Optical amplification device control method

Abstract

The present disclosure provides a control method for controlling an optical amplification device. A control method according to one embodiment comprises: acquiring a first characteristic value related to a first nonlinear medium provided in an optical amplification device; acquiring a second characteristic value related to a second nonlinear medium provided in the optical amplification device; acquiring a third characteristic value and a fourth characteristic value that are related to optical parametric amplification in the first nonlinear medium; acquiring a fifth characteristic value related to an excitation light source provided in the optical amplification device; acquiring a sixth characteristic value related to an optical amplifier provided in the optical amplification device; comparing a range predefined by thresholds associated with the first to sixth characteristic values with the first to sixth characteristic values; and stopping the optical amplification device on condition that any of the first to sixth characteristic values is outside the predefined range.

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, various studies are being conducted to realize ultra-broadband wavelength division multiplexing transmission, which can improve the transmission capacity per optical fiber by widening the optical transmission bandwidth.

[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, optical parametric amplifiers 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] Optical parametric amplification (OPA), which utilizes difference frequency generation, a second-order nonlinear optical effect, uses pump light at a frequency twice that of the degenerate frequency, which is the second harmonic. High-power optical light is required for a high-gain optical parametric amplification process, 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 strong second harmonics are 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] In optical parametric amplifiers (OPAs), the phase matching conditions change with the temperature of the medium, resulting in changes to the output state, such as amplification gain and gain spectrum shape. Therefore, it is necessary to stabilize the output state through feedback control of the medium temperature by a computer with a control algorithm or software implemented. Furthermore, in order to track changes in the output state due to changes in the medium temperature or to change the gain setting, it may be necessary to increase or decrease the light intensity of the pump light input to the optical parametric amplifier by adjusting the gain of the optical amplifier. In such cases, if any abnormality occurs in the hardware such as the medium, pump light source, and optical amplifier, or if the control algorithm or software does not function properly, the control may not converge, and the temperature of the medium or the light intensity of the pump light may increase or decrease indefinitely. In particular, if the light intensity of the pump light is outside the planned light intensity, it may damage not only the optical parametric amplifier but also peripheral equipment.

[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 a control method for an optical amplification device to detect an abnormality in an optical parametric amplifier and to perform an emergency shutdown.

[0013] A method for controlling an optical amplifier according to one embodiment of the present disclosure includes: obtaining a first characteristic value relating to a first nonlinear medium provided by the optical amplifier; obtaining a second characteristic value relating to a second nonlinear medium provided by the optical amplifier; obtaining a third and a fourth characteristic value relating to optical parametric amplification in the first nonlinear medium; obtaining a fifth characteristic value relating to an excitation light source provided by the optical amplifier; obtaining a sixth characteristic value relating to an optical amplifier provided by the optical amplifier; comparing the first to sixth characteristic values ​​with a range predetermined by thresholds associated with the first to sixth characteristic values; and stopping the optical amplifier on the condition that any of the first to sixth characteristic values ​​is outside the predetermined range.

[0014] As described above, according to the control method for an optical amplifier according to one embodiment of the present disclosure, when an abnormality in the optical parametric amplifier is detected, the optical amplifier can be stopped in an emergency, thereby preventing damage not only to the optical parametric amplifier but also to its peripheral equipment.

[0015] This is a schematic diagram showing the general configuration of an optical amplifier according to one embodiment of the present disclosure. (a) is a diagram showing the general configuration of an optical intensity detector 180 in an optical amplifier according to various embodiments of the present disclosure, and (b) is a diagram showing the general configuration of an optical intensity detector 160. This is a diagram showing the configuration of an excitation light source in an optical amplifier according to one embodiment of the present disclosure. This is a diagram illustrating the input and output light of an optical parametric amplifier. This is a flowchart showing a control method for an optical amplifier according to one embodiment of the present disclosure. This is a schematic diagram showing the general configuration of an optical amplifier with polarization diversity according to another embodiment of the present disclosure. This is a schematic diagram showing the general configuration of an excitation light source in an optical amplifier with polarization diversity according to another embodiment of the present disclosure. This is a diagram illustrating changes in the flow of the control method for an optical amplifier with polarization diversity according to another embodiment of the present disclosure.

[0016] Embodiments of the present disclosure 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 present disclosure may use other materials and numerical values ​​without departing from the spirit of the present disclosure.

