Polarization optimization for a full sensitivity in azimuthal grating coupled surface plasmon resonance

We present a method to explore the full sensitivity of grating coupled surface plasmon resonance (GCSPR) sensors on an azimuthally rotatable grating by optimizing the polarization angle of the incident light. This is the condition where double surface plasmons polaritons (SPPs) can be excited by a single wavelength [1]. This configuration provides a sensitivity up to 950°/RIU compared to a system without azimuthal control [2]. We show here that the sensitivity of this configuration is only achievable when the polarization angle of the incident light is optimized. This is due to the excitation of a fully coupled SPP (as can be observed as a deeper dip in the reflectivity spectra) which is only possible using the optimized polarization angle in an azimuthally rotated grating. This result in a well-defined, sharper spectrum and the positions of the minima are more obvious. The figure of merit (FOM) increases by 50–100% compared to spectra collected using p-polarized light. We demonstrate this sensitivity using a dodecanethiol (C12) self-assembled monolayer (SAM) on a Au grating surface, representing a thickness difference of 1.5 nm compared to the uncoated grating. Using the new configuration with optimized polarization angle, a shift in resonance angle as large as 3.6° can be observed. In principle, we expect the refractive index resolution of this method to be on the order of 5 × 10−7 RIU.