Abstract

The Needle method is currently one of the most powerful thin film design techniques. It exists in several versions described in the literature or implemented in thin film design programs.¹,²,³ This technique is an application to thin film design of some of the principles of optimal control theory. Thin layers of suitable refractive indices are inserted in a multilayer system, in appropriate positions, when no further progress be made by conventional refinement. Refinement of the modified system results in a better solution. The optimum needle positions are found by evaluating a perturbation function, which can be analytical or purely numerical. The analytical approach is more accurate and faster, while the numerical one is more flexible. Some implementations of the needle method use sophisticated second order optimization algorithms.

© 1998 Optical Society of America