An interferometric sensor for satellite drag-free control

We describe a compact interferometer, under development at the University of Birmingham, that could be employed as a zero-stiffness sensor for drag-free satellites. A prototype bench-top polarization-based homodyne interferometer is discussed that achieves a shot-noise limited displacement sensitivity of 3 × 10 −12 m Hz 1/2 above 60 Hz. We discuss a wavelength modulation technique that will render the interferometer more robust as it enables the absolute difference in interferometric armlengths to be determined.