All‐Glass 3D Optofluidic Microchip with Built‐in Tunable Microlens Fabricated by Femtosecond Laser‐Assisted Etching

Abstract

Development of tunable microlenses by taking advantage of the physical adaptability of fluids is one of the challenges of optofluidic techniques, since it offers many applications in biochips, consumer electronics, and medical engineering. Current optofluidic tuning methods using electrowetting or pneumatic pressure typically suffer from high complexity involving external electromechanical actuating devices and limited tuning performance. In this paper, a novel and simple tuning method is proposed that changes the liquid refractive index in an optofluidic channel while leaving the shape of the microlens unchanged. To create an optofluidic microlens with high robustness and optical performance, built‐in microlenses are fabricated inside 3D glass microfluidic channels by optimized single‐operation wet etching assisted by a femtosecond laser. Tuning of focusing properties is demonstrated by filling the channel with media having different indices. Continuous tuning over a wide range (more than threefold tunability for both focal length and focal spot size) is also achieved by pumping sucrose solutions with different concentrations into the microchip channels. Reversible tuning is experimentally verified, indicating intriguing properties of the all‐glass optofluidic microchip. Both the proposed tuning method and the all‐glass architecture with built‐in microlens offer great potential toward numerous applications, including microfluidic adaptive imaging and biomedical sensing.

Advances in femtosecond laser processing of optical material for device applications

“…The fabrication process was improved through refractive index matching where the 100% water solution is replaced with glycerol‐water solutions . An all‐glass optofluidic microchip with built‐in microlenses was fabricated by a method by which the refractive index of liquid in the channel is changed . A 3D microfluidic surface‐enhanced Raman spectroscopy (SERS) platform was produced using a novel technique by which a 2D periodic metal nanodot array is created inside a 3D glass microfluidic channel .…”

Etching-assisted femtosecond laser modification of hard materials

“…By using this method, complex 3D microstructures can be fabricated inside the photosensitive glass [77][78][79] . Hu et al 80 exhibited the fabrication of all-glass 3D optofluidic microlens integrated in closed microchannels by wet-etching-assisted femtosecond laser modification, as shown in Fig. 4.…”

“…Second, due to the strong nonlinear laser-matter interaction, the surface roughness of the fabricated structures is difficult to satisfy the requirements of optical devices. More efforts should be made to increase the precision and surface smoothness by investigating the mechanism of laser modification, spatiotemporal focusing and post-processing 80,[112][113][114] .…”

IR Artificial Compound Eye

“…Recently, maskless 3D micro‐manufacturing based on femtosecond lasers seems promising in high‐quality micro‐optics fabrication on the free‐form surface, especially such kind of ACE devices integrating massive sub‐apertures onto a macro‐dome surface . In this work, we present a novel IR ACE component which is fabricated by femtosecond laser‐assisted wet etching technique (FLWE) and 3D nano‐imprinting technique . By this strategy, the high‐quality ommatidium facets are efficiently fabricated onto a curved hard substrate, forming a highly integrated 3D compound eye mold, with ommatidium fill factor of 100%.…”