IMPLEMENTATION OF A NUMERICAL NEEDLE METHOD FOR THIN-FILM DESIGN

A variant of the powerful thin-film needle design technique, which was first described by Tikhonravov and his co-workers, is described. In t his method thin layers are introduced at optimum positions within the refractive-index profile of a given multilayer system. In the original method the optimum locations for the layer insertions are calculated analytically, whereas in this variant of the method they are determine d numerically. This approach, although somewhat slower, is very flexib le. With the numerical needle method it is easy to define a merit func tion that consists of quite complex spectral quantities, such as Commi ssion Internationale de 1'Eclairage color coordinates or custom spectr al properties that are defined at run time. In the program described, three different absorbing or nonabsorbing materials can be used for th e needle layers and one or more needles can be inserted into the syste m at any given time. Multilayer solutions can also be sought in which the system is defined in terms of repeating groups of layers. It is al so possible to calculate automatically a series of solutions to a part icular problem with increasing overall thicknesses or to perform simul taneous calculations on several different systems. Examples are given that illustrate these various points. (C) 1996 Optical Society of Amer ica