Accurate analysis of the efficiency of Bessel Gauss beams passing through two Cassegrain optical antennas in atmospheric turbulence

For a partially coherent Bessel–Gaussian (PCBG) vortex beam, information regarding the topological charge (TC) is hidden in the phase of the cross-spectral density (CSD) function. We theoretically and experimentally confirmed that during free-space propagation, the number of coherence singularities is equal to the magnitude of the TC. In contrast to the Laguerre–Gaussian vortex beam, this quantitative relationship only holds for the case with an off-axis reference point for the PCBG vortex beam. The phase winding direction is determined by the sign of the TC. We developed a scheme for CSD phase measurement of PCBG vortex beams and verified the aforementioned quantitative relationship at different propagation distances and coherence widths. The findings of this study may be useful for optical communications.

Coherence singularity and evolution of partially coherent Bessel–Gaussian vortex beams

Zhu¹,

Zhang²,

Wang³

et al. 2023

Set of mathematical models for Bessel-Gauss beams coupling into the parabolic-index fiber under the influence of atmospheric turbulence and random jitter

Shang

Deng

et al. 2023

The expression of efficiency for Bessel-Gauss (BG) beams coupling into the parabolic fibers (PF) after passing through the Cassegrain antenna system is first derived. The effects of atmospheric turbulence and random jitter of the coupling lens on the efficiency are also taken into account to improve the practical applicability of our model. This article use a BG beam with a wavelength of 1550 mm and fiber with a core radius R F of 50 μm and a relative refractive index difference ζ of 0.01 for simulation testing. The optimal parameters of the antenna system are determined: the radius of the primary mirror and the secondary mirror is 8.33 cm and 1.25 cm, respectively. The coupling efficiency of BG beams of different orders reaches above 94% simultaneously when the lens’s focal length is 7.8 cm. After taking into account the transmission efficiency of the antenna system, the system’s total efficiency for BG beams of different orders averages 76.33%, when the transmission distance is 1 km. The results show that the same degree of turbulence and random jitter have different influences on the coupling efficiency of BG beams of different orders, and lower-order BG beams have better resistance to turbulence and jitter during propagation and coupling. Moreover, the effect of the guided mode field on the coupling efficiency and the resistance to turbulence varies for different values of mode radial index in the fiber p. The guided mode with p = 0 not only enables the BG beams of different orders to achieve the highest transmission efficiency in the coupling system almost simultaneously but also the random jitter and turbulence have less influence on the coupling efficiency of this mode. It means that the BG beams can have higher efficiency when coupled to the mode with p = 0 after long-distance transmission. This property of the fiber mode at p = 0 provides conditions for the simultaneous propagation of multiple BG beams in a parabolic fiber, which provides a theoretical basis for higher transmission capacity. This research work provides a theoretical model for the theoretical study of vortex beams and optical communication, which is beneficial for the design and application of vortex beams and has instructive meaning for practical engineering design.

Enhancing transmission and coupling efficiency in Cassegrain optical systems with four-petal Gaussian beams

Yang,

Li,

Shang

et al. 2024

This study investigates the propagation characteristics of four-petal Gaussian beams through Cassegrain optical systems. With the properties of this new type of beam, the problem of masking loss in the Cassegrain optical system can be well solved. Analytical expressions of the optical field for beams after propagating the optical system are derived, considering atmospheric turbulence effects and random jitter on coupling efficiency. Simulation tests explore various factors affecting transmission efficiency. Acceptable axial mounting error tolerance and significant efficiency drops beyond specific communication distances under different turbulence conditions (). Achieving over 80 coupling efficiency is feasible with specific lens parameters (f = 0.4 − 0.5 mm, receiving position after 4 km) using standardized lenses. This work offers a theoretical model for four-petal Gaussian beams, aiding optical communication design and application, with practical engineering implications.