Tunable single bandpass microwave photonic filter using polarization-orthogonal optical carrier time shift

A novel microwave photonic filter (MPF) with large tunability, configurability and single passband is proposed and demonstrated in this paper. The combination of polarization modulation (PolM) and variable differential group delay (DGD) introduces optical carrier time shift between orthogonally polarized optical carrier and its modulated sidebands, which eliminates carrier suppression effect caused by fiber dispersion and shifts the filter baseband to a new tunable frequency. The MPF is experimentally implemented. By simply change DGD value, the single passband filter center frequency is widely tuned without changing the filter shape. By changing the optical filter, the filter׳s shape, bandwidth and mainlobe-to-sidelobe suppression ratio is also reconfigurable. By using polarization based differential detection, the signal to noise ratio is improved by 9.9 dB and the spurious passband brought by the residual DGD in PolM is suppressed by 20.1 dB.