Bridging Technologies: Hybrid Electronic and Photonic-Assisted Ultra-Wideband Wireless Systems for Future Communications

The rapid growth of data-driven applications like ultra-high-definition video streaming, virtual reality, augmented reality, and the Internet of Things (IoT) has fundamentally transformed the demands placed on modern wireless communication networks. These applications not only require enormous data throughput but also demand highly efficient and reliable transmission methods to support an ever-growing number of devices. Traditional infrastructure, including coaxial cables and optical fiber, often falls short in meeting these requirements due to limitations in scalability, cost, and deployment feasibility, particularly in dense urban environments. As such, researchers worldwide are pursuing innovative solutions to expand wireless network capacity. One of the most significant hurdles in achieving ultra-high-speed wireless communication lies in the effective utilization of available frequency spectrum. With lower frequency bands (sub-6 GHz) already congested by existing technologies like 4G and Wi-Fi, higher frequency bands, including millimeter-wave (mm-wave) bands (30–300 GHz), present an attractive alternative due to their wide transmission bandwidths. However, realizing their potential has proven difficult. All-electronic approaches, which have been highly successful in lower frequency ranges, face limitations at mm-wave frequencies due to high conversion losses, limited modulation bandwidth, and increased phase noise from local oscillators. These challenges reduce spectral efficiency and impair the performance of high-frequency systems. Similarly, photonics-based approaches offer significant advantages in generating mm-wave signals but face their own constraints. Systems relying on free-running lasers encounter issues such as thermal drift and frequency instability, which undermine their capacity to deliver precise and synchronized carrier frequencies. Combining electronic and photonic methods, though conceptually promising, has been difficult to implement due to the inherent complexities of synchronizing signals generated from two fundamentally different technologies.

New research paper published in Journal of Lightwave Technology, and conducted by Zichuan Zhou; Amany Kassem; James Seddon; Eric Sillekens; Izzat Darwazeh; and led by Professor Polina Bayvel and Professor Zhixin Liu  from the Department of Electronic and Electrical Engineering at University College London  addressed these challenges head-on by developing a hybrid transmission system. This system combines high-speed electronics and photonic-assisted signal generation to achieve unprecedented levels of bandwidth utilization and data rate performance. Their motivation is clear: to create a scalable, efficient, and practical wireless communication solution capable of meeting the demands of next-generation radio access networks (RANs).  The researchers built a hybrid electronic and photonic-assisted system for ultra-wideband wireless transmission. They designed an experimental setup that spanned frequencies from 5 GHz to 150 GHz, integrating cutting-edge components like high-speed arbitrary waveform generators and photonic devices. At the core of the system was the innovative combination of electronic channels operating in the 5–75 GHz range and photonic-assisted channels covering 75–150 GHz. This approach allowed them to exploit the unique advantages of both technologies while overcoming their individual limitations. The experiments began with signal generation. For the electronic channels, high-speed digital-to-analog converters (DACs) were used to create signals up to 75 GHz, demonstrating the capabilities of advanced electronics in achieving high fidelity at lower frequencies. Meanwhile, the photonic-assisted channels relied on frequency-locked laser pairs to generate mm-wave signals in the W-band (75–110 GHz) and D-band (110–150 GHz). The lasers were frequency-locked using an optical phase-locked loop, ensuring synchronized and stable carrier frequencies across the spectrum. This innovative frequency-locking technique resulted in a dramatic reduction in phase noise, improving the quality and stability of the high-frequency signals. The authors then transmitted these signals through the air over a short range of 12 centimeters, a practical limitation due to laboratory constraints. Using orthogonal frequency-division multiplexing (OFDM), the signals were transmitted across multiple frequency bands with minimal gaps between them, thanks to precise synchronization. At the receiving end, high-bandwidth analog-to-digital converters (ADCs) digitized the incoming signals, which were then processed using advanced digital signal processing techniques to recover the transmitted data. The findings from these experiments were remarkable. The hybrid system achieved a record-breaking aggregated data rate of 938 Gb/s over a total bandwidth of 145 GHz, with a net throughput of 812 Gb/s after accounting for error correction overheads. The researchers noted excellent signal-to-noise ratios (SNRs) across the frequency bands, with higher SNRs observed in the electronically generated channels due to their superior amplification. Despite the challenges associated with mm-wave signal generation and transmission, the photonic-assisted channels performed impressively, achieving stable and high-capacity data rates even at the upper end of the frequency spectrum. Further analysis revealed the importance of the frequency-locked lasers in reducing phase noise, particularly for the photonic-assisted channels. Compared to systems using free-running lasers, the locked lasers showed a 50 dB improvement in phase noise at offsets below 1 kHz. This improvement directly contributed to the high spectral efficiency of the system, as it minimized the need for guard bands between adjacent frequency channels. The authors also explored the tunability of the system, demonstrating the ability to adjust carrier frequencies with fine precision while maintaining signal integrity. This tunability is essential for dynamic spectrum management and practical deployment in real-world scenarios. Their experiments validated the practicality of using hybrid electronic and photonic methods to achieve ultra-high-speed wireless transmission, setting a new benchmark for data rates in wireless communication systems.

