Three‐dimensional arrays of SiO2 nanometer particles lead to Bragg diffraction effects of visible light—as seen for natural opals, see also this issue's cover—and applications such as photonic bandgap materials. Teh fabrication of the opalline structures is described and details are given of how to obtain ordered compacts. The Figure shows a fracture surface of a sintered sample comprising 390 nm‐diameter silica spheres. magnified image

In this work we propose and demonstrate a solution to the problems which arise when SiO2 monodisperse nanospheres of diameters under 300 nm or over 550 nm are used to obtain opal-based photonic crystals. If the nanospheres are too small, the sedimentation rate is very slow or even may not occur; if they are large enough, no significant order can be achieved because the velocity is too high. This method, based on the electrophoretic phenomenon, allows us to control the sedimentation velocity. Furthermore, other species of importance in this field, such as SiO2 spheres covered with a thick layer of TiO2, do profit from this method.

We demonstrate label-free molecule detection by using an integrated biosensor based on a Si 3 N4/Si0 2 slotwaveguide microring resonator. Bovine serum albumin (BSA) and anti-BSA molecular binding events on the sensor surface are monitored through the measurement of resonant wavelength shifts with varying biomolecule concentrations. The biosensor exhibited sensitivities of 1.8 and 3.2 nm/(ng/mm 2 ) for the detection of anti-BSA and BSA, respectively. The estimated detection limits are 28 and 16 pg/mm 2 for anti-BSA and BSA, respectively, limited by wavelength resolution.Label-free biomolecule optical sensing technologies are of great interest because of their flexibility to analyze biomolecular interactions without using fluorescence, absorptive, or radio-labels. This simplifies the assay and allows time-resolved study of the kinetics of biomolecular interactions. Integrated photonic devices used as biosensors present important advantages, such as high sensitivity, small size, and high scale integration. Thus, label-free integrated optical biosensors based on Mach-Zehnder interferometers , directional couplers , microring , and disk resonators have been demonstrated to be very sensitive label-free biosensors.Recently, we have reported an integrated photonic sensor based on a slot-waveguide resonator . This photonic structure takes advantage of the remarkable property of slot-waveguides to provide high optical intensity in a subwavelength-size low refractive index region (slot-region) sandwiched between two high refractive index strips (rails) . This permits a very high interaction between the slot-waveguide mode probe and a liquid analyte. As a result, the reported slot-waveguide sensor exhibited a bulk ambient sensitivity as high as 212.1 nm/refractive index unit (RIU), which is more than twice as large as that exhibited by ring resonator optical sensors based on conventional strip waveguides. In this Letter we demonstrate the detection of label-free molecular binding reactions on the surface of a slot-waveguide ring resonator. Bovine serum albumin (BSA) protein and anti-BSA are used to study the biosensor performance.The device consists of a 70 /mm radius slotwaveguide ring resonator made of Si 3 N 4 on Si0 2 The Si 3 N4 rails of the slot-waveguide ring are separated by 200 nm (w sht ), and their widths are 400 and 550 nm for the outer and inner rails, respectively, as illustrated in Fig. 1(a). A beam propagation method calculation of the quasi-TE optical mode of the ring slot-waveguide at 1.3 /mm operation wavelength is

In this paper, we report experiments on the scattering of surface-elastic waves by a periodic array of cylindrical holes. The experiments were performed in a marble quarry by drilling cylindrical holes in two different configurations: honeycomb and triangular lattices. The attenuation spectra of the surface waves show the existence of absolute band gaps for elastic waves in these semi-infinite two-dimensional crystals. Results are compared with theoretical calculations based on a scalar-wave approach. The scaling property of the underlying theory has led us to explore the possible application of the results obtained to the attenuation of surface waves in seismic movements. ͓S0163-1829͑99͒07419-6͔