For interferometric fiber sensors, the fiber Fabry-Perot interferometer (FFPI)1 has the simplest form and can be much more sensitive than the Mach-Zehnder arrangement, because the FFPI uses multiple-beam interference in a single fiber. We have developed new schemes for fiber sensors using these features of FFPI. Figure 1 shows the schematic diagram for a fiber-optic microphone system using FFPI. The FFPI consists of a 1-m long single-mode fiber with end surfaces which are dielectric coated at the surface reflectance of R = 80%. The input light is a frequency-stabilized single-mode He-Ne (λ= 633-nm) laser.
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