  Lithium-Niobate-On-Insulator (LNOI) has emerged as a promising platform in
the field of integrated photonics. Nonlinear optical processes and fast
electro-optic modulation have been reported with outstanding performance in
ultra-low loss waveguides. In order to harness the advantages offered by the
LNOI technology, suitable fiber-to-chip interconnects operating at different
wavelength ranges are demanded. Here we present easily manufacturable,
self-imaging apodized grating couplers, featuring a coupling efficiency of the
TE0 mode as high as $\simeq 47.1\%$ at $\lambda$=1550 nm and $\simeq 44.9\%$ at
$\lambda$=775 nm. Our approach avoids the use of any metal back-reflector for
an improved directivity or multi-layer structures for an enhanced grating
strength.
