Optical amplification device

Abstract

An optical amplification device (1a) comprises: an excitation light branching unit (12) that branches excitation light and generates first branched excitation light and second branched excitation light; a first optical amplifier (17) that amplifies the intensity of a first polarization signal light by an optical parametric amplification process using the first branched excitation light; a second optical amplifier (20) that amplifies the intensity of a second polarization signal light by an optical parametric amplification process; a first excitation light demultiplexing unit (18) that removes the first branched excitation light from the result of the optical parametric amplification process; a second excitation light demultiplexing unit (21) that removes the second branched excitation light from the result of the optical parametric amplification process using the second branched excitation light; a polarization multiplexing unit (22) that multiplexes the intensity-amplified first polarization signal light and the intensity-amplified second polarization signal light; and a filter (23) that transmits the result of multiplexing the intensity-amplified first polarization signal light and second polarization signal light. The line width of the excitation light is equal to or less than the full width at half maximum of a curve representing the generation efficiency of a second harmonic light in each second harmonic generation process of the first optical amplifier (17) and the second optical amplifier (20).

Description

Optical amplifier

[0001] The present invention relates to an optical amplifier device.

[0002] In recent years, communication traffic has been increasing exponentially with the launch of the 5th Generation Mobile Communication System and the widespread use of rich content such as high-resolution video. This has led to a demand for continuous increases in the communication capacity of optical transmission systems. In optical fiber transmission, multiple signal lights are arranged in the wavelength direction (on the frequency axis), and these multiple signal lights are multiplexed and transmitted through a single optical fiber, thereby achieving high-capacity information transmission.

[0003] By using digital coherent transmission technology to transmit signals at a high multilevel, spectral efficiency is improved, increasing the transmission capacity of long-distance optical fiber communication networks. To further improve spectral efficiency, it is necessary to reduce the noise level in the optical domain. One way to reduce the noise level in the optical domain is to increase the intensity (optical power) of the transmitted signal light.

[0004] However, in optical fiber transmission, when the intensity of the transmitted signal light increases, nonlinear optical effects in the optical fiber become apparent, distorting the waveform of the signal light. As the intensity of the transmitted signal light increases, the signal quality improves in the low-power range, but deteriorates in the high-power range. Therefore, there is an optimum value for the intensity of the transmitted signal light, and the spectral efficiency is limited. The limit of spectral efficiency in optical fiber transmission is called the nonlinear Shannon limit.

[0005] Another approach that differs from improving spectral efficiency is to broaden the optical transmission band. The wavelength range with low transmission loss in optical fiber is divided into several optical transmission bands. Long-distance optical fiber communication networks mainly use the C-band or L-band, which has the lowest transmission loss among all optical transmission bands, from approximately 4 THz to 5 THz. In this band, erbium-doped fiber amplifiers (EDFAs) are sometimes used as optical amplification repeaters.

[0006] In order to widen the optical transmission band, in addition to the combined use of the C-band and L-band, research and development of multi-band wavelength division multiplexing transmission systems using new optical transmission bands (for example, S-band) is actively underway. Furthermore, in multi-band transmission systems, it is necessary to develop new optical amplification repeater methods that can handle transmission bands that have not been used before.

[0007] Therefore, optical parametric amplification (OPA) has attracted attention as a technology for performing signal light processing such as wavelength conversion and phase conjugation using phase conjugate light (idler light) (see Patent Document 1). Optical parametric amplification uses four-wave mixing (FWM), a third-order nonlinear optical effect, and differential frequency generation (DFG), a second-order nonlinear optical effect.

[0008] At the output side of an optical parametric amplifier to which signal light is input, not only the components of the input signal light but also phase conjugate light is generated in a frequency band symmetrical to the frequency band of the signal light, with the center frequency (degenerate frequency) of the gain band of the optical parametric amplification process as the boundary. By extracting only the phase conjugate light using a wavelength filter, signal light processing such as wavelength conversion and phase conjugate conversion becomes possible.

