Simplified photonic-assisted digitalized microwave frequency measurement with improved coding efficiency and sensitivity

A simplified photonic approach to implement digitalized microwave frequency measurement with improved coding efficiency and receiving sensitivity is proposed and experimentally demonstrated. In the proposed approach, an optical phase-shifted filter array and multiple optical filters with multiplied FSRs are designed to obtain digitalized results in the form of binary encoding. Thanks to the complementary outputs, an adaptive threshold decision implemented using balanced receivers is employed to perform binary encoding, instead of a fixed power ratio threshold of 0.5, leading to an improvement in the receiving sensitivity. Besides, a high coding efficiency and a fine measurement resolution are achieved with relaxed accuracy requirement on phase shifts of the optical filters. In particular, compared with the previous approaches, larger tolerances on the phase shifts of the optical phase-shifted filters are provided in the proposed approach having the same coding efficiency and resolution. Therefore, the proposed system is easy to be implemented and robust to noise. A proof-of-concept experiment is then performed. 6-bit binary digital results with a 5-bit effective number are obtained in the range from 10 GHz to 40 GHz. In addition, an integrated version of such a filter array is designed and analyzed in simulation.