Chapter 11 - Silica Nanofibers and Subwavelength-Diameter Fibers

Abstract

Air-clad silica nanofibers, named for their submicrometer diameters, have a large core–cladding index contrast for efficient optical confinement. For single-mode operation, these fibers are usually thinner than the wavelength of the light they carry and are therefore also called sub wavelength-diameter fibers. The small diameter of a nanofiber and the large core–cladding index contrast yield a number of interesting optical properties such as tight optical confinement, large evanescent fields, strong field enhancement, and large waveguide dispersions. A few techniques can be used to fabricate silica nanowires or nanofibers such as photo or electron beam lithography, chemical growth, and taper drawing of optical fibers. The taper-drawing method exhibits simplicity in fabrication and also the ability to fabricate nanofibers with extraordinary diameter uniformities, atomic-level surface smoothness, and long length that are difficult to achieve by any other means. The nanofibers obtained with the two-step taper-drawing techniques consist of three parts—a millimeters-long taper that is connected to the starting microfiber, a uniform nanofiber with a length up to tens of millimeters, and an abruptly tapered end that is usually several to tens of micrometers in length.