  We demonstrate that a semiconductor laser perturbed by the distributed
feedback from a fiber random grating can emit light chaotically without the
time delay signature. A theoretical model is developed based on the
Lang-Kobayashi model in order to numerically explore the chaotic dynamics of
the laser diode subjected to the random distributed feedback. It is predicted
that the random distributed feedback is superior to the single reflection
feedback in suppressing the time-delay signature. In experiments, a massive
number of feedbacks with randomly varied time delays induced by a fiber random
grating introduce large numbers of external cavity modes into the semiconductor
laser, leading to the high dimension of chaotic dynamics and thus the
concealment of the time delay signature. The obtained time delay signature with
the maximum suppression is 0.0088, which is the smallest to date.
