couple mode theory

(a) The 3D structural dimensions, refractive index distribution, and related parameters of the linear taper. (b) The corresponding 3D structure and refractive index distribution of the asymmetric taper. (c) The corresponding 3D structure and refractive index distribution of the parabolic taper. (d) The normalized electric field distribution in the cross-sectional direction, including TE0, TE1, and TE2 modes.