Chip-Based Widely Tunable and Independently Switchable Multiple Narrow Bandpass Microwave Photonic Filters

Due to its uniqueness of simultaneously processing multiband radio frequency (RF) signals, multiband microwave photonic filters (MPFs) have attracted plenty of interest in multifunction radar and multiband-communication applications. In this article, we propose a chip-based widely tunable and independently switchable multiple narrow bandpass MPFs based on a tapped-delay-line structure. This multiband MPF is realized using an incoherent broadband optical source (BOS), an optical spectral shaper (OSS), a chirped waveguide grating (CWG), and a high-speed photodetector (PD). The OSS splits the broadband optical signal into multiple channels: one of the channels incorporates a high-speed phase modulator (PM) for microwave signal modulation; the other channels provide tunable time delays with respect to the PM channel. Thanks to multiple channels incorporation in the OSS, the resulting MPF has multiple passbands. The center frequency of each passband can be independently tuned by tuning the corresponding channel time delay, and the passband switchability can be implemented by controlling the insertion loss of each channel. As a proof of concept, a four-channel MPF is experimentally demonstrated with the use of a four-channel tunable optical delay lines (ODLs) chip. The proposed four-channel MPF exhibits a narrow 3-dB bandwidth of 156 MHz, a wide frequency tuning range up to 24 GHz, a high extinction ratio (ER) over 30 dB, and an independent channel switchability, which holds great potential in multifunction radar and multiband-communication applications.