Abstract

For the purposes here, a high performance sensing application is defined as one that simultaneously requires high sensitivity (1-100 fε), wide bandwidth (1-100 kHz), and large dynamic range (>120 dB). High performance fiber optic sensing applications include tactical and surveillance grade underwater acoustics, high sensitivity acceleration, and acoustic and seismic sensing for oil exploration. Traditionally, high performance fiber optic sensor systems have relied on interferometric measurement techniques to extract the strain information from the fiber optic transducer. Although performance requirements must always be met, cost is also a major factor and as a result fiber optic sensor systems usually incorporate some level of multiplexing to amortize the cost of the laser and other expensive optical components. Frequency, wavelength, and time division multiplexing (FDM, WDM, and TDM) are all applicable to fiber optic sensor multiplexing and have seen use in fielded systems with multiplexing gains from 10~ 100. Generally there is an increase in the self-noise of the interrogation system with higher multiplexing gains. This results in an equivalent decrease in the sensor sensitivity unless the scale factor of the transducer is increased accordingly. Typically the self-noise of an interferometric sensor is independent of the length of fiber on the transducer, so increasing the amount of fiber on the transducer will increase its scale factor and maintain the required sensitivity. In this way, within limits, the stale factor of interferometric transducers can be simply tailored to the sensitivity and multiplexing requirements. Multiplexing can also impact the bandwidth and dynamic range of the system. This is most noticeable in TDM architectures, where the sample rate of the system sets fundamental bandwidth and dynamic range limitations.

© 2002 Optical Society of America