Code Performance Comparison in SAC-OCDMA Systems under the Impact of Group Velocity Dispersion

摘要

In this paper, three code families for spectral amplitude coding optical code division multiple access (SAC-OCDMA) systems in terms of performance are compared to each other under the impact of group velocity dispersion (GVD). The investigated code families are m-sequence, Walsh-Hadamard and modified quadratic congruence (MQC). The performance of these codes is evaluated for three types of transmission media such as single-mode fiber (SMF), dispersion shifted fiber (DSF) and nonzero dispersion shifted fiber (NZ-DSF). Results show that in each of the three transmission media m-sequence code family offers the best performance among the investigated code sets under the impact of GVD. Systems which employ m-sequence codes can achieve longer transmission length compared to those using Walsh-Hadamard and MQC codes. In addition, a chirped fiber Bragg grating (CFBG) is designed as a compensating element to compensate the impact of GVD in a SAC-OCDMA system. Employing the designed grating in the system results in a wide opening in the eye diagram as well as improved bit error rate (BER) of the system which indicate that the impact of GVD is effectively compensated.