Single Mode, Air-Cladded Optical Waveguides Supported by a Nano-Fin Fabricated with Direct Laser Writing

Single-mode, air-cladded optical waveguides have wavelength scale diameters, making them very fragile and difficult to handle and yet highly desirable for sensing and inter-chip photonic interconnects. These contradictory qualities are resolved in this work by supporting the optical waveguide with a nano-fin structure attached to a substrate, narrow enough and sufficiently tall to minimally impact the wave-guiding metrics of the solid core while providing structural mechanical integrity. The design considerations for the nano-fin-supported waveguide and its realization using a commercial direct laser writing system based on two-photon activation of a photopolymer is reported herein. The 3D printed waveguides are characterized and experimentally assessed, demonstrating low birefringence and an estimated propagation loss for LP01x and LP01y of 2.9 dB/mm and 3.4 dB/mm, respectively, attributed to surface roughness and the relatively high refractive index contrast with air.