Multiplexed Fibre-optic Sensors Using Ring Interferometers

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Abstract
We describe a number of multiplexing techniques which may be used for fibre-optic sensors in which the sensing element is a ring resonator. The basic optical unit comprises a sensing ring resonator connected to a second interrogating ring resonator of nearly equal length, and illuminated by a source of short coherence length. A number of such units may be combined to form an array, using coherence multiplexing techniques. Using such an arrangement, the high finesse of the ring resonator may be exploited to yield a sensor of increased sensitivity over that obtainable with a two-beam interferometer. When a high-coherence source is used, then multiplexing may be accomplished using frequency-division techniques. However, in this case, the resonators must have low finesse, in order to avoid cross-talk. We also show that when a source of moderate coherence length is used, it is possible to use both frequency division and coherence multiplexing simultaneously, with the potential of realizing a large sensor array.