Simulation of Self-Aligned Optical Coupling Between Micro- and Nano-Scale Devices Using Self-Organized Waveguides

Using the finite-difference time-domain method, we simulated the growth of self-organized waveguides between a 3-μm-wide micro-scale waveguide and a 600-nm-wide nano-scale waveguide, which has a luminescent target on its core edge. The two waveguides are placed together, with gap sizes ranging from 16 to 64 μm, in a photo-induced refractive-index increase-type material. When a 400 nm wavelength write beam is introduced from the micro-scale waveguide, luminescence is generated by the luminescent target. A waveguide is then gradually self-organized between the two waveguides, even when a lateral misalignment of 600 nm exists between them, and provides a self-aligned optical coupling with a coupling loss of 1.5-1.8 dB. This indicates that the self-organized waveguide can be used as an optical solder to connect a micro-scale waveguide in a multi-chip module or printed circuit board to a nano-scale waveguide in a large-scale integrated circuit. The optimum writing time required to attain the minimum coupling loss increases with increasing lateral misalignment. The dependence of the optimum writing time on the misalignment is reduced with increasing gap distance, and the dependence almost vanishes when the gap distance is 64 μm, thus enabling unmonitored optical solder formation.