Infoscience

Thesis

High spectral resolution waveguide spectrometer with enhanced throughput for space and commercial applications

This dissertation presents the results concerning the development of an innovative high spectral resolution waveguide spectrometer, from the concept to the prototype demonstration and the test results. The main innovative aspects of this instrument are the enhanced throughput and the large spectral bandwidth in a static design without mechanism. These innovations are based on the customized pattern of nano-samplers fabricated on the surface of a planar waveguide, which allow enhancing the throughput and to increase the measurement points of the interferogram necessary for increasing the spectral bandwidth in a static way. On the other hand, the propagation in the unconfined direction of the planar waveguide is controlled using an adapted front-end optics to maintain the superposition of forwarding and reflected beams to form the interferogram under the nano-samplers. Polymeric- and silicon oxynitride-based planar waveguides were manufactured, evaluated and tested for studying mode profile in planar waveguides. The nano-samplers are gold nanodisks of few tens of nanometers in diameter and thickness, optimized for sampling the visible light coupled in the waveguide module of the spectrometer. A waveguide spectrometer prototype is made in silicon oxynitride/silicon dioxide technology and characterized in visible range at 633 and 685 nm using stable monochromatic laser sources. This waveguide spectrometer shows a nominal bandwidth of 256 nm thanks to a custom pattern of nanodisks providing 0.25 ÎŒm sampling interval at central wavelength of 633 nm. The targeted prototype in the near future is a highly integrated spectrometer, with an approximate footprint of a few cubic millimeters, excluding the volume required by the front-end optics and the detector electronics. This new type of instrument can be adapted for various spectral ranges where the material for the waveguide, the nano-samplers and the detectors are available and compatible (from ultraviolet to mid-infrared). This instrument has the potential to be used for numbers of space applications, for instance for the applications where the sample is in a close proximity to the spectrometer (e.g. mineralogy from a rover or active gas detection in a capsule or space station), or in remote sensing applications (e.g. atmospheric observations from a satellite). In addition, the principle idea is to group several of such spectrometers to allow hyperspectral imaging: a 1D array of spectrometers to form an acquisition line to image with lateral scanning, heading towards a full cube of spectrometers in a 2D image acquisition scheme to probe directly a complete scene (the concept of "FPAS" - focal plane array spectrometer). This technology is also adaptable for vast commercial applications in tele-surveillance, optical metrology, genomics and medical domain. At the system level, the full instrument optimization is taken into account in this dissertation, including front-end optics and the detector. Different subsystems are evaluated, developed and tested in order to integrate and demonstrate a complete prototype.

Fulltext

Related material