BICEP1, BICEP2 and Keck
Background Imaging of Cosmic Extragalactic Polarization (BICEP1) was a bolometric polarimeter designed to measure the inflationary B-mode polarization of the cosmic microwave background at degree angular scales. The instrument comprised a two-lens refracting telescope coupled to a focal plane of 49 orthogonal pairs of horn-coupled polarization-sensitive bolometers operating at 100 and 150 GHz. BICEP1 observed from the Amundsen-Scott South Pole Station between 2006 and 2008, mapping about 2% of the sky chosen to be uniquely clean of polarized foreground emission.
BICEP2 was a 26-cm refracting telescope that observed the cosmic microwave background (CMB) from the National Science Foundation's Amundsen-Scott South Pole Station from 2010-2012. It was designed to observe the polarization of the CMB on angular scales around one degree, near the expected peak of the B-mode polarization signal produced by inflationary gravitational waves. BICEP2 observed a patch of 400 square degrees in a single frequency band at 150 GHz.
The Keck Array consists of five BICEP2-style receivers in a single telescope mount at the South Pole. The Keck Array observes the same field as BICEP2, with five receivers beginning in 2012. These were initially all at 150 GHz; in the 2014 season two were replaced with receivers at 95 GHz; and in the 2015 season an additional two have been replaced with receivers at 220 GHz.
BICEP2 and the Keck Array have together made the most sensitive measurements to date of the polarization of the CMB.
The official website for results from the BICEP and Keck Array series of CMB polarization experiments can be found at http://bicepkeck.org/.