Tunable photonic radiofrequency filter with complementary bandpass and bandstop responses

A photonic radiofrequency (RF) filter with two complementary bandpass and bandstop responses that is capable of simultaneously providing a single transmission channel at one port and a notch rejection channel at the other port is proposed. An integrated polarization division-multiplexing Mach-Zehnder modulator and the in-fiber stimulated Brillouin scattering effect are used to control the amplitudes and phases of the RF modulation sidebands along two orthogonal states of polarization to generate two complementary bandpass and bandstop responses at two output ports, respectively. Experiments are then performed. Two complementary responses are simultaneously generated in a high-frequency resolution of ∼20  MHz, with a rejection over 35 or 51 dB being achieved for the passband or stopband. A tunable central frequency to the bandpass and bandstop responses is also demonstrated within the range from 3 to 15 GHz.