All-Optical Microwave Photonic Single-Passband Filter Based on Polarization Control Through Stimulated Brillouin Scattering

We present a novel microwave photonic single-passband filter based on polarization control through simulated Brillouin scattering (SBS). The principle of the filter is based on a vector SBS process, which is different from the previously reported scalar SBS technique. For a radio-frequency (RF) modulated signal launched to the proposed processor, the state of polarization (SOP) of the optical carrier is rotated by 90° through a two-step SBS process. As a result, the RF signals cannot be recovered in the photodetector (PD). To recover the desirable RF signal, the SOP of the RF modulated sideband is rotated by another pump wave. Since the orthogonal polarization condition between the optical carrier and the sideband is destroyed, the desirable RF signal can be recovered. By adjusting the wavelength of the pump wave, the frequency response of the filter is tunable in a frequency range from ~2 to 20 GHz with out-of-band rejection of ~30 dB and -3 dB bandwidth of ~20 MHz. In addition, for any modulation format, it is converted to the single-sideband (SSB) modulation by the proposed filter. Therefore, the system is expected to be immune to the fiber dispersion-induced power fading. Moreover, it is independent of the modulation formats of the incoming signal wave. The filter structure can be inserted anywhere in conventional fiber-optic links without the need for modifying the link configuration and the transmitter.