MHz-resolution and large-range microwave frequency identification by using an optical microresonator

The ability to identify the frequency of unknown microwave signals with high resolution, fast response, and wide measurement bandwidth is highly desirable in 6G networks, radar systems, and next-generation electronic warfare. Conventional electronic solutions face challenges in dealing with a large frequency measurement range, high speed, and high susceptibility to electromagnetic interference. Recently, there has been a surge of interest in photonic-assisted microwave frequency identification systems as a means to address the aforementioned difficulties. Nevertheless, these systems typically have a frequency resolution that exceeds 10 MHz. Here, a MHz-resolution microwave frequency identification system based on a packaged and functionalized ultrahigh-quality-factor optical microresonator is demonstrated. The unknown microwave signals can be measured through linearly mapping the microwave frequencies to the time delays of the resonance modes of the microresonator. Owing to the high-efficiency all-optical tuning enabled by the functionalized microresonator, the system eliminates the necessity for a precisely wavelength-tunable laser source. Our experimental results approve the system's capability to identify different types of microwave signals with a frequency resolution of 3 MHz. Our work establishes a solid groundwork for the development of a microwave frequency identification system that delivers an exceptional resolution.