Coherent addition of AlGaAs lasers using microlenses and diffractive coupling

A near single-lobed far-field pattern was obtained from coherent operation of a nonevanescently coupled AlGaAs laser diode array. A diffractive microlens array collimated the individual beams to approximate a plane wave, and diffractive coupling from an external cavity mirror provided mutual coherence. A diffraction-limited far-field pattern was observed with 82% of the power contained in the central lobe. The method is directly applicable to two-dimensional laser arrays and can be implemented as a single thin optical element.