Keisuke Odoi

Hole injection enhancement by sparsely dispersed Au nanoparticles on indium tin oxide electrode in organic light emitting devices

Gold nanoparticles stabilized by a hyper-branched polystyrene and adhered sparsely on indium tin oxide electrode can enhance hole injection to hole transport layer of N,N′-diphenyl-N,N′-bis(1-naphthyl)(1,1′-biphenyl)-4,4′-diamine. Although surface coverage by nanoparticles is less than 1%, the current density increases almost 1.5 orders of magnitude in hole-only device compared with the identical device without nanoparticles. This nanoparticle is also applied in typical organic light emitting diode. The driving voltage can be significantly lowered accompany with almost six times higher current density and luminance at 6 V. The local electric field induced by negatively charged nanoparticles should bring about the hole injection enhancement.

A hybrid electro-optic polymer and TiO2 double-slot waveguide modulator.

An electro-optic (EO) modulator using a TiO2 slot hybrid waveguide has been designed and fabricated. Optical mode calculations revealed that the mode was primarily confined within the slots when using a double-slot configuration, thus achieving a high EO activity experimentally. The TiO2 slots also acted as an important barrier to induce an enhanced DC field during the poling of the EO polymer and the driving of the EO modulator. The hybrid phase modulator exhibited a driving voltage (Vπ) of 1.6 V at 1550 nm, which can be further reduced to 0.8 V in a 1 cm-long push-pull Mach–Zehnder interferometer (MZI) structure. The modulator demonstrated a low propagation loss of 5 dB/cm and a relatively high end-fire coupling efficiency.

Ultra-thin silicon/electro-optic polymer hybrid waveguide modulators

Ultra-thin silicon and electro-optic (EO) polymer hybrid waveguide modulators have been designed and fabricated. The waveguide consists of a silicon core with a thickness of 30 nm and a width of 2 μm. The cladding is an EO polymer. Optical mode calculation reveals that 55% of the optical field around the silicon extends into the EO polymer in the TE mode. A Mach-Zehnder interferometer (MZI) modulator was prepared using common coplanar electrodes. The measured half-wave voltage of the MZI with 7 μm spacing and 1.3 cm long electrodes is 4.6 V at 1550 nm. The evaluated EO coefficient is 70 pm/V, which is comparable to that of the bulk EO polymer film. Using ultra-thin silicon is beneficial in order to reduce the side-wall scattering loss, yielding a propagation loss of 4.0 dB/cm. We also investigated a mode converter which couples light from the hybrid EO waveguide into a strip silicon waveguide. The calculation indicates that the coupling loss between these two devices is small enough to exploit the potential fusion of a hybrid EO polymer modulator together with a silicon micro-photonics device.

Water-proton relaxivity of hyperbranched polymers carrying TEMPO radicals

High water‐soluble hyperbranched poly(styrene) (HPS) polymers carrying stable 2, 2, 6, 6‐tetramethylpiperidine‐1‐oxyl (TEMPO) radicals, HPS‐N‐TEMPO, HPS‐Im‐TEMPO, and HPS‐Im‐(TEMPO)2, were prepared in ca. 60% introducing yield. HPS‐N‐TEMPO and HPS‐Im‐TEMPO were determined to be nearly spherical shapes of the diameter of 2.4 ± 0.6 and 2.2 ± 0.6 nm, respectively, by transmission electron microscope (TEM) images. The values of water‐proton relaxivity, r1, at 25 MHz, 0.59 T, and 25 °C were 6.0, 5.2, and 14 mM−1 sec−1 for HPS‐N‐TEMPO, HPS‐Im‐TEMPO, and HPS‐Im‐(TEMPO)2, respectively. The spin‐lattice relaxation time (T1)‐weighted images in phantom were also observed. Copyright

A straightforward electro-optic polymer covered titanium dioxide strip line modulator with a low driving voltage

An electro-optic (EO) modulator composed of an EO polymer/titanium dioxide (TiO2) hybrid waveguide has been designed and fabricated. By using a TiO2 strip line (0.3 × 0.3 μm2 cross-section) as the core, the confinement factor in the EO polymer is optimized, thus achieving a high EO activity. The coplanar electrode spacing is tuned to enable an effective poling and a small propagation loss. The measured in-device EO coefficient is 100 pm/V at 1550 nm, with a driving voltage (Vπ) 3.2 V for the 12 mm-electrode length. The results also predict a possible Vπ of ∼1 V in a push-pull MZI structure. The EO activity of the modulator exhibited an excellent temporal stability at 85 °C for 500 h due to the high glass transition temperature of the EO polymer and the temperature-insensitive TiO2 strip line.

