Fig. 6. Optical crossings.
a Microscope image of a multimode interference (MMI)-based optical waveguide crossing. MMI length (LMMI), trenches along the MMIs for penetration of hydrofluoric acid (HF) and the undercut regions are annotated. b Microscope image showing cascaded crossings to determine the insertion loss of the MMI-based waveguide crossings. c Plot showing the spread of the experimentally extracted insertion loss values over the measured wavelength range for different MMI lengths used for the crossing. The box extends from the lower to upper quartile values, the red dotted line represents the mean, and the light green line indicates the median. Inset shows the 3-D drawing