Method for controlling optical amplification device

Abstract

A method according to one embodiment of the present disclosure for controlling an optical amplification device (10) of a polarization diversity configuration comprises: detecting a first optical intensity of first polarized waves from a first amplifier (102) which is disposed between a polarization splitter (121) and a polarization combiner (122); detecting a second optical intensity of second polarized waves from a second amplifier (103) which is disposed between the polarization splitter (121) and the polarization combiner (122); detecting a third optical intensity of the first polarized waves from the polarization combiner (122) in a state where the second polarized waves are not input to the polarization combiner (122); detecting a fourth optical intensity of the second polarized waves from the polarization combiner (122) in a state where the first polarized waves are not input to the polarization combiner (122); and acquiring loss of the first polarized waves from the first amplifier (102) to the polarization combiner (122) and loss of the second polarized waves from the second amplifier (103) to the polarization combiner (122) on the basis of the first optical intensity, the second optical intensity, the third optical intensity, and the fourth optical intensity.

Description

Optical amplification device control method 【0001】 This disclosure relates to a method for controlling an optical amplifier, and more particularly to a control method for obtaining the characteristics of an optical amplifier that amplifies light by optical parametric effects. 【0002】 Traditionally, with the recent launch of fifth-generation mobile communication systems and the spread of cloud computing, communication traffic has been increasing exponentially, necessitating a continuous increase in the capacity of optical networks. In optical fiber transmission, the transmission capacity per fiber can be improved by widening the optical transmission bandwidth, and various studies are being conducted toward the realization of ultra-broadband wavelength division multiplexing transmission. 【0003】 The wavelength band with low transmission loss in optical fibers (hereinafter also referred to as the optical transmission band) can be divided into several bands. In current long-distance optical transmission networks, the C-band and L-band bands of approximately 4-5 THz are mainly used, as they have the lowest transmission loss and allow the use of high-performance amplifiers such as erbium-doped fiber amplifiers (EDFAs). In recent years, in addition to the combined use of the C-band and L-band, research and development of ultra-broadband wavelength division multiplexing transmission systems using new optical transmission bands such as the S-band and U-band has become active. Such broadband transmission systems that use multiple transmission bands are called multiband transmission systems. Multiband transmission systems require the development of new optical transceivers to send and receive optical signals in transmission bands that have not been used conventionally. Furthermore, new optical amplifiers are needed for amplification and relaying in bands where EDFAs cannot be used. 【0004】Long-distance optical transmission systems include not only optical fibers and optical transceivers that serve as transmission paths for optical signals, but also optical nodes that apply optical signal processing, such as amplifying optical signals using optical amplifiers, and performing wavelength channel add-drop and routing. Devices that perform wavelength channel add-drop are called ROADMs (Reconfigurable optical add-drop multiplexers), and the technology for switching wavelength paths for multiple directions is called optical cross connect (OXC). Within ROADMs and OXCs, wavelength channel switching is performed using wavelength selective switches (WSS). To perform wavelength conversion of channels, it is necessary to use optical transceivers to convert optical signals into electrical signals, receive them, and then re-modulate them into light of a new wavelength. On the other hand, in multiband transmission networks, optical nodes need to be able to adapt not only to the conventional optical transmission band but also to multiple new transmission bands. Furthermore, as the number of wavelength channels increases, the number of transponders required for wavelength conversion also increases, leading to challenges such as increased equipment costs and facility scale due to increased power consumption. 