We demonstrate a polarization-sensitive diffractive optical element by femtosecond laser direct writing of light-induced self-assembled nano-gratings in bulk silica glass. Manipulation of the induced form birefringence is achieved by controlling the writing parameters, in particular, the polarization azimuth of the writing beam. The performance of the diffraction-based circular-polarization beam splitter agrees with the theoretical prediction. The method allows extending the operation of space-variant subwavelength gratings of beam polarization converters to the visible range.