Research On Two-Parameter Fiber Sensing Technology Based On Cascaded F-P Interference

Fiber optic sensing technology is a relatively new technology in the field of optics,with the advantages of light weight,corrosion resistance,and speed,offering a variety of possibilities for medical science,environmental health,and underwater detection.There are many types of fiber optic sensors,among which the fiber optic Fabry-Perot(F-P)sensor is widely used because of its simple structure,smaller size and accurate measurement.However,traditional single-parameter F-P sensors are often biased by additional parameters(e.g.,temperature)when performing certain measurements(e.g.,pressure);to eliminate measurement errors,dualparameter sensors need to be constructed.However,the spectral characteristics of twoparameter sensors represented by tandem F-P cavities are usually complex,and it is difficult for existing demodulation algorithms to accurately solve their individual cavity lengths simultaneously with high accuracy.To address the above problems,a cascaded dual-cavity fiber optic F-P sensor is designed and fabricated,and a phase-based white light interference demodulation algorithm is proposed for the signal demodulation of this sensor.The problem of low accuracy of the conventional demodulation algorithm in performing demodulation of multi-F-P cavity sensors is solved.The paper presents a detailed analysis of the principle of the cascaded dual-cavity fiber optic F-P sensor,a simulation study of the proposed demodulation algorithm,and fabrication and testing of the performance of the cascaded F-P sensor,as follows:Firstly,the multi-beam interference model of the cascaded dual-cavity fiber optic F-P sensor is analyzed in depth,and the complex spectrum is derived in detail to provide basic support for the design of the demodulation algorithm.A demodulation algorithm is proposed for the cascaded dual-cavity fiber optic F-P sensor to obtain the cavity length information of each F-P cavity by separating each peak of its spectral signal and applying fast white light interference demodulation algorithm to each peak information.Secondly,the proposed demodulation algorithm is simulated and analyzed,and the four main factors affecting the demodulation accuracy are: cavity length,light source bandwidth,wavelength resolution and noise on the demodulation accuracy;the results show that the algorithm is universally applicable to cavity length 100μm-600μm,the bandwidth has a large impact on the demodulation accuracy,and the demodulation error decreases significantly with the expansion of bandwidth.Finally,the cascaded dual-cavity fiber optic F-P sensor is fabricated under laboratory conditions,and the temperature and pressure fiber optic sensing test system is built to experimentally test the proposed white light interference demodulation algorithm.The test results show that the algorithm can demodulate the cascaded dual-cavity fiber optic F-P sensor with high accuracy,and the demodulation results are consistent with the theoretical values.The cascaded dual-cavity fiber optic F-P sensor is capable of accurate temperature and pressure measurements,and the sensor has a temperature sensitivity of 35.31 nm/℃ and a pressure sensitivity of 7.461 μm/MPa.