High Optical Throughput and Low-Cost Spectral Sensing Using Photonic Structures
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Date
2016-09-27
Authors
Khodadadzadeh, Iman
Advisor
Hajian, Arsen
Saini, Simarjeet
Saini, Simarjeet
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
Spectral sensing is an accurate means of probing the environment in a non-invasive
manner. One of the most common instruments to acquire spectral data is a spectrometer.
Spectrometers continue to improve in throughput and resolution while becoming smaller
in size. However, the improvements in optics, gratings and detector performance have
plateaued in free-space spectrometers due to fundamental trade-off between the spectral
resolution and throughput of the spectrometer slit. Free space optical slicers on the other
hand, have shown that this trade off can be broken using a complex optical setup. With
the advent of nanophotonics and integrated optics, light can be routed and interact in
a much smaller footprint. While integrated optics approach provides a more robust and
smaller footprint, the throughput is still an issue since most designs only work with a very
narrow band and single mode input. In this thesis, the concept of far-field beam forming is
explored using mode coupling principles to increase the throughput of a spectrometer using
photonic structures and waveguides. Three designs are provided that use the interaction
between the modes to couple light between different size apertures at input and output.
These designs use multi-mode input fibers and could operate on a wider wavelength range
since they are not wavelength specific resonant based structures. They are fabricated and
experimentally tested to measure their performance against a conventional free space slit.
While spectrometers provide the full-range spectral information, application specific
photonic sensors that use multi-spectral sensing approach are also promising fields of re-
search. In this thesis, two such sensor designs are discussed. A multi-slot bio-sensor design
is proposed as well as its optimization procedure to increase the refractive index sensitivity
by 3×. Due to similarities between this design and the tapered waveguide designs for the
spectrometer, the fabrication techniques developed for the photonic slit concept can be
extended and applied for fabrication of this sensor. In addition, to avoid the system design
and measurement complexities of a spectrometer or a ring resonator based sensor, a simple
periodic array of silicon nanowire is proposed as a refractive index sensor. By considering
the movement of diffraction spots at multiple wavelengths, refractive index resolution of
10 −5 or higher can be achieved.
Description
Keywords
Spectroscopy, Integrated Photonics, Nanofabrication, Silicon Nanowires, optical sensing, Electron Beam Lithography, Integrated Spectrometer, Photonic Slicer