Design and fabrication of a compact augmented reality near-eye display with freeform holographic optics

A compact monochromatic augmented reality near-eye display (AR NED) system, which includes two freeform holographic optical elements (HOEs) and a freeform prism, is presented in this paper. The freeform prism consisting of three freeform surfaces is employed to fold the propagation of light, enabling a highly compact form factor. The optical combiner of the AR NED system is a freeform HOE, and another freeform HOE is employed to correct chromatic aberration caused by the combiner due to the system's spectrum bandwidth. The two freeform HOEs are fabricated by the use of a freeform recording system. A cooperative optimization is proposed to co-design the AR NED system and the recording systems. The high degrees of freedom offered by both freeform HOEs and the freeform prism allow us to achieve a very compact AR NED system with spectrum bandwidth of 8 nm, a diagonal field of view (FOV) of 20°, an average diffraction efficiency of 30%, and root mean square (RMS) fraction of the intensity distribution within the entire FOV of 0.3. A prototype is built to demonstrate the feasibility of the proposed display system.