[0009] By performing wavelength conversion between a transmission band such as the C-band and other transmission bands, it is possible to extend the transmission band while using the optical components of existing transceivers (see Non-Patent Document 1). Furthermore, distortions in the waveform of signal light caused by nonlinear optical effects in optical fibers can be compensated for by phase conjugation. This overcomes the conventional nonlinear Shannon limit, enabling further improvements in spectral efficiency and extension of transmission distances (see Non-Patent Document 2).

[0010] Furthermore, because it is possible to achieve ultra-low noise optical amplification below the theoretical limit of conventional optical amplifiers, it is expected that phase-sensitive amplification by superposing signal light and phase-conjugate light will be applied to high-sensitivity signal reception (see Patent Document 2). In particular, periodically poled lithium niobate (PPLN: periodically poled LiNbO3), a second-order nonlinear medium (nonlinear optical medium), is highly efficient and less likely to cause unwanted interactions between wavelength channels. For these reasons, periodically poled lithium niobate is a promising nonlinear medium for optical parametric amplification.

[0011] In addition, optical parametric amplification (OPA) has been reported, which uses a highly efficient PPLN waveguide to obtain a large gain. Thus, the function of OPA is being investigated not only for the application of signal light processors but also for the application of broadband optical amplifier repeaters (see Non-Patent Document 3).

[0012] JP 2020-086031 A JP 2015-161827 A

[0013] T. Kato, H. Muranaka, Y. Tanaka, Y. Akiyama, T. Hoshida, S. Shimizu, T. Kobayashi, T. Kazama, T. Umeki, K. Watanabe, and Y. Miyamoto, “S+C+L-Band WDM Transmission Using 400-Gb / s Real-Time Transceivers Extended by PPLN-Based Wavelength Converter,” in Proc. Eur. Conf. Opt. Commun. (ECOC), Sept. 2022, paper We4D.4.T. Umeki et al., “Simultaneous nonlinearity mitigation in 92 × 180-Gbit / s PDM-16QAM transmission over 3840 km using PPLN-based guard-band-less optical phase conjugation,” Optics Express, 24, 15, 16945-16951 (2016).T. Kobayashi et al., “Wide-band Inline-amplified WDM Transmission Using PPLN-based Optical Parametric Amplifier with the optical bandwidth over 10 THz,” IEEE J. Lightwave Technol., vol. 39, no. 3, pp. 787-794, Feb. 2021.

[0014] Optical parametric amplification, which uses nonlinear optical effects, has a high-speed response on the order of femtoseconds. Therefore, the phase noise and frequency noise of the pump light are transmitted directly to the phase conjugate light. Phase noise leads to degradation of the signal quality of the phase conjugate light after wavelength conversion and phase conjugation. For this reason, the above applications require pump light with a narrow linewidth and high frequency stability.

[0015] Conventional optical parametric amplification mainly uses light sources with narrow linewidths of several Hz to several kHz and high frequency stability (e.g., external cavity lasers (ECLs)). However, such light sources are expensive and consume a lot of power. Furthermore, there is a trade-off between the intensity and linewidth of pump light output from a light source, and therefore the intensity of narrow-linewidth pump light is low. For this reason, in order to obtain sufficient amplification gain in optical parametric amplification, it is necessary to amplify the intensity of the pump light using an optical amplifier such as an erbium-doped optical fiber amplifier.

[0016] Optical parametric amplification, which uses the second-order nonlinear optical effect, requires pump light (second-harmonic light) with a wavelength that is half the central wavelength (degenerate wavelength) of the gain band. However, high-output optical amplifiers that support a wavelength that is half the central wavelength of the gain band are not very practical.

[0017] Furthermore, it is not common for a second-harmonic band light source to output pump light with a narrow linewidth that satisfies the above requirements. Therefore, optical amplifiers adapted to the signal band may first amplify the pump light and then generate high-intensity second harmonics through a second harmonic generation (SHG) process. However, such a configuration increases the size, power consumption, and cost of the optical amplifier device that performs optical parametric amplification.

[0018] Thus, unless the optical amplifying device is provided with an optical amplifier that amplifies the intensity of the pump light, the intensity of the signal light cannot be amplified by optical parametric amplification.

