Self-aligned coupling waveguides experimentally formed by two-photon photochemistry for 3-D integrated optical interconnects

We propose self-organized three-dimensional (3-D) integrated optical interconnects within computers, in which two-photon self-organized lightwave networks (two-photon SOLNETs) formed by two-photon photochemistry are implemented Previously reported simulation studies and initial fabrication demonstrations of two-photon TB-SOLNETs showed the possibility of enhanced self-aligned optical coupling as well as mode-size-converting functions, eliminating the connecting problems between misaligned optical devices. Nevertheless, in the TB-SOLNET, which requires two write beams to form, inserting the write beams and guiding them through the different devices to be interconnected is not a simple task. To remove the concern about insertion of write beams for SOLNET formation, other types of SOLNETs using either only one write beam and a luminescent target illuminated with the write beam (namely two-photon R-SOLNET), or simply two luminescent regions/targets illuminated with external excitation lights (two-photon P-SOLNET and LA-SOLNET) have been explored by means of simulations. In the present paper, preliminary experimental results for two-photon TB-SOLNETs and R-SOLNETs, including the coupling efficiency at a wavelength of 448 nm to couple two multimode optical fibers placed with a gap distance of 500 μm and different lateral misalignments, are shown for the first time. Experimental measurements reveal that two-photon TB-SOLNETs can overcome lateral misalignments of 40μm with ∼2.3 dB penalty, and two-photon R-SOLNETs with luminescent targets can be formed by one write beam to overcome misalignments of 25μm with ∼1.4 dB penalty. The experimental demonstration of TB-SOLNET hints to the potential feasibility of P-SOLNET since the formation dynamics for P-SOLNET are the same as for TB-SOLNET, and the experimental demonstration of R-SOLNET using placed luminescent targets hints to the feasibility of LA-SOLNET. These results indicate that the two-photon R-, P-, and LA-SOLNETs are expected as a novel low-cost method to fabricate 3-D integrated optical interconnects involving complex optoelectronic components in a self-organized manner. To prove further the validity of the proposed fabrication method for the optical interconnects, coupling efficiency measurements at telecom relevant wavelengths need to be performed in a next stage. Experiments for two-photon P- and LA-SOLNETs, and optimization of SOLNET formation conditions also remain as future work.