arXiv:1706.04291 · Physical Review A

Channeling of spontaneous emission from an atom into the fundamental and higher-order modes of a vacuum-clad ultrathin optical fiber

Fam Le Kien, S. Sahar S. Hejazi, Thomas Busch, Viet Giang Truong, Síle Nic Chormaic

Published Oct 26, 2017• 24 citations

Abstract

We study spontaneous emission from a rubidium atom into the fundamental and higher-order modes of a vacuum-clad ultrathin optical fiber. We show that the spontaneous emission rate depends on the magnetic sublevel, the type of modes, the orientation of the quantization axis, the position of the atom, and the fiber radius. We find that the rate of spontaneous emission into the TE modes is always symmetric with respect to the propagation directions. Directional asymmetry of spontaneous emission into other modes may appear when the quantization axis does not lie in the meridional plane containing the position of the atom. When the fiber radius is in the range from 330 to 450 nm, the spontaneous emission from an atom on the fiber surface into the ${\mathrm{HE}}_{21}$ modes is stronger than into the ${\mathrm{HE}}_{11}$, ${\mathrm{TE}}_{01}$, and ${\mathrm{TM}}_{01}$ modes. At the cutoff for higher-order modes, the rates of spontaneous emission into guided and radiation modes undergo steep variations, which are caused by the changes in the mode structure. We show that the spontaneous emission from the upper level of the cyclic transition into the TM modes is unidirectional when the quantization axis lies at an appropriate azimuthal angle in the fiber transverse plane.

DOI: 10.1103/physreva.96.043859

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arXiv:1706.04291 · Physical Review A

Channeling of spontaneous emission from an atom into the fundamental and higher-order modes of a vacuum-clad ultrathin optical fiber

Fam Le Kien, S. Sahar S. Hejazi, Thomas Busch, Viet Giang Truong, Síle Nic Chormaic

Published Oct 26, 2017• 24 citations

arXiv HTML PDF

Abstract

{\mathrm{HE}}_{21}

modes is stronger than into the

{\mathrm{HE}}_{11}

{\mathrm{TE}}_{01}

, and

{\mathrm{TM}}_{01}

modes. At the cutoff for higher-order modes, the rates of spontaneous emission into guided and radiation modes undergo steep variations, which are caused by the changes in the mode structure. We show that the spontaneous emission from the upper level of the cyclic transition into the TM modes is unidirectional when the quantization axis lies at an appropriate azimuthal angle in the fiber transverse plane.

DOI: 10.1103/physreva.96.043859

Related papers

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Fam Le Kien, S. Sahar S. Hejazi, Thomas Busch +2 more

Conference on Lasers and Electro-OpticsJan 1, 20181 citation

Enhancement of the quadrupole interaction of an atom with the guided light of an ultrathin optical fiber

Fam Le Kien, Tridib Ray, Thomas Nieddu +2 more

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arXiv:2211.06000Physical Review AJan 19, 20234 citations

{\mathrm{HE}}_{21}

modes is stronger than into the

{\mathrm{HE}}_{11}

{\mathrm{TE}}_{01}

, and

{\mathrm{TM}}_{01}

^{87}\mathrm{Rb}

atom, we study the dependencies of the quadrupole Rabi frequency on the quantum numbers of the transition, the mode type, the phase circulation direction, the propagation direction, the orientation of the quantization axis, the position of the atom, and the fiber radius. We find that the root-mean-square (rms) quadrupole Rabi frequency reduces quickly but the quadrupole oscillator strength varies slowly with increasing radial distance. We show that the enhancement factors of the rms Rabi frequency and the oscillator strength do not depend on any characteristics of the internal atomic states except for the atomic transition frequency. The enhancement factor of the oscillator strength can be significant even when the atom is far away from the fiber. We show that, in the case where the atom is positioned on the fiber surface, the oscillator strength for the quasicircularly polarized fundamental mode

{\mathrm{HE}}_{11}

has a local minimum at the fiber radius $a\ensuremath{\simeq}107$ nm, and is larger than that for quasicircularly polarized higher-order hybrid modes, transverse electric modes, and transverse magnetic modes in the region

a<498.2

nm.

z

axis, the atom lies on the fiber transverse

x

axis, the quantization axis for the atomic internal states is the other orthogonal transverse

y

axis, the atomic upper and lower levels are the magnetic sublevels ${M}^{\ensuremath{'}}$ and

M

of hyperfine-structure levels of an alkali-metal atom, and the field is in a quasilinearly polarized fundamental guided mode

{\mathrm{HE}}_{11}

with the polarization $\ensuremath{\xi}=x$ or

y

. We find that the absolute value of the quadrupole Rabi frequency depends on the propagation direction of the light field in the cases of (${M}^{\ensuremath{'}}\ensuremath{-}M=\ifmmode\pm\else\textpm\fi{}1, \ensuremath{\xi}=y$) and (${M}^{\ensuremath{'}}\ensuremath{-}M=\ifmmode\pm\else\textpm\fi{}2, \ensuremath{\xi}=x$). We show that the directional dependence of the coupling leads to the directional dependence of spontaneous emission into guided modes. We find that the directional dependence of the atom-field coupling in the case of quadrupole transitions is not entirely due to spin-orbit coupling of light: there are some other contributions resulting from the gradient of the spatial phase factor of the field.