Multi-Beamforming Provided by Dual-Wavelength True Time Delay PIC and Multicore Fiber

This paper presents a multi-beamformer based on a dual-wavelength photonic integrated circuit (PIC) and multicore fiber (MCF) capable of providing independent delay tuning to two separate beams modulated on different optical carriers. This implementation enables a centralized control of the photonic beamformer, connecting each element of a phase array antenna with a dedicated core of a MCF link and controlling the induced delay (resulting steering angle) by thermo-optically adjusting the heaters of the PIC. The dual-wavelength PIC implements true time delay (TTD) based on optical ring resonators (ORRs). Six different ORR heaters' configurations are evaluated experimentally, obtaining an induced delay of up to 328 ps at 19 GHz RF. With a measured delay resolution of 4 ps, it is recommended to increase/decrease the delay in small steps (between 10 and 30 ps) in order to keep the switching time in the ms range. Higher delays increments can be induced within longer switching time, e.g. 328 ps requires 1.68 s to stabilize the heaters. The performance demonstration includes the dual-wavelength transmission over 1-km of 7-core MCF and evaluates single-carrier data signals in the K-band centered in 19 GHz RF with up to 4 GHz bandwidth (BW). Operation with OFDM standard WiFi and WiMAX signals is also demonstrated experimentally. A delay of 328 ps can be induced to data signals at 19 GHz RF with up to 3-GHz BW, while 4-GHz BW signals can operate with up to 166 ps delay increment. An almost constant EVM is obtained for each BW below 3 GHz, confirming that changing the beam-steering angle does not affect the quality of the signal.