Design and investigation of EDFA-based all-optical relaying FSO-CDMA wiretap channel

To enhance the reliability and physical layer security of free space optical (FSO) communication system simultaneously, we propose an EDFA-based all-optical relaying FSO-CDMA wiretap channel model. Two-dimensional optical encoder and decoder are designed and constructed by wavelength selective switch Add/Drop and optical delay lines. A 10 Gb/s experimental system of EDFA-based all-optical relaying FSO-CDMA wiretap channel is built and investigated for the first time. Experimental results show that the BER of the legitimate user is greatly affected by the turbulence effect, and the reliability of EDFA-based all-optical relaying FSO-CDMA can be improved significantly. Compared with the uncoded system, the optical coding scheme can enhance the physical layer security. In the experimental system, with the enhancement of turbulence, the secrecy capacity of the system will increase. At the received power -22 dBm, the secrecy capacity is 0.28 bit/symbol in weak turbulence, while the secrecy capacity is 0.35 bit/symbol in moderate turbulence.