Optical Fiber Sensing Technology And Application Research Based On Photoelectric Oscillator

With the continuous maturity of optical communication technology,optical fiber sensing technology has developed rapidly,and various types of optical fiber sensors have appeared.Optical fiber sensors are widely used in chemical engineering,geological engineering,aerospace and other fields because of their small size,lightweight,anti-electromagnetic interference,easy installation and burying,and suitable for harsh environments.One of the key technologies of the optical fiber sensor is the demodulation of the sensing signal.In the demodulation of the optical fiber sensor,traditionally,most of the optical fiber sensors use a spectrum analyzer to detect the changes of optical parameters(power,wavelength)to measure the parameters.However,the demodulation speed and accuracy of the spectrum analyzer are limited,which cannot meet the needs of high-speed and high-precision demodulation in some fields.In order to improve the demodulation performance of optical fiber sensors,it is necessary to develop high-performance optical fiber sensor demodulation technology.In recent years,with the continuous maturity of microwave photonics,the use of microwave photonics technology and electronic signal processing equipment to map the changes of optical signals to the amplitude or frequency changes of radio frequency signals for demodulation can greatly improve the demodulation speed of the sensing system and resolution.This paper proposes and experimentally verifies a high-sensitivity optical fiber temperature sensing system based on the Vernier effect of the double-ring optoelectronic oscillator.The traditional dual-ring optoelectronic oscillator is composed of a long loop and a short loop to achieve low phase noise and single-mode selection.The difference is that our proposed structure is composed of two loops of approximately equal length and does not use any radio frequency filters.The sensing unit of the optical fiber temperature sensor is part of the optical fiber of one of the loops,because of the obvious Vernier effect in the frequency response of the double-ring optoelectronic oscillators,the temperature sensor demodulation can be realized by detecting the frequency shift of the envelope peak of the frequency response curve.Compared with the traditional single-ring structure photoelectric oscillator,this kind of oscillator based on the Vernier effect and the double-ring structure has 201.25KHz/?sensitivity when applied to temperature sensing.Since the electrical spectrum analyzer has a higher scanning speed and resolution than the spectrum analyzer,it can significantly improve the resolution of temperature sensing,and the measurement results are more accurate.This paper also proposes a microwave photonic filter(MPF)based on Sagnac interferometer,and embeds it as a frequency-selective device into the structure of an electro-optical oscillator(OEO)to realize the generation of microwave signals.First,the transmission characteristics of polarization maintaining fiber are introduced,and then the working principle of SI is explained.Combining SI,phase modulator and dispersive elements,a single passband MPF is realized,and it is embedded in the OEO loop to realize the oscillation of the optoelectronic oscillator.For this structure,we have theoretically proved that the structure can not only adjust the OEO starting frequency by adjusting the length of the polarization maintaining fiber;Polarization-maintaining fiber can also be used as a temperature sensing unit to achieve high-sensitivity temperature measurement by detecting the frequency shift of the OEO starting signal.