Modal Analysis of Loss and Mode Mixing in Multimode Parabolic Index Splices

Modal Analysis of Loss and Mode Mixing in Multimode Parabolic Index Splices By I. A. W H I T E and S. C. METTLER (Manuscript received November 18,1982) In this paper we present an electromagnetic modal theory for characterizing parabolic-index multimode fiber splices with either intrinsic or extrinsic mismatches. The theory agrees with previously published theoretical results for transverse offset using a uniform power distribution. It also agrees with new experimental measurements made with a long, spliced input fiber using a published, theoretical, steady-state modal power distribution. This modal theory predicts, and experiment confirms, a previously unreported periodic fluctuation in splice loss as a function of wavelength for intrinsic parameter mismatch. The analysis also predicts a large degree of mode mixing for transverse offset but negligible mode mixing for parameter mismatch in typical multimode fiber splices. I. INTRODUCTION Theoretical predictions of splice loss in multimode fibers have been attempted by many researchers (see Ref. 1 for a list). However, these analyses1-3 do not adequately predict measured splice loss results, and most do not address mode mixing effects, which are important for the prediction of the bandwidth of concatenated lengths of fiber. The best agreement with splice loss measurement data is an empirical model based on geometric optics.2 However, such an analysis of splice loss provides only a limited description of the effect of splices. Electromagnetic theory, using the coupling coefficients of individual modes, provides a complete treatment of splice loss and mode mixing.