Self-referencing reflective multiplexing technique for fiber optic sensors and switches

An RF optical modulation technique for multiplexing and self-referencing a number of transmissive analog fiber optic intensity sensors has been extended to work with reflective fiber optic sensors and switches. Two sensor configurations, each utilizing a linear RF ramped optical signal, were investigated. In the first “star” configuration, reflective optical transducers were located at the ends of a multiport splitter, representing 3 bits of digital data and one signal used for intensity self-referencing. The second configuration involved using self-referencing reflective sensor modules connected in series. Light in each module was coupled out of the transmission line, passed to the reflective transducers, reflected, and reinjected into the transmission line. In each system, the reflective sensor's return signals were detected and electrically mixed with the input resulting in beat signals of different frequencies corresponding to the sensor arms' differing path lengths. Self-referencing compensated for source fluctuations and varying optical loss characteristics between the sensor modules and the signal processing location. The theoretical basis of the technique is presented and experimental results are given.