23 February 2005 The causes and nature of diameter variations along optical fiber
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The drawing of optical fiber is essentially a stabilization process with a 'slow’ feedback system used to control diameter drift. Such a system is capable of producing high precision fiber with a ±0.3 μm deviation around the mean diameter being standard even on a high-speed commercial tower. However an emerging demand for even greater precision in fiber diameter has focused attention on the neck-down process itself and the effect of furnace operating conditions on the stability of this crucial stage. In this paper we present the results of an extensive experimental study into the nature of cladding diameter variations along optical fibers based on real-time measurements made during fiber drawing. It was found that the statistical distribution of cladding diameter measurements is never Gaussian with multiple peaked distributions being quite common. Power spectra indicate that the change in diameter is generally random but with detectable maximum frequency components up to 5-10 Hz. An incorrectly set up furnace can produce strongly periodic variations. Results will be presented that quantify the impact of furnace temperature, furnace purge gas flow and iris aperture on the variation in fiber diameter. Some evidence of 'diameter modes’ -- that is, preferred diameters separated by gaps in the observed measurements -- has been found. The overarching conclusion is that better process control is not the route to reducing variation in fiber diameter. Rather the solution lies in moderating the extent to which short-time scale variations in the temperature and flow fields within the furnace interact with the preform neck-down region.
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Susan H. Law, Susan H. Law, Geoffrey W. Barton, Geoffrey W. Barton, Thanh N. Phan, Thanh N. Phan, } "The causes and nature of diameter variations along optical fiber", Proc. SPIE 5650, Micro- and Nanotechnology: Materials, Processes, Packaging, and Systems II, (23 February 2005); doi: 10.1117/12.581789; https://doi.org/10.1117/12.581789

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