TE to TM converters with constant 45-degrees operation are a key component in OEIC's for coherent optical system applications. A new passive TE/TM-mode converter with a laterally tilted rib waveguide fabricated on a stepped substrate is proposed and investigated. The conversion effect has been simulated using scalar and vectorial two-dimensional finite difference methods. The device fabricated on (001)-InP/GaInAsP yields 45-degrees conversion with two subsequent elements of half the TE/TM-beatlength at an excess loss of 3 dB.