JP4612243B2 - Raman optical amplifier - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a Raman optical amplifier, and more particularly to a Raman optical amplifier that performs optical amplification using stimulated Raman scattering.
[0002]
[Prior art]
Conventionally, a method of performing optical amplification using stimulated Raman scattering is known. In this optical amplification method, pumping light having a wavelength λ is incident on an optical fiber for generating Raman scattered light (hereinafter referred to as an optical fiber), and stimulated Raman scattering is generated by the pumping light, and a gain near the wavelength λ + a is generated in the optical fiber. A belt is made. For example, when λ + a signal light is incident on the optical fiber in such a state, the signal light can be amplified.
[0003]
[Problems to be solved by the invention]
However, the excitation light having the wavelength λ cannot take an arbitrary wavelength due to restrictions on the light source, has a problem that the amplifiable wavelength range is limited and the amplification factor is low, and the range of practical use is narrowed. Recently, a method for improving the amplification factor by confining Raman scattered light in an optical fiber by combining a plurality of types of fiber couplers or connecting a plurality of types of fiber Bragg gratings (FBGs) has been proposed. However, it is difficult to amplify signal light with optical gain and low noise.
[0004]
Therefore, the main object of the present invention is to be able to set the pumping light wavelength in a wide wavelength range, to greatly expand the applicable wavelength, to separate the optical fiber for generating the pumping light, and to maintain a high gain. Thus, the present invention provides a Raman optical amplifier that realizes amplification of signal light with high gain and low noise.
[0005]
[Means for Solving the Problems]
The present invention is a Raman optical amplifier, an optical oscillation source that generates Raman scattered light having a wavelength λ + α in response to incidence of a laser beam having a wavelength λ, an optical circulator, and an optical oscillation via the optical circulator optically coupled to the source, the Raman scattered light of a wavelength lambda + alpha as excitation light, is configured to include a signal light amplifying section for amplifying and outputting the signal light in response to the incident signal light having a wavelength lambda + alpha + beta The The optical circulator has first to third ports, outputs light input to the first port from the second port, and outputs light input to the third port from the first port. . The optical oscillation source includes an optical fiber for generating scattered light having a wavelength λ + α based on laser light having a wavelength λ, and a laser having a wavelength λ from the first end side of the scattered light generating optical fiber. A laser beam having a wavelength λ is provided in an optical path between an incident portion for entering light into the scattered light generating optical fiber, a second end of the scattered light generating optical fiber, and a first port of the optical circulator. The first fiber Bragg grating to be reflected and the Raman scattered light having the wavelength λ + α generated in the scattered light generating optical fiber is provided in the optical path between the first end of the scattered light generating optical fiber and the incident portion. Wavelengths generated by a pair of the second fiber Bragg grating to be reflected and a pair of both sides of the scattered light generating optical fiber on the optical path between the incident portion and the first port of the optical circulator, and generated by the scattered light generating optical fiber λ and λ + And a third fiber Bragg grating for one or more pairs of reflecting Raman scattered light having a wavelength between. The signal light amplification unit is amplified by an input unit for inputting signal light of wavelength λ + α + β, a signal light amplification optical fiber for amplifying signal light of wavelength λ + α + β input from the input unit, and a signal light amplification optical fiber And an output unit that outputs signal light of wavelength λ + α + β. The second port of the optical circulator, the output unit, the optical fiber for signal light amplification, the input unit, and the third port of the optical circulator are connected in this order in a loop .
[0006]
Preferably, the incident part is a coupler that multiplexes / demultiplexes light of wavelength λ and light of wavelength λ + α + β, and each of the input part and output part multiplexes / demultiplexes light of wavelength λ + α and light of wavelength λ + α + β. It is a coupler.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
First, the principle of the present invention will be described. When light having a wavelength λ is incident on the optical fiber, scattered light (referred to as Raman scattered light) is generated in the wavelength region of wavelength λ + a1 using the incident light as excitation light. If signal light around the wavelength λ + a1 enters the fiber in such a state, the signal light is amplified. Further, when there is no signal light at this wavelength, if the light of wavelength λ is strong, the scattered light of wavelength λ + a1 becomes large, and a chain of λ + a1 + a2 scattered light is generated using this light as excitation light.
