  We present detailed numerical simulations of the laser dynamics that describe
optical frequency comb formation by injection-locking a gain-switched laser.
The typical rate equations for semiconductor lasers including stochastic
carrier recombination and spontaneous emission suffice to show the
injection-locking behavior of gain switched lasers, and we show how the optical
frequency comb evolves starting from the free-running state, right through the
final injection- locked state. Unlike the locking of continuous wave lasers, we
show that the locking range for gain switched lasers is considerably greater
because injection locking can be achieved by injecting at frequencies close to
one of the comb lines. The quality of the comb lines are formally assessed by
calculating the FM-noise spectral density and we show that under
injection-locking conditions the FM-noise spectral density of the comb lines
tend to that of the maser laser.
