Time-varying Microwave Photonic Filter over 46-GHz Bandwidth with High Tuning Speed

Time-varying (TV) filters, with the ability to precisely process non-stationary high-speed microwave signals, are fundamental building blocks in wireless communications, Radar/Lidar systems, advanced metrology, etc. [1]–[3]. To date, it remains challenging to achieve time-varying microwave filters with fully reconfigurable spectral transfer functions, large tuning bandwidth (>10GHz), and high tuning speed (into the GHz range) simultaneously. This set of specifications are particularly interesting for applications in 5G/6G and cognitive communications. For example, digital TV filters can achieve hyperfine frequency resolution and high reconfigurability; however, their real-time processing bandwidth is inherently limited to below a few hundreds of MHz [4], [5]. Recently, significant efforts have been devoted to the development of TV microwave filters through the microwave photonics (MWP) approach, so-called MWP filters (MWPFs), as these have been shown to enable broad operation bandwidth, fast tuning speed and an important degree of flexibility. However, current TV MPFs still fall short of the set of specifications defined above, being particularly limited in regards to their versatility and tuning speed [6], [7]. For example, a notable level of reconfigurability can be achieved by cascading an optical frequency comb source and a programmable optical filter, but the reconfiguration speed is still limited by the tuning speed <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\sim$</tex> kHz) of the programmable optical filter [6]. On the other hand, a tuning speed of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sim 1$</tex> GHz has been demonstrated using other approaches, but in these solutions the degree of reconfigurability is still fairly limited [7].