A device and method for increasing the number of measurement points in a high-speed fiber grating measurement system

Abstract

The application provides a device and method for increasing the number of measuring points in a high-speed fiber grating measuring system, which comprises a laser, a circulator, a fiber grating array, a dispersion fiber and an erbium-doped fiber amplifier. The application uses only a single pulse laser and only one scanning test time to increase the number of measuring points in the high-speed fiber grating measuring system. Single scanning test is equivalent to scanning all the fiber gratings in the fiber grating array, and the fiber grating array allows the existence of fiber gratings with the same center wavelength, which greatly increases the measuring points of a single channel of the system.

Description

Technical Field

[0001] This invention belongs to the field of fiber Bragg grating measurement, and more specifically, relates to a device and method for increasing the number of measurement points in a high-speed fiber Bragg grating measurement system. Background Technology

[0002] Fiber Bragg grating (FBG) measurement technology combines high precision, high reliability, and environmental adaptability. Its unique wavelength encoding mechanism and powerful networking capabilities make it an important tool in industrial monitoring and cutting-edge scientific research. Compared with other sensing technologies, the main advantages of FBGs lie in their physical characteristics, networking capabilities, and long-term performance. By converting physical quantities of the external environment into wavelength changes in FBGs, FBG sensing technology can measure parameters in most environments.

[0003] Despite its significant advantages, fiber Bragg grating sensing still faces the same challenges as traditional electrical sensing: limitations in the number of measurement channels and the capacity of a single channel measurement point prevent the large-scale deployment of sensors. The device and method of this invention can significantly increase the number of single-channel measurement points compared to existing fiber Bragg grating demodulation systems, thus solving the problem of large-scale fiber Bragg grating sensor deployment to some extent. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a device and method for increasing the number of measurement points in a high-speed fiber optic grating measurement system. This solves the problem of being unable to deploy sensors over a large area due to the limited capacity of single-channel measurement points, thereby multiplying the number of single-channel measurement points.

[0005] According to a first aspect of the present invention, the apparatus for increasing the number of measurement points in a high-speed fiber grating measurement system comprises a laser, a circulator, a fiber grating array, a dispersive fiber, and an erbium-doped fiber amplifier. Lasers are used to emit pulsed light, with operating wavelengths between [wavelength range missing]. ~ Between, the repetition frequency is ; Circulator, the first connection terminal is used to input the pulsed light; Fiber Bragg grating array, the fiber Bragg grating array is connected to the second connection end of the circulator; Dispersive optical fiber, one end of which is connected to the third connector of the circulator; The erbium-doped fiber amplifier has its input end connected to the other end of a dispersive fiber, and its output end is used to connect to a signal detection and acquisition module. In this array, the center wavelength of all fiber gratings is located at ~ Between, and the center wavelength is denoted as , , ... Fiber gratings of different wavelengths exist in a fiber grating array. There are types of fiber gratings with the same wavelength. There are 1, and their spatial order is as follows: , , ... , , , ... , ..., , , ... ,in, The center wavelength is denoted as The x-th fiber grating, x = 1, 2, 3... y = 1, 2, 3... , ~ Let this be the xth period. Both M and are greater than or equal to 2, and the distance between adjacent fiber gratings in each period is fixed. The distance between adjacent period fiber gratings of the same wavelength is fixed. And it satisfies the following formula: ; ; In the formula, At the speed of light, The refractive index of the optical fiber. The length of the dispersive fiber, Dispersion parameters of dispersive optical fibers.

[0006] Preferably, in the device for increasing the number of measurement points in the high-speed fiber optic grating measurement system of the present invention, the laser, circulator, fiber optic grating array, dispersive fiber, and erbium-doped fiber amplifier are all single-mode fiber types.

[0007] Preferably, in the device for increasing the number of measurement points in the high-speed fiber optic grating measurement system of the present invention, the laser is a femtosecond laser, and the emitted light is pulsed broadband light.

