engleski

Comparison of gradient index and classical designs of a narrow band notch filter

Rugate structures, as well as gradient refractive index films in general, attract a lot of interest. The gradient index systems may provide advantages in both, optical performance and mechanical properties of the optical coatings. Rugates have shown to be specially interesting for design of notch filters. A lot of theoretical work on design of rugate filters has been done in the last decades. However, only few of the designs could be deposited, which is often caused by practical problems, e.g. preparing materials with the desired refractive index values. In this paper two different gradient refractive index designs are compared to a classical high-low stack. One gradient design is synthesized by an apodized sinusoidal structure that is approximated by homogeneous sublayers. The other one is based on an apodized sinusoidal structure as well, but it is approximated by a hybrid structure, i.e. a combination of linear gradient index ramps between the lowest and the highest refractive index applicable and homogeneous layers of high index values. The two gradient designs take into account the constraints posed by limitations of the real deposition systems. Both designs are compared to a classical high-low stack and the advantages and drawbacks of each approach are commented.

rugate filters; thin film design; gradient index; mixing layers; notch; band stop filters

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