Composite cavity fiber tip Fabry-Perot interferometer for high temperature sensing

Abstract A simple composite cavity fiber tip (CCFT) Fabry-Perot interferometer (FPI) is proposed and experimentally demonstrated. The composite cavity is composed of an air cavity and a silica cavity. The air cavity is an elliptical air hole embedded in the SMF. The silica cavity is a short section of SMF cascaded to the air cavity. To avoid the influence of other external physical quantities (refractive index, humidity, etc.) on the CCFT FPI, the CCFT was successfully encapsulated by a tapered-shaped silica capillary. The packaged CCFT FPIs were applied for high temperature sensing in the range of 100–800 °C. Temperature sensitivity of 14.31 pm/°C was obtained for the silica cavity. In addition, the composite cavity can be fabricated to be very small in size (dozens of micrometers) with extremely low-cost, thus the CCFT FPI can be a competitive candidate for local point temperature sensing.