The Cosmic Microwave Background (CMB) holds a remarkable wealth of information about the early universe. Observations of the CMB have recently transformed cosmology into a precision science. While the basic notion and the ingredients of an expanding universe are well established, fundamental questions remain. The polarization in the CMB provides a powerful tool to address the most important of these problems. The polarization pattern of the CMB can be decomposed into two distinct components - E-mode and B-mode. The more interesting, yet so far undetected B-mode polarization can be used in two remarkable ways: (i) the arcminute-scale, lensing induced B-mode polarization can be used to study the large scale structure of the universe, and the parameters that affect it, such as absolute neutrino mass and dark energy evolution; (ii) the degree-scale B-mode polarization carries imprints from the Cosmic Gravitational wave Background (CGB), giving us a glimpse of the universe during its birth. This signal is a direct measurement of the energy scale at which the Big Bang occurs.
BICEP3 has been commissioned at the South Pole in the austral summer of 2014/15. It consists of a large-format focal plane camera with 2,560 polarization sensitive superconducting bolometers operating at 95 GHz. For the austral winter season of 2015, BICEP3 is populated with 9 detector tiles with 1,152 bolometers. It is now fully commisioned with 20 detector tiles during 2015/16 austral summer deployment to enable the full capacity of 2,560 bolometers.