Fabrication and characterization of optical nanofiber tips

We demonstrate the fabrication of an optical nanofiber tip (ONFT) using a two-step chemical etching technique. This technique employs 30% and 24% hydrofluoric (HF) acid for the first and second steps, respectively. In the first step, a silica single-mode fiber with a clad diameter of 125 μm and a core diameter of 9 μm is immersed in the HF acid for 90 min. The resultant fiber diameter is reduced to ∼45 μm. In the second step, the fiber is again immersed in the HF acid for 60–80 min. The etching time is controlled to achieve the desired tip diameter of the ONFT. We characterize fabricated ONFTs by measuring the optical transmission and surface morphology. The observed optical transmissions are more than 30%, and the tip diameters are less than 500 nm. The measured results readily reveal the merit of the employed technique as it is easy and cost effective. Due to the strong confinement of the electromagnetic field at the tip of ONFTs, these structures have versatile platforms with potential applications in sensing, photonics, and quantum optics.