Photonic Microwave Frequency Measurement With High-Coding-Efficiency Digital Outputs and Large Measurement Range

A photonic approach to estimating microwave frequency with high-coding-efficiency digital outputs and large measurement range is proposed and experimentally demonstrated. In the proposed approach, an optical filter array that consists of N filters is designed, wherein N - 1 optical phase-shifted filters have an identical free spectral range (FSR) but a phase increment of π/(N - 1) in the transmission responses and one filter has a doubled FSR. The filters are then employed to process the single optical sideband generated by applying a microwave signal to a carrier-suppressed single-sideband (CS-SSB) modulation module, to perform the frequency-to-amplitude conversion and the analog-to-digital conversion simultaneously. After power detection and decision operation, an N-bit digital result in the form of binary code is obtained for microwave frequency measurement within the range of 2 × FSR. A proof-of-concept experiment is performed to verify the proposed approach. A 5-bit binary code with effective number of bits of four is generated to indicate the microwave frequency in the range from 10 to 40 GHz.