The performance of a coherent direct sequence optical code division multiple access (DS-OCDMA) system using quadratic congruence codes implemented with superstructured fiber Bragg gratings is experimentally analyzed. We point out that nonperiodic and sparse quadratic congruence codes reduce multipath beat noise and intersymbol interference, respectively. These two properties of the structure of the quadratic congruence codes are shown to improve the bit-error-rate (BER) performance of the coherent system. As a result, we demonstrate that the performance enhancement of the coherent DS-OCDMA system allows the data bit rate of the system to be varied from 1 Gbit/sto2.5 Gbits/s and the receiver bandwidth to be decreased from 15 GHzto5 GHz respecting the low-cost requirement of the optical access network. These data bit rate and receiver bandwidth performances are achieved with moderate BER penalty