A theoretical treatment is presented of a plasmonic interaction at an interface between a semiconductor and a dielectric, as opposed to the more traditional configuration whereby a metal/dielectric interface is investigated. Our work is to show that structures using semiconductors instead of metal to excite surface plasmon can support not only terahertz frequencies plasmons but also optical frequency (around 10 to power of 15 Hz) plasmons. / Thesis

No description available.

Fiber tapers have attracted much attention and have been successfully employed in various applications, ranging from resonators, filters, interferometers to sensors. This thesis studies the properties of fiber tapers for the purpose of making tapered-based devices and sensors in aerospace related application where small size and light weight are critical. This thesis includes theoretical derivation and experimental verifications of distributed mode coupling in tapered single-mode fibers (SMFs) with high-resolution optical frequency-domain reflectometry (OFDR) technique. The studies are realized with OFDR through phase detection of a Mach-Zehnder interferometer (MZI), which measures local refractive index change relative to the reference arm. The wavelength shifts converted by the phase change give the group index differences between the fundamental mode and higher-order modes of fiber tapers. The energy re-distribution is observed in Rayleigh backscatter amplitude as a function of fiber length with a ~13µm resolution over the entire fiber taper, and group index difference between core and cladding modes is measured with a spatial resolution of ~2cm by using autocorrelation data processing. The thermal and mechanical properties of fiber tapers have also been characterized with OFDR. The cross-correlation wavelength shift is related to the refractive index change of the modes. It is shown that residual stress induced by the tapering process results in the inhomogeneous thermal property, which can be significantly reduced by an annealing treatment. A fiber taper with a waist diameter of ~6µm has a force sensitivity of ~620.83nm/N, ~500 times higher than that of SMF. Furthermore, polarization-preserving character of tapered polarization-maintaining fibers (PMFs) is evaluated by OFDR-based distributed birefringence along tapered PMFs. Three tapered-based micro-fiber devices have been used as effective mode selecting components to build narrow-linewidth tunable Erbium-doped fiber ring lasers. The fabrication is easy and at a low cost. 1) a tapered fiber tip forms multimode interference mechanism; 2) a two-taper MZI has been demonstrated by splitting/combining the fundamental mode and higher-order modes through fiber tapers and is tuned by bending one taper waist; 3) a novel tunable fiber Fabry-Perot filter, consisting of a hollow-core photonic bandgap fiber and a micro-fiber, is employed in the reflection mode.

Fiber tapers have attracted much attention and have been successfully employed in various applications, ranging from resonators, filters, interferometers to sensors. This thesis studies the properties of fiber tapers for the purpose of making tapered-based devices and sensors in aerospace related application where small size and light weight are critical. This thesis includes theoretical derivation and experimental verifications of distributed mode coupling in tapered single-mode fibers (SMFs) with high-resolution optical frequency-domain reflectometry (OFDR) technique. The studies are realized with OFDR through phase detection of a Mach-Zehnder interferometer (MZI), which measures local refractive index change relative to the reference arm. The wavelength shifts converted by the phase change give the group index differences between the fundamental mode and higher-order modes of fiber tapers. The energy re-distribution is observed in Rayleigh backscatter amplitude as a function of fiber length with a ~13µm resolution over the entire fiber taper, and group index difference between core and cladding modes is measured with a spatial resolution of ~2cm by using autocorrelation data processing. The thermal and mechanical properties of fiber tapers have also been characterized with OFDR. The cross-correlation wavelength shift is related to the refractive index change of the modes. It is shown that residual stress induced by the tapering process results in the inhomogeneous thermal property, which can be significantly reduced by an annealing treatment. A fiber taper with a waist diameter of ~6µm has a force sensitivity of ~620.83nm/N, ~500 times higher than that of SMF. Furthermore, polarization-preserving character of tapered polarization-maintaining fibers (PMFs) is evaluated by OFDR-based distributed birefringence along tapered PMFs. Three tapered-based micro-fiber devices have been used as effective mode selecting components to build narrow-linewidth tunable Erbium-doped fiber ring lasers. The fabrication is easy and at a low cost. 1) a tapered fiber tip forms multimode interference mechanism; 2) a two-taper MZI has been demonstrated by splitting/combining the fundamental mode and higher-order modes through fiber tapers and is tuned by bending one taper waist; 3) a novel tunable fiber Fabry-Perot filter, consisting of a hollow-core photonic bandgap fiber and a micro-fiber, is employed in the reflection mode.

