Modulation format dependence on transmission reach in phase-sensitively amplified fiber links

Optical Society of America under the terms of the OSA Open Access Publishing Agreement We quantify the maximum transmission reach for phase-insensitive amplifier (PIA) and phase-sensitive amplifier (PSA) links with different modulation formats and show that the maximum transmission reach increase (MTRI) when using PSAs compared to PIAs is enhanced for higher-order modulation formats. The higher-order modulation formats are more susceptible to smaller phase rotations from nonlinearities, and PSAs are efficient in mitigating these smaller phase distortions. Numerical simulations were performed for single- and multi-span PIA and PSA links with single and multiple wavelength channels. We obtain a significant enhancement in the MTRI with PSAs compared to PIAs when using higher-order modulation formats for both the single- and multi-channel systems in single- and multi-span links. We verify the enhancement with a single-span, single-channel system experiment. We also demonstrate, for the first time, a 64-QAM modulation format fiber transmission in phase-sensitively amplified link, with a 13.3-dB maximum allowable span loss increase compared to a phase-insensitively amplified link

100-Gbps per-channel all-optical wavelength conversion without pre-amplifiers based on an integrated nanophotonic platform

All-optical wavelength conversion based on four-wave mixing attracts intense interest in many areas, especially in optical fiber communications, due to the advantages of femtosecond response, modulation-format transparency, and high flexibility in optical network management. In this paper, we present the first optical translation of 32-GBaud 16QAM signals with an integrated Si3N4 nonlinear nanophotonic waveguide. An on-chip continuous-wave conversion efficiency of up to -0.6dB from S band to C band is achieved in the dispersion-engineered low-loss Si3N4 nonlinear waveguide that is back-end compatible with complementary metal-oxide-semiconductor processes. The high conversion efficiency avoids the use of external optical amplifiers for signal demodulation. The converted idler is successfully received with a sensitivity penalty of less than 0.5dB. Moreover, pre-amplifier-free multichannel wavelength conversion of over-100-Gbps coherent signals in C band is also demonstrated using the same Si3N4 nanophotonic waveguide via changing the pump wavelength, which shows good flexibility in all-optical signal processing. Additionally, wavelength conversion with a bandwidth over 100nm can be expected by optimizing the current Si3N4 nanophotonic waveguide, which is promising for commercial coherent fiber communications and has bright prospects in various areas including optical signal processing, imaging, optical spectroscopy, and quantum optics

Phase-sensitively amplified wavelength-division multiplexed optical transmission systems

The throughput and reach in fiber-optic communication links are limited by in-line optical amplifier noise and the Kerr nonlinearity in the optical transmission fiber. Phase-sensitive amplifiers (PSAs) are capable of amplifying signals without adding excess noise and mitigating the impairments caused by the Kerr nonlinearity. However, the effectiveness of Kerr nonlinearity mitigation depends on the dispersion pre-compensation in each span. This paper investigates dense wavelength-division multiplexed PSA-amplified links using joint processing with a less complex digital domain Volterra nonlinear equalizer at the receiver. Both numerically and with experiments, it is shown that this significantly reduces the impact of the dispersion pre-compensation in each span. Also, with simulations, a substantial improvement in transmission reach is demonstrated for PSA links

Over-the-fiber Digital Predistortion Using Reinforcement Learning

We demonstrate, for the first time, experimental over-the-fiber training of transmitter neural networks (NNs) using reinforcement learning. Optical back-to-back training of a novel NN-based digital predistorter outperforms arcsine-based predistortion with up to 60\% bit-error-rate reduction

Physical Realizations of Multidimensional Voronoi Constellations in Optical Communication Systems

Abstract:Multidimensional geometric shaping has been shown to outperform uniform quadrature amplitude modulation (QAM) in optical communication systems but the complexity of symbol decision and bit mapping can often be significant as dimensionality increases. In this paper, a low-complexity geometric shaping method based on multidimensional lattices is investigated both in experiments and simulations. The modulation formats designed based on this method are called Voronoi constellations (VCs) and we study them in 8, 16, and 32 dimensions. We obtain transmission reach improvements of up to 22 and 70% for VCs compared to 4QAM and 16QAM, respectively, in nonlinear long-haul fiber transmission. Moreover, we compare different physical realizations of multidimensional VCs over wavelengths, polarizations, and time slots in both the Gaussian and nonlinear fiber channels. We demonstrate that different physical realizations perform similarly in the fiber-optic back-to-back channel. However, in long-haul transmission systems, spreading the dimensions over time slots can increase the transmission reach up to 4% compared to wavelengths and polarizations. Furthermore, the mutual information and generalized mutual information are estimated and compared to QAM formats at the same spectral efficiencies

Experimental Demonstration of 8-Dimensional Voronoi Constellations with 65,536 and 16,777,216 Symbols

We experimentally demonstrate high-cardinality, low-complexity Voronoi constellations based on the E8 lattice over multiple time slots with OSNR and launch power gains of up to 1.7 and 2.4 dB for back-to-back and 80 km fiber transmission, respectively, compared to QAM formats

Comparison of Physical Realizations of Multidimensional Voronoi Constellations in Single Mode Fibers

We investigate experimentally and numerically the impact of using different fiber dimensions to spread out the 32-dimensional Voronoi constellations. We find similar performance in experiments and less than 5.4% reach improvements in long-haul transmission simulations by spreading the constellation dimensions over time slots compared to wavelength

Over-the-fiber Digital Predistortion Using Reinforcement Learning

We demonstrate, for the first time, experimental over-the-fiber training of transmitter neural networks (NNs) using reinforcement learning. Optical back-to-back training of a novel NN-based digital predistorter outperforms arcsine-based predistortion with up to 60% bit-error-rate reduction

Symbol-Based Supervised Learning Predistortion for Compensating Transmitter Nonlinearity

We experimentally demonstrate a symbol-based nonlinear digital predistortion (DPD) technique utilizing supervised learning, which is robust against a change of modulation format. Back-to-back transmission of 30 Gbaud 32, 64 and 256QAM confirms that our scheme significantly outperforms the baseline of arcsine-based predistortion