Abstract
This article presents an innovative high spectral resolution waveguide spectrometer, from the concept to the prototype demonstration and the test results. The main goal is to build the smallest possible Fourier transform spectrometer (FTS) with state of the art technology. This waveguide FTS takes advantage of a customized pattern of nano-samplers fabricated on the surface of a planar waveguide that allows the increase of the measurement points necessary for increasing the spectral bandwidth of the FTS in a fully static way. The use of a planar waveguide on the other hand allows enhancing the throughput in a waveguide spectrometer compared to the conventional devices made of single-mode waveguides. A prototype is made in silicon oxynitride/silicon dioxide technology and characterized in the visible range. This waveguide spectrometer shows a nominal bandwidth of 256~nm at a central wavelength of 633~nm thanks to a custom pattern of nanodisks providing a μm sampling interval. The implementation of this innovative waveguide FTS for a real-case scenario is explored and further development of such device for the imaging FTS application is discussed.
Highlights
The inherent challenge in classical Michelson-based interferometers of displacing a moving mirror with high precision for producing optical path difference (OPD) has stimulated the development of simpler Fourier transform spectrometer (FTS) devices without moving parts, but at the same time without compromising the large throughput advantage [1]
A first realization of high spectral resolution waveguide spectrometer did not happen until 2007, when Le Coarer et al [5] introduced Stationary-Wave Integrated Fourier-Transform Spectrometry (SWIFTS) based on the Lippmann interference concept by taking advantage of photonics and near-field optics in which direct sampling of evanescent standing-waves is achieved using a collection of optical nano-samplers
We report the conceptual design and prototype development of a fully integrated waveguide spectrometer with enlarged throughput and enhanced spectral bandwidth, compared to conventional waveguide spectrometers [5,6,7,8,9]
Summary
The inherent challenge in classical Michelson-based interferometers of displacing a moving mirror with high precision for producing optical path difference (OPD) has stimulated the development of simpler FTS devices without moving parts, but at the same time without compromising the large throughput advantage [1]. To give an idea about the market demand on spectral resolution, the CarbonSat mission which was originally proposed to improve the global greenhouse gas monitoring capabilities, has a requested spectra resolution in NIR of 0.03 nm, and in SWIR of 0.15 nm with an SNR above 300 [24] Another example is the lamellar grating interferometer developed at University of Neuchâtel in 2004, which can be used as a time-scanning Fourier-transform spectrometer providing a 1.6 nm spectral resolution at 400 nm and 5.5 nm at 800 nm with a footprint of 5 mm×5 mm [25]. The optical input is formed by many independent planar waveguides, stacked in layers, providing an increase of throughput compared to single-waveguide input configurations [31] This device is, band-limited due to the fact that the maximum optical path difference which determines the spectral resolution is dictated by the stepwise imbalance introduced by the Mach-Zehnder interferometer integrated into the device. This concept is far from a Lippmannbased waveguide spectrometer where the optical path difference is formed in the single-waveguide itself
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