Theory for the measurement of the linear and nonlinear refractive indices of double-clad fibers using an interferometric technique

Abstract

Multiple-beam Fizeau fringes are formed across a liquid silvered wedge when it is illuminated by a collimated beam of monochromatic light. Inserting the fiber into the liquid silvered wedge causes the fringes to shift across the fiber region with respect to the fringes at the liquid region. Fringe shift is a function in the geometry of the different regions of the fiber and the refractive index profile of the fiber. In this paper, theoretical models for the fringe shift across double-clad fibers (DCFs) with rectangular, elliptical, circular, and D-shaped inner cladding are developed. An algorithm to reconstruct the linear and nonlinear terms of the refractive index profile of the DCF is outlined. Numerical examples are provided and discussed.

The Formation of Fringes of Equal Chromatic Order across Double Clad Fiber in the Presence of High Power Lasers

“…Pal and Priye pointed out that profile perturbations such as refractive index dip in the core, which were typical features of fibers made by the MCVD technology, should be given a consideration in the design of double-clad single-mode fibers [13]. Abd El-Maksoud and Omar presented theoretical models for the fringe shift across DCFs that is inserted in a liquid air wedge and is illuminated with monochromatic light [14]. A methodology to reconstruct the linear and nonlinear terms of the refractive index profile of the DCF was outlined.…”

“…A methodology to reconstruct the linear and nonlinear terms of the refractive index profile of the DCF was outlined. Abd El-Maksoud et al extended this work to include DCFs with graded-index inner cladding [15]. Accurate knowledge of the refractive index dispersion curve is essential in determining the information capacity that a fiber may transmit.…”