With many unique advantages compared to traditional sensors, optical fiber sensors have been studied and applied to many different areas. Interferometric sensors are one of the most useful sensor types due to their high sensitivities and relatively relaxed requirement on the stability of the optical source’s power level. In-line optical interferometric sensors received further attention as a result of compactness and robustness to the reference channel instability. Long period gratings (LPG) are one of the most useful components in the in-line optical fiber sensors. However, the fabrication cost is normally high due to the expensive masks and stringent photolithographic procedures. Two new sensor components, namely abrupt tapers and connector-offset attenuators, are proposed as couplers in the optical fiber to couple light from core to cladding (or reverse) to replace LPGs. Using OPTIBPM software, the coupling coefficients between core and cladding modes are calculated. For an abrupt taper, coupling mostly happens between LP01 and LP0m modes; the first ten LP0m modes account for 98% of the incident mode energy. For a connector-offset attenuator, coupling mainly happens between LP01 and LP1m modes; the first ten LP0m and first ten LP1m modes account for 92% of the incident mode energy. The relative direction of two connector-offset attenuators is found to be very important to the interference performance. Phase dependent interference (attenuation range from 1 dB to 35 dB) is observed in the simulation for the interferometers using abrupt tapers and connector-offset attenuators. Three interferometers are realized in the experiment using the abrupt tapers (Mach-Zehnder and Michelson) or the connector-offset attenuators (Michelson). Due to the interference between core and cladding modes, transmission is strongly dependent on wavelength ranging from 3 dB to 26 dB in the best implementation. Although it is difficult to make two perfect parallel connector-offset attenuators required by the Mach-Zehnder interferometers by using the fusion splicer, some evidence of constructive interference is observed in the experiment. The interferometers are tested as refractive index (RI) sensors using the maximum attenuation wavelength shift relative to the RI change. Given that the minimum resolution of optical spectrum analyzer is 10 pm, ~10-4 difference of the RI can be detected by the interferometric sensors using the abrupt tapers or the connector-offset attenuators. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2008-08-18 15:42:59.506

The demonstration of efficient single-mode fiber (SMF) coupling is a key requirement for the development of a compact, ultra-precise radial velocity (RV) spectrograph. iLocater is a next generation instrument for the Large Binocular Telescope (LBT) that uses adaptive optics (AO) to inject starlight into a SMF. In preparation for commissioning iLocater, a prototype SMF injection system was installed and tested at the LBT in the Y-band (0.970-1.065 mu m). This system was designed to verify the capability of the LBT AO system as well as characterize on-sky SMF coupling efficiencies. SMF coupling was measured on stars with variable airmasses, apparent magnitudes, and seeing conditions for six half-nights using the Large Binocular Telescope Interferometer. We present the overall optical and mechanical performance of the SMF injection system, including details of the installation and alignment procedure. A particular emphasis is placed on analyzing the instrument's performance as a function of telescope elevation to inform the final design of the fiber injection system for iLocater.

We investigate the influence of the pump and collection mode parameters on the collection efficiency of Type I down converted photons into single mode fibers. For best single and coincidence counting rates, we find that the mode sizes should be close to the same size and that the mode waists should be located near the down-conversion crystal. Larger collection waists give higher collection efficiencies, but lower singles counts.

No description available.

Intensity modulation direct detection (IMDD) transmission scheme has been the mainstay in optical communication ever since semiconductor lasers were put to use as the choice transmission sources. With the development of new improved laser types, this method will continue to dominate the third generation light wave networks where bit rates have steadily risen beyond 10Gbps mark. The main attraction of this scheme lies in its simplicity. With EDFA amplifiers providing a cost effective solution to the attenuation problem, long haul network capacity under the scheme has greatly increased. At the design stage of such systems, it is essential to accurately predict the behavior of each system component right from the laser transmitter up to the optical receiver under custom specific operating conditions and laser diodes are one of the key components for a wide range of light wave communication systems. For this purpose, computer-aided simulation techniques based on behavioral models of laser diodes have been developed and validated for a variety of applications [4-8]. A ‘representative’ behavior model, which closely approximates the device’s actual physical model, is essential to the system designer. Unfortunately, the component vendor or manufacturer may not be able to provide all the information needed to predict such behavior. The only information that can be made available, are certain measured variables over a specified measurement range. The designer therefore, needs a tool to effectively convert this data into a useful model with sufficiently accurate parameters for predicting behavior. As the complexity of the model increases, more detailed knowledge of the laser is required and the computation time for system performance calculation increases. While sophisticated models provide considerable insight into important characteristics of the lasers, for system simulation purposes a relatively simple model is often adequate. In this thesis we will propose a very robust and efficient procedure for estimating the modal parameters and go on to propose a complete solution to the 0D laser model extending to such domains as the below threshold dynamics and temperature effects. / Thesis / Master of Engineering (ME)

