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.
He, Jiaxiang; Vallejo, Luis; Giddings, Roger Philip; Jin, Wei; Faruk, Md Saifuddin; Yi, Xingwen; Tang, Jianming
Experimental Demonstrations of Chaotic Digital Filter-Based Physical Layer Security in Converged Fibre-mmWave Access Networks Journal Article
In: Journal of Lightwave Technology, vol. 43, no. 18, pp. 8839–8848, 2025, (Publisher: IEEE).
Abstract | Links | BibTeX | Tags: Bit error rate, Frequency division multiplexing, Optical signals, Phase noise, Quantum key distribution, Single mode fibers
@article{he_experimental_2025,
title = {Experimental Demonstrations of Chaotic Digital Filter-Based Physical Layer Security in Converged Fibre-mmWave Access Networks},
author = {Jiaxiang He and Luis Vallejo and Roger Philip Giddings and Wei Jin and Md Saifuddin Faruk and Xingwen Yi and Jianming Tang},
url = {https://opg.optica.org/jlt/abstract.cfm?uri=jlt-43-18-8839},
year = {2025},
date = {2025-09-01},
urldate = {2025-10-08},
journal = {Journal of Lightwave Technology},
volume = {43},
number = {18},
pages = {8839–8848},
publisher = {IEEE},
abstract = {Secure data transmission is experimentally demonstrated in a 1.67 Gb/s seamlessly converged fibre–millimeter wave (mmWave) network using the authors’ newly proposed chaotic digital filter (CDF)-based physical layer security (PLS) technique. The CDF-based encryption/decryption operates by introducing noise-like, key-dependent phase variations to conventional filter impulse responses. Validation is performed in a seamlessly converged network comprising a 25 km standard single-mode fibre (SSMF) link and a 5 m 36 GHz mmWave wireless link, utilizing cost-effective photonic-based mmWave generation and envelope detector-based reception. Experimental results show that the demonstrated PLS technique allows the encrypted signals to continuously flow between the fibre and radio frequency (RF) domains. The PLS technique also supports simultaneous optical and radio frequency access with almost identical BER transmission performances, and power penalties of <1 dB. To gain an in-depth understanding of the measured results, the CDFs’ characteristics, including their chaotic nature, sensitivity to security keys and optimum CDF design parameters, are explored both theoretically and experimentally in detail. The optimum security key properties and CDF's filter lengths are identified, which are independent of the transmission media and major characteristics of the encrypted signals. The CDF-based PLS technique offers salient advantages of ‘security-by-design’, ‘openness-by-design’, ‘dynamic security at the traffic level’, and ‘universal network compatibility’.},
note = {Publisher: IEEE},
keywords = {Bit error rate, Frequency division multiplexing, Optical signals, Phase noise, Quantum key distribution, Single mode fibers},
pubstate = {published},
tppubtype = {article}
}
Secure data transmission is experimentally demonstrated in a 1.67 Gb/s seamlessly converged fibre–millimeter wave (mmWave) network using the authors’ newly proposed chaotic digital filter (CDF)-based physical layer security (PLS) technique. The CDF-based encryption/decryption operates by introducing noise-like, key-dependent phase variations to conventional filter impulse responses. Validation is performed in a seamlessly converged network comprising a 25 km standard single-mode fibre (SSMF) link and a 5 m 36 GHz mmWave wireless link, utilizing cost-effective photonic-based mmWave generation and envelope detector-based reception. Experimental results show that the demonstrated PLS technique allows the encrypted signals to continuously flow between the fibre and radio frequency (RF) domains. The PLS technique also supports simultaneous optical and radio frequency access with almost identical BER transmission performances, and power penalties of <1 dB. To gain an in-depth understanding of the measured results, the CDFs’ characteristics, including their chaotic nature, sensitivity to security keys and optimum CDF design parameters, are explored both theoretically and experimentally in detail. The optimum security key properties and CDF's filter lengths are identified, which are independent of the transmission media and major characteristics of the encrypted signals. The CDF-based PLS technique offers salient advantages of ‘security-by-design’, ‘openness-by-design’, ‘dynamic security at the traffic level’, and ‘universal network compatibility’.
3.
Lu, Bing; Bai, Yifan; Zhang, Jiaxin; Tang, Jianming; Guo, Pengxing; Hou, Weigang; Guo, Lei
Photonic-assisted broadband RF receivers with low IF frequencies based on Kramers-Kronig processing Journal Article
In: Optics Express, vol. 33, no. 5, pp. 9176–9186, 2025, ISSN: 1094-4087, (Publisher: Optica Publishing Group).
