Fiber-coupled in-line heterodyne optical interferometer for minimally invasive sensing

In this paper, the first fiber-coupled no-moving-parts scanning heterodyne interferometer design using a single acoustooptic device (AOD) is reported. The design features a high-stability inline reflective architecture with free-space-scanned minimally invasive sensing via a multizone reflective sensor chip. The common path fiber interconnection allows robust remoting of the compact sensing front end. A proof-of-concept sensing experiment measuring voltage-dependent birefringence is successfully conducted using a voltage-controlled nematic liquid crystal (NLC) sensor chip. The system features a 4.69-dB optical loss, a 200-MHz output frequency, and a 1550-nm eye-safe operation wavelength. Applications for the system include any fiber-remoted sensing using the proposed free-space minimally invasive interrogating optical beams.