Secured fiber link system

A system for securing communication over an optical fiber, comprising:

• a transmit optical spatial coupler configured to couple a plurality of optical signals received by the transmit optical spatial coupler into respective ones of a plurality of spatial paths of an optical fiber, each of the spatial paths being able to carry an optical signal wherein at least one of the plurality of received optical signals is an optically modulated version of a desired sequence of information that is intended to be transferred over the optical fiber;
• and
• wherein at least one of the plurality of optical signals is an unmodulated optical chaff signal;
• further comprising an optical amplifier, wherein the transmit spatial coupler also couples to a respective one of the plurality of spatial paths of the optical fiber as one of the plurality of optical signals at least one other unmodulated optical chaff signal, wherein the unmodulated optical chaff signal and the at least one other unmodulated optical chaff signal are both derived from the output of the optical amplifier;
• wherein the unmodulated optical chaff signal and the at least one other unmodulated wherein the unmodulated optical chaff signal and the at least one other unmodulated optical chaff signal derived from the same optical amplifier are versions of the output of the optical amplifier that are temporally delayed relative to each other;
• whereby a tap along the fiber cannot determine the transmitted desired sequence of information.

A method for securing information transmitted over an optical fiber having a plurality of spatial paths, comprising:

• coupling each of a plurality of optical signals into at least a respective one of the plurality of spatial paths;
• wherein at least one of the plurality of optical signals is an optically modulated version of a desired sequence of information that is intended to be transferred over the optical fiber;
• wherein at least one of the plurality of optical signals is an unmodulated optical chaff signal;
• and
• wherein the optical fiber is a multi-core fiber having at least a first and a second core and wherein the optically modulated version of the desired sequence of information is coupled to the first core of the multi-core fiber and the optical chaff signal is coupled to the second core of the multi-core fiber, the first and second cores being independent cores running parallel to each other in the multicore-fiber, the multi-core fiber being arranged such that each of at least the first and second cores of the multi-core fiber are each an independent spatial path that each correspond to one of the respective spatial paths of the optical fiber and such that any signal supplied as a respective input to each respective one of the at least first and second cores of the multi-core fiber at a first end thereof arrive at a second corresponding end of each respective one of the at least first and second cores of the multi-core fiber independently in that there is substantially no coupling of signals carried by each of the at least two cores unless there is a tap of the fiber.

A method for securing information transmitted over an optical fiber having a plurality of spatial paths, comprising:

• coupling each of a plurality of optical signals into at least a respective one of the plurality of spatial paths;
• wherein at least one of the plurality of optical signals is an optically modulated version of a desired sequence of information that is intended to be transferred over the optical fiber;
• wherein at least one of the plurality of optical signals is an unmodulated optical chaff signal;
• and
• wherein at least two of the plurality of optical signals are unmodulated optical chaff signals each having a respective power, and wherein a combination of the optical powers of the at least two unmodulated optical chaff signals when coupled to their respective optical paths is such that at a tap at any point along the optical fiber a signal representing the optically modulated version of the desired sequence of information that is sufficiently strong to enable determination therefrom of the desired sequence of information cannot be obtained due to interference caused by the resultant presence of the unmodulated optical chaff signals at the tap point.

A terminal equipment for use in transmitting information over an optical fiber having a plurality of spatial paths each of which is able to carry an optical signal, comprising:

• an optical coupler configured to couple each of a plurality of optical signals into at least a respective one of the plurality of spatial paths, wherein at least one of the optical signals is an optically modulated version of a desired sequence of information that is intended to be transferred over the optical fiber and at least one of the optical signals is an unmodulated optical chaff signal;
• and
• a chaff signal generator supplying the unmodulated optical chaff signal to the optical coupler, the chaff signal generator configured to extract amplified spontaneous emission from an optical amplifier substantially within the bandwidth of the optically modulated version of the desired sequence of information;
• wherein the optical fiber is a multi-core fiber having at least a first and a second core and wherein the optically modulated version of the desired sequence of information is coupled by the optical coupler to the first core of the multi-core fiber and the at least one optical chaff signal is coupled to the second core of the multi-core fiber, the first and second cores being independent cores running parallel to each other in the multicore-fiber, the multi-core fiber being arranged such that each of the at least first and second cores of the multi-core fiber are each an independent spatial path that each correspond to one of the respective spatial paths of the optical fiber and such that any signal supplied as a respective input by the optical coupler to each respective one of the at least first and second cores of the multi-core fiber at a first end thereof proximal to the optical coupler arrive at a second corresponding end of each respective one of the at least first and second cores of the multi-core fiber distal to the optical coupler independently in that there is substantially no coupling of signals carried by each of the at least two cores unless there is a tap of the fiber.