Aperture Averaged Scintillation of Gaussian Beam in Strong Oceanic Turbulence

Abstract

Oceanic turbulence caused by salinity and temperature fluctuations underwater affects the characteristics of a transmit laser beam resulting in turbulence-induced intensity fluctuations (i.e., scintillation) at the receiver. Oceanic optical wireless communication (OOWC) systems employ a receiver lens of aperture to focus the collected light onto a photodetector. This way, aperture averaging takes place and the scintillation on the detector is reduced. Using the modified Rytov theory, aperture averaged scintillation of the Gaussian beam passing through strong oceanic turbulence is examined in this study. Effects of Gaussian beam parameters and the turbulence parameters on the aperture averaged scintillation and the aperture averaging factor are illustrated. The scintillation behaviors of the limiting cases of a spherical wave and a plane wave are also reported. Results show that aperture averaged scintillation decreases with increasing the size of the receiver aperture for any turbulence level. The effect of Gaussian size on the aperture averaged scintillation varies depends on the turbulence level. It is also shown that there is a close match between the point scintillation index values obtained from the modified Rytov theory and the conventional Rytov theory in low levels of turbulence. 

Keywords

• Oceanic optical wireless communication
• Oceanic propagation
• Aperture averaging
• Scintillation

References

1. [1] Uysal, M., Capsoni, C., Ghassemlooy, Z., Boucouvalas, A., Udvary, E., “Optical Wireless Communications: An Emerging Technology”, Springer International Publishing, Switzerland (2016).
2. [2] Zeng, Z., Fu, S., Zhang, H., Dong Y., Cheng, J., "A Survey of Underwater Optical Wireless Communications", IEEE Communications Surveys & Tutorials, 19(1): 204-238, (2017).
3. [3] Korotkova, O., Random Light Beams: Theory and Applications, CRC Press, Boca Raton, FL, (2014).
4. [4] Ata, Y., Baykal, Y., “Scintillation of optical plane and spherical waves in underwater turbulence”, J. Opt. Soc. Am. A, 31(7): 1552-1556, (2014).
5. [5] Korotkova, O., Farwell, N., Shchepakina, E., “Light scintillation in oceanic turbulence”, Waves in Random and Complex, 22(2): 260-266, (2012).
6. [6] Wang, Z., Zhang, P., Qiao, C., Lu, L., Fan, C., Ji X., “Scintillation index of Gaussian waves in weak turbulent ocean”, Opt. Commun., 380: 79-86, (2016).
7. [7] Baykal, Y., “Scintillation index in strong oceanic turbulence”, Opt. Commun., 375: 15-18, (2016).
8. [8] Baykal, Y., “Intensity fluctuations of multimode laser beams in underwater medium”, J. Opt. Soc. Am. A, vol. 32(4): 593-598, (2015).

9. [9] Baykal, Y., “Higher order mode laser beam scintillations in oceanic medium”, Waves in Random and Complex Media, 26(1): 27-29, (2016).
10. [10] Baykal, Y., “Scintillation of LED sources in underwater medium”, Appl. Opt., 55(31): 8860-8863, (2016).
11. [11] Gerçekcioğlu, H., “Bit error rate of focused Gaussian beams in weak oceanic turbulence”, J. Opt. Soc. Am. A, 31(9): 1963-1968, (2014).
12. [12] Arpali, S. A., Baykal, Y., Arpali, Ç., "BER evaluations for multimode beams in underwater turbulence", J. Mod. Opt., 63(13): 1297-1300, (2016).
13. [13] Gökçe, M. C., Baykal, Y., "Scintillation analysis of multiple-input single-output underwater optical links", Appl. Opt. 55(22): 6130-6136, (2016).
14. [14] Baykal, Y., "Bit error rate of pulse position modulated optical wireless communication links in oceanic turbulence", J. Opt. Soc. Am. A, 35(9): 1627-1632, (2018).
15. [15] Wu, T., Ji, X., Zhang, H. Li, X., Wang, L., Fan, X., “Rytov variance of spherical wave and performance indicators of laser radar systems in oceanic turbulence”, Optics. Commun., 434: 36-43, (2019).
16. [16] Sari F., Yenice, Y. E., "Lorentz-Gaussian beam performance for weak turbulence", International Conference on Broadband Communications for Next Generation Networks and Multimedia Applications (CoBCom), Graz, 1-4, (2016).
17. [17] Yi, X., Li, Z., Liu, Z., "Underwater optical communication performance for laser beam propagation through weak oceanic turbulence", Appl. Opt., 54(6): 1273-1278, (2015).
18. [18] Gökçe, M. C., Baykal, Y., “Aperture averaging and BER for Gaussian beam in underwater oceanic turbulence”, Opt. Commun., 410(5): 830-835, (2018).
19. [19] Gökçe, M. C., Baykal, Y., “Aperture averaging in strong oceanic turbulence”, Opt. Commun., 413(7): 196-199, (2018).
20. [20] Cheng, M., Guo, L., Zhang Y., "Scintillation and aperture averaging for Gaussian beams through non-Kolmogorov maritime atmospheric turbulence channels," Opt. Express, 23(25): 32606-32621, (2015).
21. [21] Baykal, Y., "Expressing oceanic turbulence parameters by atmospheric turbulence structure constant", Appl. Opt., 55(6): 1228-1231, (2016).
22. [22] Nikishov, V. V., Nikishov, V. I., “Spectrum of turbulent fluctuations of the sea-water refraction index”, Int. J. Fluid Mech. Res., 27(1): 82–98, (2000).
23. [23] Gökçe, M. C., Baykal, Y., Ata, Y., “Performance analysis of M-ary pulse position modulation in strong oceanic turbulence”, Opt. Commun., 427: 573-577, (2018).
24. [24] Gökçe, M. C., Baykal, Y., Ata, Y., “M-ary phase shift keying-subcarrier intensity modulation performance in strong oceanic turbulence”, Opt. Eng., 58(5): 056105, (2019).
25. [25] Wang, Z. Lu, L., Zhang, P., Qiao, C., Zhang, J., Fan, C., Ji, X., “Laser Beam Propagation through Oceanic Turbulence”, IntechOpen (2018).
26. [26] Alford, M. H., Gerdt D. W., Adkins C. M., “An ocean refractometer: resolving millimeter-scale turbulent density fluctuations via the refractive index”, J. Atmos. and Ocean. Tech., 23(1): 121–137, (2006).
27. [27] Andrews, L. C., Phillips, R. L., Hopen, C. Y., “Laser Beam Scintillation with Applications”, SPIE Press, Bellingham, Washington (2001).
28. [28] Andrews, L. C., Phillips, R. L., “Laser Beam Propagation through Random Media”, SPIE, Bellingham, Washington (2005).
29. [29] Wang, S. J., Baykal, Y., Plonus, M. A., “Receiver aperture averaging effects for the intensity fluctuation of a beam wave in the turbulent atmosphere”, J. Opt. Soc. Am., 73(6): 831-837, (1983).