CMB telescopes use microwave antennas (often feedhorns) to direct the electromagnetic radiation onto some kind of detector. In the case of BICEP, the detector is a superconducting bolometer, which senses small temperature changes caused by CMB photons depositing themselves onto a resistive element.

To get data, a CMB telescope is scanned across the sky for several months (or years), and the raw time signals are converted into a map of the microwave sky.

LIGO is an entirely different category of scientific instrument; it is looking for the direct influence of present-day gravitational waves on the motion of terrestrial masses.