Okihiro Sugihara

Refractive index control and Rayleigh scattering properties of transparent TiO2 nanohybrid polymer.

The surface of TiO2 nanoparticles (NPs) was modified by a coupling agent of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane to render them highly compatible with organic monomer mixtures avoiding aggregation. Such TiO2 NPs were then chemically attached with a prepolymer. The refractive index of hybrid TiO2 NPs-polymer was increased dramatically in comparison with that of pure polymer, and it can be controlled by adjusting the content of TiO2 NPs. The Rayleigh scattering of hybrid TiO2 NPs-polymer was size-dependent and increased with the increase of the TiO2 NPs content. When Rayleigh scattering of the hybrid material prepared with a milling and centrifuge process was significantly lowered, one can obtain a transparent sample, which is good for optical devices.

Phase-matched second harmonic generation in poled dye/polymer waveguide

Poled film of 2-methyl-4-nitroaniline (MNA) and poly(methyl methacrylate) is prepared. Poling effects of MNA molecular alignments are observed by reducing the absorption spectrum and increasing the refractive index of the film. Phase-matched second harmonic generation (SHG) is achieved using the mode dispersion relation of the optical waveguide with an estimated SHG conversion efficiency of 7.4 x 10(-3) % in the waveguide.

Reflection-type confocal readout for multilayered optical memory

We present a multilayered optical memory for use in reading data with a confocal reflection microscope system. We use a recording medium in which photosensitive thin films and nonphotosensitive transparent films are stacked alternately. Since the photosensitive films are thinner than the depth of focus of the recording beam, the spatial frequency distribution of the recorded bit data is extended in the axial direction. The extended distribution overlaps the coherent optical transfer function of the reflection-type confocal microscope. Urethane-urea copolymer film is used as a photosensitive material. The recording and reading of two layers are demonstrated.

Non-optically probing near-field microscopy

We present a near-field optical microscope without the use of a probe for illumination or detection or scattering of the optical fields. In our system the optical fields near specimens are converted to the topographical change of a photosensitive film, and then the topography is detected with an atomic force microscope. Urethane-urea copolymer films are used for the conversion material from the optical fields to the topography. We succeeded in imaging with a resolution higher than 50 nm.

Light-induced self-written polymeric optical waveguides for single-mode propagation and for optical interconnections

Light-induced self-written (LISW) polymeric optical waveguides were fabricated in a photopolymerizing resin mixture solution using a single-mode optical fiber. In order to realize a straight waveguide core, a pre-UV treatment was performed before core formation. Single-mode propagation of laser light at 1310 nm was realized by appropriately controlling the ratio of the resins in the mixture for the first time. Moreover, optical interconnection between two single-mode fibers was demonstrated based on this technology.

Second-Harmonic Generation from Single Crystals of N-Substituted 4-Nitroanilines

Six N-substituted derivatives of 2-methyl-4-nitroaniline (MNA) and two N-substituted derivatives of 4-nitroaniline were synthesized and their physical and optical properties were examined in the search for nonlinear optical materials with a sufficiently large second harmonic (SH) activity and applicability to practical use. Some derivatives produced single crystals and their structures were determined by X-ray crystallography. The trends of the SH intensity of these materials could be qualitatively explained based on the b tensor (the effective molecular hyperpolarizability in the crystal). Amongst the derivatives examined in this investigation, N-benzyl-MNA showed the highest SH activity (up to twice that of MNA), thermostability and phase-matching ability.

Ultraviolet photobleaching process of azo dye doped polymer and silica films for fabrication of nonlinear optical waveguides

We describe the effect of UV photobleaching of poled polymer and silica films and the application of UV photobleaching to waveguide-type optical devices. Disperse Red 1-doped poled polymer and silica films with large and stable second-order nonlinearity were used as nonlinear optical materials. We investigated the mechanism of UV photobleaching of poled films by the changes in absorption spectrum and nonlinearity and refractive index. Moreover, simple fabrication of both the channel waveguide and the chi((2)) diffraction grating based on UV photobleaching is demonstrated.

Compact Y-Branch-Type Polymeric Optical Waveguide Devices with Large-Core Connectable to Plastic Optical Fibers

Y-branch-type polymeric optical waveguides with a large core size of 1000 µm, branching angles from 2 to 10° and a branching top-part radius of 200 µm were fabricated by hot embossing. An output power ratio of 1:1 from each output port and an excessive loss of ~1.0 dB depending on branching angle were realized. A compact size Y-branch-type waveguide device with a wide branching angle was proposed.

Low-loss polymeric optical waveguides with large cores fabricated by hot embossing

A simple low-cost method of fabricating polymeric optical waveguides with large core sizes for plastic optical fibers is presented. The waveguides are fabricated by hot embossing with an ultraviolet-cured epoxy resin stamper. The stamper is fabricated by replication of a rectangular groove mold that is made from silicone rubber replicated from a ridged original silicon master. The master is fabricated by anisotropic etching of (110) single-crystal silicon. Optical waveguides with large core sizes of 100-500 microm have been fabricated, and a low propagation loss of 0.19 dB/cm at 650 nm was achieved.

Stable and large second harmonic generation in sol-gel-processed poled silica waveguides doped with organic azo dye

Sol-gel-processed silica films doped with organic azo dye, Disperse Red 1 (DR1) in a higher concentration of 21.7 wt%, were prepared at a higher baking temperature with corona poling of higher voltage than in other reports to obtain stable and large second harmonic generation (SHG) and film strength. A large effective SHG coefficient of 75 pm/V was measured for the film of 0.2-µm thickness at a fundamental wavelength of 1064 nm, and the value was unvaried for 700 h with no relaxation. Moreover, a waveguide SHG device of four-layer structure with DR1-doped sol-gel film as a top layer was fabricated for the first time, and Cherenkov-type phase-matched SHG was observed successfully.