This paper addresses the issue of inserting WDM (wavelength division multiplexing) and amplifier technologies into optical networks from network system architecture and application perspectives. In order to facilitate technology transfer into commercial applications, we need to carefully consider where we can insert the technologies, how we should utilize the technologies, and what are the benefits of employing these technologies. Through years' of investigation and development, taking into considerations of optical network environment, benefits of the technologies and implementation feasibility, we believe that there are three major roles that WDM and amplifier technologies can play in optical networks: point-to-point transmission for capacity expansion, in-fiber out-of-band control for format transparency, and optical routing for network efficiency. In this paper, we will describe each of these roles and their benefits. Progress and results of our related research programs, including optical crossbar switch testbed, will be reported.