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Abstract Generally, micro-resonators are structures for confining light. Optical micro-cavities or micro-resonators are mostly based on a spacer layer or an optical medium sandwiched between two reflecting interfaces. Light is reflected internally within the spacer layer, which creates a series of standing-wave optical modes, or resonances. Such resonator structures may be planar such as Fabry-Perot etalons, circular such as ring resonators, or even spherical. The name micro-resonator stems from the fact that its thickness is often a few micrometers. However, the spacer layer is sometimes in the nanometer range. Recently, etalon resonators have attracted much attention. They have been strongly adopted as potential color filters for their seamless no-lithography fabrication technique in addition to their ability to support angle tolerance. Angle tolerance herein may be explained in the sense of the filter’s ability to preserve its spectral transmission characteristics at different angles of incidence ( AOIs ). Angle tolerance is useful in applications involving imaging/display, sensing and communications. This is because a wide fieldof- view ( FOV ) or the feature of the ability to collect light at a wideangle is crucial in miniature devices. Recently, strong interference of light reflecting from an ultrathin semiconductor layer over a metal layer at optical frequencies has been achieved. However, being able to produce transmission 10 resonances is more desired than the strong absorption property for many practical applications. In the meantime, the need for angle-tolerant color filters has increased due to their importance in various applications as previously mentioned. Blue filters in specific are of current importance in visible light communications (VLC) employing a white LED with a phosphor coating. Blue filters are used to eliminate the yellow slow phosphor spectrum that deteriorates the overall system modulation bandwidth. In existing literature, blue dielectric filters with almost ideal transmission characteristics are considered. Such filters almost fully suppress the slow phosphor component, hence offer large effective modulation bandwidths. However, these dielectric filters are known for their narrow-angle operation. On the other hand, plasmonic filters exhibit wide-angle operation, but may not fully eliminate the yellow phosphor component due to their non-ideal transmission characteristics. In order to obtain sharp transmission characteristics, multi-cavity structures or cascaded etalons are required. On the other hand, angle tolerance in filters is mostly achieved through phase compensation technique which requires as minimum number of layers as possible to be engineered. Hence, there exists a trade-off between increasing transmission or reflection along with preserving a wide-angle operation of the filter. The main scope of this thesis is proposing hybrid plasmonic angle tolerant resonator filters that operate in the visible spectral range. The proposed structures are metal-insulator-metal (MIM)-and insulator-metalinsulator (IMI)-based. All proposed structures are seamless, lithography-free, low cost and limited complexity designs. First, an IMI filter is introduced with a wide spectral bandwidth. This is followed by proposing trans-reflective color filters that are IMI-based. Afterwards, a blue filter structure is presented for the specific application of visible light communications (VLC) systems that employ phosphorus white light emitting diodes (LEDs). The proposed blue filter is proved to enhance the VLC system’s performance in terms of effective modulations bandwidth and optical signal-to-noise-ratio. The thesis is arranged as follows: In Chapter 2, a brief overview of different angle tolerant filters techniques in literature is given. Angle tolerant mechanisms are illustrated. In Chapter 3, we propose a technique for the design of visible optical filters using a hybrid plasmonic IMI structure. The proposed IMI visible light filter exhibits high transmission (~91%) and an insertion loss of ~0.4 dB with almost an omnidirectional field-of-view ( FOV ) (0o~70o). The 11 proposed design also has a minimal polarization dependent loss ( PDL ) of 0.2 dB at AOI of 60o. The effects of design parameters on the filter’s performance are studied. Design rules of the filter are deduced along with physical justifications of the obtained results. In Chapter 4, we present a technique for designing trans-reflective optical color filters employing a hybrid plasmonic nano-resonator with a dielectric cavity. The proposed filters exhibit wide-angle operation. They offer almost an omnidirectional field-of-view ( FOV ) (0o~70o). Moreover, the proposed filters exhibit relatively high transmission and reflection (80%- 92%) with at least a 14.3% enhancement than presented in