Microwave signals have become integral to numerous modern applications such as radar, navigation, advanced communication systems, and even atomic clocks. The demands for accuracy in these systems are continually rising, pushing existing technologies to their limits. In order to achieve greater accuracy levels, precision in microwave timing stability and low noise levels are crucial, yet there is a looming realization that these requirements may soon surpass what current methods can offer.
Photonic lightwave systems are an emerging technology that appears to be poised to transform how we generate microwave signals. These systems hold the promise of delivering the clean and stable signals essential for cutting-edge applications. By harnessing the properties of light and leveraging optical components, photonic systems offer the potential to overcome the limitations of traditional microwave signal generation methods.
An overview of the technology (📷: I. Kudelin et al.)
However, despite their immense potential, photonic lightwave systems are not without their challenges. Presently, these systems are bulky and expensive, and they consume large amounts of energy, restricting their practical utility outside of laboratory environments. These limitations hinder their potential for widespread adoption in real-world applications, where efficiency and compactness are often hard requirements.
A breakthrough spearheaded by the National Institute of Standards and Technology, along with their partners in academia, promises to shrink photonic lightwave systems down to the size of a single chip, while also dramatically reducing their level of power consumption. These factors, in conjunction with the precision of the system — it was shown that timing jitter could be reduced to 15 femtoseconds — could make it usable in everyday devices in the near future.
The team heavily focused on reducing the size of the system’s components. This resulted in the development of a chip that utilizes a semiconductor laser that shines its light into a tiny box, called a reference cavity, that is lined with mirrors to direct that light. The cavity is designed to specifically amplify certain wavelengths of light, which causes the power of the light in those frequencies to build up. This provides a very stable and powerful source of light at a desired frequency, which can then be passed through a frequency comb, which converts the light into microwave signals.
The experimental setup (📷: I. Kudelin et al.)
The main chip is about the size of an SD memory card, which is far smaller than the tabletop-size devices that are presently used to build photonic lightwave systems. However, all of the necessary components are not yet integrated into that tiny package. As the researchers complete the testing of their system, and continue to optimize it, they intend to move the rest of these components into a single-chip package. But until they achieve this planned goal, the numerous applications that could benefit from the technology will have to wait.
