System and method for measuring optical fiber length of optical fiber laser

Abstract

The invention provides a system and a method for measuring the length of an optical fiber of an optical fiber laser. The measurement system comprises a linear sweep frequency laser, a first optical fiber coupler, a signal amplification module, a circulator, a second optical fiber coupler, a photoelectric detector and a to-be-measured optical fiber laser. The linear frequency sweeping laser is used for outputting continuously changing laser to the first optical fiber coupler; the first optical fiber coupler is used for dividing the laser output by the linear frequency sweeping laser into two paths according to a certain splitting ratio, one path is used as signal light to be transmitted to the signal amplification module, and the other path is used as reference light to be transmitted to the second optical fiber coupler; the signal amplification module is used for amplifying the signal light and outputting the signal light to the circulator. The measuring system effectively solves the problems of low signal-to-noise ratio, poor precision and poor stability when the optical fiber length of the optical fiber laser is measured in the prior art.

Description

Technical Field

[0001] The present invention relates to the field of laser technology, and in particular to a fiber laser optical fiber length measurement system and method thereof. Background Art Fiber lasers have been developed rapidly in recent years due to their high efficiency, small size, good beam quality, and high stability. In the design and manufacturing process of fiber lasers, accurately measuring the length of the optical fiber is a crucial step. However, the existing fiber laser fiber length measurement technology still has many problems such as poor signal-to-noise ratio, low measurement accuracy, and poor stability.

[0002] At present, commonly used methods for measuring optical fiber length include optical time domain reflectometry (OTDR), optical frequency domain reflectometry (OFDR) and optical low coherence reflectometry (OLCR).

[0003] OTDR technology is based on the interference effect of backward Rayleigh scattering in optical fiber, and can achieve long-distance optical fiber length measurement, but its spatial resolution and pulse width restrict each other. The OTDR system emits a short pulse laser signal into the optical fiber and detects the optical signal reflected back by the scattering center at different positions in the optical fiber. By analyzing the time delay of the reflected signal, the length of the optical fiber and the breakpoints or loss points in it can be measured. OTDR technology has a long measurement distance (up to kilometers), but its spatial resolution is limited by the pulse width and time sampling capabilities, and can usually only provide meter-level accuracy. Therefore, OTDR technology works better when measuring long-distance optical fibers, but has limitations in short optical fiber measurements that require high precision.

[0004] In contrast, OFDR and OLCR technologies have higher accuracy when measuring single-mode optical fibers. OFDR technology is based on the principle of frequency domain interference. It uses a frequency-scanned linear swept laser to emit a continuous optical signal, which propagates through the optical fiber and undergoes Rayleigh scattering with impurities and tiny irregularities inside the optical fiber. The scattered light interferes with the reference optical signal. By analyzing the frequency domain characteristics of the interference signal, the time delay of the scattered signal can be accurately determined. Through the frequency domain swept signal, OFDR technology can provide higher resolution than OTDR, usually reaching millimeter or even micron level accuracy. OLCR technology uses a low-coherence light source to emit a wide-spectrum optical signal. Unlike OTDR and OFDR, OLCR infers the length of the optical fiber by measuring the interference pattern of the reflected signal. The bandwidth of the low-coherence light source is wide, which enables it to have higher resolution when performing reflection signal analysis.

[0005] However, when OFDR and OLCR technologies are used to measure the fiber length in fiber lasers (including various optical devices and active optical fibers), the output power of the linear swept laser used to output the measurement signal is low, and there are various optical devices and active optical fibers in the fiber laser to be measured, resulting in a large system loss of the signal light input to the fiber laser to be measured, a significant reduction in the power of the back Rayleigh scattering signal, and a significant decrease in the signal-to-noise ratio, making it impossible to effectively measure the fiber length of the fiber laser to be measured, thus limiting the further application of these technologies in fiber lasers. Summary of the invention

[0006] The present invention provides a fiber laser optical fiber length measurement system and method thereof, which effectively improves the signal strength by adopting a signal amplification module, a balanced photodetector and / or a low-pass filter, and solves the problems of low signal-to-noise ratio, poor accuracy and poor stability in measuring the optical fiber length of the fiber laser in the prior art.

[0007] In a first aspect, the present invention provides a fiber laser fiber length measurement system, characterized in that the measurement system comprises: a linear frequency sweeping laser, a first fiber coupler, a signal amplification module, a circulator, a second fiber coupler, a photodetector and a fiber laser to be measured; wherein The linear frequency sweeping laser is used to output continuously changing laser light to the first optical fiber coupler; The first optical fiber coupler is used to split the laser output by the linear frequency sweeping laser into two paths according to a certain splitting ratio, one of which is transmitted to the signal amplification module as signal light, and the other is transmitted to the second optical fiber coupler as reference light; The signal amplification module is used to amplify the signal light and output it to the circulator; The circulator is used to guide the amplified signal light output by the signal amplification module to the optical fiber laser to be tested, and at the same time guide the back Rayleigh scattered signal output by the optical fiber laser to be tested to the second optical fiber coupler; The optical fiber laser to be tested is used to generate the backscattered Rayleigh signal by using the amplified signal light, and output it to the circulator; The second optical fiber coupler is used to receive the backscattered signal output from the circulator and the reference light output from the first optical fiber coupler, couple the two to obtain a beat frequency optical signal, and output the beat frequency optical signal to the photodetector; The photoelectric detector is used to convert the beat frequency optical signal into an electrical signal to measure the optical fiber length of the optical fiber laser to be tested.

[0008] In a second aspect, the present invention provides an optical frequency domain reflectometer (OFDR) system for enhancing the intensity of backward Rayleigh scattering signals, characterized in that the system comprises: an optical frequency domain reflectometer, a third fiber coupler, a second signal amplification module, a second circulator and a second fiber laser to be tested; wherein The optical frequency domain reflectometer includes a jumper, and the optical frequency domain reflectometer is connected to the third optical fiber coupler through the jumper, and is used to output signal light to the third optical fiber coupler, and receive a backscattered Rayleigh signal from the third optical fiber coupler to measure the optical fiber length of the second optical fiber laser to be measured; The third optical fiber coupler is used to couple the signal light and output it to the second signal amplification module, and at the same time receive the backscattered Rayleigh signal output from the second circulator, and couple the backscattered Rayleigh signal to the jumper of the optical frequency domain reflectometer; The second signal amplification module is used to amplify the signal light and output it to the second circulator; The second circulator is used to guide the amplified signal light output by the second signal amplification module to the second fiber laser to be tested, and at the same time guide the back Rayleigh scattered signal output by the second fiber laser to be tested to the third fiber coupler; The second optical fiber laser to be tested is used to generate the backscattered Rayleigh signal by using the amplified signal light.

[0009] In a third aspect, the present invention provides a method for measuring the optical fiber length of an optical fiber laser, characterized in that a system for measuring the optical fiber length of an optical fiber laser is provided, comprising: a linear frequency sweeping laser, a first optical fiber coupler, a signal amplification module, a circulator, a second optical fiber coupler, a photodetector, and an optical fiber laser to be measured; The method comprises: The linear frequency sweeping laser outputs continuously changing laser light to the first optical fiber coupler; The first optical fiber coupler splits the laser light output by the linear frequency sweeping laser into two paths according to a certain splitting ratio, wherein one path is transmitted to the signal amplification module as signal light, and the other path is transmitted to the second optical fiber coupler as reference light; The signal amplification module amplifies the signal light and outputs it to the circulator; The circulator guides the amplified signal light output by the signal amplification module to the optical fiber laser to be tested, and guides the backscattered Rayleigh signal output by the optical fiber laser to be tested to the second optical fiber coupler; The optical fiber laser to be tested generates the backscattered Rayleigh signal using the amplified signal light and outputs the backscattered signal to the circulator; The second optical fiber coupler receives the backscattered signal outputted from the circulator and the reference light outputted from the first optical fiber coupler, couples the two to obtain a beat frequency optical signal, and outputs the beat frequency optical signal to the photodetector; The photoelectric detector converts the beat frequency optical signal into an electrical signal to measure the optical fiber length of the optical fiber laser to be tested.

