Long-period fiber grating space division multiplexing demodulation system and demodulation process based on diffraction grating

Abstract

A long-period fiber grating space division multiplexing demodulation system based on a diffraction grating, wherein the input end of the optical multiplexing module is connected to the light source module and the single-chip computer module respectively, and the output end is connected to the optical demodulation module. The optical multiplexing module includes an optically controlled switch, a long-period fiber grating array and an optical coupler. The single-chip computer module includes a single-chip computer minimum system and a level and logic relationship conversion module. The computer detection system transmits the instruction of switching the optically controlled switch to the single-chip computer module through the serial port, and the single-chip computer module controls the pin level to complete the switching of the optical path after receiving the instruction. The input end of the optical demodulation module is connected to the optical multiplexing module, and the output end is connected to the computer detection system through a universal interface bus. The computer module sends a control instruction to the optical demodulation module through GPIB to complete the demodulation of the optical signal, and the demodulated data is returned to the computer for data processing. This patent can display the changes in the detection target parameters in real time and realize multi-point dispersed measurement.

Description

Technical Field

[0001] The invention belongs to the field of fiber grating sensing, and relates to a long-period fiber grating space division multiplexing demodulation system based on a diffraction grating and a demodulation process. Background Art

[0002] Fiber Bragg grating is a fiber passive device that has developed very rapidly in recent years. Fiber Bragg grating has a wide bandwidth range and good wavelength selectivity, and has the characteristics of non-conductivity, high sensitivity, high resolution, corrosion resistance, electromagnetic interference resistance, and polarization insensitivity. Due to the natural compatibility between fiber Bragg grating and optical fiber, fiber Bragg grating is easy to connect with optical fiber and has low loss, good spectral characteristics, and high reliability. These advantages make fiber Bragg grating and devices based on fiber Bragg grating ideal key devices in all-optical networks.

[0003] The basic working principle of LPFG is to input the light from the light source into the optical fiber and transmit it to the grating area through the optical fiber. In the grating area, the external measured parameters (such as temperature, curvature, refractive index, strain, etc.) interact with the light entering the grating area, thereby changing the wavelength, intensity, phase and other parameters of the light. It has high sensitivity, small size, and is easy to integrate with the substrate structure. It is a very important type of intelligent structural sensor.

[0004] Precise demodulation of sensing signals is one of the key technologies for the practical application of fiber optical sensors. To this end, a variety of technologies have been developed for wavelength-coded demodulation. For example, the matched filter method is used to demodulate the fiber Bragg grating. The sensor has a simple structure and low cost, but the method has high requirements for grating matching, a small measurement range, and a low response speed. The tunable FP cavity filter demodulation method can achieve a higher strain resolution, but the detection accuracy is affected by the stability of the FP cavity and the nonlinearity of PZT. Gan; The reflection spectrum of the fiber Bragg grating is scanned by a narrow-band spectrum with periodic wavelength changes. This method can obtain a higher signal-to-noise ratio and resolution, but requires the tunable narrow-band light source to have a narrow output spectrum and a wide spectral tuning range.

[0005] Each of the above solutions has its own advantages and is suitable for the needs of different sensing systems. However, many of the tunable devices in these solutions achieve wavelength selection by controlling piezoelectric ceramics, so there is a certain hysteresis. In addition, in actual operation, there is a limit on the slew rate (the speed at which the scanning voltage returns to the initial voltage). The demodulation devices in some solutions, such as tunable filters or tunable laser light sources, are relatively expensive, ranging from a few thousand dollars to tens of thousands of dollars, and the investment is relatively large.

