Novel approach for microwave frequency measurement based on optical power monitoring

An approach using a single laser source and two optical comb filters is proposed to performing microwave frequency measurement. In the proposed system, two filters with quadrature comb filtering responses are firstly constructed. The light wave of the laser source is modulated by a microwave signal under the carrier-suppression and single sideband modulation condition. The single sideband of the modulated light wave is simultaneously coupled into the two comb filters, at the outputs of which two optical powers having a quadrature relationship are detected. The microwave frequency to be measured is then estimated from the two quadrature power ratios (i.e., the sine-form and the cosine-form ratios), which are derived from a comparison between the two detected optical powers and a reference optical power. Since the ambiguity can be eliminated by using the two quadrature power ratios, the measurement range is enlarged from half free spectral range (FSR) to full FSR of the comb filtering responses. Thus the proposed approach using a single laser source can provide a larger measurement range, and especially a potential solution to the cascaded or parallel configurations.