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Form-birefringence elements Subwavelength 0th order gratings permit to create a phase-shift between the polarized 0th order grating modes propagating down the slits and grooves of a binary corrugation, and to transform the polarization of an incident beam. The phase-shift per unit height of the grating is an increasing function of the refractive index difference between ridges and grooves. If the ridges are made by photolithography in a resist or by polymer embossing, the low refractive index leads to a very large corrugation aspect ratio (approx. 4 for a half-wave phase-shift) that is difficult to fabricate and/or provides insufficient mechanical stability. If the ridges are made in a high index non-organic material (e.g. a semiconductor) the needed depth is reduced (although still notably larger than 1 for a half-wave phase-shift). However, another problem is now encountered: due to a more significant Fabry-Perot effect between the upper and lower boundaries of the 0th order grating [1] high transmission is guaranteed only if its resonance condition is ensured for both polarizations simultaneously. The three conditions ( phase-shift between TE and TM and both Fabry-Perot resonances) are impossible to achieve simultaneously if the corrugation is made by directly etching the substrate (same material for ridges and substrate) unless the grooves are very deep which imposes difficult etching conditions [2]. Using an inventive design by phase management of the involved grating modes [2] we have found that all thre