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Evolution of optical fiber transmission systems
Optical fiber communication uses light pulses to transmit information from a point to another.
Semiconductor devices such as light-emitting diodes (LEDs) and laser diodes are used to generate
light at the transmitter. The transmission medium consists of an optical fiber which is a dielectric cylindrical waveguide made from low-loss materials such as silica. Light pulses propagate inside the fiber due to the internal reflection between the core and the cladding [2]. Signal amplification is required to deal with fiber loss, especially for long-haul and transoceanic transmission. At the receiver side, photo-detectors ensure the conversion of the transmitted signal to the electrical domain. The advantages that stimulate the use of optical fiber for communication systems are its low attenuation and wide spectral bandwidth compared to other communication systems. Today, optical communication systems are widely used to meet the rapidly increasing demand for telecommunication capacity and internet services. Actually, optical communication is unchallenged for the high transmission capacity with low latency in long-haul and transoceanic transmission.
EDFA invention: Wavelength division multiplexing transmission
The first breakthrough in optical communications was the invention of the Erbium-Doped Fiber Amplifiers (EDFA) in the late 1980’s. It avoids the expensive optical-to-electrical-to-optical (OEO) regeneration. It also allows the amplification of a multiplex of optical signals with different wavelength inside the amplifier bandwidth. EDFA band includes 1550nm wavelength as shown in fig. 1.1. A dramatic increase in system capacity was achieved through the aggregation of several wavelengths propagating simultaneously inside the SMF. This technique enabled by optical amplifiers is called wavelength division multiplexing (WDM). WDM technology was developed in the mid-1990’s and it increased lightwave systems capacity to roughly 1Tbps by fiber around 2000 [6]. More precisely, this rate is obtained through 80 WDM wavelength, each of them with 10Gbps. It consists in transmitting independent signals using different wavelengths propagating simultaneously in the fiber. Wavelength aggregation is done using multiplexer at the transmitter, a demultiplexer at the receiver side splits them apart as presented in fig. B.1.
From 2.5Gbps to 10Gbps (per wavelength) non-coherent detection based systems
WDM systems were deployed firstly with 40 wavelengths each of them with 2.5Gbps over 800km of standard SMF. Non-Return-to-Zero On/Off Keying (NRZ-OOK) was used as modulation formats. Accumulated chromatic dispersion (CD) was the major limitation to increase further the bit rate. Increasing data rate to 10Gbps per wavelength was made possible by using dispersion compensation fiber (DCF) in addition to forward error correction codes (FEC). DCF is used in concatenation with SMF as shown in fig.1.5. In order to compensate chromatic dispersion, DCF has an opposite sign of dispersion with respect to the already installed SMF [9]. FEC consists in adding redundancy to the transmitted signal in order to make possible detection and correction of errors at the receiver. The use of Reed-Solomon (RS) FEC codes, which provide about 6 dB gain in optical to signal noise ratio (OSNR), and Enhanced-FEC (EFEC) with 8.5 dB gain in OSNR had significantly increased the transmission performance[10].
40Gbps coherent detection based systems
The migration of direct detection based OOK systems from 10Gbps to 40Gbps per wavelength was challenged by different fiber impairments. In fact, polarization mode dispersion (PMD), which has negligible effect in 10Gbps, reduces drastically the transmission performance at 40Gbps. Indeed in non-coherent based communication (with OOK) passing from 10Gbps to 40Gbps leads to divide the bit period by 4 which decreases also the tolerance on the PMD by 4. In addition, CD tolerance is divided by a factor of 16 at 40Gbps and that requires an increase of OSNR by 6dB to get similar performance to OOK 10Gbps systems [11]. This high increase of OSNR leads to a strong nonlinear distortion. An other way to increase the rate was to increase the number of WDM wavelength, but this is a very limited option due to the optical amplifier bandwidth. These limitations oriented the researches to focus the possibility to increase the spectral efficiency and so to the use of coherent detection instead of direct detection. This is the second main breakthrough on the optical-fiber communications community.