literature. The proposed filters are also polarization independent manifesting a polarization dependent loss ( PDL ) of (-0.17 to -0.5 dB) at angle of incidence ( AOI ) of 70o. Variations in design parameters are introduced to evaluate the equivalent filters performances. Design rules of the filter are presented with physical justifications of the obtained performance curves, hence deducing design guidelines for the proposed color filters that may be further applied in infrared (IR) spectral region. Chapter 5 presents a novel design of a hybrid plasmonic transmission blue filter for visible light communication systems that employ yellow phosphorcoated blue light emitting diodes (LEDs). The proposed filter balances the trade-off between transmission performance and tolerance to variation in angles of incidence (AOI), together while maintaining a low cost with limited complexity design. The designed filter operation is based upon quasi-plasmon mode excitation in a hybrid structure of alternating layers of silver (Ag) and titanium dioxide (TiO2) over a silica substrate. A primary design approach for a hybrid plasmonic filter of five alternating layers is illustrated in detail. Needle optimization technique is further applied to achieve the required filter performance. The designed filter has an insertion loss of ~1dB over a spectral range of 400-485 nm and a minimal close to zero polarization dependent loss ( PDI ) for a wide range of AOI (slightly above 50o). The tolerance of the proposed design against fabrication errors is also tested. The performances of the proposed filters are tested for individual and simultaneous variations from the designed thicknesses, with a ±10% standard deviations from each layer’s thickness. Chapter 6 studies the impact of employing blue filters on the resulting effective modulation bandwidth of VLC systems using phosphor-coated white light emitting diodes (LEDs) under wide-angle operation. Effective modulation bandwidths are assessed and compared for VLC systems with 12 ideal and non-ideal transmission blue filters at the receiver. Angle tolerance capabilities of the employed filters have also been investigated in the study. Commercially available phosphor-coated white LED and photodetector (PD) models are utilized to obtain realistic results. We show that the choice of the blue filter structure, combined with the white LED and PD affects the system’s effective modulation bandwidth. We also show that there exists a trade-off between obtaining a relatively large modulation bandwidth and preserving wide-angle operation of the system. A figure of merit ( FOM ) is also introduced to represent such a trade-off. Moreover, a simple estimation of the expected effective modulation bandwidth of a VLC system using phosphor-coated white LED is developed as a result of a weighted average of the blue and yellow light responsivity of the filter. A numerical example is also included where the optical signal to noise ratio ( OSNR ) is computed in VLC systems with and without the addition of a blue filter. OSNR shows enhancement when a blue filter with a wide rejection region is inserted in the studied VLC systems Chapter 7 experimentally evaluates the importance of employing a blue filter in VLC systems with phosphor-coated white LEDs. Phosphor-coated white LEDs though widely used commercially, are known to limit the system’s maximum data rate. Such limitation is conventionally treated by two methods: either adding a blue filter at the receiver or using orthogonal frequency multiplexing (OFDM) digital modulation technique. Adding a blue filter at the receiver is controversial in current literature and claimed to decrease the signal-to-noise-ratio (SNR) or to be inefficient if OFDM is employed. Hence, in this chapter, we experimentally evaluate the above OFDM VLC system with and without a blue filter. Results are compared to prove that adding a blue filter at the receiver boosts SNR and bit-error-rate (BER) values. This in turn helps maximize the data rates supported by such systems. The addition of a blue filter is tested with different OFDM modulation techniques. Results in this chapter remove the controversy around employing a blue filter in an OFDM VLC systems with phosphorcoated white LEDs. Improved BERs and SNRs at high data rates are observed. Specifically, this experimental work demonstrates a BER enhancement of 40% and 15% for data rates up to 12 Mbps when a blue filter is added. Off-the-shelf commercial components are used in the experiment. Moreover, another means to enhance the maximum data rate of the above VLC system is proposed. A commercial flattening response filter is inserted in the system and the system’s performance is compared to that with the commercial blue filter. 13 And finally, Chapter 8 gives a summary and conclusion of the whole work in addition to discussing possible future work |