Apparatus for forming dielectric optical waveguides

Claim 2

Apparatus for coating an optical fiber comprising: an extrusion device for extruding a sleeve of polymer; means for feeding the fiber through said extrusion device into the center of the sleeve as the sleeve is extruded, the sleeve having an internal diameter substantially greater than the fiber; and drawing means downstream of said extrusion device contacting the outer surface of said sleeve for reducing the internal diameter of said sleeve to a point where there is a small but distinct clearance between the fiber and the inner surface of the sleeve permitting relative axial movement therebetween.

Claim 3

Apparatus as claimed in claim 1 including cleaning means disposed upstream of said extrusion device for cleaning the fibre before it is coated.

Claim 4

Apparatus as claimed in claim 2 wherein said cleaning means includes a pair of juxtaposed felt pads between which the fibre is arranged to pass and a blowing ring downstream of said pads for blowing cold air onto the fibre.

Claim 5

Apparatus as defined by claim 1 wherein said extrusion device includes a screw-extruder and a cross-head die, said extruder being arranged to feed said die.

Claim 6

Apparatus as defined by claim 4 wherein said screw-extruder includes a feed tube; a clamp connecting said feed tube to said cross-head die; and a heater thermally connected to said clamp.

Claim 7

Apparatus as defined by claim 1 wherein said cross-head die has a through bore one end of which constitutes an outlet for extruding polymer; a first tubular portion which extends into the bore from its other end to a position adjacent said outlet, said first tubular portion having a tapered end portion adjacent said outlet, a second tubular portion mounted coaxially within the first tubular portion, and a third tubular portion mounted coaxially with said first and second tubular portions, said third tubular portion extending into said second tubular portion adjacent the other end of the die, out through the tapered end of the first tubular portion and terminating adjacent the outlet of said die, the arrangement being such that in use a fiber passing through said third portion is thermally insulated from the heated polymer in the die over a substantial portion of its length of travel through said die.

Claim 8

Apparatus as defined in claim 1 including a take-off drum from which fiber can be fed to said extrusion device and tensioning means between said drum and said extrusion device for maintaining the fiber under a substantially constant tension.

Claim 9

Apparatus as defined in claim 1 including a cooling bath disposed between said extrusion device and said drawing means.

Claim 10

Apparatus as claimed in claim 8 wherein said cooling bath contains a longitudinally extending guide tube through which the coated fibre is arranged to pass, the bath having inlet and outlet apertures aligned with said guide tube through which the coated fibre can pass.

Claim 11

Apparatus as defined by claim 9 including a plate located upstream of and in parallel spaced relationship with that wall of said bath having said inlet aperture, said plate having an aperture aligned with the inlet aperture, the size of said apertures being such that in use, as coated fiber enters the bath, water can flow out of the bath through said inlet aperture but is prevented by surface tension from flowing through the aperture in said plate.

Claim 12

Apparatus as claimed in claim 1 wherein said drawing means comprises a first pair of rotatable belts, spaced apart a distance corresponding substantially to the diameter of the extruded sleeve, and a second pair of rotatable belt located downstream from said first pair, said second pair of belts being spaced apart a distance substantially less than the spacing of said first pair.

Claim 13

Apparatus as defined in claim 11 including an oven between said first and second pairs of belts, positioned to allow said sleeve to pass therethrough.

Claim 14

Apparatus as claimed in claim 12 including a further oven located downstream from said second pair of belts.

Claim 15

Apparatus as claimed in claim 13 wherein said further oven has a first relatively high temperature zone, and a second relatively low temperature zone.

Claim 16

Apparatus as claimed in claim 13 wherein said further oven includes air jets which are so arranged that air can be blown therethrough onto the sleeve as it leaves the further oven.

Claim 17

Apparatus as defined in claim 13 including a capstan located downstream from said further oven said capstan having a pair of pulleys contacting the sleeve one of which is driven at a speed slightly less than the speed of rotation of the second pair of belts to allow for shrinkage of the sleeve after it leaves said further oven.