A sensing optical fiber and an optical fiber sensing system

Abstract

The application provides a sensing optical fiber and an optical fiber sensing system. The sensing optical fiber comprises an optical fiber grating array on the sensing optical fiber. The optical fiber grating array comprises a plurality of grating segments connected in series. The center wavelengths of the grating segments are different. Each grating segment comprises a plurality of gratings with the same center wavelength. The optical fiber sensing system comprises the sensing optical fiber, a first circulator and an interference component. A first interface of the first circulator is configured to receive an optical signal. A second interface of the first circulator is connected to the optical fiber grating array. A third interface of the first circulator is connected to the interference component. The first circulator is configured to transmit the received optical signal to the optical fiber grating array and transmit the reflected light returned by the optical fiber grating array to the interference component. The interference component is configured to generate an interference signal according to the received reflected light. The sensing optical fiber and the optical fiber sensing system can be used for long-distance detection.

Description

Technical Field

[0001] This application relates to the field of fiber optic sensing, and more specifically, to a sensing fiber and a fiber optic sensing system. Background Technology

[0002] Fiber optic sensing systems can use optical fibers as sensing elements to detect and measure various physical quantities, including but not limited to temperature, pressure, strain, displacement, vibration, and sound.

[0003] In fiber optic sensing systems provided by related technologies, changes in external physical quantities affect the transmission characteristics of light in the optical fiber, such as light intensity, phase, polarization, and wavelength. Therefore, changes in external physical quantities can be inferred by measuring changes in the light transmission characteristics. For example, fiber Bragg grating sensing systems can detect changes in temperature or strain by measuring changes in the wavelength of the light reflected from the grating.

[0004] However, in fiber optic sensing systems of related technologies, the grating structure of the sensing fiber often consists of only one grating segment used to reflect pulsed light of the same wavelength. During detection, the detection distance and the transmitted pulse frequency are mutually constrained. Specifically, to avoid pulse aliasing, the longer the detection distance, the lower the transmitted pulse frequency needs to be; however, if the transmitted pulse frequency is too low, it will affect the detection performance of the fiber optic sensing system. Extending the detection distance is currently a research direction. Pulse aliasing refers to the phenomenon where the received reflected light overlaps due to excessively high transmitted pulse frequencies of pulsed light of the same wavelength within the same fiber optic grating segment, causing signal distortion. Summary of the Invention

[0005] The purpose of this application is to provide a sensing fiber and a fiber optic sensing system, wherein the sensing fiber can be used for long-distance detection.

[0006] The first aspect of this application provides a sensing optical fiber, including a fiber grating array located on the sensing optical fiber, the fiber grating array including a plurality of grating segments connected in series, the plurality of grating segments having different center wavelengths, and each grating segment including a plurality of gratings with the same center wavelength.

[0007] In this way, since different grating segments in the fiber optic grating array can reflect light signals of matching wavelengths respectively, reflected light of different wavelengths is obtained. Each reflected light has a different wavelength, which provides the basis for separate processing (reflected light of different wavelengths will not interfere with each other). Therefore, it is only necessary to ensure that the length of the grating segments is not too long to avoid the influence of pulse aliasing. Then, the total length of the entire sensing fiber can be extended by increasing the number of grating segments, thereby enabling long-distance sensing and detection.

[0008] In some embodiments, the lengths of the grating segments are the same; and / or, the grating segments are identical grating segments; and / or, the grating is a weak fiber Bragg grating.

[0009] The second aspect of this application provides an optical fiber sensing system, including a sensing optical fiber, a first circulator, and an interference component provided in any of the embodiments of the first aspect described above. The first interface of the first circulator is configured to receive optical signals; the second interface of the first circulator is connected to the fiber Bragg grating array; and the third interface of the first circulator is connected to the interference component. The first circulator is configured to transmit the received optical signals to the fiber Bragg grating array and to transmit the reflected light returned by the fiber Bragg grating array to the interference component. The interference component is configured to generate an interference signal based on the received reflected light.

[0010] In this way, since different grating segments in the fiber optic grating array can reflect light signals of matching wavelengths respectively, thus obtaining reflected light of different wavelengths, each reflected light has a different wavelength, which provides a basis for separate processing. Therefore, information at different positions on the optical fiber can be detected independently through the reflected light of each grating segment, which is beneficial for realizing long-distance detection of the entire optical fiber.

[0011] In some embodiments, the fiber optic sensing system further includes: A broadband light source, connected to a first interface of the first circulator, configured to emit multiple optical signals, the wavelengths of which are respectively matched to the center wavelengths of the multiple grating segments; and a wavelength division multiplexer, the input interface of which is connected to a third interface of the first circulator, the multiple output interfaces of which are respectively connected to corresponding interference components; the wavelength division multiplexer is configured to separate reflected light with different wavelengths.

[0012] In this way, wavelength division multiplexing is achieved through a broadband light source and a suitable wavelength division multiplexer, so that reflected light of different wavelengths can be separated from each other.

[0013] In some embodiments, the fiber optic sensing system further includes: A tunable laser, the output interface of which is connected to the first interface of the first circulator, is configured to sequentially emit optical signals of different wavelengths; wherein the different wavelengths are respectively matched with the center wavelengths of the plurality of grating segments.

