Pre-optical fiber amplifier with power balancing function and use method of pre-optical fiber amplifier

Abstract

The invention relates to the technical field of optical communication, in particular to a front optical fiber amplifier with a power balancing function. On the basis of a traditional Er-doped optical fiber amplifier, incident light is divided into a signal link and a competition link through a light splitting device with a fixed proportion. The purpose of introducing the competitive link is to generate a competitive wavelength which has an obvious competitive effect with the signal light in the EDF, and gain competition is carried out in the amplification process of the signal light in the EDF; wherein the competitive link finishes conversion from signal light wavelength to wavelength with obvious competitive effect by adopting a four-wave mixing principle based on HNLF, and then reversely inputs the converted competitive light into the EDF of the signal link to carry out a light amplification process with gain competition, so that the aim of reducing the output power fluctuation range after the signal light is amplified by the EDF is fulfilled.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical communication technology, more particularly, to a pre-fiber amplifier with power equalization function and a method of using the same. BACKGROUND

[0002] As a new communication technology, free space laser communication technology (FSO) has the advantages of high speed, wide frequency band, low cost and strong security, and becomes an effective technical means for the "last mile" of optical communication network. It has great application value in scenes where optical fiber laying is difficult, such as open field and island. However, the light intensity flicker effect caused by atmospheric turbulence is the main factor restricting its development. The main architecture of FSO is that the signal is sent into a power amplifier after being modulated at the transmitting end to achieve longer distance transmission; at the receiving end, the pre-amplifier receives and amplifies the weak signal from the noise.

[0003] The most mature pre-amplifier at present is a rare earth ion doped fiber amplifier working in a constant gain mode, such as an erbium-doped fiber amplifier (EDFA), which provides the same gain level for signal light at different input levels. The light intensity flicker effect caused by atmospheric turbulence will cause the incident power at the receiving end to change constantly, resulting in fluctuations in the output power level of the pre-amplifier with the change of the input level, thereby causing the average bit error rate of communication to rise and reducing the communication quality. In view of this, researchers have proposed power equalization technology, mainly including electrically controlled power equalization and all-optical power equalization technology.

[0004] Electrically controlled power equalization refers to dynamically adjusting the gain level by converting the input signal into an electrical signal, comparing it with a standard electrical signal, and then controlling the pump current size to dynamically adjust the output power level. It has the advantages of high control precision and low noise level, but the process of electric-optical conversion determines its slow response speed and complex system.

[0005] All-optical power equalization technology includes using resonant cavities, nonlinear micro-ring resonant cavities and other methods, using the threshold value formed by laser as the judgment condition to suppress the gain of incident light higher than the laser formation threshold and amplify the incident light lower than the laser formation threshold. However, when wavelength drift occurs, the working state will be invalid, so it is not suitable for application scenarios under medium and high intensity atmospheric turbulence. In addition, by cascading amplification, the incident light is amplified to the saturation working area of the rear-stage amplifier by the front-stage amplifier, which can also achieve power equalization output. However, working in the saturation area of the erbium-doped fiber amplifier will cause the level of amplified spontaneous emission noise (ASE) to rise, which will greatly affect the communication quality. SUMMARY

[0006] In view of the fact that there is currently a lack of power equalization technical solutions with low noise level capable of working in medium and high intensity turbulence, the application provides a pre-fiber amplifier with a power equalization function, which can realize low-noise amplification of incident light with different power levels while reducing the fluctuation level of output power, and has important significance for improving the communication quality of FSO.

[0007] To achieve the above object, the application adopts the following technical solutions:

[0008] A pre-fiber amplifier with a power equalization function, the pre-fiber amplifier comprises a tunable laser light source Signal source, a coupler Coupler, a wavelength division multiplexer SWDM1, a pump laser Pump1, a circulator Circulator1, a doped fiber EDF1, a circulator Circulator2 and a band-pass filter BPF3; the tunable laser light source Signal source is connected to the input end of the coupler Coupler, the main output port of the coupler Coupler is connected to the 1 port of the circulator Circulator1 through the wavelength division multiplexer SWDM1, the pump laser Pump1 is connected to the input end of the wavelength division multiplexer SWDM1, the 2 port of the circulator Circulator1 is connected to the 2 port of the circulator Circulator2 through the doped fiber EDF1, and the band-pass filter BPF3 is connected to the 3 port of the circulator Circulator2; the pre-fiber amplifier further comprises a tunable laser light source Pump source, a polarization controller PC2, a wavelength division multiplexer SWDM2, a doped fiber EDF2, an optical isolator, a band-pass filter BPF2, a wavelength division multiplexer WDM, a high nonlinear fiber HNLF and a band-pass filter BPF1 connected in sequence, the output of the band-pass filter BPF1 is connected to the 3 port of the circulator Circulator2, and the input end of the wavelength division multiplexer SWDM2 is connected with a pump laser Pump2; the coupling port of the coupler Coupler is connected to the input end of the wavelength division multiplexer WDM through the polarization controller PC1.

