Design of a high-resolution holographic waveguide eye-tracking system operating in near-infrared with conventional optical elements.

The eye-tracking system plays an essential role in the augmented reality (AR) eyewear. Waveguide volume holographic optical elements (HOE) that can be made with high efficiency, thin form, and lightweight are well-suited for this application. Traditional holographic lenses formed with spherical wavefronts at visible wavelengths and used for near-infrared (NIR) eye-tracking systems suffer from significant image aberrations, image tilt, and ghost images. This work describes a complete holographic lens design methodology that systematically addresses these issues and details the specifications of conventional optical elements that provide the optimized wavefronts for the hologram construction beams. The resulting waveguide HOE NIR eye-tracking system has an image resolution of ∼10 lp/mm when the designed holographic lens is deposited on a waveguide with a refractive index of 1.8 and thickness of 0.5 mm.

High energy yield bifacial spectrum-splitting photovoltaic system.

In this paper a photovoltaic system is proposed that achieves high energy yield by integrating bifacial silicon cells into a spectrum-splitting module. Spectrum splitting is accomplished using volume holographic optical elements to spectrally divide sunlight onto an array of photovoltaic cells with different bandgap energies. Light that is reflected from the ground surface onto the rear side of the module is converted by the bifacial silicon cells. The energy yield of the system is optimized by tuning the volume holographic element parameters, such as film thickness, index modulation, and construction point source positions. An example is presented for utility-scale illumination parameters in Tucson, Arizona, that attains an energy yield of $1010\frac{{{ kw}\cdot { hr}}}{{{ yr}\cdot{{ m}^2}}}$1010kw⋅hryr⋅m2, which is 32.8% of the incident solar insolation.

Dynamic calibration for enhancing the stability of a channeled spectropolarimeter.

Channeled spectropolarimeters are optical instruments that measure the spectral dependence of the polarization of light without any mechanically moving parts. An important factor in achieving stable and accurate measurements is the calibration process, especially in dynamic environments where temperature fluctuations or other factors affect the retardance of the components in the polarimeter. In previous research, a self-calibration algorithm that accounts for these variations was developed, without any additional reference measurements. In this paper, we identify an ambiguity in the self-calibration phase, which limits the allowed temperature changes to surprisingly small ranges. We show how to adaptively estimate and correct for the phase ambiguity using a polynomial curve-fitting algorithm, extending the temperature range to virtually all practical scenarios. Lastly, we demonstrate the ability of the modified self-calibration algorithm to provide stable reconstruction of the Stokes vector for a temperature range >40∘C, using an experimental channeled spectropolarimeter.

Volume hologram replication system for spectrum-splitting photovoltaic applications.

A system for replicating high-efficiency volume hologram arrays, which has potential for high-volume manufacturing, is proposed. The system can meet the fabrication requirements of spectrum-splitting photovoltaic systems that are based on transmission volume holographic lens arrays. While previous hologram replication systems are mostly based on variations of the contact-copy method, the new technique is based on diffraction of reference and object beams from a master hologram through a prism and does not require contact with the copy hologram. The replication system has a number of identified advantages over contact-copy systems. An experimental volume holographic lens arrays fabricated using the proposed system had high median diffraction efficiency and low variability (95.3%+/-0.9%).

Off-axis holographic lens spectrum-splitting photovoltaic system for direct and diffuse solar energy conversion.

This paper describes a high-efficiency, spectrum-splitting photovoltaic module that uses an off-axis volume holographic lens to focus and disperse incident solar illumination to a rectangular shaped high-bandgap indium gallium phosphide cell surrounded by strips of silicon cells. The holographic lens design allows efficient collection of both direct and diffuse illumination to maximize energy yield. We modeled the volume diffraction characteristics using rigorous coupled-wave analysis, and simulated system performance using nonsequential ray tracing and PV cell data from the literature. Under AM 1.5 illumination conditions the simulated module obtained a 30.6% conversion efficiency. This efficiency is a 19.7% relative improvement compared to the more efficient cell in the system (silicon). The module was also simulated under a typical meteorological year of direct and diffuse irradiance in Tucson, Arizona, and Seattle, Washington. Compared to a flat panel silicon module, the holographic spectrum splitting module obtained a relative improvement in energy yield of 17.1% in Tucson and 14.0% in Seattle. An experimental proof-of-concept volume holographic lens was also fabricated in dichromated gelatin to verify the main characteristics of the system. The lens obtained an average first-order diffraction efficiency of 85.4% across the aperture at 532 nm.