Automatic Monitor-Based Tuning of an RF Silicon Photonic 1X4 Asymmetric Binary Tree True-Time-Delay Beamforming Network

Abstract

Photonic beamforming networks are promising candidates to achieve power-efficient transmission in future cellular communication systems. However, sensitivity to process and temperature variations necessitates an automatic calibration solution to enable robust operation. This paper demonstrates fully automatic monitor-based tuning of an integrated optical ring resonator-based 1X4 asymmetric binary tree optical beamforming network (OBFN). The proposed monitor-based tuning algorithm compensates fabrication variations and thermal crosstalk by controlling micro-heaters individually using information from electrical monitors. This algorithm is demonstrated on an OBFN that operates at 30 GHz with 2 GHz bandwidth and is fabricated in a standard silicon photonics foundry process. Successful calibration of the OBFN from a severely degraded initial response to the well-defined group delay responses required for a targeted radiating angle over 60 $^{\circ }$ (−30 $^{\circ }$ to 30 $^{\circ }$ ) in a linear beamforming antenna array is achieved. This fully automatic tuning approach opens the possibility of employing silicon OBFNs in real wideband mm-wave wireless communication systems.