Efficient fibre to X-cut Ti:LiNbO3 waveguide coupling for λ = 1.32 μm

While efficient fibre-waveguide coupling has been achieved for titanium-diffused waveguides on Z-cut Y-propagating lithium niobate crystals, previously reported results for coupling to waveguides on non-Z-cut crystals have been poor. Here we report total fibre-waveguide-fibre insertion losses as low as -1.35 dB for ˜l.5 cm-long waveguides on X-cut Y-propagating lithium niobate-the preferable orientation for polarisation conversion devices. The losses are only slightly higher than the best value for Z-cut crystals (˜ -1 dB) due to the larger waveguide mode eccentricity.