【0005】Against this backdrop, broadband amplification relay technology and all-optical wavelength conversion technology using optical parametric amplifiers are attracting attention. Representative methods include using four-wave mixing, a third-order nonlinear optical effect, and using difference frequency generation, a second-order nonlinear optical effect. Highly nonlinear optical fibers are mainly used as the medium to produce the third-order nonlinear optical effect. Periodically polarized lithium niobate (PPLN) is mainly used as the medium to produce the second-order nonlinear optical effect. When signal light is input to an optical parametric amplifier, in addition to the original signal light component, idler light is generated at the output side in a frequency band symmetrical to the center frequency (degenerate frequency) of the gain band in the optical parametric amplification process. By extracting only the idler light with a wavelength filter, all-optical wavelength conversion becomes possible. Wavelength conversion by optical parametric amplification enables wavelength conversion over a wide bandwidth, making it possible to convert wavelength-division multiplexed signals from one transmission band to a different transmission band all at once. By utilizing this broadband wavelength conversion, and performing mutual conversion between conventionally used bands (e.g., C-band) and other transmission bands, multiband transmission becomes possible without the need to prepare devices such as optical transceivers, WSS, and optical amplifiers adapted to the new transmission band (see, for example, Non-Patent Document 1). Furthermore, low-latency, low-power wavelength conversion is possible without the use of optical transceivers, i.e., without optical-to-electrical conversion. 【0006】 Furthermore, optical parametric amplifiers can amplify input signal light across a wide bandwidth. They can also be applied to various wavelength bands by designing the phase matching characteristics of the medium and the frequency arrangement of the excitation light. Therefore, they can be used for broadband simultaneous amplification relay beyond the amplification bandwidth of conventional EDFAs, and as optical amplifiers for S-band and U-band frequencies not supported by EDFAs (see, for example, Non-Patent Document 2). 【0007】In optical parametric amplification utilizing difference frequency generation, a second-order nonlinear optical effect, a pump light of the second harmonic, which has a frequency twice that of the degenerate frequency, is used. High-gain optical parametric amplification requires a pump light with high optical power, but it is difficult to obtain strong second-harmonic light for signal light in the optical communication wavelength band using ordinary communication equipment. Therefore, a configuration is used in which light at the degenerate frequency is first amplified by a high-power optical amplifier such as an EDFA, and then a strong second harmonic is obtained using the second harmonic generation (SHG) process, a second-order nonlinear optical effect. To avoid unwanted interactions between wavelength channels when amplifying a WDM signal, a configuration is used in which second-harmonic generation and optical parametric amplification are performed in different second-order nonlinear media. In the following, the pump light before it is converted to the second harmonic will be called the fundamental pump light. 【0008】 The gain and bandwidth characteristics of optical parametric amplification depend on the phase matching characteristics between the signal light and the pump light in the medium. The optical parametric amplification process in a second-order nonlinear optical medium utilizes the interaction between widely separated light waves, namely the signal light and the pump light, which is a second harmonic. Therefore, satisfying the phase matching conditions between these light waves is not easy. Thus, a method is used to achieve pseudo-phase matching by introducing a periodic polarization reversal structure into the medium. A typical example is periodically poled lithium niobate (PPLN). On the other hand, the refractive index spectrum of the medium depends on temperature. Therefore, in order to achieve the phase matching designed by periodic polarization reversal, it is necessary to maintain a predetermined medium temperature. For this reason, in optical parametric media using a second-order nonlinear optical medium, a heater or Peltier device is usually attached to the medium to control and maintain a constant medium temperature (see, for example, Patent Document 1). 