Fiber laser fiber length measurement system

Abstract

This invention provides a fiber optic laser length measurement system, comprising: a linearly swept laser, a first fiber coupler, a signal amplification module, a circulator, a second fiber coupler, a photodetector, and the fiber laser under test. The linearly swept laser outputs continuously varying laser light to the first fiber coupler. The first fiber coupler splits the laser light output from the linearly swept laser into two paths according to a certain beam splitting ratio; one path is transmitted as a signal light to the signal amplification module, and the other path is transmitted as a reference light to the second fiber coupler. The signal amplification module amplifies the signal light and outputs it to the circulator. This invention effectively solves the problems of low signal-to-noise ratio, poor accuracy, and poor stability in the prior art when measuring the fiber length of fiber lasers.

Description

Technical Field

[0001] This utility model relates to the field of laser technology, and more specifically, to a fiber optic length measurement system for fiber lasers. Background Technology

[0002] Fiber lasers have seen rapid development in recent years due to their high efficiency, small size, good beam quality, and high stability. Accurate measurement of fiber length is a crucial step in the design and manufacturing of fiber lasers. However, existing fiber length measurement technologies for fiber lasers still suffer from numerous problems, including poor signal-to-noise ratio, low measurement accuracy, and poor stability.

[0003] Currently, commonly used methods for measuring fiber length include optical time domain reflectometer (OTDR), optical frequency domain reflectometer (OFDR), and optical low coherence reflectometer (OLCR).

[0004] OTDR technology, based on the interference effect of backscattering Rayleigh scattering in optical fibers, enables long-distance fiber length measurement, but its spatial resolution and pulse width are mutually limiting. An OTDR system emits a short-pulse laser signal into the fiber and detects the light signals reflected back from scattering centers at different locations within the fiber. By analyzing the time delay of the reflected signals, the length of the fiber and its breaks or loss points can be measured. OTDR technology has a long measurement distance (up to kilometers), but its spatial resolution is limited by pulse width and time sampling capabilities, typically providing only meter-level accuracy. Therefore, OTDR technology performs well in measuring long-distance fibers, but has limitations in measuring short fibers requiring high precision.

[0005] In comparison, OFDR and OLCR technologies offer higher accuracy when measuring single-mode optical fibers. OFDR technology is based on the principle of frequency-domain interference. It uses a linearly swept laser to emit a continuous optical signal, which propagates through the fiber and undergoes Rayleigh scattering with impurities and minor irregularities within the fiber. The scattered light interferes with a reference signal, and by analyzing the frequency domain characteristics of the interference signal, the time delay of the scattered signal can be accurately determined. Through frequency-domain sweeping signals, OFDR technology can provide higher resolution than OTDR, typically achieving millimeter-level or even micrometer-level accuracy. OLCR technology, on the other hand, uses a low-coherence light source to emit a broadband optical signal. Unlike OTDR and OFDR, OLCR estimates the fiber length by measuring the interference pattern of the reflected signal. The wide bandwidth of the low-coherence light source gives it high resolution when analyzing reflected signals.

[0006] However, when OFDR and OLCR technologies are used to measure the fiber length in fiber lasers (including various optical devices and active fibers), the output power of the linearly swept laser used to output the measurement signal is low, and the presence of various optical devices and active fibers in the fiber laser under test leads to a large system loss of the signal light input to the fiber laser under test. This results in a significant reduction in the power of the backscattered Rayleigh signal and a significant decrease in the signal-to-noise ratio, making it impossible to effectively measure the fiber length of the fiber laser under test. Therefore, these technologies are limited in their further application in fiber lasers. Utility Model Content

[0007] This invention provides a fiber optic laser fiber length measurement system. By employing a signal amplification module, a balanced photodetector, and / or a low-pass filter, the system effectively improves the signal strength and solves the problems of low signal-to-noise ratio, poor accuracy, and poor stability in the prior art when measuring the fiber length of a fiber optic laser.

[0008] In a first aspect, this utility model provides a fiber optic laser fiber length measurement system, characterized in that the measurement system comprises: a linearly swept laser, a first fiber coupler, a signal amplification module, a circulator, a second fiber coupler, a photodetector, and the fiber laser under test; wherein...

[0009] The linear sweep laser is used to output continuously varying laser light to the first fiber coupler;

[0010] The first fiber coupler is used to split the laser output from the linear sweep laser into two paths according to a certain beam splitting ratio. One path is transmitted as a signal light to the signal amplification module, and the other path is transmitted as a reference light to the second fiber coupler.

[0011] The signal amplification module is used to amplify the signal light and output it to the circulator;

[0012] The circulator is used to guide the amplified signal light output from the signal amplification module to the fiber laser under test, and at the same time guide the backscattered Rayleigh signal output from the fiber laser under test to the second fiber coupler.

[0013] The fiber laser under test is used to generate the backscattered Rayleigh signal using the amplified signal light and output it to the circulator;

[0014] The second fiber coupler is used to receive the backscattered Rayleigh signal output from the circulator and the reference light output from the first fiber coupler, and couple the two to obtain a beat frequency optical signal, and output the beat frequency optical signal to the photodetector.

[0015] The photodetector is used to convert the beat-frequency optical signal into an electrical signal to measure the fiber length of the fiber laser under test.

