating 20 have a reflection wavelength band that reflects the second partial ambient light belonging to the band and re-inputs the second partial ambient light to the second semiconductor optical amplifier 16. Between the Bragg reflector 24 Or the light resonance is suppressed, stable optical signal amplifying operation is obtained. Further, since the first Bragg reflection grating 20 is provided in the control light input optical fiber (common fiber portion 18c) and the second Bragg reflection grating 16 is provided in the output optical fiber 22, the branching of the optical coupler 18 is performed. Since it is formed more easily and stably than the case where it is provided in the part, a stable and highly accurate reflection wavelength band can be obtained.

  Further, according to the present embodiment, the first Bragg reflection grating 20 has a reflection wavelength band wider than the reflection wavelength band of the second Bragg reflection grating 24, and therefore is output from the first semiconductor optical amplifier 14. The ratio of the ambient light supplied to the second semiconductor optical amplifier 16 is increased, and there is an advantage that the inverted input signal is reliably transmitted to the second semiconductor optical amplifier 16.

  Further, according to the present embodiment, the input signal light and control light input optical fiber (common fiber portion 18c) and the output optical fiber 22 are composed of polarization plane-independent optical fibers. A temperature-stable optical signal amplification output can be obtained.

  Next, another embodiment of the present invention will be described. In the following description, parts common to the embodiments are denoted by the same reference numerals and description thereof is omitted.

  The optical signal amplifying apparatus 40 of the embodiment shown in FIG. 9 is different from the optical signal amplifying apparatus 10 in the first semiconductor optical amplifier 14 at the end of the first input optical fiber 12 on the first semiconductor optical amplifier 14 side. A reflection wavelength band for reflecting the first partial ambient light belonging to one of the pair of wavelength bands sandwiching the first wavelength λ1 among the first ambient light output from the first ambient light, The difference is that a third Bragg reflection grating 42 is provided for re-inputting light to the first semiconductor optical amplifier 14 for negative feedback amplification, and the other parts are configured in the same manner. The third Bragg reflection grating 42 has a reflection wavelength band indicated by a broken line in FIG. 5, for example. The band of this reflection wavelength band is preferably about 5 nm. If it is too wide, the negative feedback amplification effect increases and the intensity of the output light Iout decreases. If it is too narrow, the negative feedback amplification effect decreases and the modulation degree cannot be sufficiently obtained.

  According to the optical signal amplifying apparatus 40 of the present embodiment, the first ambient light outputted from the first semiconductor optical amplifier 14 belongs to the first wavelength band belonging to one of the pair of wavelength bands sandwiching the first wavelength λ1. Since the third Bragg reflection grating 42 having the reflection wavelength band for reflecting the one-part ambient light is provided, the first partial ambient light is reflected by the third Bragg reflection grating 42 and the first semiconductor optical amplifier. 14, the first semiconductor optical amplifier 14 is subjected to negative feedback amplification, so that stable optical signal amplification of the first semiconductor optical amplifier 14 having a high S / N ratio is obtained. Further, since the third Bragg reflection grating 42 has a reflection wavelength band that does not overlap with the reflection wavelength band of the first Bragg reflection grating 20, the optical signal resonates or oscillates between them. There is an advantage of being suitably prevented.

  When the input signal light Iin having the first wavelength λ1 is input to the optical signal amplifying apparatus 10 via the second input optical fiber 51, the optical signal amplifying apparatus 50 of the embodiment shown in FIG. A light intensity amplification characteristic of ambient light having the first wavelength λ1 is modulated in accordance with the intensity of the signal light Iin, and the intensity is inverted with respect to the intensity of the input signal light Iin and the intensity of the input signal light Iin. The third semiconductor optical amplifier 52 that outputs the third ambient light around the wavelength λ1 and the output light Iin ′ of the first wavelength λ1 that is the amplified light of the input signal light Iin from the third semiconductor optical amplifier 52 1 is different in that it includes a waveguide 54 to be input to the semiconductor optical amplifier 14, and the other parts are configured in the same manner.

  The waveguide 54 includes a common fiber portion 58c provided with a fourth Bragg reflection grating 56 for reflecting the output light Iin ′ having the first wavelength λ1 from the third semiconductor optical amplifier 52, and the common fiber portion 58c. The first branched fiber portion 58a and the second branched fiber portion 58b branch from one end of the first optical fiber, and the first branched fiber portion 58a has an output light Iin ′ of the first wavelength λ1 from the third semiconductor optical amplifier 52. Is output from the second optical coupler 58 in which the output light Iin ′ having the first wavelength λ 1 reflected by the fourth Bragg reflection grating 56 is input to the first semiconductor optical amplifier 14 through the second branch fiber portion 58b. Composed. A tip ball lens 51z, a tip ball lens 58az, and a tip ball lens 58bz are provided on the tip surfaces of the second input optical fiber 51 and the pair of first branch fiber portion 58a and second branch fiber portion 58b, respectively. The third semiconductor optical amplifier 52 and the first semiconductor optical amplifier 14 are optically coupled to each other.

