| dc.description.abstract | During the past decades, the matured micro fabrication technology has
successfully miniaturized the dimensions of optical elements which results in the
development of micro-optics. As well, the research of nano-scaled optical elements
has also promoted the rapid development of nano-optics in the recent time owing to
the wide range of possible applications such as advanced microscopy, high-density
data storage, photon manipulation, and even probing techniques that can not achieve
in micro-optics. However, the extremely tiny size of nano-optical elements suffers
from the strict requirement in fabrication so that the practical application of
nano-optics is restricted in a certain degree. Compared with nano-optics, the
subwavelength optical elements have raised substantial interests because of their
feasible structure and versatile capabilities which should not be approached with
micro-optics and make them possessing numerous useful functions such as
antireflection surface, artificial dielectrics, polarization sensitive elements, and
resonant filters.
In this thesis, the guide-mode resonance (GMR) devices which consist of
subwavelength diffraction grating and waveguide are developed to possess the
functions of optical filters, security recognition, and biosensor. Particularly, we
developed the GMR devices with silicon-based materials since that may be potential
to integrate with other silicon micro-optical elements. The different resonant
structures are constructed such as silicon grating and free-standing silicon-nitride
(SiNx) membrane.
For the GMR devices developed with silicon grating, first, the quartz is used as the substrate to excite the resonance. We designed the transmission notch filters of
flexible bandwidths in the infrared region and then experimentally achieved a
wide-bandwidth notch filter of over 150 nm stopband and a band shape of Lorentzian
type. To improve the line shape, we utilized the asymmetric binary grating profiles to
flatten the stopband effectively. Besides the notch filter, we also proposed a
transmission bandpass filter of flattop and wide bandwidth of 200 nm using the
asymmetric binary grating profiles which is much less complex compared with the
conventional multilayer thin films structure. Furthermore, we proposed an
out-of-plane optical filter on a single silicon chip which can be used as a monolithic
optical filter on a silicon micro-optical bench. Owing to the strong modulation, i.e.
large contrast of refractive index, offered by the silicon grating, the presented GMR
devices constructed of silicon are shown to provide with high angular immunity that
can significantly decrease the strict demands of precise alignment in GMR device.
The use of silicon for optical elements is profitable only in the infrared region.
For applications in the visible region, the use of SiNx obviously has more advantages
owing to its high transparency in both visible in infrared regions. In addition, to
develop the fully silicon-based element, we constructed the GMR devices in a
free-standing SiNx membrane suspended on a silicon substrate and used as a
transmission notch filter of narrow bandwidth. The proposed structures possess
advantages of simple structure, high efficiency, and potential in integrating with other
components into a micro-system chip. The methods for tailoring the resonance
performance in the unique GMR structure including antireflection grating,
spectrum-modifying layer, and cascaded arrangement for stopband flattening are
presented.
Besides the optical filters, the novel applications of GMR device including security recognition and bio sensing are further developed. First, the SiNx GMR
membrane is experimentally demonstrated as an authentication label upon
illumination with the unpolarized white light with wide angular tolerances due to the
high refractive index of SiNx facilitates the proposed filters possess strongly
modulated gratings and immunity for the high angular deviation. The measured
reflection resonance has an angular tolerance up to ±5° under normal incidence for the
visible region for recognition by human eyes. Afterwards, collaborating with the
MOEMS laboratory leading by Prof. Tsung-Hsun Yang, the method for detecting
DNA hybridization by utilizing the GMR effect is also proposed by which the
resonance wavelength is shifted due to phase change of resonant wave induced from
the surface attachment of molecules. Owing to the high sensitivity of resonance effect,
the correlations of resonance wavelengths shifted with the length of ssDNA of the
hybridizations are demonstrated to successfully detecting the hybridization process. | en_US |