[0014] Since the tunable laser can emit light signals of different wavelengths sequentially at sufficient intervals, there is no situation where multiple reflected light of different wavelengths mix and return to the interference component. Therefore, the wavelength division multiplexer can be eliminated, and the interference effect can be achieved with only one interference component, thereby reducing the system cost.

[0015] In some embodiments, the interferometric assembly includes a second circulator, an interferometer, and a photodetector assembly; a second interface of the second circulator is connected to the interferometer, and a third interface of the second circulator is connected to the photodetector assembly; the output terminal of the interferometer is connected to the photodetector assembly. Where the fiber optic sensing system includes the wavelength division multiplexer, the first interface of the second circulator is connected to the output interface of the wavelength division multiplexer; where the fiber optic sensing system includes the tunable laser, the first interface of the second circulator is connected to the third interface of the first circulator.

[0016] In this way, for each optical signal, the optical signal can be transmitted to the interferometer, and the optical signal output by the interferometer can be transmitted to the photoelectric detection component. The photoelectric detection component can then convert the received optical signal into an electrical signal for subsequent processing.

[0017] In some embodiments, the interferometer includes a coupler, a first Faraday rotator mirror, and a second Faraday rotator mirror; The coupler includes a 3×3 coupler, whose input interface is connected to the second interface of the second circulator; the photodetector assembly includes a first photodetector, a second photodetector, and a third photodetector, with the third interface of the second circulator connected to the first photodetector; the interferometer output includes a first output and a second output, with the first output connected to the second photodetector and the second output connected to the third photodetector; the coupler is configured to transmit optical signals from the second circulator to the first Faraday rotator and the second Faraday rotator, respectively, and to receive reflected light from the first Faraday rotator and the second Faraday rotator, wherein the two reflected lights meet in the coupler and undergo coherent interference, and the interference signal is transmitted to the photodetector assembly; the difference in arm length between the coupler and the first Faraday rotator and between the coupler and the second Faraday rotator is equal to the spacing between two adjacent gratings in the same grating segment.

[0018] In this way, the Michelson interferometer is formed by the coupler, the first Faraday rotator, and the second Faraday rotator. The Michelson interferometer can detect tiny changes in optical path difference and convert these changes into phase changes in the interference light, thereby achieving detection.

[0019] In some embodiments, the fiber optic sensing system further includes: A signal acquisition device, the signal acquisition device including multiple input interfaces, the output interfaces of the first photodetector, the second photodetector and the third photodetector are respectively connected one-to-one with each input interface of the signal acquisition device; A signal processor, wherein the signal input interface of the signal processor is connected to the signal output interface of the signal acquisition unit.

[0020] In some embodiments, the fiber optic sensing system further includes a modulator; In the case where the broadband light source is included in the fiber optic sensing system, the first input interface of the modulator is connected to the output interface of the broadband light source, and the output interface of the modulator is connected to the first input interface of the first circulator; the second input interface of the modulator is connected to the signal output interface of the signal processor. In the case where the tunable laser is included in the fiber optic sensing system, the first input interface of the modulator is connected to the output interface of the tunable laser, the output interface of the modulator is connected to the first input interface of the first circulator, and the second input interface of the modulator is connected to the signal output interface of the signal processor.

[0021] This allows the fiber optic sensing system to flexibly adjust the wavelength of the optical signal according to different measurement needs and environmental conditions.

[0022] In some embodiments, the fiber optic sensing system further includes a first optical power amplifier and a first filter, wherein the input interface of the first optical power amplifier is connected to the output interface of the modulator, the output interface of the first optical power amplifier is connected to the input interface of the first filter, and the output interface of the first filter is connected to the first input interface of the first circulator. And / or, the fiber optic sensing system further includes a second optical power amplifier and a second filter. The input interface of the second optical power amplifier is connected to the third interface of the first circulator, the output interface of the second optical power amplifier is connected to the input interface of the second filter, and the output interface of the second filter is connected to the input interface of the wavelength division multiplexer or directly to the interference component.

[0023] This allows for the generation of low-noise, high-power pulsed light, which significantly improves the signal-to-noise ratio of the optical signal. This enables more precise detection of minute changes in the optical signal, thereby enhancing measurement accuracy and, to some extent, improving the accuracy of the detection.

[0024] In some embodiments, the fiber optic sensing system further includes an optical isolator; wherein, when the fiber optic sensing system includes the broadband light source, the optical isolator is connected in series between the output interface of the broadband light source and the first interface of the first circulator; when the fiber optic sensing system includes the tunable laser, the optical isolator is connected in series between the output interface of the tunable laser and the first interface of the first circulator. This can reduce the possibility of reflected light damaging the broadband light source or the tunable laser after entering it.

