There is provided a security system for use at an enclosure containing one or more passive components of an optical communication link. The security system comprises a sensor configured to detect a physical breach of the enclosure, and an optical alert signal generator coupled to the optical communication link. The optical alert signal generator is self-powered, and configured to generate an optical alert signal and transmit the optical alert signal through the optical communication link when a physical breach of the enclosure is detected by the sensor. The optical alert signal is detectable at an entity external to the enclosure and connected to the optical communication link.