Performance of Antireflection Coatings Consisting of Multiple Discrete Layers and Comparison with Continuously Graded Antireflection Coatings

The performance of discrete multilayer and continuously graded antireflection coatings for omnidirectional broadband applications are compared. It is shown that in practical cases where refractive index choices are constrained, discrete antireflection coatings can surpass the performance of continuously graded coatings by taking advantage of interference effects, which continuously graded coatings are expressly designed to avoid. A four-layer antireflection coating designed using a genetic algorithm is fabricated, and is experimentally shown to have reflectivity lower than what is achievable for continuously graded designs.