We have proposed and experimentally demonstrated a novel
technique for instantaneous microwave frequency measurement
using an optical phase modulator. The frequency of a microwave
signal was estimated by measuring the microwave powers at
the outputs of the two PDs, with the two microwave signals
carried by two different optical wavelengths that were experiencing
different power fading. The key significance of the proposed
approach is the use of an optical phase modulator. Since
no bias was needed, the biasing drifting problem existing in an
MZM-based system was completely eliminated, leading to improved
system stability. This feature is highly expected in the
defense systems. In addition, the use of an optical phase modulator
makes the system simpler with lower loss, which is also
desirable for defense applications.