Comparison of spectral beam combining based on reflecting volume Bragg grating, with and without collimating lenses

Abstract

On the basis of the principle of spectral beam combining (SBC), a simple combining system using a reflecting volume Bragg grating as a combiner was designed in which two focusing lenses were used to control the incident angles of input beams, and two concave lenses were used to solve the problem of beam divergence caused by focusing lenses. The effects of the beam divergence angle (DA) on diffraction efficiency and beam quality were analyzed theoretically. The simulation results showed that a larger DA will reduce diffraction efficiency and lead to deterioration of beam quality. In the SBC experiment, the performances of the output beam with and without concave lenses were compared. The experimental results showed that, when the concave lenses were not inserted, the measured output power was 503 mW with a combining efficiency of 85.3% and the beam quality factor of 1.68. The experiment further showed that the combined power was 566 mW with a combining efficiency of 96% and a beam quality factor of 1.31 when concave lenses were used.