A tunable photonic microwave notch filter with a negative coefficient using nonlinear behavior of a reflective semiconductor optical amplifier

ABSTRACT We propose and experimentally demonstrate a simple tunable photonic microwave notch filter with positive and negative coefficients. The negative coefficient is obtained from a single input signal (positive coefficient) using cross gain modulation (XGM) in a reflective semiconductor optical amplifier (RSOA). When the RSOA is operated in the saturated region, the signal carried on the pump wavelength is inversely copied to the probe wavelength by the XGM effect, showing a negative coefficient. This probe wavelength is easily generated by self‐injection locking the RSOA through a wavelength‐selective filter. Further, variable time delay for filter tuning is achieved using wavelength‐dependent time delay in a fiber medium by changing the Bragg wavelength of the fiber Bragg grating. The proposed microwave notch filter shows notch dips of more than 33 dB and has a tuning range from 828 to 905 MHz in a free spectral range with a wavelength change of 0.6 nm. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1328–1331, 2014