Several approximate non-linear fiber propagation models have been proposed over the years. Recent re-consideration and extension of earlier modeling efforts has led to the formalization of the so-called Gaussian-noise (GN) model. The evidence collected so far hints at the GN-model as being a relatively simple and, at the same time, sufficiently reliable tool for performance prediction of uncompensated coherent systems, characterized by a favorable accuracy versus complexity trade-off. This paper tries to gather the recent results regarding the GN-model definition, understanding, relations versus other models, validation, limitations, closed form solutions, approximations and, in general, its applications and implications in link analysis and optimization, also within a network environment.

The GN-Model of Fiber Non-Linear Propagation and its Applications

A transmission system with adjustable data rate for single-carrier coherent optical transmission is proposed, which enables high-speed transmission close to the Shannon limit. The proposed system is based on probabilistically shaped 64-QAM modulation formats. Adjustable shaping is combined with a fixed-QAM modulation and a fixed forward-error correction code to realize a system with adjustable net data rate that can operate over a large reach range. At the transmitter, an adjustable distribution matcher performs the shaping. At the receiver, an inverse distribution matcher is used. Probabilistic shaping is implemented into a coherent optical transmission system for 64-QAM at 32 Gbaud to realize adjustable operation modes for net data rates ranging from 200 to 300 Gb/s. It is experimentally demonstrated that the optical transmission of probabilistically shaped 64-QAM signals outperforms the transmission reach of regular 16-QAM and regular 64-QAM signals by more than 40% in the transmission reach.

Rate Adaptation and Reach Increase by Probabilistically Shaped 64-QAM: An Experimental Demonstration

We use a wideband optical comb source with 10THz bandwidth for 2.15 Pb/s transmission over 31km of a new, homogeneous 22-core single-mode multi-core fiber using 399 × 25GHz spaced, 6.468 Tb/s spatial-super-channels comprising 24.5GBaud PDM-64QAM modulation in each core.

2.15 Pb/s transmission using a 22 core homogeneous single-mode multi-core fiber and wideband optical comb

The design of application-specific integrated circuits (ASIC) is at the core of modern ultra-high-speed transponders employing advanced digital signal processing (DSP) algorithms. This manuscript discusses the motivations for jointly utilizing transmission techniques such as probabilistic shaping and digital sub-carrier multiplexing in digital coherent optical transmissions systems. First, we describe the key-building blocks of modern high-speed DSP-based transponders working at up to 800G per wave. Second, we show the benefits of these transmission methods in terms of system level performance. Finally, we report, to the best of our knowledge, the first long-haul experimental transmission – e.g., over 1000 km – with a real-time 7 nm DSP ASIC and digital coherent optics (DCO) capable of data rates up to 1.6 Tb/s using two waves (2 × 800G).

/pdf/800g-dsp-asic-design-using-probabilistic-shaping-and-digital-2yhfdgnk8t.pdf

800G DSP ASIC Design Using Probabilistic Shaping and Digital Sub-Carrier Multiplexing

We propose a novel low-complexity artificial neural network (ANN)-based nonlinear equalizer (NLE) for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) and compare it with the recent inverse Volterra-series transfer function (IVSTF)-based NLE over up to 1000 km of uncompensated links. Demonstration of ANN-NLE at 80-Gb/s CO-OFDM using 16-quadrature amplitude modulation reveals a Q-factor improvement after 1000-km transmission of 3 and 1 dB with respect to the linear equalization and IVSTF-NLE, respectively.

Artificial Neural Network Nonlinear Equalizer for Coherent Optical OFDM

We successfully realized layered decoding for LDPC convolutional codes designed for application in high speed optical transmission systems. A relatively short code with 20% redundancy was FPGA-emulated with a Q-factor of 5.7dB at BER of 10−15.

LDPC convolutional codes using layered decoding algorithm for high speed coherent optical transmission

The Volterra series transfer function (VSTF), in which the input-output relationship of a nonlinear system is represented by a series of nonlinear kernel functions, is an elegant tool to model nonlinear systems. The inverse of a nonlinear system can be constructed by analyzing VSTF. We propose a new electronic nonlinearity compensation scheme based on inverse VSTF. We show 1 dB improvement in Q-factor with a 256 Gb/s polarization-division-multiplexed 16-level quadratic amplitude modulation format, and 50% reduction in complexity by lowering the processing rate.

Intrachannel Nonlinearity Compensation by Inverse Volterra Series Transfer Function

We present FPGA-based emulation results of a single QC-LDPC code with 20% redundancy designed for applications in 100 Gb/s optical transmission systems. Error floor-free transmission can be achieved at BER of 10−15 with a Q factor of 5.9 dB.

FPGA verification of a single QC-LDPC code for 100 Gb/s optical systems without error floor down to BER of 10 −15

The low complexity, robust, and precise algorithm solely employs a simplified autocorrelation function of the signal spectrum for blind chromatic dispersion estimation to adapt frequency domain compensation functions in digital coherent receivers.

Frequency domain chromatic dispersion estimation

We investigate DQPSK modulation combined with QC-LDPC coding. By applying iterative demodulation and soft-decision decoding, the differential decoding penalty is reduced by 2.05dB offering an attractive solution for coherent optical systems with soft-decision FEC.

https://cgi.tu-harburg.de/~c00e8lit/cgi-bin/ivpub/download.php?file=ys%2B-ecoc2011.pdf

Qianjin Xiong

Papers

LDPC convolutional codes using layered decoding algorithm for high speed coherent optical transmission

Intrachannel Nonlinearity Compensation by Inverse Volterra Series Transfer Function

FPGA verification of a single QC-LDPC code for 100 Gb/s optical systems without error floor down to BER of 10 −15

Frequency domain chromatic dispersion estimation

Soft-decision LDPC turbo decoding for DQPSK modulation in coherent optical receivers