Ultracompact wavelength splitters in LiNbO 3 photonic wires with three different structures for 1.31 and 1.55 μm wavelengths with transverse magnetic (TM) polarization have been presented. The devices are based on the operating principle of a directional coupler in two parallel dielectric waveguides and can be designed by using the finite element method. Calculated steady-state field distributions indicate that 1.31 and 1.55 μm wavelengths are spatially separated. In a particular structure, the transmittances at 1.31 and 1.55 μm wavelength are 99.4% and 95%, respectively. The total lengths of the three different structures are 39.8, 40, and 42.6 μm, respectively. Moreover, the coupling length dependences of the transmissions, the optical transmission bandwidths, and fabrication sensitivities are evaluated, respectively.