The chaos characteristics of a DFB semiconductor laser subjected to single and double external cavity optical feedback are analyzed experimentally. The results show that the correlation dimension, bandwidth of the chaos generated by one external cavity optical feedback can be expanded by using double external cavity optical feedback. When the laser is subjected to double external cavity optical feedback, the bandwidth with one external cavity feedback is increased from 5.5 GHz to 11 GHz. Correspondingly, the correlation dimension is increased from 2.8 to 3.6. The information of the external cavity length of the chaos generated by double external cavity optical feedback can be masked in the autocorrelation function.