A long period fiber grating (LPFG) is formed by inducing the periodic refractive index variation along a fiber. A lot of work has been done to fabricate the LPFGs in the photonic crystal fibers (PCFs) to function as all-fiber band-rejection filters, interferometers, and sensing applications. In this thesis, we propose a novel LPFG based on the gel-filled PCF. The PCF filled with the UV gel was exposed to the high-intensity UV light through the mask. The periodic index variation is formed along the fiber in the cladding region, resulting in the LPFG. By measuring the propagation losses of our LPFG, three spectral dips in the transmission bands are observed at 872 nm, 1309 nm, and 1418 nm as the grating period is 600 £gm, which indicates the mode coupling from the fundamental core mode to the higher order modes (HOMs) of the gel-filled PCFs. By using a full-vector finite-difference frequency-domain (FDFD) method, we numerically calculate the phase match condition for our LPFGs. The calculated resonant wavelengths are 875 nm, 1319 nm, and 1415 nm. Very good agreement between the measured resonant wavelengths and the numerical results is obtained. We also fabricate the selectively gel-filled LPFGs to reduce the propagation losses by utilizing a simple selectively blocking technique. In addition, we measure and discuss the sensing sensitivities of the UV-induced LPFGs, including the temperature, strain, curvature, torsion, and surrounding refractive index (SRI) sensitivities. The measured sensitivity to temperature is 1.7 nm/¢XC from 25 ¢XC to 45 ¢XC. As the surrounding refractive index is increased to 1.377, the dip position has a maximum shift of 2 nm. Compared with other LPFGs, the UV-induced LPFGs are more insensitive to bending and strain due to the complete cladding structure. This could benefit the stability of the temperature sensors, based on our UV-induced LPFGs.

Fiber coils had been widely investigated as optical current sensors for a long time. In this thesis we have fabricated the LMA-10 PCF coils. By using the Sagnac fiber loop, we can obtain the transmission spectrum of the PCF coils. The measured birefringence of the SMF coil and the PCF coil are 1.49¡Ñ10^-5 at £f= 959.27 nm and 1.31¡Ñ10^-5 at £f = 1264.3 nm, respectively. The birefringence of the SMF coil agrees well with the theoretical result. The properties of PCF coils for variant fiber turns and cylinder sizes are discussed. As we increase the number of fiber turns, the fringe spacing becomes smaller due to the increasing phase difference. The birefringence of the PCF coil decreases with the increasing cylinder radius. Besides, we also measure the temperature sensitivities of the SMF coil and PCF coil to be 130 pm/oC and 64.55 pm/ oC, respectively. We have also demonstrated the sensing properties of the PCF coils. By introducing a displacement along the cylinder, the bending on the PCF coil can be induced. The measured bending sensitivity is -3.732 nm/m^-1. In addition, the water depth sensing properties are obtained by horizontally and vertically immersing the PCF coils into the water. As we put the PCF coil horizontally into the water, the shift of the measured spectra shows a exponential relation to the water depth. As for the vertically immersed PCF coil, the linear water depth sensitivity is -11.658 nm/cm. Finally, we propose the transverse displacement sensor based on the PCF coil. The measured sensitivity to transverse displacement can be as large as 903.9 nm/cm.

Semiconductor has electronic bandgap because of the periodic potential barriers. Similarly, as shown in Yablonovitch and John¡¦s original idea in 1987, and the optical bandgap can be formed by arranging the dielectric material periodically, named photonic crystal. The innovation promotes vigorous development in the last twenty years. Many applications were discovered by using the idea of photonic crystal, such as waveguide, left-hand material, slow light, optical register, etc. Conventional fibers guide light in the core by the total internal reflection principle, but Russel and co-workers demonstrated fibers with a so-called photonic crystal cladding in 1996, and these fibers guide light by a new physical mechanism different from traditional fibers. Photonic crystal fibers can be simply divided into two groups, one is index guiding fiber and the other is photonic bandgap fiber. Both of them have 2D periodic structures with designed defect structure in the center. Hence light can be confined and guided by special defect modes. We have successfully demonstrated microstructured fibers which have 2D periodic structure by LHPG method. During the fabrication processes, capillaries may collapse due to the surface tension. We discuss the hole-collapse issue and our solution. Besides, the quality of fiber extremely depends on the stability of laser power of the LHPG system, so we design an efficient feedback control to improve it. We also discuss the fibers¡¦ SEM images and optical properties. Finally the future work refers to the drawing of 3D photonic crystal fiber and improving the sharp thermal gradient by using a sapphire tube.

