Future optical metropolitan area networks (MANs) have been expected to exploit advanced optical packet switching (OPS) technologies to cost-effectively satisfy a wide range of applications having time-varying and high bandwidth demands and stringent delay requirements. In this paper, we present the architecture and access control of our experimental high-performance OPS metro WDM slotted-ring network (HOPSMAN). HOPSMAN has a scalable architecture in which the node number is unconstrained by the wavelength number. It encompasses a handful of nodes (called server nodes) that are additionally equipped with optical slot erasers capable of erasing optical slots resulting in an increase in bandwidth efficiency. In essence, HOPSMAN is governed by a novel medium access control (MAC) scheme, called probabilistic quota plus credit (PQOC). PQOC embodies a highly efficient and fair bandwidth allocation in accordance with a quota being exerted probabilistically. The probabilistic quota is then analytically derived taking the server-node number and destination-traffic distribution into account. Besides, PQOC introduces a time-controlled credit for regulating a fair use of the remaining bandwidth, particularly in the metro environment with traffic of high burstiness. Extensive simulation results show that HOPSMAN with PQOC achieves exceptional delay-throughput performance under a wide range of traffic loads and burstiness.