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 mε^?1 and 0.058 nm °C^?1, and ??0.53 nm mε^?1 and 0.055 nm °C^?1 to strain and temperature, respectively. The depth sensitivities are ??3.3 dB mε^??1, ? 0.015 dB °C^?1 and ?5.8 dB mε^?1, and 0.06 dB °C^?1 for Dips 2 and 5, respectively. It is concluded that the proposed structure is suitable for simultaneous strain and temperature measurements.