Optical position sensor

Abstract From the Canadian patent

An optical position sensor for indicating the position of a movable body with respect to a reference point. A first optical signal at one wavelength and a second optical signal at a different wavelength, both modulated at a radio frequency are, transmitted through an optical fiber to the reference point at which a semi-reflecting mirror which passes the first signal and reflects the second signal is disposed. The first signal is reflected by the body into the optical fiber and a phase, comparator coupled to the fiber compares the phases of the modulating signals on the reflected first signal and the reflected second signal to determine the position of the body relative to the mirror.