A wide range of optical sensing modalities rely on the ability to accurately measure the optical phase of an interrogating beam. This includes both fiber and free space sensors designed to measure a range of parameters which can be mapped to a change in the optical pathlength, including temperature, strain, pressure, acoustic signals, or magnetic fields. All of these systems rely on extracting the optical phase of an interrogation beam, and as a result, several methods have been developed to measure the phase. The most common techniques rely on either phase or frequency modulation and detection is performed using a single photodetector with a fast response time. Historically, this approach made sense due to the availability of low cost, high speed photodetectors.
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