An optical beam-forming chip based on switchable delay lines for Ka-band phased array

Abstract

A 1×4 optical beamforming chip with four channels of silicon switchable delay lines designed to control the Ka-band (40 GHz) phased antenna arrays is proposed. Each switchable delay line unit, which is composed of six optical switches and five waveguide delay lines with different lengths is used to control the delay of microwave signal transmitted to or received from a single sub-antenna in a phased antenna array. And for each delay line unit, 32 stages of discrete delays with a time step size of 2.95ps/stage were designed in order to achieve seven beam steering angles. We have fabricated the four-channel optical delay lines and measured the delay states of each channel. And the measured delay increment is about 3.02ps/stage, which is larger than the designed value mainly due to the fabrication tolerances. In addition, based on the measured delay times, the directional diagram of the optical beamforming network was simulated and the result shows the small delay time deviation between the measured and designed values has little impact on the performance of the optical beamforming network. Furthermore, a beam combining experiment is carried out to evaluate the performances of the optical true time delay channels experimentally, and the results agree well with the designed requirements.