Compact prisms for polarisation splitting of fibre laser beams

Simple compact monoprisms for spatial splitting of polarised laser beams with relatively small diameters (no more than 1 mm) are considered. Prisms can be made of optically inactive CaCO₃, α-BaB₂O₄ (α-BBO), LiIO₃, LiNbO₃, YVO₄, and TiO₂ crystals known in polarisation optics. The exact solution of the Snell equation for the extraordinary wave reflected from a surface arbitrarily tilted to its wave vector is obtained. The analysis of variants of the solution allows the fabrication of prisms with any deviation angles of the extraordinary wave by preserving the propagation direction of the ordinary wave. Three variants of prisms are considered: with minimised dimensions, with the Brewster output of the extraordinary beam, and with the deviation of the extraordinary wave by 90°. Calcite prisms with the deviation angles for the extraordinary beam ~19° and 90° are tested experimentally.