Signal Demodulation Of Multi-longitudinal Fiber Laser Sensor

With the breakthrough of science and technology,the information and communication industry has developed rapidly in recent years.As the main component of communication,optical fiber provides the necessary soil for the development of the communication industry.For fiber optic devices are not affected by electromagnetic interference,chemical corrosion,and have low transmission loss,researchers have invented a variety of fiber sensors which have many applications in life.The fiber laser sensor is a sensing device based on doped fiber.It has many advantages such as high signal-to-noise ratio,high sensitivity,low cost which have become a research hotspot in recent years.With further research,the fiber laser sensor will continue to enrich its sensing function,reduce its cost,and be applied in a wider range of scenarios.With the development of the fifth generation communication,fiber laser sensor will play a more important role in the Internet of Things era.This thesis is based on the beat frequency demodulation of multi-longitudinal fiber laser sensor.The main work are as follows:1.We propose an optimization method for the beat frequency demodulation of multi-longitudinal mode fiber laser sensor based on bandpass sampling technique.The bandpass demodulation technology can combine the process of down-conversion and sampling processes.Under the no aliasing condition,the bandpass signal with the center frequency at 2.625 GHz and 1.725 GHz can be sampled in the time domain with a sampling rate lower than Nyquist rate to measure frequency variation in the signal,omitting the process of signal mixing.Through the verification experiment,the sensitivity of the stress of-0.66 kHz/?? was obtained by using the ring-cavity fiber laser strain sensor and the sensitivity of the temperature of-5.77 kHz/? was obtained by using the straight cavity fiber laser temperature sensor,and the sensitivity in experiment was in agreement with the theory,which proved the effectiveness of applying bandpass demodulation to the multi-longitudinal fiber laser sensor beat frequency demodulation system.2.We propose a method for narrowing the longitudinal mode of a fiber laser sensor.The ultra-narrow fiber grating is employed to limit the longitudinal mode in the fiber laser to concentrate the energy in the fiber laser cavity.The range of longitudinal mode beat frequency obtained by the experiment is only 350MHz,the signal-to-noise ratio of the single beat frequency signal is as high as 65dB.Through the strain demodulation experiment,the accuracy and stability of the longitudinal mode beat frequency of 150MHz are ±2.O?? and±0.2kHz respectively.