An optical line termination (OLT) device (12) generates a plurality of optical signals having different respective wavelengths (lambd1, lambd2), each optical signal carrying data, and wavelength-division-multiplexes the optical signals. In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i. To begin with, we assume that we have the element parameters from a known process design kit (PDK). It facilitates etwork-ing with advanced topologies supported with redundancy features.