Nano-displacement sensor based on photonic crystal fiber modal interferometer.

A stable nano-displacement sensor based on large mode area photonic crystal fiber (PCF) modal interferometer is presented. The compact setup requires simple splicing of a small piece of PCF with a single mode fiber (SMF). The excitation and recombination of modes is carried out in a single splice. The use of a reflecting target creates an extra cavity that discretizes the interference pattern of the mode interferometer, boosting the displacement resolution to nanometer level. The proposed modal interferometric based displacement sensor is highly stable and shows sensitivity of 32 pm/nm.

Micro-tip Cantilever as Low Frequency Microphone.

We propose a very compact diaphragm free optical microphone consisting a tapered micro-tip in cantilever configuration for detection of low frequency acoustic signals. The change in the light coupling between the micro-tip and the source fiber caused by the acoustic pressure is utilized to detect the external acoustic signal. The sensitivity and working range of the sensor depend on three key factors, the length of the micro-tip cantilever, the distance between the micro-tip and SMF, and the offset between the micro-tip central axis and SMF central axis. Hence, by changing any of these parameters, the performance of the sensor can be easily tuned. Experimental results show that for a cantilever length of 15 mm, the probe has a maximum acoustic sensitivity of 10.63 mV/Pa or -159.5 dB re 1 V/µPa, noise-limited minimum detectable pressure of 19.1 mPa/√Hz and the linear frequency range is 0-400 Hz. The SMF only structure along with photodetector-based interrogation makes this acoustic sensor economical.