Single-mode waveguides for GRAVITY II. Single-mode fibers and Fiber Control Unit
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| Format: | Preprint |
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2024
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| author | Perrin, G. Jocou, L. Perraut, K. Berger, J. Ph. Dembet, R. Fédou, P. Lacour, S. Chapron, F. Collin, C. Poulain, S. Cardin, V. Joulain, F. Eisenhauer, F. Haubois, X. Gillessen, S. Haug, M. Hausmann, F. Kervella, P. Léna, P. Lippa, M. Pfuh, O. Rabien, S. Amorim, A. Brandner, W. Straubmeier, C. |
| author_facet | Perrin, G. Jocou, L. Perraut, K. Berger, J. Ph. Dembet, R. Fédou, P. Lacour, S. Chapron, F. Collin, C. Poulain, S. Cardin, V. Joulain, F. Eisenhauer, F. Haubois, X. Gillessen, S. Haug, M. Hausmann, F. Kervella, P. Léna, P. Lippa, M. Pfuh, O. Rabien, S. Amorim, A. Brandner, W. Straubmeier, C. |
| contents | The 2nd generation VLTI instrument GRAVITY is a two-field infrared interferometer operating in the K band between 1.97 and 2.43 $μ$m with either the four 8 m or the four 1.8 m telescopes of the Very Large Telescope (VLT). Beams collected by the telescopes are corrected with adaptive optics systems and the fringes are stabilized with a fringe-tracking system. A metrology system allows the measurement of internal path lengths in order to achieve high-accuracy astrometry. High sensitivity and high interferometric accuracy are achieved thanks to (i) correction of the turbulent phase, (ii) the use of low-noise detectors, and (iii) the optimization of photometric and coherence throughput. Beam combination and most of the beam transport are performed with single-mode waveguides in vacuum and at low temperature. In this paper, we present the functions and performance achieved with weakly birefringent standard single-mode fiber systems in GRAVITY. Fibered differential delay lines (FDDLs) are used to dynamically compensate for up to 6 mm of delay between the science and reference targets. Fibered polarization rotators allow us to align polarizations in the instrument and make the single-mode beam combiner close to polarization neutral. The single-mode fiber system exhibits very low birefringence (less than 23°), very low attenuation (3.6-7 dB/km across the K band), and optimized differential dispersion (less than 2.04 $μ$rad cm2 at zero extension of the FDDLs). As a consequence, the typical fringe contrast losses due to the single-mode fibers are 6% to 10% in the lowest-resolution mode and 5% in the medium- and high-resolution modes of the instrument for a photometric throughput of the fiber chain of the order of 90%. There is no equivalent of this fiber system to route and modally filter beams with delay and polarization control in any other K-band beamcombiner. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2401_10613 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Single-mode waveguides for GRAVITY II. Single-mode fibers and Fiber Control Unit Perrin, G. Jocou, L. Perraut, K. Berger, J. Ph. Dembet, R. Fédou, P. Lacour, S. Chapron, F. Collin, C. Poulain, S. Cardin, V. Joulain, F. Eisenhauer, F. Haubois, X. Gillessen, S. Haug, M. Hausmann, F. Kervella, P. Léna, P. Lippa, M. Pfuh, O. Rabien, S. Amorim, A. Brandner, W. Straubmeier, C. Instrumentation and Methods for Astrophysics The 2nd generation VLTI instrument GRAVITY is a two-field infrared interferometer operating in the K band between 1.97 and 2.43 $μ$m with either the four 8 m or the four 1.8 m telescopes of the Very Large Telescope (VLT). Beams collected by the telescopes are corrected with adaptive optics systems and the fringes are stabilized with a fringe-tracking system. A metrology system allows the measurement of internal path lengths in order to achieve high-accuracy astrometry. High sensitivity and high interferometric accuracy are achieved thanks to (i) correction of the turbulent phase, (ii) the use of low-noise detectors, and (iii) the optimization of photometric and coherence throughput. Beam combination and most of the beam transport are performed with single-mode waveguides in vacuum and at low temperature. In this paper, we present the functions and performance achieved with weakly birefringent standard single-mode fiber systems in GRAVITY. Fibered differential delay lines (FDDLs) are used to dynamically compensate for up to 6 mm of delay between the science and reference targets. Fibered polarization rotators allow us to align polarizations in the instrument and make the single-mode beam combiner close to polarization neutral. The single-mode fiber system exhibits very low birefringence (less than 23°), very low attenuation (3.6-7 dB/km across the K band), and optimized differential dispersion (less than 2.04 $μ$rad cm2 at zero extension of the FDDLs). As a consequence, the typical fringe contrast losses due to the single-mode fibers are 6% to 10% in the lowest-resolution mode and 5% in the medium- and high-resolution modes of the instrument for a photometric throughput of the fiber chain of the order of 90%. There is no equivalent of this fiber system to route and modally filter beams with delay and polarization control in any other K-band beamcombiner. |
| title | Single-mode waveguides for GRAVITY II. Single-mode fibers and Fiber Control Unit |
| topic | Instrumentation and Methods for Astrophysics |
| url | https://arxiv.org/abs/2401.10613 |