# Evaluation of Optimal Visible Wavelengths for Free-Space Optical Communications
## 5 Conclusions and Future Work  
This study presented a comprehensive experimental evaluation of three visible-wavelength laser diodes--650 nm (red), 532 nm (green), and 405 nm (violet)--to determine their suitability for short-range free-space optical (FSO) communication. Utilizing a custom-developed laboratory testbed featuring an Atmega328p microcontroller and a silicon-based photovoltaic detector, each diode's optical power output, quantum efficiency, and modulation response were systematically assessed under controlled electrical conditions. The experimental findings demonstrate that the 650 nm red laser diode outperformed its green and violet counterparts across all key performance metrics. It exhibited the highest quantum efficiency, the most stable optical output across the frequency range, and strong alignment with the spectral responsivity of silicon photodetectors. These attributes, along with its lower sensitivity to scattering, establish the red diode as a compelling choice for energy-efficient and reliable short-range FSO systems. In contrast, the 405 nm violet laser diode offered commendable modulation bandwidth and higher photon energy but was limited by reduced quantum efficiency and increased power consumption. This makes it less favorable for energy-constrained applications, such as battery-powered or IoT-integrated systems. The 532 nm green diode, while prevalent in visual signaling, demonstrated the weakest performance, with lower optical output and efficiency, and is therefore considered suboptimal for data-oriented FSO communication. Although atmospheric attenuation models (the [PERSON], [PERSON], and [PERSON] models) were not directly applied in this phase of the work, their integration provided essential theoretical context. These models will guide future studies aimed at evaluating system behavior under realistic environmental conditions. Planned expansions include testing  
Figure 5: Comparison of theoretical attenuation trends (Kruse model) and experimental quantum efficiencies for 405 nm, 532 nm, and 650 nm wavelengths. under simulated fog, haze, and aerosol environments, using fog/smoke chambers and variable particle density modeling to assess attenuation effects more rigorously. Building on the results of this study, future research will focus on the following directions:  
* Extending the transmission range to 5-10 m in controlled indoor environments (e.g., corridor setups) to examine signal integrity and beam propagation under more practical conditions. * Implementing advanced modulation schemes, such as pulse-position modulation (PPM) and orthogonal frequency-division multiplexing (OFDM) to enhance data rates, bandwidth efficiency, and noise resilience. * Investigating advanced photodetector architectures capable of simultaneous signal detection and energy harvesting, thereby improving receiver-side energy efficiency. * Embedding visible light-based FSO links into Internet of Things (IoT) platforms and Li-Fi networks, enabling scalable, low-power wireless communication for smart infrastructure and edge-computing applications. * Developing artificial intelligence (AI) models to predict environmental attenuation (e.g., fog, dust, ambient light), enabling dynamic system optimization and robust performance under varying outdoor conditions. These future efforts will further advance the development of compact, adaptive, and energy-conscious visible-light FSO systems suitable for a wide range of applications, from smart indoor networking to environmental sensing and resilient outdoor communication infrastructures. Supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/telecom6030057/s1](https://www.mdpi.com/article/10.3390/telecom6030057/s1)]([https://www.mdpi.com/article/10.3390/telecom6030057/s1](https://www.mdpi.com/article/10.3390/telecom6030057/s1)). The file includes datasheets of key components, measurement tables, quantum efficiency plots, modulation control tables, source code (VBA and AVR), and images of the experimental setup and circuit schematics.