Phase-Locked Fiber Laser Array

We present a rugged method for controlling the phase of multiple, continuous wave (cw) laser beams using a compact device for coherent addition of radiation. The concept employs an array of electro-optically controlled waveguides in Potassium Titanyl Phosphate (KTP). The phase of each beam is controlled by altering the index of refraction of each waveguide in the array with an individually addressable voltage. A fiber array containing 16 single mode fibers is aligned to an array of KTP waveguides with an average coupling efficiency of 50%. Pi phase shifts are achieved with voltages as low as 30V. This technique provides a direct path to adding up an arbitrary number of low power fiber lasers and/or fiber amplifiers to obtain a high-power output. Furthermore, KTP is transparent from 350nm to 4500nm, so the device will work with many different kinds of lasers. --Original contains color plates: All DTIC reproductions will be in black and white.