Fog computing is expected to be integrated with communication infrastructure, giving rise to the con­cept of fog-enhanced radio access networks (FeRANs) to support various mission-critical applications. Such archi­tecture brings computation capabilities closer to end users, thereby reducing the communication latency to access ser­vices. In the context of FeRAN, service migration is needed to tackle limited resources in a single fog node and to pro­vide continuous service for mobile end users. To support service migration, high capacity and low latency are required in mobile backhaul networks. Passive optical net­works can be a promising solution for such mobile back-haul, in which bandwidth is shared by both migration traffic and that which is not associated with service migra­tion. In this paper, we propose a bandwidth slicing mecha­nism, in which the bandwidth can be provisioned to the migration traffic and non-migration traffic dynamically and effectively to meet their different delay requirements. Simulation results verify that the proposed delay-aware bandwidth slicing scheme can handle the migration traffic properly, i.e., sending it within a required time threshold, while limiting the impact of the migration traffic on the latency and jitter of the non-migration traffic, particularly that with high priority.