Fiber optic accelerometer

Abstract

First and second coils (A, B) of optical fibers are disposed adjacent opposite ends of a housing (40). The housing defines an interior reservoir which contains a material (C) having substantial mass. Preferably, the material is a dense fluid such as mercury. Phase coherent light from a laser (10) is transmitted through the first and second optical fiber coils. The phase coherent light passing through the first and second coils is combined by an optical coupler (22). Under acceleration, the pressure to which the mercury subjects the two fiber optic coils varies by a pressure differential that is proportional to acceleration. The pressure differential causes a corresponding elongation and contraction of the optical fiber lengths which, in turn, causes a corresponding optical phase shift. The optical phase shift is detected interferometrically providing optical intensity changes. Photodiodes (30,32) detect the combined light and product electrical signals which vary with changes in the intensity of the combined light. A signal processor (34) translates the detected phase shift into an indication of acceleration for display on an acceleration indicator (36). Optionally, a phase modulator (62) may adjust the phase of the light transmitted through one of the fiber optic coils in such a manner that absent any acceleration, the light transmitted through the first and second fiber optic coils have a preselected phase relationship. Under acceleration an electrical feedback signal is applied to the phase modulator (62) to counter balance the acceleration produced phase shift, in which case the electrical feedback signal is translated into the acceleration indication.