Optics Express, 27, 16578 (2019)
We present the design, fabrication and characterization of LNOI fiber-to-chip inverse tapers for efficient monolithic edge coupling. The etching characteristics of various LNOI crystal cuts are investigated for the realization of butt-coupling devices. We experimentally demonstrate that the crystal cut limits the performance of mode matching tapers studied in this work. We report a butt-coupling loss of 2.5 +/- 0.5 dB/facet across the C/L-band and 6 dB/facet (at 1550 nm) by implementing 200 nm tip mode matching tapers in +Z-cut LNOI and X-cut MgO:LNOI, respectively. We anticipate that these results will provide insight into the nanostructuring of LNOI and into the further development of efficient butt-coupling in this platform.