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It is an effective approach to obtain high-power laser output by spectral beam combining (SBC) technologies. In this paper, a simple SBC system based on the superimposed reflective volume Bragg grating (RVBG) is proposed to reduce the scale of the SBC system. Considering the cross-coupling between the two gratings in a volume, two structure models of the superimposed RVBG-the superimposed RVBG with the same period and the superimposed RVBG with a different period-are analyzed and compared by using the rigorous coupled wave analysis, and their applications for SBC system are discussed. Numerical results show that the superimposed RVBG is easy to be fabricated and has the potential to combine multiple lasers with one volume. Cross-coupling can be neglected for the same period structure when the slant angle divergence is larger than 0.01 rad and for the different period structure when the spectral separation is larger than 1.0 nm. The superimposed RVBG with a different period can achieve high diffraction efficiency simultaneously for each grating with a small slant angle divergence, and is convenient to combine multiple beams with small spectral separation. The effect of wavelength shift on diffraction efficiency can be ignored.

A simple setup for radially polarized beam generation based on the reflecting volume phase grating is proposed to enhance the converting efficiency. The radially polarized beam is obtained by coherently combining the two orthogonally polarized Hermite-Gaussian HG0 1 and HG 10 beams. By using the plane wave decomposition and the three-dimensional rigorous coupled wave analysis approaches, the intensity distribution of the diffracted beam is compared with the respective incident beam. The intensity and the polarization angle divergence of the combined beam are analyzed. The results show that the intensity profile of the diffracted beam is not changed remarkably compared to that of the input beam. The radially polarized beam can be obtained with a converting efficiency of 99.93% and the degree of radial polarization approaches a unit at a given polarization angle divergence value of 1 deg when the central alignment divergence is smaller than 0.025 mm.