RESUMEN
We describe the optical and mechanical design, construction philosophy, and testing of a pair of matched, spaceflight-qualified fiber couplers. The couplers were developed for the LISA Pathfinder mission but are relevant for other applications-both on ground and in space-where a robust fiber coupler with well-controlled beam parameters and stable beam pointing is required. This particular implementation of the design called for two couplers providing collimated beams with individual waist sizes and positions. The target values were a 522 µm waist 145 mm after the collimating lens for one coupler and a virtual 520 µm waist 194 mm before the collimating lens for the second coupler. Values of (542±4) µm at (142±19) mm and (500±8) µm at (-275±8) mm were achieved, fully meeting the mission requirements. To control spurious noise effects in the interferometer, the optical system design also specified tight limits on relative beam curvature at an intended interference point. With nominal curvatures at this location of â¼2.35 m, the matching between the outputs of the two fiber couplers was measured to be λ/33 peak-valley over the central 1 mm of the beams. Results showing pointing stability of 3 µrad/°C over a 50°C range are presented. The vibration, shock, and thermal vacuum environmental testing conditions to which a pair of qualification fiber couplers were subjected-without change in performance-are listed.
RESUMEN
We describe an instrument which, coupled with a suitable coordinate measuring machine, facilitates the absolute measurement within the machine frame of the propagation direction of a millimeter-scale laser beam to an accuracy of around ±4 µm in position and ±20 µrad in angle.
