FSO Channel Design with Halo-Inclusive Source

Free-space optical (FSO) communication models typically assume either a diffraction-limited point source truncated by a circular aperture or an ideal Gaussian beam representing an extended emitter. In practice, real transmitters exhibit both finite source extent and aperture-induced diffraction, producing a characteristic halo that significantly alters far-field intensity distribution and received power. This paper presents a unified halo-inclusive framework that rigorously incorporates both effects within a single scalar field model by multiplying a Gaussian angular envelope with the classical Airy pattern and enforcing energy conservation. Closed-form expressions for total power, on-axis intensity, and channel gain are derived, together with analytical results in two limiting regimes: Gaussian-dominated extended sources and diffraction-dominated point-like sources. The general case is formulated for numerical evaluation. The analysis demonstrates that the conventional inverse-square path-loss law emerges only under restricted geometric conditions and may deviate substantially otherwise. The unified model enables more accurate
FSO link design, optimization, and performance prediction.