True Time Delay Optical Beamforming Network Based on Hybrid InP-Silicon
Nitride Integration
Abstract
We 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. 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. The
performance of the OBFN-PIC is experimentally characterized by measuring
the link gain, noise figure, and spurious free dynamic range of the
microwave photonics links. Moreover, we assess its beamforming
capabilities assuming that the OBFN-PIC is part of a wireless system
operating in the downlink direction and feeds a multielement antenna
array. Using microwave signals at 5 and 10 GHz with quadrature amplitude
modulation (QAM) formats at 500 Mbaud, we evaluate the performance of
the OBFN-PIC under various configurations. An error-free performance is
achieved for all the experimental cases validating the potential of the
proposed OBFN-PIC for high-quality beamforming performance. To our best
of knowledge, this is the first thorough performance evaluation of a
fully integrated OBFN-PIC.