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Method for producing glass preform for optical fiber containing fluorine in cladding

  • US 4,880,452 A
  • Filed: 12/22/1988
  • Issued: 11/14/1989
  • Est. Priority Date: 06/04/1984
  • Status: Expired due to Fees
First Claim
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1. A method for producing a glass preform for a single mode optical fiber having a cladding containing fluorine, and a core, comprising the steps of:

  • heating and partially fusing a porous glass rod of pure quartz to such extent that said porous glass rod is not made transparent;

    heating said partially fused glass rod in an atmosphere containing fluorine to provide the addition of fluorine only to the outer portion of said porous glass rod so that the inner portion of said porous glass rod remains free of fluorine as pure quartz and to result in said porous rod becoming a substantially transparent fused glass rod;

    drawing said fused glass rod, having an inner portion free of fluorine, to a certain diameter;

    forming a porous glass layer of pure quartz surrounding the outer surface of said fused glass rod; and

    heating said fused glass rod and said porous glass layer in an atmosphere containing fluorine to provide the addition of fluorine to said porous glass layer in an amount equal to the amount of fluorine added to said outer portion of said porous glass rod, and to result in said porous glass layer becoming substantially transparent, whereby a step index optical fiber preform is provided having a uniform amount of fluorine throughout its cladding and having a core free of fluorine.

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