Annals of Telecommunications Volume 35, Issue 1-2 , pp 61-73
01/03/1980
ABSTRACT
Une expression générale est obtenue qui décrit l’effet des microcourbures sur la transmission de fibres optiques multimodales. Cette expression est basée sur l’approximation des rayons paraxiaux.
This report summarizes the activites at the 4th International Worshop on Optical Waveguide Theory, held at Leuwenhorst Holland on 13-16 September 1979.
Electronics Letters, Volume 16, Issue 5, 28 February 1980, pp. 193 – 195
ABSTRACT
A new powerful numerical technique is proposed that quickly gives the propagation constants, group velocities and caustics of modes with specified numbers in multimode fibres of arbitrary 2-dimensional index profiles. This method is based on the adiabatic approximation of ray optics.
Electronics Letters, Vol. 16, Issue 1, 3 January 1980, p. 34 – 35
ABSTRACT
We show that the bandwidth of distorted multimode optical fibres excited by quasimonochromatic lasers is equal to the bandwidth of the undistorted fibre divided by the microbending loss measured with l.e.d. sources, to within a numerical factor. This simple result is derived for a slab model, but it may be general.
The steady-state microbending loss of step-index fibers is found to be, within the WKB approcimation, 6.27 (…/∆) dB/unit length, where … denotes the spectral density of the curvature process. The product of the square of the pulse broadening improvement factor R and loss L is 0.74 dB. Results are given for various excitation conditions.
Electronics Letters, Volume 14, Issue 20, 28 September 1978, p. 663 – 664
ABSTRACT
The modal theories of microbending that have been proposed so far postulate that modes that have the same principal mode number carry the same optical power. This assumption is shown to be incorrect. The exact result is given.
The complete solution for propagation in randomly bent, circularly symmetric multimode optical fibers is given ; the paraxial-ray-optics approximation is used. This ray-optic solution is, in principle, equivalent to the power-coupled-mode equations in the continuum limit. However, none of the assumptions usually made in modal theories is needed in the ray theory. In particular, the coupling between nonadjacent modes is effectively taken into account.
A ray theory is given for randomly bent (two-dimensional) optical fibers that have arbitrary index profiles and arbitrary curvature spectra. Simple closed form results are given for power-law profiles and spectra. No approximation is made besides the small bending approcimation and the paraxial ray optics approximation. In particular, the coupling between all modes is effectively taken into account.
A ray theory based on the time-independent Fokker-Planck equation and the integration of time along ray trajectories provides analytical expressions for the average arrival time ans spread of optical pulses propagating in randomly distorted, multimode, optical fibres. A clear physical picture emerges from the theory. The analytical expressions obtained for (t) and (t2) coincide with the ones obtained by Olshansky from coupled-form theory. The (t3) and (t4) moments of the impulse response are also calculated. Simple closed-form formulae are given for the step-index slab. The coupling between all modes is effectively taken into account in our ray theory.