Highly Reconfigurable Narrowband Microwave Photonic Filter Based on Chirp-Like Sliced ASE Source

Microwave filters are essential for front-end receivers in applications such as radar, radio over fiber (RoF), and sensing. However, conventional microwave filters implemented by electronic approaches face limitations such as susceptibility to electromagnetic interference (EMI), restricted tuning flexibility, and challenges at high frequencies, whereas microwave photonic filters (MPFs) offer a solution to those limitations. In this article, we use a chirp-like sliced amplified spontaneous emission (ASE) source to achieve an MPF that exhibits an ultranarrow bandwidth, wide frequency tunability, reliable frequency stability, and high reconfigurability. The ultranarrowband performance is achieved using a chirp-like sliced ASE source to compensate for the nonuniformity of the delay-line taps caused by third-order dispersion (TOD) in optical fibers. By chirping the sliced ASE source in the opposite direction of the TOD-induced chirp, we ensure uniformly spaced delay-line taps across a 40-nm ASE bandwidth when a 25-km single-mode fiber (SMF) is used, resulting in an ultranarrow passband of 43 MHz with the tuning range from 85 MHz to 9.4 GHz. In addition, our MPF exhibits excellent frequency stability, with frequency drifts remaining below 250 kHz at 9.4 GHz over 60 min. Finally, by incorporating a programmable optical filter, the system allows seamless switching between single-passband, dual-passband, and multipassband modes without altering the experimental setup. Each passband’s center frequency can be independently tuned while preserving ultranarrowband performance, demonstrating unprecedented levels of reconfigurability and versatility. We believe our proposed MPF will play a key role in modern radio frequency (RF) systems for next-generation radar and high data rate wireless communication.