[0016] Secondly, this utility model provides an optical frequency domain reflectometer (OFDR) system for enhancing the intensity of backscattered Rayleigh 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 under test; wherein...

[0017] The optical frequency domain reflectometer includes a jumper wire, which is connected to the third fiber coupler. The jumper wire is used to output signal light to the third fiber coupler and receive backscattered Rayleigh signals from the third fiber coupler to measure the fiber length of the second fiber laser under test.

[0018] The third fiber coupler is used to couple the signal light and output it to the second signal amplification module, while receiving the backscattered Rayleigh signal output from the second circulator, and coupling the backscattered Rayleigh signal to the jumper of the optical frequency domain reflectometer.

[0019] The second signal amplification module is used to amplify the signal light and output it to the second circulator;

[0020] The second circulator is used to guide the amplified signal light output from the second signal amplification module to the second fiber laser under test, and at the same time guide the backscattered Rayleigh signal output from the second fiber laser under test to the third fiber coupler.

[0021] The second fiber laser under test is used to generate the backscattered Rayleigh signal using the amplified signal light.

[0022] Thirdly, this utility model provides a method for measuring the fiber length of a fiber laser, characterized in that the fiber length measurement system for a fiber laser includes: a linear sweep laser, a first fiber coupler, a signal amplification module, a circulator, a second fiber coupler, a photodetector, and the fiber laser under test;

[0023] The method includes:

[0024] The linear sweep laser outputs continuously varying laser light to the first fiber coupler;

[0025] The first fiber coupler divides the laser output from the linear sweep laser into two paths according to a certain beam splitting ratio. One path is transmitted as a signal light to the signal amplification module, and the other path is transmitted as a reference light to the second fiber coupler.

[0026] The signal amplification module amplifies the signal light and outputs it to the circulator;

[0027] The circulator guides the amplified signal light output from the signal amplification module to the fiber laser under test, and simultaneously guides the backscattered Rayleigh signal output from the fiber laser under test to the second fiber coupler.

[0028] The fiber laser under test uses the amplified signal light to generate the backscattered Rayleigh signal and outputs it to the circulator;

[0029] The second fiber coupler receives the backscattered Rayleigh signal output from the circulator and the reference light output from the first fiber coupler, and couples the two to obtain a beat-frequency optical signal, which is then output to the photodetector.

[0030] The photodetector converts the beat-frequency optical signal into an electrical signal to measure the fiber length of the fiber laser under test.

[0031] Fourthly, this utility model provides a method for enhancing the intensity of backscattered Rayleigh signals using an optical frequency domain reflectometer (OFDR), characterized in that the system for providing an optical frequency domain reflectometer (OFDR) for enhancing the intensity of backscattered Rayleigh signals includes: an optical frequency domain reflectometer, a third fiber coupler, a second signal amplification module, a second circulator, and a second fiber laser under test, wherein the optical frequency domain reflectometer includes jumpers;

[0032] The method includes:

[0033] The optical frequency domain reflectometer is connected to the third fiber coupler via the jumper, outputs signal light to the third fiber coupler, and receives backscattered Rayleigh signals from the third fiber coupler to measure the fiber length of the second fiber laser under test.

[0034] The third fiber coupler couples the signal light and outputs it to the second signal amplification module. At the same time, it receives the backscattered Rayleigh signal output from the second circulator and couples the backscattered Rayleigh signal to the jumper of the optical frequency domain reflectometer.

[0035] The second signal amplification module amplifies the signal light and outputs it to the second circulator;

[0036] The second circulator guides the amplified signal light output from the second signal amplification module to the second fiber laser under test, and simultaneously guides the backscattered Rayleigh signal output from the second fiber laser under test to the third fiber coupler.

[0037] The second fiber laser under test generates the backscattered Rayleigh signal using the amplified signal light.

[0038] The fiber laser fiber length measurement system provided by this utility model has the following advantages: First, it enhances the signal strength through a signal amplification module, especially by using erbium-doped fiber as the gain fiber, which effectively amplifies the signal light and ensures that the intensity of the backscattered Rayleigh signal is sufficiently large, thereby improving the sensitivity and accuracy of the measurement. Second, it uses a combination of a balanced photodetector, a bandpass filter, and a low-pass filter to effectively filter out the DC component and noise in the electrical signal, improving the signal-to-noise ratio of the measured signal. Third, by using an optical attenuator to adjust the reference light power in the measurement system, it ensures that the power ratio between the reference light and the backscattered Rayleigh signal is appropriate, guaranteeing that they can generate clear and accurate beat frequency signals, thereby greatly improving the accuracy and reliability of fiber length measurement. Fourth, the optical frequency domain reflectometer (OFDR) system used in this utility model to enhance the intensity of the backscattered Rayleigh signal adds a signal enhancement mechanism without changing the traditional OFDR system structure. This not only improves the signal strength and signal-to-noise ratio but also reduces the complexity and cost of system modification and upgrades. For users of existing OFDR systems, this allows for improved measurement accuracy with minimal cost investment. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a schematic diagram of the fiber optic laser fiber length measurement system provided in this embodiment of the utility model;

[0041] Figure 2 This is a schematic diagram of an optical frequency domain reflectometer (OFDR) system for enhancing the intensity of backscattered Rayleigh signals, provided by an embodiment of this utility model.