[0010] In a fourth aspect, the present invention provides an optical frequency domain reflectometer (OFDR) method for enhancing the intensity of a backward Rayleigh scattered signal, characterized in that a system for providing an optical frequency domain reflectometer (OFDR) for enhancing the intensity of a backward Rayleigh scattered signal comprises: an optical frequency domain reflectometer, a third optical fiber coupler, a second signal amplification module, a second circulator and a second optical fiber laser to be tested, wherein the optical frequency domain reflectometer comprises a jumper; The method comprises: The optical frequency domain reflectometer is connected to the third optical fiber coupler through the jumper, outputs signal light to the third optical fiber coupler, and receives a backscattered Rayleigh signal from the third optical fiber coupler to measure the optical fiber length of the second optical fiber laser to be tested; The third optical fiber coupler couples the signal light and outputs it to the second signal amplification module, and simultaneously receives the backscattered Rayleigh signal output from the second circulator, and couples the backscattered Rayleigh signal to output it to the jumper of the optical frequency domain reflectometer; The second signal amplifying module amplifies the signal light and outputs it to the second circulator; The second circulator guides the amplified signal light output by the second signal amplification module to the second fiber laser to be tested, and guides the back Rayleigh scattered signal output by the second fiber laser to be tested to the third fiber coupler; The second optical fiber laser to be tested generates the backscattered Rayleigh signal using the amplified signal light.

[0011] The fiber laser fiber length measurement system and method provided by the present invention: first, the signal intensity is enhanced by a signal amplification module, especially by using erbium-doped fiber as a gain fiber, the signal light can be effectively amplified to ensure that the intensity of the backscattered Rayleigh signal is large enough, thereby improving the sensitivity and accuracy of the measurement; second, a combination of a balanced photodetector and a bandpass filter and a low-pass filter can be used to effectively filter out the DC component and noise in the electrical signal, thereby improving the signal-to-noise ratio of the measurement signal; third, by using an optical attenuator in the measurement system to adjust the reference light power, it can be ensured that the power ratio of the reference light and the backscattered Rayleigh signal is appropriate, ensuring that they can generate a clear and accurate beat frequency signal, thereby greatly improving the accuracy and reliability of the fiber length measurement; fourth, the optical frequency domain reflectometer (OFDR) system for enhancing the backscattered Rayleigh signal intensity in the present invention adds a signal enhancement mechanism on the basis of the traditional OFDR system without changing the structure of the OFDR system, which can not only improve the signal intensity and the signal-to-noise ratio, but also reduce the complexity and cost of system transformation and upgrading, and for users of the existing OFDR system, it can improve the measurement accuracy with minimal cost investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0013] Figure 1 Schematic diagram of a fiber laser fiber length measurement system provided by an embodiment of the present invention; Figure 2 Schematic diagram of an optical frequency domain reflectometry (OFDR) system for enhancing the intensity of backscattered Rayleigh scattering signals provided by an embodiment of the present invention; Figure 3 It is a flow chart of a method for measuring the optical fiber length of an optical fiber laser provided by an embodiment of the present invention; Figure 4 The present invention provides an optical frequency domain reflectometry (OFDR) method for enhancing the intensity of a backscattered Rayleigh scattering signal. DETAILED DESCRIPTION

[0014] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. SUMMARY OF THE INVENTION As mentioned above, the present invention provides a fiber laser fiber length measurement system and method thereof, which effectively solves the problems of low signal-to-noise ratio, poor accuracy and poor stability in the prior art when measuring the fiber laser fiber length.

[0016] Exemplary Systems Figure 1 Schematic diagram of a fiber laser fiber length measurement system provided in Example 1 of the present invention, Figure 1 As shown, the measurement system 100 provided in this embodiment 1 includes: a linear swept laser 101, a first fiber coupler 102, a signal amplification module 103, a circulator 104, a second fiber coupler 105, a photodetector 106, a data acquisition module 107 and a fiber laser to be measured 112.

[0017] The linear frequency sweeping laser 101 is used to output continuously changing laser light to the first optical fiber coupler 102. The laser frequency increases linearly with time.

[0018] The linear sweep laser 101 adjusts the measurement range and accuracy of the measurement system 100 by adjusting its sweep range and sweep rate.

[0019] The frequency sweep range is the total range of frequency changes of the linear frequency sweep laser 101. The frequency sweep rate refers to the speed of frequency change, usually expressed as how many hertz (Hz) the frequency increases per second. The larger the frequency sweep range, the larger the length range of the measurement; the larger the frequency sweep rate, the higher the measurement accuracy.

[0020] In short, when higher precision is required for the measurement of optical fiber length, high-resolution measurement can be achieved by increasing the sweep range, reducing the sweep rate, or reducing the frequency step. When higher measurement speed is required, the sweep speed can be increased by increasing the sweep rate or increasing the frequency step, sacrificing some precision in exchange for faster measurement results.

[0021] The first fiber coupler 102 is a 1×2 fiber coupler, which is used to split the laser output by the linear frequency sweeping laser 101 into two paths according to a certain splitting ratio, one of which is transmitted to the signal amplification module 103 as a signal light, and the other is transmitted to the second fiber coupler 105 as a reference light. The signal light provides a starting laser source for the entire measurement process. The reference light provides a stable reference signal for the measurement system 100 for comparison with the backscattered Rayleigh signal.

[0022] On the one hand, the splitting ratio needs to ensure that the intensity of the signal light is sufficient to facilitate the subsequent amplification processing, obtain a stronger signal echo, and ensure that the signal light has a high signal-to-noise ratio during transmission, amplification and processing, thereby improving the measurement accuracy; on the other hand, it is necessary to provide sufficient reference signal intensity to effectively couple with the backscattered Rayleigh scattered signal scattered back from the fiber laser 112 to be measured. The intensity of the reference light is preferably substantially the same as the intensity of the backscattered Rayleigh scattered signal, so that the beat frequency can be measured more accurately and the signal-to-noise ratio can be improved.

[0023] Preferably, the first fiber coupler 102 divides the laser into the signal light and the reference light at a splitting ratio of 9:1. The fiber coupler with a splitting ratio of 9:1 can ensure that the intensity distribution of the signal light and the reference light in the measurement system 100 is reasonable, so that the coupling effect is fully guaranteed. At the same time, as a passive component, the splitting ratio of the fiber coupler is set at the factory, and 9:1 is a common splitting ratio of the fiber coupler. Therefore, the present invention also simplifies the design and selection process of the fiber coupler and reduces the implementation cost.

[0024] On this basis, in order to further optimize the intensity of the reference light and avoid the influence of the intensity mismatch between the reference light and the backscattered Rayleigh signal on the measurement accuracy, the measurement system 100 may further include an optical attenuator, which is used to receive the reference light from the first fiber coupler 102, reduce the power of the reference light, and output the reference light with reduced power to the second fiber coupler 105. The optical attenuator is a controllable optical attenuator, which is used to adjust or switch the attenuation ratio of the optical attenuator based on the intensity of the backscattered Rayleigh signal, for example, automatically switch different dimming films for attenuation.

[0025] In the fiber length measurement, the reference light and the backscattered Rayleigh signal need to be coupled. The quality of the beat effect is highly dependent on the power balance of the reference light and the backscattered Rayleigh signal. Good power matching can make the contrast of the beat signal higher, so that it is easier to extract clear and accurate beat information in the subsequent signal processing. If the power difference between the two is too large, the beat signal will be distorted, the measurement result will be inaccurate, and the contrast of the beat signal will be reduced, making it difficult for the measurement system to distinguish small changes in the signal. Therefore, by adjusting the optical attenuator, optimizing the signal contrast can help improve the measurement accuracy of the system.

[0026] The original signal light power provided by the linear frequency sweep laser 101 is usually low. The signal amplification module 103 is used to amplify the signal light and output it to the circulator 104 .

[0027] In the conventional measurement system, the output power of the linear frequency sweep laser 101 is relatively low, and the fiber laser to be measured usually includes a variety of optical devices and active optical fibers, which causes the power of the optical signal to gradually decay during the propagation process. In particular, the power of the backward Rayleigh scattering signal is relatively weak. As the length of the optical fiber increases, the attenuation of the signal and the increase of noise further reduce the intensity of the backward Rayleigh scattering signal. The present invention amplifies the signal light by the signal amplification module 103, which can significantly improve the power of the signal light, enhance the ability of the signal light to be transmitted to the fiber laser to be measured 112, and then improve the intensity of the backward Rayleigh scattering signal. By enhancing the power of the signal light, the measurement system 100 can still maintain a high signal-to-noise ratio in a noisy environment. A high signal-to-noise ratio is essential for subsequent coupling processes, signal acquisition and data processing. A good signal-to-noise ratio can ensure that the photodetector 106 accurately captures the signal after the beat frequency, thereby improving the measurement accuracy of the optical fiber length.

