Chip-scale spectrometry based on tapered hollow Bragg waveguides

Abstract

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 approximately 1 nm and operating bandwidth >100 nm in the 1550 nm range, from a tapered waveguide with footprint approximately 50 microm x 500 microm. The device combines the small size of a Fabry-Perot instrument with the detector array compatibility and fixed optics of a grating-based instrument.

Rainbow on a Chip: Experimental Observation of the Trapped Rainbow Effect Using Tapered Hollow Bragg Waveguides

“…In respect to the LOC integration, modifying the fabrication techniques to provide an enclosed hollow waveguide core would allow for the cavity to potentially be filled with a liquid or gas analyte [7]. Potential fabrication methods to achieve this modified structure include a monolithic assembly using induced buckling [17][18][19] or grey-scale lithography and sacrificial etching [8]. These methods would also provide the necessary methods to eliminate the 'epoxy leakage' issue since they do not depend on such bonding techniques.…”

“…While prior results have been successful to varying degrees, they do not provide optimal geometries or properties for use in a on-chip spectroscopy. However, prior research by Dr. DeCroby's group in tapered waveguides using omnidirectional dielectric reflectors (ODRs) in the near IR region has offered promising results for microspectrometer use [8]. Here the ODRs confine in-coupled light toward the narrow end of the taper.…”

On-chip infrared sensors: redefining the benefits of scaling

“…A photodetector array probes the spatial field distribution and converts it into spectral information of the optical input via a linear transformation. Classical dispersive spectrometers using diffractive gratings, prisms, or resonant cavity arrays as the spectrum-splitting elements fall in this category [5][6][7][8][9][10][11][12][13] . Furthermore, the generalized "dispersive" spectrometers shown in Fig.…”

All-Optical and Thermal Tuning of a Bragg Grating Based on Photosensitive Composite Structures Containing Liquid Crystals

“…They can be used in various applications including tunable lasers [1], polarization dispersion compensation and manipulation [2], spectrometry [3], multi/demultiplexing [4], sensing [5], and spectral filtering [6]. Bragg reflectors have been demonstrated by employing waveguides made of different materials and structures such as polymers [7], silicon-oninsulator (SOI) [8], hollow capillaries [2], lithium niobate [9], metal-insulator-metal [10] silica [11] and liquid crystals [12,13].…”