Sensitivity enhancement in grating coupled surface plasmon resonance by azimuthal control.

We present a method for improving the sensing capability of grating coupled surface plasmon resonance (GCSPR) sensors. The grating is rotated azimuthally (phi) until the excitation of double surface plasmon polaritions (SPPs) by a single wavelength is possible. Close to this condition, further tuning of the incident wavelength will merge the double SPPs into a multi-SPP resonance which is angularly broad but spectrally sharp. This is the condition where the momentum vector of the propagating SPP is perpendicular to the incident light momentum. We demonstrate this sensitivity enhancement on a Au grating surface using a dodecanethiol (C12) self-assembled monolayer (SAM). Using this method, a shift in resonance angle as large as 3 degrees can be observed. The simulated sensitivity of this method shows that a sensitivity up to 800 degrees /RIU is achievable, which is one order of magnitude greater than that in a conventional fixed grating (phi = 0 degrees ) as well as the prism-coupled Kretschmann configuration.