[0012]
At this time, the fiber has a gain region around the wavelength λ + a1 + a2, and it is possible to amplify a wavelength far away from the original pumping light. The present invention improves the efficiency of this Raman amplification.
[0013]
FIG. 1 is a diagram showing a Raman optical amplifier according to an embodiment of the present invention. In FIG. 1, light having a wavelength λ1 is input from a laser 1 to a λ1 / λ5 coupler 2 as excitation light. This excitation light is input to a laser oscillation unit 5 composed of a fiber Bragg grating (FBG) 3 having a reflection wavelength of Raman scattering wavelengths λ1 to λ4 and an optical fiber 4 for generating Raman scattered light, and further, an optical circulator 6. Is input to a signal light amplifying unit 10 composed of λ4 / λ5 couplers 7 and 8 and an optical fiber 9 for signal light amplification.
[0014]
Next, the operation of the Raman optical amplifier shown in FIG. 1 will be described. The excitation light of λ1 is folded back by the FBG 3 and travels back and forth through the Raman scattered light generating optical fiber 4 to generate Raman scattered light λ2. The Raman scattered light λ2 is folded by the FBG 3 and confined in the Raman scattered light generating optical fiber 4 to generate the Raman scattered light λ3. Similarly, the Raman scattered light λ4 circulates in a loop constituted by the FBG 3, the Raman scattered light generating optical fiber 4, the optical circulator 6, the λ4 / λ5 couplers 7 and 8, and the signal light amplifying optical fiber 9. To do. At this time, when the λ5 signal light is input from the input port to the optical fiber 9 for signal light amplification via the λ4 / λ5 coupler 8 that multiplexes and demultiplexes the light of wavelengths λ4 and λ5, the light is amplified from the λ4 / λ5 coupler 7 to the output port. The signal light is output.
[0015]
In the embodiment of the present invention, since each Raman scattered light is confined in a closed loop, the Raman scattered light can be generated with high efficiency. Further, since the Raman scattered light λ4 for signal light amplification passes through the signal light amplification optical fiber 9 in a single direction, fluctuations in signal light amplification due to intensity fluctuations of Raman scattered light can be suppressed, and signal light amplification Since the λ5 noise light generated in the optical fiber 9 can be removed by a light source coupler, a low-noise amplifier can be configured.
[0016]
As a more specific embodiment, if the fiber is a light dispersion shifted optical fiber and λ1: 1.06 μm, λ2: 1.12 μm, λ3: 1.17 μm, λ4: 1.23 μ, then the λ5: 1.3 μm band Can be configured. The wavelength of the excitation light can be changed, and further amplification of a longer wavelength band can be supported by the further chain of Raman scattering.
[0017]
FIG. 2 is a diagram showing another embodiment of the present invention. This embodiment shows a method of amplifying the signal light having the wavelength λ5 by creating the Raman laser light having the wavelength λ4 by chaining the Raman scattered light using the light having the wavelength λ1 as the excitation light. The laser 1 having the wavelength λ1 is connected to a first loop including an FBG 3 having a reflection wavelength of Raman scattering wavelengths λ1 to λ3, an optical fiber 4 for generating Raman scattered light, and a 3 dB coupler 11, and this first loop is 3 dB. The coupler 11 is connected to a second loop including the λ4 / λ5 couplers 7 and 8 and the optical fiber 9 for signal light amplification.
[0018]
The excitation light of λ1 travels back and forth through the Raman scattered light generating optical fiber 4 by the FBG 3 to generate Raman scattered light λ2. The Raman scattered light λ2 is folded by the FBG 3 and confined in the Raman scattered light generating optical fiber 4 to generate the Raman scattered light λ3. Similarly generated Raman scattered light λ4 circulates in the second loop via the 3 dB coupler 11 as it circulates in the first loop. At this time, when the λ5 signal light is input from the input port to the optical fiber 9 for signal light amplification via the λ4 / λ5 coupler 8 that multiplexes and demultiplexes the light of wavelengths λ4 and λ5, the light is amplified from the λ4 / λ5 coupler 7 to the output port. The signal light is output.
[0019]
Also in this embodiment, since each Raman scattered light is confined in a closed loop, the Raman scattered light can be generated with high efficiency. Further, it can be configured only with simple optical components.