[0006] On the other hand, the multiplexing technology of optical fiber sensors is the key to building an optical fiber distributed sensing system, which determines the overall performance and manufacturing cost of the optical fiber sensing network. The so-called optical fiber sensor multiplexing is to collect the numerous sensing signals generated in the optical fiber sensing network into a single-mode optical fiber for transmission, and distinguish these signals in a certain order at the demodulation end. This is

[0007] Due to the lack of feasible multiplexing and demultiplexing technologies, sensors have not been widely used in the field of distributed fiber optic sensing. Optical multiplexing technology has emerged to tap the huge bandwidth potential of optical fibers and improve the capacity of optical fiber communications. Its working mechanism is to form a multi-type optical composite combination form through the selection and matching of optical physical parameters on a single optical fiber, construct multiple or multiple types of sensors, and realize multi-point quasi-distributed monitoring. As the three classic multiplexing forms of fiber grating multiplexing, wavelength division multiplexing, time division multiplexing and frequency division multiplexing have been widely studied in the past 20 years.

[0008] How to build a miniaturized, portable, multi-channel detection, high-sensitivity, and long-period fiber multiplexing demodulation device that can be applied to on-site real-time analysis is an urgent task to be solved. According to the needs of engineering applications, it is necessary to select and design a wavelength displacement detection technology that is small in size, low in price, high in sensitivity, high in light energy utilization, and simple to operate, which can display the changes in the detection target parameters in real time and realize multi-point dispersed measurement and centralized detection.

[0009] So far, no one has proposed a long-period fiber grating space division multiplexing real-time sensing system based on diffraction grating. The system switches the optical path through an optical switch, and uses multi-slit diffraction and interference through the diffraction grating to disperse the light beam incident on the grating according to different wavelengths, and then focuses it through the imaging mirror to form a spectrum. The transmission intensity of the light source wavelength is determined by the corresponding transmission spectrum of each sensor. Each sensor is installed in the environment that needs to be sensed. When the physical quantity to be measured in the environment changes, the resonant wavelength of each sensor drifts, and its corresponding resonant wavelength and transmittance will change. Each sensor can be distinguished by the resonant wavelength to achieve the purpose of multiplexing demodulation. Summary of the invention

[0010] In view of the above problems, the present invention provides a long-period fiber grating space-division multiplexing demodulation system and demodulation process based on diffraction grating. The demodulation scheme has a certain hysteresis. In actual operation, there is a limit on the rotation rate (the speed at which the scanning voltage returns to the initial voltage), and some demodulation devices are relatively expensive. In addition, multi-point dispersed measurement and centralized detection of fiber gratings have also become an urgent need for the practical development of fiber grating sensing technology. This patent provides a long-period fiber grating space-division multiplexing demodulation system and demodulation process based on diffraction gratings, which uses optically controlled switches for space-division multiplexing and uses diffraction gratings to demodulate wavelengths. The system is small in size, low in price, high in sensitivity, and high in light energy utilization. It can display changes in target parameters in real time and can achieve multi-point dispersed measurement.

[0011] The principle of the present invention is as follows: the light source module emits an optical signal, which is multiplexed by the optical multiplexing module, wherein the optically controlled switch in the optical multiplexing module switches the optical path through a single-chip microcomputer, and the signal after optical signal multiplexing is demodulated by the optical demodulation module to demodulate the LPFG optical signal. In the optical signal demodulation module, the optical signal modulated by the array enters the reflector, and the wavelength range of the optical signal can be scanned by adjusting the position of the diffraction grating. Different diffraction grating angles will separate different wavelengths, which are reflected by the reflector and transmitted to the detector, and finally detected by the detector to realize spectral analysis. The data of the demodulated optical signal is returned to the computer detection system for data processing;

[0012] To achieve this purpose, the present invention provides a long-period fiber grating space division multiplexing demodulation system based on a diffraction grating, comprising a light source module, an optical multiplexing module, a single-chip microcomputer module, a computer detection system and an optical demodulation module, wherein the input end of the optical multiplexing module is respectively connected to the light source module and the single-chip microcomputer module, and the output end of the optical multiplexing module is connected to the optical demodulation module, wherein the optical multiplexing module comprises an optically controlled switch, an array and an optical coupler, and the single-chip microcomputer module comprises a single-chip microcomputer minimum system and a level and logic relationship conversion module, wherein the level and logic relationship conversion module realizes USB to TTL conversion and is compatible with the single-chip microcomputer minimum system. The computer detection system transmits the instruction of switching the optical switch to the single-chip microcomputer module through the serial port. After receiving the instruction, the single-chip microcomputer module controls the pin level to complete the switching of the optical path. The input end of the optical demodulation module is connected to the optical multiplexing module, and the output end is connected to the computer detection system (4) through GPIB. The optical demodulation module includes a reflector, a diffraction grating and a detector. The computer detection system (4) sends a control instruction to the optical demodulation module through GPIB to complete the demodulation of the optical signal. The demodulated data is returned to the computer detection system for data processing.

