Аннотация:A simple compact optical sensor system consisting of a near-field external cavity coupled to a semiconductor laser is reported.In this device, a change of phase in the light fed back into the laser cavity by the perturbed external mirror modulates the output of the laser by effectively changing the laser facet reflectivity.Phase shifts of 9 .rad and rad were measured at 10 kHz and 100 Hz, respectively, using a 1-Hz bandwidth and a 98-percent reflector placed less than 10 pm from the laser facet.The sensitivity of these devices is shown to be limited by the intrinsic amplitude noise of the laser.The implementation of this sensor configuration is reported as an acoustic sensor, hydrophone, magnetic field, and current sensor as well as an accelerometer. I. INTRODUCTIONA DVANCES in optical sensors have recently occurred primarily in fiber-optic systems.These devices sense either a change in phase or amplitude of the light propagating in the fiber due to a perturbation by an external field.Phase sensitive devices consist of single-mode fiber, generally, con-