This research provides the first known procedure for cleanly and consistently reducing the diameter of single-crystal sapphire optical fiber (SCSF) below the limits of standard production methods, including the first production of subwavelength-diameter optical fiber (SDF) composed of single-crystal sapphire. The first known demonstration of an air-clad single crystal sapphire optical fiber demonstrating single-mode behavior is also presented, and the single-mode cutoff wavelength and diameter are determined. Theoretical models describing and predicting the optical behavior of low modal volume sapphire optical fibers are also presented. These models are built upon standard weakly-guiding optical fiber theory, which is found to be accurate once experimentally-determined properties of the SCSF are substituted for theoretical values. Reduced modal dispersion is also observed in the form of decreased laser pulse broadening in reduced-diameter SCSF. The improvements in spatial resolution for distributed sensing systems such as Raman distributed temperature sensing are also predicted based on the measured decrease in pulse duration. This research also provides an enhanced understanding of the etching behavior of sulfuric and phosphoric acids on sapphire surfaces, including the first reporting of etching rates and activation energies for a-plane sapphire surfaces. Morphological changes of sulfuric and phosphoric acids at and beyond the temperature ranges used in etching were also tested and discussed in detail, especially regarding their practical impact on observed etching behavior. The demonstration of LMV single-crystal sapphire optical fibers enables the adaptation of numerous sensing schemes requiring low modal volume or single-mode behavior to be utilized in extreme environments. / Ph. D.

This thesis is motivated by the need for noise control in aircraft engine with orifices and perforated liner. The presence of high-level acoustic excitation, different flow situations either bias flow, grazing flow or any combination in the aircraft engine, makes the acoustic behavior complex due to the interaction between sound and flow over the lined wall. Both systematic acoustic prediction of aircraft engines and liner optimization necessitate progress in impedance measurement methods by including the effect of the complex flow situations. The aim of the present thesis is to experimentally study the change in acoustic properties of orifices and perforated liners under bias or grazing flow. In order to study the effect of different combinations of bias flow and high-level acoustic excitation, an in-duct orifice has been investigated with finely controlled acoustic excitation levels and bias flow speeds. This provides a detailed study of the transition from cases when high-level acoustic excitation causes flow reversal in the orifice to cases when the bias flow maintains the flow direction. Nonlinear impedance is measured and compared, and a scattering matrix and its eigenvalues are investigated to study the potentiality of acoustic energy dissipation or production. A harmonic method is proposed for modelling the impedance, especially the resistance, which captures the change in impedance results at low frequencies compared with experimental results. The presence of grazing flow can increase the resistance of acoustic liners and shift their resonator frequency. So-called impedance eduction technology has been widely studied during the past decades, but with a limited confidence due to the interaction of grazing flow and acoustic waves. A comparison has been performed with different test rigs and methods from the German Aerospace Center (DLR). Numerical work has been performed to investigate the effect of shear flow and viscosity. Our study indicates that the impedance eduction process should be consistent with that of the code of wave propagation computation, for example with the same assumption regarding shear flow and viscosity. A systematic analysis for measurement uncertainties is proposed in order to understand the essentials for data quality assessment and model validation. The idea of using different Mach numbers for wave dispersion and in the Ingard-Myers boundary condition has been tested regarding their effect on impedance eduction. In conclusion, a local Mach number based on friction velocity is introduced and validated using both our own experimental results and those of previous studies. / <p>QC 20150522</p>