[0028] The signal amplification module 103 includes: a pump light source 108 , a beam combiner 109 , a gain fiber 110 and a cladding power stripper 111 .

[0029] The pump light source 108 is used to output pump light to the beam combiner 109. In order to effectively excite the erbium-doped optical fiber, a pump light source with a wavelength of 980 nm or 1480 nm is usually used.

[0030] The beam combiner 109 is used to combine the pump light and the signal light from the first optical fiber coupler 102 to obtain combined light.

[0031] The gain fiber 110 is used to receive the combined light, amplify the signal light using the pump light in the combined light, and output it to the cladding power stripper 111. Preferably, the gain fiber 110 is an erbium-doped fiber (EDF). Erbium-doped fiber has excellent gain characteristics, especially in the 1550nm wavelength range commonly used in optical communications, and can effectively enhance the intensity of signal light. At the same time, erbium-doped fiber has low noise, good stability and wide gain bandwidth, which can improve the measurement accuracy and stability of the system. Moreover, the mature technology of erbium-doped fiber makes it cost-effective and easy to integrate and implement.

[0032] The cladding power stripper 111 is used to strip the residual pump light from the signal light amplified by the gain fiber 110, and output it to the circulator 104, so as to ensure the purity of the output amplified signal light and effectively suppress the generation of spontaneous emission noise (ASE noise). Spontaneous emission noise can introduce system errors and reduce measurement accuracy. It is a common problem in fiber amplifiers and is usually generated during the laser amplification process, especially when the pump light and the signal light are not completely separated.

[0033] The circulator 104 is used to guide the amplified signal light output by the signal amplification module 103 to the fiber laser 112 to be tested, and guide the backscattered Rayleigh signal output by the fiber laser 112 to be tested to the second fiber coupler 105 .

[0034] The circulator 104 includes a first port, a second port and a third port, and is an asymmetric three-port optical device, which utilizes the non-reflective nature of light and the waveguide characteristics, and ensures the directional transmission of the signal light and the back Rayleigh scattered signal through a specific optical path design. The first port is connected to the signal amplification module 103, the second port is connected to the fiber laser 112 to be tested, and the third port is connected to the second fiber coupler 105.

[0035] The circulator 104 uses the first port and the second port to guide the amplified signal light output by the signal amplification module 103 to the fiber laser to be tested 112, and uses the second port and the third port to guide the back Rayleigh scattered signal output from the fiber laser to be tested 112 to the second fiber coupler 105. The circulator 104 uses the structural characteristics of different ports to make the signal light and the back Rayleigh scattered signal transmitted along different paths, avoiding mutual interference between the two and ensuring effective detection of the signal.

[0036] The fiber laser 112 to be tested is used to generate the backward Rayleigh scattered signal using the amplified signal light based on the Rayleigh scattering characteristics of the optical fiber, and output it to the circulator 104. The backward Rayleigh scattered signal means that when the laser beam (or signal light) propagates along the optical fiber, part of the light will be scattered due to the slight inhomogeneity of the optical fiber, and these scattered lights will propagate in the opposite direction of the propagation direction of the optical fiber, and finally return to the direction of the signal source.

[0037] The second fiber coupler 105 is a 2×2 fiber coupler, which is used to receive the backward Rayleigh scattered signal output from the circulator 104 and the reference light output from the first fiber coupler 102, and couple the two to obtain a beat frequency optical signal, and output the beat frequency optical signal to the photodetector 106. The coupling process is based on the interference effect of the reference signal and the backward Rayleigh scattered signal. Beat frequency means that when two coherent optical signals are coupled in the second fiber coupler 105, their combined light intensity will produce a periodic change of a certain frequency. The frequency of the light intensity change is the beat frequency, that is, the beat frequency means that when two coherent optical signals meet in the optical fiber, interference occurs to generate a new frequency. The frequency of the beat frequency optical signal is related to the frequency difference between the two signals, and the frequency difference reflects the length of the optical fiber.

[0038] Since the backscattered Rayleigh signal is continuously returned, the coupling process is a dynamic and continuous process, and the beat signal is also continuously generated. Since the interfaces of various components inside the fiber laser to be tested, including the two ends of the optical fiber, may generate backscattered Rayleigh signals, there may be multiple beat signals, each of which corresponds to the optical path of a reflection interface inside the fiber laser. By finding the optical path difference of the beat signals corresponding to the two ends of the optical fiber in the fiber laser, the length of the optical fiber in the fiber laser can be calculated.

[0039] The photodetector 106 is used to convert the beat optical signal into an electrical signal to measure the optical fiber length of the optical fiber laser 112 to be tested.

[0040] Among them, the electrical signal usually contains DC and AC components. The DC component is caused by various background noises in the system, differences in light source stability, and other factors, while the AC component carries frequency offset information caused by changes in optical fiber length, etc. If these noise components are not effectively removed, the quality of the signal will be seriously affected, resulting in inaccurate measurement results.

[0041] In order to improve the signal-to-noise ratio of the measurement system 100, preferably, the photodetector 106 adopts a balanced photodetector, and the balanced photodetector uses the difference between two signals to eliminate common-mode noise (including DC noise) and only retains the AC signal part, that is, the balanced photodetector is used to filter out the DC component in the electrical signal and retain the AC part.

[0042] The data acquisition module 107 is used to receive the electrical signal from the photoelectric detector 106 and perform data acquisition on the electrical signal. The data acquisition module 107 is an oscilloscope.

[0043] The measurement system 100 further includes a data processing module, which is used to receive the data collected by the data acquisition module 107 and process the data to obtain the fiber length of the fiber laser 112 to be measured. For example, an oscilloscope is used to collect data on the electrical signal, and the data is sent to a computer in the form of a digital signal for subsequent signal processing to obtain the fiber length of the fiber laser 112 to be measured.

[0044] Specifically, the current signal received by the data processing module, that is, the current signal after coupling and photoelectric conversion by the second fiber coupler 105, is a signal of the backward Rayleigh scattering signal of multiple reflection points of the optical fiber coupled with the reference light, which is a composite signal of multiple single-frequency sinusoidal signals. The frequency of each single-frequency signal is positively correlated with the position of the reflection point, and the amplitude of the signal reflects the scattering rate of the reflection point and the attenuation of the optical fiber. Therefore, the data processing module performs Fourier transform on the received data to obtain a spectrum. Each peak of the spectrum corresponds to the position of a specific reflection point on the optical fiber. The Rayleigh scattering information of each reflection point on the optical fiber can be obtained. The relationship between the position and the frequency is:

[0045] Where z is the position of the reflection point, f is the beat frequency, k is the sweep speed, and v g is the group velocity.

[0046] The difference in the NA of the optical fiber in the fiber laser 112 to be tested will directly affect the group velocity of the optical signal. When the NA is large, the core area of ​​the optical fiber can receive more light, the group velocity is large, and the optical signal propagates faster; conversely, when the NA is small, the group velocity is small, and the optical signal propagates slower. The group velocity is the speed at which the optical signal propagates along the optical fiber, which is affected by the refractive index, NA and transmission mode of the optical fiber. If the optical fiber NA used in the fiber laser 112 to be tested is different, even if the optical fiber length is the same, the time delay of the optical signal propagation will be different due to the different group velocity, thereby affecting the measurement result. Especially for optical fiber length measurement based on time domain (OTDR) or frequency domain (OFDR), the difference in group velocity may lead to deviations in the measurement results.

[0047] Generally, to measure the fiber length of a fiber laser alone, the NA needs to be known. If the NA value of the fiber to be measured cannot be obtained, the optical path difference of two identical fiber lasers is usually measured to obtain the relative difference in the fiber lengths of the two lasers.