[0013] As a further improvement of the present invention, the light source module is an ultra-wideband light source with a spectral range of 1250~1630nm and an output power greater than 8.5mW, which fully meets the loss peak range.

[0014] As a further improvement of the present invention, the optical multiplexing module is composed of an optically controlled switch, an array and an optical coupler. The optically controlled switch uses a 1×8 mechanically controllable optical switch. The optical signal is directly coupled to the output end by moving the internal optical fiber. The optical path switching time is less than 10ms. The switching of the optical path is achieved by changing the pin level. The optical coupler uses an optical fiber coupler. In the system, the number of channels of the optical switch is 8, so an 8×1 optical fiber coupler is selected to complete the eight-in-one of eight optical paths.

[0015] As a further improvement of the present invention, the single-chip microcomputer module is composed of a single-chip microcomputer minimum system and a level and logic relationship conversion module. The single-chip microcomputer minimum system is mainly composed of a power supply, a reset, an oscillation circuit and an expansion part. The level and logic relationship conversion module converts the USB level into a TTL level, that is, the level and logic relationship conversion module is connected through the single-chip microcomputer minimum system serial port, and the computer detection system and the single-chip microcomputer module are connected with a USB connection line to download programs and perform serial port communication.

[0016] As a further improvement of the present invention, the optical demodulation module is composed of a reflector, a diffraction grating and a detector. The optical signal modulated by the array enters the reflector. The wavelength range of the optical signal can be scanned by adjusting the position of the diffraction grating. Different diffraction grating angles will separate different wavelengths, which are reflected by the reflector and transmitted to the detector, and finally detected by the detector to realize spectral analysis.

[0017] As a further improvement of the present invention, the computer detection system consists of four parts: switch control, wavelength acquisition, spectrum drawing and parameter display. The switch control is connected to the serial port of the single-chip microcomputer for configuration, the serial port connected to the single-chip microcomputer is selected, and the baud rate is set to the same as that of the single-chip microcomputer. The pin level control program is written on the single-chip microcomputer connected to the optical switch, and the optical path selection is controlled by the pin level; the wavelength acquisition selects the start wavelength and the end wavelength of the scan by setting the center wavelength and the wavelength span, and performs communication with the optical demodulation module; the spectrum drawing function sets the scanning mode, the number of scanning points and the control command for executing the scan and transmits it to the optical demodulation module. The optical demodulation module will start scanning after identifying these three commands, and transmit the data of the wavelength axis and the transmittance axis to the computer after the scan is completed; the parameter display displays the measured parameters, the corresponding wavelength values ​​and the transmittance on the interface.

[0018] The present invention provides a working process of a long period fiber grating space division multiplexing demodulation system based on a diffraction grating, and the specific steps are as follows:

[0019] 1) The light source module provides light source for the optical multiplexing module;

[0020] 2) The computer detection system sends the light-controlled switch switching instruction to the single-chip microcomputer module;

[0021] 3) After receiving the instruction from the computer detection system, the single chip microcomputer module controls the pin level to complete the switching of the optical path;

[0022] 4) The computer of the computer detection system sends a control instruction to the optical demodulation module, and the optical demodulation module receives the instruction to complete the demodulation of the optical signal;

[0023] 5) The demodulated data is returned to the computer detection system for data processing, and finally the spectrum, resonant wavelength and parameters of the long-period fiber grating are restored.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) The long-period fiber grating space division multiplexing demodulation system based on the diffraction grating of the present invention adopts 1×8 optical control switching to multiplex the fiber grating, and can expand more optical switches of the optical path as needed;

