Polarisation-independent, optical multiplexing and demultiplexing systems based on ferroelectric liquid crystal phase modulators for spatial mode division multiplexing and demultiplexing

A multimode reconfigurable optical spatial mode multiplexing system, the system comprising:

• a first optical path to carry a first input beam from a first optical input;
• a second optical path to carry a second input beam from a second optical input;
• a beam combiner to combine beams from said first and second optical paths and provide a combined beam optical output;
• wherein at least one of said first and second optical paths is a phase modulating optical path and comprises a polarisation-independent reconfigurable phase modulator to impose a controllable phase profile on an input beam in the phase modulating optical path to controllably convert a spatial mode order of the input beam from a lower order spatial mode to a higher order spatial mode;
• and
• further comprising a control input to control said polarisation-independent reconfigurable phase modulator to configure said controllable phase profile to alter said conversion of said spatial mode order of said input beam;
• wherein said first and second input beams are combined into a multiple spatial mode combined beam fibre optical output independent of a polarisation of said first and second input beams;
• wherein a number of spatial modes of said combined beam is controllable with said control input to increase a number of spatial modes in said combined beam to more than a number of spatial modes in either of said first and second input beams separately;
• wherein said polarisation-independent reconfigurable phase modulator comprises a ferroelectric liquid crystal (FLC) spatial light modulator (SLM);
• and
• wherein said ferroelectric liquid crystal (FLC) spatial light modulator (SLM) comprises exactly 4 pixels tiling an active area of the SLM, one in each quadrant of the modulator.