Fiber Bragg Grating Multi-channel High-speed Demodulation System and Method

Abstract

This invention relates to a multi-channel high-speed demodulation system and method for fiber Bragg gratings, comprising: a tunable laser source for outputting a wavelength-tunable first optical signal; an optical splitter for dividing the first optical signal into multiple second optical signals; a multi-channel fiber Bragg grating for detecting high-frequency signals according to a preset optical channel opening sequence under the action of the multiple second optical signals, and outputting multiple third optical signals; an optical switch for switching the optical channels in the multi-channel fiber Bragg grating according to the preset optical channel opening sequence; a photodetector for converting the multiple third optical signals into multiple voltage signals; a data acquisition card for acquiring the voltage signals output by the photodetector; and a computer for generating control commands based on the voltage signals. This invention improves the sensitivity and stability of detection.

Description

Technical Field

[0001] This invention relates to the field of fiber Bragg grating sensing and detection technology, and in particular to a multi-channel high-speed demodulation system and method for fiber Bragg gratings. Background Technology

[0002] A fiber optic grating demodulation system is a detection system that uses demodulation methods to demodulate the center wavelength shift of a fiber optic grating into information related to the signal under test.

[0003] Traditional fiber Bragg grating demodulation systems detect signals at low frequencies, primarily used for detecting low-frequency vibrations and temperatures. Due to the frequency limitations of the demodulation method, they cannot be applied to high-frequency signal detection environments such as acoustic emission and ultrasound. Furthermore, the detection of high-frequency signals places high demands on the light source of the detection system; existing high-speed fiber Bragg grating demodulation systems mostly employ a single optical channel, limiting the detection position and resulting in low light source utilization. Additionally, the application environment of traditional fiber Bragg grating demodulation systems is susceptible to temperature variations and the influence of low-frequency stress signals, making long-term stable detection and demodulation impossible.

[0004] Therefore, how to design a fiber Bragg grating multi-channel high-speed demodulation system and method to improve detection sensitivity and stability is an urgent problem to be solved. Summary of the Invention

[0005] In view of this, it is necessary to provide a fiber Bragg grating multi-channel high-speed demodulation system and method to improve the sensitivity and stability of detection.

[0006] To address the aforementioned problems, in a first aspect, the present invention provides a fiber Bragg grating multi-channel high-speed demodulation system, comprising:

[0007] A tunable laser source for outputting a first optical signal with a tunable wavelength;

[0008] An optical splitter is used to divide the first optical signal into multiple second optical signals;

[0009] A multi-channel fiber optic grating is used to detect high-frequency signals according to a preset optical channel opening sequence under the action of multiple second optical signals, and output multiple third optical signals.

[0010] An optical switch is used to switch the optical channels in the multi-channel fiber Bragg grating according to a preset optical channel opening sequence.

[0011] A photodetector is used to convert the plurality of third optical signals into a plurality of voltage signals;

[0012] A data acquisition card is used to acquire the voltage signal output by the photodetector;

[0013] The host computer is used to generate control commands based on the voltage signal.

[0014] Furthermore, the center wavelength of each individual fiber grating in the multi-channel fiber grating is within a preset wavelength range.

[0015] Furthermore, the optical channel switching rate of the optical switch is 200kHz.

[0016] Furthermore, the host computer specifically includes:

[0017] A data display module is used to display the voltage signal;

[0018] The laser control module is used to generate a first control command for the first output wavelength of the laser source;

[0019] The optical switch control module is used to generate a second control command for opening and closing any optical channel according to a preset optical channel opening sequence.

[0020] Furthermore, the first output wavelength of the laser source is determined based on the center wavelength of the multi-channel fiber grating.

[0021] Furthermore, the multi-channel fiber grating includes multiple detection fiber gratings and one reference fiber grating, wherein the reference fiber is unaffected by stress.

[0022] Furthermore, the photodetector is also used to convert multiple third optical signals passing through the detected fiber optic grating into multiple first voltage signals, and to convert the third optical signals passing through the reference fiber optic grating into second voltage signals.

[0023] The computer is also used to calculate multiple voltage differences between the plurality of first voltage signals and the second voltage signals, and to determine the correspondence between stress and wavelength displacement based on the multiple voltage differences and the fitting curve of the center wavelength displacement of the multi-channel fiber optic grating.

