Fiber bragg grating demodulating device and method based on chromatic dispersion Mach-Zehnder interferometry

Abstract

The invention relates to a fiber bragg grating demodulating device and method based on chromatic dispersion Mach-Zehnder interferometry. The fiber bragg grating demodulating device comprises a broadband light source, a narrow-linewidth sweep frequency laser device, a first photoswitch, an optoisolator, a semiconductor optical amplifier, a pulse digital signal source, an optical circulator, a second photoswitch, a reference grating, a sensing grating array, a Faraday rotating mirror, a first optical coupler, dispersion compesation fiber, monomode optical fiber, a second optical coupler, a photoelectric detector set, a data collecting card and an upper computer. The optical fiber dispersion effect and the traditional Mach-Zehnder interferometry are combined to construct chromatic dispersion Mach-Zehnder interferometry, optical path difference caused by the chromatic dispersion effect is used for achieving phase sensibilization, interference information of all gratings in a quasi-distributed fiber bragg grating array is recorded through high-speed time-domain optical pulses, a multi-phase demodulating technology is used for processing time domain interference signals, high-sensitivity and high-speed demodulation of the fiber bragg grating array is achieved, and the demodulating device has the advantages of being high in interference resistance and capable of achieving distributed measurement.

Description

technical field [0001] The invention relates to the technical field of fiber grating demodulation, in particular to a fiber grating demodulation device and method based on dispersion Mach-Zehnder interference. Background technique [0002] In recent years, fiber gratings have been widely used in railways, bridges, aviation, industry, military, etc. Measurement of physical quantities such as temperature, strain, vibration, acceleration, etc., as well as structural health monitoring of building bridges. However, in special occasions such as ultrasonic flaw detection, aero-engine rotation monitoring, and gas pipeline leakage detection, high-speed and high-sensitivity signal detection is required, and the application of fiber gratings is limited by traditional wavelength demodulation technology. In order to make fiber grating sensing technology practical in the above special fields, there is an urgent need for ultra-high-sensitivity fiber grating high-speed demodulation technol...

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Problems solved by technology

However, there are limitations in the application of such demodulation methods, and it is difficult to simultaneously meet the needs of high-speed demodulation and high-sensitivity detection

For example, the FDML frequency-sweeping laser method uses a ring-shaped laser resonator to output a narrow-band frequency-sweeping optical signal. When the wavelength of the frequency-sweeping light coincides with the center wavelength of the grating, the photodetector receives the strongest light intensity to realize the demodulation of the center wavelength of the fiber grating. However, this method has a long frequency-sweeping laser resonator and is easily disturbed by the external environment. The grating demodulation speed is limited by the light source sweep rate, and the demodulation sensitivity is general; the tunable F-P filter method is similar to the FDML frequency-sweeping method, and its core It is a Fabry-Perot filter. The tuning signal is generated by the control circuit to drive the piezoelectric ceramic to change the F-P cavity length to realize the spectral tuning of the light source. This method is also limited by the F-P tuning rate, and the demodulation rate is generally several hundred Hz to Several kilohertz; the matched grating demodulation method uses the fiber grating that matches the wavelength of the sensing grating as a reference, and the matching grating tracks the wavelength change of the sensing grating under the action of the driving unit, and reversely deduces it by measuring the driving signal of the driving element The central wavelength of the sensing grating, the demodulation rate of this method is also limited by the speed of driving the matching grating, and a matching grating corresponds to only one sensing grating, which is difficult to apply to the demodulation of large-scale grating multiplexing systems; unbalanced M-Z interference demodulation The basic principle of the method is that the reflected light of the grating will interfere when it passes through the M-Z interferometer with two different arms. When the wavelength of the fiber grating changes, the phase of the interference signal changes, resulting in phase modulation of the interfering light. By detecting the phase change of the interferometer, the It can demodulate the center wavelength of the fiber grating. This method has high detection sensitivity, but it is easily affected by external disturbances and has insufficient stability. It is only suitable for dynamic demodulation; the fiber dispersion effect demodulation method uses high-speed pulsed light of different wavelengths in The time delay in the optical fiber is different for demodulation, which has a very high demodulation rate, but requires a high-speed oscilloscope with a high sampling rate, which is difficult to be practical in engineering, and is limited by the time-domain delay measurement accuracy, and the demodulation sensitivity is relatively general

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