Tunable and Dynamic Optofluidic Microlens Arrays Based on Droplets

Abstract

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.

Recent Progress in Droplet Structure Machining for Advanced Optics

“…In a parallel development, researchers have introduced innovative optofluidic microlens arrays (MLAs) based on water-in-oil droplets featuring a controlled droplet diameter of 200 μm ( Figure 13 b) [ 83 ]. These MLAs can be seamlessly self-assembled in a microfluidic chip, and their refractive index can be precisely tuned by adjusting flow rates.…”

Reconfigurable Microlens Array Enables Tunable Imaging Based on Shape Memory Polymers

“…By introducing liquids with different refractive indices into microfluidic chips, the focal length of MLA can be quickly tuned. 2,42 As a very important type of tunable MLA, the liquid crystal MLAs also permit dynamic modulation of their imaging performance. 43,44 Liquid crystal molecules with a tunable refraction functionalize as active optical components for imaging.…”

“…In addition to the mechanical modulation, the imaging performance can also be tuned by varying the refractive index of the MLAs. By introducing liquids with different refractive indices into microfluidic chips, the focal length of MLA can be quickly tuned. , As a very important type of tunable MLA, the liquid crystal MLAs also permit dynamic modulation of their imaging performance. , Liquid crystal molecules with a tunable refraction functionalize as active optical components for imaging. The tuning mechanisms include electrical, thermal, and chemical modulation and other methods, holding great promise for practical applications .…”

Biomimetic Compound Eyes with Gradient Ommatidium Arrays

“…Plenty of solid compound eyes have been easily manufactured by femtosecond laser direct writing, nanoimprinting, laser-assisted wet etching, surface chemical etching, 3D printing, and photolithography. − Most of these solid-material-based artificial compound eyes have uniform ommatidium arrays and exhibit good imaging performance. Liquid materials have attracted a lot of research interest due to their low cost, and reconfigurable features, , such as tunable liquid lenses and reconfigurable droplet lens arrays, have been developed. − Lenses based on liquid materials are mostly collections of a small number of lenses or large-sized single lenses, and there are still challenges in combining such zoom mechanisms with compound eye structures, especially in manufacturing artificial compound eyes with hundreds or thousands of ommatidia. Optofluidics allows precise and sensitive manipulation of light or fluid to regulate system optical performance, ,− which has injected new vitality into the development of artificial compound eyes .…”