There are three key modules in coherent optical code division multiple access (OCDMA) system: source of ultra-short optical pulse, en/decoder and receiver. Two-user 2.5 Gb/s OCDMA experiment is shown to achieve 100 km transmission using single-band application between gain switch laser diode and 63-chip equivalent phase shift superstructured fiber Bragg grating (EPS-SSFBG) phase en/decoder, and threshold adjustable receiver with broadband decision. Relations between bit error rate (BER) and decision level and time are observed in the experiment, error-free transmission is achieved in the range of 10 ps decision time and 17% decision level.