[0042] Figure 3 This is a flowchart of the fiber length measurement method for a fiber laser provided in this embodiment of the utility model;

[0043] Figure 4 This is a flowchart of an optical frequency domain reflectometer (OFDR) method for enhancing the intensity of backscattered Rayleigh signals, provided by an embodiment of this utility model. Detailed Implementation

[0044] The technical solution of this utility model will be further described in detail below with reference to the accompanying drawings and embodiments.

[0045] Overview of Utility Model

[0046] As mentioned above, this utility model provides a fiber optic laser fiber length measurement system, which effectively solves the problems of low signal-to-noise ratio, poor accuracy, and poor stability in the existing technology when measuring the fiber length of fiber optic lasers.

[0047] Exemplary System

[0048] Figure 1 This is a schematic diagram of the fiber optic laser fiber length measurement system provided in Embodiment 1 of this utility model, as shown below. Figure 1 As shown, the measurement system 100 provided in this embodiment 1 includes: a linear sweep 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 under test 112.

[0049] The linearly swept laser 101 is used to output continuously varying laser light to the first fiber coupler 102. The laser frequency increases linearly over time.

[0050] The linear sweep laser 101 adjusts its sweep frequency range and sweep rate to adjust the measurement range and accuracy of the measurement system 100.

[0051] The sweep range refers to the total range of frequency changes in the linear sweep laser 101. The sweep rate refers to the speed of frequency change, usually expressed as the frequency increase in Hertz (Hz) per second. A larger sweep range allows for a wider measurement range; a higher sweep rate results in higher measurement accuracy.

[0052] In summary, when high accuracy is required for fiber length measurement, high-resolution measurement can be achieved by increasing the sweep frequency range, reducing the sweep frequency rate, or decreasing the frequency step size. When high measurement speed is required, the scanning speed can be increased by increasing the sweep frequency rate or increasing the frequency step size, sacrificing some accuracy in exchange for faster measurement results.

[0053] The first fiber coupler 102 is a 1×2 fiber coupler, used to split the laser output from the linearly swept laser 101 into two paths according to a certain beam splitting ratio. One path is transmitted as a signal light to the signal amplification module 103, and the other path is transmitted as a reference light to the second fiber coupler 105. The signal light provides the initial laser source for the entire measurement process. The reference light provides a stable reference signal for the measurement system 100, used for comparison with the backscattered Rayleigh signal.

[0054] The splitting ratio needs to ensure, on the one hand, that the signal light intensity is sufficient to facilitate subsequent amplification and processing, obtain a stronger signal echo, and guarantee a high signal-to-noise ratio during transmission, amplification, and processing, thereby improving measurement accuracy. On the other hand, it needs to provide sufficient reference signal strength to effectively couple with the backscattered Rayleigh signal scattered from the fiber laser under test 112. Preferably, the intensity of the reference light is approximately the same as the intensity of the backscattered Rayleigh signal, which allows for more accurate measurement of the beat frequency and improves the signal-to-noise ratio.

[0055] Preferably, the first fiber coupler 102 splits the laser into the signal light and the reference light at a splitting ratio of 9:1. Using a 9:1 splitting ratio fiber coupler ensures a reasonable intensity distribution between the signal light and the reference light in the measurement system 100, thus guaranteeing a sufficient coupling effect. Furthermore, as a passive device, the splitting ratio of the fiber coupler is pre-set at the factory; 9:1 is a common splitting ratio for fiber couplers. Therefore, this invention simplifies the design and selection process of the fiber coupler and reduces implementation costs.

[0056] Building upon this, to further optimize the intensity of the reference light and avoid the influence of intensity mismatch between the reference light and the backscattered Rayleigh signal on measurement accuracy, the measurement system 100 may further include an optical attenuator. This attenuator receives the reference light from the first fiber coupler 102, reduces the power of the reference light, and outputs the reduced-power reference light to the second fiber coupler 105. The optical attenuator is a controllable attenuator, used to adjust or switch the attenuation ratio based on the intensity of the backscattered Rayleigh signal, for example, by automatically switching between different attenuation filters.

[0057] In fiber optic length measurement, the reference light and the backscattered Rayleigh signal need to be coupled. The quality of the beat frequency effect is highly dependent on the power balance between the reference light and the backscattered Rayleigh signal. Good power matching results in higher contrast of the beat frequency signal, making it easier to extract clear and accurate beat frequency information in subsequent signal processing. If the power difference between the two is too large, the beat frequency signal will be distorted, leading to inaccurate measurement results. The contrast of the beat frequency signal will also decrease, making it difficult for the measurement system to distinguish subtle changes in the signal. Therefore, optimizing the signal contrast by adjusting the optical attenuator helps improve the measurement accuracy of the system.

[0058] The original signal light power provided by the linear sweep laser 101 is typically low. The signal amplification module 103 is used to amplify the signal light and output it to the circulator 104.

