Significant reduction of crossing loss using polynorbornene based GI-core optical waveguide

In this paper, we demonstrate that crossed multimode graded-index (GI) optical waveguides show very low crossing loss. We actually fabricate multiple-perpendicularly-crossed waveguides with GI core (WG2), and quasi-GI waveguides (WG1) that have a GI profile only in the horizontal direction while a step-index profile in the vertical direction, and then compared with the SI core crossed waveguides (WG3) previously reported. We confirm that an optical loss of 0.003 dB per 90-degree crossing is observed in WG2, which is much lower than those of WG3 (0.023 dB per crossing) and even WG1 (0.017 dB per crossing). In addition, we also demonstrate that WG2 with different crossing angles from 30 to 80 degrees always shows lower crossing loss than WG1 and WG3 with the same crossing angles. This could be a specific characteristic of GI-core: that is a strong optical confinement effect. We expect that this unique GI-core waveguide will be one of the promising components giving a great impact on high performance computing systems (HPCs) in the near future.