[0048] Fourier transform converts time domain signals into frequency domain information. Through spectrum analysis, the position of each reflection point in the optical fiber can be accurately located to ensure the accuracy of optical fiber measurement. Whether the detected reflection point belongs to the optical fiber or other media (such as connectors, fiber joints, other optical components, etc.) usually depends on the analysis of the reflected signal. More specifically, the key factors to determine whether the reflection point is an optical fiber or other include the intensity of the reflection, the type of reflection, the position distribution and the characteristic frequency of the reflection. For example, the reflection intensity of the optical fiber is usually smaller than the reflection caused by the fiber joint or other optical components.

[0049] In order to further improve the signal-to-noise ratio of the electrical signal, the measurement system 100 may further include a bandpass filter or a low-pass filter, which is used to receive the electrical signal from the photodetector 106 , filter the electrical signal, and output it to the data acquisition module 107 .

[0050] The bandpass filter only allows signals within a certain frequency range to pass through, while filtering out signals with frequencies above or below the range. It can selectively pass frequency components related to the fiber length measurement and filter out irrelevant signals or noise in other frequency ranges based on the frequency characteristics of the signal. For example, the bandpass filter can be set to pass only a specific frequency range in the beat frequency signal, while filtering out interference frequencies caused by other irrelevant signal sources.

[0051] The low-pass filter allows signals below a certain frequency to pass through, while filtering out high-frequency components (such as noise or high-frequency interference signals). Since there may be high-frequency noise or other high-frequency signals interfering with the electrical signal in the measurement system 100, the low-pass filter helps to improve the signal quality by removing these high-frequency components.

[0052] By introducing a bandpass filter or a low-pass filter, the electrical signal is filtered and only the most relevant signal components are retained, that is, irrelevant frequency components in the signal (such as high-frequency noise, DC components, interference signals, etc.) are effectively eliminated, and the effective part of the signal (such as frequency components related to the change in optical fiber length) is retained. The signal is purer and the signal-to-noise ratio is greatly improved, providing a more accurate and reliable basis for subsequent data analysis and optical fiber length calculation.

[0053] Example 1 changes the internal structure of the common optical frequency domain reflectometer (OFDR) in the prior art. Through a highly integrated design, the number of required components is reduced, and the system is more compact. It also has strong scalability and supports the addition of optimized components such as balanced photodetectors, low-pass filters, and optical attenuators. These components can effectively improve the signal-to-noise ratio of the signal, filter out noise, improve measurement accuracy, and adapt to a variety of application scenarios.

[0054] Different from Example 1, Example 2 is improved on the basis of the common optical frequency domain reflectometer (OFDR) in the prior art, where the jumper is fused or pluggable with the fiber coupler, and the output end of the fiber coupler is connected to the signal amplification module to amplify the signal power, and the amplified signal light enters the first port of the circulator, and is output from the second port of the circulator to enter the fiber laser to be measured, and the generated backward Rayleigh scattered signal enters the fiber coupler from the third port of the circulator and returns to the original optical frequency domain reflectometer for coupling. That is, Example 2 improves the intensity of the backward Rayleigh scattered signal of the common optical frequency domain reflectometer by setting an additional signal enhancement mechanism specifically for the common optical frequency domain reflectometer, and effectively solves the signal attenuation problem of the traditional OFDR when measuring the fiber length in the fiber laser (including various optical devices and active optical fiber).

[0055] Figure 2 is a schematic diagram of an optical frequency domain reflectometry (OFDR) system for enhancing the intensity of backscattered Rayleigh scattering signals provided in Example 2 of the present invention, such as Figure 2 As shown, the system 200 provided in this embodiment 2 includes: an optical frequency domain reflectometer 201 (the conventional OFDR), a third fiber coupler 202 , a second signal amplification module 203 , a second circulator 204 and a second fiber laser to be tested 205 .

[0056] The optical frequency domain reflectometer 201 includes a jumper 206, and the optical frequency domain reflectometer 201 is connected to the third fiber coupler 202 through the jumper 206, and is used to output signal light to the third fiber coupler 202, and receive the backscattered Rayleigh scattering signal from the third fiber coupler 202 to measure the fiber length of the second fiber laser 205 to be tested.

[0057] The jumper 206 is an optical fiber with a certain length and interface design, which is used to transmit optical signals and is fused or pluggable with the third optical fiber coupler 202. The use of the jumper 206 simplifies the connection between the optical frequency domain reflectometer 201 and the third optical fiber coupler 202, thereby improving the integration and modularity of the system 200. The jumper 206 not only ensures the stability of signal transmission, but also facilitates the configuration and maintenance of the system 200.

[0058] The optical frequency domain reflectometer 201 further includes: a second linear frequency sweep laser 207, a fourth fiber coupler 208, a third circulator 209, a fifth fiber coupler 210, a second photodetector 211 and a second data acquisition module 212; The second linear frequency sweeping laser 207 is used to output continuously changing laser light to the fourth optical fiber coupler 208; The fourth fiber coupler 208 is used to split the laser light output by the second linear frequency sweeping laser 207 into two paths according to a certain splitting ratio, one of which is transmitted as signal light to the third circulator 209, and the other is transmitted as reference light to the fifth fiber coupler 210; The third circulator 209 has at least three ports, and is used to guide the signal light output by the fourth fiber coupler 208 to the jumper 206, and guide the backscattered Rayleigh signal output from the jumper 206 to the fifth fiber coupler 210; The fifth fiber coupler 210 is used to receive the backscattered signal output from the third circulator 209 and the reference light output from the fourth fiber coupler 208, and couple the two to obtain a beat frequency optical signal, and output the beat frequency optical signal to the second photodetector 211; The second photodetector 211 is used to convert the beat frequency optical signal into an electrical signal and couple it. The second photodetector 211 cannot use a balanced photodetector and cannot filter out the DC component. Unlike the balanced photodetector in Example 1 that receives two signals, the second photodetector 211 can only receive one signal.

[0059] The second data acquisition module 212 is used to collect data on the electrical signal from the second photodetector 211 to measure the optical fiber length of the second optical fiber laser 205 to be tested.

[0060] The third fiber coupler 202 is used to couple the signal light and output it to the second signal amplification module 203 , and at the same time receive the backscattered Rayleigh signal output from the second circulator 204 , and couple the backscattered Rayleigh signal to the jumper 206 of the optical frequency domain reflectometer 201 .

[0061] The second signal amplification module 203 is used to amplify the signal light and output it to the second circulator 204. The second signal amplification module 203 enhances the intensity of the signal light, especially when the backscattered Rayleigh scattering signal power output by the second fiber laser 205 to be tested is low and the system loss is large. By amplifying the signal, the second signal amplification module 203 ensures that the attenuation of the signal light during the propagation through the optical fiber is effectively compensated, thereby improving the signal-to-noise ratio of the system 200.

[0062] The second signal amplification module 203 includes: a second pump light source, a second beam combiner, a second gain fiber, and a second cladding power stripper; wherein The second pump light source is used to output pump light to the second beam combiner; The second beam combiner is used to combine the pump light and the signal light from the third optical fiber coupler 202 to obtain a combined light; The second gain optical fiber is used to receive the combined light, amplify the signal light using the pump light in the combined light, and output it to the second cladding power stripper, and the second gain optical fiber is an erbium-doped optical fiber; The second cladding power stripper is used to strip the residual pump light from the signal light amplified by the second gain fiber, and output it to the second circulator 204 .

[0063] The second circulator 204 has at least three ports, which are used to guide the amplified signal light output by the second signal amplification module 203 to the second fiber laser to be tested 205 , and guide the back Rayleigh scattered signal output by the second fiber laser to be tested 205 to the third fiber coupler 202 .

[0064] The second optical fiber laser to be tested 205 is used to generate the backscattered Rayleigh signal by using the amplified signal light.

[0065] The third optical fiber coupler 202, the second signal amplification module 203 and the second circulator 204 are integrated into one device. Integrating the three into one device can improve the stability, integration and efficiency of the system 200.

[0066] In summary, compared with Example 1, Example 2 improves performance by adding a signal enhancement mechanism without changing the internal structure of the traditional OFDR, that is, on the basis of the existing complete OFDR structure. Users can improve the signal-to-noise ratio and measurement accuracy of the system by simply adding new modules without completely replacing or redesigning the existing equipment. For users who have already used the traditional OFDR system, unnecessary equipment replacement can be avoided.

