A self-adjoint Fourier-type model for the iQuad wavefront sensor

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Main Authors: Laidlaw, Victoria, Fauvarque, Olivier, Miksch, Alfred, Neichel, Benoit, Ramlau, Ronny
Format: Preprint
Published: 2026
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author Laidlaw, Victoria
Fauvarque, Olivier
Miksch, Alfred
Neichel, Benoit
Ramlau, Ronny
author_facet Laidlaw, Victoria
Fauvarque, Olivier
Miksch, Alfred
Neichel, Benoit
Ramlau, Ronny
contents Advanced adaptive optics (AO) systems can use Fourier-type wavefront sensing to correct optical distortions encountered in ground-based telescopes, AO-assisted retinal imaging, and free-space optical communications (FSOC). Recently, a novel Fourier-type wavefront sensor (WFS) known as the iQuad WFS has been introduced. Its design features a focal plane tessellation with a four-quadrant phase mask (FQPM) that incorporates a $\pm π/2$ phase shift between adjacent quadrants. In this work, we establish a comprehensive mathematical framework for the iQuad WFS, including its forward models and linearizations based on the Fréchet derivative. We reveal a connection between the iQuad WFS and the 2d finite Hilbert transform and demonstrate that the linear iQuad WFS operator is self-adjoint - a unique property among Fourier-type WFSs. Additionally, we introduce the double iQuad WFS, a two-path configuration that combines two rotated iQuad WFSs. This design addresses the limitations of the single iQuad WFS by suppressing poorly-seen phase components. Moreover, the double setup simplifies the mathematical modeling. We also highlight iQuad similarities to the widely used pyramid wavefront sensor (PWFS). Finally, we extend the concept of modulation to the iQuad WFS, further enhancing its versatility. The theoretical analysis presented here lays the groundwork for the development of fast and robust model-based wavefront reconstruction algorithms for the iQuad WFS, paving the way for future applications in AO instruments.
format Preprint
id arxiv_https___arxiv_org_abs_2605_11740
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle A self-adjoint Fourier-type model for the iQuad wavefront sensor
Laidlaw, Victoria
Fauvarque, Olivier
Miksch, Alfred
Neichel, Benoit
Ramlau, Ronny
Mathematical Physics
Instrumentation and Methods for Astrophysics
Advanced adaptive optics (AO) systems can use Fourier-type wavefront sensing to correct optical distortions encountered in ground-based telescopes, AO-assisted retinal imaging, and free-space optical communications (FSOC). Recently, a novel Fourier-type wavefront sensor (WFS) known as the iQuad WFS has been introduced. Its design features a focal plane tessellation with a four-quadrant phase mask (FQPM) that incorporates a $\pm π/2$ phase shift between adjacent quadrants. In this work, we establish a comprehensive mathematical framework for the iQuad WFS, including its forward models and linearizations based on the Fréchet derivative. We reveal a connection between the iQuad WFS and the 2d finite Hilbert transform and demonstrate that the linear iQuad WFS operator is self-adjoint - a unique property among Fourier-type WFSs. Additionally, we introduce the double iQuad WFS, a two-path configuration that combines two rotated iQuad WFSs. This design addresses the limitations of the single iQuad WFS by suppressing poorly-seen phase components. Moreover, the double setup simplifies the mathematical modeling. We also highlight iQuad similarities to the widely used pyramid wavefront sensor (PWFS). Finally, we extend the concept of modulation to the iQuad WFS, further enhancing its versatility. The theoretical analysis presented here lays the groundwork for the development of fast and robust model-based wavefront reconstruction algorithms for the iQuad WFS, paving the way for future applications in AO instruments.
title A self-adjoint Fourier-type model for the iQuad wavefront sensor
topic Mathematical Physics
Instrumentation and Methods for Astrophysics
url https://arxiv.org/abs/2605.11740