Tuning Optimization of Ring Resonator Delays for Integrated Optical Beam Forming Networks

Comprehensive tuning optimization of an integrated optical ring resonator (ORR) based $1\times 4$ optical beam forming network (OBFN) for W-band millimeter wave (mmW) phased arrays is reported. The OBFN chip is implemented using a ultralow loss silicon nitride technology and a two stage binary tree topology. The delay responses of a single- and multiORR delay line were carefully measured, and the results agree well with a lossless theoretical model. Tuning of an ORR was calibrated and verification experiments were performed to verify the tuning accuracy. A flattened delay response for a 3-ORR delay line was achieved, demonstrating a bandwidth of $6\ \text{GHz}$ and dynamic tuning range of $209\ \text{ps}$ , which corresponds to a phase shift of $33.4\pi$ for an 80- $\text{GHz}$ signal. A larger bandwidth can be achieved by reducing the dynamic tuning range. The result is promising for high data rate mmW communications with beamforming.