10Gb/s Two-User Spatial Diversity FSO-CDMA Wiretap Channel Based on Reconfigurable Optical Encoder/Decoders

Abstract

Due to the effect of atmospheric turbulence, the transmission reliability and physical-layer security of free space optical (FSO) communication system are facing many challenges. In this paper, for the first time, we design and investigate a 10 Gb/s reconfigurable FSO wiretap channel based on spatial diversity and optical code division multiple access (OCDMA). Reconfigurable two-dimensional optical encoder and decoder are constructed by wavelength selective switch and optical delay lines, and reconfigurable onedimensional optical encoder and decoder are constructed by couplers and tunable optical delay lines. Under three different turbulence conditions, bit error rates (BER) of legitimate user and eavesdropper are measured. It can be seen that under turbulence effects, BER of legitimate user in spatial-diversity is lower than that of non-diversity system. By the rapid code reconfiguration of legitimate users, the eavesdropper can only use unmatched decoder. Thus, the eavesdropping methods of code interception and brute-force searching can be avoided. Experimental results show that this scheme can ensure the reliable transmission of legitimate users, and the eavesdropper can't crack the information when the extraction ratio is 1%. Hence, reliability and physical-layer security can be enhanced simultaneously.INDEX TERMS Free space optical communication, optical code division multiple access, spatial diversity, atmospheric turbulence.

PAM4-Modulated 2-Micron Band for Enhanced Indoor Optical Communications: Experimental Evaluation

“…The refractive index structure constant served as a parameter to measure the intensity of the turbulent channel. In this experiment, the refractive index structure coefficients for strong, moderate, and weak turbulence were 1.51×10 -13 m -2/3 , 3.41×10 -14 m -2/3 and 4.96×10 -15 m -2/3 [25]. We compared the eye diagrams of PAM4 signals received at the receiver under the same transmission power with those under non-turbulent conditions, as illustrated in Fig.…”

PAM4-Modulated 2-Micron Band for Enhanced Indoor Optical Communications: Experimental Evaluation

“…Different temperatures and wind speeds were used to correspond to varying degrees of turbulence effects. [25] The receiver is outfitted with collimators of matching specifications, which are essential for capturing the spatial optical signals and converting them back into fiber-optic signals. This conversion allows for further processing by photodetectors and associated devices.…”

Investigation and demonstration of all‐optical hybrid fiber‐FSO‐fiber CDMA communication system

“…Optical code division multiple access (OCDMA) is considered as a good candidate to provide physical layer security. In [12], 10 Gb/s two-user spatial diversity FSO-CDMA wiretap channel based on reconfigurable optical encoder/decoders is demonstrated. Considering the effect of weak turbulence, the FIGURE 1 Hybrid fiber-FSO-fiber CDMA system model physical layer security of OCDMA-based hybrid fiber-FSO system is analysed [13].…”