[0009] Further optimization of the technical solution further comprises a tunable attenuator VOA connected in series between the tunable laser light source Signal source and the coupler Coupler.

[0010] Further optimization of the technical solution further comprises a phase modulator PM, a voltage source, a microwave source RF and a direct current bias voltage DC, the voltage source is connected with the microwave source, and the microwave source and the direct current bias voltage DC are used to power the phase modulator PM.

[0011] The further optimization of the technical scheme is that the coupler Coupler divides the incident light into signal link incident light and competition link incident light according to the ratio of 90:10, 80:20 or 70:30; the incident light of the signal link is sent into the doped optical fiber EDF1 for optical amplification by the forward pumping mode together with the pump light.

[0012] The further optimization of the technical scheme is that the pump laser Pump1 serves as a pump source to perform optical amplification on the signal light transmitted in the doped optical fiber EDF1 in the forward direction and the competition light transmitted in the reverse direction.

[0013] The further optimization of the technical scheme is that the pump power of the pump laser Pump1 is greater than 30 dBm.

[0014] The further optimization of the technical scheme is that the high nonlinear optical fiber HNLF has a zero dispersion wavelength of 1548 nm, a dispersion slope of 0.05 ps / nm2·km, a nonlinear coefficient of 0.012 / W·km, and an optical fiber length of 200 m.

[0015] The method for using the pre-fiber amplifier with power equalization function, characterized in that it comprises the following steps:

[0016] Step 1, the signal light output by the tunable laser source Signal source is attenuated by the tunable attenuator VOA, and then the incident light is divided into signal link incident light and competition link incident light by the coupler Coupler, wherein the signal link incident light is connected to the main output end of the coupler Coupler, and the competition link incident light is connected to the coupling end of the coupler Coupler; the signal link incident light enters the wavelength division multiplexer SWDM1, and together with the continuous pump light generated by the pump laser Pump1 enters the 1 port of the circulator Circulator1, and then enters the doped optical fiber EDF1 through the 2 port; after the Er3+ in the doped optical fiber EDF1 absorbs the energy of the pump light to complete the stimulated radiation optical amplification process, the remaining pump light and the amplified signal light enter the 2 port of the circulator Circulator2, and are output from the 3 port; finally, the signal light is filtered out by the band-pass filter BPF3 with a center working wavelength of the signal light wavelength;

[0017] Step 2, a tunable laser pump source is used to generate a pump seed light; a phase modulator PM is connected to the pump seed light to perform phase broadening; the output of the phase modulator PM enters a polarization controller PC2, and then enters a doped fiber EDF2 together with continuous pump light generated by a pump laser Pump2 through a wavelength division multiplexer SWDM2 to perform power amplification on the pump seed light; the output is connected to an optical isolator Isolator, and then connected to a band-pass filter BPF2 with a center working wavelength of the wavelength of the pump seed light, and the amplified noise of the spontaneous emission of the rest wavelengths is filtered out, and then output into a wavelength division multiplexer WDM as the pump light for parametric amplification in the competition link;

[0018] Step 3, the incident light is output as the competition link incident light through the coupling end of the coupler Coupler, and the polarization state of the competition link incident light is adjusted to be consistent with the polarization state of the pump seed light output by the polarization controller PC2 in the polarization controller PC1; then the output light of the band-pass filter BPF2 is sent into a high nonlinear fiber HNLF through the wavelength division multiplexer WDM to perform a parametric amplification process; the output end of the high nonlinear fiber HNLF has pump light, competition link incident light and newly generated idler light, and a band-pass filter BPF1 with a center working wavelength of the wavelength of the idler light is connected to filter out the idler light;

[0019] Step 4, the idler light output by the band-pass filter BPF1 is connected to port 1 of a circulator Circulator2, and is reversely input into a doped fiber EDF1 through port 2, and in the doped fiber EDF1: the forward transmission signal light competes with the reverse input idler light for the Er3+ in the upper energy level to perform stimulated radiation, that is, a gain competition process; the amplified forward transmission signal light is output through port 3 of the circulator Circulator2; the amplified reverse transmission idler light is output through port 3 of the circulator Circulator1.