[0025] Other features and advantages of this application will be set forth in the following description and will be apparent in part from the description or may be learned by practicing embodiments of this application. The objectives and other advantages of this application may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 A schematic diagram showing the connection relationship between the interference component, the first circulator, and the fiber grating array of a fiber optic sensing system provided for an embodiment of this application; Figure 2 A partial structural schematic diagram of a fiber optic sensing system employing a broadband light source, provided for an embodiment of this application; Figure 3 A partial structural schematic diagram of a fiber optic sensing system employing a tunable laser, provided for an embodiment of this application; Figure 4 A schematic diagram of the structure of an interference component of an optical fiber sensing system provided for an embodiment of this application; Figure 5 A schematic diagram of a fiber optic sensing system using a broadband light source, provided for an embodiment of this application; Figure 6A schematic diagram of another fiber optic sensing system using a broadband light source provided for an embodiment of this application; Figure 7 A schematic diagram of another fiber optic sensing system using a broadband light source provided for an embodiment of this application; Figure 8 A schematic diagram of another fiber optic sensing system using a broadband light source provided for an embodiment of this application; Figure 9 A method based on the implementation of this application is provided. Figure 8 A schematic diagram of the interference signal obtained by the fiber optic sensing system is shown. Figure 10 A schematic diagram of a fiber optic sensing system using a tunable laser, provided for embodiments of this application; 1-Grate segment, 1.1-Grate, 2-First circulator, 3-Interference component, 3.1-Second circulator, 3.2-Photodetector component, 3.3-Coupler, 3.4-First Faraday rotator, 3.5-Second Faraday rotator, 4-Broadband light source, 5-Wavelength division multiplexer, 6-Signal acquisition unit, 7-Signal processor, 8-Modulator, 9-First optical power amplifier, 10-First filter, 11-Second optical power amplifier, 12-Second filter, 13-Optical isolator, 14-Tunable laser. Detailed Implementation

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The components of the embodiments of this application described and shown in the accompanying drawings can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0029] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this application, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0030] It should be noted that, where there is no conflict, the embodiments or technical features in the embodiments described in this application may be combined.

[0031] Please see Figure 1 , Figure 1 This diagram illustrates the connection relationship between an interference component, a first circulator, and a fiber optic grating array in an optical fiber sensing system according to an embodiment of this application. The fiber optic grating array is part of the sensing optical fiber. An embodiment of this application provides a sensing optical fiber including a fiber optic grating array located on it. The fiber optic grating array includes multiple grating segments 1 connected in series, each with a different center wavelength. Each grating segment 1 includes multiple gratings with the same center wavelength. Because different grating segments 1 in the fiber optic grating array can reflect light signals of matching wavelengths, different wavelengths of reflected light are obtained. Since the wavelengths of these reflected lights are different, they can be processed separately (reflected light of different wavelengths will not interfere with each other). Therefore, it is only necessary to ensure that the length of the grating segments is not too long to avoid the influence of pulse aliasing. Then, the total length of the entire sensing optical fiber can be extended by increasing the number of grating segments, making it suitable for long-distance sensing and detection.

[0032] For illustrative purposes, the embodiments of this application are explained using vibration detection. The ability to use it for long-distance detection refers to the ability to extend the length of the entire sensing fiber by improving the structure of the sensing fiber, thus enabling it to be used in conjunction with a fiber optic sensing system for sensing and detection.

[0033] In some embodiments, each of the grating segments 1 has the same length. In some embodiments, each grating segment 1 can be a km long, where a can be any value between [1,3], for example, it can be 1 km, 2 km or 3 km. The total length of n grating segments 1 is then a*n km. In this way, by connecting multiple grating segments with different center wavelengths in series, a whole optical fiber capable of long-distance detection can be formed.

[0034] In some applications, grating segment 1 can be either a high-frequency vibration signal detection grating segment or a low-frequency vibration signal detection grating segment. The length of the high-frequency vibration signal detection grating segment is less than 4 km, and the length of the low-frequency vibration signal detection grating segment is less than 20 km but greater than 4 km. Here, high-frequency vibration signal is defined as a vibration signal with a frequency greater than 5 kHz, and low-frequency vibration signal is defined as a vibration signal with a frequency less than 5 kHz.

[0035] Of course, in some other application scenarios, high-frequency vibration signals refer to signals with frequencies higher than a certain frequency. The terms "high frequency" and "low frequency" can be specifically determined for different application scenarios.

[0036] It is understandable that in some implementations, the lengths of the individual grating segments 1 may also be different. For example, one segment may be 4 km long, and another may be 6 km long.

[0037] In some implementations, the multiple grating segments 1 may include multiple high-frequency vibration signal detection grating segments and multiple low-frequency vibration signal detection grating segments. The flexible combination of high-frequency vibration signal detection grating segments and low-frequency vibration signal detection grating segments can meet the different requirements of detection frequency at different locations, while coordinating to achieve long-distance detection.

[0038] In some alternative embodiments, the grating segment 1 is an identical grating segment. An identical grating segment refers to a single grating segment 1 composed of multiple uniformly spaced gratings 1.1 with essentially the same center wavelength, reflectivity, and bandwidth. Different grating segments 1 have different center wavelengths.

[0039] In some alternative embodiments, the grating 1.1 is a weak fiber Bragg grating. A weak fiber Bragg grating refers to a fiber Bragg grating with a reflectivity of less than 0.1%. Due to its extremely low reflectivity, it can be used to form a weak grating array with thousands of gratings or even larger capacity on a single fiber, thereby enabling high-precision, wide-range detection.

[0040] Same reference Figure 1 Some embodiments of this application provide an optical fiber sensing system, which includes a fiber Bragg grating array, a first circulator 2, and an interference component 3 located on a sensing optical fiber. The fiber Bragg grating array includes multiple grating segments 1 connected in series, each segment having a different center wavelength, and each segment containing multiple gratings 1.1 with the same center wavelength. A first interface of the first circulator 2 is configured to receive an optical signal; a second interface of the first circulator 2 is connected to the fiber Bragg grating array; and a third interface of the first circulator 2 is connected to the interference component 3. The first circulator 2 is configured to transmit the optical signal to the fiber Bragg grating array and to transmit the reflected light from the fiber Bragg grating array in response to the optical signal to the interference component 3. The interference component 3 is configured to generate an interference signal based on the received reflected light.