[0008] Preferably, in the device for increasing the number of measurement points in the high-speed fiber Bragg grating measurement system of the present invention, the reflectivities of fiber Bragg gratings with the same center wavelength are as follows: , , ... This ensures that the intensity of reflected light is consistent for each grating in the fiber Bragg grating array.

[0009] Preferably, in the device for increasing the number of measurement points in the high-speed fiber Bragg grating measurement system of the present invention, the signal detection and acquisition module includes the functions of optical signal detection and analog signal acquisition, with a sampling rate of... laser repetition frequency More than 1000 times the number of samples are used to ensure sufficient sampling points for signal demodulation.

[0010] Preferably, in the device for increasing the number of measurement points in the high-speed fiber optic grating measurement system of the present invention, the laser outputs a TTL level each time it scans, and the signal detection and acquisition module uses this TTL level as the starting position for each acquisition.

[0011] According to another aspect of the present invention, the method for increasing the number of measurement points in a high-speed fiber optic grating measurement system, used in the aforementioned apparatus, comprises the following steps: The laser emits pulsed light, which is input to the circulator from the first connection terminal; The light from the circulator enters the fiber grating array from the second connection end; Light corresponding to the Bragg wavelength in the fiber Bragg grating array is reflected and enters the circulator from the second connection end, and then enters the dispersive fiber from the third connection end of the circulator; Dispersive fiber expands the reflected light from the third connection of the circulator in the time domain to achieve wavelength-time mapping; Light passing through a dispersive fiber is amplified after entering an erbium-doped fiber amplifier.

[0012] Preferably, the device for increasing the number of measurement points in the high-speed fiber optic grating measurement system of the present invention further includes the following step: The amplified optical signal from the erbium-doped fiber amplifier enters the signal detection and acquisition module for signal detection and acquisition. The reflected light of different wavelengths will exhibit characteristic peaks at different times.

[0013] Beneficial effects This invention utilizes the concept of spectral time-domain expansion. When a pulse of light passes through fiber gratings at different positions in a fiber grating array, the time required for it to reflect back varies, and the distance between adjacent fiber gratings of the same wavelength and period... satisfy Therefore, within a single laser repetition cycle, all fiber gratings of the same wavelength in the fiber grating array can be distinguished. Furthermore, within each cycle, the reflected light from the FBG forms a time-wavelength distribution through the dispersive fiber, and the length of the dispersive fiber... Dispersion parameters Laser scanning range repetition frequency By satisfying certain constraints, the reflected light of FBG at different wavelengths in each cycle will be expanded in the time domain. As a result, the time when the light from the fiber grating at different positions in the fiber grating array is reflected back to the acquisition module is different, thus realizing the measurement of all wavelength FBGs in the fiber grating array.

[0014] The present invention provides an apparatus and method for increasing the number of measurement points in a high-speed fiber grating measurement system. While increasing the number of measurement points in the high-speed fiber grating measurement system, the present invention uses only a single pulse laser and only one scan test time. A single scan test is equivalent to scanning all fiber gratings in the fiber grating array, and fiber gratings with the same center wavelength are allowed to exist in the fiber grating array, which greatly increases the number of measurement points in a single channel of the system. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a device for increasing the number of measurement points in a high-speed fiber optic grating measurement system, provided by an embodiment of the present invention. Figure 2 This is a schematic diagram of a fiber optic grating array according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the spectrum of the fiber grating array reflected light before it passes through the dispersive fiber in an embodiment of the present invention; Figure 4 This is a schematic diagram of the spectrum of the reflected light from the fiber grating array in an embodiment of the present invention after passing through a dispersive fiber; In the diagram: 1 is a laser, 2 is an optical fiber circulator, 3 is a fiber grating array, 4 is a dispersive fiber, 5 is an erbium-doped fiber amplifier, and 6 is a detection and acquisition module. Detailed Implementation

[0016] To make the technical means, creative features, achieved objectives, and effects of this invention easier to understand, the invention is further described below with reference to specific embodiments and accompanying drawings. However, the following embodiments are merely preferred embodiments of this invention and not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments described herein without creative effort are all within the protection scope of this invention.

