Fabrication of disk droplets and evaluation of their lasing action.

Disk resonators are difficult to create with droplets, since they self-form spheres due to the surface tension. In this study, disk (cylindrical) droplets were created by enclosing a dye (rhodamine 6G) solution in silicone rubber. Lasing actions of these droplets were examined by pulsed green laser excitation.

Self-enhancement and suppression of optical pulses by use of photochromism in elastomer.

When violet or green pulses were launched into an elastomer containing photochromic diarylethene, two competitive absorption bands emerged at around 400 and 520 nm. The violet pulses suppressed the former and enhanced the latter, whereas the green pulses induced the opposite reaction. Consequently, these signals self-formed their optical path in the elastomer (self-enhancement).

A spatial light modulator that uses scattering in a cholesteric liquid crystal.

When a cholesteric liquid crystal (helical pitch: 5 μm) was sandwiched between two glass plates with no alignment coating (gap: 20 μm), a random-domain texture appeared and a strong light scattering took place. This translucent texture turned to a transparent homeotropic phase when an electric voltage of 20 V was applied to the liquid crystal layer. This phase transition was used for constructing a spatial light modulator that needed no polarizers.

Fade-resistant photochromic reactions in a self-healable polymer.

Molecular diffusion in a polymer matrix was studied to prevent degradation of photochromic reactions during repeated coloration-decoloration processes. Photochromic diarylethene was dispersed in polydimethylsiloxane (cured polymer), since it promoted exchange of damaged and fresh molecules owing to high diffusivity. The diffusion coefficient was evaluated by measuring a distribution of dye molecules that were colored within a narrow laser beam path.

Stabilization of photochromic isomers by copper nanoparticles in a high-diffusivity solid matrix.

Nanoparticles that are dispersed in a solid matrix have no effect on co-dispersed molecules unless they happen to be located close to one another. A polymer with a high diffusion coefficient allows molecules to circulate in the matrix to find a particle that enhances their function. A polymer composite containing copper nanoparticles was created by a low-temperature, nonvacuum process.

Deformable silicone grating fabricated with a photo-imprinted polymer mold.

A tunable transmission grating was fabricated by molding a silicone elastomer (polydimethylsiloxane). Its optical characteristics were then evaluated during compression. For fabrication, a glass plate with a photoimprinted polymer grating film was used as a mold.

Integration of liquid crystal elements for creating an infrared Lyot filter.

An infrared Lyot filter was fabricated by integrating a polarization beam splitter and two retarders into a single device. A liquid crystal layer was constructed between two silicon pentaprisms that were designed suitably so that light was incident on this layer at 28°. At this angle, the liquid crystal transmitted p-polarized light (Brewster's angle) and reflected s-polarized light (total internal reflection).

Design and fabrication of an achromatic infrared wave plate with Sb-Ge-Sn-S system chalcogenide glass.

We designed and fabricated an achromatic infrared wave plate. To examine its phase retardation characteristics, the birefringence was calculated using the effective medium theory. A wave plate with a subwavelength grating was fabricated by direct imprint lithography on a low toxic chalcogenide glass (Sb-Ge-Sn-S system) based on calculated results.

Fabrication of a mid-IR wire-grid polarizer by direct imprinting on chalcogenide glass.

A mid-IR wire-grid polarizer with a 500 nm pitch was fabricated on a low toxic chalcogenide glass (Sb-Ge-Sn-S system) by the thermal imprinting of periodic grating followed by the thermal evaporation of Al metal. After imprinting, deposition of Al on the grating at an oblique angle produced a wire-grid polarizer. The fabricated polarizer showed polarization with TM transmittance greater than 60% at 5-9 μm wavelengths and an extinction ratio greater than 20 dB at 3.

Silicon-based liquid-crystal cell for self-branching of optical packets.

Self-controlled photonic switching was achieved by combining the photoconductivity of a semiconductor and the electrical tunability of a liquid crystal (LC). Pulse packets of 1.06 μm wavelength created free carriers in a silicon electrode of an LC cell, which triggered voltage application for LC reorientation.

Infrared wire-grid polarizer with Y2O3 ceramic substrate.

Using two-beam interference lithography and dry etching, we fabricated a mid-IR wire-grid polarizer consisting of a 350 nm pitch WSi grating on an Y(2)O(3) ceramic substrate, which has wider transparency than sapphire. The transmittance of TM polarization was greater than 70% in the 3-7 μm wavelength range without antireflection films, and the extinction ratio was over 20 dB in the 2.5-5 μm wavelength range.

