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A Large-Diameter Nanofiber Bragg Cavity for a Robust Single Photon Source

Kengo Sakamoto, Konosuke Shimazaki, Hideaki Takashima, Shigeki Takeuchi

Published Jan 1, 2026• 0 citations
Publisher

Abstract

We numerically demonstrate nanofiber Bragg cavities with twice the conventional cross-sectional area can maintain coupling efficiency of 83%. This large diameter enhances mechanical robustness at cryogenic temperatures, essential for generating coherent single photons.
DOI
10.1364/cleo_at.2026.jtu.131

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We analyze the coupling efficiency of a single dipole with a nanofiber Bragg cavity (NFBC) for single photon sources. Conventionally, NFBC diameters are set at approximately half of the emission wavelength to maximize coupling efficiency, but these thin structures are fragile at low temperatures. By employing three-dimensional finite difference time domain simulations, we investigate NFBCs with diameters ranging from 450 to 600 nm, which offer more mechanical robustness. Our results show that NFBCs with diameters of 450 and 500 nm achieve coupling efficiencies exceeding 80%. This study paves the way for practical single-photon sources with enhanced mechanical stability, which is crucial for applications in quantum networks and quantum computing.
In this talk, our recent activities for nanofiber-integrated single light emitters for photonic quantum network. First, we report the coupling of various single light emitters, including diamond nanocrystals with color centers and hexagonal Boron Nitride flakes, to ultra-thin tapered optical fibers (nano optical fiber) with a diameter as small as 300 nm, keeping the transmittance of the fiber more than 90%. Second, for further improvement of the coupling efficiency, we introduce our development of nanofiber Bragg cavity (NFBC) with the mode volume of under 1 mu m^3 and repeatable tuning capability over more than 20 nm at visible wavelengths. The improvement of Q factor using He-ion beam milling will also be reported.
Funnelling the light emitted from quantum emitters like atoms, molecules, or defect centers into the guided mode of a single mode optical fiber is highly important for scaling up quantum optics experiments, since it provides the possibility to interconnect experiments at different locations and ensures high mode overlap of photons from different sources. Here, we present a photonic nanocavity on a tapered optical fiber. The cavities are formed by two Bragg mirrors fabricated by an ion beam [1]. Characterization in terms of transmission, reflection, and polarization are performed and compared with numerical simulations [2]. The quality factors of the fabricated devices can reach values over 300 while the mode volume is smaller than the cubic wavelength. Simulations indicate that a Purcell enhancement of 19.1 with 82 % coupling efficiency can be reached using this cavities. A comparison of cavities fabricated using a gallium beam is compared with cavities made using a helium beam giving insights about implantation of gallium in the ion beam milling fabrication of resonators. Using the knowledge from experiment and simulation, new designs for nanofiber Bragg grating cavities are developed and tested. [1] A W Schell et al. Sci. Rep. 5, 9619 (2015) [2] H Takashima et al. Opt. Express 24, 15050-15058 (2016)