Narrowband ultrasonic phased array control using a photonic beamformer

A novel narrowband photonic beamformer for ultrasonic phased array control is proposed and demonstrated. The dual Bragg cell in-line optical design allows for the use of radio frequency Bragg cells for stable low frequency (DC-15 MHz) signal generation for driving ultrasonic arrays. Two tiny stamp size nematic liquid crystal devices provide the sites for signal phase (0-2π) and amplitude control. The proof-of-principle beamformer demonstrated 0-2π phase control and 55.8 dB gain control for a 10 MHz output signal that showed a carrier-to-noise ratio of 108 dB Hz^-1 at + 100 kHz offset. Both continuous and pulsed mode beamformer operation are demonstrated. Features of the photonic beamformer include analog control, wide tuning range, fiber remoting, size/weight advantages, and low control power operation.