Abstract

We present a complete two-telescope version of a fiber-linked coherent array that is meant to be used for mounting on the dish of a radio telescope. This was built with 20-cm amateur telescopes and includes three different servo subsystems for guiding, nulling of the air path difference, and fiber length control. Laboratory tests of the fully integrated system in front of a star simulator are described.

© 1995 Optical Society of America

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References

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  1. P. Connes, F. Reynaud, “Fiber tests on a radiotelescope,” in Proceedings of the National Optical Astronomy Observatory–European Space Observatory Conference on High Resolution Imaging by Interferometry, F. Merkle, ed. (European Space Observatory, Garching, Germany, 1988), pp. 1117–1129.
  2. F. Reynaud, J. J. Alleman, P. Connes, “Interferometric control of fiber lengths for a coherent telescope array,” Appl. Opt. 31, 3736–3743 (1992).
    [CrossRef] [PubMed]
  3. M. Shao, M. Colavita, “Long baseline optical and infrared stellar interferometer,” Ann. Rev. Astron. Astrophys. 30, 457–498 (1992).
    [CrossRef]
  4. P. Connes, C. Froehly, P. Facq, “A fiber-linked ground-based array,” in Proceedings of the European Space Agency Colloquium on Kilometric Optical Arrays in Space, N. Longdon, O. Melita, eds. (European Space Agency, Noordwijk, The Netherlands, 1987), p. 49.
  5. P. Connes, F. Roddier, S. Shaklan, “A fiber-linked version of project Trio,” in European Space Observatory–National Optical Astronomy Observatory Oracle Workshop, J. W. Goad, ed. (National Optical Astronomy Observatory, Tucson, Arizona, 1987), p. 165.
  6. P. Connes, F. Roddier, S. Shaklan, E. Ribak, “Fiber linked telescope arrays on the ground and in space,” in European Space Agency Workshop on Optical Interferometry in Space, N. Longdon, V. David, eds. (European Space Agency, Noordwijk, The Netherlands, 1987), p. 273.
  7. W. D. Heacox, P. Connes, “Optical fibers in astronomical instruments,” Astron. Astrophys. Rev. 3, 169–199 (1992).
    [CrossRef]
  8. V. Coude du Foresto, “Fluor: a stellar interferometer using SM infrared fibers,” in European Space Observatory Conference on High Resolution Imaging by Interferometry II, J. M. Beckers, F. Merkle, eds. (European Space Observatory, Garching, Germany, 1992), p. 731.
  9. A. Labeyrie, “Interference fringes obtained on Vega with two optical telescopes,” Astrophys. J. 196, L71–L75 (1975).
    [CrossRef]
  10. A. M. Michelson, “On the application of interferometric methods to astronomical measurements,” Astrophys. J.51, 257–262 (1920); F. G. Pease, “The new fifty-foot stellar interferometer,” Sci. Am. 143, 290 (1930). A full bibliography is given in D. Y. Gezari, F. Roddier, Cl. Roddier, “Spatial interferometry in astronomy,” NASA Ref. Publ. 1245 (1990).
    [CrossRef]
  11. Most unfortunately, the Hat-Creek radio dish has since collapsed.
  12. “Very large inflatable space-rigidified structure struts: feasibility study,” final report on ESTEC contract by Oerlikon-Contraves AG, ESA Document SR/LIS/110(90)CZ (European Space Agency, Noordwijk, The Netherlands, January1991).
  13. S. Shaklan, “Fiber beam combiner for multiple telescope interferometry,” Opt. Eng. 29, 684–689 (1989).
    [CrossRef]
  14. S. Shaklan, F. Roddier, “Coupling starlight into SM fiber optics,” Appl. Opt. 27, 2334–2338 (1988).
    [CrossRef] [PubMed]
  15. For example, in a 1-m master telescope, weight would not greatly exceed that of the primary mirror itself: at the focus, only small optical elements are required, and they do not even have to be supported by very-high-rigidity struts.
  16. See, e.g., M. B. Jorgenson, G. J. M. Aitken, “Prediction of atmospherically induced wave-front degradations,” Opt. Lett. 17, 466–469 (1992); C. Schwartz, G. Baum, E. N. Ribak, “Turbulence degraded wave-fronts as fractal surfaces,” J. Opt. Soc. Am. A 11, 444–451 (1994).
    [CrossRef] [PubMed]
  17. Since such very long focus lenses are difficult to get, each will be replaced by a zero-power positive–negative pair with adjustable separation.
  18. Balancing counterweights cannot be used: they would reintroduce coupling with dish vibrations. High-efficiency commercial linear motors provide a better solution, but proved to be too expensive.
  19. The pen recordings were regrettably lost in the move from OHP to Limoges, and the loss was not discovered until the system had been mounted on the 2-m floppy frame, making duplication too laborious.

