FBG-microfiber-FBG cascade Fabry-Perot interferometer for simultaneous measurement of temperature and refractive index

A microfiber Fabry-Perot interferometer (FPI) which employs two fiber Bragg Gratings (FBGs) as reflection mirrors and a short length microfiber as its cavity is proposed and fabricated. Theoretic study shows that the reflection spectrum of such microfiber FPI is consisted of two parts - interference fringes induced by FPI and reflection band induced by FBGs. Temperature affects both parts while ambient refractive index only influences the first part, i.e. microfiber FPI has different response to temperature and RI. Therefore, Dual-parameter measurement is experimentally demonstrated by tracking the FSR variation and the central wavelength shift of the reflection spectrum of microfiber FPI.