Determination of modal power distribution in graded-index optical waveguides from near-field patterns and its application to differential mode attenuation measurement

Abstract

A technique is introduced that determines power distribution in fibers from the measured near-field pattern, assuming that: (1) the optical power distributes uniformly among degenerated modes with the same propagation constant, (2) enough modes are excited to ensure the validity of calculation by geometrical optics, and (3) the phase of each propagation mode has no correlation. Experiments verifed that the fibers have the function of flattening power distribution among modes with the same propagation constant. This fact shows that assumption (1) does not severely limit the applicability of the technique. Wave optical calculation is done to determine the numbers of modes that must be excited to satisfy assumption (2). As an example of application of the technique, differential mode attenuation of graded-index fibers is determined from longitudinal variation of the measured near-field pattern.

Effects of uncertainties in the characterization of multi-mode fiber excitation conditions

“…Following the work originally proposed in [6] and further developed in [7], the near field intensity can be computed from the contribution of all propagating modes introducing the MTF: (1) where δ is the normalized propagation constant.…”

Near-field intensity pattern at the output of silica-based graded-index multimode fibers under selective excitation with a single-mode fiber

“…To account for the radial dependency of the refractive index in the core, the computation of the propagation coefficients β ν,µ and the modal fields e ν,µ (r, φ ), h ν,µ (r, φ ) is performed by a direct numerical integration of Maxwell's equations in their full-wave form [22]. Models based on ray optics can be also used to give the near-field intensity yielded by a mode group, however, excitation of a large number of modes is assumed and the phase of the modal amplitudes is not taken into consideration [23,24].…”

Chromatic Modulation for Optical Fibre Sensing Electromagnetic and Speckle Noise Analysis

“…A my ()) is independent of m, v) . This problem has been discussed extensively in the literature [8][9][10][11] but the more general problem of how to launch a specific combination of modes into the fibre and whether this can be advantageous for certain applications remains to be resolved . Experimentally the laser beam profile was adjusted such that the intensity across the beam launched into the fibre was constant and the beam was converging .…”

“…El X1 experimental ; -Xl theoretical (using assumption 3) ; ∎ X1 theoretical (using assumpExperimental results (points with error bars) and theoretical predictions (curves) of the chromaticity variable x 2 as a function of the (normalized) radius) . 0 X2 experimental ; • X2 theoretical (using assumption 3) ; ∎ X2 theoretical (using assumption 1) .Substituting equations (9), (17) into equation(10) and re-expressing the probability distribution as P(I1, 0 1 ; I2, 02) = [4n 2 (T1T2-ITI 2 )] -1 xexp[ -T1I1 -T2I2+2ITI(I1I2) 112 cos(01 -02+v)],…”