Fabry - Perot Etalon

Fabry - Perot Etalon is an optical device that uses multiple beam interference between two parallel reflecting surface (mirrors) and its resulting optical transmission is parodic in wavelength. In other words, an etalon is narrow band wavelength filter. It consists of two glass plates (coated with thin aluminum films of an optically polished N-B K7 substrates.) separated by small fixed distance. The reflecting surface are kept inside an assembly to form an Etalon.