[0019] In view of the above circumstances, an object of the present invention is to provide an optical amplifying device that is capable of amplifying the intensity of signal light by optical parametric amplification without including an optical amplifier that amplifies the intensity of pump light.

[0020] One aspect of the present invention includes a polarization demultiplexer that separates input signal light into first polarization signal light and second polarization signal light having polarization components orthogonal to each other, a pumping light source that generates pumping light, a pumping light branching unit that branches the pumping light to generate first branched pumping light and second branched pumping light, a first pumping light multiplexer that multiplexes the first polarization signal light and the first branched pumping light, a second pumping light multiplexer that multiplexes the second polarization signal light and the second branched pumping light, a first optical amplifier that amplifies the intensity of the first polarization signal light by an optical parametric amplification process using the first branched pumping light, and a second optical amplifier that amplifies the intensity of the second polarization signal light by an optical parametric amplification process using the second branched pumping light. a first pumping light demultiplexing unit that removes the first branched pumping light from the result of an optical parametric amplification process using the first branched pumping light; a second pumping light demultiplexing unit that removes the second branched pumping light from the result of an optical parametric amplification process using the second branched pumping light; a polarization multiplexing unit that multiplexes the first polarized signal light whose intensity has been amplified and the second polarized signal light whose intensity has been amplified; and a filter that transmits the multiplexed result of the first polarized signal light and the second polarized signal light whose intensity has been amplified, wherein the linewidth of the pumping light is equal to or less than the full width at half maximum of a curve that represents the generation efficiency of second harmonic light in each of the second harmonic generation processes of the first optical amplifier and the second optical amplifier.

[0021] According to the present invention, it is possible to amplify the intensity of signal light by optical parametric amplification without providing an optical amplifier that amplifies the intensity of pump light.

[0022] 1 is a diagram illustrating a configuration example of an optical amplifier according to a first embodiment; FIG. 2 is a diagram illustrating an example of the signal quality of signal light whose intensity has been amplified by optical parametric amplification for each linewidth according to the first embodiment; and FIG. 3 is a diagram illustrating a configuration example of an optical amplifier according to a second embodiment.

[0023] An embodiment of the present invention will be described in detail with reference to the drawings. (Summary) In the following, in a nonlinear medium (nonlinear optical medium) used to amplify the intensity of signal light, the linewidth (frequency band) of pump light stably falls within the full width at half maximum of a curve (frequency distribution) representing the generation efficiency of second-harmonic light. The generation efficiency of second-harmonic light in a nonlinear medium used to amplify the intensity of signal light is determined depending on the amount of phase mismatch between the pump light input to the nonlinear medium and the second-harmonic light generated in the nonlinear medium.

[0024] When an optical parametric amplifier is used solely as an optical amplifier that amplifies the intensity of input signal light, the component of the signal light (original signal light) input to the optical parametric amplifier is extracted at the output side of the optical parametric amplifier, instead of the phase conjugate light.

[0025] In the optical parametric amplification process using a second-order nonlinear medium, a phase conjugate light is generated by a difference frequency generation process between the signal light and the pump light input to the second-order nonlinear medium. Also, the intensity of the signal light component is amplified by the difference frequency generation process between the phase conjugate light and the pump light in the second-order nonlinear medium.

[0026] In an optical parametric amplification process using a third-order nonlinear medium, a phase conjugate light is generated by a four-wave mixing process between a signal light and a pump light input to the third-order nonlinear medium, and the intensity of the signal light component is amplified by the four-wave mixing process between the phase conjugate light and the pump light in the third-order nonlinear medium.

[0027] Since the optical parametric amplification process is completed in a very short time, the phase noise and frequency noise transmitted from the pump light to the phase conjugate light are canceled out in the process in which the signal light component is generated using the phase conjugate light and the pump light. Therefore, even if the phase noise and frequency noise are contained in the pump light, the signal quality of the signal light component does not deteriorate.

[0028] However, the efficiency of second-harmonic generation in the optical parametric amplification process depends on the phase matching characteristics of the nonlinear medium. Therefore, the linewidth of the pump light must be stably within a band that satisfies the phase matching characteristics between the pump light and the second-harmonic light. Here, the frequency stability of the pump light depends on the frequency noise and linewidth of the pump light, as well as the characteristics and implementation of the light source.

