  We present the B-BOP instrument, a polarimetric camera on board the future
ESA-JAXA SPICA far-infrared space observatory. B-BOP will allow the study of
the magnetic field in various astrophysical environments thanks to its
unprecedented ability to measure the linear polarization of the submillimeter
light. The maps produced by B-BOP will contain not only information on total
power, but also on the degree and the angle of polarization, simultaneously in
three spectral bands (70, 200 and 350 microns). The B-BOP detectors are
ultra-sensitive silicon bolometers that are intrinsically sensitive to
polarization. Their NEP is close to 10E-18 W/sqrt(Hz). We will present the
optical and thermal architectures of the instrument, we will detail the
bolometer design and we will show the expected performances of the instrument
based on preliminary lab work.