【0009】Because the optical parametric amplification process is polarization-dependent, a polarization diversity configuration is used to achieve polarization-independent operation with respect to the input signal light. This configuration involves splitting the input signal light into two orthogonal polarization components, applying optical parametric amplification to each, and then recombining them. When controlling the amplification gain in this polarization diversity configuration, it is conceivable to control each nonlinear medium used for amplification of each polarization component independently. Control for each nonlinear medium can be achieved by tapping a portion of the signal light at the output of each nonlinear medium, monitoring the gain and optical power, and adjusting the medium temperature and pump optical power. On the other hand, since the signal quality deteriorates if there is an amplification gain difference (polarization-dependent gain) between polarization components, the two polarization components need to be output with the same optical power at the output of the optical parametric amplifier (OPA). However, if the optical loss in the path of each polarization component and the measurement error of the monitor differ, simply making the amplification gain of each nonlinear medium the same will not make the polarization-dependent gain at the output of the OPA zero. Therefore, in order to achieve the desired amplification gain at the OPA output independently of polarization, including optical loss for each polarization component and measurement errors of the monitor, it is necessary to pre-calibrate the amplification gain to be realized for each nonlinear medium. 【0010】 Japanese Patent Publication No. 2020-86031 【0011】T. Kato, H. et al., “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. Kobayashi, S. et al., “103-ch. 132-Gbaud PS-QAM Signal Inline-Amplified Transmission With 14.1-THz Bandwidth Lumped PPLN-Based OPAs Over 400-km G.652.D SMF,” in Proceedings of Optical Fiber Communication Conference (OFC), Th4B.6, 2023 【0012】 This disclosure provides an optical amplifier capable of acquiring the characteristics of the optical amplifier for pre-calibrating the amplification gain to be realized in each nonlinear medium in an optical amplifier with a polarization diversity configuration, and a control method for the optical amplifier. 【0013】 A method for controlling an optical amplifier according to one embodiment of the present disclosure, comprising: detecting a first light intensity of a first polarization from a first amplifier having a nonlinear optical medium disposed between a polarization separator and a polarization combiner; detecting a second light intensity of a second polarization orthogonal to the first polarization from a second amplifier having a nonlinear optical medium disposed between the polarization separator and the polarization combiner; detecting a third intensity light of the first polarization from the polarization combiner when the second polarization is not input to the polarization combiner; detecting a fourth intensity light of the second polarization from the polarization combiner when the first polarization is not input to the polarization combiner; and obtaining the loss of the first polarization from the first amplifier to the polarization combiner and the loss of the second polarization from the second amplifier to the polarization combiner based on the first light intensity, the second light intensity, the third light intensity, and the fourth light intensity. 【0014】As described above, according to the control method for an optical amplifier according to one embodiment of the present disclosure, it is possible to acquire the characteristics of the optical amplifier. 【0015】 This figure shows a schematic of an optically parametric optical amplifier according to one embodiment of the present disclosure. This figure shows a schematic configuration of an optical intensity detector in an optical amplifier with polarization diversity according to various embodiments of the present disclosure. This figure shows a schematic configuration of an excitation light source in an optical amplifier with polarization diversity according to one embodiment of the present disclosure. This figure illustrates the input and output light of an optical parametric amplifier (OPA). This flowchart shows a control method for an optical amplifier with polarization diversity according to one embodiment of the present disclosure. This figure shows a schematic of a modified form of an optically parametric optical amplifier according to one embodiment of the present disclosure. This figure shows a schematic of a modified form of an optical amplifier with optical parametric configuration according to one embodiment of the present disclosure. 【0016】 Embodiments of the present invention will be described in detail below with reference to the drawings. Identical or similar reference numerals indicate identical or similar elements, and repeated descriptions may be omitted. Material names and numerical values ​​in the following description are illustrative, and embodiments of the disclosure may be carried out using other materials and numerical values ​​without departing from the spirit of the disclosure. 