Research On Key Technologies Of Signal Demodulation Of Fiber Optic Seismometer

As an important strategic resource,oil and gas resources are crucial to the development of the country,so we urgently need to increase the exploration and development of oil and gas resources.At present,seismic exploration technology is one of the most effective methods in oil and gas exploration.With the practical application of optical fiber,optical fiber seismometer comes into being.Among them,the interferometric fiber optic seismometer has attracted much attention in the field of seismic exploration because of its high sensitivity and anti-electromagnetic interference.As the core of detector signal processing,phase demodulation technology has become one of the research hotspots,so how to eliminate the interference of external factors on phase demodulation has important research significance and application value.In this paper,the key technologies of signal demodulation of fiber optic seismometer are studied.Firstly,the sensing principle and phase modulation and demodulation technology of interferometric fiber optic seismometer are analyzed and discussed,and the modulation and demodulation method of phase generated carrier technology is introduced.The basic demodulation ideas and theoretical derivation of differential cross multiplication(PGC-DCM)algorithm and PGC-Arctan algorithm in phase-generated carrier demodulation technology are analyzed,which provides theoretical support for further research.Secondly,through the theoretical analysis of the traditional PGC-DCM algorithm,an improved algorithm based on PGC-DCM algorithm is proposed,which can simultaneously eliminate the influence of carrier phase delay and modulation depth on the demodulation results.A complete experimental system is set up to verify the feasibility of the proposed algorithm.The experimental results show that the proposed algorithm is insensitive to modulation depth and carrier phase delay,and has better demodulation effect than the traditional PGC-DCM algorithm.The SNR is 56.15 d B and the total harmonic distortion is0.13%.Finally,aiming at some shortcomings of the traditional PGC-Arctan algorithm,an improved demodulation algorithm based on PGC-Arctan algorithm is proposed,which can compensate the modulation depth while eliminating the influence of carrier phase delay.Simulation software is used to simulate the algorithm,the feasibility of the improved algorithm is analyzed,and then the experiment is carried out in combination with the experimental system.Experimental results show that the demodulation results obtained by this algorithm are not affected by modulation depth and carrier phase delay,and the demodulation results are good.The SNR is 50.52 d B and the total harmonic distortion is 0.109%.In this paper,the traditional phase-generated carrier algorithm is improved,and the influence of external disturbance such as carrier phase delay and modulation depth on the demodulation results is successfully eliminated through the built demodulation algorithm experimental test system,which enhances the anti-interference ability of the demodulation system and improves the performance of the demodulation algorithm.It plays a certain role in promoting the practical application of fiber optic seismometer.