Design and Simulation of Multilayer GRIN Lens for Light Coupling Application in Photonic Integrated Circuits

Photonic integrated circuits (PICs) can potentially replace electronic circuits in the future. However, the fabrication of PICs is still immature and requires further research. One of the missing steps in the integration of the components in an optical circuit is to fabricate an integrated light coupler. In this paper we propose the use of multilayer gradient index (GRIN) lens for coupling the light from a laser diode into a waveguide, which is experimentally achievable. The proposed GRIN lens structure is composed of layers with different refractive indices, which are stacked in such a way that focusing of fast and slow optical axes is possible within one optical element. The layer at the optical axis has the highest refractive index and the farther away the layers are from the optical axis, the lower the refractive indices. The ray tracing results show that the optical aberration of the lens is small enough and the output beam can be coupled to waveguide with high efficiency.