Pillar-array based optical cavities have unique properties, e.g., having a large and connected low dielectric index space
(normally air space), having a large percent of electric field energy in air and standing on a substrate. These properties
make them well suitable to make ultra compact and highly sensitive label-free optical sensors to detect bio-/chemical
reactions. We designed, fabricated, and measured a silicon-on-insulator pillar array microcavity that possesses a quality
factor as high as 27,600. We studied its sensitivity for both bulk index change and surface index modification. As a bulk
index sensor, for environmental refractive index change of 0.01, a resonance peak wavelength shift of 3.5 nm was
measured. As a surface index sensor, the simulations show, for a coating with thickness of 1 nm, the resonance
wavelength shifts as large as 2.86 nm. Combining with a sharp 0.06 nm wide resonance peak, our pillar-array sensor is
able to resolve ultra small bulk and surface refractive index changes caused by target molecules.
A triplexer based on silicon nanophotonic wire structure consisting of two Bragg grating-assisted directional couplers is
proposed, which can multi/demultiplex three different wavelengths through a compact device. The device has low loss,
low crosstalk, and a footprint of only 210 ×40 μm. The 1-dB bandwidth for the three channels located at 1310, 1490 and
1550 nm are 110, 20, and 20 nm, respectively.
A bidirectional grating serving both, as a polarization beam splitter and a vertical coupler for Silicon on Insulator
nanophotonic circuits is fabricated and characterized. The measured coupling efficiency is as high as 43%. The
demonstrated device has a large 3-dB bandwidth and a high extinction ratio between two orthogonal polarizations.
In this paper we present measurement results of an ultracompact echelle-grating demultiplexer based
on silicon-on-insulator nanowire platform, in which we introduced a total internal reflection design of
the grating facets to improve the diffraction efficiency. An average increase of the diffraction
efficiency with 3.7dB is observed for the 3 channels compared to a normal design.