We propose an ultrahigh quality factor (Q) photonic crystal slab nanocavity created by the local width modulation of a line defect. We show numerically that this nanocavity has an intrinsic Q value of up to 7×107. Transmission measurements for fabricated Si photonic-crystal-slab nanocavities directly coupled to input/output waveguides have exhibited a loaded Q value of ∼800000. These theoretical and experimental Q values are very high for photonic crystal nanocavities. In addition, we demonstrate that simply shifting two holes away from a line defect is sufficient to achieve an ultrahigh Q value both theoretically and experimentally.

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Detailed propagation loss spectrum measurements for line-defect waveguides in silicon photonic crystal slabs are presented, which show record low loss values ͑5 dB/cm͒ and complicated frequency dependence. We quantitatively analyze the origin of the loss spectrum shape using a photon Green function theory and obtain a very good agreement, thus providing an explanation of the complex physical mechanisms responsible for the observed propagation loss. In particular, we demonstrate the influence of out-plane, backward, intermode, and in-plane scattering processes on the observed loss spectra, induced by the structural disorder that occurs during fabrication, and highlight the importance of backward and intermode scattering in these waveguides.

For nearly two decades, the field of plasmonics1 - which studies the coupling of electromagnetic waves to the motion of free electrons in a metal2 - has sought to realize subwavelength optical devices for information technology3–6, sensing7,8, nonlinear optics9,10, optical nanotweezers11 and biomedical applications12. Although the heat generated by ohmic losses is desired for some applications (e.g. photo-thermal therapy), plasmonic devices for sensing and information technology have largely suffered from these losses inherent to metals13. This has led to a widespread stereotype that plasmonics is simply too lossy to be practical. Here, we demonstrate that these losses can be bypassed by employing “resonant switching”. In the proposed approach, light is only coupled to the lossy surface plasmon polaritons in the device’s off-state (in resonance) where attenuation is desired to ensure large extinction ratios and facilitate sub-ps switching. In the on state (out of resonance), light is prevented from coupling to the lossy plasmonic section by destructive interference. To validate the approach, we fabricated a plasmonic electro-optic ring modulator. The experiments confirm that low on-chip optical losses (2.5 dB), high-speed operation (>>100 GHz), good energy efficiency (12 fJ/bit), low thermal drift (4‰ K-1), and a compact footprint (sub-λ radius of 1 μm) can be realized within a single device. Our result illustrates the potential of plasmonics to render fast and compact on-chip sensing and communications technologies.

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We report the observation of four-wave mixing phenomenon in a simple silicon wire waveguide at the optical powers normally employed in communications systems. The maximum conversion efficiency is about -35 dB in the case of a 1.58-cm-long silicon wire waveguide. The nonlinear refractive index coefficient is found to be 9x10-18 m2/W. This value is not negligible for dense wavelength division multiplexing components, because it predicts the possibility of large crosstalk. On the other hand, with longer waveguide lengths with smaller propagation loss, it would be possible to utilize just a simple silicon wire for practical wavelength conversion. We demonstrate the wavelength conversion for data rate of 10-Gbps using a 5.8-cm-long silicon wire. These characteristics are attributed to the extremely small core of silicon wire waveguides.

This paper describes the microstructure to improve the magnetic field dependence of the critical current density, Jc, of Y(RE)Ba2Cu3O7−x [Y(RE)123, RE: Gd and Sm] coated conductors. A columnar microstructure 10nm in diameter has been obtained by using Y123 targets including yttrium-stabilized zirconium for the pulsed-laser deposition. This columnar structure, composed of BaZrO3 and Y123, continued from the substrate to the surface of the film 0.25μm in thickness. We have named it “the bamboo structure” from its morphology. The bamboo structure was effective for increasing Jc in a magnetic field especially parallel to the c-axis. We have also found stacking faults in RE123 effective to improve Jc.