[0017] The control method for the optical amplifier according to the various embodiments described below detects an abnormality based on at least one of the following: characteristic values ​​related to the output of the fundamental wave light source (intensity and frequency of the fundamental wave), characteristic values ​​related to the output of the optical amplifier (intensity of the fundamental wave), characteristic values ​​in optical parametric amplification in the first nonlinear medium (intensity of the second harmonic after the optical parametric amplification process, and the gain of light obtained by the optical parametric effect), and the operating temperatures of the first and second nonlinear media, and then emergency stops the optical amplifier.

[0018] (First Embodiment) A control method for an 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 an optical amplifier 10 according to the embodiment. The optical amplifier 10 includes an optical parametric amplifier 102, a temperature detector 103, an excitation light source 100, a temperature regulator (TEC) 104, a gain detector 108, a light intensity detector 160, and a controller 111. The signal light is a wavelength division multiplexing (WDM) signal in which different wavelengths are multiplexed.

[0019] The optical parametric amplifier 102 is an optical parametric amplifier (hereinafter also referred to as OPA-PPLN) that uses a periodically poled lithium niobate (PPLN) waveguide as a nonlinear optical medium. The OPA-PPLN 102 has 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.

[0020] In the OPA-PPLN 102, the dichroic mirror type multiplexer 142 is configured to combine the signal light and the excitation light from the excitation light source 100. The combined signal light and excitation light are then incident on the PPLN waveguide 143. A focusing lens is positioned around the dichroic mirror type multiplexer 142.

[0021] In the 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 signal light (hereinafter also referred to as idler light). The amplified signal light and the idler light of the signal light are emitted from the PPLN waveguide 143 together with the excitation light.

[0022] In the OPA-PPLN 102, the dichroic mirror type demultiplexer 145 is configured to separate the excitation light from the light coming from the PPLN waveguide 143. The excitation light is output from the OPA-PPLN 102 and input to the light intensity detector 160. The light from which the excitation light has been separated (amplified signal light and idler light converted from the signal light) is output from the OPA-PPLN 102 and input to the optical branching coupler 106 connected to the gain detector 108.

[0023] The temperature controller (TEC) 104 is equipped with a heater or Peltier element and is configured to adjust the operating temperature of the PPLN waveguide 143 according to instructions from the controller 111.

[0024] The temperature detector 103 is configured to detect the operating temperature of the PPLN waveguide 143 and supply it to the controller 111. The temperature detector 103 may be included in the temperature controller (TEC) 104.

[0025] Referring to Figure 2(a), the configuration of the gain detector 108 will be described. It includes an optical branching coupler 200 that branches the light from the optical branching coupler 106, a wavelength filter 201C into which the branched idler light is incident, a wavelength filter 201S into which the branched signal light is incident, an optical intensity detector 202C that detects the intensity of the idler light, and an optical intensity detector 202S that detects the intensity of the signal light. The gain is obtained from the light intensity detected by the optical intensity detectors 202C and 202S and supplied to the controller 111.

[0026] Wavelength filters 201C and 201S are wavelength filters configured to transmit light of a predetermined wavelength (hereinafter also referred to as monitor light). Wavelength filter 201S is configured to transmit monitor light of WDM signal light, and wavelength filter 201C is configured to transmit monitor light of idler light.

[0027] Furthermore, for the control of the optical amplifier 10, at least one of the signal light intensity and the idler light intensity is sufficient. Therefore, in the configuration of the gain detector 108 shown in Figure 2(a), the optical branching coupler 200, wavelength filter 201C, and light intensity detector 202C may be omitted, or the optical branching coupler 200, wavelength filter 201S, and light intensity detector 202S may be omitted.