Table of contents :
LIST OF ACRONYMS
INTRODUCTION
1 STATE OF THE ART ABOUT OPTICAL FIBER COMMUNICATION SYSTEM
1.1 Evolution of optical fiber transmission systems
1.1.1 EDFA invention: Wavelength division multiplexing transmission
1.1.2 From 2.5Gbps to 10Gbps (per wavelength) non-coherent detection based systems
1.1.3 40Gbps coherent detection based systems
1.1.3-a Coherent detection
1.1.3-b Polarization division multiplexing
1.1.3-c Digital signal processing algorithms
1.1.4 100 Gbps coherent systems
1.1.5 Fiber capacity limit
1.2 Optical fiber transmission impairments
1.2.1 Attenuation
1.2.2 Chromatic dispersion
1.2.3 Polarization mode dispersion
1.2.4 Optical amplification
1.2.4-a EDFA
1.2.4-b Inline optical amplification
1.2.5 Nonlinear effects
1.2.5-a Self-phase modulation (SPM)
1.2.5-b Cross-phase modulation (XPM)
1.2.5-c Four-wave mixing (FWM)
1.2.5-d Cross-polarization modulation (XPolM)
1.3 Conclusion
2 400GBPS/1TBPS SUPERCHANNEL TRANSMISSION SYSTEM
2.1 High spectral efficiency modulation formats
2.2 Superchannel transmission systems
2.2.1 OFDM based superchannel transmission system
2.2.1-a OFDM principle
2.2.1-b Coherent optical OFDM system
2.2.2 Nyquist-WDM superchannel transmission system
2.2.2-a Nyquist-WDM superchannel concept
2.2.2-b Nyquist WDM transmitter
2.2.2-c Nyquist WDM receiver
2.3 Nonlinear effects compensation techniques: State of the art
2.3.1 Digital back propagation
2.3.2 Nonlinear effects compensation based on Volterra series
2.3.2-a Volterra Series overview
2.3.2-b Fiber model based on Volterra series
2.3.2-c Volterra based nonlinear equalizer
2.3.3 Superchannel systems simulation results
2.3.3-a MB-OFDM simulation results
2.3.3-b Nyquist-WDM simulation results
2.4 Conclusion
3 FIFTH-ORDER VOLTERRA BASED-NONLINEAR EQUALIZER IN SUPERCHANNEL SYSTEM
3.1 P-th order inverse theory
3.2 Kernels derivation and implementation
3.2.1 Kernels derivation and implementation: single-polarization configuration
3.2.1-a Technical preliminaries
3.2.1-b Closed-form expression for fiber nonlinear effects compensation
3.2.1-c Practical implementation scheme
3.2.2 Kernels derivation and implementation: dual-polarization configuration
3.2.2-a Technical preliminaries
3.2.2-b Practical implementation scheme
3.3 Fifth-order VNLE simulations results
3.4 Conclusion
4 NONLINEAR INTERFERENCE CANCELLATION
4.1 Decision feedback equalizer principle
4.2 System model
4.3 Proposed INIC approach
4.3.1 Nonlinear equalizer with nonlinear feedback: INIC(3,3)
4.3.2 Nonlinear equalizer with linear feedback: INIC(3,1)
4.3.3 Linear equalizer with linear feedback: INIC(1,1)
4.4 Simulation results
4.5 MB-OFDM simulation results
4.6 Nyquist WDM simulation results
4.7 Complexity analysis
4.8 Conclusion
CONCLUSION AND PERSPECTIVES
A DERIVATIONS OF FIFTH-ORDER INVERSE VOLTERRA KERNEL
A.1 Technical preliminaries
A.2 Closed-form expressions for nonlinear compensation in optical fiber
B CONDENSED FRENCH VERSION
B.1 Introduction
B.2 Évolution des systèmes de transmissions optiques
B.2.1 L’invention de l’EDFA et le déploiement de système de transmission WDM
B.2.2 Système à détection cohérente
B.2.3 Prochaine génération de systèmes WDM longue distance
B.2.3-a Système OFDM multi-bande
B.2.3-b Système Nyquist WDM
B.2.3-c État-de-l’art sur les techniques de compensation des effets nonlinéaires
B.3 Égaliseur nonlinéaire basé sur les séries de Volterra d’ordre
B.3.1 Principe de l’égaliseur nonlinéaire basé sur les séries de Volterra de cinquième ordre
B.3.2 Simulations et résultats
B.4 Annulation des interférences nonlinéaires
B.4.1 Principe de l’annulation des interférences nonlinéaires
B.4.2 Simulations et résultats
B.4.2-a OFDM multi-bande
B.4.2-b Nyquist WDM
B.5 Conclusion et perspectives
B.5.1 Conclusion
B.5.2 Perspectives
BIBLIOGRAPHY
