Spectral beam combining with volume Bragg gratings: Cross-talk analysis and optimization schemes

Abstract

Volume Bragg gratings (VBGs) have been recognized as critical elements in various types of beam-combining applications, such as, design of super-parallel holographic optical correlators, coherent power beam-combiners and couplers, and spectral beam combiners (SBC) in which the output beams from several distinct laser sources are combined into a single-aperture beam. The obvious advantage of VBG stems from extremely narrow spectral and/or angular selectivity compared, to any other surface grating. This feature of VBG enables combining of large number of laser beams within near-diffraction-limited divergence. The VBGs recorded in a photo-thermo-refractive (PTR) glass exhibit a long-term stability of all their parameters at total CW power at a multi-kilowatt level and have shown high-efficiency combining of high-power laser beams. In order to increase the spectral capacity of such a "beam-combiner", the overall loss resulting from absorption and cross-talk between channels should be minimized. This paper considers architecture-specific SBC scheme and addresses the cross-talk minimization problem based on optimal channel positioning. A mathematical model reveals the critical parameters for high efficiency spectral beam combining.