  FIG. 11 shows the reflection wavelength band of the fourth Bragg reflection grating 56. The fourth Bragg reflection grating 56 is for reflecting the output light Iin ′ having the first wavelength λ1 from the third semiconductor optical amplifier 52, and does not reflect ambient light. The wavelength band is set to a relatively narrow band centered on the first wavelength λ1, for example, about 1 nm.

  According to the optical signal amplifying apparatus 50 of the present embodiment, the input signal light Iin having the first wavelength λ1 from the third semiconductor optical amplifier 52 is amplified and input to the first semiconductor optical amplifier 14. Even if the intensity of the signal light Iin is low, a high-intensity output signal Iout can be obtained. In general, in order to generate mutual gain modulation, an input signal intensity of the order of mW is required, but since the output of a semiconductor optical amplifier can only obtain a maximum of about 1 to several mW, the intensity ratio (amplification factor) Since Iout / Iin was obtained only about 1 to several times or less, the output light Iout was sometimes difficult to use as an input signal of the next-stage semiconductor optical amplifier. However, according to the present embodiment, the above problem can be solved by setting the intensity of the input light Iin small and amplifying it. For example, if the intensity of Iin can be reduced to 1/10, at least 10 optical signal amplifiers can be driven. Further, according to the present embodiment, since the fourth Bragg reflection grating 56 is provided in the common fiber portion 58c, it is easily and stably formed as compared with the case where it is provided in the branch portion of the optical coupler 58. A highly accurate reflection wavelength band can be obtained.

  The optical signal amplifying apparatus 50 of the present embodiment is different from the optical signal amplifying apparatus 10 in terms of optical fibers other than the input signal light and control light input optical fiber (common fiber portion 18c) and the output optical fiber 22, that is, The second input optical fiber 51 and the second optical coupler 58 are also composed of polarization plane-independent optical fibers.

  The optical signal amplifying device 60 of the embodiment shown in FIG. 12 has the third semiconductor optical amplifier 52 of the second input optical fiber 51 that guides the input signal light Iin to the third semiconductor optical amplifier 52 with respect to the optical signal amplifying device 50. A fifth partial ambient light belonging to one of the pair of wavelength bands sandwiching the first wavelength .lamda.1 of the third ambient light output from the third semiconductor optical amplifier 52 is provided at the side end. And a fifth Bragg reflection grating 62 that has a reflection wavelength band to be input and re-inputs the fifth partial ambient light to the third semiconductor optical amplifier 52 for negative feedback amplification. The fifth Bragg reflection grating 62 has, for example, the reflection wavelength band shown in FIG. 13, and the reflection wavelength band is set so that the frequencies do not overlap with each other with respect to the fourth Bragg reflection grating 56. The filter 64 transmits light only in a relatively narrow band near the first wavelength λ1, and is provided to remove noise light other than the first wavelength λ1 included in the output light Iout.

  According to the present embodiment, stable amplification of the input signal light Iin is obtained by the negative feedback amplification action of the third semiconductor optical amplifier 52, and the modulation degree of the amplified input signal light Iin 'is increased.

  The optical signal amplifying device 70 of the embodiment shown in FIG. 14 is similar to the optical signal amplifying device 60 at the end of the second branch fiber portion 58b of the second optical coupler 58 on the first semiconductor optical amplifier 14 side. The difference is that a Bragg reflection grating 59 is provided, and the other parts are configured similarly. The sixth Bragg reflection grating 59 is configured in the same manner as the third Bragg reflection grating 42 of the second embodiment, and a pair of wavelengths sandwiching the first wavelength λ 1 of the first ambient light output from the first semiconductor optical amplifier 14. A reflection wavelength band that reflects the first partial ambient light belonging to one of the bands is reflected, and the first partial ambient light is re-input to the first semiconductor optical amplifier 14 for negative feedback amplification.

