Design of a slab waveguide multiaperture spectrometer for field observations

The concept and design of a new type of waveguide device, a multiaperture Fourier-transform planar waveguide spectrometer, implemented as a prototype instrument is presented. The spectrometer's objective is to demonstrate the ability of the new slab waveguide technology for application in remote-sensing instruments. The spectrometer will use a limb-viewing configuration to detect the 1.36µm waveband allowing the concentrations of water vapor in Earth's atmosphere to be measured. The most challenging aspects of the design, assembly, and calibration are presented. Focus will be given to the effects of packaging the spectrometer and interfacing to the detector array. Stress-induced birefringence will affect the performance of the waveguides, therefore, the design of a stress-free mounting over a range of temperatures is important. Spectral retrieval algorithms will have to correct for expected fabrication errors in the waveguides. Data-processing algorithms will also be developed to correct for nonuniformities of input brightness through the array, making use of multimode interference output couplers to capture both the in-phase and anti-phase interferometer outputs. A performance assessment of an existing breadboard spectrometer will demonstrate the capability of the instrument.