Instantaneous microwave frequency measurement with single branch detection based on the birefringence effect

Instantaneous frequency measurement (IFM) with single branch detection based on the birefringence effect is proposed and experimentally demonstrated. The unknown microwave frequencies are modulated to pump a length of polarization maintaining fiber. Due to the fiber birefringence effect, the input light signal is decomposed into two orthogonal-polarization signals with a relative time delay. After detection, an amplitude comparison function (ACF) is obtained by comparing the alternating-current and direct-current powers. Therefore, no multipath detection is needed so that the electrical variations in the photonic link can be cancelled out in ACF. A theoretical analysis is given to illustrate the mechanism of the proposed IFM system. The disturbances are investigated and discussed in simulation. A proof-of-concept experiment is carried out for verification with a result of ± 0.2 G H z over 2.2–5.2 GHz.