Abstract: Intrusion by climbing or jumping over a fence can be detected, and intrusion is detected in a wide area without large-scale equipment. FBGs (grating sections) of different types having different refractive indexes of fiber glass are arranged at predetermined intervals in a longitudinal direction of optical fibers 12, 13A, and 13B, the optical fibers are laid down between poles on the top of a fence or a side thereof, reflected waves from the FBGs are issued by photodetection devices 14, 15A, and 15B in response to an optical input to the optical fibers, and a wavelength shift detection device 16 detects a position of an FBG which exhibits a wavelength shift by swinging of the optical fibers by a stress acting on the fence.

Abstract: Intrusion by climbing or jumping over a fence can be detected, and intrusion is detected in a wide area without large-scale equipment. FGBs (grating sections) of different types having different refractive indexes of fiber glass are arranged at predetermined intervals in a longitudinal direction of optical fibers 12, 13A, and 13B, the optical fibers are laid down between poles on the top of a fence or a side thereof, reflected waves from the FBGs are issued by photodetection devices 14, 15A, and 15B in response to an optical input to the optical fibers, and a wavelength shift detection device 16 detects a position of an FBG which exhibits a wavelength shift by swinging of the optical fibers by a stress acting on the fence.

Abstract: A break-in detection system includes a detection sensor of an FBG type for detecting an intruder trying to climb over a fence around a premises, and a detection sensor of an OTDR type for detecting an intruder trying to demolish the fence. A fiber optic cable used as a detection sensor has a sensor core wire and a LAN transmission core wire arranged in parallel to form a LAN transmission channel. The LAN transmission core wire transmits videotaped image signals from ITV cameras and image control signals two ways between a monitoring room and an ITV control device. The LAN transmission channel is available for connection by IP telephone sets, a LAN terminal, a wireless LAN terminal, and an IP-BOX for internet communication. The system has excellent reliability and maintenance-free characteristics.

Abstract: The object of the invention is to provide a break-in detection system having excellent reliability and maintenance-free characteristics. The detection sensor 1 of FBG type detects an intruder trying to climb over the fence around premises. The detection sensor 2 of OTDR type detects an intruder trying to demolish the fence. A fiber optic cable used as a detection sensor has a sensor core wire and a LAN transmission core wire arranged in parallel to each other to form a LAN transmission channel. Said LAN transmission core wire is used to transmit videotaped image signals from ITV cameras 8 and image control signals two ways between the monitoring room 3 and the ITV control device 6. Said LAN transmission channel is available for connection by IP telephone sets 11, a LAN terminal 12, a wireless LAN terminal 14 and IP-BOX 15 for internet communication.

Abstract: In an unshielded twisted pair cable, a predetermined number of pairs which are twisted by a predetermined lay-length are covered by a protective sheath. Insulations for insulating conductors for the pairs and the protective sheath are wholly or partially of halogen free polymer having a low dielectric loss tangent and flame-retarding properties. The insulations have a dielectric loss tangent of less than 1.times.10.sup.-2 at 150 MHz and a 2% modulus of at least 0.3 kgf/mm.sup.2.