  We use deep observations obtained with the Photodetector Array Camera and
Spectrometer (PACS) onboard the Herschel space observatory to study the
far-infrared (FIR) properties of submm and optically faint radio galaxies (SMGs
and OFRGs). From literature we compiled a sample of 35 securely identified SMGs
and nine OFRGs located in the GOODS-N and the A2218 fields. This sample is
cross-matched with our PACS 100 um and 160 um multi-wavelength catalogs. About
half of the galaxies in our sample are detected with PACS. The dust
temperatures and the infrared luminosities of our galaxies are derived by
fitting their PACS and SCUBA 850 um (only the upper limits for the OFRGs) flux
densities with a single modified (beta=1.5) black body function. The median
dust temperature of our SMG sample is T=36+/-8K while for our OFRG sample it is
T=47+/-3K. For both samples, median dust temperatures derived from Herschel
data agree well with previous estimates. In particular, Chapman et al. (2005)
found a dust temperature of T=36+/-7K for a large sample of SMGs assuming the
validity of the FIR/radio correlation. The agreement between our studies
confirms that the local FIR/radio correlation effectively holds at high
redshift even though we find <q>=2.17+/-0.19, a slightly lower value than that
observed in local systems. The median IR luminosities of SMGs and OFRGs are
4.6*10^12 Lsun and 2.6*10^12 Lsun, respectively. We note that for both samples
the IR luminosity estimates from the radio part of the spectral energy
distribution are accurate, while estimates from the mid-IR are considerably
(x3) more uncertain. Our observations confirm the remarkably high luminosities
of SMGs and thus imply median star-formation rates of 960Msun yr^-1 for SMGs
with S(850um)>5mJy and 460Msun yr^-1 for SMGs with S(850um)>2mJy, assuming a
Chabrier IMF and no dominant AGN contribution to the far-infrared luminosity.
