@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}

}

@article{vallejo_experimental_2025,

title = {Experimental investigation of a seamlessly converged fiber-wireless access network employing free-running laser- and envelope detection-based mmWave generation and detection},

author = {Luis Vallejo and Omaro Fawzi Abdelhamid Gonem and Wei Jin and Md Saifuddin Faruk and Roger Philip Giddings and Xingwen Yi and Jianming Tang},

url = {https://opg.optica.org/oe/abstract.cfm?uri=oe-33-1-604},

doi = {10.1364/OE.532694},

issn = {1094-4087},

year  = {2025},

date = {2025-01-01},

urldate = {2025-10-08},

journal = {Optics Express},

volume = {33},

number = {1},

pages = {604–618},

publisher = {Optica Publishing Group},

abstract = {Employing free-running laser/envelope detection-based millimeter wave (mmWave) signal generation/detection at remote radio heads (RRHs)/user equipment (UE) offers a cost-effective solution for seamlessly integrating existing intensity modulation-direct detection (IM-DD)-dominated optical access networks and wireless networks. Such fiber-wireless convergence enables a continuous flow of signals with varying characteristics between the baseband unit (BBU) and UE across fiber and wireless network segments without the need for optical-electrical-optical (O-E-O) conversions and digital signal processing (DSP) at intermediate nodes. In this paper, we extensively investigate the performance of such a fiber-wireless converged access network employing free-running laser/envelope detection-based mmWave generation/detection in an IM-DD-based 1.67 Gbit/s transmission system with 25 km standard single-mode fiber (SSMF) and 5 m @38 GHz mmWave wireless links. Experimental results demonstrate that both mmWave frequency tunability and adaptive mmWave network coverage are achievable by just dynamically and adaptively configuring the output wavelength and power of the RRH-embedded free-running laser. Additionally, envelope detection allows RRHs to use low-cost MHz-linewidth-level free-running lasers while maintaining excellent performance stability.},

note = {Publisher: Optica Publishing Group},

keywords = {Fiber networks, Frequency division multiplexing, Laser sources, Optical access networks, Optical network architecture, Optical signals},

pubstate = {published},

tppubtype = {article}

}