  We report the first detailed and quantitative study of the Josephson coupling
energy in the vortex liquid, Bragg glass and vortex glass phases of
Bi_2Sr_2CaCu_2O_{8+\delta} by the Josephson plasma resonance. The measurements
revealed distinct features in the T- and H-dependencies of the plasma frequency
$\omega_{pl}$ for each of these three vortex phases. When going across either
the Bragg-to-vortex glass or the Bragg-to-liquid transition line, $\omega_{pl}$
shows a dramatic change. We provide a quantitative discussion on the properties
of these phase transitions, including the first order nature of the
Bragg-to-vortex glass transition.
