1. Department of Physics and Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
2. Centre for Optical and Electromagnetic Research and Department of Physics, Zhejiang University, Hangzhou 310027, China
3. Department of Physics, Graduate School of Science, Tohoku University, Sendai, Miyagi 9808578, Japan
4. Present address: Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, Massachusetts 02420, USA

Correspondence to: Eric Mazur¹ Correspondence and requests for materials should be addressed to E.M. (Email: mazur@deas.harvard.edu).

Abstract

Silica waveguides with diameters larger than the wavelength of transmitted light are widely used in optical communications, sensors and other applications^{1, 2, 3}. Minimizing the width of the waveguides is desirable for photonic device applications, but the fabrication of low-loss optical waveguides with subwavelength diameters remains challenging because of strict requirements on surface roughness and diameter uniformity^{4, 5, 6, 7}. Here we report the fabrication of subwavelength-diameter silica 'wires' for use as low-loss optical waveguides within the visible to near-infrared spectral range. We use a two-step drawing process to fabricate long free-standing silica wires with diameters down to 50 nm that show surface smoothness at the atomic level together with uniformity of diameter. Light can be launched into these wires by optical evanescent coupling. The wires allow single-mode operation, and have an optical loss of less than 0.1 dB mm^-1. We believe that these wires provide promising building blocks for future microphotonic devices with subwavelength-width structures.