[0029] The generation efficiency "E" of second harmonic light in the second harmonic generation process in a second-order nonlinear medium is expressed by equation (1).

[0030]

[0031] Here, "f ｐ " represents the frequency of the excitation light. "L" represents the length of the nonlinear medium. "Δk" represents the frequency "f ｐ The phase mismatch amount "Δk" is expressed as in equation (2).

[0032]

[0033] Here, "π" represents the constant of the circumference of a circle. "c" represents the speed of light. "n ｐ ” is the frequency “f ｐ " represents the refractive index of the excitation light of the wavelength associated with "n ＳＨ ” is the frequency “f ｐ "Λ" represents the refractive index of second harmonic light of a wavelength corresponding to twice the frequency of ". " " is the interval (period) of the polarization inversion structure previously applied to the nonlinear medium in order to make the phase mismatch amount "Δk" zero when pump light of a predetermined wavelength is input to the nonlinear medium.

[0034] The full width at half maximum of the curve representing the generation efficiency "E" exemplified in formula (1) is determined by the refractive index "n ｐ " and the refractive index of the second harmonic wave in the nonlinear medium "n ＳＨ " and depends on.

[0035] The full width at half maximum of the curve representing the generation efficiency "E" is on the order of several GHz. Therefore, the requirements for the frequency stability of the pump light are not high. In exchange for a wide linewidth of the pump light, an inexpensive, high-output semiconductor laser (e.g., a distributed feedback semiconductor laser) may be used as the light source of the pump light. This eliminates the need for amplification of the pump light, making it possible to realize a low-cost optical amplifier that performs optical parametric amplification.

[0036] Furthermore, a semiconductor laser with a wide linewidth in the second harmonic band can be used as the light source of the pump light, which eliminates the need for a second harmonic generation process for converting the pump light into a second harmonic.

[0037] 1 is a diagram showing an example of the configuration of an optical amplifier 1a according to the first embodiment. The optical amplifier 1a is a device that amplifies the intensity of signal light by optical parametric amplification.

[0038] The optical amplifier 1a includes an excitation light source 11, an excitation light branching section 12, a nonlinear medium 13, a nonlinear medium 14, a polarization splitting section 15, an excitation light multiplexing section 16, a nonlinear medium 17, an excitation light splitting section 18, an excitation light multiplexing section 19, a nonlinear medium 20, an excitation light splitting section 21, a polarization multiplexing section 22, and a filter 23.

[0039] The pump light source 11 outputs continuous light at the center wavelength (degenerate wavelength) of the gain band in optical parametric amplification as pump light to the pump light branching unit 12. The linewidth of the pump light is equal to or less than the full width at half maximum of the curve representing the generation efficiency "E". The intensity of this pump light is equal to or greater than the intensity required to obtain amplification gain by optical parametric amplification. Therefore, the optical amplifying device 1a does not need to include an optical amplifier that amplifies the intensity of the pump light.

[0040] The pumping light branching unit 12 branches the pumping light to generate first branched pumping light and second branched pumping light. The pumping light branching unit 12 outputs the first branched pumping light to the nonlinear medium 13. The pumping light branching unit 12 outputs the second branched pumping light to the nonlinear medium 14.

[0041] The nonlinear medium 13 (first branching conversion unit) converts the pumping light (first branched pumping light) input from the pumping light source 11 to the nonlinear medium 13 into second harmonic light (first second harmonic light) through a second harmonic generation process. That is, the nonlinear medium 13 generates second harmonic light through a second harmonic generation process using the pumping light input from the pumping light source 11 to the nonlinear medium 13.

[0042] The nonlinear medium 14 (second branching conversion unit) converts the pumping light (second branched pumping light) input from the pumping light source 11 to the nonlinear medium 14 into second harmonic light (second second harmonic light) through a second harmonic generation process. That is, the nonlinear medium 14 generates second harmonic light through a second harmonic generation process using the pumping light input from the pumping light source 11 to the nonlinear medium 14.

