Mumbai University > Electronics and telecommunication > Sem 7 > optical communication and networks

Marks: 08

Years: DEC 2015

Fabry-Perot Filters:

• A Fabry-Perot filter consists of the cavity formed by two highly reflective mirrors placed parallel to each other, as shown in Figure 4.9.

• This filter is also called a Fabry-Perot interferometer or etalon. The input light beam to the filter enters the first mirror at right angles to its surface. The output of the filter is the light beam leaving the second mirror.

Principle of Operation:

i. The principle of operation of the device is illustrated in Figure above. The input signal is incident on the left surface of the cavity.

ii. After one pass through the cavity, as shown in Figure 4.9, a part of the light leaves the cavity through the right facet and a part is reflected.

iii. A part of the reflected wave is again reflected by the left facet to the right facet. For those wavelengths for which the cavity length is an integral multiple of half the wavelength in the cavity—so that a round trip through the cavity is an integral multiple of the wavelength—all the light waves transmitted through the right facet add in phase. Such wavelengths are called the resonant wavelengths of the cavity.

iv. This is a classical device that has been used widely in interferometric applications. Fabry-Perot filters have been used for WDM applications in several optical network test beds.

v. There are better filters today, such as the thin-film resonant multicavity filter. These latter filters can be viewed as Fabry- Perot filters with wavelength-dependent mirror reflectivities.