Effect of coating thickness on thermal stresses in tungsten-coated opticalfibers

This study investigates the effect of coating thickness on the thermal stre sses in tungsten-coated optical fibers. Theoretical results indicate that t he maximum normal stress in the tungsten coating decreases with increasing coating thickness. However, the maximum shear stress at the interface of th e glass fiber and tungsten coating increases. Eight samples of tungsten-coa ted optical fibers with coating thicknesses of 58, 75, 101, 128, 158, 383, 557, and 1013 nm, respectively, are immersed in liquid nitrogen for one day . Experimental results show that thermal stresses will either break or dela minate the tungsten coating. The crack density decreases with increased coa ting thickness, while the delaminated area of tungsten coating increases. T he theoretical results can explain the break and delamination of the tungst en coating in the optical fiber. To minimize the break and delamination of the tungsten coatings in the optical fibers, the optimal thickness of the t ungsten coating is about 158 nm. (C) 2000 American Institute of Physics. [S 0021-8979(00)02308-2].