Patent ID: 8436732

Claim:
A perimeter security system, comprising: a sensing optical fiber for laying out tautly at the perimeter of an area to be secured, the sensing optical fiber having a proximal end and a distal end, the distal end of the sensing optical fiber having an optical termination for quenching reflections from the distal end of the sensing optical fiber, the sensing optical fiber having along its length at least one sensing Fiber Bragg Grating (FBG) having a center wavelength of reflection λ S ; a source of broadband optical power and means for launching the broadband optical power into the proximal end of the sensing optical fiber, the sensing FBG for reflecting narrowband optical power having a center wavelength λ S back to the proximal end of the sensing optical fiber; whereby stretching the sensing optical fiber and hence stretching the sensing FBG causes the center wavelength λ S of the reflected narrowband optical power back to the proximal end of the stretched sensing optical fiber to shift towards longer wavelengths; at least one trip wire having one end attached to the sensing optical fiber along the length of the sensing optical fiber, the other end of the trip wire for attaching to the ground of the area to be secured; and receiving and detecting means responsive to the reflected narrowband optical power having the shifted center wavelength; so that the perimeter security system is responsive to an intrusion into the area to be secured causing the stretch of the sensing optical fiber.