Silicon microring-based optical interconnects offer great potential for high-bandwidth data communication in future datacenters and high-performance computing systems. However, a lack of effective runtime power management strategies for optical links, especially during idle or low-utilization periods, is devastating to the energy efficiency and the energy proportionality of the network. In this study, we propose Polestar, i.e., POwer LEvel Scaling with Traffic-Adaptive Reconfiguration, for microring-based optical interconnects. Polestar offers a collection of runtime reconfiguration strategies that target the power states of the lasers and the microring tuning circuitry. The reconfiguration mechanism of the power states is traffic-adaptive for exploiting the trade-off between energy saving and application execution time. The evaluation of Polestar with production datacenter traces demonstrates up to 87 % reduction in pJ/b consumption and significant improvements in energy proportionality metrics, notably outperforming existing strategies.