Code Division Multiplexing Applied to FBG Sensing Networks: FBG Sensors Designed as Discrete Prolate Spheroidal Sequences (DPSS-FBG Sensors)

We propose and demonstrate a sensing system with fiber Bragg grating sensors designed as discrete prolate spheroidal sequences (DPSS). In this way, we can encode all of the sensing devices in the network making sure that each sensor is completely distinguishable from each other even under overlapping conditions. Since these devices are complex structures involving unique magnitude and phase response, the demodulation method should be able to recover the associated magnitude and phase response in order to identify each device in the sensing network. To do so, we use a single side band modulated optical source sweeping over the operational wavelength range of the sensors, the reflected signal from the sensors is sent to a vector network analyzer in which it is obtained the magnitude and phase ratio of the network in the microwave domain. Experimental demonstration has been carried out including the manufacturing of DPSS structures. Feasibility of the interrogation technique for devices involving magnitude and phase distinction has been validated, not only to identify encoded sensors in a measurement network but also to allow overlapping between them, which allow to increase the number of sensors allocated in the sensing network.