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22 September 1987 Backward Wave Couplers And Reflectors
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Proceedings Volume 0800, Novel Optoelectronic Devices; (1987)
Event: Fourth International Symposium on Optical and Optoelectronic Applied Sciences and Engineering, 1987, The Hague, Netherlands
The analysis and experimental results for weakly perturbed, narrow band, backward wave couplers and fibre reflectors, will be presented. Conventional, co-directional fibre couplers - polished, fused or coaxial - can be designed to demonstrate a sufficient wavelength dependence for some filtering and multiplexing applications. While coupled bandwidths can be sufficiently reduced by weakening the coupling between the guides and hence increasing the interaction (beat) length, useful limits of a few nms are reached for interaction lengths of a few cms. These limitations in coupled bandwidth are considerably transformed for contra-directional coupling provided by a periodic perturbation of suitable pitch (half the guide wavelength) imposed on the coupler. The inverse relationship between bandwidth and interaction length still holds, but the magnitudes are substantially improved. Calculations show that we may expect sub-Angstrom bandwidths for interaction lengths in the order of 1cm. These extremely narrow band effects depend on the successful fabrication of regular, weak, periodic perturbations over relatively long fibre lengths. We have fabricated long gratings (~ 1cm) of periodicity ~ 0.27μm on D-shaped elliptical cored fibres as a first step towards narrow band couplers. These structures can be investigated by observing reflection characteristics at ~ 800nm and the latest results will be described. A contra-directional coupler may then be formed, by joining two dissimilar D-fibres in the polished-coupler configuration with a periodic structure in between them. Additionally, the design of a special twin-core fibre coupler will be described, and its potential as a backward-wave coupler will be examined.
© (1987) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
C. Vassilopoulos and J. R. Cozens "Backward Wave Couplers And Reflectors", Proc. SPIE 0800, Novel Optoelectronic Devices, (22 September 1987);

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