TEMPERATURE SENSITIVITY OF COATED STRESS-INDUCED BIREFRINGENT OPTICALFIBERS

An approximate analytical theory is developed to describe the effects of temperature on the birefringence in a coated stress-induced birefri ngent optical fiber. Because of the mismatch in the thermal expansion coefficients of the cladding and the stress-applying sections in the f iber, the birefringence in the fiber responds directly to a change of temperature. Additional changes in the birefringence can be produced i ndirectly by the temperature-induced radial stress and axial strain in the glass fiber through the fiber coating. Depending on the coating m aterial and thickness as well as the thermoelastic properties of the f iber glasses, the indirect effect can reinforce or cancel the direct e ffect. It is possible to design a fiber with a birefringence that is i nsensitive to temperature variation over a range of temperature. Expre ssions suitable for fiber design are presented. Both plastic and metal coating materials are considered. Design examples for boron-doped fib ers are given. (C) 1997 Society of Photo-Optical Instrumentation Engin eers.