Experts discuss the future of photonic chip-based microwave generation in IEEE Journal of Selected Topics in Quantum Electronics

Imagine a future where ultra-fast data transfers and ultra-precise radar systems become possible through a device no larger than a microchip. Thanks to recent advancements in integrated photonics, this vision is now closer to reality.

Microwave signals are the foundation of modern technology, powering everything from radar systems to 6G networks. Traditionally, generating low-noise microwaves has relied on bulky and energy-intensive microwave equipment. However, by use of silicon-photonics-based resonators to create these signals, researchers have developed a groundbreaking microwave photonic approach with dramatically reduced size, weight, and power consumption.

Several collaborative teams are developing this revolutionary method to bridge optical (light) and microwave (radio) frequencies using a compact device called a “microcomb” [1-3]. And a further advance is recently detailed in the IEEE Journal of Selected Topics in Quantum Electronics paper [4].

The team employed a technique known as a two-point optical frequency division (2P-OFD). By locking frequencies of two lasers (v1 and v2 in the figure) to a Fabry-Perot reference cavity, using the lasers to stabilize optical harmonics of a microcomb, and demodulating the microcomb on a fast photodiode, they generated microwave signals with remarkable stability and minimal noise. Central to this process is the photonic divider, which operates seamlessly based on the frequency ratio of the two lasers’ frequency difference—a functionality enabled by the coherence of the microcomb. By detecting low-frequency beat notes between the lasers and the corresponding comb harmonics, subtracting them electronically from each other, and using the differenced signal to stabilize the microcomb, the frequency division of the spacing between the two optical frequencies by the N comb lines, can be achieved. The coherence of this division process is demonstrated by using different frequency spacings through the comb spectrum.

These findings have transformative implications for telecommunications, precision timekeeping, and space exploration. By integrating this system onto a single chip, the researchers have set the stage for portable and cost-effective devices. With continued development, this technology could lead to groundbreaking advancements in both civilian and military applications. The use of standard diode lasers and a compact optical reference with low sensitivity to environmental factors increase the potential for real-world applications.

[1] Kudelin, Igor, et al. “Photonic chip-based low-noise microwave oscillator.” Nature 627.8004 (2024): 534-539.

[2] Sun, Shuman, et al. “Integrated optical frequency division for microwave and mmWave generation.” Nature 627.8004 (2024): 540-545.

[3] Zhao, Yun, et al. “All-optical frequency division on-chip using a single laser.” Nature 627.8004 (2024): 546-552.

[4]  Ji, Qing-Xin, et al. “Coherent optical-to-microwave link using an integrated microcomb.” IEEE Journal of Selected Topics in Quantum Electronics (2024).

Reference

Image Caption: Photonic chip-based low-noise microwave generation using the optical frequency division technique.