Empirical Evaluation of Profile Variations in an MCVD Optical Waveguide Fiber Using Modal Structure Analysis

Empirical Evaluation of Profile Variations in an MCVD Optical Waveguide Fiber Using Modal Structure Analysis By A. C A R N E V A L E * and U. C. P A E K f (Manuscript received November 15, 1982) This paper presents a computer modeling evaluation of the effect on mode propagation of typical perturbations in the refractive index profile produced as a result of the MCVD process. Certain profile variations were eliminated, singly and/or collectively, and the resultant changes in modal structure analyzed. The most important factor in the deterioration of the bandwidth is the presence of a refractive index dip at the core center. Small shifts in the level of dopant were seen to broaden pulse shapes and thus reduce bandwidth. Much less effect on bandwidth is associated with the ripples in the profile, as is also true for dips in refractive index below the index of the cladding near the core-cladding interface. A perpendicular rise, or step, in index of refraction at the core-cladding interface reduces the number of altered modes near the cladding. I. INTRODUCTION In a previous paper 1 we reported on calculation of t h e modal structure as a function of wavelength (A) of an optical waveguide produced by the Modified Chemical Vapor Deposition (MCVD) process using an exact numerical procedure. T h i s technique 2 has been used extensively to investigate various theoretical aspects of optical waveguide propagation. 3 " 6 We observed excessive splitting and scattering in the * Bell Laboratories.