Design of optical circuit devices using topology optimization method with function-expansion-based refractive index distribution

We propose a design method for optical waveguide devices based on topology optimization with alternative expression of refractive index distribution. In our approach, a refractive index distribution in a design region is expressed by an expansion with some analytical functions and gray area, which has intermediate refractive index between usable materials, does not appear. We can obtain better results in the optimization of waveguide bends and branches,compared with the widely used density method.