Optical modulator using metal-oxide-semiconductor type Si ring resonator

Electric-field drive optical modulators using a Si ring resonator were fabricated on silicon-on-insulator (SOI) wafers. The fabricated resonators consisted of Si waveguides with width and thickness of 1.0 and 0.3 μm, respectively. In order to induce the linear electro-optic (EO) effect in the Si core layer, the strain was applied by covering the layer with Si₃N₄ film (0.26 μm thick) deposited by low pressure chemical vapor deposition (LPCVD) at 750 °C. The vertical electric-field was applied to the Si waveguide through the top and bottom cladding layers, and the optical output from the drop port at the resonance wavelength was measured. At a wavelength of 1501.6 nm, the optical modulation of 33% was obtained at 200V (electric-field at the silicon surface ∼3 × 10⁵ V/cm, nearly the breakdown field). The resonance wavelength was shifted toward the short wavelength side by applying both positive and negative voltages, this shift was explained by carrier concentration modulation. The linear EO effect in the Si core layer was not observed, presumably because the strain in the Si core layer was too small.     

Internal modes and the local symmetry of PO4 tetrahedra in K(H1−xDx)2PO4 by Raman scattering

The v₃ and v₄ internal modes of PO^3?₄ tetrahedra are observable in KH₂PO₄ even above the transition temperature in the scattering geometry x(zz)y contrary to the selection rule of the site symmetry S₄ in the D_2d space group. Tominaga et al. discussed that the origin of this broken selection rule is due to the momentary site symmetry C₂ of these tetrahedra, and that the mechanism of the phase transition is of the order-disorder type of these distorted tetrahedra. Parallel studies compatible with their results have been carried out on mixed crystals K(H_1?xD_x)₂PO₄ and the same conclusion has been obtained as to the momentary site symmetry. These internal modes increase in intensity with deuteration, and the origin of this increase is discussed.     

QUANTUM EFFICIENCY FOR THE PHOTOCONVERSION OF BACTERIORHODOPSIN AT VERY LOW TEMPERATURES

Abstract— Quantum efficiencies for photoconversion of bacteriorhodopsin (trans-bR) to a bathochromic product (batho-bR^t) and its photoreversion in purple membrane at 77 and 9 K were investigated with low temperature spectrophotometry. The kinetics of the photoconversion and its photoreversion cannot be expressed by a single exponential curve. The photoconversions at 77 and 9 K showed the same slope in the early stage. The kinetics of the photoreversions were identical at the two temperatures. These results indicate that the quantum efficiencies for the conversion of trans-bR to batho-bR^t or for its photoreversion are identical at the two temperatures.
The fact that the photoreversion cannot be expressed by a single exponential curve suggests the existence of several conformational states of batho-bR^t due to the trimer structure of the purple membrane.     

Imaging of percolative conduction paths and their breakdown in phase-separated (La1-yPry)0.7Ca0.3MnO3 with y=0.7

Local magnetization and current distribution in (La(1-y)Pr(y))0.7Ca0.3MnO3 (y=0.7) crystals are studied by a magneto-optical (MO) imaging technique. MO images below 120 K visualize inhomogeneous magnetization and conduction paths that manifest the percolative conduction originated from the mesoscopic phase separation into ferromagnetic metals and antiferromagnetic insulators. Application of large amounts of current switches the current distribution from inhomogeneous to homogeneous concomitantly with a steep increase in resistivity. These phenomena are discussed in view of current induced collapse of the phase separation through a local heating.     

Nuclear magnetic resonance study of strongly correlated superconductors

This paper introduces nuclear magnetic resonance works in the strongly correlated super-conductors: heavy-Fermion, high-T _C superconductors and Sr₂RuO₄. The analyses strongly support the spin-fluctuation-mediated superconductivity model in a high-T _C superconductor.