[0020] On the basis of a traditional Er-doped fiber amplifier, the incident light is divided into a signal link and a competition link by a fixed-ratio optical splitting device. The purpose of introducing the competition link is to generate a competition wavelength that has a significant competition effect with the signal light in the EDF, and to perform gain competition in the amplification process of the signal light in the EDF; the competition link uses the principle of four-wave mixing based on HNLF to complete the conversion from the signal light wavelength to the wavelength with significant competition effect, and then reversely inputs the converted competition light into the EDF of the signal link to perform optical amplification with gain competition, so as to achieve the purpose of reducing the output power fluctuation range of the signal light after the amplification by the EDF.

[0021] Compared with the prior art, the above technical solution has the following beneficial effects:

[0022] In the above technical solution, the all-optical scheme is used in the introduction process of the competition link, and there is no circuit feedback design, which can ensure the fast response and high precision of the system; the parametric amplification scheme of HNLF is used in the competition link, and the newly generated idler light wavelength is in the high radiation region of Er 3+ , which can have obvious competition effect with the signal light in the EDF and better power balance effect; since the gain level of parametric amplification under small signal input power remains constant, the fixed ratio of the optical splitting device is used, and when the power of the incident light changes, the output power of the idler light generated by the competition link changes linearly with the incident light power of the competition link, which avoids the ASE noise increase caused by the working of the cascade amplifier in the saturation region in the existing all-optical power balance technology, and damages the communication quality. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is a schematic diagram of the frame of the pre-fiber amplifier with power balance function;

[0024] Figure 2 It is a wavelength selection diagram of the most significant competition effect with the signal wavelength;

[0025] Figure 3 It is a gain spectrum diagram of the HNLF parametric amplification designed in the competition link;

[0026] Figure 4 It is a diagram of the change of the output power with the input power after the HNLF parametric amplification in the competition link;

[0027] Figure 5 It is a diagram of the change of the gain of the signal link forward transmission light after the gain competition of the idler light in the competition link with the total incident light power under different optical splitting ratios;

[0028] Figure 6 It is a diagram of the change of the output power of the signal link forward transmission light after the gain competition of the idler light in the competition link with the total incident light power under different optical splitting ratios. DETAILED DESCRIPTION

[0029] In order to explain the technical content, structural features, purposes and effects of the technical solution in detail, the following will be described in detail in combination with specific embodiments and the accompanying drawings.

[0030] REFERENCE Figure 1The embodiment of the present application provides a pre-fiber amplifier with a power equalization function, which comprises a tunable laser light source Signal source, a tunable attenuator VOA, a coupler Coupler, a wavelength division multiplexer SWDM1, a pump laser Pump1, a circulator Circulator1, a doped fiber EDF1, a circulator Circulator2 and a band-pass filter BPF3. The tunable laser light source Signal source, the tunable attenuator VOA and the coupler Coupler are sequentially connected, the main output port of the coupler Coupler is connected with the 1 port of the circulator Circulator1 through the wavelength division multiplexer SWDM1, the pump laser Pump1 is connected with the input end of the wavelength division multiplexer SWDM1, and the 2 port of the circulator Circulator1 is connected with the 2 port of the circulator Circulator2 through the doped fiber EDF1.

[0031] The pre-fiber amplifier further comprises a tunable laser light source Pump source, a phase modulator PM, a polarization controller PC2, a wavelength division multiplexer SWDM2, a doped fiber EDF2, an optical isolator, a band-pass filter BPF2, a wavelength division multiplexer WDM, a high nonlinear fiber HNLF and a band-pass filter BPF1 which are sequentially connected, and the output of the band-pass filter BPF1 is connected with the 3 port of the circulator Circulator2.

[0032] The output of the coupling port of the coupler Coupler is connected with the input end of the wavelength division multiplexer WDM through the polarization controller PC1.

[0033] The pre-fiber amplifier further comprises a voltage source and a microwave source which are sequentially connected, the microwave source is connected with the phase modulator PM, and a direct current bias voltage DC is used for supplying power for the phase modulator PM.

