BxGa1−xN layers as well as BxGa1−xN/GaN Distributed Bragg Reflector (DBR) structures were grown, for boron compositions between 0% and 1.3%, by Metal-Organic Vapour Phase Epitaxy. Refractive index, absorption coefficient and bandgap bowing of BxGa1−xN are extracted from a two-stage procedure based on spectroscopic ellipsometry and reflection measurements in the 250-850 nm range at room temperature. For all compositions of our BGaN alloys, we have obtained good agreement between experimental and simulated curves. It is shown that a large refractive index contrast between BGaN and GaN can be achieved for only 1% of boron. Moreover, the lattice mismatch between B0.01Ga0.99N and GaN is only 0.2%, which can lead to good structural quality of BGaN/GaN DBRs. Those properties can enable the development of innovative BGaN DBR technologies for Vertical Cavity Surface Emitting Lasers (VCSELs) in the blue-violet spectral range.