[0020]
As a more specific embodiment, a 1.3 μm band amplifier can be configured using the fiber shown in FIG. 1 and the wavelengths λ1 to λ5.
[0021]
FIG. 3 is a view showing still another embodiment of the present invention. In this embodiment, Raman scattered light is chain-generated at λ2 and λ3 using light of wavelength λ1 as excitation light to generate Raman laser light of wavelength λ4, thereby amplifying signal light of wavelength λ5. For this purpose, the λ1 / λ3 coupler 21, the coupler 22, the Raman scattered light generating optical fiber 24, and the coupler 23 shown in FIG. 3A constitute a first loop that is a λ1λ3 loop. Light of wavelength λ1 is input as excitation light from the laser 1 to one loop. The couplers 22 and 23 selectively multiplex / demultiplex λ1 and λ3 and λ2 and λ4 as shown in FIG.
[0022]
Λ2 and λ4 demultiplexed around the first loop are second λ2 loops including the coupler 22, the Raman scattered light generating optical fiber 24, the coupler 23, the coupler 25, and the coupler 26. Go around the loop. The couplers 25 and 26 selectively multiplex / demultiplex λ2 and λ4 as shown in FIG.
[0023]
Λ4 demultiplexed around the second loop is the coupler 22, the Raman scattered light generating optical fiber 24, the coupler 23, the coupler 25, the coupler 27, the coupler 28, the coupler 26, and the optical fiber. The third loop which is a λ4 loop consisting of 29 is circulated. The couplers 27 and 28 are λ4 / λ5 couplers.
[0024]
Next, the operation will be described. The λ1 excitation light circulates from the λ1 / λ3 coupler 21 through the λ1λ3 loop, which is the first loop, and the Raman scattered light λ2 is generated in the Raman scattered light generating optical fiber 24. The scattered light λ2 enters the second loop λ2 loop from the coupler 23 and circulates, and Raman scattered light λ3 is generated in the Raman scattered light generating optical fiber 24. The scattered light λ3 enters the first loop λ1λ3 loop by the coupler 23, and the Raman scattered light λ4 is generated in the Raman scattered light generating optical fiber 24.
[0025]
The scattered light λ 4 enters the λ 2 loop from the coupler 23, and further enters the third λ 4 loop by the coupler 25 and circulates, thereby forming a condition for generating the Raman scattered light λ 5 in the Raman scattered light generating optical fiber 24. At this time, when signal light is input from the input port via the λ4 / λ5 coupler 28 that multiplexes / demultiplexes light of wavelengths λ4 and λ5, the amplified signal light is output from the λ4 / λ5 coupler 27 to the output port.
[0026]
Also in this embodiment, since each Raman scattered light is confined in a closed loop, Raman scattering can be generated with high efficiency.
[0027]
As a specific embodiment, if the fiber is an optical dispersion shifted optical fiber and λ1: 1.06 μm, λ2: 1.12 μm, λ3: 1.17 μm, λ4: 1.23 μ, then λ5: 1.3 μm. A band amplifier can be constructed.
[0028]
FIG. 4 is a view showing still another embodiment of the present invention. In this embodiment, pumping light having a wavelength λ1 is obtained by a fiber ring laser, thereby amplifying signal light having a wavelength λ2. That is, the λ1 / λ2 coupler 31, the signal light amplification optical fiber 33, the λ1 / λ2 coupler 32, the wavelength tunable optical filter 34, and the broadband optical amplifier 35 constitute an optical loop. The λ1 / λ2 couplers 31 and 32 selectively multiplex / demultiplex λ1 and λ2.
[0029]
When the gain of the optical amplifier 35 exceeds the optical loss of the loop, it becomes a fiber ring laser, and laser oscillation occurs at the pass wavelength λ 1 of the wavelength tunable optical filter 34. At this time, a condition for generating Raman scattered light λ2 in the optical fiber 33 for signal light amplification is formed. Here, when the λ2 signal light is input from the input port to the signal light amplification optical fiber 33 via the λ1 / λ2 coupler, the amplified signal light is output from the output port.
[0030]
In this embodiment, since the Raman scattered light is confined in a closed loop, Raman scattering can be generated with high efficiency, and the wavelength λ1 is changed by the wavelength tunable optical filter 34 to easily change the characteristics of the optical amplifier. Is also possible.
