Fringe tracking at the IOTA interferometer

Pedretti, E.; Thureau, N.; Wilson, Edward L.; Traub, Wesley A.; Monnier, John D.; Ragland, Sam; Carleton, N. P.; Millan-Gabet, R.; Schloerb, F. Peter; Brewer, Michael K.; Berger, J.‐P.; Lacasse, M. G.

doi:10.1117/12.551625

Cited by 10 publications

(11 citation statements)

References 30 publications

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“…It was then tested briefly in an online implementation, producing good stable fringe tracking. Ettore Pedretti, in an attempt to quantitatively evaluate the online performance of this and two other algorithms [2,23], developed an experimental procedure to do so, as described in [22]. The basic result was that this adaptive DFTbased algorithm and one developed by Pedretti both were found to perform well on both moderate and low photon flux targets, as measured by the closure-phase error.…”

Section: Performancementioning

confidence: 96%

“…As noted previously, there are aspects of the algorithm that could have been further optimized (e.g., pre-calculation of the sinusoidal vectors) if this compute time had been excessive. As implemented, the speed of the algorithm was sufficiently fast that compute time was negligible as compared to the scanning period [22].…”

Section: Speedmentioning

confidence: 99%

“…Pedretti developed a fringe tracking algorithm taking a completely different approach, based on double Fourier interferometry (DFI) [2,22]. This method calculates the group delay of fringes dispersed with DFI, which is used to obtain the wavelength-dependent phase from the fringe packet.…”

Section: Related Researchmentioning

confidence: 99%

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Adaptive DFT-Based Interferometer Fringe Tracking

Wilson

Pedretti

Bregman

et al. 2005

EURASIP J. Adv. Signal Process.

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An automatic interferometer fringe tracking system has been developed, implemented, and tested at the Infrared Optical Telescope Array (IOTA) Observatory at Mount Hopkins, Arizona. The system can minimize the optical path differences (OPDs) for all three baselines of the Michelson stellar interferometer at IOTA. Based on sliding window discrete Fourier-transform (DFT) calculations that were optimized for computational efficiency and robustness to atmospheric disturbances, the algorithm has also been tested extensively on offline data. Implemented in ANSI C on the 266 MHz PowerPC processor running the VxWorks real-time operating system, the algorithm runs in approximately 2.0 milliseconds per scan (including all three interferograms), using the science camera and piezo scanners to measure and correct the OPDs. The adaptive DFT-based tracking algorithm should be applicable to other systems where there is a need to detect or track a signal with an approximately constant-frequency carrier pulse. One example of such an application might be to the field of thin-film measurement by ellipsometry, using a broadband light source and a Fourier-transform spectrometer to detect the resulting fringe patterns

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Section: Performancementioning

confidence: 96%

Section: Speedmentioning

confidence: 99%

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Adaptive DFT-Based Interferometer Fringe Tracking

Wilson

Pedretti

Bregman

et al. 2005

EURASIP J. Adv. Signal Process.

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“…17 This algorithm is sensitive to step size errors, as they change the location of the signal peak in Fourier space. Hence, the interferogram peak location is extracted by averaging the phases in the FFT over a broad range of bins.…”

Section: Opd Measuring Algorithmsmentioning

confidence: 99%

Tracking near-infrared fringes on BETTII: a balloon-borne, 8m-baseline interferometer

Rizzo

Rinehart

Barry

et al. 2012

Optical and Infrared Interferometry III

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We present the design of a fringe tracking system for the Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII). BETTII is a balloon-borne, far-infrared, 8 m-baseline interferometer with two 50 cm siderostats. Beams from the two arms are combined in the pupil plane to enable double-Fourier, spatio-spectral interferometry. To maintain the phase stability of the system, we need to actively correct of the optical path difference (OPD) between the two arms. The fringe-tracking system will work in the near-infrared and will use a reference star within the field of view to achieve two goals: overlap the beams coming from the two siderostats, and track the location of the central fringe packet, which is a measure of the OPD. The fringe tracker will share most of the optical train with the science instrument. This system is part of the overall control architecture that feeds fast steering tip/tilt mirrors and a warm delay line to ensure proper beam combination and OPD control for the science instrument. This paper investigates the different sources of perturbations that are expected at float altitude, and derives the sensitivity of the fringe-tracking system. We show progress on validating our design using a visible light, broadband Mach-Zehnder interferometer that was developed at NASA/GSFC. This system demonstrates the viability of our OPD determination approach and provides a means of testing and characterizing several OPD determination and control algorithms.

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“…There are obviously many other ways to estimate x GD from a set of data, but we assume that this is a second order problem. Indeed, Pedretti et al (2004) compared three different algorithms to estimate the group delay with a temporal method and noted only little differences in the performance, even with an algorithm as sophisticated as the one proposed by Wilson et al (2004).…”

Section: Description Of the Simulationsmentioning

confidence: 99%

Optimized fringe sensors for the VLTI next generation instruments

Blind

Absil

Bouquin

et al. 2011

A&A

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Context. With the arrival of the next generation of ground-based imaging interferometers combining from four to possibly six telescopes simultaneously, there is also a strong need for a new generation of fringe trackers able to cophase these arrays. These instruments have to be very sensitive and to provide robust operations in quickly varying observational conditions. Aims. We aim at defining the optimal characteristics of fringe sensor concepts operating with four or six telescopes. The current detector limitations lead us to consider solutions based on co-axial pairwise combination schemes. Methods. We independently study several aspects of the fringe sensing process: 1) how to measure the phase and the group delay, and 2) how to combine the telescopes to ensure a precise and robust fringe tracking in real conditions. Thanks to analytical developments and numerical simulations, we define the optimal fringe-sensor concepts and compute the expected performance of the four-telescope one with our dedicated end-to-end simulation tool sim2GFT. Results. We first show that measuring the phase and the group delay by obtaining the data in several steps (i.e. by temporally modulating the optical path difference) is extremely sensitive to atmospheric turbulence and therefore conclude that it is better to obtain the fringe position with a set of data obtained simultaneously. Subsequently, we show that among all co-axial pairwise schemes, moderately redundant concepts increase the sensitivity as well as the robustness in various atmospheric or observing conditions. Merging all these results, end-to-end simulations show that our four-telescope fringe sensor concept is able to track fringes at least 90% of the time up to limiting magnitudes of 7.5 and 9.5 for the 1.8-and 8.2-meter VLTI telescopes respectively.

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Fringe tracking at the IOTA interferometer

Cited by 10 publications

References 30 publications

Adaptive DFT-Based Interferometer Fringe Tracking

Adaptive DFT-Based Interferometer Fringe Tracking

Tracking near-infrared fringes on BETTII: a balloon-borne, 8m-baseline interferometer

Optimized fringe sensors for the VLTI next generation instruments

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