Ryohei Yagi

Modulation of Polymer Refractive Indices with Diamond Nanoparticles for Metal-Free Multilayer Film Mirrors

Modulation of the refractive index of a polymer was achieved by combining it with diamond nanoparticles (NDs). The increase in the refractive index was controlled by the amount of NDs added, according to the Lorentz-Lorenz equation. The refractive index of poly(vinyl alcohol) (PVA), which was used as the base polymer, increased from 1.52 to 1.88. A multilayer film consisting of alternating layers of ND-PVA composite and poly(methyl methacrylate) exhibited ca. 80% reflectance with 10 bilayers.

A Single Fiber Heterodyne Optical Fiber Hydrophone

A heterodyne interference type detection scheme using only one polarization-maintaining fiber is experimentally investigated for underwater sound detection. A linear relation between sound pressure and output voltage has been obtained up to a sound pressure level of 188 dB re 1 µPa. It has been confirmed that an optical fiber hydrophone of this type has a good transient response and is useful for cavitation noise detection.

On/off switching of structural color by using multi-bilayered films containing copolymers having azobenzene and biphenyl side groups

In this paper, the change in structural color of multi-bilayered films fabricated by stacking copolymers, PMAz–PMBP (m : n), consisting of azobenzene and biphenyl side chain groups, and polyvinyl alcohol (PVA) alternately, was investigated. The multi-bilayered films consisting of polyacrylates having an azobenzene side chain group and PVA were found to reflect a light of specific wavelength, and to show reversible change in the reflection intensity by thermal annealing and irradiation with non-polarized ultra violet (UV) light. However, a long irradiation time was required for the change in reflection intensity of the multi-bilayered films. Therefore, we synthesized PMAz–PMBP (m : n), consisting of azobenzene and biphenyl side chain group having no absorbance over 300 nm, and the PMAz–PMBP (m : n)/PVA multi-bilayered films were fabricated. All the multi-bilayered films showed reversible change in the reflection intensity by thermal annealing and irradiation with non-polarized UV light. The re-coloration speed of PMAz–PMBP (75 : 25)/PVA 20-multibilayered film was faster than others fabricated in this study. It is related to penetration depth of light into the films. The effect of the introduction of the biphenyl side groups in the copolymers on the response behavior of the change in the structural color will be discussed.

Simultaneous Sensing of Acoustic Wave and Temperature Using a Polarization-Maintaining Fiber

Simultaneous sensing of acoustic wave and temperature change using a polarization-maintaining fiber is experimentally investigated. Temperature change is detected by homodyne interference of the X and Y eigenmodes of the fiber, while acoustic wave is detected by heterodyne interference of the X component of the output light from the fiber and the reference beam. Simultaneous sensing was successfully demonstrated.

Fabrication of wide angle structural color with the patchy multi-bilayered films

ABSTRACT Multi-bilayered films with precisely controlled layer thickness were constructed for structural color and their reflection angular dependences were investigated. For wide angle structural color, it was intended to the macro irregularity of multi-bilayered films by randomly dispersed micron size multi-bilayered films in PDMS matrix. In addition, on-off switching of the reflection was examined with respect to the molecular orientation behavior of azobenzene chromophores by annealing and light irradiation.

Optically switchable multi-stopband of non-quarter-wavelength dielectric multilayer using azobenzene polymer liquid crystal

Non-quarter-wave stacked dielectric multilayers including azobenzene polymer liquid crystal layers are investigated in this study. The azobenzene polymer liquid crystal has a photoinduced reversible refractive index based on photoisomerization. By using the reversible refractive-index change, the reflectance of a stopband can be controlled. In this system, the azobenzene molecules change their conformation when they are irradiated with ultraviolet (UV) or visible light. In general, stacking many layers of different thicknesses can produce broadband or multicolor reflections for a dielectric multilayer. However, in a multilayer having thick azobenzene layers, UV or visible light used for controlling photoisomerization hardly reaches the bottom part of the multilayer because the light is mainly absorbed at its top surface. To solve this problem, the dependence on the thickness ratio of the multilayer is investigated and a non-quarter-wave stacked multilayer having RGB reflections is experimentally demonstrated using thin azobenzene layers.

