1.
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.
2.
Nafria, Vijay; Djordjevic, Ivan B.
Low probability of intercept (LPI) free-space optical communication with wavelength diversity in strong atmospheric turbulence regime Journal Article
In: Optics Express, vol. 32, no. 26, pp. 47270–47284, 2024, ISSN: 1094-4087, (Publisher: Optica Publishing Group).
Abstract | Links | BibTeX | Tags: Adaptive optics, Coupling efficiency, Free space optics, Signal processing, Signal transmission, Systems design
@article{nafria_low_2024,
title = {Low probability of intercept (LPI) free-space optical communication with wavelength diversity in strong atmospheric turbulence regime},
author = {Vijay Nafria and Ivan B. Djordjevic},
url = {https://opg.optica.org/oe/abstract.cfm?uri=oe-32-26-47270},
doi = {10.1364/OE.547978},
issn = {1094-4087},
year = {2024},
date = {2024-12-01},
urldate = {2025-10-08},
journal = {Optics Express},
volume = {32},
number = {26},
pages = {47270–47284},
publisher = {Optica Publishing Group},
abstract = {In physical-layer security and cryptography we are concerned with the security of the transmitted data, while in low probability of intercept (LPI) communication with protecting the privacy of the end users. In our recent publications related to LPI communications and radars over free-space optical (FSO) links we proposed to hide the constant-amplitude modulated data, imposed on thermal source beam, in ambient solar radiation to protect the end users privacy and at the same time improve the reliability and security, while reducing the detectability of transmitted signal by the adversary Willie. In order to study both LPI and covert communication concepts we have developed an FSO communication testbed at the University of Arizona campus with a 1.5 km-long FSO link. Here we present results of our FSO experiments, where we conducted both LPI and covert communications at data rates ranging from 125 Mb/s to 10 Gb/s, wherein the information beam is kept completely hidden under the ambient solar radiations as random thermal noise. To improve the system reliability to atmospheric turbulence effects we make use of wavelength diversity method as a low-cost, easy to implement and far more practical alternative to conventional adaptive optics systems.},
note = {Publisher: Optica Publishing Group},
keywords = {Adaptive optics, Coupling efficiency, Free space optics, Signal processing, Signal transmission, Systems design},
pubstate = {published},
tppubtype = {article}
}
In physical-layer security and cryptography we are concerned with the security of the transmitted data, while in low probability of intercept (LPI) communication with protecting the privacy of the end users. In our recent publications related to LPI communications and radars over free-space optical (FSO) links we proposed to hide the constant-amplitude modulated data, imposed on thermal source beam, in ambient solar radiation to protect the end users privacy and at the same time improve the reliability and security, while reducing the detectability of transmitted signal by the adversary Willie. In order to study both LPI and covert communication concepts we have developed an FSO communication testbed at the University of Arizona campus with a 1.5 km-long FSO link. Here we present results of our FSO experiments, where we conducted both LPI and covert communications at data rates ranging from 125 Mb/s to 10 Gb/s, wherein the information beam is kept completely hidden under the ambient solar radiations as random thermal noise. To improve the system reliability to atmospheric turbulence effects we make use of wavelength diversity method as a low-cost, easy to implement and far more practical alternative to conventional adaptive optics systems.
3.
Nafria, Vijay; Djordjevic, Ivan B.
In: Optics Express, vol. 32, no. 27, pp. 47908–47919, 2024, ISSN: 1094-4087, (Publisher: Optica Publishing Group).
Abstract | Links | BibTeX | Tags: Coupling efficiency, Laser communications, Optical systems, Optical transceivers, Phase conjugation, Signal transmission
@article{nafria_entanglement_2024,
title = {Entanglement assisted free-space optical communication with two-pump-based entanglement generation outperforming classical laser communication in strong turbulence regime at 10 Gb/s},
author = {Vijay Nafria and Ivan B. Djordjevic},
url = {https://opg.optica.org/oe/abstract.cfm?uri=oe-32-27-47908},
doi = {10.1364/OE.544674},
issn = {1094-4087},
year = {2024},
date = {2024-12-01},
urldate = {2025-10-08},
journal = {Optics Express},
volume = {32},
number = {27},
pages = {47908–47919},
publisher = {Optica Publishing Group},
abstract = {A high-speed entanglement assisted communication that operates at 10 Gb/s is proposed, which performs a highly efficient, PPLN-waveguide-based, entanglement generation by making the simultaneous use of S- and L-band pumps. The two-pump-based entanglement generation source satisfies the quasi-phase-matching-condition over the entire C-band. To improve the system reliability, our system performs the phase-conjugation on idler photons in contrast to conventional ways of performing the phase-conjugation on signal photons. To study the performance of the proposed entanglement-assisted system we have developed the 1.5 km long outdoor free-space optical (FSO) link at the University of Arizona campus. Experimental results indicate that the proposed entanglement-assisted system significantly outperforms the classical counterpart at 10 Gb/s, operated in strong turbulence regime. We also demonstrate that the traditional entanglement-assisted system performing the optical phase conjugation on signal photons at the receiver side is not operational at all in strong turbulence regime given that it is extremely difficult to perform the phase-conjugation on weak signal photons when the number of received photons is low. To improve the system performance the adaptive optics is performed on signal photons.},
note = {Publisher: Optica Publishing Group},
keywords = {Coupling efficiency, Laser communications, Optical systems, Optical transceivers, Phase conjugation, Signal transmission},
pubstate = {published},
tppubtype = {article}
}
A high-speed entanglement assisted communication that operates at 10 Gb/s is proposed, which performs a highly efficient, PPLN-waveguide-based, entanglement generation by making the simultaneous use of S- and L-band pumps. The two-pump-based entanglement generation source satisfies the quasi-phase-matching-condition over the entire C-band. To improve the system reliability, our system performs the phase-conjugation on idler photons in contrast to conventional ways of performing the phase-conjugation on signal photons. To study the performance of the proposed entanglement-assisted system we have developed the 1.5 km long outdoor free-space optical (FSO) link at the University of Arizona campus. Experimental results indicate that the proposed entanglement-assisted system significantly outperforms the classical counterpart at 10 Gb/s, operated in strong turbulence regime. We also demonstrate that the traditional entanglement-assisted system performing the optical phase conjugation on signal photons at the receiver side is not operational at all in strong turbulence regime given that it is extremely difficult to perform the phase-conjugation on weak signal photons when the number of received photons is low. To improve the system performance the adaptive optics is performed on signal photons.