Analysis of crosstalk drift and optimization of spatial light modulator based mode-selective multiplexers for multimode fibers.

Adaptive mode-selective multiplexers offer the potential to control the modal content within multimode fibers for space division multiplexing (SDM). To such an end, spatial light modulators allow programmable control over the phase, amplitude, and polarization of optical wavefronts. One of the major challenges is to precisely match the manipulated beam to the waveguide modes in the multimode fiber. Achieving precise alignment of optical components within the free space system is crucial for accurate mode multiplexing while active alignment may be necessary to overcome environment induced drift. In this paper, we investigate, through theory, simulations and experiments, the impact of misalignment errors in a free space telescopic Fourier system, including phase mask and lenses misposition and angular misalignment in fiber collimation. Mode multiplexing is achieved using phase holograms in the Fourier domain while mode demultiplexing is achieved through off-axis holography and Fourier domain processing. Furthermore, we analyze the crosstalk drift with time in SDM transmission over a 45 mode OM3 fiber. System stability is experimentally evaluated over a 9-hour transmission period.