[0043] The polarization demultiplexing unit 15 (polarization separator) separates the signal light input to the polarization demultiplexing unit 15 into first polarized signal light and second polarized signal light, which are orthogonal polarization components. The polarization demultiplexing unit 15 outputs the first polarized signal light to the pump light multiplexing unit 16. The polarization demultiplexing unit 15 outputs the second polarized signal light to the pump light multiplexing unit 19.

[0044] The pumping light multiplexing unit 16 (first pumping light multiplexing unit) includes an optical device such as a wavelength multiplexing filter. The pumping light multiplexing unit 16 may include an optical device such as a dichroic mirror. The pumping light multiplexing unit 16 multiplexes the first polarized signal light input from the polarization demultiplexing unit 15 with the second harmonic light (pumping light) input from the nonlinear medium 13. The pumping light multiplexing unit 16 outputs the multiplexed result of the first polarized signal light and the second harmonic light to the nonlinear medium 17.

[0045] The nonlinear medium 17 (first optical amplifier) ​​includes, for example, a PPLN waveguide as an amplification medium. The nonlinear medium 17 performs optical parametric amplification on the result of multiplexing the first polarization signal light and the second harmonic light. Here, phase conjugate light is generated in a frequency band symmetrical to the frequency band of the first polarization signal light, with the center frequency (degenerate frequency) of the gain band of the optical parametric amplification process as the boundary. The nonlinear medium 17 outputs the first polarization signal light with amplified intensity, the second harmonic light, and the phase conjugate light generated as a result of the parametric amplification to the pump light demultiplexing unit 18.

[0046] The pump light demultiplexing unit 18 (first pump light demultiplexing unit) removes the second harmonic light (pump light) from the first polarization signal light, the second harmonic light, and the phase conjugate light, the intensity of which has been amplified. The pump light demultiplexing unit 21 outputs the first polarization signal light, the intensity of which has been amplified, and the phase conjugate light to the polarization multiplexing unit 22.

[0047] The pumping light multiplexing unit 19 (second pumping light multiplexing unit) includes an optical device such as a wavelength multiplexing filter. The pumping light multiplexing unit 19 may include an optical device such as a dichroic mirror. The pumping light multiplexing unit 19 multiplexes the second polarized signal light input from the polarization demultiplexing unit 15 with the second harmonic light (pumping light) input from the nonlinear medium 14. The pumping light multiplexing unit 19 outputs the multiplexed result of the second polarized signal light and the second harmonic light to the nonlinear medium 17.

[0048] The nonlinear medium 20 (second optical amplifier) ​​includes, for example, a PPLN waveguide as an amplification medium. The nonlinear medium 20 performs optical parametric amplification on the result of multiplexing the second polarization signal light and the second harmonic light. Here, phase conjugate light is generated in a frequency band symmetrical to the frequency band of the second polarization signal light, with the center frequency (degenerate frequency) of the gain band of the optical parametric amplification process as the boundary. The nonlinear medium 20 outputs the second polarization signal light with amplified intensity, the second harmonic light, and the phase conjugate light generated as a result of the parametric amplification to the pump light demultiplexing unit 21.

[0049] The pump light demultiplexing unit 21 (second pump light demultiplexing unit) removes the second harmonic light (pump light) from the second polarization signal light, the second harmonic light, and the phase conjugate light, the intensity of which has been amplified. The pump light demultiplexing unit 21 outputs the second polarization signal light, the intensity of which has been amplified, and the phase conjugate light to the polarization multiplexing unit 22.

[0050] The polarization multiplexing unit 22 multiplexes the first polarization signal light whose intensity has been amplified, the second polarization signal light whose intensity has been amplified, and the phase conjugate light. The filter 23 attenuates the intensity of the phase conjugate light in the multiplexing result of the first polarization signal light and second polarization signal light whose intensity has been amplified and the phase conjugate light. In this way, the filter 23 removes the signal light (first polarization signal light and second polarization signal light) from the multiplexing result of the first polarization signal light and second polarization signal light whose intensity has been amplified and the phase conjugate light.

