High-Sensitivity Instantaneous Microwave Frequency Measurement Based on a Silicon Photonic Integrated Fano Resonator

Instantaneous frequency measurement (IFM) based on a silicon photonic Fano resonator with improved linearity and sensitivity is proposed and experimentally demonstrated. The Fano resonator has a steep edge in its spectral response, which is employed to translate the frequency information of a microwave signal to an optical power change. When comparing the optical powers at the output and input of the Fano resonator, a highly linear amplitude comparison function (ACF), which is used to estimate the microwave frequency is obtained. The key device in the system is the Fano resonator, which is realized by coupling a grating-based Fabry-Perot cavity resonant mode with an add-drop microring resonator mode, implemented on a silicon platform. The linearity of the ACF is characterized by its R-squared value which is calculated by fitting the ACF measurements with a linear function. In our experimental demonstration, an R-squared value as large as 0.99 is obtained. A frequency measurement range as large as 15 GHz with a resolution better than ±0.5 GHz is achieved. The use of the proposed IFM system to perform Brillouin frequency discrimination in a fiber-optic sensor for temperature measurement is demonstrated.