Polarization Effects Aboard The Space Interferometry Mission

For precision displacement measurements, laser metrology is currently one of the most accurate measurements. Often, the measurement is located some distance away from the laser source, and as a result, stringent requirements are placed on the laser delivery system with respect to the state of polarization. Such is the case with the fiber distribution assembly (FDA) that is slated to fly aboard the Space Interferometry Mission (SIM) next decade. This system utilizes a concatenated array of couplers, polarizers and lengthy runs of polarization-maintaining (PM) fiber to distribute linearly-polarized light from a single laser to fourteen different optical metrology measurement points throughout the spacecraft. Optical power fluctuations at the point of measurement can be traced back to the polarization extinction ratio (PER) of the concatenated components, in conjunction with the rate of change in phase difference of the light along the slow and fast axes of the PM fiber. Thermal variations are one of the major contributors to this change and can lead to tight spacecraft design requirements. In this presentation, we will discuss our experimentally-validated model which predicts the polarization behavior for various distribution designs, as well as present the thermal performance of various PM components and how this levies thermal control requirements on the spacecraft.