Mindaugas Jarmolovičius

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.

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.

A record continuous transmission bandwidth of 16.4 THz is demonstrated in O-band fibre transmission over an 80-km single-mode ultra low-loss fibre span. Bismuth-doped fibre amplifiers with an output power of 25 dBm and a low noise figure of 3.6 dB compensate a loss of 80-km fibre span. An O-band wavelength selective switch with a 16.4 THz bandwidth maximises the transmission capability and enabled optimisation of the input spectrum shape to reduce nonlinear interference near zero dispersion, resulting in a potential achievable information rate of over 100 Tb/s to be reached.

We model the transmission of ultrawideband signals, including wavelength-dependent fibre parameters: dispersion, nonlinear coefficient and effective fibre core area. To that end, the inter-channel stimulated Raman scattering Gaussian noise integral model is extended to include these parameters. The integrals involved in this frequency-domain model are numerically solved in hyperbolic coordinates using a Riemann sum. The model implementation is designed to work on parallel GPUs and is optimised for fast computational time. The model is valid for Gaussian-distributed signals and is compared with the split-step Fourier method, for transmission over standard single-mode fibre (SSMF) in the O-band (wavelengths around the zero-dispersion wavelength), showing reasonable agreement. Further, we demonstrated SNR evaluation over an 80 km SSFM single-span transmission using 589 × 96 GBaud channels, corresponding to almost 59 THz optical bandwidth, fully populating the O, E, S, C, L and U bands (1260 $-$ 1675 nm). The SNR evaluation is completed in just 3.6 seconds using four Nvidia V100 16 GB PCIe GPUs. Finally, we used this model to find the optimum launch power profile for this system achieving 747 Tbps of potential throughput over 80 km fibre and demonstrating its suitability for UWB optimisation routines.

Capacity enhancement by utilising the unused spectral bands of the low-loss optical window of standard single-mode fibre (SSMF) is a cost-effective solution for meeting the future demand of data traffic. The development of optical amplifiers that can operate in different spectral bands is expected to play an integral part in the establishment of multi-band networks. In this work, we perform experimental, analytical and numerical modelling of a multi-band transmission system using a hybrid distributed-discrete Raman amplifier enabling signal amplification from 1410-1605 nm. The developed amplifier was tested over 50km of SSMF using 200 Gbit/s channels, where successful transmission was achieved, well above the HD-FEC threshold of 8.5 dB. Further study on the multi-band transmission performance was carried out using a semi-analytical closed-form approximation and split-step Fourier method-based simulations for various related test cases. The analytical and numerical models are also compared with experimental results, showing reasonable agreement in terms of system performance estimation.