Wavelength-independent all-fiber mode converters

We have used two different photonic crystal fiber (PCF) techniques to make all-fiber mode converters. An LP01 to LP11 mode converter was made by the ferrule technique on a drawing tower, and an LP01 to LP02 mode converter was made by controlled hole inflation of an existing PCF on a tapering rig. Both devices rely on adiabatic propagation rather than resonant coupling; so high extinction was achieved across a wide wavelength range.