Excitation of a ridge waveguide by a normally incident light beam

The problem of excitation of a ridge waveguide by a normally incident light beam is solved. The intermode interaction is shown to have a considerable influence on the waveguide excitation process. The condition for the optimal excitation of a waveguide with a finite-length grating is derived. It is found that destructive interference of the excited modes, resulting in zero efficiency of the coupling of light into a waveguide, is possible in the case of a semi-infinite grating. The feasibility of waveguide excitation with a fairly high efficiency (24%) is demonstrated.