An active optical fiber gain bandwidth test system and a test method thereof

Abstract

The application discloses an active optical fiber gain bandwidth test system and a test method thereof. The system comprises a pumping unit, a gain unit, a downstream coupler, a spectrum analysis unit and a control unit. The input end of the gain unit is connected with the pumping unit. The input end of the downstream coupler is connected with the output end of the gain unit. The spectrum analysis unit is connected with the first output end of the downstream coupler. The control unit is connected with the second output end of the downstream coupler. The pumping unit is used for providing pumping light to the gain unit. The gain unit is used for accommodating the optical fiber to be tested and generating a gain optical signal under the action of the pumping light. The spectrum analysis unit is used for performing spectrum analysis on the gain optical signal. The control unit is used for feeding back and adjusting the pumping unit according to the characteristic information of the gain optical signal obtained from the downstream coupler. The application realizes the simplification of the test system, the improvement of the test speed and the standardization of the test results, and provides an efficient and reliable solution for the production quality control, performance comparison and research and development verification of the active optical fiber.

Description

Technical Field

[0001] This application relates to the field of optical fiber testing technology, and more specifically, to an active optical fiber gain-bandwidth testing system and testing method thereof. Background Technology

[0002] As optical communication networks continue to evolve towards higher speeds and larger capacities, wavelength division multiplexing (WDM) systems have become a key technology for enhancing fiber optic transmission capabilities. In these systems, active fiber, as the core component of the optical amplifier, directly affects the amplification uniformity of multi-wavelength signals and the system's transmission performance due to its gain-bandwidth characteristics. Therefore, accurately and efficiently evaluating the gain-bandwidth of active fiber is crucial for ensuring the performance consistency of the optical amplifier and the entire transmission system.

[0003] Currently, the conventional approach to evaluating the gain characteristics of active optical fibers is to place them directly into an actual optical fiber amplifier structure, input a multi-channel signal light source, and measure the gain value of each wavelength channel to obtain the spectral shape and bandwidth of the gain as a function of wavelength. This method relies on a complete and structurally complex amplifier platform and requires a multi-wavelength light source and a corresponding detection system.

[0004] However, the aforementioned conventional testing methods rely on specific amplifier structures and multi-wavelength light sources, resulting in complex testing systems with poor configuration flexibility, making it difficult to achieve rapid and standardized measurements of the gain characteristics of the fiber under test. Especially when performance comparisons of different batches or types of fibers are required, each test necessitates ensuring complete consistency in amplifier structure and light source conditions, making the operation cumbersome and repeatability difficult to guarantee, which is detrimental to rapid inspection and performance control during the active fiber production process. Summary of the Invention

[0005] To address at least one defect or improvement requirement in the prior art, this invention provides an active optical fiber gain bandwidth testing system and method, which solves the problem that the prior art relies on specific amplifier structures and multi-wavelength light sources, resulting in complex testing systems, poor configuration flexibility, and difficulty in achieving rapid and standardized measurement of the gain characteristics of the optical fiber under test.

[0006] To achieve the above objectives, according to a first aspect of the present invention, an active optical fiber gain-bandwidth testing system is provided, comprising: Pump unit; gain unit, whose input is connected to the pump unit; downstream coupler, whose input is connected to the output of the gain unit; spectral analysis unit, connected to the first output of the downstream coupler; control unit, connected to the second output of the downstream coupler; The pump unit is used to provide pump light to the gain unit; The gain unit is used to house the optical fiber under test and to generate a gain optical signal under the action of pump light; The spectral analysis unit is used to perform spectral analysis on the gain optical signal; The control unit is used to perform feedback adjustment of the pump unit based on the characteristic information of the gain optical signal obtained from the downstream coupler.

[0007] In one possible implementation, the pump unit includes: Pump laser; pump protector, whose input is connected to the output of the pump laser; upstream coupler, whose input is connected to the output of the pump protector; The first output terminal of the upstream coupler serves as the output terminal of the pump unit, while the second output terminal of the upstream coupler is connected to a power meter for monitoring the pump optical power.

[0008] In one possible implementation, the gain unit includes: A wavelength division multiplexer, whose pump end serves as the input end of the gain unit; the fiber under test, one end of which is connected to the multiplexing end of the wavelength division multiplexer; a mirror, which is connected to the other end of the fiber under test. In this configuration, the signal terminal of the wavelength division multiplexer serves as the output terminal of the gain unit.

