  Optical observations cannot resolve the structure of active galactic nuclei
(AGN), and a unified model for AGN was inferred mostly from indirect methods.
Optical reverberation mapping allowed us to constrain the spatial dimension of
the broad emission line region and thereby to measure the mass of supermassive
black holes. Recently, reverberation was also applied to the polarized signal
emerging from different AGN components. In principle, this should allow us to
measure the spatial dimensions of the sub-parsec reprocessing media. We modeled
scattering-induced polarization and tested different geometries for the
circumnuclear dust component. Our tests included the effects of clumpiness and
different dust prescriptions. To further extend the model, we also explored the
effects of additional ionized winds stretched along the polar direction, and of
an equatorial scattering ring that is responsible for the polarization angle
observed in pole-on AGN. The simulations were run using a time-dependent
version of the {\sc stokes} code. Our modeling confirms the previously found
polarization characteristics as a function of the observer`s viewing angle.
When the dust adopts a flared-disk geometry, the lags reveal a clear difference
between type 1 and type 2 AGN. This distinction is less clear for a torus
geometry where the time lag is more sensitive to the geometry and optical depth
of the inner surface layers of the funnel. The presence of a scattering
equatorial ring and ionized outflows increased the recorded polarization time
lags, and the polar outflows smooths out dependence on viewing angle. Together
with other AGN observables, the polarization time lag places new, independent
constraints on the inner geometry of AGN. If we conduct time-dependent
spectropolarimetric observing campaigns of AGN, this method has a high
potential for a census of supermassive black holes.
