Energy efficiency is becoming a critical issue in highspeed networks. 100 Gb/s Ethernet was standardized in 2010, and several papers have been published on power consumption reduction methods using Adaptive Link Rate (ALR) technology. ALR reduces power consumption by adapting link speed to traffic demand. However, rate switching time is a parameter that impacts the level of power reduction achievable with current ALR technologies. In this paper, we propose a new energy-efficient architecture for 100 Gb/s Ethernet. The rate switching time is reduced using coherent lightwave transmission technologies. We use simulations to evaluate how the proposed architecture impacts energy efficiency, switching time and network performance.