High-performance microwave photonic true time delays based on an integrated optical micro-comb source

Microwave photonic true time delay lines (TTDLs), which can introduce multiple progressive time delays, are one of the basic building blocks of microwave photonic systems. Offering intrinsically low loss, ultra-wide operation bandwidth, and strong immunity to electromagnetic interference, photonic TTDLs have wide applications for phased array antennas (PAAs), microwave photonic filters, analog-to digital or digital-to-analog conversion, and arbitrary waveform generation. Here, we demonstrate significantly improved performance of a microwave photonic TTDL based on optical micro-comb generated by an integrated microring resonator with a free spectral range (FSR) of ∼49 GHz, which performs as a highquality multi-wavelength source for the TTDL. The broadband (>100 nm) optical micro-comb achieved with a record low FSR of 49 GHz results in an unprecedented record high channel number (81 over the C band) the highest number of channels for an integrated comb source used for microwave photonic processing. As compared with conventional TTDLs implemented by discrete laser arrays, the system cost, size, and complexity of our TTDL can be significantly reduced. We investigate the performance of a phased array antenna based on our TTDL and show that the large channel count leads to a high angular resolution and wide tuning range of the beam steering angle. This demonstrates the feasibility of our approach as a competitive solution toward implementing integrated photonic true time delays in radar and communications systems.