[0024] The laser control module is also used to generate a third control command for the second output wavelength of the laser source based on the correspondence.

[0025] Furthermore, the wavelength of the second output light is determined in real time based on the wavelength displacement.

[0026] Secondly, the present invention also provides a method for high-speed demodulation of fiber Bragg gratings (FBGs) in multiple channels, applied to the aforementioned high-speed demodulation system, comprising:

[0027] The first output wavelength of the tunable laser source output optical signal is determined based on the center wavelength of the fiber grating.

[0028] The optical signal is output to the multi-channel fiber optic grating sensing and channel switching optical path via an optical splitter, and the opening sequence of each channel is controlled based on the optical switch.

[0029] High-frequency signal data from different optical channels are acquired and converted into voltage signal data by a photodetector, and the voltage difference between the detected fiber optic grating and the reference fiber optic grating is calculated respectively.

[0030] The wavelength displacement under the current stress is determined by fitting the voltage difference and the center wavelength displacement of the multi-channel fiber grating.

[0031] Based on the wavelength shift, the first output light wavelength of the tunable laser source output light signal is adjusted to the second output light wavelength.

[0032] Furthermore, the tunable laser light source dynamically adjusts the output light wavelength.

[0033] The beneficial effects of using the above embodiments are:

[0034] This invention employs multi-channel high-speed demodulation of fiber Bragg gratings, which expands the detection position and improves the utilization rate of the light source. Furthermore, the optical switch, as the core device for multi-channel high-frequency demodulation, can meet the functional requirements of continuous high-frequency signal detection. Since photodetectors are highly sensitive to changes in the light source, and considering the large information content of high-frequency signals and the frequency influence of low-frequency signals, a wavelength control command is generated by the output voltage signal and sent to a tunable laser source. This allows the tunable laser source to perform laser compensation, ensuring that the output wavelength of the tunable laser always tracks the wavelength displacement of the detection fiber Bragg grating and matches it within the matching wavelength range. Therefore, the high-frequency detection system can maintain high detection sensitivity and stability at all times. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of an embodiment of a fiber Bragg grating multi-channel high-speed demodulation system provided by the present invention;

[0036] Figure 2 A computer software program logic block diagram provided in an embodiment of the present invention;

[0037] Figure 3 This is a schematic diagram illustrating wavelength matching of a laser source before and after a fiber optic grating is subjected to low-frequency stress, according to an embodiment of the present invention.

[0038] Figure 4 This is a flowchart illustrating an embodiment of the fiber Bragg grating multi-channel high-speed demodulation method provided by the present invention. Detailed Implementation

[0039] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0040] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. Furthermore, "a plurality of" means two or more, unless otherwise explicitly specified. The reference to "embodiment" herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0041] The specific embodiments are described in detail below:

[0042] Please see Figure 1 , Figure 1 This is a schematic diagram of an embodiment of a fiber Bragg grating multi-channel high-speed demodulation system provided by the present invention. A specific embodiment of the present invention discloses a fiber Bragg grating multi-channel high-speed demodulation system 100, including: a tunable laser source 101, an optical splitter 102, a multi-channel fiber Bragg grating 103, an optical switch 104, a photodetector 105, a data acquisition card 106, a computer 107, a data acquisition controller 108, and a data output module 109.

[0043] The system includes: a tunable laser source 101 for outputting a wavelength-tunable first optical signal; an optical splitter 102 for splitting the first optical signal into multiple second optical signals; a multi-channel fiber Bragg grating 103 for detecting high-frequency signals according to a preset optical channel opening sequence under the action of multiple second optical signals, and outputting multiple third optical signals; an optical switch 104 for switching optical channels in the multi-channel fiber Bragg grating according to a preset optical channel opening sequence; a photodetector 105 for converting multiple third optical signals into multiple voltage signals; a data acquisition card 106 for acquiring the voltage signals output by the photodetector; and a computer 107 for generating control commands based on the voltage signals.

