A novel integrated optical sensor based on a cylindrical microcavity (MC) is proposed. A MC sustains so-called whispering-gallery modes (WGMs), in which the energy of the optical field can be efficiently stored. By monitoring the scattering intensity from the MC, one can detect minute changes in the refractive index of the WGM, for instance, as a result of analyte adsorption. Measurement of a change in refractive index of as little as 10(-4) is demonstrated experimentally. The MC-based integrated optical sensor may have a size of approximately 8mum , and it is rugged and inexpensive.

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In this review we present an overview of the progress made in recent years in the field of integrated silicon-on-insulator (SOI) waveguide photonics with a strong emphasis on third-order nonlinear optical processes. Although the focus is on simple waveguide structures the utilization of complex structures such as microring resonators and photonic crystal structures is briefly discussed as well. Several fabrication methods are explained and methods which improve optical loss, coupling efficiency and polarization dependence are presented.As the demand for bandwidth increases communication systems are forced to use higher bit rates to accommodate the load. A consequence of high-bit-rate systems is that they require short pulses where the importance of waveguide dispersion tailoring becomes increasingly important. The impact of short pulses on the efficiency of all-optical processes is discussed and recent accomplishments in this field are presented. Numerical results of femtosecond, picosecond and nanosecond pulse propagation in SOI waveguides are compared to provide an insight into the physical processes that dominate at these different time scales. In this work we focus on two-photon absorption (TPA), free-carrier absorption (FCA), plasma dispersion and the optical Kerr effect. After describing these nonlinear effects, some other important all-optical processes based on plasma dispersion and the Kerr effect are described, namely cross-absorption modulation (XAM), self-phase modulation (SPM), cross-phase modulation (XPM), four-wave mixing (FWM) and stimulated Raman scattering (SRS). The latter provides the best hope for practical and/or commercial applications and finds its use in amplification and lasing. Furthermore, we present some guidelines for efficient numerical modelling of propagation in SOI waveguides.This review is a good starting point for those who are new in this hot and rapidly emerging field and gives an overview of important considerations that need to be taken into account when designing, fabricating and characterizing SOI waveguides for ultrafast third-order nonlinear all-optical processing.

The influence of salivary pellicles on the demineralization of human dental enamel by 1% citric acid was studied. The pellicles were formed on embedded human tooth surfaces incubated in vitro with various solutions for periods of up to 6 days. Pellicles induced by unstimulated whole saliva gave an approximately 45% and those from parotid saliva a 25% inhibition of demineralization. On the other hand, a pellicle formed from mixed submandibular and sublingual (SM-SL) saliva in 30 min gave a retardation in lesion formation of at least 40% and after a 60-min exposure to SM-SL saliva, the lesion formation was completely prevented. In contrast, when the mucins were removed from SM-SL saliva by ultracentrifugation, protection against demineralization by the pellicle formed on exposure to the supernatant was only 30%. The effect of pellicles obtained by isolated salivary mucins was also studied. Human whole salivary mucins (HWSM) were isolated from both human SM-SL saliva and whole saliva of two individuals with blood group A. The mucins contained 18% protein, 72% carbohydrate, 1.4% sulfate and 0.14% phosphate. The major components of the protein moiety were threonine (14.7%), valine (12.6%) and serine (10.8%). The molar ratio of the sugar residues was: galactose: N-acetylglucosamine: N-acetylgalactose: fucose: N-acetylneuraminic acid = 6:4.5:4:7:1. A pellicle formed by a 3-day exposure to salivary mucins in vitro gave 100% protection of the tooth surface against demineralization by citric acid. These data suggest that the mucins in human saliva contribute to a large extent to its protective effect against acidic attacks on the tooth surface.

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Abstract:The propagation of 300 femtosecond optical pulses in Silicon-on Insulator waveguides has been studied by means of a pump-probe set-up. The ultrafast pulses allowed the observation of large Kerr-induced red and blue shifts (9nm and 15nm, respectively) of the probe signal depending on the delay between pump (1554nm) and probe (1683nm) pulses. A numerical model taking into account the Kerr effect, Two Photon Absorption and Free Carrier Absorption is presented and provides good agreement with our experimental data and data in literature. A microring resonator based device is proposed that exploits the observed wavelength shift for sub-picosecond all-optical switching. ©2006 Optical Society of America O. Boyraz, P. Koonath, V. Raghunathan, and B. Jalali, "All optical switching and continuum generation in silicon waveguides," Opt. Express 12, 4094-4102 (2004

A reconfigurable four channel OADM based on vertically coupled thermally tunable SilNliSiOz microring resonators has a footprint of 0.25 mm'. Each MR can be tuned over 4.3 nm and has a bandwidth >I0 GBit.