Book excerpt: To bring the high capacity of the optical fiber closer to the end users with affordable costs, passive optical network (PON) was introduced and developed as a promising access network technology over the past decade. Long-reach PON (LR-PON) extends the coverage span of PONs from the traditional 20 km range to 100 km, consolidates the multiple active sites and thus lowers the costs. Besides extending the reach, energy conservation, which is of growing concern today, gives LR-PON a brand new advantage over its competitors. In this dissertation, we focus on the intersection of these two topics, namely Energy-Efficient LR-PON. We present several distinct schemes with the potential for substantial energy savings under practical settings, while not significantly affecting the network's performance. We develop and evaluate novel architectures, protocols, and algorithms for a LR-PON to will help to improve the performance of next-generation telecom access networks. One major component of LR-PON is the optical line terminal (OLT), which is deployed in central offices. Specifically for energy savings in OLT, we propose a centralized network planning approach based on user behaviors. By considering the different network usage behaviors of different kinds of users, we develop an efficient user-assignment scheme in which users with complementary behaviors are assigned to the same network segment to share the bandwidth. This achieves high bandwidth utilization at all times, and reduces the number of wavelengths needed, thus lowing cost and energy usage. Heuristic searches can provide such assignments, and their approximate solutions are very close to the lower bound. We then extend our work to the network operation (i.e., traffic engineering) stage, where an energy-efficient dynamic wavelength allocation scheme is developed on the "ring-and-spur" LR-PON. This scheme enables a wavelength to be dropped dynamically at multiple remote nodes, making it possible for users in different network segments to share downstream capacity in a statistical multiplexing fashion. The wavelength allocation may also be dynamically changed according to the network traffic so that the OLT can efficiently utilize all operational wavelengths. The other major component of LR-PON is the optical network unit (ONU), a remote unit close to the users. We propose a service-level agreement (SLA)-based scheduling scheme, in which the sleep time of an ONU can be adjusted and the ONU can quit sleep mode to send high-priority packets. Our proposal solves the problems of slow transition of power from active mode to sleep mode in an ONU and the relatively large recovery and synchronization time needed during the wakeup process. The tradeoff in energy savings vs. delay performance is evaluated using simulations under practical power-consumption settings. We also study the effects of arrayed-waveguide grating (AWG) and erbium-doped-fiber amplifier (EDFA) on bit-error rate (BER) in LR-PON, and propose both short-term and long-term distance-aware wavelength allocation schemes to balance the BER among ONUs at different distances. Simulation results show that average BER improves and the relative standard deviation decreases.