Optical fiber preform cleaning method

Details Optical fiber preform cleaning method Optical fiber preform cleaning method

1994-03-10

2001-07-17

Hoffmann, John (Department: 1731)

Glass manufacturing

Processes of manufacturing fibers, filaments, or preforms

With measuring, controlling, sensing, programming, timing,...

C065S503000, C134S006000, C134S007000, C134S012000, C356S073100

Reexamination Certificate

active

06260386

ABSTRACT:

TECHNICAL FIELD
This invention relates to the cleaning of optical fiber preforms and, more particularly, to methods for cleaning index-matching oil from preforms.
BACKGROUND OF THE INVENTION
An optical fiber preform is a cylindrical glass body from which optical fiber is made by a process known as drawing. As is described, for example, in the patent of Glantschnig et al., U.S. Pat. No. 4,934,818, granted Jun. 19, 1990, prior to drawing, it is normally necessary to determine the optical characteristics of the preform by directing a narrow monochromatic beam of light through the preform. During this testing operation, the preform is customarily submerged in a container of oil known as index-matching oil that has a refractive index that matches that of the preform.
After the optical test, the index-matching oil must be cleaned from the preform. This is a particularly crucial step if a hollow cylindrical jacket of glass is to be fitted over the preform to expand its diameter prior to drawing. The cleaning process may include detergent cleaning, followed by a water rinse. Cleaned preforms are then finally dried in hot nitrogen. The cleaning process typically takes approximately sixty minutes and generates liquid waste, which, since it includes oil and detergent, is potentially environmentally hazardous. It would be desirable to reduce the time needed for cleaning, and to reduce or eliminate liquid waste associated with cleaning. It would also be desirable if one could recycle the index-matching oil cleaned from each preform.
SUMMARY OF THE INVENTION
In accordance with an illustrative embodiment of the invention, the cleaning step comprises contacting the preform with supercritical carbon dioxide (a liquid) which dissolves residual index-matching oil on the preform. The liquefied carbon dioxide is then converted to gaseous carbon dioxide which conveniently separates the index-matching oil from the carbon dioxide so that the oil can be recovered and reused. The gaseous carbon dioxide is likewise recycled for use in subsequent cleaning, and so there is substantially no waste. Cleaning in accordance with the invention does not normally require rinsing and drying steps and is therefore faster than prior cleaning methods. These and other objects, features and benefits of the invention will be better understood from a consideration of the following detailed description taken in conjunction with the accompanying drawing.


REFERENCES:
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patent: 4565449 (1986-01-01), Grego
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Concise Encyclopedia of Chemical Technology. Kirk-Othmer 1985, Wiley & Sons, pp. 1141-1142.*
“Supercritical Fluids to Replace VOC Cleaning Media”, by J. Williams et al., Environmentally Conscious Manufacturing Conference, Albuquerque, NM, Sep. 18-20, 1991.
“Processing of Polymers with Supercritical Fluids,” V. Krukonis,Polymer News, vol. 11, 1985, pp. 7-16.

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