What is Fabry Perot Filter,Fabry Perot Interferometer,Fabry Perot Cavity

This page on Fabry Perot Filter vs Fabry Perot Interferometer vs Fabry Perot Cavity mentions functional difference between Fabry Perot Filter, Fabry Perot Interferometer and Fabry Perot Cavity used in fibre optic domain.

Optical device which passes certain wavelength of light and blocks certain wavelength of light is known as optical filter. Following are the useful terms related to optical filter:
Centre Wavelength: It is mean wavelength between two band edges.
Peak Wavelength:It is the wavelength at which filter attenuation is least.
Nominal Wavelength: This wavelength is intended by the manufacturer which is usually printed on the device. The real centre wavelength might be different.
Bandwidth: It is distance between filter edges at particular designated distance below the peak value.

Fabry Perot Filter,cavity,interferometer

Fabry Perot Cavity:
The space between the two mirrors as shown in the figure is referred as fabry perot cavity.

Fabry Perot Interferometer:
Any meter or instrument which uses interference patterns to perform accurate measurements of waves is referred as Interferometer. If the same function is performed with the arrangement of parallel mirrors as mentioned above for any optical application then it is referred as Fabry Perot Interferometer. In this interferometer mirrors can be moved in relation to each other. When the mirrors are fixed, it is referred as "Etalon".

Fabry Perot Filter

Fabry Perot Filter:
The optical filter having two parallel and partially silvered mirrors is known as Fabry Perot Filter.

The operation of Fabry Perot Filter is explained below:
• In this setup, light is directed from outside of one of the mirrors.
• Most of the lights are reflected at mirror-1 and some of the light components enter the cavity.
• When light components reach the opposite mirror-2, some passes out. Most of them are reflected back.
• If the cavity is set to the right size, interference patterns will develop. This will cause unwanted wavelengths to influence destructive interference. At the same time one wavelength is passed out and all others are strongly attenuated.

Following should be taken care during manufacturing of Fabry Perot filter:
• The reflecting surfaces should be extremely flat.
• It should be absolutely parallel.
• The glass surfaces are silvered such that it will create 99% reflective mirror.

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