AbstractA new optical time‐spreading/frequency‐hopping differential CDMA (TS/FH CDMA) system is proposed in this paper. It uses new codes called prime/OOC codes as address codes. Fast optical frequency hopping and large capacity can be implemented with the system. By assigning two orthogonal codes for one user, and using these two codes to encode 1 and 0, respectively, the receiver can use differential detection. If they are balanced well between the 1‐branch and 0‐branch, the proposed system can effectively abate multiaccess interference (MAI), background noise, detector noise such as dark current, leakage current, and thermal noise, etc. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 29: 125–128, 2001.