1992 (4)

1989 (1)

S. Shaklan, “Fiber beam combiner for multiple telescope interferometry,” Opt. Eng. 29, 684–689 (1989).
[CrossRef]

1988 (1)

1975 (1)

A. Labeyrie, “Interference fringes obtained on Vega with two optical telescopes,” Astrophys. J. 196, L71–L75 (1975).
[CrossRef]

Aitken, G. J. M.

Alleman, J. J.

Colavita, M.

M. Shao, M. Colavita, “Long baseline optical and infrared stellar interferometer,” Ann. Rev. Astron. Astrophys. 30, 457–498 (1992).
[CrossRef]

Connes, P.

F. Reynaud, J. J. Alleman, P. Connes, “Interferometric control of fiber lengths for a coherent telescope array,” Appl. Opt. 31, 3736–3743 (1992).
[CrossRef] [PubMed]

W. D. Heacox, P. Connes, “Optical fibers in astronomical instruments,” Astron. Astrophys. Rev. 3, 169–199 (1992).
[CrossRef]

P. Connes, F. Roddier, S. Shaklan, “A fiber-linked version of project Trio,” in European Space Observatory–National Optical Astronomy Observatory Oracle Workshop, J. W. Goad, ed. (National Optical Astronomy Observatory, Tucson, Arizona, 1987), p. 165.

P. Connes, F. Roddier, S. Shaklan, E. Ribak, “Fiber linked telescope arrays on the ground and in space,” in European Space Agency Workshop on Optical Interferometry in Space, N. Longdon, V. David, eds. (European Space Agency, Noordwijk, The Netherlands, 1987), p. 273.

P. Connes, F. Reynaud, “Fiber tests on a radiotelescope,” in Proceedings of the National Optical Astronomy Observatory–European Space Observatory Conference on High Resolution Imaging by Interferometry, F. Merkle, ed. (European Space Observatory, Garching, Germany, 1988), pp. 1117–1129.

P. Connes, C. Froehly, P. Facq, “A fiber-linked ground-based array,” in Proceedings of the European Space Agency Colloquium on Kilometric Optical Arrays in Space, N. Longdon, O. Melita, eds. (European Space Agency, Noordwijk, The Netherlands, 1987), p. 49.

Coude du Foresto, V.

V. Coude du Foresto, “Fluor: a stellar interferometer using SM infrared fibers,” in European Space Observatory Conference on High Resolution Imaging by Interferometry II, J. M. Beckers, F. Merkle, eds. (European Space Observatory, Garching, Germany, 1992), p. 731.

Facq, P.

P. Connes, C. Froehly, P. Facq, “A fiber-linked ground-based array,” in Proceedings of the European Space Agency Colloquium on Kilometric Optical Arrays in Space, N. Longdon, O. Melita, eds. (European Space Agency, Noordwijk, The Netherlands, 1987), p. 49.

Froehly, C.

P. Connes, C. Froehly, P. Facq, “A fiber-linked ground-based array,” in Proceedings of the European Space Agency Colloquium on Kilometric Optical Arrays in Space, N. Longdon, O. Melita, eds. (European Space Agency, Noordwijk, The Netherlands, 1987), p. 49.