[0044] Understandably, according to Figure 1 As shown in the structural diagram of the fiber Bragg grating multi-channel high-speed demodulation system, the system consists of hardware and software components. The hardware component mainly involves the construction of the multi-channel fiber Bragg grating detection optical path for high-frequency signals, specifically including an adjustable laser source and its control circuit, a multi-channel fiber Bragg grating sensing and channel switching optical path, an optical switch control circuit, and a photodetector acquisition and data transmission circuit. The software component mainly consists of the host computer.

[0045] Specifically, the laser source control circuit is connected to the computer host via a GPIB (General Purpose Interface Bus) line. The output optical signal is then split by an optical splitter and sent to the multi-channel fiber Bragg grating sensing and channel switching optical path. Multiple optical path ports are connected to multiple branches of an optical switch, transmitting the multiple sensing signals to a photodetector. The photodetector converts the optical signals into voltage signals for output. The optical switch is connected to the computer host via a USB interface, and the photodetector is connected to the host via a BNC (Browser-Navigate Interchange) coaxial cable connector.

[0046] This invention employs multi-channel high-speed demodulation of fiber Bragg gratings, which expands the detection position and improves the utilization rate of the light source. Furthermore, the optical switch, as the core device for multi-channel high-frequency demodulation, can meet the functional requirements of continuous high-frequency signal detection. Since photodetectors are highly sensitive to changes in the light source, and considering the large information content of high-frequency signals and the frequency influence of low-frequency signals, a wavelength control command is generated by the output voltage signal and sent to a tunable laser source. This allows the tunable laser source to perform laser compensation, ensuring that the output wavelength of the tunable laser always tracks the wavelength displacement of the detection fiber Bragg grating and matches it within the matching wavelength range. Therefore, the high-frequency detection system can maintain high detection sensitivity and stability at all times.

[0047] In one embodiment of the present invention, the center wavelength of each individual fiber grating in the multi-channel fiber grating is within the same preset wavelength range.

[0048] Understandably, in order to make the detection more accurate, each individual sensing optical path in the multi-channel fiber grating sensing optical path is composed of a single fiber grating with a center wavelength similar to that of the individual sensing optical path.

[0049] In one embodiment of the present invention, the optical channel switching rate of the optical switch is 200KHz.

[0050] Understandably, as the core device for multi-channel high-frequency demodulation, the optical switch has an optical channel switching rate of up to 200kHz, which can meet the functional requirements of continuous detection of high-frequency signals.

[0051] In one embodiment of the present invention, the computer 107 further includes a host computer module 1071 and a slave computer module 1076. Figure 1 (Not shown in the image).

[0052] like Figure 2 As shown, Figure 2 This is a computer software program logic block diagram provided according to an embodiment of the present invention. The program of the lower-level module runs within the acquisition controller, and its program control logic is as follows: Figure 2As shown on the left: First, a network stream sending end is established to send data to the host computer module. Then, the program creates a queue reference as a high-frequency signal transmission channel. The data collected in the data acquisition loop is transmitted to the network stream input loop through the queue channel and then input to the host computer module through the network stream.

[0053] The host computer module's program runs on the computer, and its program control logic is as follows: Figure 2 As shown on the right: First, a network stream receiver is established. After the system starts data acquisition, the network stream receiver begins receiving data. The high-frequency signal data detected by different optical channels is converted into voltage signal data by a photodetector for normal display.

[0054] Specifically, the host computer module 1071 includes a parameter configuration module 1072, a data display module 1073, a laser control module 1074, and an optical switch control module 1075.

[0055] Data display module 1073 is used to display voltage signals;

[0056] Laser control module 1074 is used to generate a first control command for the first output wavelength of the laser source;

[0057] The optical switch control module 1075 is used to generate a second control command for opening and closing any optical channel according to a preset optical channel opening sequence.

[0058] The data display module can display the converted voltage signal; the parameter configuration module can configure the system parameters; the laser control module can control and adjust the wavelength and power of the first output light of the laser source; and the optical switch control module can control the opening / closing of multiple optical channels.

[0059] Specifically, in one embodiment of the present invention, the laser light source is used to determine the first output wavelength of the laser light source based on the center wavelength of the multi-channel fiber optic grating.

