Sensing performance optimization of the Bloch surface wave biosensor based on the Bloch impedance-matching method.

We propose a novel strategy to optimize sensing performance of the Bloch surface wave (BSW) biosensor. First of all, a one-dimensional photonic crystal with an omnidirectional photonic bandgap is designed. Except for sustaining the BSW, the omnidirectional photonic bandgap guarantees a tiny full width at half maximum (FWHM=0.84  nm) for the reflection dip induced by BSW resonance. Then, the specific dependence of wavelength sensitivity on incident angle is obtained by the Bloch impedance-matching method. Study shows that wavelength sensitivity increases with the decreases in incident angle (larger than the critical angle). At the same time, when the incident angle approaches the critical angle (θ=67.5  deg), wavelength sensitivity increases rapidly (S=1570  nm/RIU). Moreover, theoretical research reveals that biosensor sensitivity can also be further enhanced by other system parameters. Combining the tiny FWHM of the reflection dip and large wavelength sensitivity, the figure of merit of the optimized biosensor can reach as high as 1869  RIU. These results enable the design of biosensors with high performance in a predictable manner.