Spatial coupled-mode theory for surface plasmon polariton excitation at metallic gratings

We develop a framework of the spatial coupled-mode theory for surface plasmon polariton (SPP) excitation at metallic gratings. The spatial mode coupling process is investigated in order to understand the spatial field distribution during the SPP excitation. We show that the spatial mode coupling coefficients are constrained by the energy conservation, the time-reversal symmetry, and the geometry mirror symmetry. As the result, a semi-analytical form is obtained to fast compute the total field distribution for an arbitrary incident light. This study paves the way for optimizing the incident light modulation to dynamically control the localized intensity distribution of the SPP excitation, which is practically significant in surface-enhanced applications, such as plasmonic tweezers, optical sensors, and spectroscopy. (C) 2016 Optical Society of America