Mode conversion by phase filters in multimode dielectric waveguides

The different group velocities of the modes in multimode dielectric waveguides cause a spreading of transmitted signals. For a suitable mode conversion compensating the delay of the various modes to a great extent, a phase filter fixed in the cross-section of the guide half-way along its length is proposed. The theory of this method is discussed for plane symmetrical waveguides and waveguides with a quadratic cross-section. By means of a linear approximation of the dispersion relations the shape of the phase filters, their efficiency, and their influence on the pulse broadening are calculated.