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Physica Scripta

Polarization dependence of fluorescence photons from quantum dots coupled to an optical nanofiber tip

M. R. Resmi, Jelba John, Ramachandrarao Yalla

Published Sep 26, 2025• 1 citation
Publisher

Abstract

Abstract We experimentally demonstrate the emission polarization dependence of fluorescence photons from quantum dots (QDs) coupled to an optical nanofiber tip (ONFT). We observe a maximum degree of polarization of 29 (±2)%. Simulations are performed to determine the polarization response for a dipole source (DS) on the facet and the side of the ONFT. Considering the real ONFT geometry, simulations are performed to determine the polarization response for the DS on the facet and the side of a tapered ONFT. The experimentally measured results show correspondence with the simulation-predicted results. The present fiber-coupled polarization-controlled system paves the way in quantum information science as it is a key ingredient for such applications.

DOI
10.1088/1402-4896/ae0c5e

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Abstract We experimentally demonstrate the emission polarization dependence of fluorescence photons from quantum dots (QDs) coupled to an optical nanofiber tip (ONFT). We observe a maximum degree of polarization of 29 (±2)%. Simulations are performed to determine the polarization response for a dipole source (DS) on the facet and the side of the ONFT. Considering the real ONFT geometry, simulations are performed to determine the polarization response for the DS on the facet and the side of a tapered ONFT. The experimentally measured results show correspondence with the simulation-predicted results. The present fiber-coupled polarization-controlled system paves the way in quantum information science as it is a key ingredient for such applications.
We experimentally investigate the fluorescence photon emission characteristics for single q-dots by using optical nanofibers. We demonstrate that single q-dots can be deposited along an optical nanofiber systematically and reproducibly with a precision of 5 μm. For single q-dots on an optical nanofiber, we measure the fluorescence photon numbers coupled into the nanofiber and the normalized photon correlations, by varying the excitation laser intensity. We estimate the fluorescence photon coupling efficiency into the nanofiber guided modes.
We experimentally demonstrate the efficient channeling of fluorescence photons from single q dots on optical nanofiber into the guided modes by measuring the photon-count rates through the guided and radiation modes simultaneously. We obtain the maximum channeling efficiency to be 22.0(±4.8)% at a fiber diameter of 350 nm for the emission wavelength of 780 nm. The results may open new possibilities in quantum information technologies for generating single photons into single-mode optical fibers.
This thesis presents single photon generation and spectroscopy using quantum dots (q-dots) on optical nanofibers. Optical nanofibers are essentially vacuum-clad silica fibers with sub-wavelength diameter, which can support only the propagation of the fundamental mode through the guided mode. Optical nanofibers are realized using adiabatically tapered single mode optical fibers. Experiments were performed by depositing colloidal core-shell type CdSeTe (ZnS) q-dots on the optical nanofiber surface. A method is developed to deposit single q-dots systematically and reproducibly along the optical nanofiber. In the view point of investigation of fluorescence photon emission characteristics for single q-dots on optical nanofibers, the absolute fluorescence photon-count rates channeled into the nanofiber guided modes and the normalized photon correlations at various excitation laser intensities are measured. The results are able to obtain the product between the fluorescence photon channeling efficiency and the quantum efficiency of the single q-dots. However, the channeling efficiency cannot be determined without accurate information on the quantum efficiency of the single q-dots. Therefore, a method is devised to determine the channeling of fluorescence photons from single q-dots into the guided modes by measuring the fluorescence photon-count rates through the guided and radiation modes simultaneously. By measuring for various nanofiber diameters, a maximum channeling efficiency obtained to be 22.0 (±4.8)% at a fiber diameter of 350 nm for an emission wavelength of 780 nm. The measured results completely reproduce the theoretical predictions within the experimental error. We demonstrate in situ measurements of fluorescence quantum efficiency of single q-dots using the present nanofiber technique. We determine fluorescence quantum efficiency of single q-dots accurately by assuming the theoretical values for the channeling efficiency from the product of the channeling efficiency and the quantum efficiency. We demonstrate that one can pick up one q-dot on the nanofiber with fluorescence quantum efficiency higher than the average value measured for an ensemble. Thus, the optical nanofiber method offers a promising way for generating and manipulating single photons. This work should provide a basis for extending the optical nanofiber method to a general technique in quantum optics, which may open new possibilities in quantum information technologies.
A tapered optical fiber with subwavelength diameter waist, an optical nanofiber, provides a unique and all-fiber platform for manipulating atoms and photons. This paper presents some recent results towards quantum photonics on a nanofiber platform. In one direction, we demonstrate a quantum interface between trapped single atoms and fiber-guided photons using a nanofiber cavity. In the other direction, we demonstrate a polarized fiber-in-line quantum light source using a hybrid system of a single gold nanorod and single quantum dot deposited on a nanofiber.
We demonstrate a bright and polarized fiber in-line single-photon source based on plasmon-enhanced emission of colloidal single quantum dots into an optical nanofiber. We show that emission properties of single quantum dots can be strongly enhanced in the presence of single gold nanorods leading to a bright and strongly polarized single-photon emission. The single photons are efficiently coupled to guided modes of the nanofiber and eventually to a single-mode optical fiber. The brightness (fiber-coupled photon count rate) of the single-photon source is estimated to be $12.2\ifmmode\pm\else\textpm\fi{}0.6$ MHz, with high single-photon purity [${g}^{2}(0)=0.20\ifmmode\pm\else\textpm\fi{}0.04$] and degree of polarization as high as 94--97 %. The polarized and fiber-coupled single photons can be implemented for potential applications in quantum photonics.