Abstract | Links | BibTeX | Tags: Analog to digital converters, Optical components, Optical signals, Polarization control, Polarization division multiplexing, Signal recovery
@article{lu_photonic-assisted_2025,
title = {Photonic-assisted broadband RF receivers with low IF frequencies based on Kramers-Kronig processing},
author = {Bing Lu and Yifan Bai and Jiaxin Zhang and Jianming Tang and Pengxing Guo and Weigang Hou and Lei Guo},
url = {https://opg.optica.org/oe/abstract.cfm?uri=oe-33-5-9176},
doi = {10.1364/OE.545893},
issn = {1094-4087},
year = {2025},
date = {2025-03-01},
urldate = {2025-10-08},
journal = {Optics Express},
volume = {33},
number = {5},
pages = {9176–9186},
publisher = {Optica Publishing Group},
abstract = {A simplified photonic-based radio frequency (RF) receiver with a low intermediate frequency (IF) is proposed and experimentally demonstrated by utilizing direct detection and Kramers-Kronig (KK) processing. In the proposed approach, the RF and local oscillator (LO) signals are modulated onto an optical carrier using a dual-drive Mach-Zehnder modulator (DDMZM) biased at a minimum transmission point. The modulated optical signal is then directed to a single photodetector (PD) to produce the IF signal, which is designed to fall within 1.5 times the bandwidth of the RF signal. KK processing effectively mitigates the signal-signal beat interference (SSBI) when the frequency gap between the RF signal and the LO signal is 1.5 times less than the bandwidth of the RF signal, thus enabling the generation of a low IF signal. This allows for subsequent processing with a low-speed PD and an analog-to-digital converter operating at a lower sampling rate. Experimental validation using a 16-QAM RF vector signal shows that KK processing reduces the error vector magnitude (EVM) of the down-converted 16-QAM signal to 4.61%, compared to 18.57% without it when no frequency gap exists. This approach provides a streamlined design and straightforward implementation for photonic RF down-conversion.},
note = {Publisher: Optica Publishing Group},
keywords = {Analog to digital converters, Optical components, Optical signals, Polarization control, Polarization division multiplexing, Signal recovery},
pubstate = {published},
tppubtype = {article}
}
A simplified photonic-based radio frequency (RF) receiver with a low intermediate frequency (IF) is proposed and experimentally demonstrated by utilizing direct detection and Kramers-Kronig (KK) processing. In the proposed approach, the RF and local oscillator (LO) signals are modulated onto an optical carrier using a dual-drive Mach-Zehnder modulator (DDMZM) biased at a minimum transmission point. The modulated optical signal is then directed to a single photodetector (PD) to produce the IF signal, which is designed to fall within 1.5 times the bandwidth of the RF signal. KK processing effectively mitigates the signal-signal beat interference (SSBI) when the frequency gap between the RF signal and the LO signal is 1.5 times less than the bandwidth of the RF signal, thus enabling the generation of a low IF signal. This allows for subsequent processing with a low-speed PD and an analog-to-digital converter operating at a lower sampling rate. Experimental validation using a 16-QAM RF vector signal shows that KK processing reduces the error vector magnitude (EVM) of the down-converted 16-QAM signal to 4.61%, compared to 18.57% without it when no frequency gap exists. This approach provides a streamlined design and straightforward implementation for photonic RF down-conversion.
4.
Vallejo, Luis; Gonem, Omaro Fawzi Abdelhamid; Jin, Wei; Giddings, Roger Philip; Chen, Lin; Huang, Yi; Yi, Xingwen; Faruk, Md Saifuddin; Tang, Jianming
Seamlessly Converged Fiber-Wireless Access Networks With Dynamic Sub-Wavelength Switching and Tunable Photonic mmWave Generation Journal Article
In: Journal of Lightwave Technology, vol. 43, no. 6, pp. 2624–2635, 2025, (Publisher: IEEE).
Abstract | Links | BibTeX | Tags: Frequency division multiplexing, Optical signals, Optical switching devices, Signal processing, Signal transmission, Variable optical attenuators
@article{vallejo_seamlessly_2025,
title = {Seamlessly Converged Fiber-Wireless Access Networks With Dynamic Sub-Wavelength Switching and Tunable Photonic mmWave Generation},
author = {Luis Vallejo and Omaro Fawzi Abdelhamid Gonem and Wei Jin and Roger Philip Giddings and Lin Chen and Yi Huang and Xingwen Yi and Md Saifuddin Faruk and Jianming Tang},
url = {https://opg.optica.org/jlt/abstract.cfm?uri=jlt-43-6-2624},
year = {2025},
date = {2025-03-01},
urldate = {2025-10-08},
journal = {Journal of Lightwave Technology},
volume = {43},
number = {6},
pages = {2624–2635},
publisher = {IEEE},
