In this paper, we present a proposed scheme for improving the performance of the optical code division multiple access system (CDMA). This system works based on spectral encoding of noncoherent sources. The proposed scheme depends on using the orthogonal signalling in place of ASK format. A new design of optical mask is presented in order to minimize the nonflatness effect of the spectral shape of the optical source on the system performance. Analysis study on the required accuracy of the designed mask on the performance improvement has been presented.