[0051] As described above, the polarization demultiplexing unit 15 (polarization demultiplexing unit) separates the input signal light into first polarization signal light and second polarization signal light, which are orthogonal polarization components. The pump light source 11 generates pump light. Here, the linewidth of the pump light is equal to or less than the full width at half maximum of the curves representing the second-harmonic light generation efficiency in the second-harmonic generation processes of the nonlinear medium 17 (first optical amplifier) ​​and the nonlinear medium 20 (second optical amplifier). Furthermore, the wavelength of the pump light is the degenerate wavelength of the nonlinear medium 17 and the nonlinear medium 20.

[0052] The pumping light branching unit 12 branches the pumping light to generate first branched pumping light and second branched pumping light. Here, a nonlinear medium 13 (first branching conversion unit) may convert the branched pumping light into the first branched pumping light. A nonlinear medium 14 (second branching conversion unit) may convert the branched pumping light into the second branched pumping light. The wavelength of the first branched pumping light is half the degenerate wavelength of the first optical amplifier. The wavelength of the second branched pumping light is half the degenerate wavelength of the second optical amplifier.

[0053] The pump light multiplexer 16 (first pump light multiplexer) multiplexes the first polarized signal light and the first branched pump light. The pump light multiplexer 19 (second pump light multiplexer) multiplexes the second polarized signal light and the second branched pump light. The nonlinear medium 17 amplifies the intensity of the first polarized signal light by an optical parametric amplification process using the first branched pump light. The nonlinear medium 20 amplifies the intensity of the second polarized signal light by an optical parametric amplification process using the second branched pump light.

[0054] The pumping light demultiplexing unit 18 (first pumping light demultiplexing unit) removes the first branched pumping light from the result of the optical parametric amplification process using the first branched pumping light. The pumping light demultiplexing unit 21 (second pumping light demultiplexing unit) removes the second branched pumping light from the result of the optical parametric amplification process using the second branched pumping light.

[0055] The polarization multiplexer 22 multiplexes the first polarization signal light whose intensity has been amplified and the second polarization signal light whose intensity has been amplified. The filter 23 transmits the multiplexed result of the first polarization signal light and the second polarization signal light whose intensity has been amplified.

[0056] This makes it possible to amplify the intensity of signal light by optical parametric amplification without providing an optical amplifier that amplifies the intensity of pump light. It is possible to keep the price of the optical amplifier low. It is possible to reduce the power consumption of the optical amplifier. It is also possible to achieve a more compact optical amplifier.

[0057] 2 is a diagram showing an example of the signal quality of signal light whose intensity has been amplified by optical parametric amplification for each linewidth (frequency band) in the first embodiment. The horizontal axis represents the number of amplification repeats, and the vertical axis represents the signal quality (dB).

[0058] Four types of laser light sources with linewidths of "1 kHz," "15 kHz," "60 kHz," and "3 MHz" were used as pump light sources. The bandwidth in which second-harmonic light is generated in the nonlinear medium used for optical parametric amplification is approximately 10 GHz. That is, the full width at half maximum of the curve representing the generation efficiency "E" of second-harmonic light in the second-harmonic generation process in the nonlinear medium is approximately 10 GHz. Therefore, the required condition for generation efficiency "E" is met with any of the pump light sources. Furthermore, there is no significant difference in signal quality between any of the pump light sources.

[0059] Second Embodiment The second embodiment is mainly different from the first embodiment in that the optical amplifier does not include a nonlinear medium for converting pump light into second harmonic light. The second embodiment will be described focusing on the differences from the first embodiment.

[0060] 3 is a diagram showing an example of the configuration of an optical amplifier 1b according to the second embodiment. The optical amplifier 1b includes a pumping light source 11, a pumping light branching unit 12, a polarization demultiplexing unit 15, a pumping light multiplexing unit 16, a nonlinear medium 17, a pumping light multiplexing unit 19, a nonlinear medium 20, a pumping light demultiplexing unit 21, a polarization demultiplexing unit 22, a pumping light demultiplexing unit 18, and a filter 23.

