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A new microwave photonic filter structure that realizes both a multitap, flat-top radio-frequency bandpass filter and bipolar taps, while also exhibiting low-noise operation, is presented. It is based on using a phase-modulated laser signal propagating through a novel sinusoidal group delay grating, which induces tailored phase shifts to the carrier and sidebands. The filter integrates tap weighting and delays simultaneously in one unit, which enables multiple-tap low-noise signal processing together with negative coefficients. Experimental results demonstrate the realization of a flat-top bandpass filter response with 7.8-GHz free spectral range and more than 45-dB rejection ratio. Extensions to this concept by connecting additional sinusoidal group delay gratings in cascade, to provide enhanced signal processing functions, are also described.
Date of Publication: Aug.1, 2008