Heacox, W. D.

W. D. Heacox, P. Connes, “Optical fibers in astronomical instruments,” Astron. Astrophys. Rev. 3, 169–199 (1992).
[CrossRef]

Jorgenson, M. B.

Labeyrie, A.

A. Labeyrie, “Interference fringes obtained on Vega with two optical telescopes,” Astrophys. J. 196, L71–L75 (1975).
[CrossRef]

Michelson, A. M.

A. M. Michelson, “On the application of interferometric methods to astronomical measurements,” Astrophys. J.51, 257–262 (1920); F. G. Pease, “The new fifty-foot stellar interferometer,” Sci. Am. 143, 290 (1930). A full bibliography is given in D. Y. Gezari, F. Roddier, Cl. Roddier, “Spatial interferometry in astronomy,” NASA Ref. Publ. 1245 (1990).
[CrossRef]

Reynaud, F.

F. Reynaud, J. J. Alleman, P. Connes, “Interferometric control of fiber lengths for a coherent telescope array,” Appl. Opt. 31, 3736–3743 (1992).
[CrossRef] [PubMed]

P. Connes, F. Reynaud, “Fiber tests on a radiotelescope,” in Proceedings of the National Optical Astronomy Observatory–European Space Observatory Conference on High Resolution Imaging by Interferometry, F. Merkle, ed. (European Space Observatory, Garching, Germany, 1988), pp. 1117–1129.

Ribak, E.

P. Connes, F. Roddier, S. Shaklan, E. Ribak, “Fiber linked telescope arrays on the ground and in space,” in European Space Agency Workshop on Optical Interferometry in Space, N. Longdon, V. David, eds. (European Space Agency, Noordwijk, The Netherlands, 1987), p. 273.

Roddier, F.

S. Shaklan, F. Roddier, “Coupling starlight into SM fiber optics,” Appl. Opt. 27, 2334–2338 (1988).
[CrossRef] [PubMed]

P. Connes, F. Roddier, S. Shaklan, E. Ribak, “Fiber linked telescope arrays on the ground and in space,” in European Space Agency Workshop on Optical Interferometry in Space, N. Longdon, V. David, eds. (European Space Agency, Noordwijk, The Netherlands, 1987), p. 273.

P. Connes, F. Roddier, S. Shaklan, “A fiber-linked version of project Trio,” in European Space Observatory–National Optical Astronomy Observatory Oracle Workshop, J. W. Goad, ed. (National Optical Astronomy Observatory, Tucson, Arizona, 1987), p. 165.

Shaklan, S.

S. Shaklan, “Fiber beam combiner for multiple telescope interferometry,” Opt. Eng. 29, 684–689 (1989).
[CrossRef]

S. Shaklan, F. Roddier, “Coupling starlight into SM fiber optics,” Appl. Opt. 27, 2334–2338 (1988).
[CrossRef] [PubMed]

P. Connes, F. Roddier, S. Shaklan, “A fiber-linked version of project Trio,” in European Space Observatory–National Optical Astronomy Observatory Oracle Workshop, J. W. Goad, ed. (National Optical Astronomy Observatory, Tucson, Arizona, 1987), p. 165.

P. Connes, F. Roddier, S. Shaklan, E. Ribak, “Fiber linked telescope arrays on the ground and in space,” in European Space Agency Workshop on Optical Interferometry in Space, N. Longdon, V. David, eds. (European Space Agency, Noordwijk, The Netherlands, 1987), p. 273.

Shao, M.

