E. Jaunart

Theoretical and experimental study of second-order distortions in CATV DFB laser diodes

Calculation of linearity performances of a given DFB laser is a well-known problem when working with CATV AM-VSB optical links. In this paper, a nonlinear model of the DFB laser is presented. The bias and frequency dependence of second order intermodulation distortion is analyzed by combining Volterra models of the laser leakage current and rate equations. The prediction of the model is then compared to distortion measurements with a maximum discrepancy of around 1.5 dB.<<ETX>>

Feasability of AM-VSB CATV Optical Networks Using Semiconductor Laser Diodes

In the past five years practical multi-channel AM-VSB optical fibre links have moved from the R&D labs into real world applications. In this paper, we focus on the design and performance capabilities of current commercialized systems using distributed feedback lasers (DFB), single mode optical fibres and PIN optical receivers. We first discuss fundamental concepts used in IM-DD communication links. The noise and distortions sources are identified and their influence on the systems performances are presented. The use of Erbium Doped Fibre Amplifiers (EDFA) at 1550 nm is envisaged and their influence on the power budget of the CATV network is analyzed.

Chromatic dispersion modeling of single-mode optical fibers: a detailed analysis

We present here an efficient method for single-mode fiber modeling. This paper deals mainly with chromatic dispersion computation but the analysis can be extended to other single-mode characteristics. This synthesis shows that key-parameters have to be correctly chosen in order to insure an accurate modeling of chromatic dispersion. Finally, the results we obtained with this method are presented. The agreement between theoretical calculations and measurements is also explained. >

Influence of refractive index measurement accuracy on single-mode optical fiber modeling

In a paper by E. Jaunart (1990), numerical computations of the main characteristics of single-mode optical fibers (chromatic dispersion, cutoff wavelength, mode-field diameter, etc.) and their measurements on real fibers were compared. The influence of the refractive-index measurement error on the chromatic dispersion calculation has now been investigated, and it is concluded that the fiber refractive-index profile had to be accurately measured in order to obtain a good agreement between computations and measurements. This requirement is quantified, and the discrepancies found previously between computations and measurements are explained.<<ETX>>

Analysis of numerical methods efficiency for EDFA modelling

A general numerical technique for EDFA modelling is presented. An original and efficient algorithm is used to compute the light intensity distribution in the active fibre section. A fast discretization method is applied reducing the time for ASE spectra computation. Different numerical methods have been investigated for solving ordinary differential equations (ODEs): it appears that their efficiencies depend on the system size. Runge-Kutta and Bulirsch-Stoer methods seem to be most suitable for EDFA modelling. Moreover, the Dormand and Prince method allows to save 25% of computation time.<<ETX>>

Erbium-doped fiber amplifier (EDFA) noise figure computation for saturated and unsaturated regimes

This paper is divided in two parts. The first one is dedicated to the noise figure computation of noise saturated EDFA. In-line and preamplier EDFA are mainly concerned. The noise figure calculation requires the computation of the whole ASE spectra. A discretization of the fluorescence spectrum is detailed in order to rapidly and accurately compute the EDFA noise. The gain and noise values obtained with our method have been compared to those of various European research laboratories: there is no meaningful (< 1%) differences between our results and methods which consider the fluorescence at every nanometer. The same numerical accuracies are obtained leading to smaller computation times. In the second part, the noise figure of booster EDFA is investigated. In the case of booster EDFA, the input signal is quite high (a few mW). The laser levels populations are dependent on the photon number. The now classical noise figure formula have to be carefully applied because of this dependence. A direct integration of the master equation is required to compute the real noise figure of power boosters. The discrepancies between both definitions have been quantified: differences up to 3 dB have been computed for a 980 nm-forward pumped EDFA.

Simple and accurate model for erbium-doped fiber amplifier (EDFA) noise and gain computation

In many amplification regimes, the EDFA gain is saturated by noise. This is particularly true for in-line and preamplifier EDFA. The accurate computation of noise spectra is necessary to predict the EDFA exact gain and noise characteristics. In most cases, this is done by solving the rates equations describing the noise spectra. An interesting approach of noise unsaturated EDFA has been given by E. Desurvire. One ordinary differential equation (ODE) describes the whole noise spectrum in one direction. This is the usual concept of noise effective bandwidth (NEB). A set of 4 ODE is then required to compute gain and noise characteristics, leading to short computation times as a small size ODE system is concerned. The NEB definition we used has been modified in order to take into account the spatial distribution of the light power in the active fiber section and the population inversion. The NEB method we propose uses 1, 2, or 4 NEB, leading to small computation times (approximately equals 4s.). In order to generalize the results obtained by our method, several cases have been investigated: input signal powers of -40, -20, O dBm and input pump powers ranging from 10 to 30 mW. The worst case is the low input signal power because of the high noise level saturating the EDFA gain. The predictions provided by one modified NEB are at least better than the results obtained with 4 standard NEB, as defined by E. Desurvire. The computations fairly agree with the reference solution (integration of the rate equations): the larger discrepancy is lower than 0.7 dB.