Photonic approach to microwave frequency measurement with digital circular-code results.

A photonic approach to measuring microwave frequency with digital results is proposed and experimentally demonstrated. In the proposed approach, N photonic phase-shifted filters with a phase shift increment of π/N in the transmission responses are designed. The filters are then employed to process the single optical sideband generated by applying a microwave signal to a single sideband suppressed-carrier (SSB-SC) modulation module, to perform frequency-to-amplitude conversion and analog-to-digital conversion simultaneously. After the implementation of power detection and decision operation to the filtered optical sideband, an N-bit result in the form of the circular code is obtained, which indicates the frequency of the microwave signal. A proof-of-concept experiment is performed to verify the proposed approach and a 5-bit circular code is generated to indicate microwave frequency up to 40 GHz.