Rugate notch filter fabricated by atomic layer deposition.

A Rugate notch filter is fabricated by atomic layer deposition. By regulating the thickness ratio of TiO2 and Al2O3 in a nanoscale layer, the refractive index is tailored between the refractive indices of the two materials. With the method of equivalent refractive index, the continuously variable refractive index of the designed Rugate filter is dispersed into several discrete ones, so that it can be realized by the refractive index tailoring. To coincide with the thickness, the nanoscale layer is iteratively deposited in the equivalent layer. The experimental reflectance matches the designed one well, and the average reflectance is 86.7% (510-590 nm).