[0017] To address the aforementioned technical problems, this invention proposes a device and method for increasing the number of measurement points in a high-speed fiber optic grating measurement system. This solves the problem of being unable to deploy sensors over a large area due to the limited capacity of single-channel measurement points, thereby multiplying the number of single-channel measurement points.

[0018] like Figure 1As shown, the device for increasing the number of measurement points in a high-speed fiber grating measurement system includes a laser 1, a circulator 2, a fiber grating array 3, a dispersive fiber 4, and an erbium-doped fiber amplifier 5 (EDFA). The laser 1, circulator 2, fiber grating array 3, dispersive fiber 4, and erbium-doped fiber amplifier 5 are all single-mode fiber types.

[0019] Laser 1 is a femtosecond laser used to emit pulsed light, specifically broadband pulsed light, with an operating wavelength between [insert wavelength here]. ~ Between, the repetition frequency is The first connection of circulator 2 is used to input the pulsed light. Fiber Bragg grating array 3 is connected to the second connection of circulator 2. One end of dispersive fiber 4 is connected to the third connection of circulator 2. Circulator 2 is used to transfer the reflected light from fiber Bragg grating array 3 to signal detection and acquisition module 6. The input of erbium-doped fiber amplifier 5 is connected to the other end of dispersive fiber 4. Dispersive fiber 4 will spread the reflected light from the third connection of circulator 2 in the time domain, realizing wavelength-time mapping. The output of erbium-doped fiber amplifier 5 is used to connect to signal detection and acquisition module 6. Erbium-doped fiber amplifier 5 will amplify the reflected light from dispersive fiber 4. The amplified light will enter signal detection and acquisition module 6. Signal detection and acquisition module 6 includes optical signal detection and analog signal acquisition functions, with a sampling rate of... The repetition frequency of laser 1 More than 1000 times that of the laser to ensure sufficient sampling points for signal demodulation, the laser 1 outputs a TTL level each time it scans, and the signal detection and acquisition module 6 uses this TTL level as the starting position for each acquisition to ensure that the device operates with the same clock.

[0020] A schematic diagram of the fiber grating array 3 is shown below. Figure 2 As shown, the fiber grating parameters in fiber grating array 3 satisfy the following: the fiber gratings are arranged periodically, and within a single period, the wavelengths are arranged from smallest to largest, with no fiber gratings having the same wavelength; the wavelength distribution of the fiber gratings between different periods is exactly the same, differing only in reflectivity. The center wavelength of all fiber gratings in fiber grating array 3 is located at... ~ Between, and the center wavelength is denoted as , , ... Fiber gratings of different wavelengths exist in fiber grating array 3. There are types of fiber gratings with the same wavelength. There are 1, and their spatial order is as follows: , , ... , , , ... , ..., , , ... ,in, The center wavelength is denoted as The x-th fiber grating, x = 1, 2, 3... y = 1, 2, 3... , ~ Let this be the xth period. Both M and are greater than or equal to 2, for example, ~ This is designated as the first cycle. ~ This is denoted as the Mth period. The distance between adjacent fiber Bragg gratings within each period is fixed. The distance between adjacent period fiber gratings of the same wavelength is fixed. The reflectivities of fiber gratings with the same center wavelength are as follows: , , ... This ensures that the intensity of reflected light from each grating in the fiber grating array 3 is consistent.

[0021] Laser 1 emits pulsed light, which, after passing through circulator 2, enters fiber Bragg grating array 3 through the second connection end. Since it is necessary to identify fiber Bragg gratings of the same wavelength with different periods in fiber Bragg grating array 3, different delays of varying lengths are required for the gratings with different periods in the time domain. Therefore, the repetition frequency of laser 1... Distance between fiber gratings of the same wavelength in adjacent periods A relationship exists that satisfies the following formula: ; in, This refers to the number of fiber gratings with the same wavelength, which is also the number of periods in the fiber grating array. The repetition frequency of the femtosecond laser. The distance between fiber gratings of the same wavelength in adjacent periods. At the speed of light, 2 represents the refractive index of the optical fiber, and 2 indicates round trip.

