  The curl-modes of Cosmic Microwave Background (CMB) polarization probe
horizon-scale primordial gravitational waves related to inflation. A
significant source of confusion is expected from a lensing conversion of
polarization related to density perturbations to the curl mode, during the
propagation of photons through the large scale structure. Either high
resolution CMB anisotropy observations or 21 cm fluctuations at redshifts 30
and higher can be used to delens polarization data and to separate
gravitational-wave polarization signature from that of cosmic-shear related
signal. Separations based on proposed lensing reconstruction techniques for
reasonable future experiments allow the possibility to probe inflationary
energy scales down to 10^15 GeV. Beyond CMB polarization, at frequencies
between 0.01 Hz to 1 Hz, space-based laser interferometers can also be used to
probe the inflationary gravitational wave background. The confusion here is
related to the removal of merging neutron star binaries at cosmological
distances. Given the low merger rate and the rapid evolution of the
gravitational wave frequency across this band, reliable removal techniques can
be constructed. We discuss issues related to joint constraints that can be
placed on the inflationary models based on CMB polarization information and
space-based interferometers such as the Big Bang Observer.