[0061] In the second embodiment, the pumping light source 11 outputs second harmonic light (continuous light) having a wavelength that is half the central wavelength (degenerate wavelength) of the gain band as pumping light to the pumping light branching unit 12. Therefore, the optical amplifying device 1b does not need to include the nonlinear medium 13 and the nonlinear medium 14 for converting the pumping light into second harmonic light.

[0062] As described above, the wavelength of the pump light generated by the pump light source 11 may be half the degenerate wavelength of the nonlinear medium 17 and the nonlinear medium 20. This makes it possible to amplify the intensity of the signal light by optical parametric amplification without providing the nonlinear medium 13 and the nonlinear medium 14 and an optical amplifier that amplifies the intensity of the pump light. It is possible to further reduce the price of the optical amplifier device. It is possible to further reduce the power consumption of the optical amplifier device. It is also possible to further miniaturize the optical amplifier device.

[0063] (Hardware Configuration of the Control Device of the Optical Amplifier) ​​The control device of the optical amplifier (for example, a temperature control device and a gain control device) is realized as software by a processor such as a CPU (Central Processing Unit) executing a program stored in a storage device having a non-volatile recording medium (non-transitory recording medium) and a memory. The program may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as flexible disks, magneto-optical disks, ROMs (Read Only Memory), and CD-ROMs (Compact Disc Read Only Memory), and non-transitory recording media such as storage devices built into a computer system, such as a hard disk or solid state drive (SSD).

[0064] The control device of the optical amplifier device may be realized using hardware (accelerator) including an electronic circuit (electronic circuit or circuitry) using, for example, an LSI (Large Scale Integrated circuit), an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).

[0065] Although an embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and includes designs within the scope of the gist of the present invention.

[0066] The present invention is applicable to communication systems.

[0067] DESCRIPTION OF THE REFERENCE NUMERALS 1a, 1b...optical amplifier, 11...pumping light source, 12...pumping light branching section, 13...nonlinear medium, 14...nonlinear medium, 15...polarization demultiplexing section, 16...pumping light multiplexing section, 17...nonlinear medium, 18...pumping light demultiplexing section, 19...pumping light multiplexing section, 20...nonlinear medium, 21...pumping light demultiplexing section, 22...polarization multiplexing section, 23...filter

Claims

1. A polarization splitting unit that splits input signal light into first polarized signal light and second polarized signal light which are orthogonal polarization components to each other; a pumping light source that generates pumping light; a pumping light splitting unit that splits the pumping light to generate first branched pumping light and second branched pumping light; a first pumping light multiplexing unit that multiplexes the first polarized signal light and the first branched pumping light; a second pumping light multiplexing unit that multiplexes the second polarized signal light and the second branched pumping light; a first optical amplifier that amplifies the intensity of the first polarized signal light by an optical parametric amplification process using the first branched pumping light; a second optical amplifier that amplifies the intensity of the second polarized signal light by an optical parametric amplification process using the second branched pumping light; a first pumping light splitting unit that removes the first branched pumping light from a result of the optical parametric amplification process using the first branched pumping light; and a second pumping light splitting unit that removes the second branched pumping light from a result of the optical parametric amplification process using the second branched pumping light. an optical amplifier comprising: a polarization multiplexing section that multiplexes the first polarization signal light whose intensity has been amplified and the second polarization signal light whose intensity has been amplified; and a filter that transmits a result of the multiplexing of the first polarization signal light and the second polarization signal light whose intensity has been amplified, wherein the linewidth of the pump light is equal to or less than the full width at half maximum of a curve representing the generation efficiency of second harmonic light in each of the second harmonic generation processes of the first optical amplifier and the second optical amplifier.

2. An optical amplifier according to claim 1, wherein the wavelength of the first branched pump light is half the degenerate wavelength of the first optical amplifier, and the wavelength of the second branched pump light is half the degenerate wavelength of the second optical amplifier.

3. An optical amplifier as described in claim 1 or claim 2, further comprising: a first branching conversion unit that converts the branched pumping light into the first branched pumping light; and a second branching conversion unit that converts the branched pumping light into the second branched pumping light, wherein the wavelength of the pumping light is a degenerate wavelength of the first optical amplifier and the second optical amplifier.

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