Analysis of the light coupling between nano-waveguides made of tellurite glasses

This paper presents a study (simulations) of coupling losses between adjacent waveguides made of tellurite glasses. These waveguides are designed to perform parametric amplifiers (PAs). PAs have some advantageous characteristics over the other optical amplifiers: they have broadband amplification bandwidth (depending on the dispersive characteristics of the waveguide), other all-optical functionalities, and can work at ultra-high bit rates (Pbit/s). PAs are based on the nonlinear phenomena of phase matched four-wave mixing between a strong pump and a weak signal. The parametric gain increases with the waveguide length, the pump power and the nonlinear coefficient of the waveguide. The best alternative to maximize the parametric gain is to reduce the pump power as much as possible, increasing the waveguide length and/or the nonlinear coefficient of the waveguide. The latter parameter can be enhanced by increasing the nonlinear refractive index of the material (n2) or by reducing the waveguide effective area. Here we perform waveguides made of tellurite because these glasses have an n2 that goes up to 30 x 10^-19 m²/W. On the other hand, the waveguide length can be increased by using an Archimedean spiral design. This geometry allows obtaining long waveguides (∼1 m) within a small area. Using the Finite Element Method we study the separation distance between adjacent waveguides in order to obtain coupling lengths higher than the waveguide length (total losses < 2 dB/m). The waveguide dimensions are optimized to obtain a monomode waveguide with dispersive characteristics to perform PAs (around ∼1550 nm spectral region).