Research Of Quality Of Transmission Controllable Transparent Optical Networks

With the explosive growth of Internet traffic and rapid development of broadband services, the fiber channel transmission line rate and capacity is undergoing continuous upgrading and increasing. Following this trend, the hybrid transmission scenario with mixed line rates and modulation formats will exist over a considerable period of time. Stimulated by capacity booming and mixed transmission scenario, the backbone transport networks are evolving from traditional SDH based opaque processing enabled by electronic switching, toward transparent all-optical processing featured by wavelength switching, to overcome the bandwidth and energy bottlenecks incurred by current electronic processing nodes.However, in transparent wavelength switched networks, due to the lack of3R regeneration, physical impairments accumulate along transmission links, degrading system transmission performance to be unacceptable because of the lack of impairment awareness with current SDH based ASON/GMPLS control plane mechanisms. To solving this problem, the impairment controllable all optical networking method is introduced, enhancing the control capability of optical networks to the aspects of physical impairments. The relevant key techniques are investigated in depth in this paper. In addition, on the transmission level, theoretical and experimental studies on the nonlinear transmission performance of coherent optical orthogonal frequency division multiplexing techniques are carried out, achieving some leading and influential world class outcomes. In this paper, the main innovations and contributions are listed as follows:1. Physical layer impairments modeling and quality of transmission (QoT) estimation of10Gb/s NRZ-OOK,40Gb/s DQPSK channels and their mixed transmissions are achieved under the influence of combined effects of dominant linear and nonlinear impairments including chromatic dispersion (CD), polarization mode dispersion (PMD), self-phase modulation (SPM) and cross-phase modulation (XPM). Specifically, the optical pulse broadening factor are proposed as accurate evaluation indicator of combined effect of SPM and CD; The XPM impacts of lOGb/s NRZ-OOK channels on40Gb/s DQPSK channels are derived analytically. As the first reported QoT modeling of mixed line rate networks taking account of interactive nonlinear distortions between amplitude and phase modulated channels, this expression provides theoretical proofs for impairment aware or impairment controllable optical network designs and operations; Moreover, analytical expressions of nonlinear transmission performance of densely-spaced coherent optical communications systems have been derived, under impacts of various channel frequency guard bands and dispersion compensation schemes. Verified by numerical simulations with a considerable accuracy and wide application rage, this analytical expression can be used as performance criterions for numerical simulations and experiments, providing guidelines for transport network designs, as well as operations of modulation-routing and spectrum assignment in spectrum sliced elastic optical networks.2. The innovative thought of impairment controllable cross-layer designs of transparent networks has been proposed, with simultaneously consideration of lightpath physical impairments and capability of adjustable equipments in the process of network connection provisioning. Following systematic solutions of key techniques on network architecture, protocol realization, dynamic lightpath QoT optimization and controlling mechanisms, three main innovations have been proposed including (i) accurate QoT estimation based lightpath QoT optimization algorithms with consideration of characteristics of lightpath impairments and adjustable equipments. The proposed QoT optimization algorithms exhibit much more reduced tuning delay, expenditure, uncertainties while guarantee the QoT to be above the requirements;(ii) Joint routing, wavelength and dispersion compensation assignment algorithms for hybrid networks with mixed line rate and modulations, improving the network performance with differentiated consideration of connection requests, lightpath characteristics as well as relevant capability of adjustable dispersion compensators;(iii) dynamic power controlling (DPC) algorithm for mixed OOK/DQPSK networks, reducing the interchannel XPM crosstalk significantly and thus improving overall network performance considerably. This DPC work is the first reported studies and applications using the interactive QoT modes for hybrid amplitude/phase modulated networks, earlier than the second reported works by more than half years.3. As one of the major investigator, develops the key techniques of unique word based DFT-Spread OFDM and set up the fiber circulating loops as well as transceivers of PDM-OFDM system. Using these techniques, the author successfully demonstrates more than8000km transmission of1Tb/s QPSK modulated DFT-S OFDM signals over80km spaced SSMF based loops with only EDFA amplifiers. Still using the similar techniques,1010km transmissions of2Tb/s16QAM modulated DFT-S OFDM signals are demonstrated over same fiber loops, under the BER requirements of7%FEC. Up to the submission of this thesis, both of the two experiments results realize longest transmission records in the world, under the same type of situations (QPSK or16QAM modulation, SSMF based fiber spans with only EDFA amplification).4. Analytical expressions of PMD influence on the effectiveness of digital back propagation based nonlinearity compensation have been derived. Analytical calculation results show perfect consistence with numerical simulations. The numerical and theoretical result reveal for the first time in the world that the impacts of PMD is much more severe than the nonlinear signal-ASE interactions, and is thus the fundamental limitation of fiber channel capacity. Based on this theory, ultimate nonlinear Shannon capacity of single mode fibers exploiting all the possible techniques is obtained.