The manufacture of complex micro-optical elements on the ends of optical fibres, using a Focused Ion Beam Microscope

Coupling optical fibres to the new generation of silicon photonic devices typically involves direct contact of the cleaved fibre to the chip or contacting it through diffracting or lensing optics fabricated on chips, but with... [ view full abstract ]

Coupling optical fibres to the new generation of silicon photonic devices typically involves direct contact of the cleaved fibre to the chip or contacting it through diffracting or lensing optics fabricated on chips, but with large signal losses. The fabrication of optics directly onto the fibres can direct and focus light into waveguides and increase the transmitted signal. In particular, axicon lenses, which are common in light-sheet microscopy, can be fabricated onto the end of optical fibres to produce long and narrow Bessel-Gaussian beam profiles that are ideal for coupling to waveguides. As some of the cores of the single-mode fibres are only of the order of a few microns, optical elements that are larger than the core are likely to affect the total internal reflection within the optical fibres, resulting in intensity losses. We show a method for using a Focused Ion Beam microscope (FIB) to manufacture an axicon lens on the 3 micron core of a single-mode optical fibre (Figure 1a-c); we discuss a method to find the centre of the fibre and align the milled feature with it. Although we use charged particles in the milling process, we show that this method can be used effectively with insulators. We demonstrate the milling of parabolic and spherical lenses, axicons and concentric ring lenses, as well as Fresnel lenses in optical fibres. We also show other test structure, with complex footprints and 3D morphologies manufactured in a glass slide. We further measure the mode field diameter of a single-mode fibre with an axicon microlens. The manufacturing method leads to Ga ion implantation, and we discuss the effect of ion implantation on the optical properties of the fibre and ways to restrict the implant damage to the core of the optical fibre. This manufacturing method is applicable to all optical fibres and offers significant opportunities for fibre-optic coupling to chips and single fibre-optic sensing, such as for medical applications.
The work reported in this paper was partially funded by project EMPIR 14IND13 PhotInd at NPL, co-financed by the Participating States and from the European Union’s Horizon 2020 programme.