Simultaneous Detection of Multiple Fiber-Optic Fabry–Perot Interferometry Sensors With Cepstrum-Division Multiplexing

Increasing the capacity of an array of sensors is a major challenge in fiber-optic sensing networks. Whereas fiber Bragg grating (FBG) sensors can be discriminated in the spectrum domain, through the popular wavelength-division-multiplexing (WDM) approach, Fabry-Perot interferometry (FPI) sensors have a broad spectrum and are not suitable for WDM. In this paper, a novel approach for the simultaneous detection of multiple FPI sensors is proposed. The key is decoding sensors in the optical cepstrum (spectrum of the optical spectrum) domain, using a Capon estimator. Subsequently, the small cepstrum shifts are accurately detected with a fast-phase correlation method. This approach is labeled cepstrum-division multiplexing (CDM). CDM has been tested on a simulated FPI array, with a coarse wavelength grid typical of most FBG interrogators. Unambiguous and simultaneous detection of 20-39 sensors is achieved, improving over previous methods limited to 1-3 sensors; 0.04-nm accuracy on cavity length estimation has been achieved. A preliminary experimental demonstration has been set up to validate the CDM approach.