Radiative cooling textiles using industry-standard particle-free nonporous micro-structured fibers.

Thermal radiation is a major dissipative pathway for heat generated by the human body and offers a significant thermoregulation mechanism over a wide range of conditions. We could use this in garment design to enhance personal cooling, which can improve the wearing comfort of garments or even result in energy savings in buildings. At present, however, radiative cooling has received insufficient attention in commercial design and production of textiles for wearable garments.

Subwavelength Bayer RGB color routers with perfect optical efficiency.

We introduce subwavelength color routers with perfect optical efficiency in a red-green-green-blue (RGGB) Bayer layout for solid state image sensors. This is the first demonstration of a subwavelength device concept that shows the full potential of color routing, i.e.

Subambient daytime radiative cooling textile based on nanoprocessed silk.

Decreasing energy consumption is critical to sustainable development. Because temperature regulation for human comfort consumes vast amounts of energy, substantial research efforts are currently directed towards developing passive personal thermal management techniques that cool the human body without any energy consumption. Although various cooling textile designs have been proposed previously, textile-based daytime radiative cooling to a temperature below ambient has not been realized.

Scattering of electromagnetic waves by cylinder inside uniaxial hyperbolic medium.

We study electromagnetic wave scattering inside a hyperbolic medium by a circular cylinder. The hyperbolic medium's unique properties result in scattering behaviors that differ greatly from scattering by the same cylinder inside a positive isotropic medium. Incident wave polarization is preserved for all angles of incidence and the scattered waves have the same polarization in the far-field region.

Spectrally Selective Nanocomposite Textile for Outdoor Personal Cooling.

Outdoor heat stress poses a serious public health threat and curtails industrial labor supply and productivity, thus adversely impacting the wellness and economy of the entire society. With climate change, there will be more intense and frequent heat waves that further present a grand challenge for sustainability. However, an efficient and economical method that can provide localized outdoor cooling of the human body without intensive energy input is lacking.

Broadband Control of Topological Nodes in Electromagnetic Fields.

We study topological nodes (phase singularities) in electromagnetic wave interactions with structures. We show that, when the nodes exist, it is possible to bind certain nodes to a specific plane in the structure by a combination of mirror and time-reversal symmetry. Such binding does not rely on any resonances in the structure.

A dual-mode textile for human body radiative heating and cooling.

Maintaining human body temperature is one of the most basic needs for living, which often consumes a huge amount of energy to keep the ambient temperature constant. To expand the ambient temperature range while maintaining human thermal comfort, the concept of personal thermal management has been recently demonstrated in heating and cooling textiles separately through human body infrared radiation control. Realizing these two opposite functions within the same textile would represent an exciting scientific challenge and a significant technological advancement.

Warming up human body by nanoporous metallized polyethylene textile.

Space heating accounts for the largest energy end-use of buildings that imposes significant burden on the society. The energy wasted for heating the empty space of the entire building can be saved by passively heating the immediate environment around the human body. Here, we demonstrate a nanophotonic structure textile with tailored infrared (IR) property for passive personal heating using nanoporous metallized polyethylene.

Modern imaging: introduction to the feature issue.

This special issue of Applied Optics contains selected papers reflecting the various disciplines that are needed for the design, implementation and advancement of imaging technology and systems, and it highlights the state-of-the-art research developments in the areas of modern imaging use.

Radiative human body cooling by nanoporous polyethylene textile.

Thermal management through personal heating and cooling is a strategy by which to expand indoor temperature setpoint range for large energy saving. We show that nanoporous polyethylene (nanoPE) is transparent to mid-infrared human body radiation but opaque to visible light because of the pore size distribution (50 to 1000 nanometers). We processed the material to develop a textile that promotes effective radiative cooling while still having sufficient air permeability, water-wicking rate, and mechanical strength for wearability.

Complete power concentration into a single waveguide in large-scale waveguide array lenses.

Waveguide array lenses are waveguide arrays that focus light incident on all waveguides at the input side into a small number of waveguides at the output side. Ideal waveguide array lenses provide complete (100%) power concentration of incident light into a single waveguide. While of great interest for several applications, ideal waveguide array lenses have not been demonstrated for practical arrays with large numbers of waveguides.

Broadband sharp 90-degree bends and T-splitters in plasmonic coaxial waveguides.

We demonstrate numerically that sharp 90° bends and T-splitters can be designed in plasmonic coaxial waveguides at deep-subwavelength scale to operate without reflection and radiation over a broad range of wavelengths, including the telecommunication wavelength of 1.55 μm. We explain the principles of the operation using a transmission line model of the waveguide in the quasi-static limit.

Imaging systems and applications.

Imaging systems have numerous applications in industrial, military, consumer, and medical settings. Assembling a complete imaging system requires the integration of optics, sensing, image processing, and display rendering. This issue features original research ranging from fundamental theories to novel imaging modalities and provides a systems perspective to imaging.