[0067] However, compared with Example 1, Example 2 has a lower integration level and requires multiple fiber couplers, circulators and other components, resulting in a larger system volume. Since Example 2 is improved based on traditional OFDR, it does not have the flexible scalability of Example 1 and cannot flexibly add signal optimization components such as balanced photodetectors, low-pass filters, and optical attenuators on the original basis.

[0068] In summary, Example 2 is suitable for upgrading existing traditional OFDR, and users can achieve improved technical performance with minimal intervention costs.

[0069] Exemplary Methods Accordingly, an embodiment of the present invention further provides a method for measuring the fiber length of a fiber laser. A fiber laser fiber length measurement system 100 is provided, comprising: a linear frequency sweeping laser 101, a first fiber coupler 102, a signal amplification module 103, a circulator 104, a second fiber coupler 105, a photodetector 106, a data acquisition module 107, and a fiber laser to be measured 112; Figure 3 : is a flow chart of a method for measuring the optical fiber length of an optical fiber laser provided by an embodiment of the present invention, and the embodiment comprises the following steps: S301: the linear frequency sweeping laser 101 outputs continuously changing laser light to the first optical fiber coupler 102; S302: the first fiber coupler 102 splits the laser light outputted by the linear frequency sweeping laser 101 into two paths according to a certain splitting ratio, one of which is transmitted as signal light to the signal amplification module 103, and the other is transmitted as reference light to the second fiber coupler 105; S303: the signal amplification module 103 amplifies the signal light and outputs it to the circulator 104; S304: the circulator 104 guides the amplified signal light output by the signal amplification module 103 to the fiber laser 112 to be tested, and guides the backscattered Rayleigh signal output by the fiber laser 112 to be tested to the second fiber coupler 105; S305: the fiber laser 112 to be tested generates the backscattered Rayleigh signal using the amplified signal light, and outputs the backscattered Rayleigh signal to the circulator 104; S306: the second fiber coupler 105 receives the backscattered signal outputted from the circulator 104 and the reference light outputted from the first fiber coupler 102, couples the two to obtain a beat optical signal, and outputs the beat optical signal to the photodetector 106; S307 : The photodetector 106 converts the beat optical signal into an electrical signal to measure the optical fiber length of the optical fiber laser 112 to be tested.

[0070] The signal amplification module 103 includes: a pump light source 108, a beam combiner 109, a gain fiber 110 and a cladding power stripper 111; The signal amplification module 103 amplifies the signal light and outputs the amplified signal light to the circulator 104 in the following steps: The pump light source 108 outputs pump light to the beam combiner 109; The beam combiner 109 combines the pump light and the signal light from the first optical fiber coupler 102 to obtain a combined light; The gain optical fiber 110 receives the combined light, amplifies the signal light using the pump light in the combined light, and outputs the amplified signal light to the cladding power stripper 111; The cladding power stripper 111 strips the residual pump light from the signal light amplified by the gain fiber 110 , and outputs the residual pump light to the circulator 104 .

[0071] The gain fiber 110 is an erbium-doped fiber.

[0072] The method further comprises: The data acquisition module 107 receives the electrical signal from the photoelectric detector 106 and performs data acquisition on the electrical signal; The measurement system 100 also includes a data processing module; The method further comprises: The data processing module receives the data collected by the data collection module 107 and processes the data to obtain the optical fiber length of the optical fiber laser 112 to be tested.

[0073] The circulator 104 includes a first port, a second port and a third port, the first port is connected to the signal amplification module 103, the second port is connected to the fiber laser to be tested 112, and the third port is connected to the second fiber coupler 105; The circulator 104 guides the amplified signal light output by the signal amplification module 103 to the fiber laser 112 to be tested, and guides the backscattered Rayleigh signal output by the fiber laser 112 to the second fiber coupler 105 in the following specific steps: The circulator 104 guides the amplified signal light output by the signal amplification module 103 to the fiber laser 112 to be tested by using the first port and the second port, and guides the back Rayleigh scattered signal output by the fiber laser 112 to be tested by using the second port and the third port.

[0074] The first fiber coupler 102 splits the laser light into the signal light and the reference light at a splitting ratio of 9:1.

[0075] The linear sweep laser 101 adjusts the measurement range and accuracy of the measurement system 100 by adjusting its sweep range and sweep rate.

[0076] The photodetector 106 is a balanced photodetector; The method further includes: the balanced photodetector filtering out a direct current component in the electrical signal.

[0077] The measurement system 100 further includes a bandpass filter or a low-pass filter; The method further comprises: The bandpass filter or the low-pass filter receives the electrical signal from the photodetector 106 , performs filtering processing on the electrical signal, and outputs the signal to the data acquisition module 107 .

[0078] The measurement system 100 further includes an optical attenuator; The method further comprises: The optical attenuator receives the reference light from the first optical fiber coupler 102 , reduces the power of the reference light, and outputs the reference light with reduced power to the second optical fiber coupler 105 .

[0079] The data acquisition module 107 is an oscilloscope.

[0080] The embodiment of the present invention also provides an optical frequency domain reflectometer (OFDR) method for enhancing the strength of a backward Rayleigh scattered signal. The system for providing an optical frequency domain reflectometer (OFDR) for enhancing the strength of a backward Rayleigh scattered signal includes: an optical frequency domain reflectometer 201, a third fiber coupler 202, a second signal amplification module 203, a second circulator 204, and a second fiber laser to be tested 205, wherein the optical frequency domain reflectometer 201 includes a jumper 206; Figure 4 : is a flow chart of an optical frequency domain reflectometry (OFDR) method for enhancing the intensity of a backscattered Rayleigh scattering signal provided by an embodiment of the present invention, and the embodiment comprises the following steps: S401: the optical frequency domain reflectometer 201 is connected to the third fiber coupler 202 through the jumper 206, outputs signal light to the third fiber coupler 202, and receives a backscattered Rayleigh signal from the third fiber coupler 202 to measure the fiber length of the second fiber laser 205 to be tested; S402: the third optical fiber coupler 202 couples the signal light and outputs it to the second signal amplification module 203, and simultaneously receives the backscattered Rayleigh signal output from the second circulator 204, and couples the backscattered Rayleigh signal to the jumper 206 of the optical frequency domain reflectometer 201; S403: the second signal amplifying module 203 amplifies the signal light and outputs it to the second circulator 204; S404: the second circulator 204 guides the amplified signal light output by the second signal amplification module 203 to the second fiber laser to be tested 205, and guides the backscattered Rayleigh signal output by the second fiber laser to be tested 205 to the third fiber coupler 202; S405: The second optical fiber laser to be tested 205 generates the backscattered Rayleigh signal using the amplified signal light.

[0081] The optical frequency domain reflectometer 201 further includes: a second linear frequency sweeping laser 207, a fourth fiber coupler 208, a third circulator 209, a fifth fiber coupler 210, a second photodetector 211 and a second data acquisition module 212; The steps of connecting the optical frequency domain reflectometer 201 to the third fiber coupler 202 via the jumper 206, outputting signal light to the third fiber coupler 202, and receiving the backscattered Rayleigh signal from the third fiber coupler 202 to measure the fiber length of the second fiber laser 205 to be tested are specifically as follows: The second linear frequency sweeping laser 207 outputs continuously changing laser light to the fourth optical fiber coupler 208; The fourth fiber coupler 208 splits the laser light outputted by the second linear frequency sweeping laser 207 into two paths according to a certain splitting ratio, one of which is transmitted as signal light to the third circulator 209, and the other is transmitted as reference light to the fifth fiber coupler 210; The third circulator 209 guides the signal light output from the fourth fiber coupler 208 to the jumper 206, and guides the backscattered Rayleigh signal output from the jumper 206 to the fifth fiber coupler 210; The fifth fiber coupler 210 receives the backscattered signal outputted from the third circulator 209 and the reference light outputted from the fourth fiber coupler 208, couples the two to obtain a beat frequency optical signal, and outputs the beat frequency optical signal to the second photodetector 211; The second photodetector 211 converts the beat optical signal into an electrical signal and couples it.

[0082] The second data acquisition module 212 performs data acquisition on the electrical signal from the second photodetector 211 to measure the optical fiber length of the second optical fiber laser 205 to be tested.

[0083] The second circulator 204 and the third circulator 209 each have at least three ports.

[0084] The jumper 206 is an optical fiber, which is fused or pluggable with the third optical fiber coupler 202 .

