The invention relates to a system and a method for transmission over optical fiber (130) with mode or core scrambling. The system comprises a spatio-temporal encoder (110) and a plurality of modulators (125.sub.1, . . . , 125.sub.n) associated, respectively, with separate propagation modes or cores of said fiber, each modulator modulating a laser beam. Said fiber comprises a plurality of slices (130.sub.1, . . . , 130.sub.L), an amplifier (140.sup.l) being provided between any two consecutive slices of the optical fiber. A mode scrambler (150.sup.l) is associated with each amplifier in order to perform a permutation of said modes between at least two consecutive slices.

A quantum key generation system including two photon detector units, two photon entanglement chains extending between the two photon detector units, and a plurality of multicore fiber links each including at least two non-uniform cores structurally configured to provide non-uniform photon propagation delay. Each photon entanglement chain includes at least one quantum repeater structurally configured to entangle a pair of photons and first and second terminating quantum memories optically coupled the quantum repeater using the multicore fiber links such that photons received by the first and the second terminating quantum memories are entangled with photons entangled by the quantum repeater. The first and second terminating quantum memories of each of the two photon entanglement chains form first and second cross-chain quantum repeaters, and the first and the second photon detector units are structurally configured to receive the measurable entangled particles generated by the first and second cross-chain quantum repeaters, respectively.

A method and system for distributed spatial mode processing is disclosed. A number of optical signals are received over an optical link. Each optical signal is received via a respective one of a number of spatial modes of the optical link. The optical link includes a particular spatial mode not used for the receiving. A first one of the number of optical signals received from a first one of the number of spatial modes is transferred to a second one of the number of spatial modes via the particular spatial mode, wherein the first one of the number of optical signals is transmitted via the second one of the number of spatial modes.

A method for transmitting optical signals over multiple channels is provided, the method including: coding tributaries of data to be transmitted; firstly rearranging the coded tributaries, thereby scrambling the data among the coded tributaries and outputting rearranged coded tributaries; modulating optical carriers with data from one of the coded tributaries, creating modulated optical signals; transmitting the modulated optical signals; spatially multiplexing the modulated optical signals into spatially multiplexed channels; converting the spatially multiplexed optical signals into individual optical signals; receiving the individual optical signals through the multiple channels; demodulating the individual optical signals into electrical signals; decoding the electrical signals into decoded tributaries; and secondly rearranging the decoded of tributaries to recover the tributaries of data before step, wherein, a number of tributaries of data is equal to or more than two and is less than or equal to a number of the multiple channels.

The invention relates to an optical fiber comprising an optical core and an optical cladding surrounding the optical core, the optical core having a single graded-index profile with 1, and the optical core having a radius R1 and a maximal refractive index n.sub.0, said optical cladding having a refractive index n.sub.Cl. Said optical cladding comprises a region of depressed refractive index n.sub.trench, having an inner radius R.sub.2, with R.sub.2R.sub.1, and an outer radius R3, with R3>R2. According to embodiments of the invention, the -value of said graded index profile and the optical core radius R.sub.1 are chosen such that R.sub.113.5 m and so as to satisfy a criterion C of quality. Thus, the invention provides a few-mode optical fiber, which allow guiding an increased number of LP modes as compared to prior art FMFs, while reaching the lowest Differential Mode Group Delay. The system reach is thus increased over prior art.

A system, for example an optical communication system, includes an optical transmitter. The transmitter is configured to direct towards an optical fiber a spatially multiplexed optical signal. The optical fiber is configured to convey data via the multiplexed optical signal from the transmitter to a receiver. The transmitter is configured to set a signal-to-noise ratio (SNR) or a transmission capacity of the multiplexed optical signal to achieve a predetermined secrecy capacity of the transmission.

A method and system for distributed spatial mode processing is disclosed a number of optical signals are received over an optical link. Each optical signal is received via a respective one of a number of spatial modes of the optical link. The optical link includes a particular spatial mode not used for the receiving. A first one of the number of optical signals received from a first one of the number of spatial modes is transferred to a second one of the number of spatial modes via the particular spatial mode, wherein the first one of the number of optical signals is transmitted via the second one of the number of spatial modes.

This spatial division multiplexing (SDM) in power-limited optical communication systems. In general, an SDM optical transmission system may be configured to increase data capacity over the data capacity of a non-SDM optical transmission system while maintaining power consumption at or below that of the existing non-SDM optical transmission system. To realize such an improvement in performance without increasing power consumption, an example SDM optical transmission may be constructed by reducing system bandwidth, reducing and/or altering equipment for filtering, reducing optical amplifier spacing, reducing operational amplifier power consumption, etc. In this manner, increased data transmission performance may be realized even where available power may be strictly limited.

A method for securing communication over an optical fiber, comprising: supplying an optically modulated version of a desired sequence of information that is intended to be transferred over a multicore optical fiber to a first core of the multicore optical fiber; and supplying an unmodulated optical chaff signal to a second core of the multicore optical fiber that is spatially distinct from the first core; wherein the fiber is adapted to transport the optical chaff signal from a first end thereof to a second end thereof unmodified in the second core; and wherein the fiber is adapted to transport the optically modulated version of a desired sequence of information from the first end of the fiber to the second end of the fiber unmodified in the first core and independent of the chaff signal in the second core unless there is a tap of the fiber.

An MCF coupling device includes: a first MCF, a second MCF, and a third MCF, each of MCFs including cores; a first optical collimator that converts light output from cores included in the first MCF individually into collimated light and generates a group of light beams constituted of the collimated light; a first optical splitter that splits at least a part of the group of light beams, at a predetermined split ratio, in a first direction and in a second direction; a second optical collimator that couples each of beams of collimated light contained in the group of light beams being output in the first direction individually into cores in the second MCF; and a third optical collimator that couples each of beams of collimated light contained in the group of light beams being output in the second direction individually into cores in the third MCF.