1.
Vallejo, Luis; Mora, Jose; Jin, Wei; Romero-Huedo, Jaime; Chen, Lin; Tang, Jianming; Ortega, Beatriz
Centralized bidirectional heterogeneous fiber-FSO-mmWave-converged networks for 6G dense cellular network deployments Journal Article
In: Journal of Optical Communications and Networking, vol. 17, no. 12, pp. 1136–1147, 2025, ISSN: 1943-0639, (Publisher: Optica Publishing Group).
Abstract | Links | BibTeX | Tags: Frequency combs, Laser sources, Optical networks, Optical signals, Phase modulation, Signal processing
@article{vallejo_centralized_2025,
title = {Centralized bidirectional heterogeneous fiber-FSO-mmWave-converged networks for 6G dense cellular network deployments},
author = {Luis Vallejo and Jose Mora and Wei Jin and Jaime Romero-Huedo and Lin Chen and Jianming Tang and Beatriz Ortega},
url = {https://opg.optica.org/jocn/abstract.cfm?uri=jocn-17-12-1136},
doi = {10.1364/JOCN.571969},
issn = {1943-0639},
year = {2025},
date = {2025-12-01},
urldate = {2026-02-03},
journal = {Journal of Optical Communications and Networking},
volume = {17},
number = {12},
pages = {1136–1147},
publisher = {Optica Publishing Group},
abstract = {To address the unprecedented technical challenges arising from ultra-dense cellular network deployment for applications in densely populated urban areas envisioned for 6G, this paper proposes and experimentally demonstrates a novel, to our knowledge, centralized bidirectional heterogeneous access network with advanced baseband unit (BBU) pooling and cost-effective remote radio head (RRH) designs free from both lasers and digital signal processing (DSP). The network supports flexible deployments of fiber, free space optical (FSO), and millimeter wave (mmWave) segments, thus ensuring ubiquitous network connectivity. More importantly, it also seamlessly converges various network segments (fiber, FSO, and mmWave) and enables their uplink (UL) and downlink (DL) signals to concurrently and continuously flow between the BBU and user equipment (UE) without requiring optical-electrical/electrical-optical conversions and/or DSPs at any intermediate nodes. In the proposed network, DL mmWave signals are generated and detected using a free-running laser and a passive envelope detection. For the UL case, conventional electrical local oscillators and mixers are used for mmWave up-conversion and down-conversion. The performances of the proposed networks, including UL/DL channel interferences and achievable throughputs, are experimentally evaluated over a fiber-FSO-mmWave setup with 10 km fiber, 1.8 m FSO, and 3 m mmWave links (39 GHz/0.4 Gbit/s for DL, 36.5 GHz/0.2 Gbit/s for UL). The experimental results show robust bidirectional transmissions with negligible UL/DL interferences and minimal impacts from Rayleigh and Brillouin backscattering.},
note = {Publisher: Optica Publishing Group},
keywords = {Frequency combs, Laser sources, Optical networks, Optical signals, Phase modulation, Signal processing},
pubstate = {published},
tppubtype = {article}
}
To address the unprecedented technical challenges arising from ultra-dense cellular network deployment for applications in densely populated urban areas envisioned for 6G, this paper proposes and experimentally demonstrates a novel, to our knowledge, centralized bidirectional heterogeneous access network with advanced baseband unit (BBU) pooling and cost-effective remote radio head (RRH) designs free from both lasers and digital signal processing (DSP). The network supports flexible deployments of fiber, free space optical (FSO), and millimeter wave (mmWave) segments, thus ensuring ubiquitous network connectivity. More importantly, it also seamlessly converges various network segments (fiber, FSO, and mmWave) and enables their uplink (UL) and downlink (DL) signals to concurrently and continuously flow between the BBU and user equipment (UE) without requiring optical-electrical/electrical-optical conversions and/or DSPs at any intermediate nodes. In the proposed network, DL mmWave signals are generated and detected using a free-running laser and a passive envelope detection. For the UL case, conventional electrical local oscillators and mixers are used for mmWave up-conversion and down-conversion. The performances of the proposed networks, including UL/DL channel interferences and achievable throughputs, are experimentally evaluated over a fiber-FSO-mmWave setup with 10 km fiber, 1.8 m FSO, and 3 m mmWave links (39 GHz/0.4 Gbit/s for DL, 36.5 GHz/0.2 Gbit/s for UL). The experimental results show robust bidirectional transmissions with negligible UL/DL interferences and minimal impacts from Rayleigh and Brillouin backscattering.
