Waveguide characteristics of real optical strip waveguides

A study is reported of the influence of the parameters of real thin-film optical strip waveguides on their waveguide characteristics (propagation constants, localization of the mode field, etc.) allowing for the presence of transition layers in a transverse cross section of the base planar waveguide, for the real geometry of this section (which is nearly trapezoidal), and for the thickness of the guiding strip. Analytic expressions are obtained for the optical confinement coefficient and the effective mode format of a weakly guiding symmetric strip waveguide. It is shown that the coefficient representing the fundamental E₁₁^x(y) mode is practically independent of the relative thickness t/h (h is the thickness of the base planar waveguide) of the guiding strip provided t/h≥0.5. The corrections to the normalized effective refractive indices of the base planar and strip waveguides are found in order to allow for the real geometry and for the refractive index profile in the strip waveguide.