Demonstration of an adjustable 1-5 meter five-mirror piezoelectric compact delay line for space interferometry

Precise optical path length (OPL) control is essential for formation-flying interferometer mission concepts, where independent spacecraft motion continuously perturbs the optical path between collectors. For dual-tracking architectures, in which the delay line rapidly switches between a reference star and a science target, we demonstrate a compact laboratory five-mirror delay-line system capable of continuous OPL measurement and control over several meters. We integrate a tunable laser, used in conjunction with a quadrature-channel interferometer, to directly measure and validate OPL with sub-100-micron accuracy. Our demonstration shows the elements needed for dual-tracking: a continuously adjustable 1-5 m delay line with sub-100-micron control, and reliable switching between the reference and science channels.