Figure 4
From: Switchable 3D optofluidic Y-branch waveguides tuned by Dean flows

The images of confocal microscopy in different volume ratio.
The main part is around the Y-shape junction and the mini picture shows the cross section of the junction. The totally flow rate is constant. 2a means the diameter of the core flow. The ratios of core flow rate to the cladding flow rate are (a) 1:4, (b) 1:2 and (c) 1:1.