## 4 Discussion  
Optical wireless and wired communication systems will continue to speedily evolve, both in terms of capabilities and architectures, to carry the surge in various applications, like tele-surgery, augmented reality/virtual reality, industry automation, intelligent transport systems, etc. PONs have expanded over the years in respect of their hardware, architecture, capacity, underlying protocols, and algorithms. It is estimated that 40% of the world's population will possess a fiber-to-the-x link reach of 22.4 B by 2026 [23]. In comparison to experimental work operating over the C-band at a 10 Gbps data rate [16], the proposed work offers high channel capacity and spectral efficiency at a high data rate of 40 Gbps over the L/C-band. The proposed work indicates that GIMMF can be utilized in metro transmission with better nonlinearity tolerance compared to existing work, as shown in ref. [16], for its large effective mode-field coverage. Moreover, compared to LP[0,1] modal simulation work operating at the 1552.52 and 1550.12 nm wavelengths in [17], the proposed design offers a reliable GIMMF range of 5.5 km at a BER of \(10^{-9}\). Table 4 shows the comparative analysis of the proposed architecture with respect to previous works. The proposed system is realized under the impact of 5.5 km GIMMF nonlinearity, lens losses, and noise with geometric and free space path loss of a 100 m free space link under clear air and weak turbulence. It depicts the comparative analysis of the proposed work in terms of transmission distance, number of supported channels, throughput, and link distortions, including environmental conditions, spectral efficiency, and flexibility. However, the proposed bidirectional NG-PON system using integrated GIMMF-FSO offers a higher channel capacity (=4 \(\times\) DN/UP wavelengths), a high data rate (=4 \(\times\) 10/10 Gbps), a simple design, and cost-effectiveness. This system offers optimum results under the impact of fiber nonlinearity, lens focal length, reflectance, and noise compared to other existing systems without using any amplifiers, but it also suffers from a limited transmission range due to a tradeoff between distance and traffic rate. Figure 10: System performance with respect to gain and noise figure for (**a**) downlink and (**b**) uplink transmission; output signal and OSNR for (**c**) downlink and (**d**) uplink transmission. GIMMF is cheaper compared to SMF, owing to manufacturing tolerances, a larger core size, and requiring multimode transceivers instead of precise transceivers for SMF. GIMMFs are easier to install, pose fewer installation costs, and require cost-effective splicing and connector equipment. Also, GIMMF is useful for multimodal and short-range applications but has bounded scalability owing to modal attenuation and dispersion. GIMMF fibers can support multiple propagation modes, but modal dispersion restricts the number of modes over a long reach. Furthermore, in actual deployment, the adjustment of lens parameters faces engineering challenges, such as environmental factors, signal loss, modal crosstalk, and reduced system efficiency. Efficient mode transmission requires a vigilant lens design, thermally compensated mechanisms, and higher-mode coupling efficiency. In the future, the proposed system can be used for advanced mode generation by using digital signal processing algorithms to minimize the intermodal interference and EDFA amplifiers to compensate for atmospheric-induced distortions in the FSO link. Also, artificial intelligence (AI)-assisted network optimization can be realized in dynamic environmental conditions. For enhanced, secure, and energy-efficient integrated 6G and smart city scenarios, quantum key distribution and edge intelligence can be deployed for real-time traffic fiber-wireless networks. Integrated 6G and MDM-FSO-fiber systems for smart city networks will offer low-latency, ultra-fast, and high-capacity transmission.