Scintillation and bit error rate analysis of a phase-locked partially coherent flat-topped array laser beam in oceanic turbulence

Abstract

In this paper, the performance of underwater wireless optical communication (UWOC) links, which is made up of the partially coherent flat-topped (PCFT) array laser beam, has been investigated in detail. Providing high power, array laser beams are employed to increase the range of UWOC links. For characterization of the effects of oceanic turbulence on the propagation behavior of the considered beam, using the extended Huygens-Fresnel principle, an analytical expression for cross-spectral density matrix elements and a semi-analytical one for fourth-order statistical moment have been derived. Then, based on these expressions, the on-axis scintillation index of the mentioned beam propagating through weak oceanic turbulence has been calculated. Furthermore, in order to quantify the performance of the UWOC link, the average bit error rate (BER) has also been evaluated. The effects of some source factors and turbulent ocean parameters on the propagation behavior of the scintillation index and the BER have been studied in detail. The results of this investigation indicate that in comparison with the Gaussian array beam, when the source size of beamlets is larger than the first Fresnel zone, the PCFT array laser beam with the higher flatness order is found to have a lower scintillation index and hence lower BER. Specifically, in the sense of scintillation index reduction, using the PCFT array laser beams has a considerable benefit in comparison with the single PCFT or Gaussian laser beams and also Gaussian array beams. All the simulation results of this paper have been shown by graphs and they have been analyzed in detail.

Scintillation and BER analysis of the partially coherent flat-topped array laser beam in the non-Kolmogorov atmospheric turbulence on slant path

“…The fourth-order moment can theoretically be used to predict the correlation width of the irradiance fluctuations and the scintillation index [1][2][3]. Generally, in applications such as astronomical and oceanic imaging, remote sensing, and optical communications that require the transmission of modulated laser beams through the turbulent media such as atmosphere and ocean, the scintillation causes signal fading, degrades the signal-to-noise ratio (SNR), and results in a higher bit error rate (BER) [12,16,17,32]. Thus, knowledge of optical scintillation under various media conditions is highly desirable.…”

“…Moreover, finding a good solution to overcome the destructive effects of turbulence and consequently increase in quality of the communication link parameters in FSO systems is an engaging topic that has attracted theoretical and experimental researchers' attentions [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19].…”

“…To eliminate the destructive effect of scintillation on laser beam transmission, different methods, such as increasing receiver aperture size, making phase correction via adaptive optics, using different laser beam such as different shape (Gaussian beam, Flat-topped beam, array beam,...) and different spatial coherence (partially and fully coherent laser beam), have been used in turbulent media [12,13,16,17,[20][21][22][23][24].…”

“…It has been proven that partially coherent beams due to robust turbulence resistance are less sensitive to the effects of turbulence than fully coherent ones when propagating through the atmosphere [10,11]. One of the best methods in this regard to overcome the attenuating effect of turbulence is to use the combination of more than one laser beam as the source of the system that has been under intense research recently [14][15][16][17]. Also, the investigation of different laser beam propagation properties declared that the flat-topped laser beams, due to its particular properties, have attracted attention of researchers.…”

“…The most salient feature of flattopped laser beams is uniform intensity distribution in the beam cross-sectional profiles, which is providing much better data modulation compared with conventional Gaussian laser beams. Moreover, exploring researcher's literature in this field shows that a flat-topped laser beam has advantages over a Gaussian beam for dominating atmospheric turbulenceinduced degradation [4,[16][17][18][19].…”