[0059] In traditional measurement systems, the output power of the linear sweep laser 101 is relatively low, and the fiber laser under test typically includes multiple optical devices and active fibers, causing the power of the optical signal to gradually attenuate during propagation. In particular, the power of the backscattered Rayleigh signal is relatively weak, and with the increase of fiber length, signal attenuation and noise further reduce the intensity of the backscattered Rayleigh signal. This invention amplifies the signal light using the signal amplification module 103, significantly increasing the signal light power and enhancing its transmission capability to the fiber laser under test 112, thereby increasing the intensity of the backscattered Rayleigh signal. By enhancing the signal light power, the measurement system 100 can maintain a high signal-to-noise ratio even in high-noise environments. A high signal-to-noise ratio is crucial for subsequent coupling processes, signal acquisition, and data processing. A good signal-to-noise ratio ensures that the photodetector 106 accurately captures the signal after the beat frequency, thus improving the measurement accuracy of the fiber length.

[0060] The signal amplification module 103 includes: a pump light source 108, a bundler 109, a gain fiber 110, and a cladding power stripper 111.

[0061] The pump light source 108 is used to output pump light to the combiner 109. In order to effectively excite erbium-doped fiber, a pump light source with a wavelength of 980nm or 1480nm is usually used.

[0062] The combiner 109 is used to combine the pump light and the signal light from the first fiber coupler 102 to obtain combined light.

[0063] 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 erbium-doped fiber (EDF). Erbium-doped fiber has excellent gain characteristics, especially in the 1550nm wavelength range commonly used in optical communication, which can effectively enhance the intensity of the 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.

[0064] The cladding power stripper 111 is used to remove residual pump light from the signal light amplified by the gain fiber 110 and output it to the circulator 104, ensuring the purity of the output amplified signal light and effectively suppressing the generation of spontaneous emission noise (ASE noise). Spontaneous emission noise introduces systematic errors and reduces measurement accuracy. It is a common problem in fiber amplifiers and usually occurs during laser amplification, especially when the pump light and signal light are not completely separated.

[0065] The circulator 104 is used to guide the amplified signal light output by the signal amplification module 103 to the fiber laser under test 112, and at the same time guide the backscattered Rayleigh signal output from the fiber laser under test 112 to the second fiber coupler 105.

[0066] The circulator 104 includes a first port, a second port, and a third port. It is an asymmetric three-port optical device that utilizes the non-reflective properties of light and waveguide characteristics, through a specific optical path design, to ensure the directional transmission of signal light and backscattered Rayleigh signals. The first port is connected to the signal amplification module 103, the second port is connected to the fiber laser under test 112, and the third port is connected to the second fiber coupler 105.

[0067] The circulator 104 uses the first and second ports to guide the amplified signal light output from the signal amplification module 103 to the fiber laser under test 112. Simultaneously, it uses the second and third ports to guide the backscattered Rayleigh signal output from the fiber laser under test 112 to the second fiber coupler 105. Through the structural characteristics of its different ports, the circulator 104 ensures that the signal light and the backscattered Rayleigh signal travel along different paths, avoiding mutual interference and ensuring effective signal detection.

[0068] The fiber laser under test 112 is used to generate the backscattered Rayleigh signal based on the amplified signal light using the Rayleigh scattering characteristics of the fiber, and outputs it to the circulator 104. The backscattered Rayleigh signal refers to the light rays that are scattered due to the slight inhomogeneities of the fiber when the laser beam (or signal light) propagates along the fiber. These scattered rays propagate in the opposite direction along the propagation direction of the fiber and eventually return towards the signal source.

[0069] The second fiber coupler 105 is a 2×2 fiber coupler used to receive the backscattered Rayleigh signal output from the circulator 104 and the reference light output from the first fiber coupler 102, and couple them to obtain a beat-frequency optical signal, which is then output to the photodetector 106. The coupling process is based on the interference effect between the reference signal and the backscattered Rayleigh signal. Beat frequency refers to the periodic change in the combined light intensity of two coherent optical signals when coupled in the second fiber coupler 105. The frequency of this intensity change is the beat frequency; in other words, the beat frequency is the new frequency generated when two coherent optical signals meet in an optical fiber and interfere. The frequency of the beat-frequency optical signal is related to the frequency difference between the two signals, which reflects the length of the optical fiber.

[0070] Because the backscattered Rayleigh signal continuously returns, the coupling process is dynamic and continuous, and the beat frequency signal is also continuously generated. Since backscattered Rayleigh signals can be generated at the interfaces of various components inside the fiber laser under test, including at both ends of the fiber, there may be multiple beat frequency signals. Each beat frequency signal corresponds to the optical path of a reflecting interface inside the fiber laser. The length of the fiber in the fiber laser can be calculated by determining the optical path difference between the corresponding beat frequency signals at both ends of the fiber.

[0071] The photodetector 106 is used to convert the beat-frequency optical signal into an electrical signal to measure the fiber length of the fiber laser 112 under test.

[0072] Electrical signals typically contain both 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 shift information due to variations in fiber length, etc. If these noise components are not effectively removed, the signal quality will be severely affected, leading to inaccurate measurement results.

[0073] To improve the signal-to-noise ratio of the measurement system 100, preferably, the photodetector 106 is a balanced photodetector. The balanced photodetector uses the difference between the two signals to eliminate common-mode noise (including DC noise) and retains only the AC signal portion. That is, the balanced photodetector is used to filter out the DC component in the electrical signal and retain the AC component.

[0074] The data acquisition module 107 is used to receive the electrical signal from the photodetector 106 and to acquire data from the electrical signal. The data acquisition module 107 is an oscilloscope.

