Distributed feedback semiconductor lasers (DFB-SL) are the class B lasers, and would output chaotic laser under the external disturbances, such as external optical feedback and optical injection. Chaotic laser are widely applied in many fields, including optical fiber sensing, chaotic laser secure communication, and better entropy sources for generating high-speed random number, etc. However, time delay signature (TDS) will arise in the chaotic laser from the semiconductor lasers with external cavity optical feedback, and the TDS will restrict the applications of chaotic laser. On the other hand, the bandwidt (BW) of chaotic carrier signal plays the important role for the transmission rate of information signal. Therefore, the TDS and BW are two important parameters that will affect chaotic laser's applications, and they are usually used to express the chaos characteristics of chaotic laser.<br/>In this paper, we present a new scheme used to suppress the TDS and investigate the BW of chaotic laser from semiconductor laser. For this scheme, the output laser from a DFB-SL with external single optical feedback are injected by double ways into another DFB-SL with phase modulation optical feedback by self chaos light. Thus they form a semiconductor laser system with external double optical injection and phase modulation optical feedback by self chaos light (SL-EDOI-PMOFBSCL). We investigate numerically the influences of the system parameters on TDS, such as the injection coefficient and feedback coefficient, etc. Then the suppression effect on TDS are contrasted and analyzed with two other systems, that are semiconductor laser with external double optical injection and optical feedback (SL-EDOI-OF) and semiconductor laser with external single optical injection and phase modulation optical feedback by self chaos light (SL-ESOI-PMOFBSCL), respectively. The results indicate that the proposed scheme in this paper has the best suppression effect on TDS. Then the BW of the chaotic laser are investigated under the parameters conditions of effectively suppressing TDS.The simulation results show that the scheme proposed in this paper can enhance the BW of chaotic laser by properly selecting the parametric values, and the maximum BW value of the obtained chaotic laser is about 16 GHz.
