Abstract
We propose an optical coupling technique based on the reflective self-organized lightwave network (R-SOLNET), where
optical devices with different core sizes are connected, for nano-scale-waveguide-based optical interconnects. Growth of
R-SOLNET between a 3-μm-wide waveguide and a 600-nm-wide waveguide, on the core edge of which a luminescent
target has been deposited, is simulated by the finite-difference time-domain method. The two waveguides are placed with
gap distances ranging from 16 to 64 μm in a photopolymer with a refractive index that increases upon exposure to a
write beam and luminescence. When a 400 nm wavelength write beam is introduced from the micro-scale waveguide,
470 nm luminescence is generated from the target. In the area where the write beam and the luminescence overlap, the
refractive index increases rapidly. The write beam and the luminescence thus attract each other to merge into one
through the self-focusing, forming a self-aligned coupling waveguide of R-SOLNET with a coupling loss of 1.5–1.8 dB,
even when a lateral misalignment of 600 nm exists between them. This indicates that the R-SOLNET can be used as an
optical solder to connect a micro-scale waveguide to a nano-scale waveguide. 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 it almost vanishes when the distance is 64
μm, enabling unmonitored optical solder formation. R-SOLNET utilizing the two-photon photochemistry is briefly
described as the next-generation SOLNET.
