In this paper, we present the design of an experimental optical-header processing and access control system (OPACS) for an optical packet switched (OPS) WDM metro slotted-ring network. Each control header is in-band time-division-multiplexed with its payload. OPACS enables the optical headers across all parallel wavelengths to be efficiently received, modified, and re-transmitted based on a wavelength-time conversion technique. Bandwidth access in OPACS is governed by a versatile access control scheme, called the distributed multi-granularity and multi-window reservation (DMGWR) mechanism. With DMGWR, the OPACS network is shown to outperform two existing 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.