A novel S-shaped bent taper comprised the functions of bent and tapered structures is proposed to extend the applications of tapers with straight axes. The optimal combination of taper shape and refractive-index distribution in such an ideal structure is obtained by applying the conformal mapping technique to transform a single-mode straight waveguide into an equivalent tapered configuration, Furthermore, the beam propagation method in conjunction with the conformal mapping technique is used to analyze the optical propagation characteristics of ideal structures, Simulation results predict that a perfect mode-size conversion and a lateral shift of optical propagation can be achieved adiabatically.