[0009] In one possible implementation, the control unit includes: The filter, whose input terminal serves as the input terminal of the control unit, is used to filter out characteristic wavelength signals from the gain optical signal; The control circuit, connected to the output of the filter and the pump laser, is used to adjust the output of the pump unit according to the intensity of the characteristic wavelength signal.

[0010] In one possible implementation, the control circuit includes: A photoelectric detection circuit is used to convert characteristic wavelength signals into electrical signals. The microprocessor, connected to the photoelectric detection circuit, is used to process electrical signals; The pump drive circuit is connected to the microprocessor and the pump laser in the pump unit, and is used to adjust the drive current of the pump laser according to the instructions of the microprocessor.

[0011] In one possible implementation, the control circuit also includes a temperature control circuit connected to the microprocessor for temperature control of the pump laser.

[0012] In one possible implementation, both the upstream and downstream couplers are tapered fiber couplers.

[0013] In one possible implementation, the wavelength division multiplexer is a fused tapered wavelength division multiplexer.

[0014] In one possible implementation, the spectral analysis unit includes a dispersive element and a detector array for expanding the received optical signal by wavelength and detecting its intensity distribution.

[0015] According to a second aspect of the present invention, an active optical fiber gain bandwidth testing method is also provided, employing an active optical fiber gain bandwidth testing system as described in any of the possible implementations above, the method comprising: Pump light is supplied to the fiber under test to generate a gain optical signal; The gain optical signal is split into a first optical signal and a second optical signal; Spectral analysis is performed on the first optical signal to obtain the gain spectrum of the optical fiber under test; Extract characteristic wavelength signals from the second optical signal; Based on the characteristic wavelength signal, the power of the pump light is adjusted by feedback to make the intensity of the characteristic wavelength signal approach the target value.

[0016] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects: This invention provides an active optical fiber gain-bandwidth testing system that utilizes pump light to excite the inherent amplified spontaneous emission spectrum of the fiber under test (BUT) as the test signal. This eliminates the need for externally injected multi-wavelength signal light sources, simplifying the core optical path configuration required for testing. It avoids the need to build complex and expensive multi-channel light source systems and their switching control units to simulate real amplifier environments, thereby reducing system hardware complexity and manufacturing costs. By capturing and analyzing the spontaneous emission spectrum in a single operation using a spectral analysis unit, the complete gain spectral shape information of the BUT across the entire operating wavelength band can be directly obtained, improving testing efficiency and data acquisition speed. Through real-time monitoring of the feature information extracted from the gain light signal and dynamic feedback adjustment of the pump unit output, the system can automatically stabilize the test state at a preset or reference-consistent operating point. This ensures that different batches and types of optical fibers can be evaluated under uniform, stable, and repeatable testing conditions, eliminating test errors introduced by factors such as pump power fluctuations, thus ensuring high consistency and comparability of measurement results. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram of an embodiment of the active fiber gain-bandwidth testing system provided by the present invention; Figure 2 A control structure diagram of an embodiment of the active fiber gain-bandwidth testing system provided by the present invention; Figure 3 A schematic diagram of the spectrum of the optical fiber under test measured in the active optical fiber gain testing system provided by the present invention; Figure 4 A schematic diagram illustrating the gain deviation between the test fiber and the reference fiber provided by the present invention; Figure 5 This is a flowchart illustrating an embodiment of the active fiber gain-bandwidth testing method provided by the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0020] The terms "first," "second," "third," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0021] This invention provides an active optical fiber gain bandwidth testing system and its testing method, which are described below.

[0022] Please see Figure 1 , Figure 1 This is a schematic diagram of an embodiment of the active fiber gain bandwidth testing system provided by the present invention. In a specific embodiment of the present invention, an active fiber gain bandwidth testing system is disclosed, comprising: Pump unit 100; gain unit 200, whose input terminal is connected to pump unit 100; downstream coupler 300, whose input terminal is connected to output terminal of gain unit 200; spectral analysis unit 400, connected to first output terminal of downstream coupler 300; control unit 500, connected to second output terminal of downstream coupler 300; Pump unit 100 is used to provide pump light to gain unit 200; Gain unit 200 is used to accommodate the optical fiber under test 202 and generate a gain optical signal under the action of pump light; The spectral analysis unit 400 is used to perform spectral analysis on the gain optical signal; The control unit 500 is used to perform feedback adjustment on the pump unit 100 based on the characteristic information of the gain optical signal obtained from the downstream coupler 300.

