Mode-coupling processes in polymethyl methacrylate-core optical fibers

Abstract

Aperture, attenuation, and far-field radiation diagrams have been studied on short lengths of commercial polymethyl methacrylate- (PMMA-) core optical fibers. The spectral attenuation of the PMMA constituting the core has been carefully measured and compared with the attenuation that may be calculated from optical properties of PMMA. Accurate extrinsic attenuation spectra have been obtained. Moreover, the dependence of the far-field radiation diagram on the fiber length and on the launching incidence of a laser beam has been studied on this side of the mode-equilibrium length. The analysis of these diagrams, first performed with the Gloge mode-coupling model, has been improved with the hypothesis that the mode-coupling processes are a result of light diffraction by structural anomalies in the core. The average size and form of these structural anomalies has been evaluated. They may be longitudinal microcracks of the PMMA coming from stress relaxation, which occurs during the fiber-drawing process.

Calculation of the frequency response in step-index plastic optical fibers using the time-dependent power flow equation

“…2), we have obtained that the value of the coupling coefficient DE 5.02 Â 10 À 4 rad 2 /m characterizes mode coupling in the angular range of interest yE0 to 71 (in the calculations we assumed that the light beam is launched centrally along the fiber axis with FWHM¼ 10.21). One should mention here that modeling the mode coupling process with a constant D is commonly done by many other authors [5,[11][12][13][14][15].…”

Influence of intermediate layer on transmission characteristics of W-type optical fibers

“…In addition to coupling, modal attenuation and dispersion also affect transmission of the W-type optical fiber; hence, methods for calculating their contributions are needed. Launch conditions, fiber properties and fiber length determine the output optical power distribution, and hence the far-field pattern, of an optical fiber [11]. A ring-pattern launch at an angle of θ 0 40 to the axis can be reproduced in the output field pattern of only short fibers.…”

Equilibrium Mode Distribution and Steady State Distribution in Step-Index Glass Optical Fibers

“…EMD indicates a substantially complete mode coupling and is of critical importance when measuring characteristics of multimode optical fibers (linear attenuation, bandwidth, etc.). Indeed, measurement of these characteristics would only be considered as meaningful if performed at the EMD condition when it is possible to assign to a fiber a unique value of loss per unit length [2]. At distance z s (z s > L c ) from the input fiber end, all individual disk patterns corresponding to different launch angles take the same light-distribution across the fiber-section and the "steady state distribution" (SSD) is achieved.…”