Multiplexed heterodyne fiber interferometer that uses laser-diode modulation

An interferometer has been developed that uses a bundle of fibers and a current-modulated laser diode. Light from the laser diode is distributed to three fibers whose exit ends are fixed together, and fiber lengths are chosen so that their differences will not be equal. From the phase of separated heterodyne signals produced between the reference and the sensor fibers we can detect the change in optical path length that is caused in the sensor fibers by external perturbations. As an application, temperature sensing at two points has been demonstrated.