Object The optical engine design of augmented reality (AR) near-eye display is one of the research hotspots in the field of display technology. It projects virtual images to the real physical environment for display, and simultaneously enhances, merges, and complements the physical world in space. AR near-eye display optical engine has high requirements for the integration and miniaturization of optical system, and the glass-like AR near-eye display optical device is an inevitable development trend in the future. Optical metasurface is an artificial structure array composed of subwavelength unit structure periodically arranged on a two-dimensional plane. It realizes arbitrary regulation of the amplitude, phase, and polarization of the light field through the interaction of the unit structure and electromagnetic wave. At the same time, it has the characteristics of small size, high efficiency, and compact structure, and has great potential in near-eye display applications.
Methods In this paper, a metasurface structure is designed as the decoupled structure of the AR near-eye display optical waveguide (Fig.1). The decoupled part adopts a waveguide with a cutting angle of 60°. By changing the angle of incident light, the incident light propagates inside the waveguide at 50°-75°. The coupled part of the metasurface has a height of 900 nm and a radius of 50-120 nm (Fig.6). The AR near-eye display optical waveguide is simplified and simulated in FDTD. The light source is placed inside the waveguide to simulate the total reflection of the incident light, and the decoupling angle is simulated by changing the incident angle.
Results and Discussions When the collimated light is incident into the metasurface structure, the outgoing light deviates from the z-axis by −35° (Fig.7). The field intensity distribution is observed by placing a monitor or far-field calculation, and the deflection efficiency is calculated to reach 77%. In addition, the angle distribution of the outgoing light on the metasurface within the designed wavelength of ±30 nm is simulated, and it can be seen that the deflection angle of the device fluctuates within the designed angle of 5° (Fig.8). Since the same metasurface structure has a specific phase response to incident light at different angles, different wavefront adjustment of incident light at different angles can be realized. Waveguide with a cutting angle of 60° is adopted in the coupled part. By changing the incident light angle, the incident light can propagate in the waveguide at 50°-75°, and the variation range of the outgoing optical coupling angle is 0°-20°. There is a one-to-one correspondence between the angle change of the incident light and the angle change of the outgoing light (Fig.9).
Conclusions A metasurface coupling structure for AR near-eye display optical waveguide is designed. The metasurface structure can be deflected by changing the radius and height of the structure, and the wavefront of the incident light at different angles is controlled. The results show that the deflection efficiency of light at a small incident angle can be as high as 77%. By changing the total reflection angle of the incident light in the waveguide, the coupling angle changes with the change of the incident angle, and finally the field of view angle of 20° can be achieved. The introduction of metasurface provides an effective scheme for the design of AR near-eye display optical engine, which is of great significance for the realization of light-weight and compact eyeglass for a AR module, and is expected to become a potential development direction of AR near-eye display optical engine.
DownLoad: