Dual-wavelength photonic beamformer for OFDM and single-carrier broadband wireless operating over 1-km 7-core fiber fronthaul

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.