819 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
C. C. Mehta
No full textOn the life and works of Chandravadan Chimanlal Mehta, b. 1901, Gujarati author
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
Mobilities in Religious Knowledge: Phiroz Mehta and the Logics of Transreligiosity in 1970s–80s South London
No full textThis paper examines transreligiosity in the context of the transmission of South Asian concepts of spirituality to the UK in the 20th century. Between the 1920s and 1990s, Indian teacher and author Phiroz Mehta (1902–1994) crossed borders in a colonial and postcolonial shuttling between India and the UK but also transgressed conceptual and practice borders of religion, teaching Indian religious concepts to post-Christian spiritual seekers in 1970s–80s South London. Mehta cultivated an elasticity between many religious and philosophical traditions, recognising the post-institutional fatigue of subjects who sought alternative forms of ‘belonging without believing’. Privileging the domestic space for teaching, as well as transitory ‘camp’ gatherings in the UK and Germany, Mehta often operated in the social margins, combining teachings from Hinduism, Buddhism, and Christianity with Zoroastrianism, Judaism (specifically Kabbalah), and Daoism. He offered his tutees the freedom to practice religion in whatever way they chose by drawing on a broad range of traditions concurrently to create a transreligiosity. This paper examines Panagiotopoulos and Roussou’s ‘transgressional webs of practising individualised forms of alternative spirituality’ in relation to Mehta’s followers in the 1970s-1980s and asks how transreligiosity relates to other theoretical analyses, such as religious exoticism, bricolage, religious appropriation, cultural re-articulation or assemblage. This paper focuses on qualitative interviews with original members of the Mehta community conducted between 2021 and 2022.</p
Design and development of a mechatronic training simulator for adult ECMO
No full textWidespread adoption of Extracorporeal Membrane Oxygenation (ECMO) in adults has been limited by unfamiliarity with the procedure, including cannulation and safe handling of the ECMO equipment. We present the design and development of a mechatronic training simulator for ECMO that can help medical professionals acquire the needed skills, gain familiarity, and reduce errors by practicing before performing the procedure on real patients. The trainer is designed as an ultrasound-compatible, wholesome simulator with realistic components such as synthetic blood vessels, cannulation pads, and a color-changing blood simulant to simulate oxygenation and deoxygenation. The simulator is integrated with a mathematical model of human physiology to simulate real-time patient vitals and training scenarios, and to control the trainer hardware. We present results related to successful cannulation under ultrasound scanning and a simple patient scenario of hypovolemia.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2021-05-01The student, Iti Mehta, accepted the attached license on 2019-04-24 at 10:58.The student, Iti Mehta, submitted this Thesis for approval on 2019-04-24 at 11:11.This Thesis was approved for publication on 2019-04-24 at 12:45.DSpace SAF Submission Ingestion Package generated from Vireo submission #13873 on 2019-08-22 at 15:08:02Made available in DSpace on 2019-08-23T20:36:09Z (GMT). No. of bitstreams: 2
MEHTA-THESIS-2019.pdf: 84393765 bytes, checksum: 74f0edf247057995595372eb8076e513 (MD5)
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Previous issue date: 2019-04-24Embargo set by: Seth Robbins for item 112203
Lift date: 2021-08-23T20:36:18Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 112203 on 2021-08-24T09:15:24Z
Optimal Bioeconomic Management Strategies for Prevention and Control of Invasive Alien Species
No full textPaper removed by author. Please see the current version, available online January 8, 2007: Mehta, S.V. et al. Optimal detection and control strategies for invasive species management. Ecological Economics (2007), doi:10.1016/j.ecolecon.2006.10.024Environmental Economics and Policy,
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