[0028] Referring to Figure 2(b), the configuration of the light intensity detector 160 will be explained. The light intensity detector 160 consists of a light intensity detector 202 configured to detect the light intensity of the excitation light separated by the dichroic mirror type demultiplexer 145. The light intensity detected by the light intensity detector 160 is supplied to the controller 111. Instead of detecting the light intensity of the excitation light separated by the dichroic mirror type demultiplexer 145 of the OPA-PPLN 102 with the light intensity detector 160, the light intensity of the excitation light output from the PPLN waveguide 143p of the excitation light source 100, which will be described later referring to Figure 3, may be detected by the light intensity detector 160. In this case, an optical branch coupler 106 and the light intensity detector 160 will be placed between the PPLN waveguide 143p and the dichroic mirror type multiplexer 142 of the OPA-PPLN 102. When the light intensity of the excitation light separated by the dichroic mirror type demultiplexer 145 of the OPA-PPLN 102 is detected by the light intensity detector 160, there is an advantage that there is no excessive loss in the optical coupling between the output of the excitation light source 100 and the input of the OPA-PPLN 143. On the other hand, when the light intensity of the excitation light is detected between the PPLN waveguide 143p and the dichroic mirror type demultiplexer 145 of the OPA-PPLN 102, there are no factors other than the operating temperature of the optical amplifier 301p and the OPA-PPLN 102 that cause fluctuations in the output of the second harmonic generation (excitation light), so the controllability of the optical amplifier may be improved.

[0029] The excitation light source 100 is a light source that emits excitation light which is combined with the signal light and incident on the OPA-PPLN 102. The excitation light source 100 is configured to change the intensity of the excitation light according to instructions from the controller 111.

[0030] Figure 3 shows the configuration of the excitation light source 100. The excitation light source 100 includes a fundamental wave light source 300, an optical amplifier 301p that amplifies the light from the fundamental wave light source, an optical branching coupler 303, an optical intensity detector 302 that detects the intensity of a portion of the amplified light, a PPLN waveguide 143p as a nonlinear medium, a temperature detector 103p, and a TEC 104p.

[0031] The fundamental wave 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 optical parametric effect of the OPA-PPLN 102. The fundamental wave light source 300 has a function to detect the intensity and frequency of the output light and is configured to supply the detected light intensity and frequency of the fundamental wave light to the controller 111.

[0032] The optical amplifier 301p is, for example, an erbium-doped fiber amplifier (EDFA). Since it is difficult to directly provide excitation light with high optical power and narrow linewidth at the second harmonic frequency, a configuration is used in which continuous light at the degenerate frequency (ω0) is amplified by an EDFA as a high-power optical amplifier 301p, and then converted to the second harmonic using the second harmonic generation (SHG) process in a second-harmonic nonlinear medium. The optical amplifier 301p is configured to operate according to instructions from the controller 11 and to adjust the light intensity of the fundamental wave light it outputs.

[0033] The optical branching coupler 303 is configured to branch off a portion of the output of the optical amplifier 301p, i.e., amplified light (approximately 1% to 10% of the light intensity).

[0034] The light intensity detector 302 is configured to detect the intensity of light branched off from the light amplified by the light amplifier 301p. The light intensity detected by the light intensity detector 302 is supplied to the controller 111.

[0035] The PPLN waveguide 143p, acting as a nonlinear medium, is excited by the SHG process from the fundamental pump light (wavelength λ0, frequency ω0) amplified in the optical amplifier 301p to excitation light (wavelength λ0). p , frequency ω p This generates (= 2ω0).

[0036] The TEC 104p is equipped with a heater or Peltier element and is configured to adjust the operating temperature of the PPLN waveguide 143p according to instructions from the controller 111.

[0037] The temperature detector 103p is configured to detect the operating temperature of the PPLN waveguide 143p and supply it to the controller 111. The temperature detector 103p may be included in a thermoelectric cooler (TEC) 104p.

[0038] Referring to Fig. 4, input / output light of an optical parametric amplifier (OPA) will be described. Fig. 4 shows the frequency relationship among pump light, signal light, and converted light in the OPA. Fig. 4 shows the wavelength λ p (frequency 2ω0) of the pump light is set to 786.5 nm when the wavelength λ0 (frequency ω0) of the fundamental wave light is 1573 nm, and illustrates the wavelength conversion band of the PPLN waveguide. The wavelength λs (frequency ω s s) of the input signal light (WDM signal light) ranges from 1536 nm to 1567 nm, then according to 2ω0−ω s s, idler light (converted light of the WDM signal) with a wavelength λc ranging from 1579 nm to 1611 nm is generated. Fig. 4 also shows the power of noise output from the nonlinear medium (noise floor of parametric fluorescence).

