Abstract
We present the theoretical study of a novel highly sensitive,
miniaturized, integrated optic refractive index sensor based on a Au-Ag
surface grating. The grating is considered to be made of alternate layers of
equi-thick Au and Ag regions along the direction of propagation, on the
surface of the waveguide. Due to the same thickness of both the metals, the
surface plasmon polaritons (SPP) for both metals have their field maxima at
the same transverse distance, leading to an increased modal overlap in the
grating region and hence a reduced grating length. An exact
coupled-mode-theory based on the local mode matching has been used to
analyze the mode coupling between the guided mode and the SPP. It has been
shown that the proposed design requires nearly one fourth of the grating
length as compared to the corrugated metal grating for the same metal
thickness. Further, for co-propagating mode coupling (LPG based sensor) the
structure is found to be maximum sensitive at an optimum metal thickness,
however, such an optimum metal thickness does not exist for
counter-propagating coupling (FBG based sensor).
© 2010 IEEE
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