The time-delay characteristic and effective bandwidth of three chaotic laser systems including optical feedback, optical phase modulation, and external laser injection systems are studied. The intensity, periodic characteristic, and bandwidth of the time-delay characteristic peak are analyzed and compared. The advantages and disadvantages of the three systems applied to the confidential optical communication system are discussed. Based on practical applications, the influences of several physical parameters of the optical injection chaotic laser system on the delay characteristic peak and effective bandwidth are studied in depth. We find that it is feasible to expand the parameter space of the confidential system by adjusting the external cavity delay and injection delay of the driving laser. By matching the appropriate feedback intensity and injection intensity, the time-delay characteristic peaks can be effectively suppressed, and the effective bandwidth can be enlarged.