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TWO-DIMENSIONAL GUIDED MODE RESONANT STRUCTURES FOR SPECTRAL FILTERING APPLICATIONS
Title
TWO-DIMENSIONAL GUIDED MODE RESONANT STRUCTURES FOR SPECTRAL FILTERING APPLICATIONS.
Creator
Boonruang, Sakoolkan, Moharam, M. G., University of Central Florida
Abstract / Description
Guided mode resonant (GMR) structures are optical devices that consist of a planar waveguide with a periodic structure either imbedded in or on the surface of the structure. The resonance anomaly in GMR structures has many applications as dielectric mirrors, tunable devices, sensors,and narrow spectral band reflection filters. A desirable response from a resonant grating filter normally includes a nearly 100% narrowband resonant spectral reflection (transmission), and a broad angular...
Show moreGuided mode resonant (GMR) structures are optical devices that consist of a planar waveguide with a periodic structure either imbedded in or on the surface of the structure. The resonance anomaly in GMR structures has many applications as dielectric mirrors, tunable devices, sensors,and narrow spectral band reflection filters. A desirable response from a resonant grating filter normally includes a nearly 100% narrowband resonant spectral reflection (transmission), and a broad angular acceptance at either normal incidence or an oblique angle of incidence. This dissertation is a detailed study of the unique nature of the resonance anomaly in GMR structures with two-dimensional (2-D) periodic perturbation. Clear understanding of the resonance phenomenon is developed and novel 2-D GMR structures are proposed to significantly improve the performance of narrow spectral filters. In 2-D grating diffraction, each diffracted order inherently propagates in its distinct diffraction plane. This allows for coupled polarization dependent resonant leaky modes with one in each diffraction plane. The nature of the interaction between these non-collinear guides and its impact on spectral and angular response of GMR devices is investigated and quantified for 2-D structures with rectangular and hexagonal grids. Based on the developed understanding of the underlying phenomenon, novel GMR devices are proposed and analyzed. A novel controllable multi-line guided mode resonant (GMR) filter is proposed. The separation of spectral wavelength resonances supported by a two-dimensional GMR structure can be coarse or fine depending on the physical dimensions of the structure and not the material properties. Multiple resonances are produced by weakly guided modes individually propagating along multiple planes of diffraction. Controllable two-line and three-line narrow-band reflection filter designs with spectral separation from a few up to hundreds of nanometers are exhibited using rectangular-lattice and hexagonal-lattice grating GMR structures, respectively. Broadening of the angular response of narrow band two-dimension guided mode resonant spectral filters, while maintaining a narrow spectral response, is investigated. The angular response is broadened by coupling the diffracted orders into multiple fundamental guided resonant modes. These guided modes have the same propagation constant but propagating in different planes inherent in multiple planes of diffraction of the 2-D gratings. The propagation constants of the guided resonant modes are determined from the physical dimensions of the grating (periodicity and duty cycle) and the incident direction. A five-fold improvement in the angular tolerance is achieved using a grating with strong second Bragg diffraction in order to produce a crossed diffraction. A novel dual grating structure with a second grating located on the substrate side is proposed to further broaden the angular tolerance of the spectral filter without degrading its spectral response. This strong second Bragg backward diffraction from the substrate grating causes two successive resonant bands to merge producing a resonance with symmetric broad angular response.
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Date Issued
2007
Identifier
CFE0001825, ucf:47346
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001825
DESIGN AND FABRICATION OF SPACE VARIANT MICRO OPTICAL ELEMENTS
Title
DESIGN AND FABRICATION OF SPACE VARIANT MICRO OPTICAL ELEMENTS.
Creator
Srinivasan, Pradeep, LiKamWa, Patrick, University of Central Florida
Abstract / Description
A wide range of applications currently utilize conventional optical elements to individually transform the phase, polarization, and spectral transmission/reflection of the incident radiation to realize the desired system level function. The material properties and the feasibility of fabrication primarily impact the device and system functionality that can be realized. With the advancement in micro/nano patterning, growth, deposition and etching technology, devices with novel and multiplexed...
Show moreA wide range of applications currently utilize conventional optical elements to individually transform the phase, polarization, and spectral transmission/reflection of the incident radiation to realize the desired system level function. The material properties and the feasibility of fabrication primarily impact the device and system functionality that can be realized. With the advancement in micro/nano patterning, growth, deposition and etching technology, devices with novel and multiplexed optical functionalities have become feasible. As a result, it has become possible to engineer the device response in the near and far field by controlling the phase, polarization or spectral response at the micro scale. One of the methods that have been explored to realize unique optical functionalities is by varying the structural properties of the device as a function of spatial location at the sub-micron scale across the device aperture. Spatially varying the structural parameters of these devices is analogous to local modifications of the material properties. In this dissertation, the optical response of interference transmission filters, guided mode resonance reflection filters, and diffraction gratings operated in Littrow condition with strategically introduced spatial variation have been investigated. Spatial variations in optical interference filters were used to demonstrate wavelength tunable spatial filters. The effect was realized by integrating diffractive and continuous phase functions on the defect layer of a one-dimensional photonic crystal structure. Guided mode resonance filters are free space optical filters that provide narrow spectral reflection by combining grating and waveguide dispersion effects. Frequency dependent spatial reflection profiles were achieved by spatially varying the grating fill fraction in designed contours. Diffraction gratings with space variant fill fractions operating in Littrow condition were used to provide graded feedback profiles to improve the beam quality and spatial brightness of broad area diode lasers. The fabrication of space variant structures is challenging and has been accomplished primarily by techniques such as ruling, electron beam writing or complex deposition methods. In order to vary the desired structural parameter in a designed manner, a novel technique for the fabrication of space variant structures using projection lithography with a fidelity that rivals any of the current technologies was also developed as a part of this work. The devices exhibit wavelength dependent beam shaping properties in addition to spatial and spectral filtering and have potential applications in advanced imaging systems, graded reflectivity laser mirrors, and engineered illumination. The design, modeling, microfabrication and experimental characterization of space variant micro optical elements with novel optical functionalities are presented.
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Date Issued
2009
Identifier
CFE0002843, ucf:48066
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002843