2.
Majumder, Debparna; Bottrill, Kyle R. H.; Petropoulos, Periklis
Fibre-Based Dynamic Speckle Generation for Emulation of Atmospheric Turbulence Proceedings Article
In: 2025 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), pp. 1–1, 2025, ISSN: 2833-1052, (ISSN: 2833-1052).
Abstract | Links | BibTeX | Tags: Emulation, Europe, Free-space optical communication, Generators, Low earth orbit satellites, Optical fibers, Phase modulation, Satellites, Speckle, System performance
@inproceedings{majumder_fibre-based_2025,
title = {Fibre-Based Dynamic Speckle Generation for Emulation of Atmospheric Turbulence},
author = {Debparna Majumder and Kyle R. H. Bottrill and Periklis Petropoulos},
url = {https://ieeexplore.ieee.org/abstract/document/11110258},
doi = {10.1109/CLEO/Europe-EQEC65582.2025.11110258},
issn = {2833-1052},
year = {2025},
date = {2025-06-01},
urldate = {2025-10-08},
booktitle = {2025 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)},
pages = {1–1},
abstract = {Mitigating the impact of atmospheric turbulence induced speckle is a major challenge for free-space optical communications (FSOC). Such turbulence results in a multimodal, speckled beam which can be challenging to couple into the small active-area photoreceivers needed for high-bandwidth detection. Naturally, lab-based turbulence emulators are needed to benchmark FSOC system performance and develop turbulence mitigating subsystems. Common approaches to turbulence emulation include: rotating phase plates (PPs) [1], spatial light modulators (SLMs) [2] and turbulent-air generators [3]. In this work, we present a fibre-based, dynamic speckle generator, notable for its simplicity, cost-effectiveness (especially compared to SLMs and PPs), and unobtrusive in-lab use (compared to turbulent-air approaches). Unlike today's SLMs, which currently struggle to replicate the fast-changing distortion caused by high slew-rate Low-Earth-Orbit (LEO) satellite tracking, our all-fibre speckle generator can be easily scaled to faster modulation speeds (demonstrated here with a modest 230RPM).},
note = {ISSN: 2833-1052},
keywords = {Emulation, Europe, Free-space optical communication, Generators, Low earth orbit satellites, Optical fibers, Phase modulation, Satellites, Speckle, System performance},
pubstate = {published},
tppubtype = {inproceedings}
}
Mitigating the impact of atmospheric turbulence induced speckle is a major challenge for free-space optical communications (FSOC). Such turbulence results in a multimodal, speckled beam which can be challenging to couple into the small active-area photoreceivers needed for high-bandwidth detection. Naturally, lab-based turbulence emulators are needed to benchmark FSOC system performance and develop turbulence mitigating subsystems. Common approaches to turbulence emulation include: rotating phase plates (PPs) [1], spatial light modulators (SLMs) [2] and turbulent-air generators [3]. In this work, we present a fibre-based, dynamic speckle generator, notable for its simplicity, cost-effectiveness (especially compared to SLMs and PPs), and unobtrusive in-lab use (compared to turbulent-air approaches). Unlike today's SLMs, which currently struggle to replicate the fast-changing distortion caused by high slew-rate Low-Earth-Orbit (LEO) satellite tracking, our all-fibre speckle generator can be easily scaled to faster modulation speeds (demonstrated here with a modest 230RPM).