errors due to temperature and wavelength improving the tolerance with respect to operational conditions application_number US 201214360989 A description to fully appreciate the innovative features of the present invention this description begins with a discussion of the inventor 39 s discoveries relating to the origin of the intolerances of polarization converter designs briefly it is found that the difficulty lies in maintaining the polarization angle of the modes close enough to the optimal 45 u00b0 condition the description then discloses new polarization converter designs that correct for possible errors in this angle consequently the new polarization converter designs are much more tolerant to fabrication errors but also to ambient conditions and wavelength deviation the tolerant converters make use of two sloped sidewall sections whose cross sections are mirror images of each other in one embodiment the new device is doubled in length with respect to a conventional single section device fig1 shows a conventional polarization converter device having inp upper cladding layer 100 inp lower cladding layer 102 and ingaasp core layer 104 sandwiched between them in this device polarization conversion of light propagating along the z axis is obtained with a narrow waveguide having one slanted sidewall due to the electromagnetic boundary conditions this design rotates the polarization of the modes with a careful design the rotation will be 45 u00b0 in that case a te or tm mode from a symmetric input waveguide equally excites the two rotated orthogonal modes these modes propagate with different propagation constants u03b2 1 and u03b2 2 after half of the beat length l u03bb 2 u03c0 2 u03b2 1 u2212 u03b2 2 the rotated modes recombine to a tm or te mode in a symmetric output waveguide in.