10 research outputs found
Nonlinear properties of silicon core optical fibres
No full textSilica optical fibres are renowned for the framework they have set in modern communications systems, sensors, and biotechnology. One particular trend in current research aims to investigate materials with enhanced optical functionality, high optical efficiency, robustness, and a small device footprint. Amongst the many material choices, semiconductors are emerging as a promising route. In this work, optical fibres and semiconductors are elegantly unified to create a hybrid structure with the potential of seamless integration into current fibre infrastructures. Silica capillaries form the fibre templates in which amorphous semiconductor materials such as silicon and/or germanium are impregnated. This thesis will present the first comprehensive description of the fabrication, characterisation, and the implementation of silicon optical fibres for all-optical signal processing. The fibres are fabricated via a novel high pressure chemical deposition procedure. Each fibre is analysed to determine the exact material composition, uniformity, and more importantly the optical quality. Linear and nonlinear optical characterisations are performed experimentally and supported by intensive numerical studies to validate the results.The high nonlinearity of silicon is exploited for all-optical signal processing. Several investigations have been performed to determine key nonlinear coefficients that were previously unknown in these fibres. Nonlinear absorption experiments allowed for the determination of the degenerate and non-degenerate two-photon absorption coefficients, free carrier cross sections, and free carrier lifetimes of a number of silicon fibres. Nonlinear refraction investigations were then used to establish the Kerr nonlinearity. The strength of this parameter allowed for demonstration of strong self-phase and cross-phase modulation effects. With the insight gained in nonlinear absorption and refraction in silicon optical fibres, all-optical amplitude modulation and wavelength switching was demonstrated at ultrafast sub-picosecond speeds
Nonlinear pulse dynamics in multimode silicon core optical fibers
No full textMultimode propagation in silicon core optical fibers is investigated via numerical modeling of the coupled mode equations. The simulations consider spectral evolution in two fibers with different micrometer-sized cores that have experimentally been shown to exhibit nonlinear broadening. The results indicate that most of the coupled power is propagated in the fundamental mode of each fiber, with a small contribution from the higher-order modes affecting the spectral shape but not the width of the broadening
Thermal nonlinearity in silicon microcylindrical resonators
No full textWe explore the thermally induced nonlinearity in hydrogenated amorphous silicon microcylindrical resonators that are fabricated from the silicon optical fiber platform. In particular, we use a pump-probe technique to experimentally demonstrate thermally induced optical modulation and determine the response time. Through characterization of the thermal properties and the associated resonance wavelength shifts we will show that it is possible to infer the material absorption coefficient for a range of whispering gallery mode resonators
Nonlinear absorption and self-phase modulation in silicon optical fibres
No full textSilicon optical fibres are generating much interest as a means to directly integrate semiconductor functionality within the fibre architecture to provide a platform for compact all optical signal processing. For example, the high optical nonlinearity of the core material opens up the potential for these fibres to be used for signal regeneration in very short device lengths. In this paper we characterise the nonlinear optical properties of a step index hydrogenated amorphous silicon (a-Si:H) optical fibre and demonstrate its use for broadband self-phase modulation (SPM). The fibre was fabricated using a high pressure chemical fluid technique [1] to deposit the semiconductor into the central hole of a silica capillary. The resulting fibre had a core diameter of 6mm and a length of 1.5cm, with the linear transmission losses measured to be as low as 1.7dB/cm at 1550nm. As the effective nonlinear interaction length is reduced by the material loss, the realization of low losses is a necessary requirement for the observation of these processes
Mid-infrared transmission properties of amorphous germanium optical fibers
No full textGermanium optical fibers have been fabricated using a high pressure chemical deposition technique to deposit the semiconductor material inside a silica capillary. The amorphous germanium core material has a small percentage of hydrogen that saturates the dangling bonds to reduce absorption loss. Optical transmission measurements were performed to determine the linear losses over a broad mid-infrared wavelength range with the lowest loss recorded at 10.6 µm. The extended transmission range measured in the germanium fibers demonstrates their potential for use in mid-infrared applications
