CONFINEMENT AND MODAL GAIN IN DIELECTRIC WAVE-GUIDES

Two exact expressions are derived for the effective mode indices of di electric slab waveguides with complex refractive indices. One is for T E modes, the other for TRI modes. The identities are valid for any gui ded mode of any dielectric slab waveguide and can be succesfully emplo yed to check the accuracy of mode solvers. They explain why TE gain ca n be much greater than TM gain even when the confinement factors are c omparable. Also, it is shown that an often used approximation for the TM gain is unreliable under practical conditions. A correct approximat ion is given.