O.A. Prokudin

Optical filters are used in communication lines. It allows to compensate disturbances that look like a signal. There are several methods of division and amplification of optical signals. The usage of thin lenses is the easiest method. For this method the width of transmission region depends on the thickness of a lens. It leads to great weakening of the signal. The method of phase contrast allows to filter the signal without weakening. In this method the energy of phase is transformed into the energy of amplitude. Such filter always works in one frequency domain. Method of changing the refraction ratio. The refraction ratio of a filter is changing under the influence of external electric field. It allows to realize reorganizing systems but the signal weakening in this case is stronger than using the method of phase contrast. The final choice of a method depends on conditions of its application and requirements of the device.