Optical Beamforming Network for Multi-Beam Operation With Continuous Angle Selection

We propose an optical beamforming network (OBFN) for multi-beam operation and continuous selection of the beam angles. The OBFN is based on the use of wavelength-division multiplexing elements for the generation and manipulation of the signals that correspond to different beams and different antenna elements (AEs), and on the use of optical delay lines for the introduction of tunable time delays to these signals. We analyze the operating principle of the proposed OBFN in the downlink and uplink directions of a wireless system, and we experimentally demonstrate its proof of concept in the downlink direction up to the photodetection stage, using a 2\times 4 setup based on commercial components. The implemented OBFN has the potential to support the steering of two beams and the excitation of four AEs. Using microwave signals with 15-GHz carrier frequency, high-order modulation formats, and symbol rates up to 1 Gbaud, we modulate two optical carriers and investigate the performance of the OBFN in four experimental cases, employing different combinations of signals, steering angles, and antenna excitation schemes. Through the analysis of the expected radiation pattern and off-line measurements of the BER of the decoded signals at the intended steering angles, we validate the feasibility of the proposed OBFN. The vision for actual implementations of the proposed OBFN would be enabled by means of photonic integration techniques.