Optical fiber preform fabrication

One sign of progress is the extent to which sophisticated research on transport phenomena, particularly mass transfer, has penetrated several other fields, including those described in later papers of this volume. Examples include fundamental work on the mechanics of trickle beds [17] within reactor engineering studies of dispersion in laminar flows [18] in the context of separations important to biotechnology coupling between fluid flows and mass transfer in chemical vapor deposition processes for fabrication of semiconductor devices [19] and optical fiber preforms [20] and the simulation of flows in mixers, extruders, and other unit operations for processing polymers. 

In the final step, the tube is removed from the lathe after sufficient layers have been deposited, and the entire preform is heated to the softening point of the quartz tube. The tube collapses and is drawn into fiber. In this process, the inner core that remains after MCVD layering is removed. Typical preforms are on the order of 1 m in length, from which hundreds of kilometers of continuous optical fiber can be fabricated. 

K. Yoshida, T. Satoh, N. Enomoto, T. Yagi, H. Hihara and M. Oku, Fabrication of large preforms for low loss single mode optical fibers, Glastechnische Berichte (1996). 

Optical fibers are usually made of glass, and most often this is an oxide glass based on silica (Si02) and some additives. A rod of glass (called preform) is heated until soft, and then a fiber is drawn from its end. This fiber consists only of a core. The preform itself may consist of two glasses, of different indices of refraction, such as shown schematically in Fig. 2(b). In this case a core/clad fiber is fabricated by drawing. In both cases the outer diameter of the fiber is less fhan 0.1 mm, in order to obtain flexibility. Fibers in use today are generally core/clad fibers. 

There are many methods to measure the RIP of the preform and the fiber. However, the RIP might be changed by the heat-drawing process, but some fabrication methods, such as coextrusion, can produce optical fibers directly from raw materials, not via preforms (see Chapter 5). In addition, we are interested in the final RIP of the fiber and not in the RIP of the preform during fabrication. Thus, this section focuses on measurements of the RIP of the fiber. 

Bise R., Trevor D.J., Monberg E., Dimarcello F. Impact of preform fabrication and fiber draw on the optical properties of microstructured fibers. In Proceedings International Wide Cable Symposium Proceedings 2002 51 339-343... 

Bogdanovich, A.E., Wigent III, D.E., Whitney, T.J., 2003. Fabrication of 3-D woven preforms and composites with integrated fiber optic sensors. SAMPE J. 39 (4), 6-15. 

These challenges in fabrication have driven the development of sol-gel processing in pure silica. Several new methods that combine the low temperature processing afforded by working with nanometer sized particles with flexible silica chemistry (MacChesney, 1997 Wang, 2003 Yoon, 2003) have recently come to commercial fruition. This chapter describes the OFS Sol-Gel process used to make over 1(X) tons (MacChesney, 1998 Trevor, 2001) of dimensionally precise high piuity silica glass for fiber optic preform jackets. 

Extrusion also allows the fabrication of core/clad preforms. Savage et al. successfully reported the coextrusion of a Ge-As-Se preform and its subsequent fiber drawing [152], The coextrusion technique produces preforms with optimum core/clad interface quality. Fibers with optical losses of 1.7 dB/m at 6.0 pm were fabricated. Recently Abouraddy et al. have extended the technology by coextruding composite macroscopic preforms made of two ChG materials and a thermoplastic polymer cladding [153], yielding mechanically robust fibers. 

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