Passive Optical Network (PON) is a promising solution to the last-mile problem in access networks. Security is a very crucial aspect to be considered especially in the current environments that are characterized by much larger data transport capacity. Moreover, securing the physical layer requires urgent attention as it will become more critical in future PON that has much longer distance with the involvement of more users. Thus, it is vulnerable to a variety of attacks, including denial of service (DoS) which jams a network, eavesdropping and masquerade. DoS attack can take place when a continuous upstream signal is transmitted from Optical Network Unit (ONU) to Optical Line Terminal (OLT) with high enough power, causing the OLT to receive the data with high bit error rate. This research proposes a method to secure PON from high power injection attack. The solution is based on the idea of deploying an optical attenuator in the upstream communication towards the splitter to prevent any high signal power injection attack and restrict it up to an acceptable power level. One of the most important benefits of the proposed work is its straightforward implementation in the existing GPON network with minimum cost and effort. The GPON network under studied that focuses on the upstream communication based on standard ITU-T G.984 ( data rate of 1.25 Gbps) examined the effects of varied optical fiber distances and number of ONUs. The performance of the proposed method is evaluated using Optisystem to determine the feasibility of the concept. Findings from the simulation results revealed that the optical attenuator compensated the jamming degradation attack up to eight ONUs and maximum distance of 20 km. The proposed system design also found that the method has limitation to reduce the attack at higher ONU numbers e.g. 16 and 32 due to high insertion loss. The overall performance confirms that this method is useful to protect the GPON system and minimize the high power for low insertion loss power splitter
