Functional field transformation with irregular waveguide structures

We demonstrate functional field transformation in irregular waveguide structures having strong scatter from a stepped conducting wall geometry. The resulting degrees of freedom and significant evanescent field content make it possible to accomplish virtually perfect transformation in a distance of several wavelengths. A microwave experiment verifies frequency-dependent transformation, suggesting that wavelength division multiplexing based on this principle is possible. A mode-selective transformation, which exhibits disparate reflectivities for different modes at the same frequency, may find application in multimode laser cavities.