## 1 Introduction  
Optical networks have become an important part of telecommunication systems because they are the preferred choice of every operator, providing a high quality of service (QoS), improving system performance, and achieving higher transmission speeds than routers and switches. They are characterized by their transparency to data formats and protocols, which allows for increased functionality and flexibility to meet network requirements [1; 2; 3; 4; 5]. In 1980, the technique of optical code division multiple access (OCDMA) was proposed for optical networks and communications, resulting in rapid advancements in fiber optic techniques to increase data rates, the number of users, and the potential for mitigating multiple access interference (MAI), among other benefits [1]. OCDMA is one of the multiplexing and internetworking techniques that encodes and decodes signals using passive optical components that are cost-effective and simple [1]. It has become necessary in communication networks because it enables fast transmission of information for a large number of users in both time and frequency, using one optical fiber channel, where each user has a specific code [6; 7]. In an OCDMA system, noise arises from various physical effects that are due to the system design itself. For example, there can be relative intensity noise (RIN), shot noise, thermal noise, and phase-induced intensity noise (PIIN) [8]. Accordingly, OCDMA systems suffer from multiple drawbacks that impede their performance and severely limit the signal-to-noise ratio (SNR). One of the main issues is multiple access interference (MAI), which occurs due to the overlap between the spectra of different users and leads to phase-induced intensity noise (PIIN) and other types of noise [9]. To address this issue, spectral amplitude coding optical code division multiple access (SAC-OCDMA) systems were developed. This scheme improves the system performance by encoding spectral components and completely eliminating the MAI effect [10]. The classification of optical access networks depends on the components used in the network, resulting in two categories: passive and active. Networks that use electrical de-multiplexers are called active optical networks (AONs), while those that use optical de-multiplexers are called passive optical networks (PONs). However, the difference between them is not only related to the nature of the de-multiplexers but also to the amount of energy they consume. A PON is generally considered to be an energy-efficient option, as it consumes less energy compared to an AON [11]. In recent years, passive optical networks (PONs) have garnered significant attention from researchers due to their numerous advantages. These advantages include the ability to spread optical fibers over long distances of multiple tens of kilometers or more, as well as providing quality of service (QoS), high-speed internet access, scalability, and the capability to share a single optical fiber between multiple users. This reduces system complexity by minimizing the number of components used, decreasing costs, allowing for service transparency, and increasing the system's potential [12]. The original objective of PON technology was to enable fiber-to-the-home (FTTH) communication using passive components. However, the objective of next-generation PONs (NG-PONs) has shifted towards increasing the bandwidth available to users. To achieve this, downstream and upstream currents must be made equivalent or closer, allowing for Gigabit PON (GPON) speeds to be reached [13]. A PON is a broadcast technique that allows data to be distributed from a single point to multiple points with the use of passive components such as splitters, combiners, and optical fibers. To meet the growing capacity demands, network operators are expanding their optical infrastructure, moving closer to end-users, and using resources more efficiently. In this context, researchers have shown a great interest in passive optical networks (PONs) [14].