Ultra-long-period fiber grating cascaded to a knob-taper for simultaneous measurement of strain and temperature

This study presents a simple Mach-Zehnder interferometer (MZI) to obtain the bimodal characteristics that realize simultaneous measurement of strain and temperature through cascading an ultra-long-period fiber grating and a knob-shaped taper. We obtain the multi-dip feature from the MZI, and the Dips 2 and 5 are selected from 11 interference dips. Experimental results indicated that the wavelength sensitivities of Dips 2 and 5 are - 0.54 nm m epsilon(-1) and 0.058 nm degrees C-1, and - 0.53 nm m epsilon(-1) and 0.055 nm degrees C-1 to strain and temperature, respectively. The depth sensitivities are - 3.3 dB m epsilon(-1), - 0.015 dB degrees C-1 and -5.8 dB m epsilon(-1), and 0.06 dB degrees C-1 for Dips 2 and 5, respectively. It is concluded that the proposed structure is suitable for simultaneous strain and temperature measurements.