Terahertz wire-grid polarizers with micrometer-pitch Al gratings.

We fabricated a terahertz wire-grid polarizer consisting of a micrometer-pitch Al grating on a Si substrate by photolithography and wet etching. The ratio of TM and TE transmittances (extinction ratio) was over 35 dB at 0.5 THz.

Transmittance enhancement of a wire-grid polarizer by antireflection coating.

We examined the effect of an antireflection (AR) coating to enhance the TM transmittance of the wire-grid polarizer. The polarization transmission spectra were calculated using the rigorous coupled-wave analysis. As a result, we verified that an AR film should be inserted between a wire-grid and a Si substrate as regards the TM transmittance and the polarization function.

Modeling, fabrication, and characterization of tungsten silicide wire-grid polarizer in infrared region.

We designed and fabricated a tungsten silicide wire-grid polarizer. To examine its polarization characteristics, the transmission spectra of the polarizer were simulated using the effective medium theory. The polarizer was fabricated based on the simulation results.

Tunable whispering gallery mode emission from a microdroplet in elastomer.

A fluorescent microdroplet was formed in elastomer to facilitate handling and wavelength tuning. A methanol solution of rhodamine 6G was put into a solidifying polysiloxane resin with a needle. Addition of surfactant was effective to stabilize the droplet.

Photochromism induced by infrared two-photon absorption.

An IR laser of 940 nm wavelength induced photochromic reaction in acrylate that contained both spirobenzopyran and rare-earth doped oxide (Gd(2)O(2)S:YbEr). The rare-earth elements were excited by two 940 nm photons and emitted a 550 nm photon, which caused photochromic isomerization of spirobenzopyran. This acrylate turned to its original orange color by either thermal relaxation or ultraviolet irradiation, and was bleached again by IR laser irradiation.

Mid-infrared wire-grid polarizer with silicides.

An infrared (IR) polarizer with tungsten silicide (WSi) wire grid was fabricated by two-beam interference exposure and reactive ion etching. To enhance TM transmittance, silicon monoxide was deposited between the WSi wire grid (400 nm period) and a Si substrate. The transmittance was over 80% in the 4-5 microm wavelength range.

Time-resolved infrared spectrometry with a focal plane array and a galvano-mirror.

Time-resolved spectrometry was conducted in the mid-infrared region (2.8-4.6 microm).

Full-color illumination that needs no electric power.

Red, green, and blue phosphorescent resins were developed to realize full-color illuminators that shine without the need for electric power. Red phosphorescence, which used to be weak with conventional red phosphors, was enhanced notably with dye-doped resins in which green or blue phosphors were dispersed uniformly; i.e.

Photochromic isomerization of spirobenzopyran in nanoholes of anodic alumina.

A notable change in the photochromic characteristics was observed when the benzene solution of spirobenzopyran was put in nanoholes of anodic alumina. The absorption peak that appeared in the ultraviolet irradiation process shifted to a shorter wavelength, and the decay time of the decoloration process became approximately 200 times longer than that of the original solution. After a preservation period of several days, however, both the absorption wavelength and the decay time recovered to those of the original solution.

Direct laser writing of thermally stabilized channel waveguides with Bragg gratings.

Thermally stabilized photo-induced channel waveguides with Bragg gratings were fabricated in Ge-B-SiO2 thin glass films by exposure with KrF excimer laser and successive annealing at 600 degrees C. The annealing reversed the photo-induced refractive index pattern and also enhanced its thermal stability. The stabilized channel waveguide with a Bragg grating showed diffraction efficiency of 18.

Emergency illumination panel that displays different pictures depending on room brightness.

We fabricated an emergency illumination panel by stacking two translucent pictures, one of which was painted with ink and the other with phosphors. When the panel was illuminated by backlight or room light, only the ink-printed picture was visible to the human eye and only the phosphorescent picture was visible in darkness. A two-way mirror was inserted between the two pictures both to prevent super-imposition of the two images and to enhance phosphorescence.

Complex refractive-index spectrum of liquid crystal in the infrared.

The ordinary and extraordinary complex refractive indices, n(o) - j kappa(o) and n(e) - j kappa(e), of a nematic liquid crystal were measured in the infrared region at 3.0-11.5-microm wavelength.