Numerical modeling of ion exchange waveguide for the tasks of quantum computations

This paper is devoted to the simulation of a single-mode ion-exchange waveguide and the 3dB directional coupler for quantum chips. We performed diffusion modeling of Na$^+\leftrightarrow$ K$^+$ ions in the R$_2$O–SnO$_2$–SiO$_2$ glass and optical modeling by the beam propagation method. A wavelength of 1064 nm was used corresponding to the requirements of the single-mode regime for our waveguide. Simulation of diffusion has shown that the profile of the refractive index of overlapping areas can be modeled by summing two separate profiles, which is crucial for optimizing performance. In the process of optical modeling it was possible to minimize losses on s-bends of changing the width of the bend and reducing the interaction length to zero. So we looked at many aspects of device optimization and performed a design, manufacture and characteristics simulation of a directional 3dB coupler. The overall transmittance of proposed device was evaluated as 0.96.