In this paper we investigate the effect of photodetector nonlinearity on the optimum transmit power setting in an asynchronous optical CDMA network. Network impairments as well as thermal noise, shot noise and multiple access interference (MAI) are taken into account. Unlike in traditional systems, the optical detector generated shot noise adds a new self-interference normally not considered previously as part of the MAI. We formulate a centralized power control algorithm and propose novel, iterative, Nonlinear Optical Power Control (NOPC) algorithm. Furthermore, convergence properties of the proposed algorithm are studied. We prove that the iterative NOPC converges to a unique point. Solution feasibility is then formulated in terms of the employed network parameters, MAI and target SIR. Finally, simulation results are given illustrating the theoretical analysis.