M. Shao, M. Colavita, “Long baseline optical and infrared stellar interferometer,” Ann. Rev. Astron. Astrophys. 30, 457–498 (1992).
[CrossRef]

Ann. Rev. Astron. Astrophys. (1)

M. Shao, M. Colavita, “Long baseline optical and infrared stellar interferometer,” Ann. Rev. Astron. Astrophys. 30, 457–498 (1992).
[CrossRef]

Appl. Opt. (2)

Astron. Astrophys. Rev. (1)

W. D. Heacox, P. Connes, “Optical fibers in astronomical instruments,” Astron. Astrophys. Rev. 3, 169–199 (1992).
[CrossRef]

Astrophys. J. (1)

A. Labeyrie, “Interference fringes obtained on Vega with two optical telescopes,” Astrophys. J. 196, L71–L75 (1975).
[CrossRef]

Opt. Eng. (1)

S. Shaklan, “Fiber beam combiner for multiple telescope interferometry,” Opt. Eng. 29, 684–689 (1989).
[CrossRef]

Opt. Lett. (1)

Other (12)

Since such very long focus lenses are difficult to get, each will be replaced by a zero-power positive–negative pair with adjustable separation.

Balancing counterweights cannot be used: they would reintroduce coupling with dish vibrations. High-efficiency commercial linear motors provide a better solution, but proved to be too expensive.

The pen recordings were regrettably lost in the move from OHP to Limoges, and the loss was not discovered until the system had been mounted on the 2-m floppy frame, making duplication too laborious.

A. M. Michelson, “On the application of interferometric methods to astronomical measurements,” Astrophys. J.51, 257–262 (1920); F. G. Pease, “The new fifty-foot stellar interferometer,” Sci. Am. 143, 290 (1930). A full bibliography is given in D. Y. Gezari, F. Roddier, Cl. Roddier, “Spatial interferometry in astronomy,” NASA Ref. Publ. 1245 (1990).
[CrossRef]

Most unfortunately, the Hat-Creek radio dish has since collapsed.

“Very large inflatable space-rigidified structure struts: feasibility study,” final report on ESTEC contract by Oerlikon-Contraves AG, ESA Document SR/LIS/110(90)CZ (European Space Agency, Noordwijk, The Netherlands, January1991).

V. Coude du Foresto, “Fluor: a stellar interferometer using SM infrared fibers,” in European Space Observatory Conference on High Resolution Imaging by Interferometry II, J. M. Beckers, F. Merkle, eds. (European Space Observatory, Garching, Germany, 1992), p. 731.

P. Connes, F. Reynaud, “Fiber tests on a radiotelescope,” in Proceedings of the National Optical Astronomy Observatory–European Space Observatory Conference on High Resolution Imaging by Interferometry, F. Merkle, ed. (European Space Observatory, Garching, Germany, 1988), pp. 1117–1129.

P. Connes, C. Froehly, P. Facq, “A fiber-linked ground-based array,” in Proceedings of the European Space Agency Colloquium on Kilometric Optical Arrays in Space, N. Longdon, O. Melita, eds. (European Space Agency, Noordwijk, The Netherlands, 1987), p. 49.

P. Connes, F. Roddier, S. Shaklan, “A fiber-linked version of project Trio,” in European Space Observatory–National Optical Astronomy Observatory Oracle Workshop, J. W. Goad, ed. (National Optical Astronomy Observatory, Tucson, Arizona, 1987), p. 165.

P. Connes, F. Roddier, S. Shaklan, E. Ribak, “Fiber linked telescope arrays on the ground and in space,” in European Space Agency Workshop on Optical Interferometry in Space, N. Longdon, V. David, eds. (European Space Agency, Noordwijk, The Netherlands, 1987), p. 273.

For example, in a 1-m master telescope, weight would not greatly exceed that of the primary mirror itself: at the focus, only small optical elements are required, and they do not even have to be supported by very-high-rigidity struts.

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Figures (16)

Fig. 1
Fig. 1

View of the proposed radio-dish mounted array.

Fig. 2
Fig. 2

Overall block diagram that illustrates the functions of the three servos.

