3D integration of microfluidics and microoptics inside photosensitive glass by femtosecond laser direct writing for photonic biosensing

Optical waveguides with a propagation loss of around 0.5 dB/crn are written inside photosensitive Foturan glass by internal modification of refractive index using femtosecond (fs) laser. Integration of the optical waveguides with a micromirror enables us to bend the guided laser beam at an angle of 90 degrees with a bending loss of less than 0.3 dB. In the meanwhile, a plano-convex microlens is completely embedded inside the Foturan glass chip via formation of a three-dimensional (3D) hollow microstructure using fs laser direct writing followed by heat treatment and successive wet etching. This technique can also be used to fabricate microfluidic devices and therefore realizes 3D integration of microoptical and microfluidic components by one continuous procedure. Subsequently, microoptical waveguides are further integrated into the single glass chip. Demonstration of optical measurements using the integrated microchip reveals that photonic biosensing can be performed with an efficiency increased by a factor of 8 for fluorescence detection and by a factor of 3 for absorption detection.