Abstract
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.
Highlights
Low frequency acoustic signal detection is one of the major fields of interest owing to its application in the field of differential acoustic resonance spectrometry (DARS), cervical auscultation and low frequency vibro-acoustic analysis[1,2,3]
In order to overcome the complexity involved with diaphragm fabrication and to avoid the requirement of costly phase/wavelength measuring devices, we propose a very compact diaphragm free acoustic sensor consisting an optical fiber micro-tip in cantilever configuration
Detailed theoretical and experimental analysis is done on the performance of our acoustic sensor for different cantilever lengths and the experimental results are in good agreement with theoretical analysis
Summary
The tapered micro-tip is tightly clamped on a V-groove attached to a computer-controlled stage P1 in such a way that it creates a cantilever of length ~15 mm, as shown in the Fig. 1. As it can be seen, the photodetector output for distinct values of x follow Gaussian distribution curve. This distribution is similar to that of the fundamental mode (LP01) profile of standard SMF shown in the inset of Fig. 2(b), and the variation of electric field along the core axis is plotted in Fig. 2(b) by black line.
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