【0017】 The polarization diversity optical amplifier according to the various embodiments described below is configured to separate the input signal light into X-polarized and Y-polarized signals, amplify each of them with an optical parametric amplifier (OPA), and then combine them again. The control method for the optical amplifier according to the disclosure involves stopping one of the outputs of the OPA corresponding to the X-polarized signal and the OPA corresponding to the Y-polarized signal, and acquiring the characteristics of the optical amplifier while the output of one OPA is stopped and the other OPA is outputting. 【0018】 (First Embodiment) A control method for a polarization diversity optical amplifier according to the first embodiment of the present disclosure will be described with reference to Figures 1 to 5. Figure 1 shows a schematic configuration of a polarization diversity optical amplifier 10 according to the embodiment. 【0019】The optical amplifier 10 in Figure 1 includes a polarization beam splitter (PBS) 121 that separates the signal light into X-polarization and Y-polarization, a PBS 122 that combines the X-polarization and Y-polarization of the signal light, an optical parametric amplifier 102 and shutter 150, and an optical parametric amplifier 103 and shutter 150, and a controller 111, which are positioned between the PBS 121 and PBS 122. The optical parametric amplifiers 102 and 103 are OPAs that use periodically poled lithium niobate (PPLN) waveguides as a nonlinear optical measure (hereinafter also referred to as OPA-PPLN). OPA-PPLN 102 is positioned to receive the X-polarization of the signal light, and OPA-PPLN 103 is positioned to receive the Y-polarization of the signal light. The signal light is a wavelength-division multiplexed signal (WDM) with different wavelengths multiplexed. 【0020】 The optical amplification device 10 includes an excitation light source 100, a temperature regulator (TEC) 104, an excitation light source 101, and a temperature regulator (TEC) 105. 【0021】 The excitation light source 100 is a light source that emits excitation light (hereinafter also referred to as X-excitation light) that is combined with the X-polarization of the signal light and incident on the OPA-PPLN 102. The excitation light source 100 is configured to change the intensity of the X-excitation light according to instructions from the controller 111. Similarly, the excitation light source 101 is a light source that emits excitation light (hereinafter also referred to as Y-excitation light) that is combined with the Y-polarization of the signal light and incident on the OPA-PPLN 103. The excitation light source 101 is configured to change the intensity of the Y-excitation light according to instructions from the controller 111. 【0022】 TEC 104 is configured to adjust the operating temperature of OPA-PPLN 102 according to instructions from controller 111. Similarly, TEC 105 is configured to adjust the operating temperature of OPA-PPLN 103 according to instructions from controller 111. 【0023】OPA-PPLN102 and OPA-PPLN103 each include a dichroic mirror type multiplexer 142, a PPLN waveguide 143, and a dichroic mirror type demultiplexer 145. The nonlinear optical medium constituting the PPLN waveguide 143 can be, for example, LiNbO3, LiTaO3, LiNb(x)Ta(1-x)O3 (0≦x≦1), or one of these containing at least one additive selected from the group consisting of Mg, Zn, Sc, and In. 【0024】 In OPA-PPLN 102, the dichroic mirror multiplexer 142 is configured to combine the X-polarized signal light from PBS 121 with the X-excitation light from the excitation light source 100. The combined X-polarized and X-excitation light is then incident on the PPLN waveguide 143. Similarly, in OPA-PPLN 103, the dichroic mirror multiplexer 142 is configured to combine the Y-polarized signal light from PBS 121 with the Y-excitation light from the excitation light source 101. The combined Y-polarized and Y-excitation light is then incident on the PPLN waveguide 143. Focusing lenses are positioned around the dichroic mirror multiplexers 142 and 143. 【0025】 In OPA-PPLN 102, the PPLN waveguide 143 is configured to generate the X-polarized signal light amplified by the optical parametric effect and the converted light of the X-polarized signal light (hereinafter also referred to as idler light). The amplified X-polarized signal light and the idler light of the X-polarized signal light are emitted from the PPLN waveguide 143 together with the excitation light. Similarly, in OPA-PPLN 103, the PPLN waveguide 143 is configured to generate the Y-polarized signal light amplified by the optical parametric effect and the idler light of the Y-polarized signal light. The amplified Y-polarized signal light and the idler light of the Y-polarized signal light are emitted from the PPLN waveguide 143 together with the excitation light. 