Pixel scaling in infrared focal plane arrays.

We discuss effects that arise in pixels of IR focal plane arrays (FPAs) when pixel size scales down to approach the wavelength of the incident radiation. To study these effects, we perform first-principles electromagnetic simulations of pixel structures based on a mercury-cadmium-telluride photoconductor for use in FPAs. Specifically, we calculate the pixel quantum efficiency and crosstalk as pixel size scales from 16 μm, which is in the range of current detectors, down to 0.

Routing of deep-subwavelength optical beams and images without reflection and diffraction using infinitely anisotropic metamaterials.

Interfaces between media with infinite anisotropy, defined by infinite permittivity or permeability in one direction, offer new opportunities for controlling and manipulating light at the nanoscale. Reflectionless, diffraction-free routing of deep-subwavelength optical beams and images using interfaces between infinitely anisotropic media are demonstrated. It is shown how to achieve extremely large anisotropy using metamaterial designs that can be implemented with existing materials.

From electromagnetically induced transparency to superscattering with a single structure: a coupled-mode theory for doubly resonant structures.

We observe from simulations that a doubly resonant structure can exhibit spectral behavior analogous to electromagnetically induced transparency, as well as superscattering, depending on the excitation. We develop a coupled-mode theory that explains this behavior in terms of the orthogonality of the radiation patterns of the eigenmodes. These results provide insight in the general electromagnetic properties of photonic nanostructures and metamaterials.

Imaging systems and applications.

Imaging systems are used in consumer, medical, and military applications. Designing, developing, and building imaging systems requires a multidisciplinary approach. This issue features current research in imaging systems that ranges from fundamental theories to novel applications.

Digital camera simulation.

We describe a simulation of the complete image processing pipeline of a digital camera, beginning with a radiometric description of the scene captured by the camera and ending with a radiometric description of the image rendered on a display. We show that there is a good correspondence between measured and simulated sensor performance. Through the use of simulation, we can quantify the effects of individual digital camera components on system performance and image quality.

Transverse electromagnetic modes in aperture waveguides containing a metamaterial with extreme anisotropy.

We use metamaterials with extreme anisotropy to solve the fundamental problem of light transport in deep subwavelength apertures. By filling a simply connected aperture with an anisotropic medium, we decouple the cutoff frequency and the group velocity of modes inside apertures. In the limit of extreme anisotropy, all modes become purely transverse electromagnetic modes, free from geometrical dispersion, propagate with a velocity controlled by the transverse permittivity and permeability, and have zero cutoff frequency.

Nanopatterned metallic films for use as transparent conductive electrodes in optoelectronic devices.

We investigate the use of nanopatterned metallic films as transparent conductive electrodes in optoelectronic devices. We find that the physics of nanopatterned electrodes, which are often optically thin metallic films, differs from that of optically thick metallic films. We analyze the optical properties when performing a geometrical transformation that maintains the electrical properties.

Microlens performance limits in sub-2mum pixel CMOS image sensors.

CMOS image sensors with smaller pixels are expected to enable digital imaging systems with better resolution. When pixel size scales below 2 mum, however, diffraction affects the optical performance of the pixel and its microlens, in particular. We present a first-principles electromagnetic analysis of microlens behavior during the lateral scaling of CMOS image sensor pixels.

Phase front design with metallic pillar arrays.

We demonstrate numerically, using a three-dimensional finite-difference frequency-domain method, the ability to design a phase front using an array of metallic pillars. We show that in such structures, the local phase delay upon transmission can be tuned by local geometry. We apply this knowledge to demonstrate a metallic microlens.

Deep-subwavelength focusing and steering of light in an aperiodic metallic waveguide array.

We consider an aperiodic array of coupled metallic waveguides with varying subwavelength widths. For an incident plane wave, we numerically demonstrate that a focus of as small as one-hundredth of a wavelength can be achieved for a focal distance that is much longer than the wavelength. Moreover, the focusing behavior can be controlled by changing either the incident wavelength or the angle of incidence, thus providing the capability of nanoscale beam steering.

Optical confinement methods for continued scaling of CMOS image sensor pixels.

The pixels that make up CMOS image sensors have steadily decreased in size over the last decade. This scaling has two effects: first, the amount of light incident on each pixel decreases, making optical efficiency, i.e.

Planar lenses based on nanoscale slit arrays in a metallic film.

We experimentally demonstrate planar lenses based on nanoscale slit arrays in a metallic film. Our lens structures consist of optically thick gold films with micron-size arrays of closely spaced, nanoscale slits of varying widths milled using a focused ion beam. We find excellent agreement between electromagnetic simulations of the design and confocal measurements on manufactured structures.