PZT-modulated coherent four-beam combination system with high-control bandwidth by using modified multi-dithering theory

A modified multi-dithering theory (M-LOCSET) with piezoelectric ceramic transducer (PZT) tubes as phase modulators is presented. It can overcome the insufficient bandwidth control of PZT tubes for combining beams, while highlighting the merits of the PZT tubes such as high-damage threshold, low loss, and low costs. To prove its reliability through experiments, four coherent fiber beams are combined through the M-LOCSET technique with PZT tubes, recording residual phase error of λ/24 at 100 Hz control bandwidth, which indicates that its control bandwidth is far higher than 100 Hz. To our knowledge, this is the first case to date of combining four coherent beams with PZT tubes as phase modulators and yielding such good results.