KEYWORDS: Telecommunications, Signal to noise ratio, Fiber optic communications, Optical amplifiers, Digital signal processing, Fiber amplifiers, Modulation, Binary data, Systems modeling
Due to the high transmission capacity, optical fiber systems have been widely applied in the modern telecommunication infrastructure to meet the ever-increasing demand of data traffic. Optical amplifiers have been employed to amplify optical signals and to compensate for the transmission losses. They play a key role in relaying the signals in ultra-wideband optical fiber communication systems. However, the amplified spontaneous emission (ASE) noise will be introduced and will pose constraints on the transmission information rates. The mutual information (MI) and the generalized mutual information (GMI) have been applied to evaluate the information rates in communication systems. In this work, we have investigated the impact of ASE noise on the MI and the GMI, and developed corresponding analyses across different modulation formats. Our work aims to explore the limit and requirements on optical amplifiers in next-generation ultra-wideband optical fiber communication systems.
KEYWORDS: Signal to noise ratio, Telecommunications, Modulation, Optical fibers, Digital signal processing, Systems modeling, Interference (communication), Transmittance, Optical amplifiers, Optical communications
Coherent optical fiber systems can achieve long-distance, large-capacity and high data-rate transmissions. The system performance of communication systems is generally evaluated with regard to the data capacity and the transmission reach. In this work, the performance of multi-channel (up to C-band) Nyquist-spaced coherent optical communication systems has been assessed in terms of achievable information rates, transmission distances and signal-to-noise ratios, considering different influencing factors, such as nonlinearity compensation, signal input power and modulation format. Numerical simulations and enhanced Gaussian noise (EGN) model have been carried out for different modulation formats including quadrature phase shift keying (QPSK), 16-ary quadrature amplitude modulation (16-QAM), 64-QAM and 256-QAM. It is found that in C-band (151-channel) Nyquist-spaced systems, the achievable information rates at the transmission distance of 6000 km are 19.3 Tbit/s for dual-polarization QPSK (DP-QPSK), 30.9 Tbit/s for DP-16QAM, 32.0 Tbit/s for DP64QAM and 32.2 Tbit/s for DP-256QAM, respectively, when electronic dispersion compensation is applied only. Such achievable information rates can be increased up to 38.3 Tbit/s for DP-16QAM, 47.2 Tbit/s for DP-64QAM and 47.8 Tbit/s for DP-256QAM, respectively, when the nonlinearity compensation is employed.
The efficient and accurate evaluation of the transmission performance of high-capacity optical communication systems has always attracted significant research attentions. The enhanced Gaussian noise (EGN) model is considered as an excellent solution to predict the system performance taking into account linear and nonlinear transmission impairments. Since the conventional form of the EGN model is complicated and intractable for a fast computation, the closed-form simplification has been regarded as a direction to significantly reduce the computational complexity. However, the accuracy of such a closed-form EGN model becomes a main concern in the application of ultra-wideband optical communication systems. In this work, we have investigated the accuracy of the closed-form EGN model for ultra-wideband optical fiber communication systems, where the performance of the system using electronic dispersion compensation, multi-channel nonlinearity compensation and full-field nonlinearity compensation has been evaluated in terms of symbol rate, number of channels and signal power. Our work will provide an insight on the application of the EGN model in next-generation ultra-wideband long-haul optical fiber communication networks.
KEYWORDS: Signal to noise ratio, Telecommunications, Digital signal processing, Optical fibers, Distortion, Optical communications, Optical amplifiers, Transmittance, Modulation, Fiber lasers
In digital signal processing (DSP) based coherent optical communication systems, the effect of equalization enhanced phase noise (EEPN) will seriously degrade the transmission performance of high-capacity optical transmission system. In this paper, we have investigated the influence of EEPN on 9-channel 32-Gbaud dual-polarization 64-ary quadrature amplitude modulation (DP-64QAM) Nyquist-spaced superchannel optical field trial by using electronic dispersion compensation (EDC) and multi-channel digital backpropagation (MC-DBP). The deteriorations caused by EEPN on the signal-to-noise-ratio (SNR) and achievable information rates (AIRs) in high-speed optical communication systems have been studied. The system performance versus back-propagated bandwidth under different laser linewidth have also been demonstrated. The SNR penalty due to the distortion of EEPN achieves ~5.11 dB when FF-DBP is implemented, which informs that FF-DBP is more susceptible to EEPN, especially when the LO laser linewidth is larger. The system AIR versus different transmission distance under different EEPN interference using EDC-only and MC-DBP have also been evaluated, which show that there is a trade-off on the selection of lasers and back-propagated bandwidths to achieve a target AIR.
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