QPS Photronics Inc. has launched large sensor arrays that have up to 100 FBGs in each array, with the length of the fiber stretching to a distance of up to 20 km. Through a front-end switch matrix, 16 of the fiber arrays can be connected to form a star network that contains 1600 sensors. The networks are interrogated via time division multiplexing technology, by which the FBGs are separated by fixed distances of between 10 and 100 m. The interrogation unit sends a narrow pulse of light energy down each fiber channel, and light reflection from the first FBG arrives first at the detector, followed by reflections from the others in the array. The receiver contains a time-gated detection circuit with an edge filter to convert the light signal back to the wavelength domain.

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