Optical packet switching (OPS) has been considered to be a promising paradigm to support a wide range of applications with different time-varying and high bandwidth demands for future optical metropolitan area networks (MANs). In this paper, we present the design of an experimental optical-header processing and access control system (OPACS) for an OPS wavelength-division multiplexing metro slotted-ring network. On the slotted ring, each control header is in-band time-division-multiplexed with its corresponding payload within a slot. OPACS enables the optical headers across all parallel wavelengths to be efficiently received, modified, and retransmitted by means of a wavelength-time conversion technique. Moreover, OPACS embodies a versatile medium access control (MAC) scheme, referred to as the distributed multigranularity and multiwindow reservation (DMGWR) mechanism, which is particularly advantageous for traffic of high and varying loads and burstiness. Basically, DMGWR requires each node to make reservation requests prior to transmissions while maintaining a distributed queue for ensuring fair access of bandwidth. By "multigranularity," each node can make a reservation of multiple slots at a time. By "multiwindow," each node is allowed to have multiple outstanding reservations within the window size. From simulation results that pit the OPACS network against two other existing networks, we show that the OPACS network outperforms these networks with respect to throughput, access delay, and fairness under various traffic patterns. Experimental results demonstrate that all optical headers are removed and combined with the data in a fully synchronous manner, justifying the viability of the system.