[0034] A use method of a pre-fiber amplifier with a power equalization function, and the specific steps are as follows:

[0035] Step 1, the tunable laser source CW1 outputs signal light with wavelength of 1568 nm and power of 6 dBm, which is attenuated to -40 dBm by tunable optical attenuator VOA, and then is split into signal link incident light and competitive link incident light by 90:10 coupler Coupler, wherein the signal link connects the 90% output end of the coupler Coupler, and the competitive link connects the 10% output end. The signal link incident light enters wavelength division multiplexer SWDM1, and together with the 980 nm continuous pump light generated by pump laser Pump1 enters the 1 port of circulator Circulator1, and then enters doped fiber EDF1 through the 2 port; after amplification in the doped fiber EDF1, it enters the 2 port of circulator Circulator2, and then is output from the 3 port; finally, it is filtered out by the band-pass filter BPF3 with a center wavelength of 1568 nm.

[0036] Step 2, the tunable laser source CW2 generates pump seed light with wavelength of 1549 nm and power of 6 dBm; then it is connected with phase modulator PM, which uses microwave source RF to generate a modulation voltage with a frequency of 200 MHz, and uses 220 V to 12 V voltage source to power the microwave source RF, and uses 5 V DC bias voltage DC to ensure the stable working state of the phase modulator PM; the output of the phase modulator PM passes through the polarization controller PC2, and then enters the doped fiber EDF2 together with the 980 nm continuous pump light generated by the pump laser Pump2 through the wavelength division multiplexer SWDM2 to amplify the power to 31 dBm; then it is connected with optical isolator Isolator to prevent the amplified spontaneous emission noise ASE transmitted forward from being reflected at the end face or fusion joint of the subsequent devices and then entering the doped fiber EDF2 in the reverse direction, causing the output power of the EDF2 to be unstable and the noise to accumulate; then it is connected with 100G band-pass filter BPF2 with a center working wavelength of 1549 nm, and the filtered output light is connected with the wavelength division multiplexer WDM.

[0037] Step 3, the output of the 10% port of the coupler Coupler (90:10) is connected with the polarization controller PC1; then it is sent into the high nonlinear fiber HNLF together with the output light of the band-pass filter BPF2 through the wavelength division multiplexer WDM, and then it is connected with 100G band-pass filter BPF1 with a center working wavelength of 1530 nm, as shown in the reference Figure 4 , the power of the output idler light changes linearly with the total incident signal light power.

[0038] The zero dispersion wavelength of the high nonlinear fiber HNLF is 1548 nm, the dispersion slope is 0.05 ps / nm2·km, the nonlinear coefficient is 0.012 / W·km, and the fiber length is 200 m.

[0039] Step 4, as shown in the referenceFigure 1 As shown, the idle light output from the band-pass filter BPF1 is input into the doped fiber EDF1 through port 2 of the circulator 2, and competes with the signal light transmitted in the doped fiber EDF1 in gain; the signal light transmitted in the doped fiber EDF1 is output through port 3 of the circulator 2; as shown in the figure, the signal light is input into the doped fiber EDF2 through port 1 of the circulator 3, and competes with the idle light transmitted in the doped fiber EDF2 in gain; the idle light transmitted in the doped fiber EDF2 is output through port 2 of the circulator 3; the signal light output from the doped fiber EDF2 is input into the doped fiber EDF1 through port 2 of the circulator 1, and competes with the signal light transmitted in the doped fiber EDF1 in gain; the signal light transmitted in the doped fiber EDF1 is output through port 3 of the circulator 1. Figure 5 And Figure 6 After the incident light passes through the preamplifier with power equalization function designed by the application, the gain has a selection characteristic to the input power level of the signal light, and the gain level decreases smoothly with the increase of the total incident power, effectively reducing the fluctuation range of the signal light output power, which is of great significance to improve the communication quality of the FSO system.

