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arXiv:2410.14192

Optimizing the image projection of spatially incoherent light from a multimode fiber

Ken Deng, Zhongchi Zhang, Huaichuan Wang, Zihan Zhao, Jiazhong Hu

Published Oct 18, 2024• 0 citations
arXivHTMLPDF

Abstract

We study the spatially incoherent light generated by a multimode fiber(MMF) in the application of image projection designed for the ultracold-atom experiments. Inspired by previous half-analytic methods concerning the incoherent light, here a full-numerical model is established to provide more quantitative descriptions, and part of results is compared with experiments. Particularly, our model about the MMF is also compatible with light propagation in free space. Based on this, we study both the intrinsic speckle and the perturbation robustness of a MMF light field, under the influence of light propagation and fiber parameters. We point out several guidelines about choosing the suitable MMF in creating a spatially incoherent light source, which is useful in the context of the ultracold-atom experiments associating with the optical potential projection.

DOI
10.48550/arxiv.2410.14192

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We study the spatially incoherent light generated by a multimode fiber(MMF) in the application of image projection designed for the ultracold-atom experiments. Inspired by previous half-analytic methods concerning the incoherent light, here a full-numerical model is established to provide more quantitative descriptions, and part of results is compared with experiments. Particularly, our model about the MMF is also compatible with light propagation in free space. Based on this, we study both the intrinsic speckle and the perturbation robustness of a MMF light field, under the influence of light propagation and fiber parameters. We point out several guidelines about choosing the suitable MMF in creating a spatially incoherent light source, which is useful in the context of the ultracold-atom experiments associating with the optical potential projection.
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We have formulated and experimentally demonstrated an improved algorithm for design of arbitrary two-dimensional holographic traps for ultracold atoms. Our method builds on the best previously available algorithm, MRAF, and improves on it in two ways. First, it allows for creation of holographic atom traps with a well defined background potential. Second, we experimentally show that for creating trapping potentials free of fringing artifacts it is important to go beyond the Fourier approximation in modelling light propagation. To this end, we incorporate full Helmholtz propagation into our calculations.
Real-world deployment of quantum technologies requires systems in low SWaP-C packages. Quantum platforms based on ultracold atoms typically trap and control atoms with optical tweezers using light focused through bulky objective lenses, which are costly and sensitive to misalignment. Multimode fibers (MMFs) offer a compact route to focusing light, but their use in forming optical tweezers for cold atoms has been limited to a single fiber. Here we use a 2x1 MMF fused coupler to obtain two independent control paths sharing a common distal facet. We form near-diffraction-limited tweezers through each channel, suppress interference by applying a small frequency offset between the channels, and demonstrate that the tweezer separation is insensitive to misalignment of the input coupling. This work provides a route to reconfigurable single-atom arrays in low SWaP-C environments.
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We introduce an absorption imaging technique for ultracold gases that suppresses interference fringes and coherence-induced artifacts by reducing the transverse spatial coherence of the imaging light. The method preserves the narrow spectral bandwidth required for resonant absorption imaging and is implemented as a modular extension to standard imaging setups using a rotating diffuser. We demonstrate tunability of the illumination light's coherence without modifying the imaging optics. Using this approach, we achieve reliable imaging of ultracold atomic clouds in micron-scale proximity to complex surfaces, where standing waves, edge diffraction, and speckle severely limit conventional absorption imaging.