Integrating 3D photonics and microfluidics using ultrashort laser pulses

Abstract

The integration of photonics and microfluidics can beneft both information technology and sensor technology. On the one hand, optical devices that incorporate liquid elements can be modified by changing or modifying the fluid, which could eventually revolutionize the optical communications industry. On the other hand, optical methods, such as fluorescence detection and photoabsorption spectroscopy, have been popularly used in chemical and biological sensors. Compared with complex and expensive external bulk optical elements, incorporating micro-optical components into the sensors offers substantial benefits for creating compact and cost-effective devices. At present, fabrication of microfluidic devices integrated with optical elements relies heavily on planar technologies, such as soft lithography. The main drawback of these methods is the difficulty involved in making 3D structures. Multistack bonding is often needed, which results in many process steps and, consequently, increased complexity and cost. To get around this problem, we have been working on a new approach using femtosecond laser direct writing in a photoetchable glass called Foturan. Both microfluidic and micro-optical structures can be formed and three-dimensionally deployed in a single glass chip by one continuous process. Microstructuring photoetchable glass with UV light can be traced back to the mid-20 century. Since UV-light modification of Foturan glass is performed by a single-photon process, it inherently occurs at the surface of the glass. For this reason, we turned to a multiphoton-based approach that can be realized using a femtosecond laser operating at a near-IR wavelength. Figure 1 illustrates our fabrication approach, which consists of four Figure 1. (a) Femtosecond laser direct writing creates 3D patterns in Foturan glass. (b) The sample is inscribed with the latent image. (c) In the postannealing step, the sample is heated in a programmable furnace. (d) The modified areas turned brown. Note that the channel buried in glass is out of the focus of the optical microscope. (e) Diluted HF acid etches the sample. (f) This results in hollow structures fabricated both on the surface of and inside the sample. The last step of smoothing the internal surface by additional annealing is not shown.