We review the principles underpinning the Kramers-Kronig (KK) receiver operation and its various implementations. These include direct-detection based schemes, where the information-carrying signal is transmitted along with a CW field that is necessary for the implementation of the KK algorithm, as well as other schemes, where the CW is added at the receiver, owing to the availability of a local oscillator. Polarization-multiplexing with the KK receiver will also be discussed. Finally, an up-to-date review of the experimental implementations of KK transceiver solutions will be presented.
We discuss the modeling of linear and nonlinear propagation in multi-mode optical fibers in the context of
optical communications. A generalized Stokes space representation is introduced for handling multi-mode fiber
propagation in the presence of mode coupling. Using this formalism, we define the modal dispersion vector and
characterize its statistics. We also show that nonlinear propagation in the presence of random mode coupling is
described by coupled multi-component Manakov equations, giving rise to interesting new physical phenomena.