[0040] The parametric amplification process of the competition link is based on the nonlinear effect of four-wave mixing. When the polarization directions of the pump light and the signal light are the same and the wave vector matching condition is met, significant four-wave mixing phenomenon will occur in the HNLF. The wave vector matching condition is:

[0041] Δk=k3+k4-k1-k2=(n3ω3+n4ω4-n1ω1-n2ω2) / c=0

[0042] Where Δk is the phase mismatch factor, k1 and k2 are the wave vectors of the pump light, k3 and k4 are the wave vectors of the signal light and the generated idle light, ω i is the circular frequency;

[0043] When a single pump with high power is incident, the frequency of the pump light, the frequency of the signal light, and the frequency of the idle light maintain a fixed frequency relationship:

[0044] f S +f I =2f P

[0045] In the formula, f S represents the frequency of the signal light, f I represents the frequency of the idle light, and f P represents the frequency of the pump light; that is, after parametric amplification by the HNLF, the output light contains signal light, idle light, and pump light with frequencies f S , f I , and f P .

[0046] The propagation equation of the signal light, the pump light, and the idle light in the HNLF is:

[0047]

[0048] Where P p is the pump light power; P s is the signal light power; Pi is the idler light power; Δβ represents the phase mismatching amount; θ represents the phase difference among the pump light, the signal light and the idler light;

[0049] Δβ can be represented as:

[0050]

[0051] where λ0 is the zero-dispersion wavelength of the HNLF; is the dispersion slope at the zero-dispersion wavelength; λ p is the pump light wavelength; λ s is the signal light wavelength;

[0052] θ can be represented as:

[0053]

[0054] where is the phase considering both the nonlinear phase shift in the transmission process and the initial phase; when the pump light loss is not considered and the pump light power is much larger than the signal light power, the idler light rapidly increases in a very short distance, at this time θ(0) = π / 2 is considered;

[0055] The output end of the HNLF parametric amplification of the competitive link is connected to the center frequency f I of the band-pass filter BPF1, the idler light is filtered out and connected to the reverse output end of the signal link EDF1 through the circulator Circulator2, to realize the gain competition of the idler light with the frequency f I , which is reversely transmitted in the EDF1, to the forward transmission signal light, to achieve the purpose of reducing the power band range of the forward transmission signal light at the output end of the EDF1. The gain of the signal light can be represented as:

[0056]

[0057] where P sout is the signal light output power, P sin is the input power of the signal light.

[0058] It is to be noted that, in the present text, terms such as first and second, and the like, merely serve to identify a difference between one entity or action and another entity or action, and do not necessarily require or imply that there is any such actual relationship or order between these entities or actions. Moreover, the terms "comprising", "including", or any other variant thereof are intended to cover a non-exclusive inclusion, such that processes, methods, articles, or apparatuses that comprise a list of elements are not required to comprise only those elements, but can include other elements not expressly listed or inherent to such processes, methods, articles, or apparatuses. Without further limitation, an element preceded by "comprises a" or "comprises" does not, without more limitations, preclude the existence of further elements of the process, method, article, or apparatus that includes the element. Furthermore, in the present text, "greater than", "less than", "exceed", and the like are understood to exclude the number itself; "and above", "and below", "and within", and the like are understood to include the number itself.

[0059] Although the above-mentioned embodiments have been described, those skilled in the art can make further changes and modifications to these embodiments once they know the basic inventive concept, so the above description is only for the embodiments of the present application, and does not limit the patent protection scope of the present application, and any equivalent structure or equivalent process transformation using the content of the present application specification and drawings, or direct or indirect application in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A pre-fiber amplifier with power equalization function, characterized in that: The preamplifier includes a tunable laser source (Signal source), a coupler, a wavelength division multiplexer (SWDM1), a pump laser (Pump1), a circulator (Circulator1), an erbium-doped fiber (EDF1), a circulator (Circulator2), and a bandpass filter (BPF3). The tunable laser source is connected to the input of the coupler. The main output port of the coupler is connected to port 1 of the circulator (Circulator1) via the SWDM1. The pump laser (Pump1) is connected to the input of the SWDM1. Port 2 of the circulator (Circulator1) is connected to the circulator (Circulator2) via the erbium-doped fiber (EDF1). The preamplifier includes a tunable laser source (Pumpsource), a polarization controller (PC2), a wavelength division multiplexer (SWDM2), an erbium-doped fiber (EDF2), an optical isolator, a bandpass filter (BPF2), a wavelength division multiplexer (WDM), a high nonlinear fiber (HNLF), and a bandpass filter (BPF1), all connected in sequence. The output of the bandpass filter (BPF1) is connected to port 3 of the circulator (Circulator2). The input of the wavelength division multiplexer (SWDM2) is connected to the pump laser (Pump2). The coupling port of the coupler is connected to the input of the wavelength division multiplexer (WDM) via the polarization controller (PC1).

