Shared-Memory Optical Packet (SMOP) switch architecture is very promising for significantly reducing the amount of required optical memory, which is typically constructed from fiber delay lines (FDLs). The current reservation-based scheduling algorithms for SMOP switches can effectively utilize the FDLs and achieve a low packet loss rate by simply reserving the departure time for each arrival packet. It is notable, however, that such a simple scheduling scheme may introduce a significant packet out of order problem. In this paper, we first identify the two main sources of packet out of order problem in the current reservation-based SMOP switches. We then show that by introducing a “last-timestamp” variable and modifying the corresponding FDLs arrangement as well as the scheduling process in the current reservation-based SMOP switches, it is possible to keep packets in-sequence while still maintaining a similar delay and packet loss performance as the previous design. Finally, we further extend our work to support the variable-length burst switching.