Freestanding optical fibers fabricated in a glass chip using femtosecond laser micromachining for lab-on-a-chip application

We describe the fabrication of freestanding optical fibers in a glass chip by femtosecond laser three-dimensional (3D) micromachining. The process has mainly four steps: (1) femtosecond laser scanning of the areas surrounding the fibers; (2) postannealing of the sample for the modification of the exposed areas; (3) chemical etching of the sample for the selective removal of the modified areas; and (4) second postannealing for smoothening the surfaces of the fibers. The measured optical loss of the fibers is approximately 0.7dB/cm. Integrating the freestanding fibers with 3D micromirrors is also demonstrated, enabling functions such as light folding or splitting in the glass chips. Furthermore, we demonstrate that the freestanding fibers can be incorporated into a microfluidic circuit for on-chip biophotonic applications.