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arXiv:2604.18426

High precision micro-optical elements on fiber facets via focused-ion beam machining

Raman Kumar, Sebastian Will

physics.opticsphysics.app-phphysics.atom-phquant-phSubmitted Apr 20, 2026• Announced Apr 21, 2026
v1 · Apr 20, 2026v2 · Oct 3, 2026
arXivHTMLPDF

Abstract

Fiber-integrated micro-optical elements promise a scalable approach to photon collection and beam shaping for quantum information processing. Here, we demonstrate single-step fabrication of micro-spherical, micro-spiral, and micro-axicon structures directly on the core of single-mode optical fibers using focused ion beam (FIB) machining with nanometer-scale precision. Atomic force microscopy reveals that micro-concave and micro-convex spherical surfaces achieve shape accuracies of approximately $λ/80$ and $λ/50$ at $λ= 780$ nm, respectively. Optical characterization using a He-Ne laser at 633 nm confirms the expected far-field donut beam patterns for the micro-spiral and micro-axicon structures. Mach-Zehnder interferometry further verifies the corresponding azimuthal and radial phase profiles of the light emitted from the spiral and axicon fibers. Surface metrology shows that the optimized FIB process preserves optical-grade surface quality, introducing no measurable additional roughness at spatial scales relevant to visible and near-infrared operation. These monolithically integrated fiber micro-optical elements enable a broad range of applications in quantum technology, including fiber micro-cavities for cavity quantum electrodynamics, beam shaping for neutral atom trapping, and the generation of structured light for free-space quantum network links.

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Designing and integrating micro-optical components into atom and ion traps are enabling steps toward miniaturizing trap dimensions in quantum computation applications.The micro-optic must have a high numerical aperture for precise illumination of the ion and should not introduce scatter.Due to the extreme optical efficiency requirements in trapped ion and atom-based quantum information processing, even slight losses from integrated micro-optics are detrimental.We have designed and fabricated aspheric micro-lenses through grayscale transfer into a fused silica in an effort to realize increased transmissive efficiency and decreased scatter compared to an equivalent diffractive optical element.The fabricated grayscale lens profile matched the desired lens profile well, and the measured and predicted optical performances were in good agreement.The pattern was transferred via coupled plasma reactive-ion etching smoothly into the fused silica with a RMS roughness ~35 nm.The micro-lens had a diameter of 88 um and 14.2 um sag, with an as-designed focal length of 149 um and spot diameter of 2.6 um.The maximum measured efficiency was ~80% (86% of theoretical, possibly due to rms roughness).This realized efficiency is superior to the equivalent diffractive lens efficiency, designed to the same use parameters.The grayscale approach demonstrated an increase in collection efficiency, at the desired optical focal length, providing the potential for further refinement.
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Ion-trapped-based quantum computers offer long coherence times of over 2 seconds with high fidelity and hence constitute a promising architecture for realizing quantum computer systems beyond the NISQ classification. Utilizing a fiber-coupled laser source at a wavelength of 396 nm our setup is able to manipulate any combination of 40Ca+ ions inside a coherent chain of 10 ions simultaneously, while also being able to collect the readout of each individual ion. Our setup achieves an ion-sided mode field diameter of less than 2 μm and a pointing accuracy of 250 nm for one chain of ions. A micro-lens integrated waveguide carrier chip with linear optics is used to create 10 separate laser beams at the actual ion dimensions. The modularity of the systems allows the system to be arranged onto additional linked ion trap chains, pathing the way for a scalable quantum computer.
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