J.-C. Froidure

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. >

Physical layer characterization of hybrid fibre coax (HFC) networks

This paper reviews the future prospects of cable television networks through their evolution towards HFC topology. This upgrade will allow cable operators to provide full broadband bi-directional communications (image, data and voice) and generate new revenues from their existing network. This article focuses on: what is an HFC topology, what are the relevant parameters to characterize its physical layer, what are the technological key issues and future trends?RésuméCet article passe en revue les perspectives d’avenir des réseaux de télédistribution classiques à travers leur évolution vers une structure hybride comprenant de la fibre optique et du câble coaxial : un réseau de type HFC. Par ce biais, les câblo-distributeurs fourniront une structure large bande de communication bidirectionnelle, capable de supporter la voix, les données et l’image, et généreront de nouveaux revenus à partir de leur réseau existant. Les principaux points abordés sont : qu ’est-ce qu’une structure HFC, quels sont les paramétres pertinents nécessaires pour caractériser la couche physique, quelles sont les technologies essentielles utilisées et comment se profile l’avenir de ces réseaux.

Experimental and Theoretical Evaluation of Distortion Effects on SCM Optical Transmissions Due to the Joint Action of Static Chirping, Dynamic Chirping and Dispersive Channel

In optical CATV systems based on subcarrier-multiplexing technique, the joint action of semiconductor laser chirp and fiber chromatic dispersion gives rise to intermodulation distortion phenomena affecting the transmission performance. This problem has been explained analytically, leading to a model valid for every kind of modulating signal and explored in the case of a Gaussian process. In this paper, the model is developed for the important specific case of an analogue SCM modulating signal. The results are assessed experimentally.

PMD measurements on single-mode optical fibre below the interferometer limit

In this paper, we presented Polarisation Mode Dispersion (PMD) measurements of single-mode fibres obtained with a modified Michelson interferometer. We were able to characterise fibres with PMD values below the coherence time of the interferometer source. PMD measurements of birefringent and telecommunication fibres have been carried out. PMD values from 0.1 ps to 0.049 ps have been achieved with a RMS better than 0.011 ps and remaining within the calculated uncertainty. A comparison of this method with the Wavelength Scanning Fourier Transform (WSFT) is currently under investigation.

Optical and electrical methods comparison for accurate measurement of erbium-doped fiber amplifiers (EDFA) gain and noise figure

At the present time, standards are not yet available to characterize EDFA performances. Several methods have to be tested to provide an accurate and reproducible measurement technique. This paper presents such an investigation for optical and electrical measurement methods. In the first part, the interpolation and polarization nulling optical techniques are presented. The experimental set-up is described in detail. These methods have been applied to measure the gain and the noise figure of EDFA. These measurements have been carried on a commercial EDFA. Meaningful discrepancies have been highlighted. These discrepancies have been analyzed. More especially, the insertion of a narrow band optical filter and the polarization dependence of noise have been investigated. Conclusions have been drawn explaining the measurement results differences. In the second part, the electrical method is detailed and analyzed. The influence of the laser RIN on the noise figure measurement is put into light. The signal spontaneous noise becomes a major contribution and care has to be taken to avoid it. Optical filtering of the signal is then highly recommended. Finally both electrical and optical methods are compared. The errors originating from respective methods are highlighted.

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>>

Non-Linear Behavior Characterization Methods for HFC Networks Return Path Devices and Their Relationship

This paper presents a measurement methodology to characterize the non-linear behavior of HFC (Hybrid Fiber Coax) return path components and sub-systems. The measurement method, based on NPR (Noise Power Ratio), takes into account the spectral and statistical nature of return path signals, those being different from downstream signals. The paper describes a reliable measurement set-up based on a filtered white noise source and a spectrum analyzer. Correction figures to apply to spectrum analyzer measurements, experimental best practices and measurement uncertainty are developed. The automation of the set-up is presented as well as some results concerning an electric return path amplifier and an optical return path system. The temperature behavior of those devices is compared by the way of the NPR. Also, a theoretical analysis of the relationship between tones distortions characterization and the NPR method is established and experimentally demonstrated. Therefrom, an alternative measurement method for return path systems is proposed to the attention of laboratories which do not possess NPR measurement capabilities.

Distortions due to the joint action of static and dynamic chirping and dispersive fibre in SCM optical systems: theory and experiment

The propagation of an SCM signal in a dispersive optical fibre, considering the AM-FM conversion effect due the semiconductor laser static and dynamic chirping has been analyzed. An analytical model was suitable extended in order to derive closed expressions for the composite second order and composite triple beat distortion induced. The comparison with the developed theory was done in the case of a mismatch liaison, consisting of an analogue 1550 nm DFB laser coupled with different lengths of standard fibre. Good agreement was found within the measurement uncertainty.