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A significant fraction of compact radio-loud quasars display most of thecharacteristics of relativistically beamed, high-optical polarization blazars,yet are weakly polarized in the optical regime. We have used the VLBA at 22 and43 GHz to look for differences in the parsec-scale magnetic field structures of18 high- and low-optically polarized, compact radio-loud quasars (HPQs andLPRQs, respectively). We find a strong correlation between the polarizationlevel of the unresolved parsec-scale radio core at 43 GHz and overall opticalpolarization of the source, which suggests a common (possibly co-spatial)origin for the emission at these two wavelengths. The magnetic fields of thepolarized 43 GHz radio cores are aligned roughly transverse to the jet axis.Similar orientations are seen in the optical, suggesting that the polarizedflux at both wavelengths is due to one or more strong transverse shocks locatedvery close to the base of the jet. In LPRQs, these shocks appear to be weaknear the core, and gradually increase in strength down the jet. The LPRQs inour sample tend to have less luminous radio cores than the HPQs, and jetcomponents with magnetic fields predominantly parallel to the flow. Thecomponents in HPQ jets, on the other hand, tend to have transverse alignments.These differences cannot be accounted for by a simple model in which HPQs andLPRQs are the same type of object, seen at different angles to the line ofsight. A more likely scenario is that LPRQs represent a quiescent phase ofblazar activity, in which the inner jet flow does not undergo strong shocks.

Intrinsic Differences in the Inner Jets of High and Low Optically Polarized Radio Quasars