Agarose-Gel Based Guided-Mode Resonance Humidity Sensor

A photonic relative-humidity (RH) sensor employing the guided-mode resonance effect is designed, fabricated, and characterized. An agarose-gel transduction layer is integrated with a periodic silicon-nitride film to form a sensitive optical resonance structure. As the agarose-gel humidifies, the resonance wavelength shifts. Comparison with rigorous diffraction models allows quantification of the gel's refractive index and the attendant relative humidity. For the example sensor structure treated, the resonance wavelength shifts by ~9 nm on relative-humidity change from 20% RH to 80% RH