To meet the overall isolation and alignment requirements for the optics in Advanced LIGO, the planned upgrade to LIGO, the US laser interferometric gravitational wave observatory, we are developing three sub-systems: a hydraulic external pre-isolator for low frequency alignment and control, a two-stage active isolation platform designed to give a factor of ~1000 attenuation at 10 Hz, and a multiple pendulum suspension system that provides passive isolation above a few hertz. The hydraulic stage uses laminar-flow quiet hydraulic actuators with millimeter range, and provides isolation and alignment for the optics payload below 10 Hz, including correction for measured Earth tides and the microseism. This stage supports the in-vacuum two-stage active isolation platform, which reduces vibration using force feedback from inertial sensor signals in six degrees of freedom. The platform provides a quiet, controlled structure to mount the suspension system. This latter system has been developed from the triple pendulum suspension used in GEO 600, the German/UK gravitational wave detector. To meet the more stringent noise levels required in Advanced LIGO, the baseline design for the most sensitive optics calls for a quadruple pendulum, whose final stage consists of a 40 kg sapphire mirror suspended on fused silica ribbons to reduce suspension thermal noise.
We discuss a polarisation based homodyne interferometer that demonstrates a promising sensitivity of approximately 3x10-12 m/Hz1/2. This performance figure is limited above 10Hz by the resolution of the current analogue-to-digital converter (ADC). Sensitivity below 10Hz is influenced by environmental factors and / or noise inherent in the laser. We then describe the development of a compact interferometric sensor, undertaken at The University of Birmingham, discussing its application as a zero-stiffness sensor for drag-free satellites and suggest a geometry of electrostatic actuator also with zero-stiffness.