[0041] In use, the fiber Bragg grating array can receive optical signals of different wavelengths. The wavelengths of the different optical signals are respectively matched with the center wavelength of each grating segment 1. In this way, since different grating segments 1 in the fiber Bragg grating array can reflect optical signals of matched wavelengths respectively, reflected light of different wavelengths is obtained. The different wavelengths of each reflected light provide a basis for separate processing (reflected light of different wavelengths will not interfere with each other). Therefore, it is only necessary to ensure that the length of the grating segment 1 is not too long (for example, a km as mentioned above) to avoid the influence of pulse aliasing. Then, the total length of the entire sensing fiber can be extended by increasing the number of grating segments, thereby enabling long-distance sensing and detection.

[0042] It should be noted that the defects in the solutions in the above-mentioned related technologies are all the result of the inventors' practice and careful research. Therefore, the discovery process of defects and problems, as well as the solutions proposed by the embodiments of this application in response to the above problems, should all be contributions made by the inventors to this application.

[0043] For details, please continue reading. Figure 1 The fiber optic sensing system provided in this application includes a fiber optic grating array, a first circulator 2, and an interference component 3 located on a sensing fiber. The fiber optic grating array includes multiple grating segments 1 connected in series, with different center wavelengths among the multiple grating segments 1. Each grating segment 1 includes multiple gratings 1.1 with the same center wavelength; thus, different grating segments 1 can reflect reflected light of different wavelengths, and gratings 1.1 within the same grating segment 1 can reflect reflected light of the same wavelength. The first interface of the first circulator 2 is configured to receive optical signals, the wavelengths of which are respectively matched with the center wavelengths of each of the plurality of grating segments 1; the second interface of the first circulator 2 is connected to the fiber grating array, and the third interface of the first circulator 2 is connected to the interference component 3; the first circulator 2 is configured to transmit the received optical signals to the fiber grating array and to transmit the reflected light returned by the fiber grating array to the interference component 3; thus, for each optical signal emitted by the light source, the optical signal can be transmitted to the interference component 3 after being reflected by the grating 1.1, so that the interference component 3 can generate an interference signal based on the received reflected light.

[0044] It is understood that a fiber optic grating array includes multiple grating segments 1 connected in series with different center wavelengths. Each grating 1.1 within a grating segment 1 can reflect light corresponding to its own center wavelength. For the reflected light from adjacent gratings 1.1 within the same grating segment 1, the interference component 3 can generate an interference signal based on the two, thereby enabling detection based on the interference signal.

[0045] Furthermore, in practical applications, optical fibers containing fiber optic grating arrays can be deployed in the work area, thereby enabling the detection of the work area using the aforementioned fiber optic sensing system including the fiber optic grating array. The work area may, for example, include an intrusion detection area or a vandalism detection area.

[0046] Please continue reading. Figure 2In some embodiments, the fiber optic sensing system further includes a broadband light source 4 and a wavelength division multiplexer 5. The broadband light source 4 is connected to the first interface of the first circulator 2, and is configured to emit multiple optical signals, the wavelengths of which are respectively matched to the center wavelengths of the multiple grating segments 1. This allows each grating 1.1 within each grating segment 1 of the fiber optic grating array to reflect the optical signal corresponding to its center wavelength, thereby enabling long-distance detection of the entire optical fiber.

[0047] The aforementioned broadband light source 4 may include, but is not limited to, broadband semiconductor light sources, superfluorescent fiber light sources, etc.

[0048] It should be noted that the fiber optic grating array includes multiple grating segments 1, and the center wavelengths of these multiple grating segments 1 are different. Therefore, wavelength division multiplexing (WDM) can be used to separate reflected light of different wavelengths for signal acquisition and demodulation processing. Thus, the aforementioned fiber optic sensing system can achieve the WDM effect using a WDM multiplexer 5. Specifically, the input interface of the WDM multiplexer 5 is connected to the third interface of the first circulator 2, and the multiple output interfaces of the WDM multiplexer 5 are respectively connected to corresponding interference components 3; the WDM multiplexer 5 is configured to separate reflected light of different wavelengths.

[0049] In this embodiment, wavelength division multiplexing is achieved through a broadband light source 4 and a compatible wavelength division multiplexer 5.

[0050] In some alternative implementations, please refer to Figure 3 In some embodiments, the fiber optic sensing system further includes a tunable laser 14, the output interface of which is connected to the first interface of the first circulator 2, and the tunable laser 14 is configured to sequentially emit optical signals of different wavelengths; wherein the different wavelengths are respectively matched with the center wavelengths of the plurality of grating segments 1.

