Label Free All-Fiber Static Pressure Sensor Based on Vernier Effect with Temperature Compensation

This paper reported a label free, all-fiber static pressure sensor constructed by cascading two single mode fiber(SMF) - few-mode fiber(FMF) - single mode fiber(SFS) critical wavelength structures. Vernier effect was adopted to magnify the static pressure wavelength sensitivity of the interference peaks and the superimposed transmission spectrum has an envelope which the free spectrum range varies with wavelength and reaches maximum when approaching the envelope critical wavelength (CWL_E). Thus, the envelope peaks near the CWL_E in the transmission spectrum with the modified Vernier effect is label free, which is easy to recognize and entirely different from the envelope peaks in a transmission spectrum with uniform free spectrum range. Both theoretical and experimental results show that the envelope peaks near the CWL_E exhibit different static pressure and temperature wavelength sensitivities, and the wavelength sensitivity increase significantly when the envelope peak approaching the CWL_E. The experimental results show that the left envelope peak 1 and the left envelope peak 2, which numbered from the peak on the left side and closest to the CWL_E, have different static pressure sensitivities of 4.072 nm/MPa and 2.649 nm/MPa, respectively, and temperature sensitivities of 1.753 nm/°C and 1.045 nm/°C, respectively. The performances of this proposed approach can be further improved by optimizing the physical lengths of the FMF employed in the sensing and reference SFS structures, to satisfy the requirements in practical applications, especially the extreme conditions and two-parameter measurement of ultra-high pressure and high temperature.