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Title: Nonlinear fiber-optic communications using nonlinear frequency division multiplexing
Authors: Gui, Tao
Degree: Ph.D.
Issue Date: 2018
Abstract: This thesis presents the new frameworks of nonlinear frequency division multiplexing (NFDM) techniques based on the revived nonlinear Fourier transform (NFT) for fiber-optic communication system. The NFT describes the optical signal propagated in the ideal Nonlinear Schrodinger Equation (NLS) by a nonlinear spectrum (or eigenvalues) and results in a simple linear channel transfer function without mutual interference. Consequently, the nonlinear spectrums (comprised of the continuous and discrete spectrum) have recently been suggested as more suitable signal degrees-of-freedom for information transmission in optical fiber, and the NFDM has been proposed as a potential technique to overcome Kerr nonlinearity that the key limitation for nowadays fiber optic communications systems. After a brief review of the theoretical foundations of NFT, this thesis starts from exploring the multi-eigenvalue communication scheme in which information encoded using only the locations of the discrete eigenvalues. We experimentally demonstrate, for the first time, the independently modulated three-eigenvalue NFDM signals over a successful 1800 km link transmission with Raman amplification and digital coherent receivers. In addition, we propose a novel decision metrics for this multi-eigenvalue communication scheme, which perform similarly to conventional methods but avoids root searching and thus significantly reduce computational complexity. Following, the thesis moves to study the phase and amplitude modulation on the discrete eigenvalues as new degrees of freedom to encode information. For communications using discrete eigenvalues λεC+, information are encoded and decoded in the spectral amplitudes q(λ)=b(λ)/(da(λ)/dλ) at the root λrt where a(λrt)=0. A detailed investigation of practical issues are conducted firstly, in which the impact of filtering, laser phase noise, carrier phase estimation (CPE) techniques on signal bandwidth and transmission performance are evaluated and the sensitivity to signal launched power is highlighted. Then, we propose a novel decoding method using b(λ) instead of q(λ) as decision metrics, and show that the noise in da(λ)/dλ and λrt after transmission are all correlated with that in b(λrt). A linear minimum mean square error (LMMSE) estimator of the noise in b(λrt) is derived based on such noise correlation and transmission performance is considerably improved for QPSK and 16-QAM systems on discrete eigenvalues. Based on the proposed decoding method, we demonstrate a record 4 GBaud 16-APSK on the spectral amplitude plus 2-bit eigenvalue modulation (total 6 bit/symbol at 24 Gb/s) transmission over 1000 km. Finally, the thesis extend to explore the polarization-division multiplexed (PDM) NFDM transmission based on pure continuous components to improve the achievable rates We experimentally demonstrate for the first time, to our knowledge, dual-polarization NFDM of the continuous spectrum by using a normal dispersion transmission fiber. We obtain a 0.4 dB Q-factor (1 dB in SNR) gain when compared with OFDM, for transmissions over 1680 km at the burst rate of 128 Gbit/s. Our results pave the way toward doubling the information rate of NFT-based fiber optics communication systems.
Subjects: Hong Kong Polytechnic University -- Dissertations
Optical fiber communication
Fiber optics
Nonlinear optics
Pages: xv, 87 pages : color illustrations
Appears in Collections:Thesis

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