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Among the improvements planned for the 1997 upgrade of the D0 detector at Fermilab are installation of a new scintillating-fiber central tracker and a new lead-scintillator preshower counter read out with wave-shifting fibers. Because of space limitations, fibers in both systems may need to undergo bends of fairly small radius, and the resulting stresses and strains may cause light losses. This paper presents interim results from a study of the effects of deformation on fiber light transmission. A variety of scintillating, wave-shifting, and clear fibers with diameters near 1 mm have been examined. Particular emphasis was placed on the new, multiclad fibers developed by Kuraray. Light loss was measured by injecting light into one end of a fiber sample and measuring the exiting light before, during, and after controlled deformation of the fiber. The deformations studied include bending, tensile elongation, compression, and torsion. Generally, except for severe bending or considerable compression, light loss was found to be less than a few percent. The effect of bending were investigated using single-turn and multiple-turn loops of various radii. Light loss was found to increase with decreasing radius, but little dependence on either core dopants or diameter was observed. Generally, the light loss, L, in an N-turn loop of radius r could be parameterized by the form L equals A(root)N/rn, where A is a constant and n is near 1.5. Kuraray multiclad fiber was found to be superior to single-clad fiber in that the former can be bent into single- turn loops with radii as small as 1 cm before introducing a light loss of 3%, while the latter produces this loss at a 2 cm radius. Tensile stress for forces up to 1.3 kg for 2-m-long fibers produced less than 1% light loss. On the other hand, compressive stress exerted over a 10-cm- long fiber section could cause a loss of 10%. Finally, a single observation of the effects of torsion indicated no change in light transmission for a 360 degree(s) twist at the center of a 4-m- long fiber with fixed ends. The observations made indicate that multiclad fibers produce smaller light losses under deformation than single-clad fibers, and that their use, together with avoidance of bends with radii smaller than a few centimeters, should avoid light loss due to stress and strain.
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