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November 22, 2011

Single pixel contact lens display

Journal of Micromechanics and Microengineering - A single-pixel wireless contact lens display This is an advance on prior work in 2008

We (University of Washington researchers) present the design, construction and in vivo rabbit testing of a wirelessly powered contact lens display. The display consists of an antenna, a 500 × 500 µm2 silicon power harvesting and radio integrated circuit, metal interconnects, insulation layers and a 750 × 750 µm2 transparent sapphire chip containing a custom-designed micro-light emitting diode with peak emission at 475 nm, all integrated onto a contact lens. The display can be powered wirelessly from ~1 m in free space and ~2 cm in vivo on a rabbit. The display was tested on live, anesthetized rabbits with no observed adverse effect. In order to extend display capabilities, design and fabrication of micro-Fresnel lenses on a contact lens are presented to move toward a multipixel display that can be worn in the form of a contact lens. Contact lenses with integrated micro-Fresnel lenses were also tested on live rabbits and showed no adverse effect.

Prior work has demonstrated different types of contact lens functionalization. Contact lens mounted biosensors have been developed to measure eye movement, tear glucose concentration, corneal temperature, blood oxygen and intraocular pressure. Although it is not contact lens based, an implanted intraocular vision aid (IOVA) is similar in concept to this project in that it projects images onto the retina from a system of light emitting diodes (LEDs) and microlenses.

They previously investigated the fabrication and deployment of red LEDs on contact lenses. To move toward a full color display, we chose to fabricate blue micro-LEDs. GaN and its alloys were deemed suitable due to nontoxicity, high efficiency and appropriate achievable emission wavelength. The present micro-LED design, with peak intensity at ∼475 nm, is adequate to illuminate the retina.

Conceptual rendition of a multipixel contact lens display. (a) A contact lens display comprising a multipixel light emitting diode (LED) chip (1), power-harvesting/control circuitry (2), antenna (3), and interconnects (4). These subsystems are encapsulated in a transparent polymer (5), creating a system to project virtual images (6) perceivable by the eye of the wearer. (b) LED chip with 100 pixels. LED active layers can be grown atop a transparent substrate. Emitted light travels through the substrate and is reimaged using planar Fresnel lenses. (c) Magnified view with one pixel activated, showing Fresnel lenses opposite each LED pixel.

9 page pdf






Testing the contact lens display on a live rabbit. (a) Photograph of a completed contact lens system. (b) The contact lens display is placed on the eye of a live rabbit and powered by a dipole antenna, showing bright emission from the on-lens pixel. (c) Subsequent tests using fluoresce in showed no corneal epithelial damage.

We have demonstrated the operation of a contact lens display powered by a remote radiofrequency transmitter in free space and on a live rabbit. This verifies that antennas, radio chips, control circuitry and micrometer-scale light sources can be integrated into a contact lens and operated on live eyes. Although our display has only a single controllable pixel, we have provided the first proof-of-concept technology demonstrations for producing multipixel and in-focus images using a contact lens by producing multipixel micro-LED array chips on transparent substrates and micrometer-scale Fresnel lenses that can be integrated into a contact lens. The demonstration of Fresnel lenses on contact lenses points toward the potential of integrating other passive and active micro-optical components on a contact lens for vision correction and enhancement.

Significant improvements are necessary to produce fully functional, remotely powered, high-resolution displays. Although we could power our system in free space from more than a meter, operating distances on the rabbit eye were reduced to the cm range. Matching, interface and absorption losses are likely causes of the limited operational distance. We are working to improve matching losses, to ensure that power received by the contact lens is maximized at the frequency of best antenna-to-chip matching, and to optimize LED efficiency and duty cycling to reduce power consumption of individual pixels. Although only microwatts of power is available on the contact lens, most light generated by the optical components directly enters the eye. Thus, the display could efficiently generate an image while consuming little power. PET has been our contact lens substrate of choice thus far due to the ease of performing some microfabrication processes; however, PET has poor oxygen permeability and its extended use could lead to lactate build-up and corneal swelling. It will be necessary to adapt our processes to more common rigid gas permeable or hydrogel contact lens materials. This work is currently in progress in our laboratory. We have demonstrated the integration of blue and red micrometer-scale light sources on contact lenses. The integration of green emitting micrometer-scale light sources must be achieved in order to fully extend the color gamut.

A display with a single controllable pixel could be used in gaming, training, or giving warnings to the hearing impaired. We also believe it is possible to develop systems with better resolution, color, range and computing power. Displays with a handful of pixels could be used to provide directional information, and displays with hundreds of pixels used to read short emails or text messages. Although high
resolution, full-color, stand-alone contact lens displays might be many years away, the technological demonstrations to date depict a clear path containing a number of useful intermediate devices that can be feasibly produced in the near to medium terms. If such displays were successfully deployed, they would fundamentally change the nature of interaction between humans and visual information.

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