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Single-photon source using a rare-earth ion doped in an optical fiber

Kaito Shimizu

Published Mar 20, 2026• 0 citations
Publisher

Abstract

In this thesis, we study the single-photon source using a rare-earth (RE) ion doped in a tapered fiber.Single-photon sources are key components for various optical quantum information technologies, and the development of low-cost single-photon sources has been desired for their implementation.A wide variety of emitters for single-photon sources have been studied.Among these emitters, RE ions have attracted much attention as single-photon emitters due to their high stability of luminescence and the sharpness of the emission spectrum with 4f transitions.In our single-photon source, we obtain spatially isolated single RE ions, which are separated from each other beyond the diffraction limit by tapering a commercially available RE-ion-doped silica fiber.RE ions doped in the silica fiber can be optically activated at room temperature.Therefore, our single-photon source does not need cryogenic systems.In addition, the emission wavelength can be selected based on the type of RE ions doped in the fiber.These features of our single-photon source enable the development of a low-cost and wavelength-selectable source.We performed the autocorrelation measurements using a neodymium (Nd 3+ ) ion in the tapered fiber, and showed the generation of single photons from the ion.In addition, we proposed a method to selectively excite a single RE ion in the tapered fiber, which can directly generate single photons within the tapered fiber, and collect them through the tapered fiber with high collection and channeling efficiencies.Generating single photons with this excitation method is proved by the autocorrelation measurements.We also observed the optical properties of the single photon emitted from the single Nd 3+ ion in the tapered fiber, such as the fluorescence lifetime, saturation intensity and polarization states.The fluorescence lifetime is one of the most important parameters for a single-photon source because this parameter is closely related to the emission rate.We observed the fluorescence lifetime of the single Nd 3+ ion in the tapered silica fiber and an 1 ensemble of the Nd 3+ ion in the unstructured silica fiber.The saturation power of the excitation laser and the saturated fluorescence intensity tell us the appropriate excitation power for generating single photons with high signal-to-noise ratio.Here, we measured the relationship between the fluorescence intensity from the single Nd 3+ ion and the power of the excitation light.In addition, the polarization state of the single photons emitted from the single Nd 3+ ion in the tapered fiber was observed.Our results will lead to the implementation of the low-cost and wavelength-selectable single-photon source to realize various optical quantum information technologies.

