Photonic approach with multiple FSRs for instantaneous frequency measurement

A photonic approach with multiple free spectral ranges (FSRs) is proposed to perform instantaneous frequency measurement. In the proposed approach, multiple channels are firstly designed with the use of multiple laser sources operating at different wavelengths and a comb filter, leading to the generation of multiple FSRs at these channels. The microwave signal with its frequency to be measured is imposed on these channels. After passing through the comb filter, optical powers at the outputs of the multiple channels are then detected and processed to estimate the frequency, with multiple FSRs or multiple measurement ranges derived during the measurement process. Such an approach is demonstrated by an experimental setup where two channels operating at 1520nm and 1550nm and a delay line interferometer based comb filter are implemented to get two different FSRs. Within the range of 12~35GHz, the measured frequencies are in a good agreement with the input frequencies being measured.