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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Realization of a high-g factor nanofiber Bragg cavity using a He focused ion beam milling system

Hideaki Takashima, Atsushi Fukuda, Yusuke Iwabata, Hironaga Maruya, Andreas Wolfgang Schell, Shigeki Takeuchi

Published Jun 1, 2017• 0 citations
Publisher

Abstract

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 %.

DOI
10.1109/cleoe-eqec.2017.8087093

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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 %.
Funnelling the light emitted from quantum emitters like atoms, molecules, or defect centers into the guided mode of a single mode optical fiber is highly important for scaling up quantum optics experiments, since it provides the possibility to interconnect experiments at different locations and ensures high mode overlap of photons from different sources. Here, we present a photonic nanocavity on a tapered optical fiber. The cavities are formed by two Bragg mirrors fabricated by an ion beam [1]. Characterization in terms of transmission, reflection, and polarization are performed and compared with numerical simulations [2]. The quality factors of the fabricated devices can reach values over 300 while the mode volume is smaller than the cubic wavelength. Simulations indicate that a Purcell enhancement of 19.1 with 82 % coupling efficiency can be reached using this cavities. A comparison of cavities fabricated using a gallium beam is compared with cavities made using a helium beam giving insights about implantation of gallium in the ion beam milling fabrication of resonators. Using the knowledge from experiment and simulation, new designs for nanofiber Bragg grating cavities are developed and tested. [1] A W Schell et al. Sci. Rep. 5, 9619 (2015) [2] H Takashima et al. Opt. Express 24, 15050-15058 (2016)
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.
We report a new gateway to enhance the sponatnesous emission rate of single quantum emitters by introducing a cavity in tilted nanofiber Bragg grating (TNFBG). We found that light emitter's coupling efficiency into the tilted grating structure's guided mode is 65%, with 70 grating periods. This novel tilted structure has a high Q factor ~ 1408.71 and low mode volume ~ 0.66 microm3- an important requirement. Further, the Purcell factor of a quantum light emitter inside the nanofiber is nine times more than that of an emitter on the cavity's surface. The further optimized system with enhanced perfromance can be used the next generation quantum information and quantum metrology application.
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.
We present a novel approach to enhance the spontaneous emission rate of single quantum emitters in an optical nanofiber-based cavity by introducing a narrow air-filled groove into the cavity. Our results show that the Purcell factor for single quantum emitters inside the groove of the nanofiber-based cavity can be at least six times greater than for such an emitter on the fiber surface when using an optimized cavity mode and groove width. Moreover, the coupling efficiency of single quantum emitters into the guided mode of this nanofiber-based cavity can reach up to ∼80% with only 35 cavity-grating periods. This new system has the potential to act as an all-fiber platform to realize efficient coupling of photons from single emitters into an optical fiber for quantum information applications.
We propose a single-sided optical nanofiber cavity (SSONFC) to facilitate cavity quantum electrodynamics (cQED). The structure is designed and analyzed throughs finite-difference time-domain simulations. A systematic evaluation of the cavity properties and spontaneous emission characteristics has been conducted. Our findings demonstrate that this design significantly enhances the spontaneous emission rate of a single quantum emitter (SQE). A Purcell factor of ∼22\sim 22∼22 and a maximum unidirectional single-photon coupling efficiency of around 72%72 \%72% into the ONF’s guided mode can be achieved when an SQE is positioned on the SSONFC surface. Additionally, a high scattering limited quality factor (Q∼2510Q \sim 2510Q∼2510) is obtained for the fundamental cavity mode. The structure’s dimensions can be adjusted to accommodate different SQE emission wavelengths, making it a versatile solution. This fiberintegrated single-photon device holds potential for applications in quantum phase switches, and single-photon transistors.