TiO2 ring-resonator-based EO polymer modulator

In this work, an electro-optic (EO) ring resonator modulator was designed and fabricated in a waveguide consisting of a titanium dioxide (TiO)₂ core, silicon dioxide (SiO₂) buffer layer, EO polymer claddings, and electrodes. By optimizing the thickness of the TiO₂ and SiO₂layers, the modulator could satisfy the single-mode requirement; furthermore 52.5% TM mode was confined in the active EO polymer layers. The designed modulator could also pole the EO polymer effectively regardless of its resistivity. Therefore, the EO modulator was observed to show a high resonance wavelength shift of 2.25 × 10(-2) nm/V. The intensity modulation at 1550 nm showed a Vp-p = 1.9 V for a 3dB distinction ratio.

Low driving voltage Mach-Zehnder interference modulator constructed from an electro-optic polymer on ultra-thin silicon with a broadband operation

An electro-optic (EO) polymer waveguide using an ultra-thin silicon hybrid has been designed and fabricated. The silicon core has the thickness of 50 nm and a width of 5 μm. The waveguide was completed after covering the cladding with the high temperature stable EO polymer. We have demonstrated a low half-wavelength voltage of 0.9 V at the wavelength of 1.55 μm by using a Mach-Zehnder interference modulator with TM mode operation. The measured modulation corresponded to an effective in-device EO coefficient of 165 pm/V. By utilizing the traveling-wave electrode on the modulator the high-frequency response was tested up to 40 GHz. The 3 dB modulation bandwidth was measured to be 23 GHz. In addition, the high frequency sideband spectral measurement revealed that a linear response of the modulation index against the RF power was confirmed up to 40 GHz signal.

High thermal stability 40 GHz electro-optic polymer modulators

As a consequence of the urgent demand for an electro-optic (EO) polymer modulator with an elevated temperature stability, we have prepared a selection of EO polymers having glass transition temperatures of up to 194°C. The measured half-wave voltage characteristics of the fabricated Mach-Zehnder interference modulators revealed an excellent thermal resistance at 105°C for approximately 2,000 hours. By utilizing traveling-wave electrodes on the modulator, the high-frequency response at 10-40 GHz was evaluated under ascending temperatures. The advantage of such high-temperature stability EO polymer modulators was clearly demonstrated by the continuous frequency response up to 130°C.

An electro-optic polymer-cladded TiO2 waveguide modulator

Organic electro-optic (EO) materials and their hybrid systems have received considerable attention for high-performance modulators. In this work, we demonstrate the design and fabrication of an EO modulator with a low half-wave voltage (Vπ) and a RF modulation response up to at least 10 GHz. The polymer used in this work has a glass transition temperature of 172 °C, which makes it stable even under high temperature RF sputtering. As a result, an EO polymer-cladded titanium dioxide (TiO2) waveguide structure can be utilized to enlarge the confinement factor, and thus, enable a low Vπ. The response of the modulator from 4 to 10 GHz has been measured, which shows a flat frequency response up to 10 GHz and a potential for the application in several tens GHz.

One dimensional polymeric photonic crystal doped with second-order nonlinear optical chromophore

Organic nonlinear optical (NLO) materials have attracted much interest for their potential applications over the past two decades mainly because of their faster electronic response and larger optical nonlinearities than the conventional inorganic materials. Especially, electro-optic (EO) polymers have been promising candidates for fast and broadband EO modulators as a result of the development of the 2nd-order NLO chromophore. In this manuscript, we report fabrication and design of one dimensional (1D) polymeric photonic crystals (PCs) to additionally enhance the optical nonlinearities of the organic NLO materials. We fabricated polymeric high-reflection mirrors for 1D PCs by a simple alternatively spin-coating two polymers under control of their optical thickness, in which a novel polymer was applied to the higher refractive index layer. We also designed defect-mode 1D polymeric PC for effective light-localization in the defect layer and discussed their effect for enhancement of the 2nd-order optical nonlinearities.