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Title: Robust transmission of RF signals over multimode fibre (MMF) beyond the fibre-bandwidth
Author: Hartmann, P.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2007
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Because of its limited bandwidth Multi-Mode Fibre (MMF) was until recently thought unsuitable to carry high dynamic range RF modulated ranges. Although it was observed that the response of a laser-based MMF shows a passband response with only little attenuation beyond the 3 dB-bandwidth, researchers have found this passband response to be very unstable and segmented by deep troughs. In this work a controlled launch technique is proposed, which results in stable and low-penalty transmission over the majority of installed-base MMF links. It was found that more than 99 % of all 62.5 μm core-diameter MMFs (62MMF) in the installed base will support RF carrier frequencies up to at least GHz over distances of up to 600 m. Furthermore, low-penalty transmission is possible beyond 1000 m for a smaller percentage of fibres. It is also shown that the tolerance on the launch position is large enough to allow for a low-cost design of the optical components. Further, a number of semiconductor lasers, designed for uncooled digital applications, were assessed in terms of their analogue modulation performance. It was found that different laser structures (DFB, EP and VCSEL) exhibit sufficiently linearity performance for analogue operation with a typical spurious-free dynamic range (SFDR) of at least 90 dB . Hz2/3, even when operated uncooled at elevated temperatures of 85 °C, which is a value high enough to support most current in-building wireless systems. Finally it is shown for the first time that low-bandwidth MMF and low-cost digital lasers can be combined for the implementation of high-speed analogue optical links. A link analysis was carried out which showed that even with passband losses of up to 24 dBe, which is the maximum attenuation observed in 99 % of the installed base 62MMF, a high dynamic range RoF system with a SFDR of above 95 dB . Hz2/3 can be designed. A link is presented which supports the transmission of RF signals at carrier frequencies of up to 20 GHz with very little penalty, using a directly modulated laser diode and both low- and high-bandwidth MMF.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available