OCDMA allows multiple users to share a common optical channel simultaneously and asynchronously, and thus has many advantages, such as great system capacity, efficient bandwidth utilization, asynchronous access, secure communication, and so on. Many studies on OCDMA techniques have been made in recent years. In direct-sequence (DS) incoherent OCDMA systems, each user is assigned a unique signature sequence (1’s and 0’s) for spreading and identification purposes. Through the use of encoding process, the user signal is spread in the frequency domain so that each user occupies the entire bandwidth available at all times. This results in a total bandwidth utilization. The optical medium is superbly suited to spread spectrum multiple access communications due to its extremely large bandwidth, however the spectral efficiency of OCDMA system is an important factor. This paper analyses the spectrum efficiency of incoherent OCDMA systems, emphatically discusses several kinds of codes, compares and evaluates their performances.