[0031]
As a more specific embodiment, when a thulium-doped optical fiber amplifier is used as the optical amplifier 35, λ1 can be varied from 1.46 μm to 1.48 μm, and an optical amplifier near the 1.55 μm band can be configured.
[0032]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
[0033]
【The invention's effect】
As described above, according to the present invention, in response to the light of wavelength λ being incident on the optical oscillation source as excitation light, Raman scattered light of wavelength λ + α is generated and optically coupled to the optical oscillation source, The Raman scattered light with the wavelength λ + α circulates, and the signal light around the wavelength λ + α can be amplified and output in response to the signal light amplifying unit being incident.
[0034]
Therefore, a 1.06 μm laser that can easily obtain a high-power laser beam, or a signal with a wavelength of 1.3 μm band, 1.44 μm band, 1.52 μm band, etc. for which amplification technology has not been established by using a fiber laser as excitation light. Optical gain and low noise amplification can be realized. As a result, it can be expected that the wavelength of signal light for optical communication will be greatly expanded.
[Brief description of the drawings]
FIG. 1 is a diagram showing a Raman optical amplifier according to an embodiment of the present invention.
FIG. 2 is a diagram showing another embodiment of the present invention.
FIG. 3 is a view showing still another embodiment of the present invention.
FIG. 4 is a diagram showing still another embodiment of the present invention.
[Explanation of symbols]
1 laser, 2 λ1 / λ5 coupler, 3 fiber Bragg grating (FBG), 4,24 optical fiber for Raman scattered light generation, 5 laser oscillation unit, 6 optical circulator, 7, 8, 27, 28 λ4 / λ5 coupler, 9 , 29, 33 Optical fiber for signal light amplification, 10 Signal light amplifier, 21 λ1 / λ3 coupler, 22, 23, 25, 26 Coupler, 31, 32 λ1 / λ2 coupler, 34 Tunable optical filter, 35 Optical amplifier.

Claims (2)

An optical oscillation source that generates Raman scattered light of wavelength λ + α in response to the incidence of laser light of wavelength λ;
Having first to third ports, outputting light input to the first port from the second port, and outputting light input to the third port from the first port; , With optical circulator,
Optically coupled to said optical oscillation source through the optical circulator, the Raman scattered light of the wavelength lambda + alpha as excitation light, amplifies the signal light in response to the incident signal light having a wavelength lambda + alpha + beta A signal light amplification unit ,
The optical oscillation source is:
An optical fiber for generating scattered light that generates Raman scattered light having a wavelength λ + α based on the laser light having the wavelength λ,
An incident part that makes the laser light having the wavelength λ incident on the optical fiber for scattered light generation from the first end side of the optical fiber for scattered light generation;
A first fiber Bragg grating provided in an optical path between the second end of the scattered light generating optical fiber and the first port of the optical circulator, and reflecting the laser light having the wavelength λ;
A second light path is provided in the optical path between the first end of the scattered light generating optical fiber and the incident portion, and reflects the Raman scattered light having the wavelength λ + α generated in the scattered light generating optical fiber. Fiber Bragg grating,
The optical path between the incident part and the first port of the optical circulator is provided in a pair on both sides of the scattered light generating optical fiber, and has a wavelength λ and λ + α generated by the scattered light generating optical fiber. One or more pairs of third fiber Bragg gratings that reflect Raman scattered light having a wavelength between,
The signal light amplifier is
An input unit for inputting the signal light having the wavelength λ + α + β;
An optical fiber for signal light amplification that amplifies the signal light of the wavelength λ + α + β input from the input unit;
An output unit that outputs the signal light of the wavelength λ + α + β amplified by the signal light amplification optical fiber;
The second port of the optical circulator, the output unit, the optical fiber for signal light amplification, the input unit, and the third port of the optical circulator are connected in a loop in this order, Raman light amplifier. The incident portion is a coupler that multiplexes / demultiplexes light of wavelength λ and light of wavelength λ + α + β,
2. The Raman optical amplifier according to claim 1, wherein each of the input unit and the output unit is a coupler that multiplexes and demultiplexes light having a wavelength λ + α and light having a wavelength λ + α + β.

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