FUnctionalization of tapered NanoFibres for Inline Light Manipulation – FUNFILM

Sensors, optical sources and other active or passive optical components need to be pigtailed for an easy integration inside all-fibre architectures. The system design is greatly simplified; it is less sensitive to vibrations and is inherently protected against dust. Using such fibre pigtailed components simplifies the maintenance; a failed component is in field replaced by a technician, thus reducing the maintenance costs. One underlying problem of these components is the fabrication cost associated with the pigtailing. Indeed, the optical beam size at the output of the fibre is less than 10 µm, requiring a very accurate positioning of the optical elements. Moreover, the mode profile inside the component may differ from the fibre one. All these points lead to extra cost and optical losses. One solution to these drawbacks is to fabricate “inline optical components” made from the fibre itself, thus alleviating all the pigtailing problems. Our aim in this project is to create a new class of optical components based on the same pervasive platform: a tapered silica nanofibre. Nanofibres are produced by pulling heated optical fibres, typically telecom fibres, down to diameters of a few hundred nanometres. This pulling technique results in a nanofibre linked to the un-stretched sections of the original fibre by two tapered sections. During its propagation in these tapers, the mode guided by the core of the initial un-tapered fibre is adiabatically transformed into a mode guided inside the nanofibre section. First advantage, this propagation in the whole device, including the nanofibre and the tapered sections, presents very large transmissions, higher than 99%. Second advantage, the light confinement as the fibre diameter is reduced enhances the intensity up to a few hundred times. This extreme light confinement associated with their very high optical damage threshold makes nanofibres an ideal platform for implementing optical nonlinear interactions. Third advantage, for diameters lower than the wavelength, the guided optical mode presents a large evanescent field outside the fibre, paving the way to the external world probing. This makes nanofibres an ideal system for developing sensors. This feature also allows a simple tailoring of the nanofibre properties by depositing functional materials onto its surface. For other applications, this implies an encapsulation of the nanofibre to protect this evanescent field. These nanofibres can thus be seen as a generic platform for developing inline optical components. As an additional advantage, this generic platform breaks down one of the main technical barriers preventing expansion of high performance organic materials in the optical waveguide world that is the complexity of the technological processes for waveguide fabrication and connectorization. The use of a nanofibre thin enough to give access for the light to the surrounding material would greatly simplify the waveguide fabrication and would allow more rapid screening of potential high performance organic materials, thereby allowing novel materials to be developed. In this project, we will thus develop a new equipment for pulling nanofibres with high reproducibility, low tolerances and with on demand shapes. Simultaneously, we will study new processes for nanofibre functionalization using multilayer polymer coatings and metallic deposits (allowing Surface Brillouin scattering and interaction with plasmons, and surface second order and third order nonlinearities). Then, in order to exemplify the versatility of this platform, we develop three high demanding applications requiring different functionalizations: sources for quantum information, surface Brillouin sensors, frequency comb generation for radar signal processing. At the end of this project, we will propose a new class of inline components all based on a single versatile technological nanofibre platform and an exploitation plan for their future industrialization.