Chip-scale spectrometry based on tapered hollow Bragg waveguides

We describe a micro-spectrometer that exploits out-of-plane radiation at mode cutoff in a tapered leaky waveguide clad by omnidirectional Bragg reflectors. The device can be viewed as a side-coupled, tapered Fabry-Perot cavity. An effective-index transfer-matrix model reveals that optimal resolution is dependent on the reduction or mitigation of back-reflection and standing waves leading up to the cutoff point. We address this by insertion of low numerical aperture optics between the taper and the detector, and demonstrate an experimental resolution as small as similar to 1 nm and operating bandwidth >100 nm in the 1550 nm range, from a tapered waveguide with footprint similar to 50 mu m x 500 mu m. The device combines the small size of a Fabry-Perot instrument with the detector array compatibility and fixed optics of a grating-based instrument. (C) 2009 Optical Society of America