Four variants of the optical data center network architecture (DCN1 - DCN4) based on optical circuit switching and elastic optical switching elements are proposed. For each variant theoretical limits for non-blocking operation have been derived and proved. The proposed networks are also compared in terms of the required number of switching elements. Our results show that variant DCN1 is more appropriate for very small data centers with tens of racks with servers, while variant DCN4 requires much fewer switching elements in data centers with hundreds or thousands of such racks.