Jiaqian Yang

We experimentally investigate the nonlinearity compensation performance of full-field split nonlinearity compensation (split NLC) schemes for single- and three-channel systems at baud rates of 16, 32, 64, and 128 GBd. Our results show that at 1000 km, receiver-side NLC achieves the best performance as transmitter-side schemes are limited by high peak-to-average power ratio when implementing dispersion pre-compensation. At 7696 km, split NLC reduces the penalty imposed by signal-noise interactions, increasing SNR by up to 1.39 dB at 64 GBd versus transmitter/receiver-side NLC only. This work illustrates the potential of split NLC algorithms for mitigating nonlinear throughput limitations in single-mode fiber.

We present a novel closed-form model for nonlinear interference (NLI) estimation in low-dispersion O-band transmission systems. The formulation incorporates the four-wave mixing (FWM) efficiency term as well as the coherent contributions of self- and cross-phase modulation (SPM/XPM) across multiple identical spans. This extension enables accurate evaluation of the NLI in scenarios where conventional closed-form Gaussian Noise (GN) models are limited. The proposed model is validated against split-step Fourier method (SSFM) simulations and numerical integration across 41-161 channels, with a 96 GBaud symbol rate, bandwidths of up to 16.1 THz, and transmission distances from 80 to 800 km. Results show a mean absolute error of the NLI signal-to-noise ratio (SNR) below 0.22 dB. The proposed closed-form model offers an efficient and accurate tool for system optimisation in O-band coherent transmission.

The role of ultrawideband transmission in future telecommunications systems has been actively discussed and debated over the past decade. Despite the challenges posed by the need for new optical sources, modulators, coherent receivers, optical amplifiers, and fibre types, significant theoretical and experimental progress has been made in recent years. This paper reviews the key challenges and breakthroughs in ultrawideband transmission modeling and experiments, and examines their potential impact on optical network throughput. We present modeling results for extending the utilised bandwidth from the C-band (4 THz) to the full O- to U-band range (60 THz), as well as our experimental demonstrations of ultrawideband transmission over distances exceeding 1000 km.

We present a novel closed-form model for nonlinear interference (NLI) estimation in low-dispersion O-band transmission systems. The formulation incorporates the four-wave mixing (FWM) efficiency term as well as the coherent contributions of self- and cross-phase modulation (SPM/XPM) across multiple identical spans. This extension enables accurate evaluation of the NLI in scenarios where conventional closed-form Gaussian Noise (GN) models are limited. The proposed model is validated against split-step Fourier method (SSFM) simulations and numerical integration across 41-161 channels, with a 96 GBaud symbol rate, bandwidths of up to 16.1 THz, and transmission distances from 80 to 800 km. Results show a mean absolute error of the NLI signal-to-noise ratio (SNR) below 0.22 dB. The proposed closed-form model offers an efficient and accurate tool for system optimisation in O-band coherent transmission.

We demonstrate the first SCL-band long-haul transmission using G.654.E-compliant fibre, achieving 100.8 Tb/s (GMI) over 1552 km, despite its 1520 nm cutoff wavelength. Due to the fibre's ultra-low loss and low nonlinearity, the achievable-information-rate with lumped amplification is comparable to that of G.652.D-compliant fibre links with distributed-Raman-amplification.

We present the first experimental investigation of SOAs for long-haul high-speed communications. The impact on performance when using both SOA and EDFA amplification for multi-span WDM transmission systems was compared. For three-channel transmission over distances of up to 2064 km using a recirculating optical fibre loop, we observed a >5 dB and >2.5 dB penalty in optimal SNR when using the SOAs for 15GBd and 49.5 GBd channels, respectively. This is attributed to the SOA’s higher noise figure and nonlinearities. At 516km this equates to a throughput reduction of 28% at optimal launch power, demonstrating the impact of device nonlinearities that needs to be overcome for the development of low power consumption optical transmission systems. This experimental first sets a baseline for long-haul high-speed optical communication using SOAs for inline amplifiers.

A record transmission throughput of 202.3 Tb/s (189.5 Tb/s after decoding) is reported over a 39 km field-deployed metropolitan standard single-mode fibre link using ultra-wideband geometrically-shaped signals, with lumped amplification and total launch power constrained to 20.9 dBm. An experimentally-optimised 5 dB tilt launch power pre-emphasis over the 15.6 THz optical bandwidth was applied to mitigate inter-channel stimulated Raman scattering. Compared to C+L-band transmission, extension to S+C+L-band, using 63.4 % more optical bandwidth, resulted in a 51.2 % increase in throughput under the same total launch power constraint. The trade-off between the addition of S-band channels, and the associated reduction in C+L-band SNR, was further explored for long-haul transmission, and it was shown that a similar percentage throughput increase (from 48.1 Tb/s to 73.1 Tb/s), but with 77.3 % higher bandwidth, could be achieved for 1014 km transmission over field-deployed fibre configured in a recirculating fibre loop. This work demonstrates the potential to enhance data throughput in deployed fibre systems by using S+C+L-bands.

A 223 km unrepeatered link transmission is experimentally demonstrated, transmitting 490 polarisation-division multiplexed channels with adaptively optimised geometrically-shaped constellation quadrature amplitude modulation signals. The transmission band covered nearly the entire S-, C-, and L-bands, spanning 121 nm (15.6 THz) of optical bandwidth. Lumped Thulium- and Erbium-doped fibre amplifiers were used for amplification, and bidirectional distributed Raman amplification, together with pre-emphasis of signal launch power spectrum, were used to mitigate the interchannel stimulated Raman scattering (ISRS) effect. The signal power pre-emphasis and the powers of the Raman pumps were experimentally optimised with a differential evolution algorithm to improve the received signal-to-noise ratio and the throughput. The closed-form ISRS Gaussian noise model was used to support and explain the experimental results: it accurately reproduces the evolution of the signal spectral power and estimates the contributions of nonlinear interference noise and amplified spontaneous emission noise in the unrepeatered link. The combined use of the hybrid amplification scheme, adaptive constellation shaping, and system optimisation techniques resulted in a total throughput of 122.62 Tb/s, from the generalised mutual information (113.95 Tb/s after decoding), achieving the highest throughput to date for unrepeatered links over 200 km.

Ultra-wideband, field-deployed metropolitan fibre transmission is experimentally demonstrated, measuring a record 202.3 Tb/s GMI and 189.5 Tb/s after decoding with 20.9 dBm launch power and lumped amplification only. An experimentally-optimised 5 dB pre-tilt over the 15.6 THz optical bandwidth was applied to overcome ISRS.