[0051] In some applications, the wavelength of the light signal emitted by the tunable laser 14 can be matched (e.g., equal) to the center wavelength of each center wavelength in grating segment 1. Then, a light signal with the matched wavelength is generated and only that light signal is transmitted. After passing through the grating 1.1 corresponding to the center wavelength, reflected light of the corresponding wavelength can be obtained. This reflected light is then transmitted to the interference component 3 to obtain an interference signal. Since the tunable laser can emit light signals of different wavelengths sequentially at sufficient intervals, there is no situation where multiple reflected lights of different wavelengths mix and return to the interference component 3. Therefore, the wavelength division multiplexer 5 can be eliminated, and the interference effect can be achieved with only one interference component 3, thereby reducing system costs.

[0052] Of course, in some implementations, if the interval between the tunable laser emitting light signals of different wavelengths is too short, a wavelength division multiplexer 5 can also be added.

[0053] For ease of understanding, this application will use an optical fiber sensing system including a broadband light source 4 and a wavelength division multiplexer 5 as an example to illustrate other devices that may exist in the system.

[0054] For some alternative implementation methods, please refer to [link / reference needed]. Figure 4 The interference component 3 includes a second circulator 3.1, an interferometer, and a photoelectric detection component 3.2; wherein, the first interface of the second circulator 3.1 is connected to the output interface of the wavelength division multiplexer 5, the second interface of the second circulator 3.1 is connected to the interferometer, the third interface of the second circulator 3.1 is connected to the photoelectric detection component 3.2, and the output end of the interferometer is connected to the photoelectric detection component 3.2.

[0055] The aforementioned interferometers may include, for example, the Michelson interferometer and the Mach-Zehnder interferometer.

[0056] In this embodiment, for each optical signal, the optical signal can be transmitted to an interferometer, and the optical signal output by the interferometer can be transmitted to the photoelectric detection component 3.2. The photoelectric detection component 3.2 can then convert the received optical signal into an electrical signal for subsequent processing.

[0057] In some optional embodiments, the interferometer includes a coupler 3.3, a first Faraday rotator 3.4, and a second Faraday rotator 3.5; wherein the coupler 3.3 includes a 3×3 coupler, the input interface of which is connected to the second interface of the second circulator 3.1; the photodetector assembly 3.2 includes a first photodetector (not shown), a second photodetector (not shown), and a third photodetector (not shown), the third interface of the second circulator 3.1 is connected to the first photodetector, and the output end of the interferometer includes a first output end and a second output end (i.e., the first output end and the second output end of the coupler 3.3); the first output end of the interferometer is connected to the second photodetector, and the second output end of the interferometer is connected to the third photodetector.

[0058] The coupler 3.3 is configured to transmit the optical signal from the second circulator 3.1 to the first Faraday rotator 3.4 and the second Faraday rotator 3.5 respectively, and to receive the reflected light from the first Faraday rotator 3.4 and the second Faraday rotator 3.5 in the coupler 3.3, wherein the two reflected lights meet in the coupler 3.3 and undergo coherent interference, and the interference signal is transmitted to the photodetector 3.2; the difference in arm length between the coupler 3.3 and the first Faraday rotator 3.4 and between the coupler 3.3 and the second Faraday rotator 3.5 is equal to the spacing between two adjacent gratings 1.1 in the same grating segment 1.

[0059] It is understandable that the coupler 3.3, the first Faraday rotator 3.4, and the second Faraday rotator 3.5 constitute a Michelson interferometer. Since the aforementioned length difference is equal to the spacing between two adjacent gratings 1.1 in the same grating segment 1, the reflected light from the first Faraday rotator 3.4 and the reflected light from the second Faraday rotator 3.5 can coherently interfere in the coupler 3.3, thereby generating an interference signal.

[0060] In this embodiment, a Michelson interferometer is formed by a coupler 3.3, a first Faraday rotator 3.4, and a second Faraday rotator 3.5. The Michelson interferometer can detect minute changes in optical path difference, which helps to improve the accuracy of detection to a certain extent.

[0061] Please continue reading. Figure 5 In some embodiments, the fiber optic sensing system further includes a signal acquisition unit 6 and a signal processor 7. The signal acquisition unit 6 includes multiple input interfaces, each connected to the output interface of the photodetector component 3.2; that is, the output interfaces of the first photodetector, the second photodetector, and the third photodetector are connected one-to-one to each input interface of the signal acquisition unit 6. The signal acquisition unit 6 converts the electrical signal into a digital signal. The signal input interface of the signal processor 7 is connected to the signal output interface of the signal acquisition unit 6. The signal processor 7 is configured to detect vibration information in the fiber optic grating array based on the digital signal, i.e., to perform demodulation analysis.

[0062] Understandably, the multiple output interfaces of the wavelength division multiplexer 5 are each connected to a corresponding interference component 3. Therefore, each interference component 3 can include a photoelectric detection component 3.2.

[0063] Furthermore, after obtaining the digital signal, the signal acquisition unit 6 can transmit it to the signal processor 7, which may include, for example, an FPGA (Field Programmable Gate Array), an embedded controller, etc.

[0064] After receiving the digital signal transmitted by the photoelectric detection component 3.2, the signal processor 7 can determine the vibration information on the optical fiber based on the digital signal. This vibration information may include, for example, information about whether a vibration event has occurred and the location of the vibration event.

[0065] Please continue reading. Figure 6 In some embodiments, the fiber optic sensing system further includes a modulator 8. When the fiber optic sensing system includes the broadband light source 4, the first input interface of the modulator 8 is connected to the output interface of the broadband light source 4, and the output interface of the modulator 8 is connected to the first input interface of the first circulator 2. The second input interface of the modulator 8 is connected to the signal output interface of the signal processor 7. The modulator 8 is configured to modulate the optical signal into pulsed light, or to modulate the optical signal into pulsed light according to the instructions of the signal processor 7.