[0022] The light in the pulsed light corresponding to the Bragg wavelength in the fiber grating array 3 is reflected back to the circulator 2 and enters the dispersive fiber 4 from the third connection end of the circulator 2. The dispersive fiber 4 spreads the reflected light from the circulator 2 in the time domain, achieving wavelength-time mapping. The length of the spread is determined by the length of the dispersive fiber 4. Dispersion parameters Laser 1 scanning range repetition frequency The number of gratings with the same wavelength as in fiber optic grating array 3 The decision is made jointly, and the following conditions are met: ; Considering the first period in fiber grating array 3 and There is still a certain spatial distance, therefore the above formula needs to be modified to... ; In the formula, At the speed of light, The refractive index of the optical fiber. The length of dispersive fiber 4, The dispersion parameters of dispersive fiber 4 and Let and represent the start and stop wavelengths of laser 1, and 2 represent the round trip wavelength. The number of fiber gratings of the same wavelength, which is the number of periods of the fiber grating array 3, is the light that enters the erbium-doped fiber amplifier 5 after passing through the dispersive fiber 4. The light is then amplified and finally enters the signal detection and acquisition module 6, where it is saved as data for subsequent calculations.

[0023] Within each cycle, the reflected light from the FBG (Fiber Bragg Grating) forms a time-wavelength distribution through the dispersive fiber. The length of the dispersive fiber, the dispersion parameter, the laser scanning range, and the repetition frequency satisfy the aforementioned formula. Therefore, the reflected light from different wavelengths of the FBG will expand in the time domain within each cycle. Ultimately, the time it takes for the light from the FBG at different positions in the fiber Bragg grating array to return to the acquisition module is different, enabling the measurement of all wavelengths of FBG in the array. Since the FBGs of different wavelengths are located at positions with similar optical path differences, the reflected light will also return within the same cycle. Based on the existing FBG demodulation system, the number of measurement points per channel is increased exponentially, solving to some extent the problem of deploying FBG sensors over a large area.

[0024] According to another aspect of the present invention, the method for increasing the number of measurement points in a high-speed fiber optic grating measurement system, used in the aforementioned apparatus, comprises the following steps: Laser 1 emits pulsed light, which is input from the first connection terminal to circulator 2.

[0025] The light from the circulator 2 enters the fiber optic grating array 3 from the second connection end.

[0026] Light corresponding to the Bragg wavelength in fiber grating array 3 is reflected and enters circulator 2 from the second connection end, then enters dispersive fiber 4 from the third connection end of circulator 2. Within the same period, the gratings are separated by distance between adjacent fiber gratings. Therefore, the return time to the three ports of circulator 2 will have slight differences, exhibiting a phenomenon where shorter wavelengths arrive first and longer wavelengths arrive later. There is a distance between fiber gratings of the same wavelength between adjacent periods. Therefore, the return times to the three ports of circulator 2 will vary considerably, exhibiting a phenomenon where the previous cycle arrives first and the next cycle arrives later. The overall wavelength of the reflected light is as follows: Figure 3 As shown.

[0027] The dispersive fiber 4 expands the reflected light from the third connection end of the circulator 2 in the time domain, achieving wavelength-time mapping. When the reflected light from the fiber grating array 3 enters the dispersive fiber 4, different wavelengths of light undergo different degrees of dispersion. Specifically, shorter wavelengths of light exit the dispersive fiber, while longer wavelengths exit. The final intensity of the reflected light from all fiber gratings in the fiber grating array 3 is as follows: Figure 4 As shown, within the same period of the fiber grating array 3, the fiber gratings exhibit different wavelengths, meaning their dispersion parameters differ within the dispersive fiber 4. Therefore, in the time-wavelength domain, the gratings within the same period will show a phenomenon where shorter wavelengths precede longer wavelengths. This phenomenon is compounded by the different return times of reflected light from fiber gratings at different spatial locations. Conversely, light of the same wavelength within different periods maintains the same dispersion parameter within the dispersive fiber 4, thus the time interval remains constant after the dispersive fiber 4 is unfolded in the time domain.

