Vortex beams possess orbital angular momentum(OAM). This work analyzes the properties of non-integer vortex beams when propagating through fractional Fourier planes. Based on the definition of fractional Fourier transform (FrFT), the theoretical formula is analyzed to discuss the effects of the parameters of non-integer vortex beams. Numerical results of the evolution of non-integer vortex beams through different fractional Fourier planes are illustrated. The results show that the fractional order of the FrFT has great influence on the normalized intensity distributions and the phase distributions of non-integer vortex beams. The beams show the same evolution trends, but different shapes.
Optical code-division multiple access (OCDMA) systems usually allocate orthogonal or quasi-orthogonal codes to the active users. When transmitting through atmospheric scattering channel, the coding pulses are broadened and the orthogonality of the codes is worsened. In truly asynchronous case, namely both the chips and the bits are asynchronous among each active user, the pulse broadening affects the system performance a lot. In this paper, we evaluate the performance of a 2D asynchronous hard-limiting wireless OCDMA system through atmospheric scattering channel. The probability density function of multiple access interference in truly asynchronous case is given. The bit error rate decreases as the ratio of the chip period to the root mean square delay spread increases and the channel limits the bit rate to different levels when the chip period varies.