Large single-mode rib waveguide in lithium niobate on insulator

We present theoretical studies on single-mode conditions of direct-bonded lithium niobate (LN) ridge waveguide and BCB-bonded lithium niobate on insulator (LNOI) rib waveguide. Propagated mode distributions of these two waveguides are calculated by using finite difference beam propagation method (FD-BPM). With special designs, the LNOI waveguide can simultaneously support single-mode propagation of both fundamental wave (1550 nm) and second harmonic wave (775 nm). The single-mode LNOI rib waveguide can be several microns wide and high allowing efficient coupling to single-mode fibers.