  In the optical signal amplifying apparatus 80 of the embodiment shown in FIG. 15, the bias light of the third wavelength .lamda. The difference is that light (Ib) passes through the fourth Bragg reflection grating 56 and is supplied to the first semiconductor optical amplifier 14, and the other parts are configured in the same manner. Since the first Bragg reflection grating 20 has a reflection wavelength band indicated by a solid line in FIG. 5, the first Bragg reflection grating 20 is input from the other end of the common fiber portion 58 c of the second optical coupler 58 and amplified by the first semiconductor optical amplifier 14. The bias light Ib having the third wavelength λ3 different from the first wavelength λ1 is applied to the second wavelength band of the first ambient light output from the first semiconductor optical amplifier 14 and belonging to the other wavelength band sandwiching the first wavelength λ1. One part of the light is reflected together with ambient light and input to the second semiconductor optical amplifier 16. As a result, the light intensity of the wavelength λ3 subjected to the mutual gain modulation in the second semiconductor optical amplifier 16 is enhanced. As a result, an output light Iout amplified with an optical signal having a higher intensity is obtained.

  As mentioned above, although one Example of this invention was described based on drawing, this invention is applied also in another aspect.

  For example, in the above-described embodiment, the control light Ic has the same first wavelength λ1 as the input signal light Iin. However, the control light Ic is not necessarily the first wavelength λ1, and is different from the first wavelength λ1. It may have a wavelength λ2. In this case, the output light Iout having the second wavelength λ2 is output.

  In the above-described embodiment, the first Bragg reflection grating 20 has a reflection wavelength band on the short wavelength side with respect to the first wavelength λ1, as shown by the solid line in FIG. As shown by the broken line, the reflection wavelength band on the long wavelength side with respect to the first wavelength λ1 is set so that the reflection wavelength bands do not overlap each other, but conversely, the first Bragg reflection grating 20 May be set on the long wavelength side with respect to the first wavelength λ1, and the reflection wavelength band of the second Bragg reflection grating 24 may be set on the short wavelength side with respect to the first wavelength λ1. Further, the reflection wavelength band of the first Bragg reflection grating 20 and the reflection wavelength band of the second Bragg reflection grating 24 may be set to the same wavelength band with respect to the first wavelength λ1. In short, it is only necessary that the frequency bands are set so as not to overlap each other. The overlapping frequency bands need only be in a state where they do not substantially overlap within a range where oscillation does not occur. For example, a range of −3 dB in the frequency bands may not overlap.

  In the above-described embodiments of FIGS. 12, 14, and 15, the filter 64 having a transmission wavelength characteristic of a relatively narrow band centered on the first wavelength λ1 is used as the output light in order to transmit the output light Iout. Although provided in the fiber 22, it is not necessarily provided. 1, 9, and 10 may be provided as necessary.

  Some or all of the first optical coupler 18 and the second optical coupler 58 provided in the above-described embodiment may be replaced with other optical elements or a combination of the optical elements as long as they have the same function. Good.

  In addition, the first Bragg reflection grating 20 and the second Bragg reflection grating 24 of the above-described embodiment may be replaced with other optical elements having the same function, such as a multilayer filter and a wavelength selection mirror.

  Although not illustrated one by one, the present invention can be implemented in variously modified and improved modes based on the knowledge of those skilled in the art.

10, 40, 50, 60, 70, 80: optical signal amplifier 12: first input optical fiber 14: first semiconductor optical amplifier 16: second semiconductor optical amplifier 18: first optical coupler 18c: common fiber section ( (Optical fiber for control light input)
20: first Bragg reflection grating 22: output optical fiber 24: second Bragg reflection grating 42: third Bragg reflection grating 51: second input optical fiber 56: fourth Bragg reflection grating 58: second optical coupler 59: Sixth Bragg reflection grating 62: Fifth Bragg reflection grating

Claims (12)

