Abstract
In present day telecommunication systems the topical problem is protection of the subscribers' personal data against possible thefts and hacking fiber-optic information transmission guide lines, as this causes a number of dangerous situations and problems. The attackers, in spite of the legislative framework for the information protection, are still trying to read information from a fiber-optic transmission line (FOTL). This possibility arises due to incorrect installation and configuration of error protection, unauthorized access to information is possible. This article discusses two methods of detecting unauthorized admission (unauthorized access). The results of the study using an optical laser radiation source and power meter, as well as a YOKOGAWA optical reflectometer are presented. As a result, it was concluded that the method of preventing unauthorized access at the wavelength of 1625 nm can be used, since continuous FOTL monitoring will not interfere with the traffic.