Experimental measurements of the origin of self-phasing in passively coupled fiber lasers.

We have directly measured the intensity distribution, gain, and induced phase shift between two fiber lasers that are coherently combined by a Dammann grating. The induced phase shift between the lasers has been shown to approximately cancel out any applied phase error introduced into the cavity, allowing the combined resonator to operate at an efficient low-loss state. We show that the origin of this self-phasing stems from a redistribution of power between the two lasers.

Direct observation of Kramers-Kronig self-phasing in coherently combined fiber lasers.

A highly stable coherent beam-combining system has been designed to measure self-phasing in fiber lasers due to nonlinear effects. Whereas self-phasing in previous coherent combination experiments has been principally attributed to wavelength shifting, these wavelength effects have been efficiently suppressed in our experiment by using a dual-core fiber with closely balanced optical path lengths. The self-phasing from nonlinear effects could then be measured independently and directly by common-path interferometry with a probe laser.