Propagation of Bessel Beam for Ground-to-Space Applications

Abstract

We model the propagation of Gaussian and Bessel beams from ground through 22km altitude of atmospheric turbulence. We observe the Bessel beam has better performance based on RMS intensity error and the captured beam power. OCIS codes: (010.1300) Atmospheric propagation; (000.1330) Atmospheric turbulence. Free Space Optics (FSO) for data transmission has so far largely focused on the propagation of Gaussian beams. However, Gaussian beams suffer from diffraction, causing the spread of the beam's energy and so lowering the signal to noise ratio at the receiver. This paper investigates improvements to FSO by simulating the propagation of non-diffracting beams through unguided media. With the main impairments to FSO known to be diffraction and atmospheric turbulence, Durnin's (1) idea of a non-diffracting self-healing Bessel beam could potentially mitigate these problems. Bessel beams possess an intensity profile that is cylindrically symmetrical: a central core surrounded by a set of concentric rings. It has been shown that the central core of a Bessel beam is remarkably resistant to diffractive spreading compared to that of a Gaussian beam with a similar beam radius (2,3). Bessel beams can be decomposed into an infinite set of plane wavefronts at different azimuths, but at a fixed inclination towards the direction of travel. When propagating, these wavefronts travel inwardly adding up to the energy of the central core (1,4,5). This inward diffraction helps the on-axis intensity to remain constant as it propagates. Another effect of the inward diffraction is an attribute called self- healing: the beam is capable of recovering back its profile after being partially scattered by an obstruction. These properties make Bessel beams very promising for various applications such as observatory astronomy as well as terrestrial and satellite communications. In this paper, we simulate the propagation of both Gaussian and Bessel beams from ground level, through atmospheric turbulence. Previously, Nelson et al (4) investigated the propagation of these beams over a short ground-to-ground range of 6.4km, with constant strength of turbulence C n 2 . In this paper we investigate the more difficult propagation problem from ground to space by considering the C n 2 to be larger in the lower atmosphere but gradually weakening with altitude, based on some modifications to the Hufnagel-Valley model (6,7)over a considerably larger distance. 2. Background