Leaf-inspired luminescent solar concentrator based on two-stage photoconversion.

Geometrical gain of a luminescent solar concentrator is drastically increased by laying out a luminescent fiber in a luminescent plate with air gap around it and attaching a photovoltaic (PV) cell to the tip of the fiber. The plate converts an incident photon to a first photoluminescence (PL) photon, and the fiber converts it to a second PL photon. Thus, the fiber carries the optical power as a leaf vein transports water and nutrients.

Position detection of a beta particle emitter by utilizing self-absorption in a scintillation fiber.

Self-absorption in a plastic scintillation fiber can be utilized to determine the incident position of single beta particles. A dichroic mirror directs scintillation photons with shorter wavelengths to one Si photomultiplier and those with longer wavelengths to another. An index calculated from the two signals is a monotonic function of the distance between the tip of the fiber and the incident point.

Luminance, color gamut, and energy-harvesting characteristics of luminescent layers placed above a solar cell.

One can display images and harvest energy by utilizing ambient light with a stack of an optical shutter array, a luminescent layer and a solar cell. In our experiment, a luminescent layer and a corresponding color filter were attached to a polycrystalline Si solar cell with 13% power conversion efficiency. For each configuration using BBOT, Coumarin 6 and Lumogen F Red 305, the power conversion efficiency was measured to be 6.

Spectral study on utilizing ambient light with luminescent materials for display applications.

A luminous reflective display can be constructed by placing an electro-optic shutter on the stack of a luminescent layer, a color filter, and a reflector in this order. The luminescent materials convert a part of the incident light to photoluminescence photons. The reflector redirects the downward photon flux toward an observer.

Concentric re-emission pattern from a planar waveguide with a thin uniform luminescent layer.

When a beam of light excites a single spot on a thin luminescent layer embedded in a planar waveguide, a concentric re-emission pattern is observed. An analytical expression is formulated by following the series of events in the waveguide: generation of angle-dependent photoluminescence spectra, reflection at the waveguide-air boundary, absorption by the luminescent layer, and generation of next-generation photoluminescence. The formula reproduces the peak radii observed in the experiments with some organic dyes.

Cross talk and optical efficiency of an energy-harvesting color projector utilizing ceramic phosphors.

A color projector screen was fabricated by filling three kinds of ceramic phosphor powders in the periodic hollow columns formed in a ${50}\;{{\rm mm}}\; \times \;{50}\;{{\rm mm}}\; \times \;{10}\;{{\rm mm}}$50mm×50mm×10mm acrylic waveguide. When a blue laser beam excited a single spot on the screen, a disk-shaped cross-talk pattern appeared. Its intensity was 5 orders of magnitude lower than that of the excited spot.

Illumination uniformity of an edge-lit backlight with emission angle control.

Viewing range of a liquid crystal display can be controlled by a liquid crystal device inserted between a light source and a light-guide of an edge-lit backlight unit. Here, we propose an output coupler with a vertical optical window through which light is extracted from a light-guide. Rays with large propagation angles and those with small angles have a comparable probability of hitting this window.

Dual-LED imaging for finger liveliness detection and its evaluation with replicas.

Unattended fingerprint identification systems need to reject input attempts by a replica. Previously, we proposed detecting the color changes of a finger during an input action as a signature of liveliness. To improve its reliability, a dual-LED imaging system is investigated.

Recognition of living fingers with a sensor based on scattered-light detection.

To prevent fraud by use of replicas of human fingers for identity verification, we propose to check variations in color and in a series of previously acquired fingerprint images. Movement of a finger on a human hand induces blood movement, and light scattered inside the finger carries this life-related information. In experiments, we found characteristic changes in color and luminance extracted from the central parts of fingerprint images.

Active optical interconnect based on liquid-crystal grating.

We propose a transparent plate of a liquid-crystal grating to be used as a light guide for optical interconnection. To this end, we are empowering the connection itself with active functions, such as switching, wavelength division, power adjustment, etc. In experiments, we built a grating based on in-plane switching.

Theoretical considerations for arrayed waveguide displays.

An arrayed waveguide display (AWD) is proposed in which a linear emitter array is coupled to a waveguide array upon which liquid-crystal (LC) switches are formed. Images are displayed by line-by-line control of light, including emission by the emitter array, injection into the waveguide array, propagation inside, and extraction by use of the LC switches. With mostly polymeric materials, an AWD can be made thin and tough.