[0085] The second signal amplification module 203 includes: a second pump light source, a second beam combiner, a second gain fiber, and a second cladding power stripper; The second signal amplifying module 203 is used to amplify the signal light and output it to the second circulator 204 in the following steps: The second pump light source outputs pump light to the second beam combiner; The second beam combiner combines the pump light and the signal light from the third optical fiber coupler 202 to obtain a combined light; The second gain optical fiber receives the combined light, amplifies the signal light using the pump light in the combined light, and outputs the amplified signal light to the second cladding power stripper; The second cladding power stripper strips the residual pump light from the signal light amplified by the second gain fiber, and outputs the residual pump light to the second circulator 204 .

[0086] The second gain optical fiber is an erbium-doped optical fiber.

[0087] The third optical fiber coupler 202, the second signal amplifying module 203 and the second circulator 204 are an integrated device.

[0088] It should be noted that although several devices, units, or modules of the fiber laser fiber length measurement system are mentioned in the above detailed description, this division is only exemplary and not mandatory. In fact, according to an embodiment of the present invention, the features and functions of two or more modules described above can be embodied in one module. Conversely, the features and functions of one module described above can be further divided into multiple modules to be embodied.

[0089] In addition, although the operations of the fiber laser fiber length measurement method of the present invention are described in a specific order in the drawings, this does not require or imply that these operations must be performed in this specific order, or that all the operations shown must be performed to achieve the desired results. Additionally or alternatively, some steps may be omitted, multiple steps may be combined into one step, and / or one step may be decomposed into multiple steps.

[0090] Although the spirit and principle of the present invention have been described with reference to several specific embodiments, it should be understood that the present invention is not limited to the disclosed specific embodiments, and the division of various aspects does not mean that the features in these aspects cannot be combined to benefit, and such division is only for the convenience of expression. The present invention is intended to cover various modifications and equivalent arrangements included in the spirit and scope of the attached claims.

[0091] The present invention provides: 1. A fiber laser fiber length measurement system, characterized in that the measurement system comprises: a linear frequency sweep laser, a first fiber coupler, a signal amplification module, a circulator, a second fiber coupler, a photodetector and a fiber laser to be measured; wherein The linear frequency sweeping laser is used to output continuously changing laser light to the first optical fiber coupler; The first optical fiber coupler is used to split the laser output by the linear frequency sweeping laser into two paths according to a certain splitting ratio, one of which is transmitted to the signal amplification module as signal light, and the other is transmitted to the second optical fiber coupler as reference light; The signal amplification module is used to amplify the signal light and output it to the circulator; The circulator is used to guide the amplified signal light output by the signal amplification module to the optical fiber laser to be tested, and at the same time guide the back Rayleigh scattered signal output by the optical fiber laser to be tested to the second optical fiber coupler; The optical fiber laser to be tested is used to generate the backward Rayleigh scattered signal by using the amplified signal light, and output it to the circulator; The second optical fiber coupler is used to receive the backscattered signal output from the circulator and the reference light output from the first optical fiber coupler, couple the two to obtain a beat frequency optical signal, and output the beat frequency optical signal to the photodetector; The photoelectric detector is used to convert the beat frequency optical signal into an electrical signal to measure the optical fiber length of the optical fiber laser to be tested.

[0092] 2. The measurement system according to item 1 is characterized in that the signal amplification module comprises: a pump light source, a beam combiner, a gain fiber and a cladding power stripper; wherein The pump light source is used to output pump light to the beam combiner; The beam combiner is used to combine the pump light and the signal light from the first optical fiber coupler to obtain combined light; The gain optical fiber is used to receive the combined light, amplify the signal light using the pump light in the combined light, and output it to the cladding power stripper; The cladding power stripper is used to strip the residual pump light from the signal light amplified by the gain optical fiber, and output it to the circulator.

[0093] 3. The measurement system according to item 2 is characterized in that the gain fiber is erbium-doped fiber.

[0094] 4. The measurement system according to any one of items 1 to 3, characterized in that the measurement system further comprises a data acquisition module, which is used to receive the electrical signal from the photodetector and perform data acquisition on the electrical signal; The measurement system also includes a data processing module, which is used to receive the data collected by the data collection module and process the data to obtain the optical fiber length of the optical fiber laser to be measured.

[0095] 5. The measurement system according to any one of items 1 to 3, characterized in that the circulator comprises a first port, a second port and a third port, the first port is connected to the signal amplification module, the second port is connected to the fiber laser to be measured, and the third port is connected to the second fiber coupler; The circulator guides the amplified signal light output by the signal amplification module to the fiber laser to be tested by using the first port and the second port, and guides the back Rayleigh scattered signal output by the fiber laser to be tested to the second fiber coupler by using the second port and the third port.

[0096] 6. The measurement system according to any one of items 1 to 3, characterized in that the first fiber coupler splits the laser into the signal light and the reference light at a splitting ratio of 9:1.

[0097] 7. The measurement system according to any one of items 1 to 3 is characterized in that the linear sweep laser adjusts the measurement range and accuracy of the measurement system by adjusting its sweep range and sweep rate.

[0098] 8. The measurement system according to any one of items 1 to 3 is characterized in that the photodetector is a balanced photodetector, and the balanced photodetector is also used to filter out a DC component in the electrical signal.

[0099] 9. The measurement system according to item 4 is characterized in that the measurement system also includes a bandpass filter or a low-pass filter, which is used to receive the electrical signal from the photodetector, filter the electrical signal, and output it to the data acquisition module.

[0100] 10. The measurement system according to any one of items 1 to 3 is characterized in that the measurement system also includes an optical attenuator, which is used to receive the reference light from the first optical fiber coupler, reduce the power of the reference light, and output the reference light with reduced power to the second optical fiber coupler.

[0101] 11. The measurement system according to item 4 is characterized in that the data acquisition module is an oscilloscope.

[0102] 12. An optical frequency domain reflectometer (OFDR) system for enhancing the intensity of backscattered Rayleigh scattering signals, characterized in that the system comprises: an optical frequency domain reflectometer, a third fiber coupler, a second signal amplification module, a second circulator, and a second fiber laser to be tested; wherein The optical frequency domain reflectometer includes a jumper, and the optical frequency domain reflectometer is connected to the third optical fiber coupler through the jumper, and is used to output signal light to the third optical fiber coupler, and receive a backscattered Rayleigh signal from the third optical fiber coupler to measure the optical fiber length of the second optical fiber laser to be measured; The third optical fiber coupler is used to couple the signal light and output it to the second signal amplification module, and at the same time receive the backscattered Rayleigh signal output from the second circulator, and couple the backscattered Rayleigh signal to the jumper of the optical frequency domain reflectometer; The second signal amplification module is used to amplify the signal light and output it to the second circulator; The second circulator is used to guide the amplified signal light output by the second signal amplification module to the second fiber laser to be tested, and at the same time guide the back Rayleigh scattered signal output by the second fiber laser to be tested to the third fiber coupler; The second optical fiber laser to be tested is used to generate the backscattered Rayleigh signal by using the amplified signal light.

[0103] 13. The system according to item 12 is characterized in that the optical frequency domain reflectometer further comprises: a second linear frequency sweeping laser, a fourth fiber coupler, a third circulator, a fifth fiber coupler, a second photodetector and a second data acquisition module; wherein The second linear frequency sweeping laser is used to output continuously changing laser light to the fourth optical fiber coupler; The fourth fiber coupler is used to split the laser light output by the second linear frequency sweeping laser into two paths according to a certain splitting ratio, one of which is transmitted to the third circulator as a signal light, and the other is transmitted to the fifth fiber coupler as a reference light; The third circulator is used to guide the signal light output by the fourth optical fiber coupler to the jumper, and guide the back Rayleigh scattered signal output from the jumper to the fifth optical fiber coupler; The fifth optical fiber coupler is used to receive the backscattered signal output from the third circulator and the reference light output from the fourth optical fiber coupler, couple the two to obtain a beat frequency optical signal, and output the beat frequency optical signal to the second photodetector; The second photodetector is used to convert the beat frequency optical signal into an electrical signal and perform coupling.

[0104] The second data acquisition module is used to collect data on the electrical signal from the second photodetector to measure the optical fiber length of the second optical fiber laser to be tested.

