  The 2D HgTe quantum well is analyzed based on the assumption that the width
fluctuations convert the system to a random mixture of domains with positive
and negative energy gaps. The borders between ordinary and topological
insulator phases form a network of the edge states covering the overall sample.
The optical transitions within the edge states yield the 2D absorption. The
qualitative consideration is based on the model of optical intraedge
transitions in curved edge states together with the percolation arguments.
