ECOC 1975 - ECOC 2013

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......... ... ...J «... '" o o ...J ----- '" '"3 I 32 500 900 1300 1700 2100 2500 2900 3300 FIG. 1 HYDROXYL IN SODIUM 100 90 80 70 E 60 .>
33 THE DEVELOPMENT OF OPTICAL FIBRE USING SODIUM BOROSILICATE GLASSES AND THE DOUBLE CRUCIBLE TECHNIQUE C R Day, K J Beales, J E Midwinter and G R Newns Introduction We wish to report work carried out in developing the double crucible fibre drawing process to the point at which it is limited primarily by the bulk glass loss. The double crucible method has been described previously1,2. It is now possible to draw many kilometres of fibre in a continuous process from platinum crucibles with very high reproducibility of fibre attenuation. During the course of the work a number of problems have been identified and controlled independently, and these are described below, followed by some of the results achieved. Recontamination Operation of the crucibles at high temperatures causes leaching of trace impurities, in particular iron and copper, from the platinum. This effect was observed by Newns et a13 using the sodium calcium silicate (NCS) glass system. By careful choice of glass compositions in the sodium borosilicate (NBS) system,compatible glass pairs can be found which have viscosities suitable for fibre pulling at temperatures low enough to reduce the leaching rate to a negligible level. The operating temperature can thus be reduced from -1100 0 C for NCS glasses to -850 C for NBS glasses. In current fibre there is no increase in loss with time which can be attributed to recontamination. Loading Relatively large gas bubbles may be trapped in the melt by a poor glass loading technique. The glasses used for loading the crucibles were in the form of canes 6 to 8 mm in diameter, pulled directly from the melt, and subjected to a minimum of handling and exposure to the atmosphere. The canes must be fed in at low speed so that a positive meniscus is formed between the melt and the rod. This prevents cold rod from being thrust into the pool of glass and drawing in gas bubbles. The rod should a1so enter the melt at a fixed position to prevent fold-over effects which could also trap gas. Atmosphere control When the crucibles are operated open to the air, streams o·f minute scattering centres can be observed at the core-claddingiriterface of the fibre. These were postulated to be gas bubbles released as a result of an electrolytic cell formed be 4 ween the core and cladding glasses and the tip of the core crucible nozzle. The driving force of the cell appears to be oxygen in the atmosphere which diffuses through the cladding glass. The The authors are with the Post Office Research Centre, Martlesham Heath, Suffolk.
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Cable Testing and Use 85 In additio
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Fig. 3 98
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141 HI GH-PERFORMANCE, WIDEBAND FIB
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144 A 32 MB/S REGENERATIVE REPEATER
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PRACTICAL DESIGN REQUIREMENTS FOR O
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160 Fig. 3 indicates that .ptical a
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166 A number of experimental optica
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Conclusion: 170 To summarize, FO of
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180 In the short to medium distance
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185 TELEVISION TRANSMISSION EQUIPME
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191 SPECTRAL LOSS PERFORMANCES OF O
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193 Co J. SPACER TYPE CABLE Steel t
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202 One Optical Cable Performance M
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209 DATA TRANSMISSION IN NAVAL SHIP
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ECOC 1975 - ECOC 2013

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