Imaging System for Eyeglass-Based Display Devices

Disclosed are imaging systems and eyeglass-based display devices. In one embodiment, an imaging system includes an image source and a partial mirror that defines a non-rotationally symmetric surface, wherein the partial mirror reflects images generated by the image source to an eye of an observer

Imaging Systems for Eyeglass-Based Display Devices

Disclosed are imaging systems and eyeglass-based display devices. In one embodiment, an imaging system includes an image source that generates images, a optical element that manipulates the images, and a beam splitter positioned between the image source and the optical element that reflects the images onto an eye of a user of the imaging system, wherein each of the image source, optical element, and beam splitter are aligned along the same optical axis

Meshfree Approximation Methods For Free-form Optical Surfaces With Applications To Head-worn Displays

Compact and lightweight optical designs achieving acceptable image quality, field of view, eye clearance, eyebox size, operating across the visible spectrum, are the key to the success of next generation head-worn displays. The first part of this thesis reports on the design, fabrication, and analysis of off-axis magnifier designs. The first design is catadioptric and consists of two elements. The lens utilizes a diffractive optical element and the mirror has a free-form surface described with an x-y polynomial. A comparison of color correction between doublets and single layer diffractive optical elements in an eyepiece as a function of eye clearance is provided to justify the use of a diffractive optical element. The dual-element design has an 8 mm diameter eyebox, 15 mm eye clearance, 20 degree diagonal full field, and is designed to operate across the visible spectrum between 450-650 nm. 20% MTF at the Nyquist frequency with less than 3% distortion has been achieved in the dual-element head-worn display. An ideal solution for a head-worn display would be a single free-form surface mirror design. A single surface mirror does not have dispersion; therefore, color correction is not required. A single surface mirror can be made see-through by machining the appropriate surface shape on the opposite side to form a zero power shell. The second design consists of a single off-axis free-form mirror described with an x-y polynomial, which achieves a 3 mm diameter exit pupil, 15 mm eye relief, and a 24 degree diagonal full field of view. The second design achieves 10% MTF at the Nyquist frequency set by the pixel spacing of the VGA microdisplay with less than 3% distortion. Both designs have been fabricated using diamond turning techniques. Finally, this thesis addresses the question of what is the optimal surface shape for a single mirror constrained in an off-axis magnifier configuration with multiple fields? Typical optical surfaces implemented in raytrace codes today are functions mapping two dimensional vectors to real numbers. The majority of optical designs to-date have relied on conic sections and polynomials as the functions of choice. The choice of conic sections is justified since conic sections are stigmatic surfaces under certain imaging geometries. The choice of polynomials from the point of view of surface description can be challenged. A polynomial surface description may link a designer s understanding of the wavefront aberrations and the surface description. The limitations of using multivariate polynomials are described by a theorem due to Mairhuber and Curtis from approximation theory. This thesis proposes and applies radial basis functions to represent free-form optical surfaces as an alternative to multivariate polynomials. We compare the polynomial descriptions to radial basis functions using the MTF criteria. The benefits of using radial basis functions for surface description are summarized in the context of specific head-worn displays. The benefits include, for example, the performance increase measured by the MTF, or the ability to increase the field of view or pupil size. Even though Zernike polynomials are a complete and orthogonal set of basis over the unit circle and they can be orthogonalized for rectangular or hexagonal pupils using Gram-Schmidt, taking practical considerations into account, such as optimization time and the maximum number of variables available in current raytrace codes, for the specific case of the single off-axis magnifier with a 3 mm pupil, 15 mm eye relief, 24 degree diagonal full field of view, we found the Gaussian radial basis functions to yield a 20% gain in the average MTF at 17 field points compared to a Zernike (using 66 terms) and an x-y polynomial up to and including 10th order. The linear combination of radial basis function representation is not limited to circular apertures. Visualization tools such as field map plots provided by nodal aberration theory have been applied during the analysis of the off-axis systems discussed in this thesis. Full-field displays are used to establish node locations within the field of view for the dual-element head-worn display. The judicious separation of the nodes along the x-direction in the field of view results in well-behaved MTF plots. This is in contrast to an expectation of achieving better performance through restoring symmetry via collapsing the nodes to yield field-quadratic astigmatism

Technique for Design of Color Robust As-Built Optical Coatings

This disclosure describes techniques for the design of optical coatings with low color variation in the presence of manufacturing tolerances, and which are robust to color as-built. Sample stacks of optical coatings are generated using a Monte Carlo technique based on initial design specification parameter(s) of an optical coating stack. The initial design parameter(s) are utilized as a starting point for the optical coating stack that meets color and reflectance requirements nominally prior to tolerances. Each sample stack applies an error in the design parameter(s) based on manufacturing (as-built) error distributions. A merit function that is indicative of the optical coating performance is evaluated for each as-built sample. The evaluated merit function is combined (summed) over all as-built samples, which is then minimized using an optimization method to yield an optimal as-built optical coating design specification

Techniques for Checking As-Worn Alignment of Eyewear with Display Optics or Progressive Prescription Lenses

Fitting eyewear with display optics to a user’s head can be problematic because lenses of the eyewear are typically not on hand during product development. This can cause problems with alignment of eyeboxes of the lenses when the user wears the eyewear with finished display optics. Generally, the eyebox of a lens or display optic is a volume within the lens such that parameters of image quality criteria is met. For example, if the eyeboxes of the lenses do not align correctly with the user’s eyes, then the eyewear does not fit or align with the user’s head. Incorrect alignment can cause degraded image quality, dimming, and/or clipping of corners of a displayed image of the eyewear, and may cause an unsatisfactory and unpleasant experience for the user. This problem of alignment may also occur with respect to progressive prescription lenses. Accordingly, techniques to build an eyebox simulator and check as-worn alignment of eyewear with display optics or prescription lenses (e.g., progressive lenses) are provided

Low Refractive Index Coating and Index Matched Adhesive Bonding for Lightguide Applications

Composite curved lightguides including prescription layers and/or protective layers are bonded together using index-matched adhesives. To obtain total internal reflection within the lightguide, a Chiolite layer is included on at least one side of the lightguide. For example, a Chiolite layer is included between the lightguide and an outer, world-facing protective layer, which is index matched to the lightguide. Due to the moisture susceptibility of the Chiolite, the adhesive coats the Chiolite layer to provide a moisture barrier