Ultra-sensitive and dual-polarization refractive-index biosensors based on annular photonic crystals

We report new refractive-index biosensors with obviously enhanced sensitivity based on annular photonic crystals. Due to the introduction of dielectric rods into the air holes, the upper frequency edge of band gap of annular photonic crystals will be drawn to lower frequencies. This is quite helpful for annular photonic crystals to support as high as 2–3 times relative sensitivity than conventional photonic crystals. Based on this feature, a novel slotted annular photonic crystal waveguide is proposed to show its ultra-sensitive performance. More interesting contribution of this work is that we have proposed a new definition of relative sensitivity by measuring the difference of cross-polarization relative sensitivity of annular photonic crystals. Based on such definition, a novel conception of dual-polarization refractive-index biosensors with ultra-sensitive performance has been proposed and successfully demonstrated in theory.