Diffraction-engineered holography: Beyond the depth representation limit of holographic displays.

Holography is one of the most prominent approaches to realize true-to-life reconstructions of objects. However, owing to the limited resolution of spatial light modulators compared to static holograms, reconstructed objects exhibit various coherent properties, such as content-dependent defocus blur and interference-induced noise. The coherent properties severely distort depth perception, the core of holographic displays to realize 3D scenes beyond 2D displays. Here, we propose a hologram that imitates defocus blur of incoherent light by engineering diffracted pattern of coherent light with adopting multi-plane holography, thereby offering real world-like defocus blur and photorealistic reconstruction. The proposed hologram is synthesized by optimizing a wave field to reconstruct numerous varifocal images after propagating the corresponding focal distances where the varifocal images are rendered using a physically-based renderer. Moreover, to reduce the computational costs associated with rendering and optimizing, we also demonstrate a network-based synthetic method that requires only an RGB-D image.

Actuating compact wearable augmented reality devices by multifunctional artificial muscle.

An artificial muscle actuator resolves practical engineering problems in compact wearable devices, which are limited to conventional actuators such as electromagnetic actuators. Abstracting the fundamental advantages of an artificial muscle actuator provides a small-scale, high-power actuating system with a sensing capability for developing varifocal augmented reality glasses and naturally fit haptic gloves. Here, we design a shape memory alloy-based lightweight and high-power artificial muscle actuator, the so-called compliant amplified shape memory alloy actuator. Despite its light weight (0.22 g), the actuator has a high power density of 1.7 kW/kg, an actuation strain of 300% under 80 g of external payload. We show how the actuator enables image depth control and an immersive tactile response in the form of augmented reality glasses and two-way communication haptic gloves whose thin form factor and high power density can hardly be achieved by conventional actuators.

Rings, igloos, and pebbles of salt formed by drying saline drops.

It is well-known that evaporation of sessile drops with suspended particles like colloids and coffee powders can yield a variety of two-dimensional patterns depending on the particle shapes and internal flow patterns. Here we show that ordered three-dimensional structures can be built via evaporation of saline drops on highly hydrophobic substrates like pristine PP (polypropylene) with micropores and nanostructured low-surface-energy PP. On pristine PP having a high contact angle but a large contact angle hysteresis (CAH) with water, either rings or igloos of salt are formed depending on the salt concentration and evaporation rate. On nanostructured low-surface-energy PP having extreme water repellency with a very low CAH, pebbles of salt are formed regardless of salt concentration and evaporation rate. These observations lead us to conclude that combined effects of solubility, evaporation rate, and mobility of the contact line determine the final three-dimensional shape of the salt precipitate.