  Phase noise can be modulated onto the output of a laser with an electro-optic
phase modulator (EOM) to create a highly incoherent broadened source with low
intensity noise. This technique leaves a small but finite fraction of the
coherent carrier power that can be highly detrimental in applications requiring
incoherent light. This paper shows that the carrier suppression in a laser
broadened by this technique can be calculated for an arbitrary noise
probability density function. The carrier suppression can be varied
experimentally by adjusting the noise voltage standard deviation $Gv_{\sigma}$
and saturation voltage $V_{sat}$ of the amplifier that amplifies the noise
source that drives the EOM. Simulations show that suppressions better than -30
dB are attainable for reasonable tolerances in $Gv_{\sigma}$, for example an
EOM with a $V_{\pi}$ of 4.7 V, a $V_{sat}$ of 6.3V, and $Gv_{\sigma}/V_{\pi} =
0.73\pm0.03$. Even greater tolerances can be achieved with a higher $V_{sat}$
(21 V), lower $V_\pi$ (3.5 V), and $Gv_{\sigma}/V_{\pi} \approx 3.2 \pm 2.3$.
This model aids in selecting these parameters such that the carrier suppression
is resilient to fluctuations in these voltages due to temperature variations
and aging of the components. The model predictions are validated by testing a
fiber optic gyroscope interrogated with a broadened laser for various
$Gv_{\sigma}$ and $V_{sat}$ and inferring the carrier suppression from its
measured noise. A -44-dB carrier suppression was observed for a nonlinear
amplifier with $Gv_{\sigma}$ = 3.43 V, $V_{sat}$ = 6.3 V, and an EOM with
$V_{\pi}$ = 4.7 V, in agreement with predictions.
