Optical intrusion detection system using mode coupling

An optical intrusion detection system including a light source, an optical splitter for splitting light emitted from the light source and transmitted via an optical fiber, a plurality of detectors for detecting light power values split by the optical splitter, and a determiner for determining intrusion or non-intrusion by performing a predetermined operation on the output of each of the detectors. According to this system, light having mode coupling while traveling through a multi-mode optical fiber is split, and the split light power values are measured and compared to each other, so that a dynamic change of an optical signal and a static change in light loss due to the physical disturbance from an intruder can be simultaneously measured. Also, an optical splitter can be designed in consideration of the external environment.