  We propose a simple and all-optical method for fast random number generation
based on the laser mode hopping. Through periodically restarting a two-mode
laser operating in the bistable state, a random number stream can be generated
due to the spontaneous emission noise. To validate the feasibility of this
method, we perform a theoretical simulation using the common vertical-cavity
surface-emitting laser (VCSEL) with two polarization modes. Numerical results
demonstrate that fast 2.5 Gb/s random number streams can be continuously
obtained with verified randomness. This scheme provide a fully monolithic
solution for random number generator, due to its simple and all-optical
structure.
