Femtosecond laser micromachining of suspended silica-core liquid-cladding waveguides inside a microfluidic channel.

• 4 to 13 µm wide silica-cores suspended inside a microfluidic channel are fabricated • Thermal annealing is performed to reshape the core and reduce its surface roughness • Waveguiding properties are studied with LP 01 and LP 02 modes being excited • Mode profile is reconfigurable and determined by the external refractive index • Mode mismatch between coupling and suspended waveguides causes interference pattern This work addresses the fabrication of straight silica-core liquid-cladding suspended waveguides inside a microfluidic channel through fs-laser micromachining. These structures enable the reconfiguration of the waveguide's mode profile and enhance the evanescent interaction between light and analyte. Further, their geometry resembles a tapered optical fiber with the added advantage of being monolithically integrated within a microfluidic platform. The fabrication process includes an additional post-processing thermal treatment responsible for smoothening the waveguide surface and reshaping it into a circular cross-section. Suspended waveguides with a minimum core diameter of 3.8 µm were fabricated. Their insertion losses can be tuned and are mainly affected by mode mismatch between the coupling and suspended waveguides. The transmission spectrum was studied and it was numerically confirmed that it consists of interference between the guided LP 01 mode and uncoupled light and of modal interference between the LP 01 and LP 02 modes. [ABSTRACT FROM AUTHOR]