  We present a novel platform to construct high-performance nanophotonic
devices in low refractive index dielectric films at telecoms wavelengths. The
formation of horizontal slots by PECVD deposition of high index amorphous
silicon provides a convenient and low-cost way to tailor nanophotonic devices
to application needs. Low propagation loss of less than 2 dB/cm is obtained
allowing us to fabricate optical resonators with measured high optical quality
factors exceeding 10^5. We design and experimentally demonstrate on-chip
grating couplers to efficiently couple light into integrated circuitry with
coupling loss of 4 dB and optical bandwidth exceeding 110 nm. The entire
on-chip circuitry consisting of input/output couplers, Mach-Zehnder
interferometers with high extinction ratio and ring, racetrack resonators are
designed, fabricated and characterized.
