title: Coherent coupling of vertical-cavity surface-emitting laser arrays and efficient beam combining by diffractive optical elements: concept and experimental verification.
abstract: A phase-locked diode-laser system based on master-slave coupling of two-dimensional vertical-cavity surface-emitting laser (VCSEL) arrays by injection locking is presented. Frequencies and phases are adjusted by laser-trimmed microresistors. Additional beam-transformation optics consisting of two diffractive optical elements (DOEs) and a Fourier lens concentrates most of the far-field power in a nearly diffraction-limited beam. Both the VCSEL array and the microlens array are monolithically integrated and mounted in a compact module. With an array of 21 slave lasers a system coherence of 95% (for several hours) and of nearly 90% (for several months) has been demonstrated without any active phase control. The scalability of the output power has been verified by locking of an array of 77 slave lasers with a system coherence of 78%. The optical system efficiency is 20-23%; with beam-transformation optics this efficiency could be improved to 44%.
authors.affiliation: Institut für Technische Physik, Deutsches Zentrum für Luft-und Raumfahrt e.V., Pfaffenwaldring 38-40, 70569 Stuttgart, Germany.
authors.forename: Guido
authors.initials: G
authors.lastname: Hergenhan
authors.forename: Bernd
authors.initials: B
authors.lastname: Lücke
authors.forename: Uwe
authors.initials: U
authors.lastname: Brauch