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The embedding of nanoscopic metal structures into polymeric matrices represents a convenient way to stabilise a controlled dispersion of protected nanoparticles whilst taking advantage of their physical characteristics. Supercritical carbon dioxide (scCO2) has been used to produce silver nanoparticles in optically transparent polycarbonate (PC) matrices allowing fine scale dispersions of particles to be produced within a prefabricated polymer component. Characterization of these nanocomposites has been performed using transmission electron microscopy (TEM) and UV‐vis spectroscopy. The substrates give excellent responses in surface‐enhanced Raman spectroscopy (SERS) for both 4‐aminothiophenol and rhodamine 6G target molecules. They offer significant benefits over more conventional SERS substrates in that they are cheap, flexible, mechanically robust and temporally stable. Post‐processing the films via simple etching techniques, provides an additional degree of design control and the potential to fabricate devices with unique excitation and detection geometries for a wide range of applications.

We investigate the surface roughness of polycrystalline silicon core optical fibers fabricated using a high-pressure chemical deposition technique. By measuring the optical transmission of two fibers with different core sizes, we will show that scattering from the core-cladding interface has a negligible effect on the losses. A Zemetrics ZeScope three-dimensional optical profiler has been used to directly measure the surface of the core material, confirming a roughness of only ~0.1 nm. The ability to fabricate low-loss polysilicon optical fibers with ultrasmooth cores scalable to submicrometer dimensions should establish their use in a range of nonlinear optical applications.

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The recent advancements in on-chip silicon photonics has lead to the demonstration of a number of compact optoelectronic devices owing to the unique material properties of the semiconductor. Although to date most of the major advancements have been based on single-crystal silicon waveguides , lately there has been an increased interest in polycrystalline structures for integrated devices as the deposition process is easier, allowing for more design flexibility. As a photonics material, polysilicon offers good optical and electronic properties but it is typically associated with large losses due to scattering off grain boundaries and surface imperfections at the corecladding interface.Our silicon core optical fibres are fabricated by depositing silicon inside a silica capillary template using a high-pressure processing technique [1]. This process has several advantages: firstly, the potential to integrate the semiconductor chip and optical fibre technologies will greatly simplify device coupling and design. Secondly, using silica capillaries as templates (which have an internal surface roughness of < l nm) ensures an extremely smooth core-cladding interface, so that the waveguide losses are primarily due to the bulk material losses. Furthermore, this technique allows for easy control of the waveguide dimensions by simply choosing the appropriate silica capillary template, giving a further degree of design flexibility so that the mode confinement and dispersion properties can be tailored.In this paper we present measurements of the optical losses of our silicon core fibres as a function of wavelength. Fig. lea) shows a silicon core fibre under brightfield microscope illumination. The lack of scatter and the smooth core-cladding boundaries indicate an absence of microscopic imperfections. The polycrystalline grain size has been estimated by TEM measurements, shown in Fig. l(b), to be 0.5-1J1lll. To quantify the wavelength dependent losses of the silicon fibres we have preformed cut-back measurements by filtering the output of a supercontinuum source to yield an average launch power of -0.5mW. Fig. l(c) shows loss measurements for a 5.61lm silicon core fibre. From these we obtain a loss of~8dB/cm at 1.55J.lffi, comparable with the lowest losses reported in the literature, and the good agreement with a A.-4 fit indicates that the losses are primarily due to Rayleigh scattering. Comparing these measurements over the telecoms wavelength band with a silicon fibre with a reduced core size of 1.3J1lll, so that the waveguided modes have a larger interaction with the core-cladding interface, we have found that the losses are comparable as shown Fig. I(d), confirming the negligible role of surface scatter. Using this technique, we have the potential to fabricate silicon core waveguides with dimensions down to hundreds of nm, where the losses are primarily limited by the materials quality.