Optical Beamforming System Based on Polarization Manipulation With Amplitude-Phase Coupling Suppression

Traditional phased arrays based on phase shifters suffer severely from the beam-squint problem when operating at the wideband mode. Optical beamforming is one feasible solution for broadband beam steering, of which the performance, however, is affected by the amplitude-phase coupling. To solve this problem, we propose an optical beamforming system with amplitude-phase coupling suppression based on polarization manipulation. A polarization controller is used to control the transmission of carrier light along the fast or slow axis in the polarization-maintaining fiber. As there is a fixed transmission time difference between the two orthogonal modes, the phase adjustment can be achieved with low amplitude variation because of the low polarization-dependent loss. In addition, the intensity of the signal can be controlled using a polarizer with negligible phase variation, realizing amplitude control with low phase coupling. Experimental results show that the amplitude-phase coupling coefficient is about 5.8\times 10^{-3} ps/dB, while the phase-amplitude coupling is less than 7.5\times 10^{-3} dB/ps. The performance of the optical beamforming is analyzed by numerical simulation and proof-of-concept experiment, showing that the beam pointing deflection is less than 0.1°, while the main-lobe-to-sidelobe suppression ratio deteriorates less than 1 dB when the beam scans from 0° to 45°.