Photonic devices are coming in smaller and smaller packages, giving rise to a demand for nanoscale components. To that end, investigators at the University of Southampton in the UK are working on an approach to be used in nanoscale nonlinear optical devices and have achieved what they believe is the first demonstration of the efficient modulation of light with light in a single nanoparticle.They grew the metallic nanoparticle at the tip of a tapered silica glass optical fiber with a nanoaperture of about 100 nm at its end by placing the fiber in a vacuum chamber, cooling it to about 80 K and exposing it to a gallium atomic beam. To demonstrate control of light with light in the nanoparticle, they used a CW diode laser operating at 1310 nm as a probe, and another, operating at 1550 nm, as a pump.The scientists observed transformations induced by the pump between various structural phases of gallium in the nanoparticle as its temperature varied from 80 to 300 K. The transformations are reversible and are accompanied by substantial changes in the optical properties of the nanoparticle. In the experiments, these led to changes in the reflectivity of the fiber tip blocked by the nanoparticle and, therefore, in the intensity of the reflected probe signal. Just a few tens of nanowatts of pump power are sufficient to induce the effect — leading the researchers to believe that the particles may serve as switching and memory elements in photonic devices based on nanoparticle chain waveguides or nanoapertures and may be used as scattering centers in tunable photonic bandgap or plasmon-polariton waveguides.The demonstration ushers in a new domain of photonics, said lead researcher Nikolay I. Zheludev, for which the scientists have coined the name “nano3 photonics” to reflect the scale of the dimensions involved; i.e., nanometers, nanowatts and nanoseconds. With that in mind, they will move from a proof-of-principle demonstration to finding materials suitable for operating at higher temperatures in an optical circuit.Nano Letters, online Aug. 26, 2005, doi:10.1021/nl0515652.