High-refractive index glass wafers for waveguide-based augmented reality wearables

Abstract

Advantages of high-refractive index (HRI) glass wafers for augmented reality wearables (ARWs) include high transparency, low birefringence and total thickness variation, high durability and optical quality, high mechanical stability, stiffness, and geometrical stability. ARWs enable users to see computer-generated images overlaid on top of normal view. ARWs give the user an enhanced experience and are hands-free. Waveguide technology uses a combination of diffractive or reflective gratings and HRI glass wafers to transfer or project images from the light source (projector) to the user’s eye through total internal reflection (TIR). With all these advantages, glass is truly one of the world’s most transformative materials. To make the waveguide-based devices a reality, Corning has developed a series of HRI glass wafers with a diameter of up to Φ300 mm. Corning augmented reality solution (ARS) provides high-throughput metrology expertise, fully automated laser cutting technology, and the capability to capture the total thickness variation over the entire glass wafers using a frequency stepping interferometer. In this paper, we first conducted optical characterization of uncoated high-refractive index glass wafers. Corning® Tropel® Flatmaster® MSP-300 was used to characterize the wafer profile properties of manufactured high-refractive index glass wafers. A variable angle spectroscopic ellipsometer (VASE) J.A. Woollam M-2000 was applied to evaluate the refractive index homogeneity of the high-refractive index glass wafers. A Metricon 2010/M system was used to measure the losses of optical waveguide at a wavelength of 409 nm, 448 nm, and 519 nm, respectively. A refractive index homogeneity of 99.976% and an optical thickness homogeneity of 99.979% were realized. Finally, an anti-reflective coating over a broad visible spectral range was added on top of a glass wafer for surface reflectance suppression. SiO2 and Nb2O5 were selected as low- and high-refractive index coating materials. The anti-reflective coating leads to a visible reflectance below 0.5% with a desired neutral aesthetic appearance. © The Authors.