Ultradense Bidirectional Optical Transmission

Present efforts towards construction of large capacity long -haul links are focused on either increase of channel data rate of introducing very dense channel plans. The latter is of particular interest since it enables spectrally efficient WDM links simply by multiplying the channel count of existing transmission lines. Unfortunately, very dense channel spacing necessarily leads to increased four-wave (FWM) mixing penalty. FWM penalty can be decreased in straightforward manner by lowering signal launch power. Indeed, high spectral efficiency optical link operating with 25GHz spaced signals has been recently demonstrated using hybrid Raman/EDFA amplificiation architecture: FWM process is minimized by operating in quasiliner transmission regime. A different approach that does not require deployment of Raman amplifiers relays on combining two closely spaced counterpropagating interleaved channel grids. Limiting design issues encountered in very dense bidirectional optical lines will be discussed. While bidirectional link potentially doubles deployed deployed capacity over single strand of fiber, its realization is made more difficult by host of fundamentally new problems, commonly not seen in conventional unidirectional lines. We described latest efforts in constructing very dense bidirectional long-haul links over standard and non-zero dispersion shifted fiber.