Noise Suppression in the Signal Spectral Induced by Atmospheric Turbulence on the FSO (Free-Space Optical) Communications

Beam wander and spatial noise that are modulated on optical propagation produce noise modulation in the signal spectral before being received by a Photodetector (PD). In order to suppress noise modulation in the signal spectral, we present an Optical Spatial Filter (OSF) method that is composed of the cone reflector and a pinhole as a detection method. A cone reflector is designed to suppress beam wander in order to minimize temporal noise that fluctuates randomly and governs reflection of the deflected focus spot into the narrow region of pinhole. The pinhole governs the Fresnel diffraction in order to suppress spatial noise in the center of focus spot that undergoes fluctuation and random frequencies as well. Through simultaneous suppression in temporal noise caused by beam wander and spatial noise using the OSF method, noise modulation in the signal spectral can be minimized optimally. We compared the OSF with the Direct-Detection (DD) method by experimentation. The results of the experiment show significant improvements for noise suppression in the signal spectral. The average values of the Signal-to-Noise Ratio (SNR) increase, namely, 37.5 dB, 38.5 dB, 38.7 dB and 39.2 dB for pinhole diameters of 50 µm, 40 µm, 30 µm, and 20 µm, respectively.

Beam wander, Cone reflector, FSO, Pinhole, Optical Spatial Filter, Spatial noise

Andrews, L.C., Philips, R.L., 2005. Laser Beam Propagation through Random Media. 2nd Edition, SPIE PRESS, Washington, pp. 364–367

Caplan, D.O., 2007. Laser Communication Transmitter and Receiver Design, Journal of Optical Fiber Communications Reports, Volume 4, pp. 225–362

Ciaramella, E., Arimoto, Y., Contestabile, G., Presi, M., D’Errico, A., Guarino, V., Matsumoto, M., 2009. 1.28 terabit/s (32×40 Gbit/s) WDM Transmission System for Free-space Optical Communications. IEEE J. on Select. Areas in Commun., Volume 27, pp. 1639–1645

Darusalam, U., Priambodo, P.S., Rahardjo, E.T., 2015. Optical Spatial Filter to Suppress Beam Wander and Spatial Noise Induced by Atmospheric Turbulence in Free-space Optical Communications. Advances in Optical Technologies, Volume 2015, pp. 1?6

Darusalam, U., Priambodo, P.S., Rahardjo, E.T., 2015. SNR and BER Performance Enhancement on FSO Induced by Atmospheric Turbulence using Optical Spatial Filter. International Journal of Optics and Applications, Volume 5(3), pp. 51–57

Jeong, M.-C., Lee, J.-S., Kim, S.-Y., Namgung, S.-W., Lee, J.-H., Cho, M.-Y., Huh, S.-W., Ahn, Y.-S., Cho, J.-W., Seung, J., 2003. 8×10-Gb/s Terrestrial Optical Free-space Transmission over 3.4 km using an Optical Repeater. IEEE Photon. Technol. Lett., Volume 15(1), pp. 171–173

Majumdar, A.K., 2005. Free-space Laser Communication Performance in the Atmospheric Channel. Journal of Optical and Fiber Communications Reports, Volume 2(4), pp. 345–396

Nykolak, G., Szajowski, P.F., Tourgee, G., Presby, H., 1999. 2.5 Gbit/s Free Space Optical Link over 4.4 km. Electron. Lett., Volume 35(7), pp. 578–579

Pedireddi, L.B., Srinivasan, B., 2010, Characterization of Atmospheric Turbulence Effects and their Mitigation using Wavelet-based Signal Processing. IEEE Trans. on Commun., Volume 58, pp. 1795–1802

Prasad, N.S., 2005. Optical Communications in the Mid IR Spectral Band. Journal of Optical and Fiber Communications Reports, Volume 2, pp. 347?391

Priambodo, P.S., Darusalam, U., Rahardjo, E.T., 2015. Free-space Optical Propagation Noise Suppression by Fourier Optics Filter Pinhole. International Journal of Optics and Applications, Volume 5(2), pp. 27–32

Ricklin, J.C., Hammel, S.M., Eaton, F.D.. Svetlana, L., 2006. Atmospheric Channel Effects on Free-space Laser Communication. Journal of Optical and Fiber Communications Reports, Volume 3(2), pp. 111–158

Si, C., Zhang, Y., Wang, Y., Wang, J., Jia, J., 2012. Average Capacity for non-Kolmogorov Turbulent Slant Optical Links with Beam Wander Corrected and Pointing Errors. International Journal for Light and Electron Optics, Volume 123(1), pp. 1–5

Song, D.-Y., Hurh, Y.-S., Cho, J.-W., Lim, J.-H., Lee, D,-W., Lee, J.-S., Chung, Y., 2000. 4×10 Gb/s Terrestrial Optical Free Space Transmission over 1.2 km using an EDFA Preamplifier with 100 GHz Channel Spacing. Optics Express, Volume. 7, pp. 280–284

Toselli, I., Andrews, L.C., Phillips, R.L., Ferrero, V., 2009. Free-space Optical System Performance for a Gaussian Beam Propagating through non-Kolmogorov Weak Turbulence. Antennas and Propagation, IEEE Transactions, Volume 57(6), pp. 1783–1788

Weyrauch, T., Vorontsof, M.A., 2004. Free-space Laser Communications with Adaptive Optics: Atmospheric Compensations. Journal of Optical and Fiber Communications Reports, Volume 1(4), pp. 355–379

Zhu, X., Kahn, J.M., 2007. Communication Techniques and Coding for Atmospheric Turbulence Channels. Journal of Optical and Fiber Communications Reports, Volume 4(6), pp. 363–405