Optical Packet Switches (OPS) could provide the needed low latency transmissions in today large data centers. OPS can deliver lower latency and higher bandwidth than traditional electrical switches. These features are needed for parallel High Performance Computing (HPC) applications. For this purpose, it has been recently designed full optical network architectures for HPC system such as the Architecture-On-Demand (AoD) network infrastructure. Although light-based transmission has its advantage over electrical-based transmissions, optical devices such as OPS cannot store light. Therefore, in case of an optical packet collision occurs for accessing the same output port in OPS only one packet can proceed and the others must be dropped, triggering afterwards a retransmission procedure. Obviously, packet retransmissions are delaying the actual transmission and also increase the buffer utilization at the network interfaces cards (NICs) that deals with retransmissions. In this paper, it is proposed a technique based on mapping application processes to servers reducing the number of simultaneous packets in the network (Concurrency) and therefore, it is able to significantly reduce optical collisions at the OPS while substantially reduces the resource needed at the NICs for retransmissions. Our proposed concurrency-aware mapping technique can reduce the extra buffer size utilization up to 4.2 times and the execution time degradation up to 2.6 times.