Research On Spatial Frequency Drift Compensation And Distance Expansion In Optical Fiber F-P Pressure Sensing And Demodulating

Optical fiber F-P sensor shows great application prospect in safety monitoring field like aerospace and civil infrastructure for its advantages like small volume,light quality,immunity to electromagnetic interference,high sensitivity and reliability and so on,a significant step is the demodulation of F-P cavity length.Low-coherence interferometry demodulation method,for its immunity to 2? ambiguity and theoretically unlimited measurement range,becomes one of the main methods for optical fiber F-P cavity length demodulation.However,traditional low-coherence interferometry demodulation method shows several defects,the phenomenon of spatial frequency drift greatly affect the demodulation precision,the power of LED source is too low to meet the need of long-distance sensing.In this paper,we aim at the defects that low-coherence interferometry has,analyze the cause and influence of spatial frequency drift and compensate it with a compensation algorithm.For the defect of short sensing distance,we use SLED with higher power as the light source,with the method of double SLED method,we solved the problem that the envelope of interference fringes changing too slowly to correctly identify fringe peaks.We optimized the demodulation beam path design,built the light power mathematical model of our system and conducted the long-distance optical fiber F-P pressure sensing and demodulating experiment,the experimental results suited well with our theoretical analysis.The main content is as following:1)for the problem of spatial frequency drift in lo-coherence interferometry,we analyzed the influence of non-perpendicular incidence of light to the OPD distribution on CCD.Then we analyzed the cause of spatial frequency drift on the basis of that and discussed the influence of system parameters to spatial frequency drift.At last,we proposed a compensation algorithm combining phase algorithm to compensate the influence of spatial frequency drift to help avoid the interference-order misidentification;2)For the need of long-distance sensing,we built a long-distance optical fiber F-P pressure sensing and demodulating system with double-SLED-light-source method.To reduce the size of demodulation module,we introduce a negative lens to help increase the incidence angle of the light from the fiber;3)We analyzed the influence of the light power to the low-coherence inteferogram,and for our long-distance F-P sensing system we built the light power mathematical model to help compensate the light power loss in the system.4)For our long-distance F-P sensing system,we designed a demodulation algorithm.With the any-extreme method with double thresholds,we conducted the long distance optical fiber F-P sensing and demodulation experiment.Experimental results showed that,within the sensing distance limit,our algorithm could achieve higher demodulation precision.