## 5 Conclusions  
In this work, the ability of WDM multiplexing for enhancing the system capacity of bidirectional NG-PON-FSO, realized under the impact of GIMMF fiber nonlinearity and link losses for both downlink and uplink transmission, is investigated. The maximum GIMMF fiber range of 5.4-5.5 km and 5.5 km with a 100 m FSO is achieved in the downlink and uplink transmission, respectively, at a symmetric data rate of 40 Gbps. The impact of lens parameters such as focal length and reflectance on the LP[0,1] modal signal shows that the downlink signals require a minimum of a 0.085 m focal length in the downlink and 0.08 to 0.085 m in the uplink direction for achieving a BER limit of 1 \(\times\) 10\({}^{-9}\) over a 5 km fiber range. Also, the lens reflectance values vary from 12 to 14.5% and from 17 to 19% for the downlink and uplink signals, respectively, for optimum system performance  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Design**} & \multirow{2}{*}{**Distance**} & \multirow{2}{*}{ \begin{tabular}{c} **No. of** \\ **Channels** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **Data** \\ **Rate** (Gbps)** \\ \end{tabular}  } & \multirow{2}{*}{**Mode(s)**} & \multirow{2}{*}{**Transmission**} & \multirow{2}{*}{**Amplifier**} & \multirow{2}{*}{ \begin{tabular}{c} **Link** \\ **Distortions** \\ \end{tabular}  } & \multirow{2}{*}{**Cost**} & \multirow{2}{*}{**BER**} \\  & & & & & & & & & & \\ \hline PON- & \multirow{2}{*}{ \begin{tabular}{c} MDM[10] \\ \end{tabular}  } & 0.4 m & \multirow{2}{*}{1} & \multirow{2}{*}{10} & OAM & Unidirectional & EDFA & \ \begin{tabular}{c} Fiber and FSO \\ link losses \\ \end{tabular}  & Low & Medium & \(1\times 10^{-3}\) \\ \hline \multirow{2}{*}{ \begin{tabular}{c} MDM[12] \\ \end{tabular}  } & 10 m & \multirow{2}{*}{1} & \multirow{2}{*}{10} & LF[0,1],1],1,over a 5 km range. Moreover, the power fraction for generated LP modes ranges from 0.52 to \(\sim\)1 \(\times\) 10\({}^{-11}\) and 0.52 to 1 \(\times\) 10\({}^{-10}\) for the downlink and uplink transmission, respectively, while the corresponding LP mode phase changes from 0.23 to 4.79 rad in the downlink and 0.96 to 5.81 rad in the uplink. Moreover, the maximum gain, low noise figure, high output signal, and high OSNR are \(-\)29.47 dB, 34.54 dB, \(-\)21.86 dBm, and 30.51 dB for the downlink, while the values of \(-\)25.58 dB, 28.84 dB, \(-\)18.46 dBm, and 18.05 dB are obtained for the uplink transmission, respectively. Compared to other existing systems, the proposed design offers a high transmission rate, a reliable transmission range, high energy efficiency, a high channel capacity, and cost-effectiveness under various fiber and link impairments. This work can be extended for higher-order modes for integrated fiber-wireless scenarios using an appropriate amplifier. The proposed system can be employed for high-speed, high-capacity, long-reach, and energy-efficient applications. For higher-order LP modes, the proposed system undergoes large crosstalk, intermodal dispersion attenuation, and phase distortion over a long-reach fiber-FSO link. Thus, it is recommended to prioritize the LP[0,1], LP[1,1], LP[2,1], etc., modes to minimize the intermodal interference along with the utilization of a Raman or an EDFA amplifier. To generate the precise LP modes, advanced mode converters can be used, especially using AI-driven mode generators and wavelength assignments under severe climate conditions. To further enhance the spectral efficiency, hybrid multiplexing techniques, such as TDM-WDM-MDM, can be used along with quantum LP modal transmission. [PERSON] and [PERSON] discussed the plan and agreed on it. [PERSON] drafted designs for the manuscript. The original manuscript was written by [PERSON] The manuscript was edited by [PERSON]. All authors reviewed and commented on the original draft of the manuscript. All authors have read and agreed to the published version of the manuscript. [PERSON] wants to thank CTTC for providing the resources to conduct this research.