12 Platform one February/March 2024 | Uncrewed Systems Technology Researchers in the US have used silicon photonics rather than electronics to tackle dynamic radio-frequency (RF) interference (writes Nick Flaherty). This is an increasing problem for uncrewed systems, both in the air and on the ground. Radar altimeters are the sole indicators of altitude above a terrain. 5G cellular bands pose a significant risk of jamming altimeters, and impact flight landing and take-off. As wireless technology expands in frequency coverage and uses spatial multiplexing, RF interference is becoming a pressing issue. To address it, RF front ends with low latency are crucial. There are also challenges from the physical movement of transceivers, resulting in time-variant mixing ratios between interference and the signal-ofinterest (SoI). This requires real-time adaptability in mobile wireless receivers to handle fluctuating interference, particularly when it carries safety-to-life critical information for navigation and autonomous driving, such as for aircraft and ground vehicles. The photonic integrated circuits (PICs) process broadband information by converting radio frequencies into optical frequencies. Unlike traditional analogue RF components or digital electronics, PICs reduces latency through direct analogue processing. But, integrating a complete system on a chip for microwave processing has faced design, control and packaging challenges. Current PICs require bulky external devices for signal analysis and control, leading to impractical size, weight and power metrics. Professor Paul Prucnal from Lightwave Lab at the Department of Electrical and Computer Engineering, Princeton University, USA, and his co-workers have micro-ring resonator (MRR) weight banks and photodetectors on a single chip, significantly reducing processing latency to less than 15 picoseconds. In addition, a field-programmable gate array (FPGA) with integrated peripherals handles high-throughput statistical analysis and high-level blind-source separation (BSS) algorithms. This enables real-time execution at a refresh rate of 305 Hz, which is a marked improvement on previous systems. The research team successfully tested this device in two dynamic interference scenarios – mobile communications and radar altimeters. The results were convincible, demonstrating error-free operation and maintaining signal-to-noise ratios over 15 dB. This shows the potential of the device to address real-world interference challenges effectively. Radio Lower latency photonics developed a system-on-chip (SoC) that uses silicon photonics for a palm-sized, standalone photonic device. The device integrates modulators, The device significantly reduces processing latency to less than 15 picoseconds This enables real-time execution at a refresh rate of 305 Hz, which is a marked improvement on previous systems
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