Subwavelength-diameter silica wires for microscale optical components

Optical components built from structures that are tens of micrometers wide are playing a key role in current optical communication networks, optical sensors, and medical optical devices. The demand for improved performance, broader applications, and higher integration density, together with rapid advances in nanotechnology for electronics and optoelectronics, has spurred an effort to reduce the size of basic optical components. However, the miniaturization of optical components with subwavelength and nanometer-sized optical guiding structures through established fabrication methods is challenged by the requirements of submicrometer-precision and the high cost associated with fabrication techniques such as EUV, X-ray and e-beam lithography. In addition the high optical losses of current nanometer-sized waveguides -- e.g., surface plasmon waveguides -- severely limit applications. We have recently developed a new type of optical wave guiding structure -- subwavelength-diameter silica wires -- as low-loss nanometer-sized building blocks for microscale optical components. By means of a high-temperature drawing/tapering approach that is much simpler than most of other methods, highly uniform silica wires as thin as 50 nm can be fabricated with surface roughness less than 0.5 nm (RMS). Within the visible and near-infrared spectral ranges, these wires can be used as subwavelength-diameter single-mode waveguides with optical losses down to 0.3 dB/cm, which is low enough for building microscale optical components. Using high-precision micro-/nano-manipulators, basic components such as waveguide bends and optical couplers are assembled from finely tailored silica wires. Important properties of these wires for practical applications, such as mechanical strength, low-index support and cross talk are also investigated. Both theoretical and experimental results show that the subwavelength-diameter silica wires reported here are promising for building microscale optical components of significantly reduced size and high flexibility.