The article “True Time Delay Optical Beamforming Network Based on Hybrid InP-Silicon Nitride Integration” written by Christos Tsokos, Efstathios Andrianopoulos, Adam Raptakis, Nikolaos Lyras, Lefteris Gounaridis, Panos Groumas, Roelof Bernardus Timens, Ilka Visscher, Robert Grootjans, Lennart S. Wevers, Dimitri Geskus, Edwin J. Klein, Hercules Avramopoulos, Rene G. Heideman, Christos Kouloumentas, Chris G. H. Roeloffzen demonstrate a broadband and continuously tunable 1×4 optical beamforming network (OBFN), based on the hybrid integration of indium phosphide (InP) components in the silicon nitride (Si3N4) platform is online!

The photonic integrated circuit (PIC) comprises a hybrid InP-Si3N4 external cavity laser, a pair of InP phase modulators, a Si3N4 optical single-sideband full carrier (SSBFC) filter followed by four tunable optical true time delay lines (OTTDLs), and four InP photodetectors. Each OTTDL consists of eight cascaded thermo-optical micro-ring resonators (MRRs) that impose tunable true time delay on the propagating optical signals. The OBFN-PIC is designed to facilitate the steering of a microwave signal with carrier frequency up to 40 GHz over a continuous set of beam angles. The authors evaluate the performance of the OBFN-PIC to handle and process microwave signals, measuring the link gain, the noise figure (NF), and the spurious-free dynamic range (SFDR) parameters. Moreover, they assess its beamforming capabilities assuming that the OBFN-PIC is part of a wireless system operating in the downlink direction and feeds a multi-element antenna array. Using microwave signals at 5 and 10 GHz with quadrature amplitude modulation (QAM) formats at 500 Mbaud, they evaluate the performance of the OBFN-PIC under various configurations. The authors show that error-free performance can be achieved at both operating frequencies and for all the investigated beam angles ranging from 45 to 135, thus validating its potential for high-quality beamforming performance.

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