Temperature-insensitive photonic crystal fiber interferometer for absolute strain sensing

Abstract

The authors report a highly sensitive $(\sim 2.8\mathrm{pm}∕\mu \epsilon )$ wavelength-encoded strain sensor made from a piece of photonic crystal fiber (PCF) spliced to standard fibers. The authors intentionally collapse the PCF air holes over a short region to enlarge the propagating mode of the lead-in fiber which allows the coupling of only two modes in the PCF. The transmission spectrum of the interferometer is stable and sinusoidal over a broad wavelength range. The sensor exhibits linear response to strain over a large measurement range, its temperature sensitivity is very low, and for its interrogation a battery-operated light emitting diode and a miniature spectrometer are sufficient.