Wide field-of-view waveguide coupling metasurfaces used on augmented reality system

In recent years, Augmented reality (AR) technology has gained great attention. One critical component of AR devices is the see-through optical combiner. Several approaches have been proposed, such as using either refractive, reflective, diffractive, holographic optics, or a combination of them. Meta-surfaces can realize the design of more required optical element due to its superb abilities of controlling the amplitude, phase, polarization or other parameters of wave-front at subwavelength scale. Thus, we proposed a waveguide coupler based on a polarization independent doublet meta-surface, which can realize field of view (FOV) to 50° at the wavelength of 638 nm. Compare to the diffractive grating based optical combiner architecture, our doublet meta-surfaces improve the problem of FOV limited by the refractive index of the waveguide and uneven brightness in AR display devices. The polarization independent doublet meta-surfaces presented in this paper can provide a large phase mutation rate to achieve a large deflection angle. The meta-surfaces consist of a group of Silicon nanofins with different side length, but same height arranged on a rectangle glass substrate lattice with the reflection index of 1.764. Each unit structure has different electromagnetic responses to plane electromagnetic waves with different incident angles. By designing the shape and size of each silicon nanorods and other parameters, the phase and amplitude modulation we need can be achieved. Here we only consider one-dimensional eye-box expansion at a single wavelength. The design approach can be generalized to two-dimensional eye-box expansion. Besides, full-color display can be achieved by coordination of the coupling-in and coupling-out device in waveguides.