[0028] The light passing through the dispersive fiber 4 is amplified after entering the erbium-doped fiber amplifier 5.

[0029] The amplified optical signal from the erbium-doped fiber amplifier 5 enters the signal detection and acquisition module 6 for signal detection and acquisition. The reflected light of different wavelengths will exhibit characteristic peaks at different times.

[0030] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0031] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A device for increasing the number of measurement points in a high-speed fiber optic grating measurement system, characterized in that, Include: Lasers are used to emit pulsed light, with operating wavelengths between [wavelength range missing]. ~ Between, the repetition frequency is ; Circulator, the first connection terminal is used to input the pulsed light; Fiber Bragg grating array, the fiber Bragg grating array is connected to the second connection end of the circulator; Dispersive optical fiber, one end of which is connected to the third connector of the circulator; The erbium-doped fiber amplifier has its input end connected to the other end of a dispersive fiber, and its output end is used to connect to a signal detection and acquisition module. In this array, the center wavelength of all fiber gratings is located at ~ Between, and the center wavelength is denoted as , , ... Fiber gratings of different wavelengths exist in a fiber grating array. There are types of fiber gratings with the same wavelength. There are 1, and their spatial order is as follows: , , ... , , , ... , ..., , , ... ,in, The center wavelength is denoted as The x-th fiber grating, x = 1, 2, 3... y = 1, 2, 3... , ~ Let this be the xth period. Both M and are greater than or equal to 2, and the distance between adjacent fiber gratings in each period is fixed. The distance between adjacent period fiber gratings of the same wavelength is fixed. And it satisfies the following formula: ； ； In the formula, At the speed of light, The refractive index of the optical fiber. The length of the dispersive fiber, Dispersion parameters of dispersive optical fibers.

2. The apparatus according to claim 1, characterized in that, The laser, circulator, fiber grating array, dispersive fiber, and erbium-doped fiber amplifier are all single-mode fiber types.

3. The apparatus according to claim 1, characterized in that, The laser is a femtosecond laser, and the emitted light is pulsed broadband light.

4. The apparatus according to claim 1, characterized in that, The reflectivities of fiber gratings with the same center wavelength are as follows: , , ... This ensures that the intensity of reflected light is consistent for each grating in the fiber Bragg grating array.

5. The apparatus according to claim 1, characterized in that, The signal detection and acquisition module includes functions for optical signal detection and analog signal acquisition, with a sampling rate of... laser repetition frequency More than 1000 times the number of samples are used to ensure sufficient sampling points for signal demodulation.

6. The apparatus according to claim 1, characterized in that, The laser outputs a TTL level during each scan, and the signal detection and acquisition module uses this TTL level as the starting position for each acquisition.

7. A method for increasing the number of measurement points in a high-speed fiber Bragg grating measurement system, used in the apparatus as described in any one of claims 1-6, characterized in that, It includes the following steps: The laser emits pulsed light, which is input to the circulator from the first connection terminal; The light from the circulator enters the fiber grating array from the second connection end; Light corresponding to the Bragg wavelength in the fiber Bragg grating array is reflected and enters the circulator from the second connection end, and then enters the dispersive fiber from the third connection end of the circulator; Dispersive fiber expands the reflected light from the third connection of the circulator in the time domain to achieve wavelength-time mapping; Light passing through a dispersive fiber is amplified after entering an erbium-doped fiber amplifier.

8. The method according to claim 7, characterized in that, It also includes the following steps: The amplified optical signal from the erbium-doped fiber amplifier enters the signal detection and acquisition module for signal detection and acquisition. The reflected light of different wavelengths will exhibit characteristic peaks at different times.

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