Fiber tapers have attracted much attention and have been successfully employed in various applications, ranging from resonators, filters, interferometers to sensors. This thesis studies the properties of fiber tapers for the purpose of making tapered-based devices and sensors in aerospace related application where small size and light weight are critical. This thesis includes theoretical derivation and experimental verifications of distributed mode coupling in tapered single-mode fibers (SMFs) with high-resolution optical frequency-domain reflectometry (OFDR) technique. The studies are realized with OFDR through phase detection of a Mach-Zehnder interferometer (MZI), which measures local refractive index change relative to the reference arm. The wavelength shifts converted by the phase change give the group index differences between the fundamental mode and higher-order modes of fiber tapers. The energy re-distribution is observed in Rayleigh backscatter amplitude as a function of fiber length with a ~13µm resolution over the entire fiber taper, and group index difference between core and cladding modes is measured with a spatial resolution of ~2cm by using autocorrelation data processing. The thermal and mechanical properties of fiber tapers have also been characterized with OFDR. The cross-correlation wavelength shift is related to the refractive index change of the modes. It is shown that residual stress induced by the tapering process results in the inhomogeneous thermal property, which can be significantly reduced by an annealing treatment. A fiber taper with a waist diameter of ~6µm has a force sensitivity of ~620.83nm/N, ~500 times higher than that of SMF. Furthermore, polarization-preserving character of tapered polarization-maintaining fibers (PMFs) is evaluated by OFDR-based distributed birefringence along tapered PMFs. Three tapered-based micro-fiber devices have been used as effective mode selecting components to build narrow-linewidth tunable Erbium-doped fiber ring lasers. The fabrication is easy and at a low cost. 1) a tapered fiber tip forms multimode interference mechanism; 2) a two-taper MZI has been demonstrated by splitting/combining the fundamental mode and higher-order modes through fiber tapers and is tuned by bending one taper waist; 3) a novel tunable fiber Fabry-Perot filter, consisting of a hollow-core photonic bandgap fiber and a micro-fiber, is employed in the reflection mode.

This thesis investigates the generation and radio-over-fibre (RoF) transport of unlicensed 60 GHz millimetre-wave (mm-wave) frequency band. The investigated benefits of transmission schemes applicable for the mm-wave generation include optical carrier suppression (OCS), optical frequency multiplication (OFM) and remote heterodyne detection (RHD). For the in-door cabling of the mm-wave transmission, a low-cost polymer optical fibre (POF) along with bend-insensitive single mode fibre (BI-SMF) has been investigated for short-range networks. Transporting mm-wave generated signals over POF and BI-SMF cables based on OCS scheme showed results with the highest spectral efficiency and least inter-symbol interference over a 2.5 Gbit/s data delivery. Based on this thesis analysis, OCS simulation of POF showed the most reliable power penalty performance and receiver sensitivity at 30-m whilst the BI-SMF fiber produced equal observations at 150-m and more. In observing the free space links of delivering the RoF signal, the attenuation on the received signal power for both POF and BI-SMF was insignificant but expected, as the simulation assumed complete and total collimation of the light beams onto the aperture of the photodetector. OCS scheme for mm-wave generation and transport was explored based on the cost effectiveness of using one external modulator compared to other generation schemes that utilised more than one external modulator. OFM scheme was simulated to transport LTE and Wi-Fi signals along with 60 GHz RF band through both SMF and MMF-POF/BI-SMF cables. OFM transport scheme produced the highest attenuation on LTE, Wi-Fi and mm-wave signals carrying 100 Mbit/s data as simulated POF lengths increased. The best performance POF length was observed at 10-m. The application of offset launch technique at the coupling of SMF and POF showed insignificant improvement on signal bandwidth. The free space OFM transmission also demonstrated negligible change to the received signal power. This reinforces the attributes of deploying OWC system in an in-door environment. In other investigation, the simulated successful delivery of mm-wave signal using RHD scheme modulated and transported 10 Gbit/s data signal over POF and BI-SMF cables. Additional observed unrecorded result also showed BI-SMF cable maintained a 2% reduction of received power for 450-m fiber cable from 150-m. The attributes to RHD includes its low operating power system application and delivery of localised 60 GHz signal for uplink RoF transmission. The conceptualised design of Gigabit data delivery for indoor customer applications either through POF or BI-SMF cable, transporting various wireless channels has been presented in this thesis for the design of a robust next generation Broadband access network to reinforce the fiber-inside-the-home (FiTH) deployment.