[0066] It is understandable that modulator 8 can modulate the optical signal emitted by broadband light source 4 so as to encode the vibration information to be measured into the optical signal, thereby realizing the detection of vibration information.

[0067] Furthermore, the modulator 8 mentioned above may include, but is not limited to, SOA (Semiconductor Optical Amplifier), EAM (Electro-Absorption Modulator), AOM (Acousto-Optic Modulator), etc.

[0068] In some applications, modulator 8 can modulate the optical signal according to a preset wavelength to generate pulsed light that matches the center wavelength of each grating segment 1.

[0069] In other application scenarios, modulator 8 can also receive instructions from signal processor 7, which may include wavelength information. This allows modulator 8 to dynamically adjust the wavelength of the optical signal according to these instructions, generating pulsed light of the corresponding wavelength. This dynamic modulation method enables the fiber optic sensing system to flexibly adjust the wavelength of the optical signal according to different measurement requirements and environmental conditions. The dynamic wavelength modulation by modulator 8 is existing technology and is not specifically limited.

[0070] Please refer to section 7. In some embodiments, the fiber optic sensing system further includes a first optical power amplifier 9 and a first filter 10. The input interface of the first optical power amplifier 9 is connected to the output interface of the modulator 8, and the output interface of the first optical power amplifier 9 is connected to the input interface of the first filter 10. The first optical power amplifier 9 is configured to amplify the optical power corresponding to the pulsed light. The output interface of the first filter 10 is connected to the first input interface of the first circulator 2. The first filter 10 is configured to filter noise generated by the first optical power amplifier 9.

[0071] In these application scenarios, the first optical power amplifier 9 may include, but is not limited to, EDFA (Erbium-Doped Fiber Amplifier) ​​and TDFA (Thulium-Doped Fiber Amplifier).

[0072] For example, modulator 8 can output pulsed light, EDFA can receive the pulsed light, then amplify the optical power of the pulsed light, and then transmit the amplified pulsed light to the first filter 10. The first filter 10 filters out the noise generated after the EDFA amplification process, thereby obtaining low-noise, high-power pulsed light.

[0073] In this embodiment, low-noise, high-power pulsed light can be obtained through the first optical power amplifier 9 and the first filter 10. This low-noise, high-power pulsed light can significantly improve the signal-to-noise ratio of the optical signal, thereby improving the measurement accuracy and, to a certain extent, the detection accuracy.

[0074] Additionally, please refer to section 7. In some of the described embodiments, the fiber optic sensing system further includes a second optical power amplifier 11 and a second filter 12, wherein the input interface of the second optical power amplifier 11 is connected to the third interface of the first circulator 2, and the output interface of the second optical power amplifier 11 is connected to the input interface of the second filter 12; the second optical power amplifier 11 is configured to amplify the optical power corresponding to the reflected light; the output interface of the second filter 12 is connected to the input interface of the wavelength division multiplexer 5; and the second filter 12 is configured to filter the noise generated by the second optical power amplifier 11.

[0075] Similarly, the second optical power amplifier 11 may include, but is not limited to, EDFA (Erbium-Doped Fiber Amplifier) ​​and TDFA (Thulium-Doped Fiber Amplifier).

[0076] For example, the EDFA can receive the reflected light output from the first circulator 2, amplify the optical power of the reflected light, and then transmit the amplified reflected light to the second filter 12. The second filter 12 filters out the noise generated after the EDFA amplification process, thereby obtaining low-noise, high-power reflected light.

[0077] In this embodiment, low-noise, high-power reflected light can also be obtained through the second optical power amplifier 11 and the second filter 12, thus significantly improving the signal-to-noise ratio of the optical signal.

[0078] In some alternative implementations, please refer to 8. The fiber optic sensing system further includes an optical isolator 13, wherein, when the broadband light source 4 is included in the fiber optic sensing system, the input interface of the optical isolator 13 is connected to the output interface of the broadband light source 4, and the output interface of the optical isolator 13 is connected to the first interface of the first circulator 2 (that is, the optical isolator string 13 is connected in series between the output interface of the broadband light source 4 and the first interface of the first circulator 2). Please refer to [further details omitted]. Figure 10 In the case where the tunable laser 14 is included in the fiber optic sensing system, the input interface of the optical isolator 13 is connected to the output interface of the tunable laser 14; the output interface of the optical isolator 13 is connected to the first interface of the first circulator 2 (that is, the optical isolator 13 is connected in series between the output interface of the tunable laser 14 and the first interface of the first circulator 2); wherein, the optical isolator 13 is configured to isolate the reflected light of the fiber grating array.

[0079] Here, the optical isolator 13 can utilize optical isolation mechanisms (such as Faraday rotation or magneto-optical effect) to ensure that the optical signal can only pass in one direction. When the optical signal is emitted from the broadband light source 4 and passes through the optical isolator 13, the optical isolator 13 allows the optical signal to pass through. If any reflected light attempts to return to the broadband light source 4, the optical isolator 13 will block these reflected lights to prevent the reflected light from interfering with the light source and to reduce the possibility of the reflected light damaging the broadband light source 4 or the tunable laser 14 after entering the tunable laser 14.

