  A simple prediction of the well-known unification model of active galactic
nuclei is that a sample of sources should exhibit an anti-correlation between
the solid angle of the dusty torus and of the ionization cone (as the sum of
them shall equal 4$\pi$), which however has never been detected. In this work,
we analyze the correlation between [OIII] 5007 narrow emission line equivalent
width and $L_{\rm IR}(\lambda)/L_{\rm bol}$ for a large sample of luminous
quasars. For the first time, we detect a clear intrinsic anti-correlation
between them, which immediately verifies the torus/ionization-cone geometry in
luminous quasars. More interestingly, the anti-correlation significantly
weakens with increasing wavelength from $\sim$ 2 to 12 $\mu$m, and disappears
at $\sim$ 12 $\mu$m. Simulations show a cool dust component (in addition to
equatorial torus) with its strength positively correlating with the solid angle
of the ionization cone is required to explain the observations. This shows that
the polar dust seen in nearby active galaxies also exists in luminous quasars,
with its contribution to total dust emission increasing with $\lambda$ (from
$\sim$ 2 to 12 $\mu$m) and reaching between 39%-62% (model dependent) at rest
frame 12 $\mu$m. Our findings provide a unique approach to map the otherwise
spatially unresolvable inner structure of quasars.
