The significant features of coherence multiplexing technique are applied to a turbo-coded optical pulse position modulated (PPM) code division multiple access (CDMA) system with differential detection, and its performance is evaluated in terms of bit-error rate (BER) by including the effects of thermal noise, beat noise, and shot noise. It is shown that around 98 users can be accommodated at a signal-to-noise ratio (SNR) of 2.0 dB for a fixed BER of 9.6688 × 10-6. A significant reduction in BER of around 3.2355 × 10-16 is achieved for an increased SNR of 7.2916 dB supporting 53 users for a source linewidth of 20 nm. On increasing the linewidth to 40 nm, the number of users is found to increase from 53 to 75 for the same BER and SNR. The reduction of BER of 3.2355 × 10-16, 6.6473 × 10-18, and 2.1089 × 10-19 is obtained at an SNR of 7.29 dB for increasing interleaver lengths of 10,32, and 100, respectively. The BER reduction by decreasing the user data rates is also presented. On comparison with the direct detection, the number of simultaneous users that can be accommodated at a BER of 10-16 is found to increase from 31 to 54 users. © 2007 Society of Photo-Optical Instrumentation Engineers.