Chonghua Zhou
S. V. Letcher
Dept. of Phys., Univ. of Rhode Island, Kingston, RI 02881
A. Shukla
Raman Singh
Univ. of Rhode Island, Kingston, RI 02881
Both interferometric and reflective-intensity fiber-optic microphones that exploit the fiber-optic advantages of electromagnetic-interference immunity, small size, and robustness are described. The interferometric microphone is a low-finesse Fabry--Perot sensor in which interference occurs between the light reflected from the end face of the fiber and that reflected from the membrane. The return signal is directed to a fast photodiode. The sensor has a flat frequency response from 50 Hz to 20 kHz. The phase shift is directly proportional to the amplitude of the diaphragm displacement with a broad dynamic range. The sensitivity is 2 rad/Pa and the minimum detectable pressure is less than 0.001 Pa when the phase shift is measured at quadrature. The intensity-reflection microphone simply measures the change of the intensity of light that is recaptured by the fiber after reflection from the diaphragm. It has the advantage of low cost and ease of sound reproduction. In a dynamic range of more than 60 dB, it is linear and has a flat frequency response from 50 Hz to 20 kHz. The minimum detectable pressure is 0.1 Pa. [This work is supported, in part, by NSF Grant No. MSS-9101514.]