A conjugate optical confocal Fabry-Perot interferometer for enhanced ultrasound detection

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Abstract
To detect ultrasound remotely, an optical detection scheme is described which uses a confocal Fabry-Perot interferometer and conjugate detection. A conjugate signal is derived from the interferometer by making simultaneous use of signals derived from optical back reflection, and optical transmission, through the interferometer. Theoretical analysis and experimental results have demonstrated that the new scheme has a higher sensitivity than those described previously. Sensitivity enhancements between 2 and 17 times can be expected. Depending on mirror reflectivity, the frequency response is approximately flat in the range of 10 MHz and above, limited only by the free spectral range of the interferometer device.