  We investigate the two-pion interferometry in ultrarelativistic heavy ion
collisions in the granular source model of quark-gluon plasma droplets. The
pion transverse momentum spectra and HBT radii of the granular sources agree
well with the experimental data of the most central Au-Au collisions at
$\sqrt{s_{NN}}=200$ GeV at RHIC and Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$
TeV at LHC. In the granular source model the larger initial system breakup time
for the LHC collisions as compared to the RHIC collisions may lead to the
larger HBT radii $R_{\rm out}$, $R_{\rm side}$, and $R_{\rm long}$. However,
the large droplet transverse expansion and limited average relative emitting
time of particles in the granular source lead to the ratio of the transverse
HBT radii $R_{\rm out}/R_{\rm side} \sim 1$.
