# Wheel-Based MDM-PON System Incorporating OCDMA for Secure Network Resiliency
## 1 Introduction
### Related Work  
Recently, several researchers presented their proposed systems and experimental/simulation results on PON employing different topologies. [PERSON] et al. demonstrated a WDM-PON using ring topology to analyze the system reliability and network scalability. It was found that a maximum of eight remote nodes can be connected with a receiver sensitivity of \(-26\) dBm [5]. [PERSON] et al. investigated a tree-based PON employing self-restorable apparatus against the optical fiber cable. It was found that restoration time and protection of the PON can be obtained within \(7\) ms [6]. [PERSON] and [PERSON] presented an experimental demonstration of ring-based PON utilizing asymmetric passive splitters. It was reported that the designed network could offer full restoration of the traffic if one OLT failed in real applications [7]. [PERSON] and [PERSON] proposed a hybrid ring-tree topology in a WDM system with polarization shift keying/non-return to zero (NRZ) at \(60\) Gbit/s data rate for \(64\) consumers. The results depict that the performance of the system is affected by input signal power, channel spacing and data rate. Moreover, the orthogonal modulation format enhances the system performance in terms of high bandwidth for future access networks [8]. [PERSON] and [PERSON] investigated the performance of a hybrid ring-star-based dense wavelength division multiplexing (DWDM) system utilizing add/drop multiplexers. The results show that the suggested system runs a high transmission range of 150 km at a 15 Gbit/s data rate for 128 end users [9]. [PERSON] and [PERSON] investigated the semiconductor optical amplifier (SOA) 400 mA biased current-based performance of ring and bus topologies supporting 100 nodes at 10 Gbit/s [10]. Additionally, in [11], a dual ring-based WDM system employing hybrid fiber/free space optics (FSO) link over 5 km transmission distance at 20 Gbit/s data rate was proposed. Moreover, a ring-based integrated WDM-TDM PON over 20 km single mode fiber (SMF) at 10 Gbit/s was reported [12]. In another work, a self-protected integrated FSO-fiber link-based WDM-PON system over 25 km SMF and 2 m FSO range at 24.3 Gbit/s transmission rate was successfully presented [13]. Furthermore, due to the faster development over the last few years, the SMF-based transmission system has progressively arrived at its Shannon capacity limit [14; 15; 16]. To further enhance the system capacity by keeping less extensive inline devices such as optical amplifiers, etc., for minimal cost and energy consumption/bit, mode division multiplexing (MDM) technique employing multimode fiber (MMF) or few-mode fiber (FMF) has recently been demonstrated and comprehensively reported [17]. In the MDM technique, a single fiber is utilized for transmitting distinct optical spatial modes via the single core fiber. It can also encourage the transmission abilities of fiber by '_n_' times. The TWDM-PON employing MDM can be further engaged to widen the network capacity for a definite set of channels to implement the high-speed PONs [18]. [PERSON], [PERSON] et al. suggested a four channels MDM-PON system employing self-homodyne detection. The results show that the suggested system delivers a high transmission rate of 160 Gbit/s over 55 km FMF successfully [19]. Moreover, [PERSON], [PERSON] et al. presented a bidirectional MDM-TDM PON using a reflective semiconductor optical amplifier (RSOA) over 10 km FMF and 20 km SMF at 10 Gbit/s transmission rate [20]. Additionally, [PERSON], [PERSON] et al. proposed a four-channel WDM-MDM PON using two linearly polarized (LP) modes over 10 km MMF at a 25 Gbit/s data rate [18]. [PERSON], [PERSON] et al. experimentally demonstrated a full-duplex PON-MDM transmission system using two LP modes over 10 km two-mode fiber at 10 Gbit/s data rate [21]. In [22], they also proposed an MDM-GPON incorporating 10 km wavelength insensitive weakly coupled FMF and 10 km SMF at a 2.5 Gbit/s transmission rate. [PERSON], [PERSON] et al.