Paper TF+BI-ThA2
Sensitivity Enhancement in Grating Coupled Bloch Surface Wave Resonance by Azimuthal Control

Thursday, November 10, 2016, 2:40 pm, Room 104E

Bloch surface waves (BSWs) are electromagnetic excitation modes that exist at the interface of truncated dielectric multilayer structures and a homogeneous medium. Although BSWs are intrinsically present at such interfaces, they cannot be directly excited by light incident from the homogeneous medium due to their non-radiative and evanescent nature. The use of a grating coupler or a prism mitigates this inability by providing an additional momentum to the free-space wave vector required to satisfy the phase matching condition with the BSW wave vector. Since Grating-coupled Bloch surface wave resonance (GCBSWR) bio-sensors do not require a bulky prism to couple light into BSWs, they are strong candidates for nanoscale bio-sensors. But GCBSWR bio-sensors, based on either wavelength or angular interrogation, are observed to be less sensitive compared to prism-coupled Bloch surface wave resonance (PCBSWR) bio-sensors. However, due to their inhomogeneous surface architecture, GCBSWR bio-sensors can be interrogated by rotating the grating platform azimuthally. Exploiting this ability, here we present a new method for improving sensing capability of GCBSWR bio-sensors. We demonstrate computationally, using a three-dimensional scattering matrix based rigorous coupled wave analysis method, that the proposed azimuthal angle interrogation technique highly enhances the sensitivity of GCBSWR bio-sensors. For our study we use a sixteen layered TiO₂-SiO₂ multilayer with SiO₂ gratings on the top sensing platform. We fix the wavelength and incident angle of the incoming light, and sweep over the azimuthal angle to simulate the sensitivity as a function of changing refractive index of the sensing layer. Furthermore, we show that contrary to conventional GCBSWR bio-sensors that only work for transverse electric mode, azimuthal angle based GCBSWR bio-sensors work for both transverse electric and transverse magnetic modes.