This paper reports a dual-wavelength photonic beamformer implementing optical true time delay (OTTD) to realize microwave beam steering. The beamformer is capable of providing independent delay tuning to two separate beams modulated on different optical carriers. The integrated TTD chip includes a multiplexer that combines the two input wavelengths, an optical sideband filter (OSBF) and optical ring resonators (ORRs) that induce different optical delays. The ORRs are thermo-optically tuned to change the coupling ratio and obtain an incremental delay in each optical path. The experimental demonstration includes a full-compliant WiFi channel (at 5 GHz or 18 GHz RF bands) transmitted in one optical carrier and a WiMAX channel (at 5.4 GHz or 19 GHz RF) in another optical carrier operating in the resonance slope of the ORRs. The different antenna elements are connected with 1-km of 7-core fiber, achieving EVM-compliant levels at the antennas with beam-steering angles ranging from -40° to +80°. The performance comparison considering single-carrier broadband RF signals at the same frequency bands is also reported in this work.
This paper describes and evaluates experimentally a Si3N4 photonic chip based on optical ring resonators (ORRs) assisted by multi-core fiber (MCF) that enables radio beamsteering in 5G by the continuous tuning of the time delay applied to an antenna array. Each ORR includes two heaters: one for tuning the resonance wavelength and another to set the coupling coefficient. In this way, the configuration for beamsteering can be implemented by heater tuning or by wavelength shifting. Each optical path of the photonic chip comprises a thermally tunable optical side band filter (OSBF) and an ORR in cascade configuration. The output of each optical path is transmitted through a core of a MCF to distribute the modulated 5G signals to each array element at the transmitter antenna. This ensures that all the optical paths have the same length and enables the delay tuning of each array antenna element directly set from the photonic chip. Experimental demonstration is carried out with a four-core MCF with 26 GHz signals suitable for 5G transmission.