Silicon fibre nano-spike for robust coupling to silica fibres

Summary form only given. Making use of the attractive properties of silicon (Si), a wide array of highly functional photonic devices have been demonstrated over the past few decades [1]. Although planar platforms are still the most prominent choice for integrated systems, more recently silicon fibres have gained increased attention due to their simple fabrication methods and flexible device designs [2]. However, despite their physical similarity to traditional single-mode fibres (SMFs), coupling light efficiently into and out of these devices remains a difficult task due to the high refractive index of the Si core, which results in significant reflection losses and a large mode mismatch. A few solutions have been proposed to overcome this integration challenge, including the use of microstructured fibre designs to better match the mode area [2] and chemical etchants to reduce the reflection at the interface [3], though so far no method has addressed both issues simultaneously. Thus a promising alternative solution would be to adapt the well-established inverse taper approach widely employed by the planar community [4], which is also gaining attention within the novel material fibre community [5]. The key idea behind this approach is that by decreasing the Si core to nanoscale dimensions at the facet, the guided mode spreads out to better match both the area and the effective index of the SMF mode. In this paper, we demonstrate the fabrication and optical characterization of the first Si fibre nano-spike which has been directly spliced to SMF.