[0075] The measurement system 100 further includes a data processing module, which receives the data acquired by the data acquisition module 107 and processes it to obtain the fiber length of the fiber laser 112 under test. For example, an oscilloscope is used to acquire the electrical signal data, 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 under test.

[0076] Specifically, the current signal received by the data processing module, i.e., the current signal after coupling and photoelectric conversion by the second fiber coupler 105, is the signal coupled between the backscattered Rayleigh scattering signals from multiple reflection points in the fiber and the reference light. It is a composite signal of multiple single-frequency sinusoidal signals, where the frequency of each single-frequency signal is positively correlated with the position of the reflection point, and the signal amplitude reflects the scattering rate of the reflection point and the fiber attenuation. Therefore, the data processing module performs a Fourier transform on the received data to obtain the spectrum. Each peak in the spectrum corresponds to the position of a specific reflection point on the fiber, thus obtaining the Rayleigh scattering information of each reflection point on the fiber. The relationship between position and frequency is as follows:

[0077]

[0078] Where z is the position of the reflection point, f is the beat frequency, k is the sweep frequency speed, and v g Group velocity.

[0079] The difference in the NA (Negative Array) of the fiber in the fiber laser under test 112 directly affects the group velocity of the optical signal. A larger NA allows the core region of the fiber to receive more light, resulting in a higher group velocity and faster optical signal propagation. Conversely, a smaller NA results in a lower group velocity and slower optical signal propagation. Group velocity is the speed at which an optical signal propagates along an optical fiber, influenced by the fiber's refractive index, NA, and transmission mode. If the fiber laser under test 112 uses fibers with different NAs, even with the same fiber length, the different group velocities will lead to different time delays in optical signal propagation, thus affecting the measurement results. This is especially true for fiber length measurements based on time-domain (OTDR) or frequency-domain (OFDR), where differences in group velocity can cause deviations in the measurement results.

[0080] Generally, measuring the fiber length of a single fiber laser requires the NA (navigation distance) to be known. If the NA value of the fiber under test cannot be obtained, the optical path difference between two identical fiber lasers is usually measured to obtain the relative difference in fiber length between the two lasers.

[0081] Fourier transform converts time-domain signals into frequency-domain information. Through spectral analysis, the location of each reflection point in the optical fiber can be precisely located, ensuring the accuracy of fiber optic measurements. Whether a detected reflection point belongs to the optical fiber or other media (such as connectors, fiber optic splices, other optical components, etc.) typically depends on the analysis of the reflected signal. More specifically, key factors in determining whether a reflection point is from the optical fiber or something else include the intensity of the reflection, the type of reflection, its location distribution, and the characteristic frequency of the reflection. For example, the reflection intensity of an optical fiber is typically lower than that caused by fiber optic splices or other optical components.

[0082] To further improve the signal-to-noise ratio of the electrical signal, the measurement system 100 may also 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.

[0083] A bandpass filter allows signals within a specific frequency range to pass through, while filtering out signals with frequencies higher or lower than that range. It can selectively pass through frequency components relevant to fiber length measurements based on the signal's frequency characteristics, filtering out irrelevant signals or noise in other frequency ranges. For example, a bandpass filter can be configured to pass only a specific frequency range within a beat frequency signal, filtering out interference frequencies caused by other unrelated signal sources.

[0084] A 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 electrical signals in the measurement system 100, the low-pass filter helps improve signal quality by removing these high-frequency components.

[0085] By introducing bandpass or lowpass filters, the electrical signal is filtered, retaining only the most relevant signal components. Irrelevant frequency components (such as high-frequency noise, DC components, and interference signals) are effectively removed, while the effective components (such as frequency components related to fiber length variations) are preserved. The signal is cleaner, and the signal-to-noise ratio is significantly improved, providing a more accurate and reliable foundation for subsequent data analysis and fiber length calculations.

[0086] Example 1 changes the internal structure of the common optical frequency domain reflectometer (OFDR) in the prior art. Through a highly integrated design, it reduces the number of required components, making the system more compact. It is also highly scalable, supporting 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, filter out noise, improve measurement accuracy, and adapt to various application scenarios.

[0087] Unlike Example 1, Example 2 is an improvement on the commonly used optical frequency domain reflectometer (OFDR). A jumper is fused to or pluggable with a fiber coupler. The output of the fiber coupler is connected to a signal amplification module for signal power amplification. The amplified signal light enters the first port of a circulator and exits from the second port to the fiber laser under test. The resulting backscattered Rayleigh signal enters the fiber coupler from the third port of the circulator and returns to the original OFDR for coupling. In other words, Example 2 improves the intensity of the backscattered Rayleigh signal of a common OFDR by setting an additional signal enhancement mechanism specifically for it, effectively solving the signal attenuation problem of traditional OFDRs when measuring fiber length in fiber lasers (including various optical devices and active fibers).

[0088] Figure 2 This is a schematic diagram of an optical frequency domain reflectometer (OFDR) system for enhancing the intensity of backscattered Rayleigh signals, as provided in Embodiment 2 of this utility model. 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 under test 205.

[0089] The optical frequency domain reflectometer 201 includes a jumper 206, which connects the optical frequency domain reflectometer 201 to the third fiber coupler 202. The optical frequency domain reflectometer 201 is used to output signal light to the third fiber coupler 202 and receive backscattered Rayleigh signals from the third fiber coupler 202 to measure the fiber length of the second fiber laser under test 205.

