Hybrid Plasmonics: Structures for Optical Sensors, Modulators and Other Applications

Hybrid plasmonic (HP) waveguides, supporting a hybrid mode between surface plasmon polaritons
(SPPs) and photonics, can enable subwavelength scale optical confinement, relatively low
propagation loss and other unique properties in bio-sensing and optical communication/interconnect
applications. Over the past twelve years, various types of HP waveguide structures have been
proposed and fabricated to enhance the functions of conventional photonic integrated circuits (ICs),
like highly confined wave guiding, sharp waveguide bends and large sensitivity to the refractive index
change of tested liquids, nonlinear or gain materials. Especially for the ones based on silicon-oninsulator
(SOI) platform, the HP waveguide structures can work compatibly with conventional passive
SOI devices, and compensate the lacking characteristics of Si materials. In this chapter, we will
review the HP waveguides and devices considering principles of operation, structures and
applications. As an example we describe in details an ultra-high sensitivity double-slot hybrid
plasmonic (DSHP) ring resonator, used for optical sensors and modulators. Due to high index
contrast, as well as plasmonic enhancement, a considerable part of the optical energy is concentrated
in the narrow slots between Si and plasmonic materials, which leads to high sensitivity to the
infiltrating liquids. By partial opening of the outer plasmonic circular sheet of the DSHP ring, a
conventional side-coupled SOI bus waveguide can be used. Experimental results demonstrate ultrahigh
sensitivity (687.5 nm/RIU) of the developed DSHP ring resonator, which is about five-times
higher than for the conventional Si ring with the same geometry. Further discussions show that a very
low detection limit (5.37 × 10-6 RIU) can be achieved after loaded Q factor modifications. In addition,
the plasmonic metal structures offer also the way to process optical and electronic signals along the
same hybrid plasmonic circuits with small capacitance (~0.275 fF) and large electric field, which leads
to possible applications in compact high-efficiency electro-optic modulators, where no extra electrodes
for electronic signals are required.