Horizontal Microlenses Integrated in Microfluidics

In previous chapters, many emerging microlenses based on various mechanisms covering non-tunable and tunable types were presented. However, these microlenses have their optical axes perpendicular to the substrates, thus requiring optical alignment of the different layers. This causes complicated structures for applications such as labs on chips. In this chapter, we discuss horizontal microlenses integrated in microfluidics. Their optical axes are parallel to the substrates of the microfluidic networks. These horizontal microlenses include those formed by a hot embossing process hydrodynamically tuned cylindrical microlenses and tunable and movable liquid droplets as microlenses. 

In the previous chapters, the optical axes of the tunable microlenses discussed were perpendicular to their substrates. However, in-plane micro-lenses utilizing the curvature formed by the interfaces between two immiscible liquids or between air and liquid can be introduced to observe objects in microfluidic channels. Their optical axes are parallel to the substrate of microlenses—a distinctly different system from what we have seen previously. 

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