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

The authors investigate and demonstrate an all-optical hybrid fiber-free space optical (FSO)-fiber communication system based on optical code division multiple access (OCDMA). Under different turbulence effects, the interception probability and interception distance are used as security metrics, and optimal parameters are obtained when the system meets the requirements of reliability and security simultaneously. The interception probability increases with the enhancement of turbulence effect, and decreases as the number of interfering users increases. In the case of strong turbulence, the maximum interception probability is 4.14 x 10(-4). The authors design and build a 10 Gb/s all-optical hybrid fiber-FSO-fiber CDMA communication system. It is shown that, under the soft-decision forward-error-correction threshold of 2 x 10(-2), this scheme can guarantee physical layer security in the second 20-km optical fiber link under different turbulence conditions, while the interception distance is 8 km in the first optical fiber link. Under the hard-decision forward-error-correction threshold of 3.38 x 10(-3), the whole system can ensure the physical layer security.