Intrusion detection system for use on an optical fiber using a translator of transmitted data for optimum monitoring conditions

A method for monitoring movement of a fiber indicative of potential intrusion in an optical transmission system having an optical transmitter for transmitting intelligence from a source through the system at a first optical wavelength and an optical receiver for receiving the intelligence at the first optical wavelength, the method comprising:

• providing an optical fiber for monitoring having a first and second ends;
• detecting movement of the fiber along the length thereof by:
• injecting light pulses into one end of the optical fiber;
• detecting at a position on the fiber a series of received light signals which have been transmitted along the fiber as a result of the injected light pulses;
• comparing at least some of the received light signals relative to data obtained from previously received ones of the received light signals to detect changes in the received light signals relative to the previously received light signals;
• analyzing the changes to determine any changes which are indicative of movement of the optical fiber causing at a portion thereof along the length thereof;
• and generating an alarm in response to the detection of any such changes which are indicative of movement;
• wherein there is provided a translator which receives the intelligence from the optical transmitter at the first wavelength and which translates the intelligence into the light pulses which are transmitted along the optical fiber at a second wavelength which is different from the first wavelength and is optimized for injection into the optical fiber such that the received light signals are optimized for monitoring of movement of the optical fiber;
• and
• wherein the fiber to be monitored is a multi-mode fiber and the translator provides an offset launch of the signals which are offset from the center of a core of the multi-mode optical fiber so as to establish a non-uniform mode field power distribution in the optical fiber.

A method for monitoring movement of a fiber indicative of potential intrusion in an optical transmission system having an optical transmitter for transmitting intelligence from a source through the system and an optical receiver for receiving the intelligence, the method comprising:

• providing an optical fiber for monitoring having first and second ends;
• detecting movement of the fiber along the length thereof by:
• injecting light pulses into one end of the optical fiber;
• detecting at a position on the fiber a series of received light signals which have been transmitted along the fiber as a result of the injected light pulses;
• comparing at least some of the received light signals relative to data obtained from previously received ones of the received light signals to detect changes in the received light signals relative to the previously received light signals;
• analyzing the changes to determine any changes which are indicative of movement of the optical fiber causing at a portion thereof along the length thereof;
• and generating an alarm in response to the detection of any such changes which are indicative of movement;
• wherein there is provided a translator which receives the intelligence from the optical transmitter and which translates the intelligence into the light pulses which are transmitted along the optical fiber and are optimized for monitoring of movement of the optical fiber;
• and
• wherein there is provided a second translator at the second end which is symmetrical to the translator and translates the received light pulses signals back to a signal compatible with the optical receiver.