Anomalous angular dispersion in lithium niobate one-dimensional waveguide array in the near-infrared wavelength range

Knowing the dispersion properties of a device is important in many applications (e.g., wavelength separation). For an isolated waveguide, besides the material dispersion, one must consider the waveguide influence as well, through waveguide dispersion and mode dispersion. For a waveguide array, one must consider the influence of evanescent coupling between adjacent waveguides as well. We investigate by the Finite Element Method the angular dispersion of a LiNbO₃ waveguide array using two techniques. The first one assumes the Coupled Mode Theory in a 2-waveguide system. The other one uses the actual diffraction curve determined in a 7-waveguide system. In both approaches, we find that by decreasing the array period, one passes from normal angular dispersion by an achromatic point to anomalous angular dispersion. We then illustrate the wavelength separation by the waveguide array by doing Runge-Kutta light propagation simulations. As all the values of parameters are technologically feasible, this opens new possibilities for optical data processing, such as WDM and dispersion compensation.