【0026】In OPA-PPLN 102, the dichroic mirror demultiplexer 145 is configured to separate the excitation light from the light coming from the PPLN waveguide 143. The separated light (the X-polarized amplified signal light and the idler light of the X-polarized signal light) is output from OPA-PPLN 102. Similarly, in OPA-PPLN 103, the dichroic mirror demultiplexer 145 is configured to separate the excitation light from the light coming from the PPLN waveguide 143. The separated light (the Y-polarized amplified signal light and the idler light of the Y-polarized signal light) is output from OPA-PPLN 103. 【0027】 Shutter 150 is configured to block or open the path of light (the X-polarized amplified signal light and the idler light of the X-polarized signal light) from OPA-PPLN 102 to BS 122, according to instructions from controller 111. Similarly, shutter 151 is configured to block or open the path of light (the Y-polarized amplified signal light and the idler light of the Y-polarized signal light) from OPA-PPLN 103 to BS 122, according to instructions from controller 111. Shutters 150 and 151 can be Mach-Zehnder (MZI) type light intensity modulators, electronic shutters, or mechanical shutters. 【0028】 Figure 2 shows a schematic configuration of an optical intensity detector in an optical amplification device with a polarization diversity configuration according to various embodiments. An optical branching coupler 200 is arranged in the optical path of the optical amplification device of this disclosure to branch the light. The optical intensity detector 108 has a wavelength filter 201 that extracts light of a desired wavelength from the light branched by the optical branching coupler 200, and an optical intensity detector 202 that detects the intensity of the light extracted by the wavelength filter 201. The light intensity detected by the optical intensity detector 202 is supplied to the controller 111. 【0029】Figure 3 shows a schematic configuration of an excitation light source in an optical amplification device 10 with a polarization diversity configuration according to one embodiment. The excitation light sources 100 and 101 each include an optical branching coupler 106 that splits the light from the pump light source 300 into two, an amplifier 301 that amplifies the light branched by the optical branching coupler 106, and a PPLN waveguide 143 as a nonlinear medium. 【0030】 The pump light source 300 is configured to generate fundamental pump light (hereinafter also referred to as fundamental wave light), which is continuous or pulsed light with a degenerate frequency ω0 in the parametric effect of the OPA-PPLN 102. The amplifier 301 is, for example, an erbium-doped fiber amplifier (EDFA). 【0031】 The excitation light sources 100 and 101 are configured to amplify the fundamental wave light with amplifier 301, and then generate excitation light of frequency 2ωo by second harmonic generation (SHG) in the PPLN waveguide 143. The excitation light from excitation light source 100 is supplied to OPA-PPLN 102. The excitation light from excitation light source 101 is supplied to OPA-PPLN 103. Alternatively, one set of amplifier 301 and PPLN waveguide 143 may generate excitation light from the fundamental wave light from the pump light source 300, and then split it into two using the optical branching coupler 106. 【0032】 In the OPA-PPLN 143 of the OPA-PPLN 102, which receives the X-polarization of the signal light from the polarizing beam splitter (PBS) 121 and the excitation light from the excitation light source 100, the amplified X-polarization of the signal light and idler light of the X-polarization of the signal light are generated due to the optical parametric effect. Similarly, in the OPA-PPLN 143 of the OPA-PPLN 103, which receives the Y-polarization of the signal light from the PBS 121 and the excitation light from the excitation light source 101, the amplified Y-polarization of the signal light and idler light of the Y-polarization of the signal light are generated due to the optical parametric effect. 【0033】 Refer to Figure 4 to explain the input and output light of the optical parametric amplifier (OPA). Figure 4 shows the relationship between the frequencies of the excitation light, signal light, and conversion light in the OPA. In Figure 4, the wavelength λ0 (frequency ω0) of the fundamental light is 1573 nm, and the wavelength of the excitation light is λ pIt shows the wavelength conversion band of the PPLN waveguide when the (frequency 2ω0) is 786.5 nm. If the wavelength λs (frequency ω s ) of the input signal light (WDM signal light) is 1536 to 1567 nm, then 2ω0 - ω s generates an idler light (converted light of the WDM signal) with a wavelength λc of 1579 to 1611. 