2. The preamplifier fiber amplifier with power equalization function as described in claim 1, characterized in that: It also includes a tunable attenuator (VOA) connected in series between the tunable laser source and the coupler.

3. The pre-fiber amplifier with power equalization function as described in claim 1, characterized in that: It also includes a phase modulator PM, a voltage source, a microwave source RF, and a DC bias voltage DC, wherein the voltage source is connected to the microwave source, and the microwave source and the DC bias voltage DC are used to power the phase modulator PM.

4. The pre-fiber amplifier with power equalization function as described in claim 1, characterized in that: The coupler Coupler divides the incident light into signal link incident light and competing link incident light in a ratio of 90:10, 80:20 or 70:30; the signal link incident light is fed into the erbium-doped fiber EDF1 together with the pump light through forward pumping for optical amplification.

5. The pre-fiber amplifier with power equalization function as described in claim 1, characterized in that: The pump laser Pump1 serves as a pump source to amplify the signal light propagating in the forward direction and the competing light propagating in the reverse direction in the erbium-doped fiber EDF1.

6. The pre-fiber amplifier with power equalization function as described in claim 5, characterized in that: The pump power of the pump laser Pump1 is greater than 30 dBm.

7. The preamplifier fiber amplifier with power equalization function as described in claim 1, characterized in that: The high nonlinear optical fiber HNLF has a zero-dispersion wavelength of 1548nm, a dispersion slope of 0.05ps / nm2·km, a nonlinear coefficient of 0.012 / W·km, and a fiber length of 200m.

8. The method of using a preamplifier fiber optic amplifier with power equalization function as described in any one of claims 1-7, characterized in that, Includes the following steps: Step 1: The signal light output from the tunable laser source is attenuated by a tunable attenuator (VOA) and then split into a signal link incident light and a competing link incident light by a coupler. The signal link incident light is connected to the main output of the coupler, and the competing link incident light is connected to the coupling end of the coupler. The signal link incident light enters the wavelength division multiplexer (SWDM1) and, together with the continuous pump light generated by the pump laser (Pump1), enters port 1 of the circulator (Circulator1) and then enters the erbium-doped fiber (EDF1) through port 2. The Erbium-doped fiber (EDF1) contains Erbium... 3+ After absorbing the energy of the pump light to complete the stimulated emission amplification process, the remaining pump light and the amplified signal light enter from port 2 of the circulator 2 and exit from port 3; finally, the signal light is filtered out by the bandpass filter BPF3, whose center operating wavelength is the wavelength of the signal light. Step 2: A tunable laser source is used to generate a pump seed light; this is then connected to a phase modulator PM to broaden the phase of the pump seed light; the output of the phase modulator PM enters the polarization controller PC2, and then, together with the continuous pump light generated by the pump laser 2, it enters the erbium-doped fiber EDF2 through a wavelength division multiplexer SWDM2 to amplify the power of the pump seed light; the output is connected to an optical isolator, and then to a bandpass filter BPF2 with the center operating wavelength being the pump seed light wavelength, which filters out the spontaneous emission amplification noise of other wavelengths, and the output is connected to the wavelength division multiplexer WDM as the pump light for parametric amplification in the competing link; Step 3: The incident light outputs the competing link incident light at the coupling end of the coupler. In polarization controller PC1, the polarization state of the competing link incident light is adjusted to match the polarization state of the pump seed light output by polarization controller PC2. Then, the output light of the bandpass filter BPF2 is sent to the high nonlinear fiber HNLF through wavelength division multiplexer (WDM) for parametric amplification. There are pump light, competing link incident light and newly generated idler light at the output end of the high nonlinear fiber HNLF. It is necessary to connect a bandpass filter BPF1 with the center operating wavelength of the idler light to filter out the idler light. Step 4: The idler light output from bandpass filter BPF1 is connected to port 1 of circulator 2, and then enters the erbium-doped fiber EDF1 via port 2. Inside the erbium-doped fiber EDF1: the forward-propagating signal light and the reverse-input idler light compete for the higher energy level Er. 3+ Stimulated emission, i.e., the gain competition process, is carried out; the amplified forward transmission signal light is output through port 3 of Circulator 2; the amplified reverse transmission idler light is output through port 3 of Circulator 1.

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