a system is provided for conversion of a first electromagnetic field into a desired second electromagnetic field , for example for coupling modes between waveguides or into microstructured waveguides . the system includes a complex spatial electromagnetic field converter that is positioned for reception of at least a part of the first electromagnetic field and that is adapted for conversion of the received field into the desired electromagnetic field , and wherein at least one of the first and second fields matches a mode of a microstructured waveguide . an advantage of the system is that the full effect of an incident light beam may be utilized for exciting a desired complicated mode of a specific waveguide . another advantage is that the power of the incident beam may be coupled into one specific mode and not others , whereby a high mode suppression ratio may be achieved .