Tunable Narrowband Microwave Photonic Filter Using Stimulated Brillouin Scattering by Precisely Controlling the Gain and Loss Spectra

A novel scheme of narrowband microwave photonic filter based on stimulated Brillouin scattering (SBS) is proposed and experimentally demonstrated. The frequency response of a conventional SBS-based microwave photonic filter depends on the shape of Brillouin gain spectrum. It has a 3 dB bandwidth of about 10 MHz to 30 MHz. In this work, the bandwidth is reduced through a composite SBS process in which two Brillouin loss lines are superimposed upon a central Brillouin gain. By carefully tuning the frequency detuning between the gain and loss pumps and their power ratios, the 3 dB and 20 dB bandwidths are reduced to 5.4 MHz and 14.2 MHz, respectively. The tunability of center frequency is also verified. In addition, the filter has a high out-of-band rejection of 55 dB over a large frequency range due to the vector attributes of SBS amplification.