Design of a large aperture tunable refractive Fresnel liquid crystal lens.

A large aperture tunable lens based on liquid crystals, which is considered for near-to-eye applications, is designed, built, and characterized. Large liquid crystal lenses with high quality are limited by very slow switching speeds due to the large optical path difference (OPD) required. To reduce the switching time of the lens, the thickness is controlled through the application of several phase resets, similar to the design of a Fresnel lens. A main point of the paper is the design of the Fresnel structure to have a minimal effect on the image quality. Our modeling and experimental results demonstrate that minimal image degradation due to the phase resets is observable when the segment spacing is chosen by taking into account human eye resolution. Such lenses have applications related to presbyopia and, in virtual reality systems, to solve the well-known issue of accommodation-convergence mismatch.

Nonmechanical zoom lens based on the Pancharatnam phase effect.

We present a nonmechanical zoom lens system based on the Pancharatnam phase effect, which is controlled by the state of circularly polarized light. The device is shown to allow for a compact design for a wide range of zoom ratios. A demonstration system is shown, which has a 4× zoom ratio between its two electrically switchable states. We show its observed image quality experimentally and compare it with calculated expectations.

Thin-film Pancharatnam lens with low f-number and high quality.

We have made an ultra-thin (~2.26 µm) f/2.1 lens based on the Pancharatnam phase effect using the polarization holography alignment technique. This lens exhibits a continuous phase profile, high efficiency (>97%), and is switchable from having a positive focal length to a negative one by changing the handedness of input circularly polarized light. We analyzed its optical performance and simulated it as a gradient index lens for further comparison, and to discuss its bandwidth limitation. The conditions required for improving the performance and its low-cost fabrication method is discussed. Because of the nature of Pancharatnam devices and the demonstrated fabrication method, these results are applicable to a wide size range.

Concept for a transmissive, large angle, light steering device with high efficiency.

A device concept is presented to allow very large angle deflection of light passing through a transmissive device. Deflection of light, switchable between angles larger than ±60 deg, is shown to be possible with efficiencies approaching 100%.

Analysis of a dual-twist Pancharatnam phase device with ultrahigh-efficiency large-angle optical beam steering.

It has been previously shown that a Pancharatnam phase device with a dual-twist structure can deflect light up to 60° with nearly perfect efficiency. This was beyond the limits previously assumed for these types of devices, which were considered to be optically similar to Raman-Nath gratings. In this paper we first consider the range of parameters that will allow for high efficiency and show the results for a structure that demonstrates 80° deflection. We then explore the light propagation through these devices to point out interesting intensity variations in the deflected mode of light as it traverses the deflecting layer. Finally, we explain the key to understanding the efficiency of these devices, which is not the typical parameters that are important for traditional diffractive devices, but rather the control of the polarization state of light. We provide a simple design approach for optimizing the twist angle and retardation for high efficiency.

Surface localized polymer aligned liquid crystal lens.

The surface localized polymer alignment (SLPA) method allows complete control of the polar pretilt angle as a function of position in liquid crystal devices. In this work, a liquid crystal (LC) cylindrical lens is fabricated by the SLPA method. The focal length of the LC lens is set by the polymerization conditions, and can be varied by a non-segmented electrode. The LC lens does not require a shaped substrate, or complicated electrode patterns, to achieve a desired parabolic phase profile. Therefore, both fabrication and driving process are relatively simple.

Improving Speech Understanding and Monitoring Health with Hearing Aids Using Artificial Intelligence and Embedded Sensors.

This article details ways that machine learning and artificial intelligence technologies are being integrated in modern hearing aids to improve speech understanding in background noise and provide a gateway to overall health and wellness. Discussion focuses on how Starkey incorporates automatic and user-driven optimization of speech intelligibility with onboard hearing aid signal processing and machine learning algorithms, smartphone-based deep neural network processing, and wireless hearing aid accessories. The article will conclude with a review of health and wellness tracking capabilities that are enabled by embedded sensors and artificial intelligence.

Switchable polarization-independent liquid-crystal Fabry-Perot filter.

A new approach to a polarization-independent twisted liquid-crystal (LC) structure, where phase difference between orthogonal eigenmodes is tuned to be an integer multiple of 2pi, is demonstrated with a numerical model. For select wavelengths, polarization-independent operation can be achieved by tuning the twist rate and thickness of the LC cavity. Applications can be found in polarization- independent switches and field sequential wavelength selection devices.