A beam displacer is a rectangular slab made of a birefringent crystal material. The beam displacer exhibits large birefringence when the incidence angle of the light is 0 degrees; it can split an unpolarized light beam into two orthogonally polarized, parallel beams at a certain spacing. The most widely used materials for beam displacers are yttrium vanadate (YVO4) crystal, barium borate (α-BBO) crystal, calcite crystal, and rutile crystal. Due to the good thermal and mechanical properties and large birefringence of YVO4, it is the most widely used material for beam displacers. It can be used to produce ﬁber-optic devices such as circulators, WSS, interleavers, and high-power isolators for ﬁber lasers.