(Sub)millimeter disk polarization is an exciting new field of research that has been revolutionized by ALMA. In contrast to its canonical picture, the polarization on the disk scale revealed does not come from magnetic fields but mostly from scattering. This scattering-induced polarization is very sensitive to the sizes of dust grains and local radiation fields. It is a powerful tool for studying grain growth and dust settling. I will discuss how the polarization signatures depends on the dust scale height and present detailed modeling on protoplanetary disks and constraints on the dust settling. Theoretically, the large (mm-sized) grains in protoplanetary disks cannot be aligned by magnetic fields due to their long Larmor precision timescale and short gas-damping timescale, which agrees with ALMA’s non-detection of magnetic fields. The magnetic alignment conditions are much better in the disk atmosphere, inhabited by micron-sized dust grains. We propose a brand-new method to probe magnetic fields using the near-IR polarimetry. Last but not the least, I will introduce our recent development of a Neural-Network aided GPU MCRT code to solve scattering by large aligned dust grains.
