US Patent 10031286 Waveguide structures in anisotropic lasing and nonlinear optical media

A laser or nonlinear optical waveguide is presented that is formed from a core anisotropic crystal sandwiched by a cladding of anisotropic crystals of the same material but slightly rotated optical axes. The core and cladding crystals can be cut from the same crystal boule and bonded without adhesives between them. Because the crystals are anisotropic, the core and slightly skewed cladding crystals exhibit different refractive indexes to a propagating light beam. The difference in refractive indexes should be ≥1.2×10−6 for mode confinement and 2d/λ*Sqrt(ncore2−nclad2)≤1.37 to achieve single mode operation in a square cross section, ≤1 for a planar cross section. Alternative embodiments use slightly different doping amounts in crystals to achieve the difference in refractive indexes between the core and cladding.