Analysis and Design of Compact Adiabatic Mode Converters Based on Adiabatic Mode Evolutions

This paper investigates the mode conversion in ridge waveguides. Based on the adiabatic mode evolution, several compact adiabatic mode converters with optimized waveguide shapes are proposed. Three types of adiabatic mode conversion from TM to TE modes are proposed. It is found that the designed adiabatic device is greatly shorter than the one based on the linear shape case, but is capable of achieving the same power mode conversion efficiency. Furthermore, an adiabatic TM
₀
mode maintaining waveguide taper is proposed to guide the TM
₀
mode from narrow waveguide to wide waveguide. The efficiency of the designed adiabatic TM
₀
mode maintaining waveguide taper considerably exceeds that obtained with the parabolic design. Then, combining the TE
₁
mode to TM
₀
mode adiabatic mode converter and TM
₀
mode to TE
₃
mode adiabatic mode converter, a TE
₁
mode to TE
₃
mode adiabatic mode converter (which is difficult to design and cannot be achieved even with a linear-shape connection) with a total length of 760 μm and 94% power mode conversion is proposed.