[0060] It should be noted that the reflection spectrum of a fiber Bragg grating is a Gaussian curve with the center wavelength as its axis of symmetry, and its spectral slope varies in different regions. When detecting signals using fiber Bragg gratings, the higher slope region shows greater sensitivity to the detected signal. Therefore, in laser wavelength demodulation methods, the output wavelength of the laser source is generally set in the high-slope region of the fiber Bragg grating spectrum. Figure 3 As shown, Figure 3 This is a schematic diagram illustrating wavelength matching of a laser source before and after a fiber optic grating is subjected to low-frequency stress, as provided in an embodiment of the present invention. The matching principle is as follows:

[0061] Find the center wavelength of the fiber Bragg grating and the wavelengths at 3dB bandwidth positions on both sides of the main peak of the fiber Bragg grating, and keep the laser wavelength within this wavelength range. For multi-channel fiber Bragg gratings, the matching principle is the same as that for single-channel fiber Bragg gratings. In practical applications, select multi-channel fiber Bragg gratings with similar center wavelengths to lock the output wavelength of the laser source within the matching wavelength range of the multi-channel fiber Bragg gratings. Furthermore, due to the fast switching speed of the optical switch channels, the system can detect high-frequency signals from multiple channels.

[0062] In one embodiment of the present invention, the multi-channel fiber grating includes multiple detection fiber gratings and one reference fiber grating, wherein the reference fiber is unaffected by stress.

[0063] The photodetector is also used to convert multiple third optical signals passing through the detected fiber optic grating into multiple first voltage signals, and to convert the third optical signal passing through the reference fiber optic grating into a second voltage signal.

[0064] The computer is also used to calculate multiple voltage differences between multiple first voltage signals and multiple second voltage signals, and to determine the correspondence between stress and wavelength displacement based on the fitting curve of multiple voltage differences and the center wavelength displacement of the multi-channel fiber optic grating.

[0065] The laser control module is also used to generate a third control command for the second output wavelength of the laser source based on the correspondence.

[0066] When the host computer control software is turned on, the optical switch software control part controls the optical switch to complete the opening and closing cycle of each optical channel, and each optical channel realizes the sensing and reference functions respectively.

[0067] It is understandable that when there are low-frequency signals affecting the detection environment, the center wavelength of the fiber grating in the detection environment will shift. Furthermore, the fiber grating spectrum will shift left and right when subjected to low-frequency stress, but other spectral information will not change. When the tunable laser source scans at the original wavelength and original optical power, the scanning output voltage at different positions of the fiber grating will change. The voltage generated by the original matching laser source wavelength will also change after the fiber grating wavelength shifts due to the change in the matching position. To meet the requirements of long-term stable detection, the output matching wavelength of the tunable laser source needs to be kept within the matching wavelength range.

[0068] Specifically, because photodetectors are highly sensitive to changes in the light source and high-frequency signals contain a large amount of information, the average and difference of the output voltages of the channels before and after the low-frequency stress effect within 10ms are calculated. The wavelength displacement of the fiber grating caused by the low-frequency stress is then retrieved from the voltage difference-wavelength displacement curve using this voltage difference. Finally, the wavelength displacement is fed back to the tunable laser for laser compensation. In other words, the laser source wavelength is updated via serial communication to track the wavelength displacement, meeting the long-term stable detection and demodulation requirements of the demodulation system.

[0069] In one embodiment of the present invention, the laser control module is further configured to determine the wavelength of the second output light in real time based on the wavelength displacement.

[0070] This invention enables the tunable laser output wavelength to always track the wavelength displacement of the detection fiber grating and match it with the detection fiber grating within the matching wavelength range, thereby ensuring that the high-frequency detection system can always maintain high detection sensitivity and stability.

[0071] To better implement the fiber Bragg grating multi-channel high-speed demodulation system in this embodiment of the invention, based on the fiber Bragg grating multi-channel high-speed demodulation system, please refer to the corresponding documentation. Figure 4 , Figure 4 This is a flowchart illustrating an embodiment of the fiber Bragg grating multi-channel high-speed demodulation method provided by the present invention. The embodiment of the present invention provides a fiber Bragg grating multi-channel high-speed demodulation method applied to the above-mentioned fiber Bragg grating multi-channel high-speed demodulation system, comprising:

[0072] Step S401: Determine the first output light wavelength of the tunable laser source output light signal based on the center wavelength of the fiber grating;

[0073] Step S402: Output the optical signal to the multi-channel fiber Bragg grating sensing and channel switching optical path via the optical splitter, and control the opening sequence of each channel based on the optical switch;

[0074] Step S403: The high-frequency signal data detected by different optical channels are converted into voltage signal data by a photodetector, and the voltage difference between the detected fiber optic grating and the reference fiber optic grating is calculated respectively.

