Performance of a passive multilayer optical RIS for tropical FSO links in Malaysian rain and humidity

Mohd Razali, Shahrizan and Ngah, Razali and A. Al-Gailani, Samir and Mohd Nor, Norhanis Aida (2025) Performance of a passive multilayer optical RIS for tropical FSO links in Malaysian rain and humidity. Semarak Climate Science Letters, 5 (1). pp. 1-16. E-ISSN 3083-9580

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Abstract

Free-space optical (FSO) backhaul promises fibre-like capacity and low latency, but its usable range in practice is constrained by geometric spreading, misalignment loss, and severe tropical weather such as humidity and heavy rain. This work designs and evaluates a purely passive, five-layer optical reflective intelligent surface (RIS) and quantifies how it affects link sustainability under Malaysian atmospheric conditions. The RIS is modelled as a multilayer dielectric or semiconductor or metal stack, and its angular reflectance is obtained using Fresnel coefficients and Snell’s law for s- and p-polarized light, together with a transfer-matrix formulation for multilayer interference. The resulting passive surface is then embedded into an FSO link model with coherent QPSK reception. We simulate received optical power, effective SNR, and BER versus distance (0.5–10 km) under three tropical cases: clear/dry air, high humidity (>80% RH), and heavy rain representative of Malaysian convective downpours (>100 mm/h). Results show that, in clear or humid air, the passive RIS maintains high reflectance (>0.9 linear), supports SNR >10 dB out to multi-kilometre ranges, and achieves BER <10⁻⁶ for coherent QPSK, indicating carrier-grade performance. Under heavy rain, however, added attenuation drives received power down by >30 dB at 10 km, forcing SNR below 0 dB beyond ~5 km and causing BER to exceed 10⁻². We also show that sub-degree pointing errors at the RIS can introduce tens of dB of coupling loss, highlighting alignment as a critical design factor even without turbulence. Overall, the study provides a quantitative baseline for passive optical RIS deployment in tropical FSO links and identifies rain, not humidity, as the dominant barrier to long-distance reliability in Malaysian conditions

Item Type:	Article (Journal)
Uncontrolled Keywords:	Passive RIS, Free Space Optic (FSO), Malaysia weather, BER and SNR, MATLAB Simulation
Subjects:	T Technology > TK Electrical engineering. Electronics Nuclear engineering T Technology > TK Electrical engineering. Electronics Nuclear engineering > TK7800 Electronics. Computer engineering. Computer hardware. Photoelectronic devices T Technology > TK Electrical engineering. Electronics Nuclear engineering > TK7800 Electronics. Computer engineering. Computer hardware. Photoelectronic devices > TK7885 Computer engineering
Kulliyyahs/Centres/Divisions/Institutes (Can select more than one option. Press CONTROL button):	Kulliyyah of Engineering > Department of Science
Depositing User:	Dr Norhanis Aida Mohd Nor
Date Deposited:	25 Nov 2025 09:56
Last Modified:	25 Nov 2025 09:56
Queue Number:	2025-11-Q181
URI:	http://irep.iium.edu.my/id/eprint/124648

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