Numerical analysis of the ultra-wide tunability of nanofiber Bragg cavities

authored by: Hideaki Takashima, Andreas W. Schell, Shigeki Takeuchi
Abstract: Nanofiber Bragg cavities (NFBCs) are solid-state microcavities fabricated in optical tapered fiber. They can be tuned to a resonance wavelength of more than 20 nm by applying mechanical tension. This property is important for matching the resonance wavelength of an NFBC with the emission wavelength of single-photon emitters. However, the mechanism of the ultra-wide tunability and the limitation of the tuning range have not yet been clarified. It is important to comprehensively analyze both the deformation of the cavity structure in an NFBC and the change in the optical properties due to the deformation. Here, we present an analysis of the ultra-wide tunability of an NFBC and the limitation of the tuning range using three dimensional (3D) finite element method (FEM) and 3D finite-difference time-domain (FDTD) optical simulations. When we applied a tensile force of 200 µN to the NFBC, a stress of 5.18 GPa was concentrated at the groove in the grating. The grating period was extended from 300 to 313.2 nm, while the diameter slightly shrank from 300 to 297.1 nm in the direction of the grooves and from 300 to 298 nm in the direction orthogonal to the grooves. This deformation shifted the resonance peak by 21.5 nm. These simulations indicated that both the elongation of the grating period and the small shrinkage of the diameter contributed to the ultra-wide tunability of the NFBC. We also calculated the dependence of the stress at the groove, the resonance wavelength, and the quality Q factor while changing the total elongation of the NFBC. The dependence of the stress on the elongation was 1.68 × 10^-2 GPa/µm. The dependence of the resonance wavelength was 0.07 nm/µm, which almost agrees with the experimental result. When the NFBC, assumed to have the total length of 32 mm, was stretched by 380 µm with the tensile force of 250 µN, the Q factor for the polarization mode parallel to the groove changed from 535 to 443, which corresponded to a change in Purcell factor from 5.3 to 4.9. This slight reduction seems acceptable for the application as single photon sources. Furthermore, assuming a rupture strain of the nanofiber of 10 GPa, it was estimated that the resonance peak could be shifted by up to about 42 nm.
Organisation(s): Institute of Solid State Physics
External Organisation(s): Kyoto University
National Metrology Institute of Germany (PTB)
Johannes Kepler University of Linz (JKU)
Type: Article
Journal: Optics express
Volume: 31
Pages: 13566-13575
No. of pages: 10
ISSN: 1094-4087
Publication date: 24.04.2023
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: Atomic and Molecular Physics, and Optics
Electronic version(s): https://doi.org/10.1364/OE.483843 (Access: Open)

BibTeX

@article{2e9f30f4618c40ceb4c7d52065405399,
title = "Numerical analysis of the ultra-wide tunability of nanofiber Bragg cavities",
abstract = "Nanofiber Bragg cavities (NFBCs) are solid-state microcavities fabricated in optical tapered fiber. They can be tuned to a resonance wavelength of more than 20 nm by applying mechanical tension. This property is important for matching the resonance wavelength of an NFBC with the emission wavelength of single-photon emitters. However, the mechanism of the ultra-wide tunability and the limitation of the tuning range have not yet been clarified. It is important to comprehensively analyze both the deformation of the cavity structure in an NFBC and the change in the optical properties due to the deformation. Here, we present an analysis of the ultra-wide tunability of an NFBC and the limitation of the tuning range using three dimensional (3D) finite element method (FEM) and 3D finite-difference time-domain (FDTD) optical simulations. When we applied a tensile force of 200 µN to the NFBC, a stress of 5.18 GPa was concentrated at the groove in the grating. The grating period was extended from 300 to 313.2 nm, while the diameter slightly shrank from 300 to 297.1 nm in the direction of the grooves and from 300 to 298 nm in the direction orthogonal to the grooves. This deformation shifted the resonance peak by 21.5 nm. These simulations indicated that both the elongation of the grating period and the small shrinkage of the diameter contributed to the ultra-wide tunability of the NFBC. We also calculated the dependence of the stress at the groove, the resonance wavelength, and the quality Q factor while changing the total elongation of the NFBC. The dependence of the stress on the elongation was 1.68 × 10-2 GPa/µm. The dependence of the resonance wavelength was 0.07 nm/µm, which almost agrees with the experimental result. When the NFBC, assumed to have the total length of 32 mm, was stretched by 380 µm with the tensile force of 250 µN, the Q factor for the polarization mode parallel to the groove changed from 535 to 443, which corresponded to a change in Purcell factor from 5.3 to 4.9. This slight reduction seems acceptable for the application as single photon sources. Furthermore, assuming a rupture strain of the nanofiber of 10 GPa, it was estimated that the resonance peak could be shifted by up to about 42 nm.",
author = "Hideaki Takashima and Schell, {Andreas W.} and Shigeki Takeuchi",
note = "Funding Information: Acknowledgments. We gratefully acknowledge financial support in the form of Kakenhi Grants-in-Aid (Nos. 21H04444, 26220712, 22H01155, and 19K03686) from the Japan Society for the Promotion of Science (JSPS), the CREST program of the Japan Science and Technology Agency (JST) (JPMJCR1674), and the MEXT Quantum Leap Flagship Program (MEXT Q-LEAP) (JPMXS0118067634). H. T. acknowledges the support of the Matsuo Foundation and JST, PRESTO Grant Number JPMJPR2257, Japan. A. W. S. was supported by Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany{\textquoteright}s Excellence Strategy - EXC-2123 Quantum Frontiers - 390837967.",
year = "2023",
month = apr,
day = "24",
doi = "10.1364/OE.483843",
language = "English",
volume = "31",
pages = "13566--13575",
journal = "Optics express",
issn = "1094-4087",
publisher = "OSA - The Optical Society",
number = "9",
}