NARROW-BAND ULTRASONIC PHASED-ARRAY CONTROL USING A PHOTONIC BEAMFORMER

A novel narrowband photonic beamformer for ultrasonic phased array con trol is proposed and demonstrated. The dual Bragg cell in-line optical design allows for the use of radio frequency Bragg cells for stable l ow frequency (DC-15 MHz) signal generation for driving ultrasonic arra ys. Two tiny stamp size nematic liquid crystal devices provide the sit es for signal phase (0-2 pi) and amplitude control. The proof-of-princ iple beamformer demonstrated 0-2 pi phase control and 55.8 dB gain con trol for a 10 MHz output signal that showed a carrier-to-noise ratio o f 108 dB Hz(-1) at +100 kHz offset. Both continuous and pulsed mode be amformer operation are demonstrated. Features of the photonic beamform er include analog control, wide tuning range, fiber remoting, size/wei ght advantages, and low control power operation.