The security issue is of vital importance in chaos-based communications. The characteristics of feedback delay and coupling delay in chaotic optical communication systems has been numerically studied, based on a chaos-based communication system composed of two mutually coupled semiconductor lasers driven by an external cavity semiconductor laser. Numerical simulation of the model is established with the Runge-Kutta method. The emphasis has been devoted to the following analysis: by adjusting some controllable parameters (coupling delay and injection strength), one can reasonably change the discrepancy between the amplitudes of feedback delay and coupling delay in autocorrelation function for the mutually coupled semiconductor lasers output. For this reason, the feedback delay is effectively concealed, and thus a better chaotic carrier can be obtained. More importantly, our numerical results demonstrate that the coupling delay is able to be employed to improve the security of chaotic optical communication systems. Finally, the discussion of synchronization quality of the dedicated system, under the optimized chaotic carrier circumstance, is given.