Fibre optic communication systems have traditionally carried data using binary (on-off) encoding of the light amplitude. However, next generation systems will exploit both the amplitude and phase of the optical carrier to achieve higher spectral efficiencies and thus higher overall data capacities 1,2. Although this approach requires highly complex transmitters and receivers, the increased capacity and many further practical benefits that accrue from a full knowledge of the amplitude and phase of the optical-field 3 , more than outweigh this additional hardware complexity and can greatly simplify optical network design. However, use of the complex optical-field gives rise to a new dominant limitation to system performance, namely nonlinear phase noise 4,5. A device for removal of this noise therefore becomes of great technical importance. Here we report the development of the first practical ('black-box') all-optical regenerator capable of removing both phase and amplitude noise from binary phase-encoded optical communication signals.

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Abstract:We propose and demonstrate phase-sensitive amplification based on cascaded second harmonic generation and difference frequency generation within a periodically poled lithium niobate waveguide. Excellent agreement between our numerical simulations and proof-of-principle experiments using a 3-cm waveguide device operating at wavelengths around 1550 nm is obtained. Our experiments confirm the validity and practicality of the approach and illustrate the broad gain bandwidths achievable. Additional simulation results show that the maximum gain/attenuation factor increases quadratically with input pump power, reaching a value of ±19.0dB at input pump powers of 33 dBm for a 3 cmlong waveguide. Increased gains/reduced powers for a fixed gain could be achieved using longer crystals.

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