[0105] 14. The system according to item 13, characterized in that the second circulator and the third circulator each have at least three ports.

[0106] 15. The system according to any one of items 12 to 14, characterized in that the jumper is an optical fiber, which is fused or pluggable with the third optical fiber coupler.

[0107] 16. The system according to any one of items 12 to 14, characterized in that the second signal amplification module comprises: a second pump light source, a second beam combiner, a second gain fiber and a second cladding power stripper; wherein The second pump light source is used to output pump light to the second beam combiner; The second beam combiner is used to combine the pump light and the signal light from the third optical fiber coupler to obtain combined light; The second gain optical fiber is used to receive the combined light, amplify the signal light using the pump light in the combined light, and output it to the second cladding power stripper; The second cladding power stripper is used to strip the residual pump light from the signal light amplified by the second gain optical fiber, and output it to the second circulator.

[0108] 17. The system according to item 16 is characterized in that the second gain fiber is erbium-doped fiber.

[0109] 18. The system according to any one of items 12 to 14, characterized in that the third fiber coupler, the second signal amplification module and the second circulator are an integrated device.

[0110] 19. A method for measuring the length of an optical fiber laser, characterized in that a system for measuring the length of an optical fiber laser is provided, comprising: a linear frequency sweeping laser, a first optical fiber coupler, a signal amplification module, a circulator, a second optical fiber coupler, a photodetector and an optical fiber laser to be measured; The method comprises: The linear frequency sweeping laser outputs continuously changing laser light to the first optical fiber coupler; The first optical fiber coupler splits the laser light output by the linear frequency sweeping laser into two paths according to a certain splitting ratio, wherein one path is transmitted to the signal amplification module as signal light, and the other path is transmitted to the second optical fiber coupler as reference light; The signal amplification module amplifies the signal light and outputs it to the circulator; The circulator guides the amplified signal light output by the signal amplification module to the optical fiber laser to be tested, and guides the backscattered Rayleigh signal output by the optical fiber laser to be tested to the second optical fiber coupler; The optical fiber laser to be tested generates the backscattered Rayleigh signal using the amplified signal light and outputs the backscattered signal to the circulator; The second optical fiber coupler receives the backscattered signal outputted from the circulator and the reference light outputted from the first optical fiber coupler, couples the two to obtain a beat frequency optical signal, and outputs the beat frequency optical signal to the photodetector; The photoelectric detector converts the beat frequency optical signal into an electrical signal to measure the optical fiber length of the optical fiber laser to be tested.

[0111] 20. The measurement method according to item 19 is characterized in that the signal amplification module comprises: a pump light source, a beam combiner, a gain fiber and a cladding power stripper; The steps of the signal amplification module amplifying the signal light and outputting it to the circulator are specifically as follows: The pump light source outputs pump light to the beam combiner; The beam combiner combines the pump light and the signal light from the first optical fiber coupler to obtain combined light; The gain optical fiber receives the combined light, amplifies the signal light using the pump light in the combined light, and outputs the amplified signal light to the cladding power stripper; The cladding power stripper strips the residual pump light from the signal light amplified by the gain optical fiber, and outputs the residual pump light to the circulator.

[0112] 21. The measurement method according to Item 20 is characterized in that the gain fiber is erbium-doped fiber.

[0113] 22. The measurement method according to any one of items 19 to 21, characterized in that the measurement system further comprises a data acquisition module; The method further comprises: The data acquisition module receives the electrical signal from the photoelectric detector and performs data acquisition on the electrical signal; The measurement system also includes a data processing module; The method further comprises: The data processing module receives the data collected by the data collection module, and processes the data to obtain the optical fiber length of the optical fiber laser to be measured.

[0114] 23. The measurement method according to any one of items 19 to 21, characterized in that the circulator comprises a first port, a second port and a third port, the first port is connected to the signal amplification module, the second port is connected to the fiber laser to be measured, and the third port is connected to the second fiber coupler; The circulator guides the amplified signal light output by the signal amplification module to the optical fiber laser to be tested, and guides the backscattered Rayleigh signal output by the optical fiber laser to be tested to the second optical fiber coupler in the following specific steps: The circulator guides the amplified signal light output by the signal amplification module to the fiber laser to be tested by using the first port and the second port, and guides the back Rayleigh scattered signal output by the fiber laser to be tested to the second fiber coupler by using the second port and the third port.

[0115] 24. The measurement method according to any one of items 19 to 21 is characterized in that the first fiber coupler splits the laser into the signal light and the reference light at a splitting ratio of 9:1.

[0116] 25. The measurement method according to any one of items 19 to 21 is characterized in that the linear sweep laser adjusts the measurement range and accuracy of the measurement system by adjusting its sweep range and sweep rate.

[0117] 26. The measurement method according to any one of items 19 to 21, characterized in that the photodetector is a balanced photodetector; The method further includes: the balanced photodetector filtering out a direct current component in the electrical signal.

[0118] 27. The measurement method according to item 22, characterized in that the measurement system further comprises a bandpass filter or a low-pass filter; The method further comprises: The bandpass filter or the low-pass filter receives the electrical signal from the photodetector, performs filtering processing on the electrical signal, and outputs the signal to the data acquisition module.

[0119] 28. The measurement method according to any one of items 19 to 21, characterized in that the measurement system further comprises an optical attenuator; The method further comprises: The optical attenuator receives the reference light from the first optical fiber coupler, reduces the power of the reference light, and outputs the reference light with reduced power to the second optical fiber coupler.

[0120] 29. According to the measurement method described in Item 22, it is characterized in that the data acquisition module is an oscilloscope.

[0121] 30. An optical frequency domain reflectometer (OFDR) method for enhancing the intensity of a backscattered Rayleigh scattering signal, characterized in that a system for providing an optical frequency domain reflectometer (OFDR) for enhancing the intensity of a backscattered Rayleigh scattering signal comprises: an optical frequency domain reflectometer, a third optical fiber coupler, a second signal amplification module, a second circulator, and a second optical fiber laser to be tested, wherein the optical frequency domain reflectometer comprises a jumper; The method comprises: The optical frequency domain reflectometer is connected to the third optical fiber coupler through the jumper, outputs signal light to the third optical fiber coupler, and receives a backscattered Rayleigh signal from the third optical fiber coupler to measure the optical fiber length of the second optical fiber laser to be tested; The third optical fiber coupler couples the signal light and outputs it to the second signal amplification module, and simultaneously receives the backscattered Rayleigh signal output from the second circulator, and couples the backscattered Rayleigh signal to output it to the jumper of the optical frequency domain reflectometer; The second signal amplifying module amplifies the signal light and outputs it to the second circulator; The second circulator guides the amplified signal light output by the second signal amplification module to the second fiber laser to be tested, and guides the back Rayleigh scattered signal output by the second fiber laser to be tested to the third fiber coupler; The second optical fiber laser to be tested generates the backscattered Rayleigh signal using the amplified signal light.

[0122] 31. The method according to item 30, characterized in that the optical frequency domain reflectometer further comprises: a second linear frequency sweeping laser, a fourth fiber coupler, a third circulator, a fifth fiber coupler, a second photodetector and a second data acquisition module; The steps of connecting the optical frequency domain reflectometer to the third optical fiber coupler through the jumper, outputting signal light to the third optical fiber coupler, and receiving the backscattered Rayleigh signal from the third optical fiber coupler to measure the optical fiber length of the second optical fiber laser to be tested are specifically as follows: The second linear frequency sweeping laser outputs continuously changing laser light to the fourth optical fiber coupler; The fourth fiber coupler splits the laser light output by the second linear frequency sweeping laser into two paths according to a certain splitting ratio, wherein one path is transmitted to the third circulator as signal light, and the other path is transmitted to the fifth fiber coupler as reference light; The third circulator guides the signal light output by the fourth optical fiber coupler to the jumper, and guides the back Rayleigh scattered signal output from the jumper to the fifth optical fiber coupler; The fifth optical fiber coupler receives the backscattered signal outputted from the third circulator and the reference light outputted from the fourth optical fiber coupler, couples the two to obtain a beat frequency optical signal, and outputs the beat frequency optical signal to the second photodetector; The second photodetector converts the beat frequency optical signal into an electrical signal and couples it.

[0123] The second data acquisition module performs data acquisition on the electrical signal from the second photodetector to measure the optical fiber length of the second optical fiber laser to be tested.