[0080] Please continue reading. Figure 8The broadband light source 4 can emit optical signals covering the center wavelength of each of the multiple fiber segments 1 in the fiber grating array. These optical signals can enter the modulator 8 through the optical isolator 13. After passing through the modulator 8, the optical signals can generate pulsed light of the corresponding wavelength. After passing through the first optical power amplifier 9, the pulsed light can obtain high-power pulsed light. Then, after passing through the first filter 10 to filter out the noise, low-noise, high-power pulsed light can be obtained. The pulsed light is further transmitted to the first circulator 2, and then transmitted to the fiber grating array through the first circulator 2. The fiber grating array can reflect the above-mentioned pulsed light, thereby obtaining reflected light of different wavelengths. These reflected lights are respectively transmitted through the first circulator 2 to the second optical power amplifier 11. After being amplified by the second optical power amplifier 11, they enter the second filter 12 to filter out the noise, thereby obtaining high-power, low-noise reflected light. The reflected light of different wavelengths is separated one by one by the wavelength division multiplexer 5. Then, it is transmitted to the corresponding interference component 3 through the respective output interface of the wavelength division multiplexer 5. Within each interferometer component 3, reflected light from the wavelength division multiplexer 5 is transmitted to the coupler 3.3 via a second circulator 3.1. Adjacent reflected light beams are then transmitted to the first Faraday rotator 3.4 and the second Faraday rotator 3.5, respectively. After reflection, an interference signal is generated within the coupler 3.3. This interference signal is then transmitted to the second circulator 3.1, and subsequently to the photodetector component 3.2, where it is converted into an electrical signal. The photodetector component 3.2 of each interferometer component 3 then transmits the output electrical signal to the signal acquisition unit 6. The signal acquisition unit 6 acquires these electrical signals and converts them into digital signals, which are then transmitted to the signal processor 7 for processing to achieve detection. Additionally, the signal processor 7 can send commands to the modulator 8 to instruct it to modulate pulsed light of the corresponding wavelength.

[0081] Please continue reading. Figure 9 It illustrates an embodiment of the present application based on Figure 8 The diagram shows the interference signal obtained by the fiber optic sensing system, as shown below. Figure 9 As shown, the reflected light from the first Faraday rotator 3.4 and the second Faraday rotator 3.5 undergoes an interference effect in the coupler 3.3, thereby obtaining an interference signal.

[0082] This application further describes an optical fiber sensing system including a tunable laser 14. It is understood that the wavelength division multiplexer 5 may not be present in this optical fiber sensing system.

[0083] It is understood that, when using the tunable laser 14, the fiber optic sensing system may also include the modulator 8, the first optical power amplifier 9 and the first filter 10, the second optical power amplifier 11 and the second filter 12, the signal acquisition unit 6, the signal processor 7, the optical isolator 13, etc., and the structure within the interference component 3 may be the same as or similar to that in the above embodiments.

[0084] Please see Figure 10 This illustrates yet another fiber optic sensing system provided by an embodiment of this application, such as... Figure 10 As shown, the narrow-linewidth optical signals emitted sequentially by the tunable laser 14 can enter the modulator 8 through the optical isolator 13. After passing through the modulator 8, the optical signals can generate pulsed light of the corresponding wavelength. This pulsed light passes through the first optical power amplifier 9 to obtain high-power pulsed light. Then, after passing through the first filter 10 to filter out the noise, low-noise, high-power pulsed light can be obtained. This pulsed light is further transmitted to the first circulator 2, and then transmitted to the fiber optic grating array. The fiber optic grating array can reflect the pulsed light, thereby obtaining reflected light of different wavelengths. These reflected lights are respectively transmitted through the first circulator 2 to the second optical power amplifier 11. After being amplified by the second optical power amplifier 11, they enter the second filter 12 to filter out the noise, thereby obtaining high-power, low-noise reflected light. The reflected light is then directly transmitted to the interference component 3. Inside the interference component 3, the reflected light from the second filter 12 is transmitted to the coupler 3.3 via the second circulator 3.1. Adjacent reflected light beams are transmitted to the first Faraday rotator mirror 3.4 and the second Faraday rotator mirror 3.5, respectively. After reflection by both mirrors, interference light is generated within the coupler 3.3. The coupler 3.3 then transmits this interference light to the second circulator 3.1, which in turn transmits it to the photodetector component 3.2. The photodetector component 3.2 converts the interference light into an electrical signal. The photodetector component 3.2 then transmits the output electrical signal to the signal acquisition unit 6. The signal acquisition unit 6 acquires these electrical signals and converts them into digital signals, which can then be transmitted to the signal processor 7 for processing to achieve detection. Additionally, the signal processor 7 can send instructions to the modulator 8 to modulate pulsed light of the corresponding wavelength.

[0085] It should be noted that the structure, purpose, and technical effects of each device are described in the corresponding sections above, and will not be repeated here. Furthermore, in the absence of the broadband light source 4 and the wavelength division multiplexer 5, the first interface of the first circulator 2 is connected to the tunable laser 14, and the third interface of the first circulator 2 is directly connected to an interference component 3. The connection methods of the remaining devices are also described in the corresponding sections above, and will not be repeated here.

