Design of fiber-matched uncladded rib waveguides on InP with polarization-independent mode matching loss of 1 dB

A waveguide taper design for uncladded rib or channel waveguides on InGaAsP-InP with polarization-independent coupling loss to the fiber is proposed. The spot size variation of the guided mode along the taper is investigated numerically by a two-dimensional finite difference method. By introducing thin guiding layers below the waveguide it is shown that the taper structure can be designed to have relaxed fabrication tolerances and a mode matching loss to the fiber of 1 dB.