When the input signal light of the first wavelength is input, the light intensity amplification characteristic of the ambient light of the first wavelength is modulated according to the intensity of the input signal light, and the input signal light is amplified and the input signal When the first semiconductor optical amplifier that outputs the first ambient light that does not include the first wavelength, the intensity of which is inverted with respect to the intensity of the light, and the second input signal light of the second wavelength are input, the second input The light intensity amplification characteristic of light other than the second wavelength is modulated according to the intensity of the signal light, and the intensity is inverted with respect to the intensity of the output light amplified from the second input signal light and the intensity of the second input signal light. A second semiconductor optical amplifier that outputs second ambient light that does not include a second wavelength, and the first ambient light is selected from the light output from the first semiconductor optical amplifier and is sent to the second semiconductor optical amplifier. The first wavelength selection element to be input and the second circumference of the light output from the second semiconductor optical amplifier A second wavelength selection element that reflects light and re-inputs the second ambient light to the second semiconductor optical amplifier for negative feedback amplification, and the control light having a wavelength different from that of the first ambient light is An optical signal amplifying apparatus that outputs the output light having the same wavelength as the control light by being input to the second semiconductor optical amplifier as a second input signal light,
The optical signal amplification device, wherein the first wavelength selection element and the second wavelength selection element have reflection wavelength bands that do not overlap each other. A common fiber portion, and a pair of first branch fiber portion and second branch fiber portion branched from one end of the common fiber portion, and light output from the first semiconductor optical amplifier to the first branch fiber portion Is input, the control light is input to the common fiber portion, and the first optical coupler is input from the second branch fiber portion to the second semiconductor optical amplifier;
An output optical fiber for guiding the light output from the second semiconductor optical amplifier,
The first wavelength selection element is provided in the common fiber portion, and belongs to one wavelength band among the wavelength bands sandwiching the first wavelength of the first ambient light output from the first semiconductor optical amplifier. The first partial ambient light having a reflection wavelength band for reflecting the partial ambient light, and the first partial ambient light being input to the second semiconductor optical amplifier;
The second wavelength selection element is provided in the output optical fiber, and belongs to the other wavelength band among the wavelength bands sandwiching the first wavelength in the second ambient light output from the second semiconductor optical amplifier. A second Bragg reflection grating having a reflection wavelength band for reflecting the second partial ambient light and re-inputting the second partial ambient light to the second semiconductor optical amplifier is provided. Item 4. The optical signal amplifying apparatus according to Item 1. A first input optical fiber for guiding the input signal light to the first semiconductor optical amplifier;
The first portion surroundings belonging to one of the wavelength bands sandwiching the first wavelength of the first ambient light provided in the first input optical fiber and output from the first semiconductor optical amplifier A third Bragg reflection grating having a reflection wavelength band for reflecting light and re-inputting the first partial ambient light to the first semiconductor optical amplifier for negative feedback amplification. Or 2 optical signal amplifiers.   When the input signal light of the first wavelength is input, the light intensity amplification characteristic of the ambient light of the first wavelength is modulated according to the intensity of the input signal light, and the input light and the input light are amplified. 2. A third semiconductor optical amplifier that outputs third ambient light around the first wavelength, the intensity of which is inverted with respect to the intensity of the signal light, to the first semiconductor optical amplifier. 2. Optical signal amplifying device.   A common fiber portion provided with a fourth Bragg reflection grating for reflecting the output light of the first wavelength, which is an amplified light of the input signal light from the third semiconductor optical amplifier, and one end of the common fiber portion A pair of the first branch fiber part and the second branch fiber part branching, and the first wavelength output light from the third semiconductor optical amplifier is input to the first branch fiber part; 5. The apparatus according to claim 4, further comprising: a second optical coupler in which the output light having the first wavelength reflected by the Bragg reflection grating is input to the first semiconductor optical amplifier via the second branch fiber portion. Optical signal amplifier. A second input optical fiber for guiding the input signal light to the third semiconductor optical amplifier;
A fifth partial ambient light which is provided in the second input optical fiber and belongs to one of the wavelength bands sandwiching the first wavelength among the third ambient light output from the third semiconductor optical amplifier. And a fifth Bragg reflection grating having a reflection wavelength band for reflecting the light and re-inputting the fifth partial ambient light to the third semiconductor optical amplifier for negative feedback amplification. 5. Optical signal amplifying device of 5.   One wavelength of a pair of wavelength bands sandwiching the first wavelength of the first ambient light from the first semiconductor optical amplifier at the end of the second branching portion of the second optical coupler on the first semiconductor optical amplifier side 6. The optical signal amplifying apparatus according to claim 5, further comprising a sixth Bragg reflection grating having a reflection wavelength band for reflecting the first partial ambient light belonging to the band to the first semiconductor optical amplifier.   The first Bragg reflection grating receives bias light having a third wavelength different from the first wavelength input from the other end of the common fiber portion of the second optical coupler and amplified by the first semiconductor optical amplifier. The first ambient light output from the first semiconductor optical amplifier is reflected to the second semiconductor optical amplifier together with the first partial ambient light belonging to the other of the wavelength bands sandwiching the first wavelength. The optical signal amplifying apparatus according to claim 5, wherein   9. The optical signal amplifying device according to claim 2, wherein the first Bragg reflection grating has a reflection wavelength band wider than a reflection wavelength band of the second Bragg reflection grating.   The optical signal amplifying apparatus according to claim 2, wherein the optical fiber and the output optical fiber constituting the first optical coupler are configured by polarization plane-independent optical fibers.   The optical fiber constituting the first and second optical couplers and / or the first or second input optical fiber or / and the output optical fiber are made of polarization plane-independent optical fibers. An optical signal amplifying device according to any one of claims 2, 5 to 9.   12. The optical signal amplifying apparatus according to claim 1, wherein the wavelength of the control light is the first wavelength.

Images