Optical engineering?What is fish windows,and Refractive index?

I would like to talk about optical engineering before writing about fish windows, refractive index.
History of light physics.
Newton explained that light is a kind of particle and that it goes straight because power is applied. The person named Huygens took the idea of a secondary source to explain the straightness of light. In addition, Young's interference experiment in the 19th century made it decisive that light was a wave. . .
References The best in optical engineering
Technical critic Japan
Will be continue...