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Optics Continuum

Evaluation of the coupling efficiency of large-diameter nanofiber Bragg cavities

Kengo Sakamoto, Konosuke Shimazaki, Hideaki Takashima, Shigeki Takeuchi

Published Nov 12, 2025• 0 citations
Publisher

Abstract

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.

DOI
10.1364/optcon.578681

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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.
Abstract We report on a simulation of a nanophotonic cavity constructed by designing periodic holes on an optical nanofiber to realize light–matter interaction. The cavity is designed using finite-difference time-domain simulations to maximize the coupling of spontaneous emission from a quantum emitter into fiber-guided modes. We systematically analyze the dependence of spontaneous emission on the quantum emitter position, polarization, and the grating strength (number of periods). We show that coupling efficiencies as high as 87% and 83% can be realized for a dipole emitter placed at the center of the nanofiber with polarization perpendicular ( x -pol) and parallel ( y -pol) to the hole-axis, respectively. This system may attract various quantum photonic applications based on single-photon sources.
Efficient coupling of photons emitted from single light emitters into the single guided mode of an optical fiber is important to realize photonic quantum network devices [1], such as single photon sources [2] and quantum phase gates [3]. For this purpose, we have developed nanofiber Bragg cavities (NFBCs) and observed the enhanced photon emission from the single light emitter [4]. Here, we report the development of the NFBC with the Q-factor of 1560, which is about 5 times larger than our previous NFBC fabricated by a gallium focused ion beam (FIB) milling system [4]. According to numerical simulation, the NFBC with such high-ß factor can be realized Purcell factor of about 18 and the coupling efficiency of about 80 %.