[0023] In the above embodiments, the core function of the pump unit 100 is to generate and output a highly stable pump light of a specific wavelength. In order to ensure the repeatability of test conditions, the pump unit 100 has a precise power stabilization and temperature control mechanism. Its output pigtail can be equipped with components such as fiber gratings to lock the pump wavelength and avoid spectral drift from affecting the test results.

[0024] The main function of the gain unit 200 is to house and optically connect the active fiber under test (AD), efficiently coupling the pump light from the pump unit 100 into the AD fiber 202. When a strong pump light acts on the active fiber, it excites rare-earth ions (such as erbium ions) in the fiber, causing them to produce stimulated emission and spontaneous emission. The amplified spontaneous emission (ASE) light propagating along the fiber constitutes the test signal of this system—the gain light signal. The shape of this ASE spectrum directly reflects the intrinsic gain spectrum characteristics of the active fiber under small-signal conditions. The gain unit 200 ensures that the AD fiber 202 can be stably and repeatedly installed and achieve low-loss connections with other optical components.

[0025] The downstream coupler 300 employs a fixed splitting ratio fiber optic coupler, whose input receives a gain optical signal containing rich spectral information output from the gain unit 200. Subsequently, the coupler splits the optical signal into two paths: its first output feeds most of the optical power (e.g., 95% or 99%) to the spectral analysis unit 400 to ensure sufficient signal-to-noise ratio for spectral measurements; its second output directs a small portion of the optical power (e.g., 1% or 5%) to the control unit 500 for real-time signal feedback and system control, achieving parallel processing of the same optical signal and balancing the requirements of high-precision measurement and real-time control.

[0026] The spectral analysis unit 400 is responsible for performing precise spectral analysis on the strong optical signal from the first output end of the downstream coupler 300. This unit typically contains dispersive elements (such as gratings) and a photodetector array. The dispersive elements expand the incident composite light spatially according to wavelength, forming a spectrum; the photodetector array simultaneously measures the light intensity of each wavelength component, and finally synthesizes and outputs a complete gain spectrum curve. By analyzing the gain spectrum curve, key parameters such as the gain bandwidth, gain flatness, and peak gain wavelength of the fiber under test 202 can be directly obtained.

[0027] The control unit 500 receives a weak light signal from the second output of the downstream coupler 300 and extracts specific characteristic information from it. This characteristic information can be the optical power value at a specific wavelength (e.g., the peak gain wavelength or a predetermined reference wavelength). The control unit 500 internally includes a photoelectric conversion circuit, a signal processing module (such as a microprocessor MCU), and a feedback output circuit. The processing module compares the real-time monitored characteristic power with an internally preset target value, and generates an adjustment command based on the difference (error signal) using a specific control algorithm (such as a PID algorithm). This command is then sent to the pump unit 100 to dynamically adjust the drive current of its pump laser 101, thereby changing the output power of the pump light.

[0028] The system workflow and coordination mechanism can be briefly described as follows: Pump light is injected into the fiber under test 202 in the gain unit 200, generating a broadband ASE spectrum; this spectrum is split in two by the downstream coupler 300; most of the light is used for spectral analysis to obtain the final data, and a small portion of the light is used for the control loop; the control unit 500 analyzes the power of the characteristic wavelength and adjusts the pump power in reverse to form a closed-loop feedback, actively maintaining constant test conditions. For example, by stabilizing the power of the characteristic wavelength at the target value through feedback control, changes in test conditions caused by batch differences in the fiber under test 202, fluctuations in connection loss, or slow drift of the pump laser 101 itself can be offset, thereby ensuring that each measurement is performed under consistent and comparable conditions, ultimately significantly improving the repeatability, accuracy, and reliability of the measurement.