In their findings, the researchers emphasized the potential applications of this technology. While the short-range demonstration in the lab was limited, they projected that the system could achieve long-distance transmissions exceeding 100 meters with the use of focused antennas. This capability positions the technology as a strong candidate for next-generation base station interconnects and other high-capacity wireless applications, such as short-range kiosk downloads and intra-data center communication. By combining robust experimental design with cutting-edge findings, the researchers have laid the foundation for the future of ultra-wideband wireless systems.

The research work of Professor Polina Bayvel and colleagues at UCL is an important advancement in wireless communication, addressing one of the most pressing challenges in modern networking—achieving ultra-high-speed data transmission across a broad frequency spectrum. By successfully demonstrating a hybrid system that combines the strengths of electronic and photonic technologies, the researchers have unlocked new possibilities for utilizing the vast potential of mm-wave frequency bands. This innovation is particularly significant as global demand for high-speed, reliable data transfer continues to surge, driven by applications like virtual reality, autonomous systems, and the Internet of Things. The ability to achieve 938 Gb/s over a wide range of frequencies highlights the feasibility of pushing wireless communication systems beyond current limitations. Unlike traditional approaches, which either struggled with high phase noise or limited frequency range, the proposed hybrid system achieves unparalleled synchronization and stability across 145 GHz of bandwidth. This breakthrough sets a benchmark for high-capacity point-to-point connections, making it a cornerstone for next-generation RANs. One of the most impactful implications of the study lies in its potential to overcome urban connectivity challenges. Many urban environments cannot rely on optical fiber deployment due to logistical and financial constraints. The hybrid system demonstrated in this research offers an alternative by enabling high-capacity wireless links between base stations. These links could serve as the backbone of future 5G and 6G networks, ensuring seamless connectivity even in areas where wired infrastructure is infeasible. Another key implication is the scalability and adaptability of the technology. The tunability of the frequency-locked lasers, coupled with minimal inter-band gaps, offers a highly efficient use of spectrum. This feature is critical for flexible spectrum allocation and dynamic frequency management, making the system suitable for a wide range of use cases. From urban telecommunications to specialized applications like intra-data center communications and kiosk downloads, the technology can be tailored to meet diverse needs. Furthermore, the study’s success in minimizing phase noise and maximizing spectral efficiency opens doors for research into terahertz communication, a field widely regarded as the next frontier in wireless technology. By addressing technical bottlenecks such as phase instability and limited bandwidth utilization, this research sets the stage for even higher data rates and broader frequency ranges. The findings also have implications for global telecommunications policy and infrastructure development. As regulatory bodies allocate additional frequency bands for wireless use, the ability to fully exploit these resources becomes paramount. The demonstrated system not only aligns with but also anticipates the requirements of these future spectrum allocations, ensuring that the technology remains relevant for decades to come.