[0090] The patch cord 206 is an optical fiber with a specific length and interface design, used to transmit optical signals. It is either fused to or pluggable with the third fiber coupler 202. The use of patch cord 206 simplifies the connection between the optical frequency domain reflectometer 201 and the third fiber coupler 202, thereby improving the integration and modularity of the system 200. While ensuring signal transmission stability, patch cord 206 also facilitates the configuration and maintenance of the system 200.

[0091] The optical frequency domain reflectometer 201 further includes: a second linearly swept 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; wherein

[0092] The second linear sweep laser 207 is used to output continuously varying laser light to the fourth fiber coupler 208;

[0093] The fourth fiber coupler 208 is used to split the laser output from the second linear sweep laser 207 into two paths according to a certain beam splitting ratio. One path is transmitted as a signal light to the third circulator 209, and the other path is transmitted as a reference light to the fifth fiber coupler 210.

[0094] The third circulator 209 has at least three ports for guiding the signal light output from the fourth fiber coupler 208 to the jumper 206, and simultaneously guiding the backscattered Rayleigh signal output from the jumper 206 to the fifth fiber coupler 210.

[0095] The fifth fiber coupler 210 is used to receive the backscattered Rayleigh 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.

[0096] 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 be a balanced photodetector and cannot filter out the DC component. Unlike the balanced photodetector in Embodiment 1, which receives two signals, the second photodetector 211 can only receive one signal.

[0097] The second data acquisition module 212 is used to acquire the electrical signal from the second photodetector 211 to measure the fiber length of the second fiber laser under test 205.

[0098] The third fiber coupler 202 is used to couple the signal light and output it to the second signal amplification module 203, while receiving the backscattered Rayleigh signal output from the second circulator 204, and coupling the backscattered Rayleigh signal to the jumper 206 of the optical frequency domain reflectometer 201.

[0099] The second signal amplification module 203 amplifies the signal light and outputs it to the second circulator 204. The second signal amplification module 203 enhances the intensity of the signal light, especially when the backscattered Rayleigh signal output from the second fiber laser under test 205 has low power and high system loss. By amplifying the signal, the second signal amplification module 203 ensures that the attenuation of the signal light during propagation through the optical fiber is effectively compensated, thus improving the signal-to-noise ratio of the system 200.

[0100] The second signal amplification module 203 includes: a second pump light source, a second bundler, a second gain fiber, and a second cladding power stripper; wherein

[0101] The second pump light source is used to output pump light to the second beam combiner;

[0102] The second beam combiner is used to combine the pump light and the signal light from the third fiber coupler 202 to obtain combined light;

[0103] The second gain 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 gain fiber is an erbium-doped fiber.

[0104] The second cladding power stripper is used to strip the residual pump light in the signal light amplified by the second gain fiber and output it to the second circulator 204.

[0105] The second circulator 204 has at least three ports for guiding the amplified signal light output from the second signal amplification module 203 to the second fiber laser under test 205, and simultaneously guiding the backscattered Rayleigh signal output from the second fiber laser under test 205 to the third fiber coupler 202.

[0106] The second fiber laser under test 205 is used to generate the backscattered Rayleigh signal using the amplified signal light.

[0107] The third fiber coupler 202, the second signal amplification module 203, and the second circulator 204 are integrated into one device. Integrating these three components into a single device can improve the stability, integration, and efficiency of the system 200.

[0108] In summary, compared to Example 1, Example 2 improves performance by adding a signal enhancement mechanism without altering the internal structure of a traditional OFDR—that is, based on the existing complete OFDR structure. Users can improve the system's signal-to-noise ratio and measurement accuracy by simply adding a new module without completely replacing or redesigning existing equipment. For users already using traditional OFDR systems, this avoids unnecessary equipment replacement.

[0109] However, compared to Embodiment 1, Embodiment 2 has a lower integration level and requires multiple fiber couplers, circulators, and other components, resulting in a larger system size. Since Embodiment 2 is based on an improvement of a traditional OFDR, it does not have the flexible scalability of Embodiment 1 and cannot flexibly add signal optimization components such as balanced photodetectors, low-pass filters, and optical attenuators to the original system.

[0110] In summary, Example 2 is suitable for upgrading existing conventional OFDRs, allowing users to improve technical performance with minimal intervention costs.

[0111] Exemplary methods

[0112] Accordingly, this utility model embodiment also provides a method for measuring the fiber length of a fiber laser. The fiber length measurement system 100 for a fiber laser includes: a linear sweep 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 under test 112. Figure 3 This is a flowchart of a fiber optic laser fiber length measurement method provided in an embodiment of the present invention. The embodiment includes the following steps:

[0113] S301: The linear sweep laser 101 outputs continuously varying laser light to the first fiber coupler 102;

[0114] S302: The first fiber coupler 102 divides the laser output from the linear sweep laser 101 into two paths according to a certain beam splitting ratio. One path is transmitted as a signal light to the signal amplification module 103, and the other path is transmitted as a reference light to the second fiber coupler 105.

[0115] S303: The signal amplification module 103 amplifies the signal light and outputs it to the circulator 104;

[0116] S304: The circulator 104 guides the amplified signal light output by the signal amplification module 103 to the fiber laser under test 112, and at the same time guides the backscattered Rayleigh signal output from the fiber laser under test 112 to the second fiber coupler 105.