abstract = {For implementing next-generation radio access networks (NG-RANs) supporting services/applications in the beyond-5G (B5G) era, seamless fiber-wireless network convergence is vital for enabling heterogeneous signals of various characteristics to continuously flow between the optical and electrical domains, i.e., the baseband unit (BBU) and user equipment (UE), without optical-electrical-optical (O-E-O) conversions or digital signal processing (DSP) at any intermediate nodes. To address such challenges, this paper proposes and experimentally demonstrates, for the first time, a cost-effective fiber-wireless converged flexible and dynamic access network based on intensity modulation and direct detection (IM-DD). The demonstrated network utilizes O-E-O conversion-free Soft-reconfigurable optical add/drop multiplexers (Soft-ROADMs) at remote nodes to dynamically establish connections between the BBU and the remote radio heads (RRHs) at the sub-wavelength level. In addition, free-running laser-enabled photonic millimeter-wave (mmWave) signal generation and passive electrical envelope detector-enabled mmWave down-conversion are also used, respectively, at the RRHs and UEs to achieve mmWave frequency tunability and adaptive wireless network coverage. The network performance and optimum network configuration are experimentally explored extensively in a fiber-wireless converged access network with 3 × 1.333 Gbps dynamic BBU-UE connections over a 10 km IM-DD fiber link and a 5 m, 38 GHz mmWave wireless link. The results show that wide mmWave frequency tuning ranges and adaptive mmWave coverages are achievable by just adjusting the RRH-laser frequency and output powers.},
note = {Publisher: IEEE},
keywords = {Frequency division multiplexing, Optical signals, Optical switching devices, Signal processing, Signal transmission, Variable optical attenuators},
pubstate = {published},
tppubtype = {article}
}
For implementing next-generation radio access networks (NG-RANs) supporting services/applications in the beyond-5G (B5G) era, seamless fiber-wireless network convergence is vital for enabling heterogeneous signals of various characteristics to continuously flow between the optical and electrical domains, i.e., the baseband unit (BBU) and user equipment (UE), without optical-electrical-optical (O-E-O) conversions or digital signal processing (DSP) at any intermediate nodes. To address such challenges, this paper proposes and experimentally demonstrates, for the first time, a cost-effective fiber-wireless converged flexible and dynamic access network based on intensity modulation and direct detection (IM-DD). The demonstrated network utilizes O-E-O conversion-free Soft-reconfigurable optical add/drop multiplexers (Soft-ROADMs) at remote nodes to dynamically establish connections between the BBU and the remote radio heads (RRHs) at the sub-wavelength level. In addition, free-running laser-enabled photonic millimeter-wave (mmWave) signal generation and passive electrical envelope detector-enabled mmWave down-conversion are also used, respectively, at the RRHs and UEs to achieve mmWave frequency tunability and adaptive wireless network coverage. The network performance and optimum network configuration are experimentally explored extensively in a fiber-wireless converged access network with 3 × 1.333 Gbps dynamic BBU-UE connections over a 10 km IM-DD fiber link and a 5 m, 38 GHz mmWave wireless link. The results show that wide mmWave frequency tuning ranges and adaptive mmWave coverages are achievable by just adjusting the RRH-laser frequency and output powers.
5.
Vallejo, Luis; Gonem, Omaro Fawzi Abdelhamid; Jin, Wei; Faruk, Md Saifuddin; Giddings, Roger Philip; Yi, Xingwen; Tang, Jianming
In: Optics Express, vol. 33, no. 1, pp. 604–618, 2025, ISSN: 1094-4087, (Publisher: Optica Publishing Group).
Abstract | Links | BibTeX | Tags: Fiber networks, Frequency division multiplexing, Laser sources, Optical access networks, Optical network architecture, Optical signals
@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}
}
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.
6.
Vallejo, Luis; Jin, Wei; Tang, Jianming
Seamlessly Converged Optical-Wireless Access Networks Using Free-Running Laser-enabled mmWave Signal Generation and RF Envelope Detection Proceedings Article
In: CLEO 2024 (2024), paper JTu2A.80, pp. JTu2A.80, Optica Publishing Group, 2024.
Abstract | Links | BibTeX | Tags: Bit error rate, Optical access networks, Optical networks, Optical signals, Phase noise, Signal processing
@inproceedings{vallejo_seamlessly_2024,
title = {Seamlessly Converged Optical-Wireless Access Networks Using Free-Running Laser-enabled mmWave Signal Generation and RF Envelope Detection},
author = {Luis Vallejo and Wei Jin and Jianming Tang},
url = {https://opg.optica.org/abstract.cfm?uri=CLEO_AT-2024-JTu2A.80},
doi = {10.1364/CLEO_AT.2024.JTu2A.80},
year = {2024},
date = {2024-05-01},
urldate = {2025-10-08},
booktitle = {CLEO 2024 (2024), paper JTu2A.80},
pages = {JTu2A.80},
publisher = {Optica Publishing Group},
abstract = {Low-cost component-based converged optical-wireless networks without DSP at intermediate RRHs are proposed and experimentally demonstrated, supporting 1.67 Gbit/s/ch dynamic and continuous BBU-UE data flows over 50 km SSMF and 3 m 38 GHz wireless links.},
keywords = {Bit error rate, Optical access networks, Optical networks, Optical signals, Phase noise, Signal processing},
pubstate = {published},
tppubtype = {inproceedings}
}
Low-cost component-based converged optical-wireless networks without DSP at intermediate RRHs are proposed and experimentally demonstrated, supporting 1.67 Gbit/s/ch dynamic and continuous BBU-UE data flows over 50 km SSMF and 3 m 38 GHz wireless links.