We propose and experimentally demonstrate a novel all-optical microwave filter with high quality factor (Q). It is based on a recirculating delay line (RDL) loop in which a semiconductor optical amplifier (SOA) is followed by a tunable narrow-band optical filter and a 1x2 10:90 optical coupler. Converted signal used as a negative tap is generated through wavelength conversion employing the cross-gain modulation (XGM) of the amplified spontaneous emission (ASE) spectrum of the SOA. The converted signal can circulate in the RDL loop so that the proposed filter realizes a high Q factor response after photo-detection. The 1x2 10:90 coupler is employed to extract 10% optical power from the loop as output. A frequency response with a high Q factor of 543, a rejection ratio of 40 dB is experimentally demonstrated.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.