[0117] S305: The fiber laser under test 112 uses the amplified signal light to generate the backscattered Rayleigh signal and outputs it to the circulator 104;

[0118] S306: The second fiber coupler 105 receives the backscattered Rayleigh signal output from the circulator 104 and the reference light output from the first fiber coupler 102, and couples the two to obtain a beat frequency optical signal, and outputs the beat frequency optical signal to the photodetector 106.

[0119] S307: The photodetector 106 converts the beat-frequency optical signal into an electrical signal to measure the fiber length of the fiber laser 112 under test.

[0120] The signal amplification module 103 includes: a pump light source 108, a bundler 109, a gain fiber 110, and a cladding power stripper 111;

[0121] The specific steps of the signal amplification module 103 amplifying the signal light and outputting it to the circulator 104 are as follows:

[0122] The pump light source 108 outputs pump light to the beam combiner 109;

[0123] The combiner 109 combines the pump light and the signal light from the first fiber coupler 102 to obtain combined light;

[0124] The gain fiber 110 receives the combined light, amplifies the signal light using the pump light in the combined light, and outputs it to the cladding power stripper 111.

[0125] The cladding power stripper 111 strips the residual pump light from the signal light amplified by the gain fiber 110 and outputs it to the circulator 104.

[0126] The gain fiber 110 is an erbium-doped fiber.

[0127] The method further includes:

[0128] The data acquisition module 107 receives the electrical signal from the photodetector 106 and performs data acquisition on the electrical signal;

[0129] The measurement system 100 also includes a data processing module;

[0130] The method further includes:

[0131] The data processing module receives the data collected by the data acquisition module 107 and processes it to obtain the fiber length of the fiber laser 112 under test.

[0132] 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 under test 112, and the third port is connected to the second fiber coupler 105.

[0133] The specific steps of the circulator 104 guiding the amplified signal light output from the signal amplification module 103 to the fiber laser under test 112, and simultaneously guiding the backscattered Rayleigh signal output from the fiber laser under test 112 to the second fiber coupler 105 are as follows:

[0134] 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 under test 112, and at the same time uses the second port and the third port to guide the backscattered Rayleigh signal output from the fiber laser under test 112 to the second fiber coupler 105.

[0135] The first fiber coupler 102 splits the laser into the signal light and the reference light at a splitting ratio of 9:1.

[0136] The linear sweep laser 101 adjusts its sweep frequency range and sweep rate to adjust the measurement range and accuracy of the measurement system 100.

[0137] The photodetector 106 is a balanced photodetector;

[0138] The method further includes: the balanced photodetector filtering out the DC component in the electrical signal.

[0139] The measurement system 100 also includes a bandpass filter or a lowpass filter;

[0140] The method further includes:

[0141] The bandpass filter or the lowpass filter receives the electrical signal from the photodetector 106, filters the electrical signal, and outputs it to the data acquisition module 107.

[0142] The measurement system 100 also includes an optical attenuator;

[0143] The method further includes:

[0144] The optical attenuator receives the reference light from the first fiber coupler 102, reduces the power of the reference light, and outputs the reduced-power reference light to the second fiber coupler 105.

[0145] The data acquisition module 107 is an oscilloscope.

[0146] This invention also provides a method for enhancing the intensity of backscattered Rayleigh signals using an optical frequency domain reflectometer (OFDR). The system providing the optical frequency domain reflectometer (OFDR) for enhancing the intensity of backscattered Rayleigh signals 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 under test 205. The optical frequency domain reflectometer 201 includes a jumper 206. Figure 4 This is a flowchart of an optical frequency domain reflectometer (OFDR) method for enhancing the intensity of backscattered Rayleigh signals, provided by an embodiment of the present invention. The embodiment includes the following steps:

[0147] 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 backscattered Rayleigh signals from the third fiber coupler 202 to measure the fiber length of the second fiber laser under test 205.

[0148] S402: The third fiber coupler 202 couples the signal light and outputs it to the second signal amplification module 203, while receiving the backscattered Rayleigh signal output from the second circulator 204, and coupling the backscattered Rayleigh signal to the jumper 206 of the optical frequency domain reflectometer 201.

[0149] S403: The second signal amplification module 203 amplifies the signal light and outputs it to the second circulator 204;

[0150] S404: The second circulator 204 guides the amplified signal light output by the second signal amplification module 203 to the second fiber laser under test 205, and at the same time guides the backscattered Rayleigh signal output from the second fiber laser under test 205 to the third fiber coupler 202.

[0151] S405: The second fiber laser under test 205 generates the backscattered Rayleigh signal using the amplified signal light.

[0152] The optical frequency domain reflectometer 201 further includes: a second linear 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.

[0153] The optical frequency domain reflectometer 201 is connected to the third fiber coupler 202 via the jumper 206, outputs signal light to the third fiber coupler 202, and receives the backscattered Rayleigh signal from the third fiber coupler 202 to measure the fiber length of the second fiber laser under test 205. The specific steps are as follows:

[0154] The second linear sweep laser 207 outputs continuously varying laser light to the fourth fiber coupler 208;

[0155] The fourth fiber coupler 208 divides the laser output from the second linear sweep laser 207 into two paths according to a certain beam splitting ratio. One path is transmitted as a signal light to the third circulator 209, and the other path is transmitted as a reference light to the fifth fiber coupler 210.

