  Recently, several theoretical proposals adressed the generation of an active
optical frequency standard based on atomic ensembles trapped in an optical
lattice potential inside an optical resonator. Using atoms with a narrow
linewidth transition and population inversion together with a "bad" cavity
allows to the realize the superradiant photon emission regime. These schemes
reduce the influence of mechanical or thermal vibrations of the cavity mirrors
on the emitted optical frequency, overcoming current limitation in passive
optical standards. The coherence time of the emitted light is ultimately
limited by the lifetime of the atoms in the optical lattice potential.
Therefore these schemes would produce one light pulse per atomic ensemble
without a phase relation between pulses. Here we study how phase coherence
between pulses can be maintained by using several inverted atomic ensenbles,
introduced into the cavity sequentially by means of a transport mechanism. We
simulate the light emission process using the Heisenberg-Langevin approach and
study the frequency noise of the intracavity field.
