Wavelength insensitive three-mode directional coupler designed by wavefront matching method for broadband mode-dependent-loss equalizer

A wavelength insensitive three-mode directional coupler for mode-dependent-loss (MDL) equalizer is proposed. By using powerful optimization method, the waveguide geometry is automatically obtained, and designed device exhibits almost wavelength independent operation. The proposed device is useful for constructing broadband MDL equalizer used in multiple-input-multipleoutput signal processing in mode-division-multiplexing transmission.