Ultrasensitive dual Fano resonance sensor based on coupling of plasmonic and multi-order waveguide modes

The Fano resonance (FR)-enhanced surface plasmon resonance (SPR) sensor has garnered extensive research attention because of its original advantages of label-free and real-time monitoring. However, most work is limited to a single FR, thus lacking the capability for multi-parameter sensing. In this paper, based on the coupling of surface plasmon polariton (SPP) mode with multi-order planar waveguide (PWG) modes, a dual-FR sensor for simultaneous refractive index and temperature sensing is designed and analyzed. To investigate the coupling behavior, a theoretical model integrating the electromagnetic system and oscillator system is established. Compared to a traditional multilayer uniform structure, the silicon (Si) subwavelength grating (SWG) used as the sensing waveguide layer offers greater design flexibility and enhanced sensitivity. The sensing characteristics of dual FRs and the dual-parameter sensing performance are also analyzed in detail. The proposed sensor not only exhibits extremely high intensity sensitivity and figure of merit (FOM) in dual-parameter sensing but also shows that the order of FRs has a high linearity with intensity sensitivity. Our work provides significant potential for ultra-high sensitivity multi-parameter sensing.