Polarization-maintaining Fiber Sensor Based On Reflective Lyot Structur

Based on the orthogonal polarization modes in fast and slow axis transmission of polarization maintaining fibers,a polarization maintaining fiber Sagnac-loop structure and a polarization maintaining fiber(PMF)reflective Lyot structure were constructed,respectively.Compared with the two structures,it was found that the reflective Lyot structure has the advantages of compact structure,material saving,and easy fabrication,making it a research focus in the fiber sensor field.This article investigates the sensing characteristics of circular and reflective structures,and investigates the sensitization scheme of reflective Lyot structures based on the cursor effect.The main research content includes:The spectral characteristics of polarization maintaining fiber Sagnac-loop structure were studied using Jones matrix theory and numerical simulation methods.We also conducted strain,torsion,and temperature sensing experiments with different PMF lengths.When the PMF length was 15 cm,the sensitivities were 13.58 pm/ με,26.8 pm/°,-1.772 nm/℃,respectively.In temperature sensing testing,FBG was used to modulate the spectrum,achieving the conversion from wavelength demodulation to intensity demodulation.When the PMF length was 30 cm,the sensitivity was 11.3 d B/℃.The spectral characteristics of polarization maintaining fiber reflective Lyot structures were studied using Jones matrix theory and numerical simulation methods.Strain,torsion,and temperature sensing experiments were conducted on PMFs of different lengths.When the PMF length was 15 cm,the sensitivities were 12.61 pm/με,57.6 pm/°,-1.71nm/℃,respectively.The experimental results show that the reflection structure is more compact than the ring structure.The FSR of the reflection structure with a PMF length of 15 cm is 22.7 nm,which is the same as that of the ring structure with a PMF length of 30 cm.To achieve the same FSR interference spectrum,only half of the length of the ring structure requires a polarization maintaining fiber.Based on the polarization maintaining fiber reflective Lyot structure,an F-P interferometer that also belongs to the reflective structure is selected for vernier amplification matching.Select the appropriate length of two structures that match the cursor through numerical simulation.Study the parallel,cascade,and series vernier schemes of reflective Lyot structures and F-P cavities,respectively.Strain,torsion,and temperature sensing experiments were conducted on three schemes,and the series scheme was optimized.By comparison,it was found that the system structure of the direct melting series vernier scheme is the most compact,with stable and controllable interference and vernier effects.It has a good tolerance for the energy difference between two interference spectra,and the structure preparation is simple,which can be used in the strain and temperature related sensing,with great practicality.