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العنوان
Micro Plasmonic Optical Resonator /
المؤلف
Anous, Noha Hassan.
هيئة الاعداد
باحث / Noha Hassan Anous
مشرف / Diaa AbdelMaguid Khalil
مشرف / Tarek Abdel Azeem Ramadan
مناقش / Tarek Abdel Azeem Ramadan
تاريخ النشر
2019.
عدد الصفحات
200p. :
اللغة
الإنجليزية
الدرجة
الدكتوراه
التخصص
الهندسة الكهربائية والالكترونية
تاريخ الإجازة
1/1/2019
مكان الإجازة
جامعة عين شمس - كلية الهندسة - الهندسة
الفهرس
Only 14 pages are availabe for public view

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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
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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
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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
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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.
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And finally, Chapter 8 gives a summary and conclusion of the whole
work in addition to discussing possible future work