Multilongitudinal Mode Fiber Laser Sensor Demodulation Based on Bandpass Sampling

This letter proposes a novel demodulation system for multilongitudinal mode (MLM) fiber laser sensors via bandpass sampling receivers. The MLM fiber laser sensor generates a wideband multitone signal, wherein any tone can be used as a sensing signal, so the wideband signal can be filtered into a bandpass signal from which the applied measurand can be demodulated. If the bandpass signal satisfies the unaliasing condition for the bandpass sampling, it can be digitized and down-converted by a low-sample-rate analog-to-digital converter (ADC) without aliasing. Unlike the conventional superheterodyne receiver, which down-converts the RF signal to the IF signal before the ADC in the demodulation system, the bandpass sampling receiver does not require a frequency translation stage which is typically the source of a number of potential difficulties, including age-based, temperature-based, and nonlinear performance. We performed a proof-of-concept experiment in which an MLM fiber laser sensor with a ring cavity was successfully demodulated by the proposed bandpass sampling receiver.