Submillimeter polarimetry associated with grain alignment is accepted as one of the major avenues for detection of interstellar magnetic fields. The submm spectropolarimetry, on the other hand, is still unexplored beyond the molecular clouds. Fine structure lines are polarized due to ground state alignment (GSA) by optical pumping. The polarization of the submillimeter fine-structure lines induced could be substantial. This method is applicable to all radiative-excitation dominant region, e.g., H II Regions, PDRs. The potential of the new magnetic tracer has been clearly revealed by the first detection of GSA effect on a binary system where 3D magnetic fields are precisely mapped (see my poster). Our results demonstrate submillimeter polarimetry as a powerful magnetic tracer and is readily applicable for ALMA today if polarisation at band 8 is commissioned