[0039] In the present embodiment, the gain detector 108 is configured such that part of the signal light amplified by the OPA-PPLN 102 and part of the idler light converted from the signal light (about 1% to 10% of the light intensity) is branched by the optical branching coupler 106, then monitor light of a desired wavelength is extracted by the wavelength filter 201S and the wavelength filter 201C, and the light intensity is detected by the light intensity detectors 202S and 202C. The wavelength of the monitor light is the wavelength λ H closest to the wavelength λ0 (frequency ω0) of the fundamental wave light among the plurality of signal lights included in the WDM signal, and the wavelength λ L farthest from the wavelength λ0. Alternatively, it may be the wavelength λ L ' farthest from the wavelength λ0 of the fundamental wave light and the wavelength λ H ' closest to the wavelength λ0 among the plurality of wavelengths of the idler light converted from the WDM signal. The gain detector 108 acquires a gain from the detected light intensity and supplies the gain to the controller 111. The gain Gs of the signal light is acquired from the light intensity of the signal light, and the gain Gc of the idler light is acquired from the light intensity of the idler light. The gain supplied to the controller 111 is, for example, based on two pieces of monitor light (λ H and λL ), can be an average value of values obtained by multiplying the light intensity of ) by a predetermined proportional constant α. Alternatively or additionally, the gain supplied to the controller 111 is, for example, two monitor lights for idler light (λ H' and λ L' ), can be an average value of values obtained by multiplying the light intensity of ) by a predetermined proportional constant α.

[0040] The controller 111 may be a general-purpose device that executes various tasks such as a microprocessor or a CPU coupled to a memory, or a dedicated device such as an FPGA or an ASIC. The controller 111 is configured such that the general-purpose device executes a control algorithm or software stored in a memory to control the operation of the optical amplifying device 10.

[0041] (Control Method for Optical Amplifying Device in Normal State) As described above, in an OPA, the phase matching condition changes depending on the temperature of a nonlinear medium, and as a result, output states such as amplification gain and gain spectrum shape change. Therefore, the controller 111 adjusts the temperature of the PPLN waveguide 143 by controlling the TEC 104 so that the gains of the two monitor lights supplied from the gain detector 108 are equalized. In this way, the amplification gain and the gain spectrum shape are stabilized.

[0042] On the other hand, in SHG, the controller 111 controls the excitation light source 100 such that second harmonic waves having a desired frequency and light intensity are supplied to the OPA. Specifically, the controller 111 controls the optical amplifier 301p such that the fundamental wave light has a desired light intensity, and controls the TEC 104p such that the phase matching condition of the nonlinear medium 143p is maintained. The controller 111 constantly changes the operating temperature of the nonlinear medium 143p, and uses the hill-climbing method to keep the output of the PPLN waveguide 143 near the maximum value.

[0043] (Control method for the optical amplifier in case of abnormality) If any abnormality occurs in the hardware such as the fundamental wave light source 300, optical amplifier 301p, PPLN waveguides 143 and 143p, or if the control algorithm or software of the controller 111 does not operate normally, the control by the controller 111 may not converge, and the temperature of the PPLN waveguides 143 and 143p and the light intensity of the fundamental wave may increase or decrease indefinitely. Therefore, in the control method of this disclosure, the controller 111 emergency stops the optical amplifier 10 when it detects an abnormality.

[0044] Next, with reference to Figure 5, the control method for the optical amplification device 10 of the present disclosure will be described. In step 501, the controller 111 determines whether an abnormality has been detected based on various monitor values ​​supplied. Step 501 is repeated until an abnormality is detected.

[0045] In step 501, the controller 111 compares each of the supplied monitor values ​​with a predetermined range defined by the threshold associated with each, and determines that an abnormality has been detected if the supplied monitor value is outside the threshold range. The threshold range may be defined by an upper threshold and a lower threshold, or by either an upper threshold or a lower threshold.

[0046] The monitor values ​​used for detecting anomalies are the following characteristic values ​​(a) to (f): (a) the operating temperature of the PPLN waveguide 143 supplied from the temperature detector 103; (b) the operating temperature of the PPLN waveguide 143p supplied from the temperature detector 103p; (c) at least one of the gain Gs of the signal light and the gain Gc of the idler light supplied from the gain detector 108; (d) the light intensity of the excitation light supplied from the light intensity detector 160; (e) the light intensity and frequency of the fundamental light supplied from the fundamental light source 300; (f) the light intensity of the light output from the optical amplifier 301p supplied from the light intensity detector 302.

