  We demonstrate a silicon nitride trench waveguide deposited with bowtie
antennas for plasmonic enhanced optical trapping. The sub-micron silicon
nitride trench waveguides were fabricated with conventional optical lithography
in a low cost manner. The waveguides embrace not only low propagation loss and
high nonlinearity, but also the inborn merits of combining micro-fluidic
channel and waveguide together. Analyte contained in the trapezoidal trench
channel can interact with the evanescent field from the waveguide beneath. The
evanescent field can be further enhanced by plasmonic nanostructures. With the
help of gold nano bowtie antennas, the studied waveguide shows outstanding
trapping capability on 10 nm polystyrene nanoparticles. We show that the bowtie
antennas can lead to 60-fold enhancement of electric field in the antenna gap.
The optical trapping force on a nanoparticle is boosted by three orders of
magnitude. A strong tendency shows the nanoparticle is likely to move to the
high field strength region, exhibiting the trapping capability of the antenna.
Gradient force in vertical direction is calculation by using a point-like
dipole assumption, and the analytical solution matches the full-wave simulation
well. The investigation indicates that nanostructure patterned silicon nitride
trench waveguide is suitable for optical trapping and nanoparticle sensing
applications.
