Ms. Hiyam Debary Profile

Hiyam Debary

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Proceedings Article | 12 July 2023 Open Access

Interferometric imaging as an alternative to telescopes

Hiyam Debary, Vincent Michau, Laurent Mugnier, Frédéric Cassaing, Matthieu Castelnau, Sébastien Lopez

Proceedings Volume 12777, 127770C (2023) https://doi.org/10.1117/12.2688803

KEYWORDS: Spatial frequencies, Imaging systems, Interferometry, Telescopes, Equipment, Interferometers, Photons, Visibility, Spatial resolution, Photonic integrated circuits

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A concept of optical interferometric imager was proposed by Lockheed-Martin in the early 2010s. In this concept, the aperture is paved by lenses. The optical signals collected by these lenses are combined in photonic integrated circuits, allowing the simultaneous measurement of the Fourier components of the observed object at a number of spatial frequencies. This concept allows one to consider a very significant reduction of the size of optical telescopes, e.g., for Earth observation. Indeed, the transverse dimension of a device based on this concept remains close to that of a telescope of the same resolution since the transverse size determines the spatial resolution. On the other hand, its size along the optical axis is much smaller than that of a conventional telescope. After a quick description of this concept, its intrinsic performance will be analyzed. The field of this device, its spatial resolution, the spectral constraints imposed by the interferometric measurement will be presented. Based on these preliminary considerations, the noise on the measurement will be evaluated. The measurement noise will be compared to that obtained with a focal plane imaging instrument. The geometry of combination of the signals collected by the lenses, or aperture configuration, is a key issue to minimize the size of the device and optimize the quality of the reconstructed image at a given spatial resolution. The literature proposes solutions leading to a partial frequency coverage. In this communication, solutions will be presented leading to a frequency coverage that is more suitable for applications such as Earth observation.

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Proceedings Article | 27 August 2022 Presentation + Paper

Optical interferometry imaging from space: optimization of the aperture configuration of a dense array

Hiyam Debary, Laurent Mugnier, Vincent Michau, Sébastien Lopez

Proceedings Volume 12180, 121800L (2022) https://doi.org/10.1117/12.2629257

KEYWORDS: Spatial frequencies, Telescopes, Interferometry, Interferometers, Photonic integrated circuits, Optical transfer functions, Optical imaging, Imaging systems, Optical interferometry

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The advent of photonic integrated circuits (PICs) will allow the replacement of the large aperture of an optical telescope by a dense array of small apertures combined interferometically. The light coming from aperture pairs can be combined by a PIC in order to extract interferogram characteristics known as complex visibilities, from which the observed object can then be reconstructed. In such a compact interferometric imager, the optical components dedicated to image formation in a regular telescope are no longer necessary. In particular, such a concept is relevant for space missions where weight and size are critical. To date, the proposed concepts are made of one-dimensional arrays radially disposed in a circular instrument. The way of combining the apertures defines the optical transfer function of the instrument, which is key to the imaging performance. In this communication, our goal is to optimize the aperture configuration. Signal-to-noise considerations suggest using each aperture once and only once in order to avoid splitting the flux received on each aperture. Moreover, non-redundant configurations allow a broader spatial frequency coverage. We study aperture configurations based on these two conditions. We describe this problematic formally and we apply results from combinatorial theory to prove the existence of solutions to some problems of aperture configuration optimization, and to exhibit some explicit solutions. Firstly, we suggest new aperture configurations leading to a dense spatial frequency coverage. Secondly, we use these results to propose an optimal frequency coverage for a SPIDER-like design. Then, by complementing the latter instrument with a monolithic telescope, we propose a new aperture configuration that extends the spatial frequency coverage. Lastly, additional strategies to further extend the cut-off spatial frequency are explored and presented.

Proceedings Article | 27 August 2022 Poster + Paper

Analysis of a compact interferometric imager

L. Mugnier, V. Michau, H. Debary, F. Cassaing

Proceedings Volume 12180, 121803J (2022) https://doi.org/10.1117/12.2629311

KEYWORDS: Imaging systems, Interferometry, Spatial frequencies, Photons, Photonic integrated circuits, Visibility, Modulation transfer functions, Interferometers, Telescopes, Waveguides

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The advent of photonic integrated circuits (PICs) will allow the replacement of the large aperture of an optical telescope by a dense array of small apertures combined interferometically. The light coming from aperture pairs can be combined by a PIC in order to extract interferogram characteristics known as complex visibilities, from which the observed object can then be reconstructed. In such a compact interferometric imager, the optical components dedicated to image formation in a regular telescope are no longer necessary. In particular, such a concept is relevant for space missions where weight and size are critical. In this communication, we study such an instrument concept, focusing on signal-to-noise considerations. We recall the design basis for the field and the spatial resolution, and we show that the spectral resolution must be no less than the field to resolution ratio. Then, we analyze the signal-to-noise ratio of this concept, assuming that each spatial frequency is recorded only once, and compare the signal-to-noise ratio with that of a monolithic telescope. We perform the comparison in Fourier space for an identical number of recorded photons. We show that the noise propagation of the interferometric imager is identical to that of a monolithic telescope that would have a flat Modulation Transfer Function with a level roughly given by the ratio of the small apertures’ diameter to the maximum baseline. We conclude that the noise propagation in low and medium spatial frequencies is unfavorable for the interferometric imager.

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