all-optically mode conversion of beams carrying orbital angular momentum using 2d multi-mode interference coupler

In this work, a two dimensional multimode interference (2d mmi) coupler for switching between orbital angular momentum (oam) modes with opposite topological charge of l=+-1 has been designed. the proposed device consists of two mmi waveguides and four intermediate ports including two linear waveguides and two tapering phase shifters. input oam mode is decomposed into four field patterns at up, down, right and left sides of the end of the first mmi waveguide. up and down field patterns are related to the real part of the input oam mode and sided field patterns are related to its imaginary part. based on the fact that oam modes with opposite topological charges have π phase difference in imaginary parts and identical real parts, the phase shifters are controlled by the waveguide width at the end of the first mmi waveguide in such a way to apply π phase shift between the sided output field patterns. following the intermediate ports, second mmi waveguide manipulates the field patterns in order to provide the output oam mode with topological charge opposite to the input one.

All-optically mode conversion of beams carrying orbital angular momentum using 2D multi-mode interference coupler

In this work, a two dimensional multimode interference (2D MMI) coupler for switching between orbital angular momentum (OAM) modes with opposite topological charge of l=+-1 has been designed. The proposed device consists of two MMI waveguides and four intermediate ports including two linear waveguides and two tapering phase shifters. Input OAM mode is decomposed into four field patterns at up, down, right and left sides of the end of the first MMI waveguide. Up and down field patterns are related to the real part of the input OAM mode and sided field patterns are related to its imaginary part. Based on the fact that OAM modes with opposite topological charges have π phase difference in imaginary parts and identical real parts, the phase shifters are controlled by the waveguide width at the end of the first MMI waveguide in such a way to apply π phase shift between the sided output field patterns. Following the intermediate ports, second MMI waveguide manipulates the field patterns in order to provide the output OAM mode with topological charge opposite to the input one.