CWDM is based on the idea of low-cost optical components, without using optical amplifiers. Directly modulated lasers without temperature stabilization are used as light sources. The main application areas of this communication system are city networks. Tunable CWDM optical filter system can be used as a wavelength selective element, which allows quick transmission system parameter measurements on all channels with a single unit. These devices are chosen for the realization of an optical filter of the Fabry - Perot interferometer base with an external control unit. Tunable operation is performed with piezoelectric crystal that deforms by changing the voltage of the external control unit. Thus changing the distance between the semi-silver plated mirrors of FP filter and adjusting the filter parameters by wavelength.