[0029] Compared with existing technologies, the active fiber gain bandwidth testing system provided in this embodiment utilizes pump light to excite the fiber under test 202 to generate its inherent amplified spontaneous emission spectrum as a test signal. This eliminates the need for externally injected multi-wavelength signal light sources, simplifying the core optical path configuration required for testing. It avoids the need to build complex and expensive multi-channel light source systems and their switching control units 500 to simulate real amplifier environments, thereby reducing system hardware complexity and manufacturing costs. By capturing and analyzing the spontaneous emission spectrum in a single operation through the spectral analysis unit 400, the complete gain spectrum information of the fiber under test 202 across the entire operating wavelength band can be directly obtained, improving testing efficiency and data acquisition speed. By real-time monitoring of the feature information extracted from the gain light signal and dynamically adjusting the output of the pump unit 100, the test state can be automatically stabilized at a preset or reference-consistent operating point. This ensures that different batches and types of fibers can be evaluated under uniform, stable, and repeatable test conditions, eliminating test errors introduced by factors such as pump power fluctuations, thus ensuring high consistency and comparability of measurement results.

[0030] In some embodiments of the present invention, the pump unit 100 includes: Pump laser 101; pump protector 102, the input of which is connected to the output of pump laser 101; upstream coupler 103, the input of which is connected to the output of pump protector 102; The first output terminal of the upstream coupler 103 serves as the output terminal of the pump unit 100, and the second output terminal of the upstream coupler 103 is connected to a power meter 104 for monitoring the pump optical power.

[0031] In the above embodiment, the pump unit 100 adopts an optimized structure with multiple protection and real-time monitoring functions. Specifically, the unit includes a pump laser 101 as the core light source, whose output end is sequentially connected to a pump protector 102 and an upstream coupler 103. The pump protector 102 effectively isolates the reverse-transmitted optical signal, preventing reflected light from damaging the pump laser 101 and ensuring long-term stable operation of the light source. The upstream coupler 103 adopts an asymmetric beam splitting design; its first output end serves as the main output end of the pump unit 100, delivering most of the pump light to the subsequent gain unit 200; while its second output end is connected to a high-precision power meter 104 for real-time monitoring of the pump light output power. The upstream coupler 103 enables the system to continuously monitor the operating status of the pump light source while testing, providing important assurance for the reliability and repeatability of the test results.

[0032] In some embodiments of the present invention, the gain unit 200 includes: The wavelength division multiplexer 201 has its pump end serving as the input end of the gain unit 200; the fiber under test 202 has one end connected to the multiplexing end of the wavelength division multiplexer 201; and the reflector 203 is connected to the other end of the fiber under test 202. The signal terminal of wavelength division multiplexer 201 serves as the output terminal of gain unit 200.

[0033] In the above embodiment, the gain unit 200 adopts a resonant structure including a wavelength division multiplexer 201, an optical fiber under test (ODT) 202, and a reflector 203. The pump end of the wavelength division multiplexer 201 serves as the input end of the gain unit 200, receiving pump light from the pump unit 100; its multiplexing end is fused to one end of the ODT 202, efficiently coupling the pump light into the ODT 202. The other end of the ODT 202 is connected to a high-reflectivity reflector 203, which reflects the residual pump light and the generated signal light transmitted through the ODT 202 back into the fiber, forming a bidirectional pumping effect. This significantly improves the utilization efficiency of the pump light, thereby enhancing the amplified spontaneous emission light signal generated by the ODT 202. The signal end of the wavelength division multiplexer 201 serves as the output end of the gain unit 200, outputting the enhanced gain light signal to downstream components.

[0034] In some embodiments of the present invention, the control unit 500 includes a filter 501 and a control circuit 502. The input terminal of the filter 501 serves as the input terminal of the control unit 500 and is used to filter out the characteristic wavelength signal from the gain optical signal; the control circuit 502 is connected to the output terminal of the filter 501 and is used to adjust the output of the pump unit 100 according to the intensity of the characteristic wavelength signal.

[0035] In the above embodiment, the control unit 500 consists of a filter 501 and a control circuit 502. The input terminal of the filter 501 serves as the input port of the control unit 500. Its function is to selectively filter out optical signals of specific characteristic wavelengths from the gain optical signal transmitted from the downstream coupler 300. These characteristic wavelengths are typically selected near the peak of the gain spectrum or in a band crucial for performance evaluation. The control circuit 502 is connected to the output terminal of the filter 501. Its core function is to monitor the intensity of the filtered characteristic wavelength signal in real time and generate control commands based on this intensity information to precisely adjust the output power of the pump unit 100.

