External cavity phase-locked semiconductor tapered lasers

This work relates to combining a phase corrected array of tapered laser diodes, emitting at lambda = 975 nm, coherently using the Talbot effect. Diffractive coupling of semiconductor lasers by use of the Talbot effect provides a means for coherent beam addition of multiple elements in laser diode arrays and makes possible a very compact external cavity. We have used, in this work, fully index guided tapered laser diodes. They contain a ridge waveguide, which acts as a modal filter, and a tapered section of increasing width, which provides high power. We have realized arrays of several emitters (N=10), which are not optically coupled to each other. First, to improve the beam quality of the array, a phase correcting micro system, achieving collimation in the fast axis, correction of the wave front tilts in both directions and also a slow axis collimation, was added. The FWHM divergences of the array were reduced from 34 degrees to 0.17 degrees in the fast-axis and from 3.5 degrees to 0.7 degrees in the slow-axis at 6A, 3.7 W. Then, to be close to diffraction limit, we have combined this corrected array coherently using the Talbot effect. We have obtained quasi-monolobe slow axis far field profile for the in phase mode with a central peak divergence of only 0.27 degrees at 1.5 A, 315 mW under CW operation and of only 0.20 degrees at 2.5 A, 787 mW under pulsed operation.