Tunable and Dynamic Optofluidic Microlens Arrays Based on Droplets.

Microlens arrays (MLAs) are acquiring a key role in the micro-optical system, which have been widely applied in the fields of imaging processing, light extraction, biochemical sensing, and display technology. Compared with solid MLAs, liquid MLAs have received extensive attention due to their natural smooth interface and adjustability. However, manufacturing tunable liquid MLAs with ideal structures is still a key challenge for current technologies. In this paper, a novel and simple optofluidic method is demonstrated, enabling the tunable focusing and high-quality imaging of liquid MLAs. Tunable droplets are fabricated and self-assembled into arrays as the MLAs, which can be easily adjusted to focus, form images, and display different focal lengths. Tuning of MLAs' focusing properties (range from 550 to 5370 μm) is demonstrated by changing the refractive index (RI) of the droplets with a fixed size of 200 μm, which can be changed by adjusting the flow rates of the two branch streams. Also, the corresponding numerical apertures of the MLAs range from 0.026 to 0.26. Furthermore, the MLAs' functionality for microparticle imaging applications is also illustrated. Combining the MLAs with a 4× objective, microparticle imaging is magnified two times, and the resolution has also been improved on the original basis. Besides, both the size and RI of the MLAs in an optofluidic chip can be further adjusted to detect samples at different positions. These MLAs have the merits of high optical performance, a simple fabrication procedure, easy integration, and good tunability. Thus, it shows promising opportunities for many applications, such as adaptive imaging and sensing.