Highly-Sensitive Temperature Sensor Based on an All-in-Fiber Directional Coupler

A highly-sensitive all-in-fiber temperature sensor was designed and demonstrated based on a directional coupler by infiltrating self-made refractive index matching fluid (RIMF) into a single eccentric hole-assistant dual-core fiber (DCF). The beam propagation method was used to analyze the coupling characteristics of the single eccentric hole-assistant DCF, which demonstrated that the central core and the suspended core of the DCF would couple to form a directional coupler when the refractive index of the RIMF is between 1.452 and 1.453. Then, this in-fiber directional coupler was fabricated and used for temperature sensing. The experimental results showed that the temperature sensitivity of the sensor could be up to 52.194 nm/°C in the temperature range from 7.207 °C to 10.920 °C. In addition, the sensor had good stability, repeatability, and hysteresis. It is expected to have great potential in highly-sensitive sensing applications.