[pt] Neste trabalho, desenvolvemos um laser a fibra, monomodo e de cavidades acopladas, cujo meio de ganho é uma Fibra Dopada com Érbio. As duas cavidades, C1 e C2, foram feitas no mesmo pedaço de fibra dopada, com a mesma concentração de Érbio (Er) e mesmo índice de refração. A Fibra Dopada com Érbio usada era também dopada com Germânio (Ge), que aumenta a fotossensitividade da fibra. Portanto, foi possível escrever Redes de Bragg na mesma fibra para serem usadas como os espelhos da cavidade. A configuração do laser consiste em três Redes de Bragg, escritas no mesmo núcleo da fibra, centradas em 1532nm e separadas por 30cm. As reflectividades das Redes de Bragg eram de 95 por cento, 80 por cento e 60 por cento. Com essa configuração simples de cavidades acopladas, conseguimos uma emissão laser estável e monomodo. Será apresentado também um estudo teórico para descrever o sistema. / [en] In this work, we developed a single mode coupled cavity fiber laser, in which the gain medium is an Erbium Doped Fiber. The two cavities, C1 and C2, were made in the same piece of the doped fiber, with the same concentration of Erbium (Er) and the same refraction index. The Erbium Doped Fiber used was codoped with Germanium (Ge), which increases the photosensitivity of the fiber. Therefore, it was possible to write bragg Gratings in the same fiber to be used as the cavity mirrors. The laser configuration consists of three Bragg Gratings, written in the core of the fiber, centered in 1532 nm and separated by 30cm. Ther Bragg Grating reflectivities were 95 per cent, 80 per cent and 60 per cent. With this simple configuration of coupled cavities, a stable, single mode laser emission was achieved. A theoretical study to describe the system will also be presented.

The dissertation focuses on the analysis and design for the new fiber-optic passive components based on the photonic-crystal-fiber (PCF). The vector boundary element method (VBEM) and the finite-difference time-domain (FDTD) method are employed to the propagation characteristics of PCF components. A novel octagonal microstructured fiber (OMF) with eight air-holes in the first ring has been proposed. The OMF has significantly wider wavelength range for single-mode operation, more circular-like field distribution, and less confinement loss. In addition, a novel compact polarization beam splitter (PBS) based on the twin-elliptical-core PCF (TEC-PCF) has also been proposed. It behaves with high extinction ration and broad bandwidth with significantly short splitter length. The design concept and the coupling mechanism are presented in this dissertation based on the normal-mode coupling theory and VBEM.

Sensing rotation has been an essential topic in navigation and many other applications. Gyroscopes based on propagation of light beams over fixed distances have gained interest with the development of the laser. Since the 1970s, with the development of fiber optics these laser based gyroscopes have developed into compact devices, which can fit in the palm of your hand. In this thesis, we describe and analyze the development of a fiber-optic gyroscope. Fiber optic gyroscopes (also called fiber gyro or FOG) have been under development for different types of applications for more than 30 years all around the world. The physical basis of the fiber gyro is the Sagnac effect that was discovered in the early 1900s and is named after its discoverer. In this work, we first explain the principle of operation of the Sagnac effect and we derive the fundamental formulations in order to have an analytical understanding of the theory. Then, we examine the fiber optic gyro configuration component by component, starting with the laser diode pumped broadband light emitting Erbium-doped superfluorescent source. In addition, the principle of phase modulation, electro-optic phase modulators, fiber optic cables and fiber winding techniques, such as quadrupolar winding is explained within the context of development of the FOG. v The FOG that was assembled was based on circulation and sensing of broadband light centered around 1550nm. The fiber coil was 5km long in order to increase sensitivity in the FOG device. Since single-mode fibers were used steps were taken to ensure successful operation even with polarization dependent errors. The constructed system demonstrated a low sensitivity with a large uncertainty while sensing typical rotation rates. Reasons behind the errors and low sensitivity, as well as improvements that can be made are discussed.