[0036] In some embodiments of the present invention, the control circuit 502 includes a photodetector circuit, a microprocessor, and a pump drive circuit. The photodetector circuit is used to convert a characteristic wavelength signal into an electrical signal; the microprocessor is connected to the photodetector circuit and is used to process the electrical signal; the pump drive circuit is connected to the microprocessor and the pump laser 101 in the pump unit 100, and is used to adjust the drive current of the pump laser 101 according to the instructions of the microprocessor.

[0037] In the above embodiment, the photodetector circuit is responsible for converting the characteristic wavelength optical signal output by the filter 501 into a corresponding electrical signal. The microprocessor receives this electrical signal and compares and processes it with a preset target power value using a built-in algorithm. The pump drive circuit, according to the instructions issued by the microprocessor, precisely adjusts the drive current of the pump laser 101 in the pump unit 100, thereby achieving closed-loop control of the pump light output power and ensuring the stability of the test conditions.

[0038] In some embodiments of the present invention, the control circuit 502 further includes a temperature control circuit connected to a microprocessor for temperature control of the pump laser 101.

[0039] In the above embodiment, the temperature control circuit is dedicated to precise temperature control of the pump laser 101. Given that the output wavelength and power of semiconductor lasers are extremely sensitive to temperature, maintaining the pump laser 101 at a constant temperature effectively avoids changes in spectral characteristics caused by temperature drift, thereby ensuring the long-term reliability of the entire testing system and the accuracy of the measurement data.

[0040] In some embodiments of the present invention, both the upstream coupler 103 and the downstream coupler 300 are tapered fiber optic couplers.

[0041] In the above embodiments, both the upstream coupler 103 and the downstream coupler 300 are tapered fiber couplers. These couplers are manufactured using a fused biconical tapering process and offer advantages such as low insertion loss, stable splitting ratio, and good environmental reliability, making them suitable for use in test systems requiring long-term stable operation.

[0042] In some embodiments of the present invention, wavelength division multiplexer 201 is a fused biconical wavelength division multiplexer 201.

[0043] In the above embodiments, the fused tapered wavelength division multiplexer 201 can achieve efficient separation and synthesis of optical signals of different wavelengths through a specific tapering process. It has low insertion loss and high isolation at the designed wavelength, which can ensure efficient coupling and separation of pump light and signal light in the gain unit 200.

[0044] In some embodiments of the present invention, the spectral analysis unit 400 includes a dispersive element and a detector array for expanding the received optical signal by wavelength and detecting its intensity distribution.

[0045] In the above embodiments, dispersive elements (such as gratings or prisms) can spatially expand the received composite optical signal according to its wavelength components. The detector array is arranged accordingly to synchronously detect the light signal intensity at each wavelength position. Finally, these information are synthesized to output a complete spectral intensity distribution map, thereby intuitively and accurately presenting the gain-bandwidth characteristics of the fiber under test 202.

[0046] As a preferred embodiment, the device is preferably as follows: In some embodiments of the present invention, the pump laser 101 is a pump laser with a wavelength of 900~1100nm. The output pigtail has a fiber grating for precise wavelength control. The laser bandwidth is less than 6nm, and the power fluctuation of the laser output power within 24 hours is less than 1%, thereby ensuring the stability and accuracy of the pump light signal in terms of wavelength and power.

[0047] In some embodiments of the present invention, the pump protector 102 operates at a wavelength of 900~1100nm, has a maximum power handling capacity of 5W, and has a return light isolation greater than 35dB, preventing the back-propagating optical signal from interfering with or even damaging the pump laser 101.

[0048] In some embodiments of the present invention, the upstream coupler 103 is a 1x2 structure tapered coupler with a working wavelength of 900~1100nm, a maximum power handling capacity of 5W, and an isolation of more than 35dB for the returned light. In some embodiments of the present invention, the power meter 104 is a power meter 104 that uses a rough surface as a reflective surface. When measuring power, it is not affected by the uniformity of the beam, the divergence angle, the beam shape or the incident angle, and the power loss is small.

[0049] In some embodiments of the present invention, the wavelength division multiplexer 201 is a fused biconical tapered wavelength division multiplexer 201, with an insertion loss of less than 0.2 dB at the pump end in the range of 900-1100 nm and an insertion loss of greater than 30 dB at the range of 1400-1700 nm. The insertion loss at the output end of the wavelength division multiplexer 201 is less than 0.5 dB at the range of 1400-1700 nm and greater than 30 dB at the range of 900-1100 nm. The multiplexing end of the wavelength division multiplexer 201 outputs mixed light with wavelengths of 900-1100 nm and 1400-1700 nm.