Doctor of Philosophy / Department of Physics / Brian R. Washburn / Optical frequency combs produced by mode-locked fiber lasers are useful tools for high precision frequency metrology and molecular spectroscopy in a robust and portable format. We have specifically investigated erbium doped fiber mode-locked lasers that use single-walled carbon nanotubes as a saturable absorber. We have, for the first time, developed and phase- stabilized a carbon nanotube fiber laser (CNFL) frequency comb. The carbon nanotube saturable absorber, which was fabricated using an optically driven deposition method, permits a high repetition frequency (>150 MHz) since an optical nonlinearity of fibers is not used for mode-locking. The CNFL comb combined with a parabolic pulse erbium doped fiber amplifier (EDFA) has shown a compact, robust, and cost-effective supercontinuum source. The amplified pulse from the parabolic pulse EDFA was compressed with a hollow-core photonic bandgap fiber, which produced a wave-breaking-free pulse with an all-fiber set-up. The stabilized comb has demonstrated a fractional instability of 1.2 ×10[superscript]-11 at 1 sec averaging time, the reference-limited instability. We have performed optical frequency metrology with the CNFL comb and have measured an optical frequency, P(13) which is a molecular overtone transition of C2H2. The measured frequency has shown a good agreement with the known value within an uncertainty of 10 kHz. In order to extend the application of the CNFL comb such as multi-heterodyne dual comb spectroscopy, we have investigated the noise of the CNFL comb and particularly, the broad carrier envelope offset frequency (f[subscript]0) linewidth of the CNFL comb. The primary noise source is shown to be white amplitude noise on the oscillator pump laser combined with the sensitivity of the mode-locked laser to pump power fluctuations. The control bandwidth of f[subscipt]0 was limited by the response dynamics of the CNFL comb. The significant reduction of comb noise has been observed by implementing a phase-lead compensation to extend control bandwidth of the comb and by reducing the pump relative intensity noise simultaneously. Therefore the f[subscipt]0 linewidth has been narrower from 850 kHz to 220 kHz. The integrated phase noise for the f[subscipt]0 lock is 1.6 radians from 100 Hz to 102 kHz.

Les états quantiques multimodes sont au coeur des protocoles detraitement quantique de l’information et de métrologie quantique. Àpartir d’un peigne de fréquence optique injectant un oscillateurparamétrique optique pompé en mode synchrone (SPOPO) nousavons généré des états multimodes en temps/fréquence. Unsimulateur quantique est alors mis en place à partir de ce SPOPO et demise en forme d’impulsion, et permet de mettre en évidence de étatsclusters pouvant compter jusque 12 noeuds et un protocole departage de secret quantique à six partenaires. De plus, une détectionmultipixel résolue en fréquence est développée et utilisée pourréaliser un état cluster linéaire à 8 noeuds. Nous avons égalementutilisé cette source pour développer un spectromètre ayant unesensibilité allant au delà de celle imposée par les fluctuations du videquantique. / Multimode squeezing plays an essential role in quantum informationprocessing and quantum metrology. Using optical frequency combs,we generate multi-temporal-mode state from a synchronouslypumped optical parametric oscillator (SPOPO). An on-demandquantum network simulator is developed using the SPOPO andultrafast pulse shaping; up-to-twelve-node cluster states and asix-partite quantum secret sharing protocol are experimentallyemulated with this simulator. Furthermore, frequency resolvedmultipixel detectors are employed, and used to realize aline-shape-eight-node cluster state. We also developed a multimodequantum spectrometer, which is able to exceed the standardquantum limit for measuring manifold parameters of ultrafast pulses.

In this project laser absorption spectroscopy was performed on a flame in a Fabry-Pérot cavity, using an optical frequency comb. Optical frequency comb spectroscopy is a technique that allows broadband ultra-sensitive detection of molecular species in gas phase. Optical frequency combs are generated by femtosecond mode-locked lasers, which generate short pulses and whose spectrum consists of a comb of sharp laser lines covering a broad spectral range. Doing spectroscopy with optical frequency combs can hence be compared to measurements with thousand of synchronised continuous wave lasers simultaneously, which enables broadband sensitive measurements in short acquisition times. A Vernier spectrometer uses the filtering ability of the cavity to allow sequential transmission of parts of the frequency comb spectrum. Its technical simplicity and robustness make it a good candidate for measuring in turbulent environments. The aim of the project was to implement continuous-filtering Vernier spectroscopy in a setup for measuring absorption spectra in air and in a flame. This was done by using an Er:fiber femtosecond laser emitting in the near-infrared wavelength range and a Fabry-Pérot cavity containing the flame. The cavity, which consists of two highly reflective mirrors, lets the light of the comb interact with the molecules in the flame for each of the many round-trips it perform; thus increasing the sensitivity to absorption. An active locking mechanism was implemented to stabilize the coupling of the optical frequency comb to the cavity. The locking allowed multiple measurements to be averaged which reduced noise. A galvanometer scanner was added to the system which was used to measure a broad part of the comb spectrum. Hot water absorption lines were detected in the swept comb spectrum and a candidate absorption peak for OH absorption was recorded. The spectrometer today has opportunities for improvements. A frequency calibration should be implemented which is essential for making estimates of reactant/product concentrations in combustion processes.

