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Q: Fachverband Quantenoptik und Photonik

Q 74: Photonics II

Q 74.7: Vortrag

Freitag, 14. März 2025, 16:00–16:15, HS Botanik

Measuring deviations from a perfectly circular cross-section of an optical nanofiber at the Ångström scale — •Jihao Jia, Felix Tebbenjohanns, Jürgen Volz, Arno Rauschenbeutel, and Philipp Schneeweiss — Humboldt-Universität zu Berlin, Germany

Tapered optical fibers (TOFs) with sub–wavelength–diameter waists, known as optical nanofibers, are powerful tools for interfacing quantum emitters and nanophotonics. This demands stable polarization of the fiber–guided light field. However, the linear birefringence resulting from Ångström–scale deviations in the nanofiber’s ideally circular cross–section can lead to significant polarization changes within millimeters of light propagation.

Here, we experimentally investigate such deviations using two in-situ approaches. First, we measure the resonance frequencies of hundreds of flexural modes of the nanofiber, which can be thought of as a doubly clamped beam in this context. Assuming an elliptical cross-section with a and b, the differing second moments of area for vibrations along these axes result in a splitting of the resonance frequencies. By analyzing the measured resonance pairs, we estimate |a − b| ≈ 3 Ångström for a nanofiber with a nominal diameter of 500 nm. An analytical model links this elliptical cross–section to the linear birefringence of the nanofiber. Second, we monitor the polarization of the guided light field along the nanofiber [1]. By analyzing the scattered light as a function of the axial position, we confirm the birefringence inferred from the flexural mode frequencies.

[1] IEEE J. Quantum Electron. 18, 1763 (2012)

Keywords: Tapered optical fiber