as parameters of copper and nickel thickness is shown in fig3 each circle or u201c x u201d indicates that metal coated fiber having cu and ni of various thickness was made and bending test was done after heating the test results as indicated demonstrate that the structure having more than 5 micron of electrolytic copper and more than 0 5 micron of electrolytic nickel showed good ductility against atmospheric heating of 500 deg c for 5 hours as noted above transmission loss performance in addition to ductility after heat treatment is an important characteristic for downhole applications the inventors fabricated long metal coated fiber for evaluation of transmission characteristics as an example metal coating thicknesses of six 6 micron of electrolytic copper and one 1 micron of nickel may be utilized referring now to fig4 long optical fiber having carbon layer and water soluble polymer may be produced using the illustrated apparatus in this regard a single mode fiber preform 20 is heated by heater 22 to a suitable temperature e g 2000 deg c the drawn fiber 24 enters carbon coating furnace 26 in line with the drawing furnace acetylene or other hydrocarbons are decomposed thermally and amorphous carbon is deposited on glass surface during passing through the chamber then carbon coated fiber 28 goes through coating die 30 for application of water soluble polymer in one example the water soluble polymer may be oks 8049 nichigo 20 aqueous solution the coated fiber 32 passes through a curing oven 34 and is taken up into.