[0026] (2) The long-period fiber grating space division multiplexing demodulation system based on the diffraction grating of the present invention adopts the diffraction grating as the key component of demodulation, thus avoiding the limitation of the rotation rate and having relatively low cost;

[0027] (3) The long-period fiber grating space division multiplexing demodulation system based on the diffraction grating of the present invention uses an interface developed by a computer detection system as a human-computer interaction interface, which is easy to operate, highly readable, and has a beautiful interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the structure of a long-period fiber grating space division multiplexing demodulation system based on a diffraction grating;

[0029] Figure 2 This is the demodulation process of the computer detection system of the present invention.

[0030] Label names in the figure:

[0031] 1. Light source module; 2. Optical multiplexing module; 3. Single chip microcomputer module; 4. Computer detection system; 5. Optical demodulation module. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments:

[0033] This patent provides a long-period fiber grating space division multiplexing demodulation system and demodulation process based on diffraction grating, which uses optically controlled switches for space division multiplexing and uses diffraction gratings to demodulate wavelengths. The system is small in size, low in price, high in sensitivity, high in light energy utilization, can display the changes in the detection target parameters in real time, and can realize multi-point dispersed measurement.

[0034] Figure 1 The structure diagram of the long period fiber grating space division multiplexing demodulation system based on diffraction grating of the present invention is shown. The system includes a light source module 1, an optical multiplexing module 2, a single chip module 3, a computer detection system 4 and an optical demodulation module 5. The input end of the optical multiplexing module 2 is connected to the light source module 1 and the single chip module 3 respectively, and the output end is connected to the optical demodulation module 5. The optical multiplexing module 2 includes an optically controlled switch, an LPFG array and an optical coupler. The single chip module 3 includes a single chip minimum system and a level and logic relationship conversion module. The input end of the optical demodulation module 5 is connected to the optical multiplexing module 2, and the output end is connected to the computer detection system 4 through GPIB. The optical demodulation module 5 includes a reflector, a diffraction grating and a detector. The computer detection system 4 sends a control instruction to the optical demodulation module 5 through GPIB to complete the demodulation of the optical signal, and the demodulated data is returned to the computer detection system 4 for data processing.

[0035] The hardware of the long-period fiber grating space-division multiplexing demodulation system based on diffraction grating of the present invention is: OEBLS-2000 ultra-wideband light source; LPFG written into hydrogen-doped germanium optical fiber with the same parameters by an excimer laser through an amplitude mask method; 1×8 mechanical controllable optical switch; 8×1 optical fiber coupler; MC68HC08KX8 single-chip microcomputer; diffraction grating; reflector, etc.

[0036] Combination Figure 2 , the demodulation process of the long period fiber grating space division multiplexing demodulation system based on diffraction grating of this embodiment and the computer detection system is as follows:

[0037] 1) The system starts the optical path selection, and the microcontroller controls the optical switch to switch to the configured optical path;

[0038] 2) Return the optical path information to the system, and the system controls the demodulation module to scan;

[0039] 3) Return the scanned wavelength and transmittance information to the system;

[0040] 4) Restore the LPFG spectrum and the central loss peak resonant wavelength and parameter values ​​of LPFG;

[0041] 5) The restored LPFG spectrum and the demodulated resonant wavelength and temperature data are displayed on the host computer.

[0042] The above description is only a preferred embodiment of the present invention and does not constitute any other form of limitation to the present invention. Any modification or equivalent change made based on the technical essence of the present invention still falls within the scope of protection required by the present invention.

