We demonstrate the coherent combining of three beams with a phase-locking controller using VLSI multi-dithering technique. Three fiber-coupled phase shifters are used to compensate phase distortions in the beam propagation path. The highest dither frequency in our system is ~70MHz. The achieved closed-loop compensation bandwidth of three beamlets is up to 100KHz.
Effective compensation of phase noise in laser communication calls for fast, real-time, adaptive wavefront control. We
present an analog, continuous-time, high-speed VLSI (Very Large Scale Integration) controller implementing multi-dithering
perturbative gradient descent optimization of a direct measure of optical performance. The system applies parallel
sinusoidal perturbations to the wavefront over a range of frequencies, and performs parallel synchronous detection of
the metric signal to derive the gradient components over each frequency band. The system operates over a wide range
of frequencies, supporting applications of model-free adaptive optics extending from compensation of slow atmospheric
turbulence to compensation of fast random phase fluctuations in the actuators and laser amplifiers. The system has been
tested as a phase controller for a multiple laser beam wavefront propagating through a highly turbulent medium. The results
indicate a compensation bandwidth exceeding 300 kHz matching the turbulence bandwidth.