Achievable Information Rates Estimation for 100-nm Raman- Amplified Optical Transmission System

The achievable information rates of optical communication systems using ultra-wide bandwidth 100-nm distributed Raman amplification have been investigated for each individual subchannels, based on the first-order perturbative analysis of nonlinear distortions. Introduction To date, optical fibre communications have achieved unprecedented growth and success over the past three decades and now stand alone as the enabling technology that underpins the global information infrastructure. The data rates of optical communication systems have been raised from 100-Mbit/s per fibre in the 1970s to 10-Tbit/s in current commercial systems, an astonishing 100,000-fold increase. The key technologies that fueled this surge in capacity were wavelength division multiplexing (WDM), improved fibre design and fabrication, optical amplification and coherent detection. The use of Erbium-doped and Raman fibre amplifiers negated the need for electronic regenerators and enabled dense WDM transmission, although the success and performance of these amplifier technologies is seen as limiting the usable fibre bandwidth to approximately 10-15 THz, ultimately limiting the maximum throughput of optical systems. Within the usable optical bandwidth, the increase of the spectral efficiency in Nyquistspaced WDM systems is determined by the densest constellation that can be used. Denser constellations, however, typically operate well only at high signal-to-noise ratios (SNRs), where high optical launch power is required 1 . In such schemes, the achievable information rate (AIR) of optical fibre communication systems is essentially limited by nonlinear (NL) distortions due to the optical Kerr effect manifesting itself as self-phase modulation, cross-phase modulation and four-wave mixing (FWM). The AIRs have been evaluated for the total bandwidth of approximately the optical C-band (~4.3-THz) under the key assumption of ideally distributed Raman amplification schemes, while the Raman pump power and the distribution of the optical field-gain along the amplifier span have not been taken into account 2 . In this paper, for the first time to our knowledge, the AIR of optical communication system using ultra-wideband optical Raman amplification extended to ~100-nm (12.51-THz) optical bandwidth in a standard single mode fiber (SSMF) has been numerically estimated by using a large-bandwidth first-order perturbative analysis of NL distortions. These estimations have been carried out separately for each subchannel in Nyquist-spaced WDM transmission system. The AIR of the Raman-amplified transmission system with 1251-Channel× 10GHz using linear electronic dispersion compensation (EDC) and full-field (FF) nonlinear compensation (NLC) has been analysed. A firstorder perturbative analysis was implemented to numerically evaluate the NL distortions for each individual sub-channel in Nyquist-spaced WDM transmission system, by removing the assumption of the "whiteness" of the NL distortion spectra. Raman amplified optical system We examine the backward-pumped geometry of optical Raman amplification. In this model, the Raman power gain is independent of the laser wavelength, and the pump depletion effect is neglected. The AIRs are evaluated in the optical communication system with distributed Raman amplification over ~100-nm (12.51-THz). We consider the transmission consisting of 1251 sub-channels with a symbol rate of 10-Gbaud and a channel spacing of 10-GHz. The detailed Tab. 1: System parameter values