A network control system may be embodied in various elements of a communication network which communicates optical signals multiplexed by wavelength division multiplexing. By implementing the quantization technique, the primary error buffer can be reduced from an 8-bits-per-bin error buffer to a 2-bits-per-bin error buffer for 256 grayscale. The ellipsometric properties of the substrate are such that the variations of the ellipsometric parameters of the sample are displayed with a contrast greater than the contrast produced in the absence of such substrate.