Abstract
Nanofibres, optical fibres narrower than the wavelength of light, degrade in hours on exposure to air. We show that encapsulation in hydrophobic silica aerogel (refractive index 1.05) provides protection and stability (over 2 months) without sacrificing low attenuation, strong confinement and accessible evanescent field. The measured attenuation was <0.03 dB/mm, over 10 × lower than reported with other encapsulants. This enables many nanofibre applications based on their extreme small size and strong external evanescent field, such as optical sensors, nonlinear optics, nanofibre circuits and high-Q resonators. The aerogel is more than a waterproof box, it is a completely-compatible gas-permeable material in intimate contact with the nanofibre and hydrophobic on both the macroscopic and molecular scales. Its benefits are illustrated by experiments on gas sensing (exploiting the aerogel's porosity) and supercontinuum generation (exploiting its ultra-low index).
Highlights
Optical nanofibres confine light to a small core, with strong evanescent fields and high optical nonlinearity [1,2,3,4,5]
We show that encapsulation in hydrophobic silica aerogel provides protection and stability without sacrificing low attenuation, strong confinement and accessible evanescent field
The measured attenuation was
Summary
Optical nanofibres confine light to a small core, with strong evanescent fields and high optical nonlinearity [1,2,3,4,5]. Better support can be achieved on a low-index substrate such as MgF2 [10] or silica aerogel [9], or between two such substrates [4], but these do not eliminate movement or ingress of moisture Encapsulation in polymers such as Teflon (PTFE) [7,13,14,15,16] protects and stabilises nanofibres but at the expense of greatly increased attenuation (~2 dB/mm for 900 nm diameter [15] and 0.4 dB/mm for 1000 nm diameter [16] nanofibres at 1550 nm wavelength). Encapsulating a nanofibre in hydrophobic aerogel (rather than laying the nanofibre on the aerogel [9]) mechanically stabilises and protects the nanofibre from degradation, while the aerogel's porous structure allows the evanescent sensing of gases without exposing the bare nanofibre
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