Adaptive photonic and microfluidic chip packaging via 3D alignment structures

Combining photonic integrated circuits (PICs) with microfluidic devices offers new possibilities for optofluidic lab-on-a-chip applications. Their accurate assembly and packaging, particularly with precise alignment, remain challenging. This work presents a versatile optofluidic integration of photonic and microfluidic chips, designed for seamless implementation in diverse laboratory environments. A 3D-printed holder for stable, cost-effective, and convenient fiber-to-chip bonding is used to configure optical in- and outputs. It can be readily adapted to accommodate various grating coupler designs. The microfluidic chip side is fabricated via soft-lithography in polydimethylsiloxane (PDMS), and positioned onto the photonic chip via cone-shaped alignment guides that were printed directly onto it. For this, the conventional PDMS plasma bonding process was adapted for passive self-alignment with the PIC chip between the 100 μm-wide microfluidic channel and two grating couplers, each measuring 15 μm in length and 50 μm in width. In a proof-of-principle experiment, we detect the fluorescence of a fluorescein solution inside the microfluidic channels by delivering excitation and emission light through dedicated grating couplers. This configuration can address multiple sampling points along an optofluidic system to multiplex assays in a way that would be challenging to realize with conventional optical fibers.