  Optical switches are one of the most important elements of integrated
photonics. Here, we designed, fabricated and characterized several nanophotonic
optical switches (NOSs) in silicon that exhibit ultra-compact footprint, along
with excellent extinction ratios and operating bandwidths. Simulations indicate
that our best device of dimensions 3umX3um and 0.3um device height can provide
about 10dB extinction ratio with a bandwidth of 12nm, centered at the design
wavelength of 1550nm. Three-dimensional finite-difference time-domain analysis
in conjunction with a modified version of direct binary search algorithm was
used to design the nanophotonic device structure. The modulation is a result of
optical modulation of the refractive index of a photochromic material and an
optimized geometry of the digital metamaterials that comprise the device. The
devices are CMOS fabrication compatible and examples of ones designed using
multi-state geometric optimization that will lead to a new class of
ultra-compact and multi-functional active integrated-silicon devices.
