Efficient Fibre-chip Coupling using Ion-milled Alignment Grooves on Lithium Niobate at λ = 1.3μm.

To make realistic use of the vast range of integrated optic devices, both active and passive, on lithium niobate, as in other substrates, it is necessary to produce efficient, reliable and repeatable fibre to waveguide couplers. High efficiency can be achieved (Ref.1) by micro manipulating the fibre butted to the waveguide, while also taking steps to reduce modal field mismatch. Manipulating the fibre is however a complex and time-consuming operating which does not easily lend itself to multi-port devices. The use of silicon 'V' grooves (Ref.2) can aid fibre alignment and reduce the complexity of the operation while maintaining a high coupling efficiency. However, the component utilises two technologies and the alignment of multi-port devices face down onto the silicon surface poses problems. Problems may also arise from silicon and lithium niobate having different thermal expansion coefficients.