[0050] In some embodiments of the present invention, the reflector 203 has an insertion loss of less than 1 dB in the 900-1700 nm range and a reflectivity of greater than 90%.

[0051] In some embodiments of the present invention, the downstream coupler 300 is a tapered coupler with a 1x2 structure, a maximum power handling capacity of 5W, and an isolation of more than 35dB for the returned light.

[0052] In some embodiments of the present invention, the spectral analysis unit 400 expands the received light signal in space according to the wavelength dimension through a dispersion system, converts the light signal into an electrical signal through a detector array, amplifies and filters the electrical signal to improve the signal-to-noise ratio, and finally converts the electrical signal into spectral information to present the light intensity distribution of different wavelengths.

[0053] In some embodiments of the present invention, the filter 501 typically has a center wavelength corresponding to the peak of the gain curve, a transmission bandwidth of 0.8 nm, an isolation greater than 30 dB, and a maximum power handling capacity of 500 mW.

[0054] In some embodiments of the present invention, the control circuit 502 includes a microprocessor and communication circuit, a pump drive, a TEC temperature control and a photoelectric detection circuit. The MCU and the photoelectric detection circuit monitor the amount of light power filtered by the filter 501 in real time. Based on the difference between the current power and the target power, the drive current of the pump laser 101 is controlled, thereby adjusting the output power of the pump unit 100 and matching the current power after the filter 501 with the target power.

[0055] Please see Figure 2 , Figure 2 The control structure diagram of an embodiment of the active fiber gain bandwidth testing system provided by the present invention includes a microprocessor and communication circuit, a pump drive, a TEC temperature control and photoelectric detection circuit.

[0056] The microprocessor and communication circuit mainly include an MCU minimum system and a level conversion chip. The MCU receives signals from the photoelectric detection circuit, determines the difference between the current output power and the target power, and continuously adjusts the pump drive current to achieve the power target and continuous stability. At the same time, the MCU also needs to set the target temperature value of TEC and monitor it in real time. The level conversion chip is mainly used to match the level standard of the upper computer control signal.

[0057] The pump drive described above primarily implements constant current source driving, employing a continuous driving method. Power is adjustable by regulating the current flowing through the pump, and it comprises both analog and digital components. The analog section mainly consists of a voltage-controlled constant current source circuit composed of operational amplifiers, power MOSFETs, and current sampling resistors, responsible for providing a stable driving current to the pump laser 101. The digital section consists of an MCU and a digital-to-analog converter, providing the control voltage for the voltage-controlled constant current source.

[0058] The TEC temperature control mentioned above is the temperature control circuit 502 for the TEC cooler, and the extreme value of the TEC cooler's drive current is ±1.5A. By continuously collecting the difference between the current temperature and the target temperature, a PID controller is used to precisely adjust the direction and magnitude of the TEC cooler's drive current, so that the laser temperature is always kept near the target temperature.

[0059] The aforementioned photoelectric detection circuit is mainly used to detect the power after filter 501. The photodetector uses an InGaAs photodiode, with a power detection range of -35 to 15 dBm. The photodetector converts the power after filter 501 from an optical signal to an electrical signal, performs logarithmic calculations through a logarithmic amplifier to obtain the characteristic wavelength optical power, and feeds it back to the microprocessor.

[0060] Please see Figure 3 , Figure 3 This is a schematic diagram of the spectrum of the optical fiber under test 202 provided by the present invention measured in an active optical fiber gain testing system. The 3dB bandwidth of the spectrum is 49.35dB, and the wavelength ranges from 1564.93nm to 1614.28nm.

[0061] Please see Figure 4 , Figure 4This is a schematic diagram illustrating the gain deviation between the test fiber and the reference fiber provided by the present invention. The solid line shows the spectral shape deviation between the fiber under test 202 and the reference fiber obtained by the active fiber gain bandwidth testing system. The dashed line shows the gain spectral deviation between the fiber under test 202 and the reference fiber measured by a multi-channel light source with a wavelength interval of 0.8 nm from 1529 to 1567 nm under a single-stage amplification structure. The spectral shape deviation of the solid line is 0.47 dB in the wavelength range of 1529 to 1567 nm, and the gain spectral shape deviation of the dashed line is 0.482 dB in the wavelength range of 1529 to 1567 nm. The two curves show similar trends with wavelength, indicating that the spectral shape deviation measured by the active fiber gain bandwidth testing system is similar to the gain spectral shape deviation measured by a multi-wavelength light source under a single-stage amplification structure.

