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21 July 2010 The Fiber Coupler subsystem of the future VLTI instrument GRAVITY
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We present the Fiber Coupler subsystem of the future VLTI instrument GRAVITY. GRAVITY is specifically designed to deliver micro-arcsecond astrometry and deep interferometric imaging. The Fiber Coupler is designed to feed the light from a science and a reference object into single-mode fibers. The Fiber Coupler consists of four independent units. The units de-rotate the FoV. A motorized half-wave plate allows rotating the liner polarization axis. Each unit provides actuators for fast piston actuation, tip-tilt correction and pupil stabilization for one of the beams from four VLT telescopes. The actuators are operated in closed-loop. Together with a dedicated Laser Guiding System, this allows to stabilize the beams and maximize the coherently coupled light. The fast piston actuator provides the crucial fringe tracking capability at a bandwidth of >220Hz. A special roof prism design allows to either split the FoV or to serve as a 50/50 beam splitter without changing the optical path. This offers the possibility of on-axis as well as off-axis fringe tracking. The optical train consists solely of mirrors, which ensures an achromatic behavior and maximum throughput. The sophisticated optical design compensates for aberrations which are introduced by off-axis parabolic mirrors. This allows to achieve Strehl ratios of >95% across the FoV.
© (2010) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
O. Pfuhl, F. Eisenhauer, M. Haug, M. Thiel, S. Kellner, A. Amorim, W. Brandner, J. P. Berger, K. Rousselet-Perraut, G. S. Perrin, C. Straubmeier, S. Gillessen, H. Bartko, and A. P. Gräter "The Fiber Coupler subsystem of the future VLTI instrument GRAVITY", Proc. SPIE 7734, Optical and Infrared Interferometry II, 77342A (21 July 2010);


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