A novel scheme of hyperbolic-end microlens using the arc technology

This study proposes a new scheme of the tapered hyperbolic-end fiber (THEF) by etching the fiber end in a hydrofluoride (HF) solution with a thin layer of oil floating on top of the HF. This study makes it possible to fabricate the hyperbolic microlenses using unique etching and fusion techniques. Compared with previous hemispherical microlenses, the study shows that a THEF with a smaller taper angle and longer taper length fabricated by lower oil density exhibits a smaller radius of curvature, thus resulting in a better coupling efficiency. The THEF microlens results in a more than 2 dB improvement in coupling efficiency when compared with the currently available hemispherical microlenses. The calculation of the effect of oil density in HF etching solution on taper angle and taper length based on an empirical model is in agreement with the measured results. The THEFs have demonstrated up to 86% coupling efficiency for a laser with an aspect ratio of 1:1.5 at a wavelength of 1550 nm.