Phase-coherent repetition rate multiplication of a mode-locked laser   from 40 MHz to 1 GHz by injection locking
  We have used injection locking to multiply the repetition rate of a passively mode-locked femtosecond fiber laser from 40 MHz to 1 GHz while preserving optical phase coherence between the master laser and the slave output. The system is implemented almost completely in fiber and incorporates gain and passive saturable absorption. The slave repetition rate is set to a rational harmonic of the master repetition rate, inducing pulse formation at the least common multiple of the master and slave repetition rates. 
D. Kielpinski and O. Gat
physics.optics