A waveguide includes a pair of complementary surfaces arranged to provide waveguiding therebetween. A first surface of the pair of complementary surfaces includes a plurality of first layers and a plurality of second layers. Each first layer includes a first dielectric. Each second layer includes a second dielectric. Each first and second layer has a first end and a second end. A percentage change in the thickness of each layer from the first end to the second end of that layer has one of a plurality of discrete allowable values. The total number of first and second layers is greater than the total number of discrete allowable values. A difference in refractive index between the first dielectric and second dielectric is greater than 0.4.