[0124] 32. The method according to item 31 is characterized in that the second circulator and the third circulator each have at least three ports.

[0125] 33. The method according to any one of items 30 to 32, characterized in that the jumper is an optical fiber, which is fused or pluggable with the third optical fiber coupler.

[0126] 34. The method according to any one of items 30 to 32, characterized in that the second signal amplification module comprises: a second pump light source, a second beam combiner, a second gain fiber and a second cladding power stripper; The second signal amplification module is used to amplify the signal light and output it to the second circulator in the following steps: The second pump light source outputs pump light to the second beam combiner; The second beam combiner combines the pump light and the signal light from the third optical fiber coupler to obtain combined light; The second gain optical fiber receives the combined light, amplifies the signal light using the pump light in the combined light, and outputs the amplified signal light to the second cladding power stripper; The second cladding power stripper strips the residual pump light from the signal light amplified by the second gain optical fiber, and outputs the residual pump light to the second circulator.

[0127] 35. The method according to item 34 is characterized in that the second gain fiber is erbium-doped fiber.

[0128] 36. The method according to any one of items 30 to 32, characterized in that the third fiber coupler, the second signal amplification module and the second circulator are an integrated device.

Claims

1. A fiber laser fiber length measurement system, characterized in that: The measuring system comprises: a linear frequency sweeping laser, a first optical fiber coupler, a signal amplification module, a circulator, a second optical fiber coupler, a photoelectric detector and an optical fiber laser to be measured; wherein The linear frequency sweeping laser is used to output continuously changing laser light to the first optical fiber coupler; The first optical fiber coupler is used to split the laser output by the linear frequency sweeping laser into two paths according to a certain splitting ratio, one of which is transmitted to the signal amplification module as signal light, and the other is transmitted to the second optical fiber coupler as reference light; The signal amplification module is used to amplify the signal light and output it to the circulator; The circulator is used to guide the amplified signal light output by the signal amplification module to the optical fiber laser to be tested, and at the same time guide the back Rayleigh scattered signal output by the optical fiber laser to be tested to the second optical fiber coupler; The optical fiber laser to be tested is used to generate the backward Rayleigh scattered signal by using the amplified signal light, and output it to the circulator; The second optical fiber coupler is used to receive the backscattered signal output from the circulator and the reference light output from the first optical fiber coupler, couple the two to obtain a beat frequency optical signal, and output the beat frequency optical signal to the photodetector; The photoelectric detector is used to convert the beat frequency optical signal into an electrical signal to measure the optical fiber length of the optical fiber laser to be tested.

2. The measuring system according to claim 1, characterized in that The signal amplification module includes: a pump light source, a beam combiner, a gain optical fiber and a cladding power stripper; wherein The pump light source is used to output pump light to the beam combiner; The beam combiner is used to combine the pump light and the signal light from the first optical fiber coupler to obtain combined light; The gain optical fiber is used to receive the combined light, amplify the signal light using the pump light in the combined light, and output it to the cladding power stripper; The cladding power stripper is used to strip the residual pump light from the signal light amplified by the gain optical fiber, and output it to the circulator.

3. The measuring system according to claim 2, characterized in that The gain optical fiber is erbium-doped optical fiber.

4. The measuring system according to any one of claims 1 to 3, characterized in that: The measurement system further comprises a data acquisition module, which is used to receive the electrical signal from the photoelectric detector and perform data acquisition on the electrical signal; The measurement system also includes a data processing module, which is used to receive the data collected by the data collection module and process the data to obtain the optical fiber length of the optical fiber laser to be measured.

5. The measuring system according to any one of claims 1 to 3, characterized in that: The circulator comprises a first port, a second port and a third port, the first port is connected to the signal amplification module, the second port is connected to the optical fiber laser to be tested, and the third port is connected to the second optical fiber coupler; The circulator guides the amplified signal light output by the signal amplification module to the fiber laser to be tested by using the first port and the second port, and guides the back Rayleigh scattered signal output by the fiber laser to be tested to the second fiber coupler by using the second port and the third port.

6. The measuring system according to any one of claims 1 to 3, characterized in that: The first optical fiber coupler splits the laser light into the signal light and the reference light at a splitting ratio of 9:

1.

7. The measuring system according to any one of claims 1 to 3, characterized in that: The linear frequency sweeping laser adjusts the measurement range and accuracy of the measurement system by adjusting its frequency sweeping range and frequency sweeping rate.

8. An optical frequency domain reflectometry (OFDR) system for enhancing the intensity of backscattered Rayleigh scattering signals, characterized in that: The system comprises: an optical frequency domain reflectometer, a third optical fiber coupler, a second signal amplification module, a second circulator and a second optical fiber laser to be tested; wherein The optical frequency domain reflectometer includes a jumper, and the optical frequency domain reflectometer is connected to the third optical fiber coupler through the jumper, and is used to output signal light to the third optical fiber coupler, and receive a backscattered Rayleigh signal from the third optical fiber coupler to measure the optical fiber length of the second optical fiber laser to be measured; The third optical fiber coupler is used to couple the signal light and output it to the second signal amplification module, and at the same time receive the backscattered Rayleigh signal output from the second circulator, and couple the backscattered Rayleigh signal to the jumper of the optical frequency domain reflectometer; The second signal amplification module is used to amplify the signal light and output it to the second circulator; The second circulator is used to guide the amplified signal light output by the second signal amplification module to the second fiber laser to be tested, and at the same time guide the back Rayleigh scattered signal output by the second fiber laser to be tested to the third fiber coupler; The second optical fiber laser to be tested is used to generate the backscattered Rayleigh signal by using the amplified signal light.

9. A method for measuring the length of an optical fiber laser, characterized in that: Provided is a fiber laser fiber length measurement system comprising: a linear frequency sweeping laser, a first fiber coupler, a signal amplification module, a circulator, a second fiber coupler, a photodetector and a fiber laser to be measured; The method comprises: The linear frequency sweeping laser outputs continuously changing laser light to the first optical fiber coupler; The first optical fiber coupler splits the laser light output by the linear frequency sweeping laser into two paths according to a certain splitting ratio, wherein one path is transmitted to the signal amplification module as signal light, and the other path is transmitted to the second optical fiber coupler as reference light; The signal amplification module amplifies the signal light and outputs it to the circulator; The circulator guides the amplified signal light output by the signal amplification module to the optical fiber laser to be tested, and guides the backscattered Rayleigh signal output by the optical fiber laser to be tested to the second optical fiber coupler; The optical fiber laser to be tested generates the backscattered Rayleigh signal using the amplified signal light and outputs the backscattered signal to the circulator; The second optical fiber coupler receives the backscattered signal outputted from the circulator and the reference light outputted from the first optical fiber coupler, couples the two to obtain a beat frequency optical signal, and outputs the beat frequency optical signal to the photodetector; The photoelectric detector converts the beat frequency optical signal into an electrical signal to measure the optical fiber length of the optical fiber laser to be tested.

10. An optical frequency domain reflectometry (OFDR) method for enhancing the intensity of backscattered Rayleigh scattering signals, characterized in that: A system for providing an optical frequency domain reflectometer (OFDR) for enhancing the intensity of a backward Rayleigh scattered signal comprises: an optical frequency domain reflectometer, a third fiber coupler, a second signal amplification module, a second circulator and a second fiber laser to be tested, wherein the optical frequency domain reflectometer comprises a jumper; The method comprises: The optical frequency domain reflectometer is connected to the third optical fiber coupler through the jumper, outputs signal light to the third optical fiber coupler, and receives a backscattered Rayleigh signal from the third optical fiber coupler to measure the optical fiber length of the second optical fiber laser to be tested; The third optical fiber coupler couples the signal light and outputs it to the second signal amplification module, and simultaneously receives the backscattered Rayleigh signal output from the second circulator, and couples the backscattered Rayleigh signal to output it to the jumper of the optical frequency domain reflectometer; The second signal amplifying module amplifies the signal light and outputs it to the second circulator; The second circulator guides the amplified signal light output by the second signal amplification module to the second fiber laser to be tested, and guides the back Rayleigh scattered signal output by the second fiber laser to be tested to the third fiber coupler; The second optical fiber laser to be tested generates the backscattered Rayleigh signal using the amplified signal light.

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