Performance analysis of a compact auto-phoropter for accessible refractive assessment of the human eye.

We present the performance analysis and specifications of a portable auto-phoropter system that can be employed for fast refractive assessment of a large population. A customized Shack-Hartmann wavefront sensor is developed to accurately measure the defocus and astigmatism of the eye within ±10D and ±6D, respectively. Three fluidic lenses are designed to correct the vision in real time. A digital Snellen chart is integrated into the system to validate the accuracy of the measurement and the correction by means of achieving 20/20 vision. The refractive error of eight subjects (16 eyes) has been measured objectively (without patient's feedback) using the proposed system and the results are compared with their clinical prescription through the Bland-Altman method. It is shown that the auto-phoropter takes less than 8 s to measure and correct the eye refractive error with an accuracy of ±0.25D.

Holographic curved waveguide combiner for HUD/AR with 1-D pupil expansion.

We are presenting the optical ray tracing as well as an experimental prototype of a curved waveguide combiner with pupil expansion for augmented reality (AR) and mixed reality (MR) glasses. The curved waveguide combiner takes advantage of holographic optical elements both for injection and extraction of the image to correct the aberrations introduced during the propagation of light inside the waveguide. The holographic curved combiner presented has a cylindrical outer radius of curvature of 171.45 mm with a field of view of 13° (H) × 16° (V) at a viewing distance of 1 cm with a 5 × horizontal 1 dimension pupil expansion for an eyebox of 6.2 mm × 42.7 mm.

Examining aberrations due to depth of field in holographic pupil replication waveguide systems.

Pupil expansion using waveguide propagation and pupil replication has been a popular method of developing head-up displays and near-to-eye displays. This paper examines one of the limits of pupil replication, which involves projecting images at a finite distance through a single waveguide by holographic optical elements and seeing the image doubling artifact. A Zemax model and a demonstrator were developed to determine the cause of image doubling. A relationship between the designed outcoupled image distance of a waveguide, pupil size, optical path length, and angle of image doubling is established. In waveguide pupil replication, the internally propagating light should be close to collimated to mitigate image doubling. We also provide a solution to project the image at different distances, which is an important factor for some applications, such as automotive head-up display and the seamless integration of augmented reality information with the natural environment.

Holographic waveguide head-up display with 2-D pupil expansion and longitudinal image magnification.

Head-up displays (HUDs) are used in aircraft to overlay relevant flight information on the vehicle's externals for pilots to view with continued focus on the far field. In these systems, the field of view (FOV) is traditionally limited by the size of the projection optics. Though classical HUD systems take a significant amount of space in the flight deck, they have become a necessity in avionic transportation. Our research aims to reduce the size of the HUD footprint while offering a wide FOV projected in the far field with an expanded pupil. This has been accomplished by coupling the image-bearing light into a waveguide under total internal reflection conditions, redirecting that light in the orthogonal direction, and then outcoupling the light toward the pilot. Each step was achieved using holographic optical elements. The injection hologram has optical power to obtain longitudinal magnification, whereas the redirection hologram expands the pupil in one dimension and the extraction hologram expands the pupil in a second dimension. Varying diffraction efficiency along the direction of the light propagation ensures even image intensity throughout the expanded pupil. We used ray tracing optical simulations to optimize the design of the system and present a fully operational demonstrator of the HUD. This HUD produces an image with a FOV of 24°×12.6° at a viewing distance of 4.5 in. (114 mm) from the waveguide, with infinite longitudinal magnification and 1.9× by 1.6× horizontal and vertical pupil expansion, respectively.