[0062] Please see Figure 5 , Figure 5 This is a flowchart illustrating an embodiment of the active fiber gain bandwidth testing method provided by the present invention. According to a second aspect of the present invention, an active fiber gain bandwidth testing method is also provided, employing the active fiber gain bandwidth testing system as described in any of the above embodiments. The method includes: S501, Provide pump light to the fiber under test 202 to generate a gain optical signal; S502, Split the gain optical signal into a first optical signal and a second optical signal; S503. Perform spectral analysis on the first optical signal to obtain the gain spectrum of the optical fiber 202 under test; S504. Extract the characteristic wavelength signal from the second optical signal; S505. Based on the characteristic wavelength signal, the power of the pump light is adjusted to make the intensity of the characteristic wavelength signal approach the target value.

[0063] In the above embodiment, pump light of a specific wavelength is generated by pump unit 100 and injected into the fiber under test 202 in gain unit 200. When the pump light acts on the fiber under test 202, it excites active ions in the fiber to undergo energy level transitions, thereby generating a gain optical signal containing an amplified spontaneous emission spectrum. This gain optical signal fully reflects the intrinsic gain characteristics of the fiber under test 202 under small signal conditions.

[0064] The downstream coupler 300 splits the gain optical signal into a first optical signal and a second optical signal. The first optical signal, with a higher power ratio, is used for subsequent spectral analysis; the second optical signal, with a lower power ratio, is used for feedback control. This beam splitting design ensures that the two channels can perform their respective functions without interfering with each other.

[0065] The spectral analysis unit 400 performs spectral analysis on the first optical signal to obtain the gain spectrum of the optical fiber under test 202. It uses a dispersive element to expand the first optical signal in the wavelength dimension and uses a detector array to synchronously detect the intensity distribution of each wavelength component, and finally constructs a complete gain spectrum curve of the optical fiber under test 202. Key parameters such as gain bandwidth, peak gain wavelength, and gain flatness can be directly read.

[0066] The characteristic wavelength signal is extracted from the second optical signal by the filter 501 in the control unit 500. The filter 501 is configured as a bandpass filter 501 with a specific center wavelength and narrow bandwidth, which can accurately separate the characteristic wavelength signal from the broadband second optical signal. The characteristic wavelength is usually selected at the peak of the gain spectrum or a critical wavelength point that is sensitive to system performance.

[0067] The control unit 500 adjusts the pump light power based on the intensity of the characteristic wavelength signal, bringing the intensity of the characteristic wavelength signal closer to a preset target value. First, the characteristic wavelength signal is converted into an electrical signal by a photoelectric detection circuit. The microprocessor compares this signal with the stored target value and generates an adjustment command based on the difference using a control algorithm. The pump drive circuit adjusts the drive current of the pump laser 101 according to the command, thereby precisely controlling the output power of the pump light and forming a complete closed-loop control system.

[0068] The core value of the closed-loop control mechanism lies in maintaining the stability of the characteristic wavelength signal intensity, thereby ensuring that the fiber under test 202 is under the same or comparable pump conditions during each test. This overcomes the variations in test conditions caused by factors such as device aging, changes in ambient temperature, and fluctuations in connection loss, thus ensuring high repeatability and comparability of measurement results. This method provides reliable data support, especially when comparing the performance of different batches of fibers or conducting long-term stability tests.

[0069] It is worth noting that steps S503 and S504, S505 are executed in parallel, enabling the system to maintain stable test conditions while performing accurate spectral analysis. This ensures both the accuracy of the measurement data and improves test efficiency. Compared with traditional open-loop testing methods, the method provided by this invention, by introducing an intelligent feedback mechanism, automates and standardizes the testing process, significantly reducing the technical requirements for operators while improving the reliability of test results.

[0070] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to this application. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to this application.

[0071] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0072] In the several embodiments provided in this application, it should be understood that the disclosed apparatus can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some service interface; the indirect coupling or communication connection between devices or units may be electrical or other forms.

[0073] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0074] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0075] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage device (CMD). Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a memory and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned memory includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0076] Those skilled in the art will understand that all or part of the steps in the various methods of the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, which may include: a flash drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk, etc.

[0077] The foregoing description is merely an exemplary embodiment of this disclosure and should not be construed as limiting the scope of this disclosure. Any equivalent changes and modifications made in accordance with the teachings of this disclosure shall still fall within the scope of this disclosure. Those skilled in the art will readily conceive of embodiments of this disclosure upon considering the specification and practicing the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not described herein. The specification and embodiments are to be considered exemplary only, and the scope and spirit of this disclosure are defined by the claims.

[0078] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0079] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An active optical fiber gain-bandwidth testing system, characterized in that, include: Pump unit; A gain unit, the input of which is connected to the pump unit; A downstream coupler, the input of which is connected to the output of the gain unit; A spectral analysis unit is connected to the first output terminal of the downstream coupler; The control unit is connected to the second output terminal of the downstream coupler; The pumping unit is used to provide pump light to the gain unit; The gain unit is used to accommodate the optical fiber under test and generate a gain optical signal under the action of pump light; The spectral analysis unit is used to perform spectral analysis on the gain optical signal; The control unit is used to perform feedback adjustment of the pump unit based on the characteristic information of the gain optical signal obtained from the downstream coupler; the control unit includes a filter and a control circuit, the input terminal of the filter serves as the input terminal of the control unit, and is used to filter out the characteristic wavelength signal from the gain optical signal; the control circuit is connected to the output terminal of the filter and to the pump laser in the pump unit, and is used to adjust the output of the pump unit according to the intensity of the characteristic wavelength signal.

2. The active optical fiber gain-bandwidth testing system according to claim 1, characterized in that, The pumping unit includes: Pumped laser; A pump protector, the input of which is connected to the output of the pump laser; An upstream coupler, the input of which is connected to the output of the pump protector; The first output terminal of the upstream coupler serves as the output terminal of the pump unit, and the second output terminal of the upstream coupler is connected to a power meter for monitoring the pump optical power.

3. The active optical fiber gain-bandwidth testing system according to claim 2, characterized in that, The gain unit includes: A wavelength division multiplexer, the pump terminal of which serves as the input terminal of the gain unit; The optical fiber to be tested has one end connected to the multiplexing end of the wavelength division multiplexer. A reflector is connected to the other end of the optical fiber under test; The signal terminal of the wavelength division multiplexer serves as the output terminal of the gain unit.

4. The active optical fiber gain-bandwidth testing system according to claim 1, characterized in that, The control circuit includes: A photoelectric detection circuit is used to convert the characteristic wavelength signal into an electrical signal; A microprocessor, connected to the photoelectric detection circuit, is used to process the electrical signals; A pump drive circuit, connected to the microprocessor and the pump laser in the pump unit, is used to adjust the drive current of the pump laser according to the instructions of the microprocessor.

5. The active optical fiber gain-bandwidth testing system according to claim 4, characterized in that, The control circuit also includes a temperature control circuit connected to the microprocessor for temperature control of the pump laser.

6. The active optical fiber gain-bandwidth testing system according to claim 2, characterized in that, Both the upstream coupler and the downstream coupler are tapered fiber optic couplers.

7. The active optical fiber gain-bandwidth testing system according to claim 3, characterized in that, The wavelength division multiplexer is a fused conical wavelength division multiplexer.

8. The active optical fiber gain-bandwidth testing system according to claim 1, characterized in that, The spectral analysis unit includes a dispersive element and a detector array, used to expand the received light signal by wavelength and detect its intensity distribution.

9. A method for testing the gain and bandwidth of active optical fiber, employing the active optical fiber gain and bandwidth testing system as described in any one of claims 1 to 8, characterized in that, The method includes: Pump light is supplied to the fiber under test to generate a gain optical signal; The gain optical signal is split into a first optical signal and a second optical signal; Perform spectral analysis on the first optical signal to obtain the gain spectrum of the optical fiber under test; Extract the characteristic wavelength signal from the second optical signal; Based on the characteristic wavelength signal, the power of the pump light is adjusted to make the intensity of the characteristic wavelength signal approach the target value.

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