A document discusses a sensor made from off-the-shelf electro-optical photo-diodes and electronics that achieves 20 nm/(Hz)1/2 displacement sensitivity at 1 mHz. This innovation was created using a fiber-coupled laser diode (or Nd:YAG) through a collimator and an aperture as the illumination source. Together with a germanium quad photodiode, the above-mentioned displacement sensor sensitivities have been achieved. This system was designed to aid the Laser Interferometer Space Antenna (LISA) with microthruster tests and to be a backup sensor for monitoring the relative position between a proof mass and a spacecraft for drag-free navigation. The optical displacement sensor can be used to monitor any small displacement from a remote location with minimal invasion on the system.
This work was done by Alexander Abramovici, Meng P. Chiao, and Frank G. Dekens of Caltech for NASA’s Jet Propulsion Laboratory. NPO-30681