【0034】 In the optical amplification device 10 of this embodiment, the X polarization component of the amplified signal light from the OPA-PPLN 102 and the idler light of the X polarization component of the signal light are branched at the optical branching coupler 106bx (about 1% to 10% of the light intensity), and at the light intensity detector 108bx, light of a predetermined wavelength (λ) (for example, one selected from the idler lights) is extracted from one of the branched lights and the intensity is detected, and the other branched light is incident on the polarization beam splitter (PBS) 122. Similarly, the Y polarization component of the amplified signal light from the OPA-PPLN 103 and the idler light of the Y polarization component of the signal light are branched at the optical branching coupler 106bx, and at the light intensity detector 108by, light of a predetermined wavelength (λ) is extracted from one of the branched lights and the intensity is detected, and the other branched light is incident on the PBS 122. 【0035】 Also, the light (the X polarization component of the amplified signal light and the idler light of the X polarization component of the signal light, and the Y polarization component of the amplified signal light and the idler light of the Y polarization component of the signal light) that is incident on the PBS 122 and combined is branched at the optical branching coupler 106c (about 1% to 10% of the light intensity), and at the light intensity detector 108c, light of a predetermined wavelength (λ) is extracted and the intensity is detected. 【0036】 (Control method of the optical amplification device) Next, referring to FIG. 5, the control method of the optical amplification device 10 of the present disclosure will be described. Here, it is assumed that the input signal light has no bias in the optical power after being split into the X polarization component and the Y polarization component by the polarization beam splitter (PBS) 121. Therefore, the signal light is, for example, a polarization multiplexed signal, unpolarized light such as spontaneous emission light, or continuous light of linearly polarized light at 45 degrees with respect to the polarization splitting plane of the PBS 121. 【0037】In step S101, each of the light intensity detectors 108bx and 108by detects the intensities Poutx(λ) and Pouty(λ) of light of a predetermined wavelength λ and supplies them to the controller 111. The controller 111 acquires the intensity Poutx(λ) as the intensity Pmed_X [dB] of the light that has propagated through the nonlinear medium of OPA-PPLN 102, and acquires the intensity Pouty(λ) as the intensity Pmed_Y [dB] of the light that has propagated through the nonlinear medium of OPA-PPLN 103. 【0038】 In step S102, the controller 111 releases the shutter 151 in the path of the Y-polarized wave (blocks the light) and closes the shutter 150 in the path of the X-polarized wave (allows the light to pass through). 【0039】 In step S103, the light intensity detector 108c detects the intensity Pout(λ) of light of a predetermined wavelength λ and supplies it to the controller 111. The controller 111 acquires this as the intensity Pout_X [dB] of the light that has passed through only the path of the X-polarized wave. 【0040】 In step S104, the controller 111 opens (blocks the light) the shutter 150 in the path of the X-polarized wave. 【0041】 In step S105, the controller 111 closes (allows the light to pass through) the shutter 151 of the Y-polarized wave. 【0042】 In step S106, the light intensity detector 108c detects the intensity Pout(λ) of light of a predetermined wavelength λ and supplies it to the controller 111. The controller 111 acquires this as the intensity Pout_Y [dB] of the light that has passed through only the path of the Y-polarized wave. 【0043】 In step S107, the controller 111 calculates the losses T X and T Y The losses T X and T Y [dB] are obtained as the difference between the acquired Pmed_X and Pout_X (Equation (1)), and the difference between Pmed_Y and Pout_Y (Equation (2)). T X = Pmed_X - Pout_X Equation (1) T Y= Pmed_X−Pout_X Equation (2) 【0044】 Therefore, in order to achieve the desired amplification gain Ga at the output of the polarization diversity configuration optical amplifier 10, the amplification gain Gmed of the nonlinear medium of OPA-PPLN 102 and 103 is X and Gmed, Y These are Ga + T X and Ga+T Y You should set it to this. Here, Gmed, X and Gmed, Y This is the amplification gain from the input of the optical amplifier 10 to the output of the nonlinear medium of the OPA-PPLN 102 and 103. X and Gmed, Y [dB] is calculated using the intensity Pin of the signal light input to the optical amplifier 10, Gmed, X = Pmed_X−Pin−3 Equation (3) Gmed, Y = Pmed_Y - Pin - 3 is defined as equation (4). 