US Patent 11148321 Polycrystalline waveguide

A waveguide includes a body of material having a width, a thickness, and a length, where the width is orthogonal to the thickness, and the length is orthogonal to the thickness and the width. The material includes polycrystalline ceramic that is transmissive such that the body is configured as a waveguide. The thickness is no more than 5 millimeters and at least 20 nanometers, the width is greater than or equal to the thickness, and the length is at least 100 times greater than the width. The body of material has a granular profile such that grains of the material protrude generally outward from a surface of the body with a height of at least 25 nanometers and no more than 100 micrometers relative to recessed portions of the surface of the body at boundaries between the grains.