[0075] Step S404: Determine the wavelength displacement under the current stress based on the fitting curve of voltage difference and center wavelength displacement of multi-channel fiber grating;

[0076] Step S405: Adjust the first output light wavelength of the tunable laser source output light signal to the second output light wavelength based on wavelength shift.

[0077] It should be noted that the fiber optic grating multi-channel high-speed demodulation method provided in the above embodiments can realize the technical solutions described in the above system embodiments, and will not be repeated here.

[0078] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0079] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A fiber grating multi-channel high speed demodulation system, characterized in that, The method comprises the following steps: a tunable laser light source is used to output a first light signal with adjustable wavelength; an optical splitter is used to split the first light signal into a plurality of second light signals; a multi-channel fiber grating is used to detect high-frequency signals according to a preset light channel opening sequence under the action of the plurality of second light signals, and output a plurality of third light signals, wherein the multi-channel fiber grating comprises a plurality of detection fiber gratings and a reference fiber grating, and the reference fiber grating is not affected by stress; an optical switch is used to switch the light channels in the multi-channel fiber grating according to the preset light channel opening sequence; a photodetector is used to convert the plurality of third light signals into a plurality of voltage signals; a capture card is used to capture the voltage signals output by the photodetector; a computer is used to generate control instructions based on the voltage signals, and the computer specifically comprises a data display module for displaying the voltage signals, a laser control module for generating a first control instruction for the first output light wavelength of the laser light source, and an optical switch control module for generating a second control instruction for opening and closing any light channel according to the preset light channel opening sequence; the switching rate of the light channels of the optical switch is 200 KHz; the photodetector is also used to convert the plurality of third light signals passing through the detection fiber gratings into a plurality of first voltage signals, and convert the third light signal passing through the reference fiber grating into a second voltage signal; the computer is also used to calculate a plurality of voltage differences of the plurality of first voltage signals and the second voltage signal respectively, and determine the corresponding relationship between stress and wavelength displacement based on the plurality of voltage differences and a fitting curve of the center wavelength displacement of the multi-channel fiber grating, the laser control module is also used to generate a third control instruction for the second output light wavelength of the laser light source based on the corresponding relationship.

2. The fiber grating multi-channel high speed demodulation system according to claim 1, wherein, The center wavelength of each single fiber grating in the multi-channel fiber grating is within the same preset wavelength range.

3. The fiber grating multi-channel high speed demodulation system according to claim 1, wherein, The laser control module is specifically used to determine the first output light wavelength of the laser light source based on the center wavelength of the multi-channel fiber grating.

4. The fiber grating multi-channel high speed demodulation system according to claim 1, wherein, The laser control module is specifically used to determine the second output light wavelength in real time based on the wavelength displacement.

5. A method for fiber grating multi-channel high speed demodulation, applied to the fiber grating multi-channel high speed demodulation system as claimed in any one of claims 1-4, characterized in that, The method comprises the following steps: determine the first output light wavelength of the output light signal of the tunable laser light source based on the center wavelength of the fiber grating; output the light signal to the multi-channel fiber grating sensing and channel switching optical path through the optical splitter, and control the opening sequence of each channel based on the optical switch; obtain the high-frequency signal data detected by different light channels, convert the high-frequency signal data into voltage signal data through the photodetector, and calculate the voltage difference of the detection fiber grating and the reference fiber grating respectively; determine the wavelength displacement under the current stress based on the voltage difference and the fitting curve of the center wavelength displacement of the multi-channel fiber grating; adjust the first output light wavelength of the output light signal of the tunable laser light source to the second output light wavelength based on the wavelength displacement.

6. The fiber grating multi-channel high-speed demodulation method according to claim 5, characterized in that, The tunable laser light source adjusts the output light wavelength dynamically.

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