[0047] If an abnormality is detected in at least one monitor value in step 501, the process proceeds to step 502.

[0048] First, in step 502, the controller 111 stops the operation of the optical amplifier 301p. Next, in step 503, the controller 111 stops the operation of the fundamental wave light source 300.

[0049] If the order of steps 502 and 503 is reversed, and the operation of the controller 111 is stopped after the operation of the fundamental wave light source 300, a transient response may occur in the optical amplifier 301p. If the light output from the fundamental wave light source 300 is not instantaneously cut off, but is cut off gradually while the light intensity increases and decreases, a transient response may occur in the fundamental wave light source 300, potentially causing damage. Therefore, as in this disclosure, it is desirable to stop the operation of the fundamental wave light source 300 after stopping the operation of the optical amplifier 301p.

[0050] Subsequently, in step 504, the controller 111 stops controlling the optical amplifier 10.

[0051] Finally, in step 505, the controller 111 notifies that it has detected an abnormality. For example, it causes an indicator such as a lamp or display on the optical amplifier 10 to show the abnormal condition. In another example, it sends a signal to a remote monitoring device for the optical amplifier 10 to inform it of the abnormal condition.

[0052] As described above, the control method of this embodiment makes it possible to emergency stop the optical amplification device and prevent damage not only to the optical parametric amplifier but also to its peripheral devices.

[0053] (Second Embodiment) The control method of the optical amplification device according to the second embodiment will be described with reference to Figures 6 to 8. In this embodiment, the optical amplification device has a polarization diversity configuration in which two optical amplification devices with the configuration described with reference to Figure 1 are placed between two polarizing beam splitters (PBSs).

[0054] Figure 6 shows a schematic configuration of an optical amplification device 30 according to an embodiment. The optical amplification device 30 includes a polarization beam splitter (PBS) 121 that separates the X-polarization and Y-polarization of the signal light, a PBS 122 that combines the X-polarization and Y-polarization of the signal light, and optical parametric amplifiers (OPA-PPLNs) 102x and 102y arranged between the PBS 121 and PBS 122, which use a periodically poled lithium niobate (PPLN) waveguide as a nonlinear optical medium. The OPA-PPLN 102x is configured to receive the X-polarization of the signal light, and the OPA-PPLN 102y is configured to receive the Y-polarization of the signal light. The signal light is a wavelength-division multiplexed signal (WDM) in which different wavelengths are multiplexed. The optical amplifier 30 includes an excitation light source 100x associated with OPA-PPLN 102x, a temperature controller (TEC) 104x, a temperature detector 103x, a gain detector 108x, and a light intensity detector 160x, and an excitation light source 100y associated with OPA-PPLN 102y, a temperature controller (TEC) 104y, a temperature detector 103y, a gain detector 108y, and a light intensity detector 160y. The controller 111 acquires detected values ​​from the temperature detector 103x, the gain detector 108x, and the light intensity detector 160x associated with OPA-PPLN 102x corresponding to X polarization, and controls the excitation light source 100x and the temperature controller (TEC) 104x. Similarly, the controller 111 acquires detection values ​​from the temperature detector 103y associated with the OPA-PPLN 102y corresponding to Y polarization, the gain detector 108y, and the light intensity detector 160y, and controls the excitation light source 100y and the temperature controller (TEC) 104y.

[0055] The controller 111 is configured to perform the control described in the first embodiment for both the X-polarization and Y-polarization.

[0056] Figure 7 shows the configuration of the excitation light source 100x and excitation light source 100y. The excitation light source 100x and excitation light source 100y are configured to have the same configuration as the excitation light source 100 described with reference to Figure 3, with the light from the fundamental wave light source 300 being split by the optical branching coupler 106 and supplied to the excitation light source 100x and excitation light source 100y, respectively. Alternatively, the optical branching coupler 106 may be provided on the output side of the excitation light source 100 described with reference to Figure 3, so that the branched excitation light is supplied to the optical parametric amplifiers (OPA-PPLN) 102x and 102y.

