Security Improvement Using -Phase-Shifted SSFBG En/Decoder in Time-Spreading OCDMA

摘要

The existence of dips in the waveform encoded by $0/pi$-phase-shifted superstructured fiber Bragg grating ($0/pi$ -SSFBG) allows eavesdroppers to extract code sequence straightforwardly. In this letter, the code extraction technique for $0/pi$-SSFBG is summarized and demonstrated. To address this security issue, we propose using $pmpi/2$-phase-shifted $pmpi/2$-SSFBG as encoder/decoder to improve security in time-spreading optical code-division multiple-access. The security and coding performances for both $pmpi/2$-SSFBG and $0/pi$-SSFBG are compared; $pmpi/2$-SSFBG exhibits improved security and better coding performance. The influence of input pulse over the security performance for $pmpi/2$ -SSFBG is discussed. Short input pulse can improve the security of the encoded signal.