Because of the fast growing in communications, the quality of signal transmission in optical fiber becomes very important. Concurrently, photonic crystal fiber (PCF) consisting of a central defect region surrounded by multiple air holes is attracting much attention in recent years because of its unique properties, such as full photonic bandgaps, wideband, dispersion, endlessly single mode and birefringence, etc. This thesis is mainly focused on the development of the photonic band structures and propagation properties of PCF. And we propose a novel ideal about 3-D PCF, which can be fabricated using the laser heated pedestal growth (LHPG) method. In the thesis, we study the optical properties of 2-D and 3-D PCFs made by Pyrex using the software RSoft. From the result of simulation, the 2-D out-of-plane bandgaps for a hexagonal close packed structure appear between the air filling fraction range from 0.30 to 0.88 for the incident light of wavelength range from 0.7 to 1

Based on a full-wave formulation, a vector boundary element method (VBEM) is proposed to model the photonic crystal fibers (PCFs) (microstructured fibers). The accuracy and efficiency of the approach are confirmed by comparing the results calculated with those in previous literatures. With employing the VBEM, the guiding characteristics, including the effective indexes, vector mode patterns, and the polarization properties of the PCFs are investigated. There polarization characteristics of the PCFs with elliptical air holes (EPCFs) and the one ring air-hole EPCF embedded in the step-index core are studied and discussed. In addition, based on the VBEM formulations, a novel and efficient numerical approach to calculate the dispersion parameters of the PCFs is also proposed. The effect of the PCF geometrical structure on the group velocity dispersion property is reviewed, and then the one-ring defect and two-ring defect PCFs are studied and designed for the ultra-flattened dispersion applications. As an example, a four-ring (two-ring defect) PCF with flattened dispersion of ¡Ó0.25 ps/km/nm from 1.295£gm to 1.725£gm wavelength is numerically demonstrated.

Abstract A projected fringe profilomertry ¡]PFP¡^ using a supercontinuum light illumination for micro-scale measurement is proposed. The supercontinuum light is generated by launching ultra short laser into a highly nonlinear photonic crystal fibers. The supercontinuum light with the following advantage¡G ¡]1¡^ Depth of the field is very large in the projected system. ¡]2¡^No speckle noise in the illumination system. Experiment results has shown that using supercontinuum light is superior to other illumination system This study indicates that the proposed measurement scheme could be applied to 3D shape measurements with large depth variation, especially for semi-conductor devices¡Bmicro electro-mechanical devices and biomedical species.

No description available.

Research towards the development of a gas-discharge fibre laser using noble gases, with target emission wavelengths in the mid-IR. Additional and separate work on gas treatment methods for managing the formation of photo-induced defects in silica glass.

Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The concept of broadband coherent supercontinuum (SC) generation in all-normal dispersion (ANDi) fibers in the near-infrared, visible and ultraviolet (UV) spectral regions is introduced and investigated in detail. In numerical studies, explicit design criteria are established for ANDi photonic crystal fiber (PCF) designs that allow the generation of flat and smooth ultrabroad spectral profiles without significant fine structure and with excellent stability and coherence properties. The key benefit of SC generation in ANDi fibers is the conservation of a single ultrashort pulse in the time domain with smooth and recompressible phase distribution. In the numerical investigation of the SC generation dynamics self-phase modulation and optical wave breaking are identified as the dominant nonlinear effects responsible for the nonlinear spectral broadening. It is further demonstrated that coherence properties, spectral bandwidth and temporal compressibility are independent of input pulse duration for constant peak power. The numerical predictions are in excellent agreement with experimental results obtained in two realizations of ANDi PCF optimized for the near-infrared and visible spectral region. In these experiments, the broadest SC spectrum generated in the normal dispersion regime of an optical fiber to date is achieved. The exceptional temporal properties of the generated SC pulses are verified experimentally and their applicability for the time-resolved study of molecular dynamics in ultrafast transient absorption spectroscopy is demonstrated. In an additional nonlinear pulse compression experiment, the SC pulses obtained in a short piece of ANDi PCF could be temporally recompressed to sub-two cycle durations by linear chirp compensation. Numerical simulations show that even shorter pulse durations with excellent quality can be achieved by full phase compensation. The concept is further extended into the UV spectral regime by considering tapered optical fibers with submicron waist diameter. It is shown that coherent SC spectra with considerable spectral power densities in the usually hard to reach wavelength region below 300 nm can be generated using these freestanding photonic nanowires. Although technological difficulties currently prevent the fabrication of adequate nanofibers, the concept could be experimentally verified by coherent visible octave-spanning SC generation in tapered suspended core fibers with ANDi profile. The work contained in this thesis therefore makes important contributions to the availability and applicability of fiber-based broadband coherent SC sources with numerous high-impact applications in fundamental science and modern technology. / AFRIKAANSE OPSOMMING: Die konsep van breëband koherente superkontinuum (SK) in alles-normaal dispersiewe (ANDi) vesels in die naby-infrarooi, sigbare en ultraviolet (UV) spektrale gebiede word voorgestel en in detail ondersoek. In numeriese studies word eksplisiete ontwerpskriteria vasgestel vir ANDi fotoniese kristal vesel (FKV) ontwerpe wat dit moontlik maak om plat en gladde ultra-breë spektrale profiele te genereer sonder noemenswaardige fynstruktuur en met uitstekende stabiliteit en koherensie eienskappe. Die sleutel voordeel van SK genering in ANDi vesels is die behoud van ’n enkele ultrakort puls in tyd met ’n gladde en saamdrukbare fase distribusie. In die numeriese ondersoek van die SK generering is die dinamika van fase selfmodulering geïdentifiseer as die dominante nie-lineêre effek wat verantwoordelik is vir die nie-lineêre spektrale verbreding. Daar word voorts aangetoon dat die koherensie eienskappe, spektrale bandwydte en saamdrukbaarheid in tyd onafhanklik is van die inset pulsduur vir konstante drywing. Die numeriese voorspellings stem uitstekend ooreen met die eksperimentele resultate wat verkry is met twee ANDi FKVÕs wat optimeer is vir die naby-infrarooi en sigbare spektrale gebied. In hierdie eksperimente is die breedste SK spektrum gegenereer wat tot hede in die normaal dispersiewe regime met ’n optiese vesel behaal is. Die besondere eienskappe van die genereerde SK pulse is eksperimenteel bevestig en die toepasbaarheid vir tyd opgelosde studie van molekulêre dinamika is gedemonstreer. In ’n addisionele nie-lineêre puls kompressie eksperiment is SK pulse verkry in ’n kort stuk ANDi FKV wat in tyd saamgedruk kon word tot sub-twee siklus tydsduur deur liniêre tjirp kompensering. Numeriese simulasies toon aan dat selfs korter pulse met uitstekende kwaliteit behaalbaar is met volledige fase kompensasie. Die konsep is verder uitgebrei na die UV spektrale gebied deur ’n koniese vesel te beskou met sub-mikron diameter. Daar is aangetoon dat koherente SK spektra met noemenswaardige spektrale drywing in die golflengte gebied onder 300 nm, wat gewoonlik as moeilik toeganklik beskou word, bereik kan word deur hierdie vrystaande fotoniese nano-vesels aan te wend. Alhoewel tegnologiese probleme die vervaardiging van voldoende nano-vesels verhinder, kon die konsep eksperimenteel bewys word deur koherente sigbare oktaafspannende SK te genereer in koniese gesuspendeerde kern vesels met ’n ANDi profiel aan te wend. Die werk wat in die tesis vervat is, maak dus belangrike bydraes tot die beskikbaarheid en toepasbaarheid van vesel gebaseerde breëband koherente SK bronne met verskeie hoë impak toepassings in fundamentele wetenskap en moderne tegnologie.

Doctor of Philosophy / Department of Physics / Kristan L. Corwin / This research has focused on the development, demonstration, and characterization of a new type of laser based on optically-pumped gases contained within hollow optical fibers. These novel lasers are appealing for a variety of applications including frequency metrology in the mid-infrared, free-space communications and imaging, and defense applications. Furthermore, because of the hollow core fibers used, this technology may provide the means to surpass the theoretical limits of output power available from high power solid-core fiber laser systems. Gas-filled hollow-core fiber lasers based on population inversion from acetylene ([superscript]12C[subscript]2H[subscript]2) and hydrogen cyanide (HCN) gas contained within the core of a kagome-structured hollow-core photonic crystal fiber have now been demonstrated. The gases are optically pumped via first order rotational-vibrational overtones near 1.5 μm using 1-ns duration pulses from a home-built optical parametric amplifier. Narrow-band laser emission peaks in the 3-μm region corresponding to the ΔJ = ±1 dipole allowed rotational transitions between the pumped vibrational overtone modes and the fundamental C-H stretching modes have been observed in both molecules. High gain resulting from tight confinement of the pump and laser light together with the active gas permits these lasers to operate in a single pass configuration, without the use of any external resonator structure. Studies of the generated mid-infrared pulse energy, threshold energy, and slope efficiency as functions of the launched pump pulse energy and gas pressure have been performed and show an optimum condition where the maximum laser pulse energy is achieved for a given fiber length. The laser pulse shape and the laser-to-pump pulse delay have been observed to change with varying pump pulse energy and gas pressure, resulting from the necessary population inversion being created in the gases at a specific fiber length dependent on the launched pulse energy. Work is on going to demonstrate the first continuous wave version of the laser which may be used to produce a single coherent output from many mutually incoherent pump sources.