Photonic Lantern Based Spatial Mode Multiplexer and Mode Equalizer

Abstract: The ever increasing demand for high capacity has led to the simultaneous implementation of dense wavelenght division multiplexing (DVDM), polarization multiplexing and higher order modulation formats. Nevertheless, studies show that the single mode fiber (SMF) capacity is fast approaching the theoretical capacity limit imposed by the Shannon's information theory and nonlinear fiber effects. This calls for an alternative dimension to be explored to increase the capacity of SMF, which is space. Space division Multiplexing (SDM) happens to be the solution.

Mode multiplexing (MDM) ystems perform SDM. Usually MDM De/MUX approaches are based on beam optics, which uses mode splitters, combiners and mode converters. Due to lack of scalability and splitting and combining losses of the system De/MUX, alternative approaches, namely waveguide couplers, fiber butt coupling structures and fused fiber power dvidier are being used.

This thesis deals with the use of Phtonic lantern (PL), which is a type of fused fiber power divider as a mode converter. The purpose of this study is to optimize the waveguide separation function in order to minimize the cross coupling between the modes and estimating the length of the lantern for minimum crosstalk using coupled mode theory. Also the PL performance is computed in terms of the overall crosstalk between input MMF modes and output SMF modes using transfer matrix model. As a final step, optical MIMO equalizer filter with directional couplers design is discussed.