【0045】 The intensity Pin(λ) can be detected by the optical intensity detector 108a, which extracts light of a predetermined wavelength (λ) from a portion of the signal light (approximately 1% to 10% of the light intensity) at the optical branching coupler 106a located on the input side of the optical amplifier 10. 【0046】 As explained above, the characteristics of a polarization diversity optical amplifier can be obtained by using shutters placed in each polarization path and light intensity detectors placed on the input / output side and the output side of the nonlinear medium in each polarization path. These characteristics can be used to calibrate the polarization diversity optical amplifier. 【0047】 In this embodiment, one wavelength of idler light was selected as a predetermined wavelength λ, and the light intensities Pmed_X, Pmed_Y, Pout_X, and Pout_Y were measured. However, the light intensity may also be measured using the power of the noise output from the nonlinear medium (the light intensity of the wavelength at the noise floor of parametric fluorescence as shown in Figure 4). 【0048】 (Second Embodiment) A control method for a polarization diversity optical amplifier according to a second embodiment of the present disclosure will be described with reference to Figure 6. The polarization diversity optical amplifier 20 shown in Figure 6 differs from the optical amplifier 10 in that it does not have shutters 150 and 151 which were located between PBS 121 and PBS 122. Descriptions of identical or similar elements will be omitted. 【0049】 In the optical amplification device 20, the controller 111 is configured to switch and block the excitation light supplied from the excitation light source 100 to the optical parametric amplifier 102 and the excitation light shared from the excitation light source 101 to the optical parametric amplifier 103. Specifically, the controller 111 is configured to turn off one of the amplifiers 301 of the excitation light source 100 and the amplifier 301 of the excitation light source 101, and the other. Alternatively, shutters may be placed between the amplifiers 301 and the nonlinear medium 143 in the excitation light sources 100 and 101. In this case, the controller 111 is configured to open one of the shutters of the excitation light source 100 and the shutter of the excitation light source 101 (blocking light) and close the other (allowing light to pass through). 【0050】 In this embodiment, although the X and Y polarizations of the input signal light cannot be blocked, idler light for one of the polarizations for which the excitation light is blocked will not be generated. Therefore, the characteristics of the optical amplifier 20 can be obtained in the same procedure as in the first embodiment by detecting the intensity of light of a predetermined wavelength λ in the band of idler light for the other polarization for which the excitation light is not blocked, and the optical amplifier can be calibrated using the obtained characteristics. 【0051】 (Control method for the optical amplifier) ​​The changes from the control method described above will be explained below with reference to Figure 5. 【0052】 In step S102, the controller 111 turns off the amplifier 301 of the excitation light source 101 and turns on the amplifier 301 of the excitation light source 100. 【0053】 In step S104, the controller 111 turns off the amplifier 301 of the excitation light source 100. 【0054】 In step S105, the controller 111 turns on the amplifier 301 of the excitation light source 101. 【0055】 As described above, in this embodiment as well, the characteristics of the optical amplifier 20 can be acquired, and the acquired characteristics can be used to calibrate the optical amplifier. 【0056】 (Third Embodiment) Referring to Figure 7, a control method for a polarization diversity optical amplifier according to a third embodiment of the present disclosure will be described. The polarization diversity optical amplifier 30 shown in Figure 7 differs from the optical amplifier 10 shown in Figure 1 in that it has a control light source 700 and an optical multiplexing coupler 701 that combines the control light from the control light source 700 with the signal light. Descriptions of identical or similar elements will be omitted. 【0057】 The control light source 700 is a light source that generates control light of a predetermined wavelength λ, which is different from the wavelength band of the input signal light. The control light source 700 is a light source configured to output unpolarized light, such as spontaneous emission light, or continuous light linearly polarized at a 45-degree angle to the polarization splitting plane of the polarization beam splitter 121. 