DOI
10.20604/0002000501

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•Jan 1, 2012•1 citation
In this thesis, we study the single-photon source using a rare-earth (RE) ion doped in a tapered fiber.Single-photon sources are key components for various optical quantum information technologies, and the development of low-cost single-photon sources has been desired for their implementation.A wide variety of emitters for single-photon sources have been studied.Among these emitters, RE ions have attracted much attention as single-photon emitters due to their high stability of luminescence and the sharpness of the emission spectrum with 4f transitions.In our single-photon source, we obtain spatially isolated single RE ions, which are separated from each other beyond the diffraction limit by tapering a commercially available RE-ion-doped silica fiber.RE ions doped in the silica fiber can be optically activated at room temperature.Therefore, our single-photon source does not need cryogenic systems.In addition, the emission wavelength can be selected based on the type of RE ions doped in the fiber.These features of our single-photon source enable the development of a low-cost and wavelength-selectable source.We performed the autocorrelation measurements using a neodymium (Nd 3+ ) ion in the tapered fiber, and showed the generation of single photons from the ion.In addition, we proposed a method to selectively excite a single RE ion in the tapered fiber, which can directly generate single photons within the tapered fiber, and collect them through the tapered fiber with high collection and channeling efficiencies.Generating single photons with this excitation method is proved by the autocorrelation measurements.We also observed the optical properties of the single photon emitted from the single Nd 3+ ion in the tapered fiber, such as the fluorescence lifetime, saturation intensity and polarization states.The fluorescence lifetime is one of the most important parameters for a single-photon source because this parameter is closely related to the emission rate.We observed the fluorescence lifetime of the single Nd 3+ ion in the tapered silica fiber and an 1 ensemble of the Nd 3+ ion in the unstructured silica fiber.The saturation power of the excitation laser and the saturated fluorescence intensity tell us the appropriate excitation power for generating single photons with high signal-to-noise ratio.Here, we measured the relationship between the fluorescence intensity from the single Nd 3+ ion and the power of the excitation light.In addition, the polarization state of the single photons emitted from the single Nd 3+ ion in the tapered fiber was observed.Our results will lead to the implementation of the low-cost and wavelength-selectable single-photon source to realize various optical quantum information technologies.
A fiber-coupled single-photon source is an essential component for the implementation of optical quantum communication technologies. Using the rare-earth ion doped in an optical fiber as an emitter is a significant method to construct such a photon source at room temperature, as well as achieving high coupling and channeling efficiency. In this study, we experimentally demonstrated the generation of single photons at room temperature by selectively exciting a sole rare-earth ion isolated within a tapered silica fiber. The key advantages of our method are the ability to manipulate a purely single ion and the efficient collection of photons from the guided mode of the fiber, owing to the single ion's emission of photons directly within the fiber. These features make our system a promising building block for realizing all-fiber-integrated optical quantum networks. We have also measured the optical lifetime of a single neodymium ion in the tapered fiber, and the result supports that the single-photon correlation time is practically determined by the absorption time of the ion.
The realization of single-photon generation is important for implementing various quantum information technologies. The use of rare-earth ions in an optical fiber is a promising single-photon generation method due to its ability to operate at room temperature as well as the low cost involved. Neodymium ions are especially interesting because the ions are one of the most commercially affordable rare-earth materials in the current industry. The neodymium ion also has the advantage of having a rich energy level structure, which offers several possible wavelengths for emitted single photons from visible to near-telecommunication wavelengths. In this paper, we experimentally demonstrated single-photon generation using an isolated single neodymium ion in tapered silica fiber at room temperature. Our results have significant implications as a platform for low-cost wavelength-selectable single-photon sources and photonic quantum applications.
The fiber-coupled single-photon source, which can operate at room temperature, is an essential component for implementing optical quantum communication technologies such as quantum internet and quantum key distribution. Here, we experimentally demonstrated the generation of single photons at room temperature from a single Rare-Earth (RE) ion isolated in the optical tapered fiber. Our single photon source is fabricated based on commercially available RE ion doped fibers, which can be prepared at low cost. To investigate the characteristics of our single-photon source, several optical properties were also observed such as saturation intensity of the single RE ion. Our results will lead to the realization of various photonic quantum information technologies such as optical quantum communication networks.
Rare-earth (RE) atoms in solid-state materials are attractive components for photonic quantum information systems because of their coherence properties even in high-temperature environments. We have experimentally performed the single-site optical spectroscopy and optical addressing of a single RE atom in an amorphous silica optical fiber at room temperature. The single-site optical spectroscopy of the tapered RE-doped fiber shows nonresonant emission lines similar to those seen in the case of an unstructured fiber and the autocorrelation function of photons emitted from the fiber shows the antibunching effect due to the spatial isolation given by the tapered fiber structure. The ability to address single RE atoms at room temperature provides a very stable and cost-effective technical platform for the realization of a solid-state system for a large-scale quantum optical network and other quantum technologies based on a large number of spectral channels from visible to midinfrared wavelengths.
High Resolution Image Download MS PowerPoint Slide Crystals and fibers doped with rare-earth (RE) ions provide the basis for most of today’s solid-state optical systems, from lasers and telecom devices to emerging potential quantum applications such as quantum memories and optical to microwave conversion. The two platforms, doped crystals and doped fibers, seem mutually exclusive, each having its own strengths and limitations, the former providing high homogeneity and coherence and the latter offering the advantages of robust optical waveguides. Here we present a hybrid platform that does not rely on doping but rather on coating the waveguide─a tapered silica optical fiber─with a monolayer of complexes, each containing a single RE ion. The complexes offer an identical, tailored environment to each ion, thus minimizing inhomogeneity and allowing tuning of their properties to the desired application. Specifically, we use highly luminescent Yb 3+ [Zn(II) MC (QXA)] complexes, which isolate the RE ion from the environment and suppress nonradiative decay channels. We demonstrate that the beneficial optical transitions of the Yb 3+ are retained after deposition on the tapered fiber and observe an excited-state lifetime of over 0.9 ms, on par with state-of-the-art Yb-doped inorganic crystals.
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.