Orientadores: Flávio Caldas da Cruz, Paulo Clóvis Dainese Júnior / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-28T22:50:49Z (GMT). No. of bitstreams: 1 SaquinaulaBrito_JoseLuis_M.pdf: 4387885 bytes, checksum: 7b7c41672acbabf5abc5b7c398df00c0 (MD5) Previous issue date: 2015 / Resumo: Nos últimos 15 anos os pentes de frequências ópticas baseados em lasers de femtossegundos representaram uma revolução na área de metrología e medidas de precisão, permitindo medir diretamente frequências de várias centenas de THz assim como posibilitando o advento de relógios atômicos ópticos. Estes pentes também têm encontrado importantes aplicações em outras áreas da Física, tais como espectroscopia de alta resolução e precisão, geração de altos harmônicos na região da ultravioleta e raios X moles, ou até na procura de exoplanetas através da calibração de espectrômetros astrofísicos. Neste trabalho, estudamos a geração de pentes de frequências ópticas baseados em moduladores eletro-ópticos e fibras altamente não lineares, com o objetivo de implementar novas configurações, alternativas aos pentes baseados em lasers de femtossegundos. Um objetivo é implementar pentes com a maior largura de banda possível que ao mesmo tempo preservem alta coerência entre as frequências geradas, aproveitando componentes comercialmente disponíveis, desenvolvidos para comunicações ópticas na região espectral de 1550 nm. Buscamos implementar dois tipos de pentes de frequências ópticas. Um deles usa um modulador eletro-óptico e gera um pente com pequena largura de banda (10 nm) e espaçamento entre frequências de 25 GHz. O outro pente, gerado com base em fenômenos não lineares em fibras ópticas, fornece maior largura de banda (270 nm) com espaçamento entre frequências de 776 GHz. No caso do pente de frequências gerado pelo modulador (pente eletro-óptico), o processo é devido ao fenômeno eletro-óptico (efeito Pockels) dentro de um cristal de Niobato de Lítio que também forma uma cavidade óptica ressonante. Utilizamos um laser semicondutor contínuo e de frequência única em 1550 nm para gerar um pente (eletro-óptico) com largura espectral de 10 nm com espaçamento de 25 GHz entre as frequências. O outro pente de frequências ópticas é baseado na criação em cascata de produtos da mistura de quatro ondas produzidos a partir de dois lasers semicondutores contínuos, que foram utilizados tanto em onda contínua (cw) ou pulsados, i.e., com modulação de amplitude. Obtivemos espectros com largura de 269 nm (1431 nm ¿ 1700 nm) e espaçamento entre linhas de 6.3 nm (776 GHz). Finalmente, foi alargado o espectro do pente de frequências ópticas gerado pelo modulador eletro-óptico ao usar fibras altamente não lineares. O espectro obtido apresentaram um alargamento modesto, com largura de 23 nm e separação de 25 GHz entre as frequências / Abstract: In the last 15 years, optical frequency combs based on femtosecond lasers have represented a revolution in the area of metrology and precision measurements, making it possible to directly measure frequencies of several hundred terahertz, and affording the advent of optical atomic clocks. These frequency combs today are used in important applications in other areas of Physics, such as high resolution and accuracy spectroscopy, generation of high harmonics in the ultraviolet and soft X-rays region, or even in the search of exoplanets through calibration of Astrophysics spectrometers. In this work, we study the generation of optical frequency combs based on electro-optic modulators and highly nonlinear fibers, with the goal of implementing new configurations, which can be alternative to frequency combs based on femtosecond lasers. One particular goal is to implement frequency combs with the largest possible bandwidth, while still preserving the coherence between the generated frequencies, and taking advantage of commercially available components developed for optical communications, in the 1550 nm spectral region. We were interested in implement two types of optical frequency combs. One of them uses an electro-optical modulator and generates a frequency comb with small bandwidth (10 nm) and 25 GHz frequency spacing. The other comb, generated by nonlinear phenomena in optical fibers, provides greater bandwidth (270 nm) with a frequency spacing of 776 GHz. In the case of the frequency comb generated by the modulator (electro-optical comb), the process is due to the electro-optical phenomenon (Pockels effect) within a Lithium Niobate crystal which also forms a resonant optical cavity. We use a continuous-wave, single frequency semiconductor laser at 1550 nm to generate a frequency comb with a spectral width of 10 nm and 25 GHz frequency spacing. The other optical frequency comb is based on the creation of cascaded four-wave mixing products, produced from two continuous semiconductor lasers that were used both in continuous-wave (cw) or pulsed operation, i.e., with amplitude modulation.We obtained spectra with a width of 269 nm (1431 nm - 1700 nm) and line spacing of 6.3 nm (776 GHz). Finally, we combined both combs by using the highly nonlinear fiber to expand the optical comb spectrum generated by the electro-optical modulator. The resulting spectra showed a modest broadening, with a width of 23 nm and 25 GHz separation between frequencies / Mestrado / Física / Mestre em Física / 1186840 / 134295/2013-7 / CAPES / CNPQ