Simplified Hollow-Core Fiber-Based Fabry–Perot Interferometer With Modified Vernier Effect for Highly Sensitive High-Temperature Measurement

In this paper, a high-temperature fiber sensor based on an optical fiber Fabry–Perot interferometer is fabricated by splicing a section of simplified hollow-core fiber between two single-mode fibers (SMFs) and cleaving one of the two SMFs to a certain length. With the superposition of three beams of light reflected from two splicing joints and end face of the cleaved SMF, the modified Vernier effect will be generated in the proposed structure and improve the sensitivity of temperature measurement. The envelope of spectrum reflected from the proposed sensor head is modulated by the ambient temperature of the sensor head. By monitoring and measuring the shift of spectrum envelope, the measurement of environment temperature is carried out experimentally, and high temperature sensitivity of 1.019
$\hbox{nm}/^{\circ}\hbox{C} $
for the envelope of the reflected spectrum was obtained. A temperature measurement as high as 1050
$^{\circ}\hbox{C}$
has been achieved with excellent repeatability.