Fig. 3
Fig. 3

Schematic view of the four subsystems: OYZ is parallel to the wave plane; OX is the star direction; B1, B2, BM, aluminum U beams; T1, T2, TM, telescopes; G1, G2, GM, autoguiders; TA1, TA2, moving tables. The fiber-length servo is explained in Fig 4, the guiders in Fig 6, the actual path of red laser beams (dashed) in Figs. 9 and 10. Sky-pointing units are bolted to the radio-dish frame. The mixing table is located in the laboratory. BS, beam splitters; BM, beam mixer; OPM, optical path-difference modulator (piezoelectric transducer-mounted plane mirror); PM, photomultipliers.

Fig. 4
Fig. 4

Simplified view of the fiber-length servo (see Ref. 1 for a full diagram and operating instructions). B.S., beam splitters. Slave fibers are 20 m long, and master fibers are 10 m long.

Fig. 5
Fig. 5

Atmospheric turbulence effects as interpreted by the master guider: W, actual wave front; P N , normal wave plane (i.e., the one that would be obtained in the absence of turbulence); P G , guided wave plane; F 1, F 2, fiber inputs.

Fig. 6
Fig. 6

Autoguiders beam diagram. Above, guiders G1 and G2 for array telescopes T1 and T2. A pierced mirror M0 and a small CCD video camera act as finders. Below, master guider GM; only the differences with G1 and G2 are shown. GM does not have a moving table, and the fiber is replaced by a red laser and a beam expander (exp). Initial alignment was done by inserting a cube-corner prism; the dichroic plate reflects enough laser light to operate the guider.

Fig. 7
Fig. 7

Fast-guiding mirror assembly. PZT, piezoelectric transducer.

Fig. 8
Fig. 8

Guider electronics block diagram. Analog conversion is done from the three 120° signals to Cartesian coordinates; residual error signals are shown by two bar graphs (BG); servo response is adjusted by a proportional integrator–derivative (PID). Bimorph pairs are excited in push–pull. H.V., high voltage.

Fig. 9
Fig. 9

Wave-plane-servo laser beams. Above, front view; below, side view with only one beam pair shown. In the future N-telescope array N pairs of pentaprisms would be located along the rim of the (much larger) pupil.

Fig. 10
Fig. 10

Laser beams (side view) and moving tables TA1 and TA2 on parallelogram-type mounts, each with eight flexure hinges: Pos, Vel, Acc, position, velocity, and acceleration transducers, respectively. P1, etc., four-quadrant Si detectors. The lenses and beam size are not shown. Rot. Mot., rotary motor; Tach., tachometer; Lin. Mot., linear motor.

Fig. 11
Fig. 11

Wave-plane-servo block diagram. The Y-coordinate signals are displayed by bar graphs (BG) but are not used by the servo. PA, power amplifier.

Fig. 12
Fig. 12

Star simulator, which is adjusted by autocollimation on the three-mirror bar (TE) and whose fringes are observed at D. When the TE is removed, the three telescopes, T1, TM, and T2, can be fed with three beams, and fringes are observed by the photomultipliers shown in Fig. 3.

Fig. 13
Fig. 13

Photoguide error signal after step perturbation. The vertical scale is arbitrary, with the error proportional to step size; the horizontal scale is 5 ms/div. The response is optimized for fiber-feeding guiders, with the error wholly corrected after 3 ms. For a master telescope, the response is much slower.

Fig. 14
Fig. 14

Typical dx path-error signal from four-quadrant cells at 1-m distance on a floppy frame in the open air, with the wave-front-servo loop closed.

Fig. 15
Fig. 15

Typical residual dx motion of table TA1 relative to B1 as measured by a temporary Michelson interferometer and a 633-nm laser. Above, servo on; below, servo off with fringes on the same scale. The error signal is also shown (80-Hz bandwidth) with the scale expanded by a factor of 5 when the servo is on.

Fig. 16
Fig. 16

Fringe signal (300-Hz bandwidth) at the output of the mixing table from a complete system in front of the simulator. A triangular wave produces linear scanning. Above, a 30-nm bandwidth beam from a dye laser; below, a 300-nm beam from a Xe lamp.

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