Coherent combination of fiber lasers using heterodyne method

The coherent combination system of two fiber lasers based on heterodyne method has been constructed using a 1064 nm, 1 W seed laser. In this system, two graded index (GRIN) lenses with polarization maintaining (PM) fiber is used to receive interference signals for getting better high-contrast strips, compared with interference signals directly received by detectors. The phase noise is studied, and the influence of phase noise on phase control precision is discussed. The phase noise is found to result from electrical crosstalk and environmental perturbation. When the phase noise bandwidth increases, the phase control precision drops. The ways to improve phase control precision are shown. When the phase of two fiber lasers is locked in the experiment, the power in the bucket(PIB) is 21.3%, the Strehl ratio is 79%, and the phase control precision is 0.008.