【0058】 In the first embodiment, one wavelength of the idler light converted from the signal light by the optical parametric effect was set to a predetermined wavelength λ. In this embodiment, the light intensity detector 108 is configured to detect the intensity of the back control light, and the light intensity detectors 108bx, 108by, and 108c are configured to detect the light intensity of the amplified control light (frequency ω) or the idler light (frequency 2ω0-ω) converted from the control light, respectively. The control method for the optical amplifier 30 is the same as the control method described with reference to Figure 5, so the description is omitted. 【0059】(Fourth Embodiment) After calibration, it is conceivable that the difference between the path loss of the X-polarized signal light and the path loss of the Y-polarized signal light in the polarization diversity optical amplifier may change due to degradation over time. In such cases, it is desirable to be able to correct the change in the state of the optical amplifier during service. Such correction can also be performed by saving the intensity Pmed_X of the light guided through the nonlinear medium of OPA-PPLN 102 and the intensity Pmed_Y of the light guided through the nonlinear medium of OPA-PPLN 103, which were obtained using the control method of the optical amplifier described above, and correcting the amount of change from these values. 【0060】 It becomes possible to acquire the characteristics of an optical amplifier with a polarization diversity configuration. Using these acquired characteristics, it becomes possible to calibrate the optical amplifier with a polarization diversity configuration. 【0061】 10, 20, 30 Optical amplifier with polarization diversity configuration 100 X-polarized excitation light source 101 Y-polarized excitation light source 102 X-polarized OPA-PPLN 103 Y-polarized OPA-PPLN 104 X-polarized temperature controller (TEC) 105 Y-polarized temperature controller (TEC) 106 Optical splitter coupler 108 Light intensity detector 111 Controller 121, 122 Polarizing beam splitter (PBS) 142 Dichroic mirror type multiplexer 143 PPLN waveguide 145 Dichroic mirror type demultiplexer 300 Pump light source 301 Amplifier 700 Control light source 701 Optical multiplexer coupler

Claims

1. A method for controlling an optical amplifier, comprising: detecting a first optical intensity of a first polarization from a first amplifier having a nonlinear optical medium, which is positioned between a polarization separator and a polarization combiner; detecting a second optical intensity of a second polarization orthogonal to the first polarization from a second amplifier having a nonlinear optical medium, which is positioned between the polarization separator and the polarization combiner; detecting a third optical intensity of the first polarization from the polarization combiner when the second polarization is not input to the polarization combiner; detecting a fourth optical intensity of the second polarization from the polarization combiner when the first polarization is not input to the polarization combiner; and obtaining the loss of the first polarization from the first amplifier to the polarization combiner and the loss of the second polarization from the second amplifier to the polarization combiner based on the first optical intensity, the second optical intensity, the third optical intensity, and the fourth optical intensity.

2. The method according to claim 1, wherein, when the second polarization is not input to the polarization combiner, detecting the third intensity light of the first polarization from the polarization combiner includes blocking the path of the first polarization from the first amplifier to the polarization combiner with a first shutter, and when the first polarization is not input to the polarization combiner, detecting the fourth intensity light of the second polarization from the polarization combiner includes blocking the path of the second polarization from the second amplifier to the polarization combiner with a second shutter.

3. The method according to claim 1, wherein, when the second polarization is not input to the polarization combiner, detecting the third intensity light of the first polarization from the polarization combiner includes blocking the first excitation light supplied to the first amplifier, and when the first polarization is not input to the polarization combiner, detecting the fourth intensity light of the second polarization from the polarization combiner includes blocking the second excitation light supplied to the second amplifier.

4. The method according to claim 1, wherein the first light intensity, the second light intensity, the third light intensity, and the fourth light intensity are light intensities relating to the control light input from the polarization separator.

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