[0086] It should be noted that the above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A sensing optical fiber, characterized by, The fiber grating array is located on a sensing fiber, the fiber grating array comprising multiple grating segments connected in series, the center wavelengths of the multiple grating segments being different, and each grating segment comprising multiple gratings with the same center wavelength.

2. The sensing optical fiber according to claim 1, characterized in that, All the grating segments are of the same length; and / or, The grating segment is an identical grating segment; and / or, The grating is a weak fiber Bragg grating.

3. An optical fiber sensing system characterized by, Includes the sensing fiber, the first circulator, and the interference component as described in any one of claims 1-2; The first interface of the first circulator is configured to receive optical signals; the second interface of the first circulator is connected to the fiber Bragg grating array; and the third interface of the first circulator is connected to the interference component. The first circulator is configured to transmit the received optical signals to the fiber Bragg grating array and to transmit the reflected light returned by the fiber Bragg grating array to the interference component. The interference component is configured to generate an interference signal based on the received reflected light.

4. The optical fiber sensing system of claim 3, wherein, The fiber optic sensing system also includes: A broadband light source, connected to a first interface of the first circulator, configured to emit multiple optical signals, the wavelengths of which are respectively matched to the center wavelengths of the multiple grating segments; and A wavelength division multiplexer, wherein the input interface of the wavelength division multiplexer is connected to the third interface of the first circulator, and the multiple output interfaces of the wavelength division multiplexer are respectively connected to corresponding interference components; the wavelength division multiplexer is configured to separate reflected light with different wavelengths.

5. The optical fiber sensing system of claim 3, wherein, The fiber optic sensing system also includes: A tunable laser, the output interface of which is connected to the first interface of the first circulator, is configured to sequentially emit optical signals of different wavelengths; wherein the different wavelengths are respectively matched with the center wavelengths of the plurality of grating segments.

6. The optical fiber sensing system according to any of claims 4-5, characterized in that, The interference assembly includes a second circulator, an interferometer, and a photoelectric detection assembly. The second interface of the second circulator is connected to the interferometer, and the third interface of the second circulator is connected to the photoelectric detection assembly. The output terminal of the interferometer is connected to the photoelectric detection assembly. Where the fiber optic sensing system includes the wavelength division multiplexer, the first interface of the second circulator is connected to the output interface of the wavelength division multiplexer; where the fiber optic sensing system includes the tunable laser, the first interface of the second circulator is connected to the third interface of the first circulator.

7. The optical fiber sensing system of claim 6, wherein, The interferometer includes a coupler, a first Faraday rotator, and a second Faraday rotator; The coupler includes a 3×3 coupler, whose input interface is connected to the second interface of the second circulator; the photodetector assembly includes a first photodetector, a second photodetector, and a third photodetector, with the third interface of the second circulator connected to the first photodetector; the interferometer output includes a first output and a second output, with the first output connected to the second photodetector and the second output connected to the third photodetector; the coupler is configured to transmit optical signals from the second circulator to the first Faraday rotator and the second Faraday rotator, respectively, and to receive reflected light from the first Faraday rotator and the second Faraday rotator, wherein the two reflected lights meet in the coupler and undergo coherent interference, and the interference signal is transmitted to the photodetector assembly; the difference in arm length between the coupler and the first Faraday rotator and between the coupler and the second Faraday rotator is equal to the spacing between two adjacent gratings in the same grating segment.

8. The optical fiber sensing system of claim 7, wherein, The fiber optic sensing system also includes: A signal acquisition device, the signal acquisition device including multiple input interfaces, the output interfaces of the first photodetector, the second photodetector and the third photodetector are respectively connected one-to-one to each input interface of the signal acquisition device; A signal processor, wherein the signal input interface of the signal processor is connected to the signal output interface of the signal acquisition unit.

9. The optical fiber sensing system of claim 8, wherein, The fiber optic sensing system also includes a modulator; In the case where the broadband light source is included in the fiber optic sensing system, the first input interface of the modulator is connected to the output interface of the broadband light source, and the output interface of the modulator is connected to the first input interface of the first circulator; the second input interface of the modulator is connected to the signal output interface of the signal processor. In the case where the tunable laser is included in the fiber optic sensing system, the first input interface of the modulator is connected to the output interface of the tunable laser, the output interface of the modulator is connected to the first input interface of the first circulator, and the second input interface of the modulator is connected to the signal output interface of the signal processor.

10. The fiber optic sensing system according to claim 9, characterized in that, The fiber optic sensing system further includes a first optical power amplifier and a first filter. The input interface of the first optical power amplifier is connected to the output interface of the modulator, the output interface of the first optical power amplifier is connected to the input interface of the first filter, and the output interface of the first filter is connected to the first input interface of the first circulator. And / or, The fiber optic sensing system further includes a second optical power amplifier and a second filter. The input interface of the second optical power amplifier is connected to the third interface of the first circulator, the output interface of the second optical power amplifier is connected to the input interface of the second filter, and the output interface of the second filter is connected to the input interface of the wavelength division multiplexer or directly to the interference component. And / or, The fiber optic sensing system further includes an optical isolator, wherein, when the fiber optic sensing system includes the broadband light source, the optical isolator is connected in series between the output interface of the broadband light source and the first interface of the first circulator; and when the fiber optic sensing system includes the tunable laser, the optical isolator is connected in series between the output interface of the tunable laser and the first interface of the first circulator.

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