Displacement and temperature sensor based on whispering gallery effect within unsymmetrical U-type fiber structure

We experimentally demonstrate displacement and temperature sensing based on the whispering gallery effect (WGE) within an unsymmetrical U-shaped tapered-fiber. The tapered-fiber (TF) is created by heat pulling a single-mode fiber (SMF) and bent in the region transition using the three-dimensional control platform to form an unsymmetrical U-shaped. Due to the light leaks into the cladding, most of the light is transmitted along the inner wall of the cladding in the form of WME. The Mach-Zehnder interference (MZI) fringes are caused by the cladding mode and the core mode. The can be used in a small space within 2.3 mm. The proposed sensor can achieve displacement measurement in the micron scale and has a maximum displacement sensitivity of about 38 pm/μm and 0.048 dB/μm over a displacement range of 10−60 μm at room temperature. The temperature sensitivity reaches 10.1 pm/°C when the waist diameter is 2.3 μm at the range of 20−60 °C. The device is compact, robust in mechanical strength, simple in fabrication, and can be easily used in small space physical measurements.