[0057] The control flow for the optical amplifier 30 is similar to the control flow of the first embodiment described with reference to Figure 5. Since the optical amplifier 30 has a polarization diversity configuration, the controller 111 detects abnormalities in the monitor values ​​related to X polarization and Y polarization in step 501. Furthermore, the step of turning off the output of the optical amplifier (step 502) is a substep 802x that turns off the output of the optical amplifier 301x related to X polarization and a substep 802y that turns off the output of the optical amplifier 301y related to Y polarization. Steps 503 to 505 in the control method for the optical amplifier 30 of this embodiment are the same as the flow described in the first embodiment.

[0058] Thus, according to the control method of this embodiment, it is possible to emergency stop the optical amplification device and prevent damage not only to the optical parametric amplifier but also to its peripheral devices.

[0059] The control method disclosed herein makes it possible to detect abnormalities in the hardware components of the optical amplifier, or in the control algorithm or software of the optical amplifier, based on the characteristics indicated by various monitor values, thereby enabling emergency shutdown of the optical amplifier and preventing damage to its components.

[0060] 10, 30 Optical Amplifier 100 Excitation Light Source 102 Optical Parametric Amplifier (OPA-PPLN) 103 Temperature Detector 104 Temperature Controller (TEC) 106 Optical Splitter Coupler 108 Gain Detector 111 Controller 121, 122 Polarizing Beam Splitter (PBS) 142 Dichroic Mirror Multiplexer 143 PPLN Waveguide 145 Dichroic Mirror Demultiplexer 160 Light Intensity Detector 200 Optical Splitter Coupler 201 Wavelength Filter 202 Light Intensity Detector 300 Fundamental Wave Source 301 Optical Amplifier (EDFA) 302 Light Intensity Detector 303 Optical Splitter Coupler

Claims

1. A control method performed in a controller of an optical amplifier for controlling the optical amplifier, comprising: acquiring a first characteristic value relating to a first nonlinear medium provided by the optical amplifier; acquiring a second characteristic value relating to a second nonlinear medium provided by the optical amplifier; acquiring a third and a fourth characteristic value relating to optical parametric amplification in the first nonlinear medium; acquiring a fifth characteristic value relating to an excitation light source provided by the optical amplifier; acquiring a sixth characteristic value relating to an optical amplifier provided by the optical amplifier; comparing the first to sixth characteristic values ​​with a range predetermined by thresholds associated with the first to sixth characteristic values; and stopping the optical amplifier on the condition that any of the first to sixth characteristic values ​​is outside the predetermined range.

2. The control method according to claim 1, wherein stopping the optical amplification device includes stopping the operation of the optical amplifier in the optical amplification device, and stopping the operation of the fundamental wave light source in the optical amplification device after stopping the operation of the optical amplifier.

3. The control method according to claim 1, wherein the optical amplification device has a polarization diversity configuration, the first nonlinear medium includes two first nonlinear media for a first polarization and a second polarization orthogonal to the first polarization, and the second nonlinear medium includes two second nonlinear media for the first polarization and the second polarization.

4. The control method according to claim 1, wherein the first characteristic value is the operating temperature of the first nonlinear medium, the second characteristic value is the operating temperature of the second nonlinear medium, the third characteristic value is at least one of the gain value of the signal light and the gain value of the idler light obtained through the optical parametric amplification process in the first nonlinear medium, the fourth characteristic value is the light intensity of the excitation light obtained through the optical parametric amplification process in the first nonlinear medium, the fifth characteristic value is the light intensity and frequency of the fundamental wave light from the excitation light source, and the sixth characteristic value is the light intensity of the fundamental wave light amplified in the optical amplifier.

5. The control method according to claim 4, wherein the operating temperature of the first nonlinear medium is detected by a first temperature detector and supplied to the controller; the operating temperature of the second nonlinear medium is detected by a second temperature detector and supplied to the controller; at least one of the gain value of the signal light and the gain value of the idler light is calculated based on the light intensity detected by the gain detector and supplied to the controller; the light intensity and frequency of the fundamental wave light from the excitation light source are detected by a function of the excitation light source and supplied to the controller; the light intensity of the excitation light after undergoing the optical parametric amplification process is detected by a first light intensity detector and supplied to the controller; and the light intensity of the amplified fundamental wave light is detected by a second light intensity detector and supplied to the controller.

6. The control method according to claim 4, wherein the amplified fundamental wave light is input to the first nonlinear medium as excitation light for the optical parametric amplification process after undergoing a second harmonic generation process in the second nonlinear medium.

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