Optical systems and display engines for augmented reality and near-eye headsets

An optical system, comprising:

• a waveguide combiner having a first side and a second side that is opposite the first side, the waveguide combiner comprising a polarization-sensitive input grating;
• a polarizer at the first side of the waveguide combiner, the polarizer to receive an unpolarized light beam from a display device and output a polarized light beam of a first type of polarization that passes through the polarization-sensitive input grating;
• a quarter wave plate at the second side of the waveguide combiner, the quarter wave plate to receive the polarized light beam of the first type of polarization from the waveguide combiner and output the polarized light beam;
• and
• a reflective element arranged such that the quarter wave plate is between the reflective element and the waveguide combiner, the reflective element to receive the polarized light beam output by the quarter wave plate and reflect the polarized light beam back to the quarter wave plate,
• the quarter wave plate to receive the polarized light beam reflected by the reflective element and output the polarized light beam with a second type of polarization to the waveguide combiner, and the polarization-sensitive input grating to couple the polarized light beam with the second type of polarization into the waveguide combiner.