Fiber Optic Fabry Perot Vector Sensor Arrays

Conventional accelerometers are non-optimal for many submarine sensor applications, especially for hydrophone towed arrays. Limitations include size and weight, need for heavy copper conductors, susceptibility to electromagnetic interference and electrical cross talk, and limited cable drive capability. VIP Sensors proposes to develop a sensor measuring system consisting of optical MEMS vector sensors distributed on a single optic fiber, each working at different frequency ranges. A broadband high intensity LED is used as a light source for the serially connected accelerometers. Each optical sensor, tuned to work at a unique frequency of the spectrum, shifts (modulates) its corresponding input signal frequency proportional to the measured pressure and lets pass all other frequency signals. The light at the end of the optic fiber contains the information for all sensors at different preset frequency slots, in a scheme similar to Wave Division Multiplexing. An optical demultiplexer located at the fiber end separates the signal spectrum. A photodiode array converts the photons to electrons and specialized circuitry quantifies the frequency shift corresponding to each sensor. The sensor is sculptured on silicon wafer using MEMS processes. It consists of a mass hanging on a flexure hinge. A strand of optical fiber is attached on the surface of the sensor chip with an intrinsic Fabry Perot cavity laid between the mass and the rigid frame. The inertia force rotates the hanging mass about the flexure hinge. The mass displacement stretches or compresses the fiber. The strain in the fiber changes the length of the Perot cavity, which causes the shift of the incoming light wavelength. The shift of wavelength is thus proportional the inertia force or acceleration.