[0156] The third circulator 209 guides the signal light output from the fourth fiber coupler 208 to the jumper 206, and at the same time guides the backscattered Rayleigh signal output from the jumper 206 to the fifth fiber coupler 210.

[0157] The fifth fiber coupler 210 receives the backscattered Rayleigh signal output from the third circulator 209 and the reference light output from the fourth fiber coupler 208, and couples the two to obtain a beat frequency optical signal, and outputs the beat frequency optical signal to the second photodetector 211.

[0158] The second photodetector 211 converts the beat-frequency optical signal into an electrical signal and couples it.

[0159] The second data acquisition module 212 acquires the electrical signal from the second photodetector 211 to measure the fiber length of the second fiber laser under test 205.

[0160] Both the second circulator 204 and the third circulator 209 have at least three ports.

[0161] The jumper 206 is an optical fiber, which is fused to or pluggable with the third optical fiber coupler 202.

[0162] The second signal amplification module 203 includes: a second pump light source, a second bundler, a second gain fiber, and a second cladding power stripper;

[0163] The second signal amplification module 203 amplifies the signal light and outputs it to the second circulator 204. The specific steps are as follows:

[0164] The second pump light source outputs pump light to the second beam combiner;

[0165] The second beam combiner combines the pump light and the signal light from the third fiber coupler 202 to obtain combined light;

[0166] The second gain fiber receives the combined light, amplifies the signal light using the pump light in the combined light, and outputs it to the second cladding power stripper.

[0167] The second cladding power stripper removes the residual pump light from the signal light amplified by the second gain fiber and outputs it to the second circulator 204.

[0168] The second gain fiber is an erbium-doped fiber.

[0169] The third fiber coupler 202, the second signal amplification module 203, and the second circulator 204 are an integrated device.

[0170] It should be noted that although several devices, units, or modules of the fiber laser fiber length measurement system have been mentioned in the detailed description above, this division is merely exemplary and not mandatory. In fact, according to embodiments of this 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 and embodied by multiple modules.

[0171] Furthermore, although the operation of the fiber laser fiber length measurement method of this invention is described in a specific order in the accompanying drawings, this does not require or imply that the operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

[0172] While the spirit and principles of this invention have been described with reference to several specific embodiments, it should be understood that this invention is not limited to the disclosed specific embodiments, and the division of aspects does not imply that features in these aspects cannot be combined for benefit; such division is merely for ease of description. This invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A fiber optic laser fiber length measurement system, characterized in that, The system includes: an optical frequency domain reflectometer, a third fiber coupler, a second signal amplification module, a second circulator, and a second fiber laser under test; wherein... The optical frequency domain reflectometer includes a jumper wire, which is connected to the third fiber coupler. The jumper wire is used to output signal light to the third fiber coupler and receive backscattered Rayleigh signals from the third fiber coupler to measure the fiber length of the second fiber laser under test. The third fiber coupler is used to couple the signal light and output it to the second signal amplification module, while receiving the backscattered Rayleigh signal output from the second circulator, and coupling 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 from the second signal amplification module to the second fiber laser under test, and at the same time guide the backscattered Rayleigh signal output from the second fiber laser under test to the third fiber coupler. The second fiber laser under test is used to generate the backscattered Rayleigh signal using the amplified signal light.

2. The fiber optic length measurement system for a fiber laser according to claim 1, characterized in that, The optical frequency domain reflectometer further includes: a second linearly swept laser, a fourth fiber coupler, a third circulator, a fifth fiber coupler, a second photodetector, and a second data acquisition module; wherein... The second linearly swept laser is used to output continuously varying laser light to the fourth fiber coupler; The fourth fiber coupler is used to split the laser output from the second linear sweep laser into two paths according to a certain beam splitting ratio. One path is transmitted as a signal light to the third circulator, and the other path is transmitted as a reference light to the fifth fiber coupler. The third circulator is used to guide the signal light output from the fourth fiber coupler to the jumper, and at the same time guide the backscattered Rayleigh signal output from the jumper to the fifth fiber coupler. The fifth fiber coupler is used to receive the backscattered Rayleigh signal output from the third circulator and the reference light output from the fourth fiber coupler, and 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 then couple it. The second data acquisition module is used to acquire the electrical signal from the second photodetector in order to measure the fiber length of the second fiber laser under test.

3. The fiber optic length measurement system for a fiber laser according to claim 2, characterized in that, Both the second circulator and the third circulator have at least three ports.

4. The fiber optic length measurement system for a fiber laser according to any one of claims 1-3, characterized in that, The jumper is made of optical fiber and is either fused to or pluggable with the third optical fiber coupler.

5. The fiber optic length measurement system for a fiber laser according to any one of claims 1-3, characterized in that, The second signal amplification module includes: a second pump source, a second bundler, 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 fiber coupler to obtain combined light; The second gain 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 in the signal light amplified by the second gain fiber and output it to the second circulator.

6. The fiber optic length measurement system for a fiber laser according to claim 5, characterized in that, The second gain fiber is an erbium-doped fiber.

7. The fiber optic laser fiber length measurement system according to any one of claims 1-3, characterized in that, The third fiber coupler, the second signal amplification module, and the second circulator are an integrated device.

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