Dispersion effects in elliptical-core highly birefringent fibers

Modal birefringence and its sensitivity to temperature and hydrostatic pres sure were measured versus wavelength in three elliptical-core fibers and on e fiber with stress-induced birefringence. We carried out the measurements in the spectral range from 633 to 843 nm by using interferometric methods. In fibers with elliptical cores all the measured parameters showed high chr omatic dependence, whereas in fibers with stress-induced birefringence this dependence was weak. We modeled the dispersion characteristics of two elli ptical-core fibers by using the modified perturbation approach first propos ed by Kumar. The modification consists of introducing into the expression f or the normalized propagation constants an additional perturbation term tha t contains information about stress-induced birefringence. The results of m odeling show that the temperature and pressure sensitivity of elliptical-co re fiber are associated primarily with variations in stress induced by thes e parameters. The agreement between measured and calculated values of sensi tivity in the worst case was equal to 20% for modal birefringence and tempe rature sensitivity and 50% for pressure sensitivity. Lower agreement betwee n measured and calculated values of pressure sensitivity is Most probably a ssociated with uncertainties in the material constants used in modeling. (C ) 2001 Optical Society of America.