Photo-induced orientation behaviors of azobenzene liquid crystal copolymers for photonic crystals

A certain wavelength of incident light is forbidden based on the optical periodicity related to the intervals and refractive indices of the comprising materials. For multi-bilayered films with periodicity, on–off switching of reflection is possible due to the presence or absence of a refractive index difference between two consisting films. Changes in the refractive index can be induced by stimuli-responsive orientation behaviors of liquid crystal (LC) molecules with birefringence. Azobenzene (Az) groups are employed for photo response and copolymerized with non-photo-responsive LC mesogen groups for cooperative orientation to improve light penetration by the dilution of Az concentration. LC mesogen groups are designed to have a high refractive index to improve the reflection contrast. The refractive indices and the orientation behaviors of the copolymer films are investigated. On–off switching of reflection for multi-bilayered films consisting of alternate Az-containing LC copolymers and poly vinyl alcohol is conducted using ultraviolet and visible light irradiation, and their reflection intensity and response speed are compared between the different LC mesogen types and molar ratios.

Dielectric Multilayer Including Azobenzene Polymer Liquid Crystal with Non-quarter-wave Stack

Dielectric multilayer including azobenzene polymer liquid crystal acts as a one-dimensional photonic crystal and has optical-switchable reflection bands. The reflection intensity can be controlled by irradiation of ultraviolet (UV) or visible light, in which the optical switch is based on cis-trans photoisomerization. An increase in the number of layers prevents photoresponse in the multilayer including azobenzen layers because UV or visible light for control cis-trans isomerization hardly reach the bottom of the multilayer due to exponential decay of light intensity. In this study, the multilayer consisting of thin azobenzene layers is investigated. According to numerical calculations, the non-quarter-wave structured multilayer has multiwavelength reflection band. Angular dependence of reflection color from multiwavelength stopband is also studied using the XYZ color space. The non-quarter-wave multilayer suppresses reflection color change compared with conventional quarter-wave multilayer.

Fabrication of Photo Responsive Multi-bilayered Film consisting of Azobenzene containing Copolymers and Polyvinyl Alcohol

In this study, faster response speed of ON/OFF switching of multi-bilayered films containing azo-functionalized polymer liquid crystal and polyvinyl alcohol, PVA, is investigated. The multi-bilayered films were found to reflect a light of specific wavelength, and showed reversible change in the reflection intensity by irradiation with non-polarized visible light and UV light. The multi-bilayered film having high absorbance around 300-500 nm due to stacking several decades of azobenzene containing layer. So, the change in reflection intensity of multi-bilayered film takes long time by light irradiation. We synthesized polyacrylates copolymers with azobenzene and biphenyl side chains where biphenyl groups is having no absorbance at UV and visible region. Multi-bilayered films were fabricated by spin-coating method and the switching time of reflection was investigated comparing to the multi-bilayered film containing azobenzene homopolymer, the ON switching times of reflection for the copolymers were faster than homopolymer needing 900 s. It is attributed to that inducing UV light (λ = 365 nm) easily entered into the film by introducing of biphenyl groups.

Fabrication of Multilayer Film Type Laser Devices Containing Azobenzene Polymer and Control of Polarized Laser Emission

We prepared multi-bilayered films consisting of methacrylate polymer having azobenzene side chain groups (PMAz6Mc), polyvinyl alcohol and lasing dye. We investigated effects of molecular orientation of azobenzene moieties on the lasing behavior by measuring laser emission of the multi-bilayered films with/without polarized visible light irradiation to cause trans-cis-trans photoisomerization of azobenzene moieties. After irradiation of the polarized visible light, significant dependence of polarization direction of the laser emission intensity was observed, corresponding to the change in the molecular orientation of azobenzene moieties.