  Self-heterodyne fiber interferometers have been shown to be capable of
stabilizing lasers to ultra-narrow linewidths and present an excellent
alternative to high finesse cavities for frequency stabilization. In addition
to suppressing frequency noise, these devices are highly tunable, and can be
manipulated to produce high speed frequency sweeps over the entire range of the
laser. We present an analytic approach for choosing a delay-line length for
both optimal noise suppression and highest in-loop frequency sweep rate. Using
this model we have implemented a fiber-based active Michelson interferometer as
a frequency discriminator for a conventional diode laser and demonstrated a
linewidth of 700 Hz over millisecond timescales. We also demonstrate a
frequency scan rate of 1 THz/s and independently measure the maximum deviation
in frequency from the linear sweep to be 100 kHz, predominantly limited by
acoustic resonances in the apparatus.