Claims

1. A long-period fiber grating space division multiplexing demodulation system based on a diffraction grating, comprising a light source module (1), an optical multiplexing module (2), a single-chip computer module (3), a computer detection system (4) and an optical demodulation module (5), characterized in that: The input end of the optical multiplexing module (2) is respectively connected to the light source module (1) and the single-chip computer module (3); the output end of the optical multiplexing module (2) is connected to the optical demodulation module (5); the optical multiplexing module (2) comprises an optical switch, an array and an optical coupler; the single-chip computer module (3) comprises a single-chip computer minimum system and a level and logic relationship conversion module; the level and logic relationship conversion module realizes USB to TTL conversion and is connected to the single-chip computer minimum system; the computer detection system (4) transmits the optical switch switching instruction to the single-chip computer via the serial port. A single-chip computer module (3), wherein the single-chip computer module (3) controls the pin level to complete the switching of the optical path after receiving the instruction, the input end of the optical demodulation module (5) is connected to the optical multiplexing module (2), and the output end is connected to the computer detection system (4) via GPIB, the optical demodulation module (5) comprises a reflector, a diffraction grating and a detector, the computer detection system (4) sends a control instruction to the optical demodulation module (5) via GPIB to complete the demodulation of the optical signal, and the demodulated data is returned to the computer detection system (4) for data processing; The light source module (1) is an ultra-wideband light source with a spectral range of 1250-1630 nm and an output power greater than 8.5 mW; The optical multiplexing module (2) is composed of an optical switch, an array and an optical coupler. The optical switch is a 1×8 mechanical controllable optical switch. The optical signal is directly coupled to the output end by moving the internal optical fiber. The optical path switching time is less than 10ms. The switching of the optical path is achieved by changing the pin level. The optical coupler is an optical fiber coupler. In the system, the number of channels of the optical switch is 8, so an 8×1 optical fiber coupler is selected to complete the eight-in-one of eight optical paths. The single-chip microcomputer module (3) is composed of a single-chip microcomputer minimum system and a level and logic relationship conversion module. The single-chip microcomputer minimum system is mainly composed of a power supply, a reset circuit, an oscillation circuit, and an expansion part. The level and logic relationship conversion module converts the USB level into a TTL level, that is, the level and logic relationship conversion module is connected to the single-chip microcomputer minimum system serial port, and the computer detection system (4) and the single-chip microcomputer module (3) are connected by a USB connection line to download programs and perform serial port communication; The optical demodulation module (5) is composed of a reflector, a diffraction grating and a detector. The optical signal modulated by the array enters the reflector. The wavelength range of the optical signal can be scanned by adjusting the position of the diffraction grating. Different diffraction grating angles will separate different wavelengths, which are reflected by the reflector and transmitted to the detector. Finally, they are detected by the detector to achieve spectral analysis. The computer detection system (4) is composed of four parts: switch control, wavelength acquisition, spectrum drawing and parameter display. The switch control is connected to the serial port of the single-chip microcomputer for configuration, selects the serial port connected to the single-chip microcomputer, and sets it to the same baud rate as the single-chip microcomputer. The single-chip microcomputer connected to the optical switch is written with a pin level control program, and the optical path selection is controlled by the pin level. The wavelength acquisition selects the start wavelength and the end wavelength of the scan by setting the center wavelength and the wavelength span, and performs communication with the optical demodulation module (5); The spectrum drawing function sets the scanning mode, the number of scanning points and the control command for executing the scanning and transmits it to the optical demodulation module (5). The optical demodulation module (5) starts scanning after recognizing the three commands, and transmits the data of the wavelength axis and the data of the transmittance axis to the computer after the scanning is completed; the parameter display displays the measured parameters, the corresponding wavelength values ​​and the transmittance on the interface.

2. The demodulation method of the long period fiber grating space division multiplexing demodulation system based on the diffraction grating according to claim 1, characterized in that: The specific steps are as follows: 1) The light source module (1) provides light source for the light multiplexing module (2); 2) the computer detection system (4) sends the light-controlled switch switching instruction to the single-chip computer module (3); 3) After receiving the instruction from the computer detection system (4), the single chip microcomputer module (3) controls the pin level to complete the switching of the optical path; 4) The computer of the computer detection system (4) sends a control instruction to the optical demodulation module (5), and the optical demodulation module (5) receives the instruction to complete the demodulation of the optical signal; 5) The demodulated data is returned to the computer detection system (4) for data processing, and finally the spectrum, resonant wavelength and parameters of the long-period fiber grating are restored.

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