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Journal of Optics

Optimization of nanofiber gratings for efficient single-photon collection

Subrat Sahu, K. P. Nayak, Rajan Jha

Published Sep 29, 2022• 19 citations
Publisher

Abstract

Abstract We report on a simulation of a nanophotonic cavity constructed by designing periodic holes on an optical nanofiber to realize light–matter interaction. The cavity is designed using finite-difference time-domain simulations to maximize the coupling of spontaneous emission from a quantum emitter into fiber-guided modes. We systematically analyze the dependence of spontaneous emission on the quantum emitter position, polarization, and the grating strength (number of periods). We show that coupling efficiencies as high as 87% and 83% can be realized for a dipole emitter placed at the center of the nanofiber with polarization perpendicular ( x -pol) and parallel ( y -pol) to the hole-axis, respectively. This system may attract various quantum photonic applications based on single-photon sources.

DOI
10.1088/2040-8986/ac9632

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Abstract We report on a simulation of a nanophotonic cavity constructed by designing periodic holes on an optical nanofiber to realize light–matter interaction. The cavity is designed using finite-difference time-domain simulations to maximize the coupling of spontaneous emission from a quantum emitter into fiber-guided modes. We systematically analyze the dependence of spontaneous emission on the quantum emitter position, polarization, and the grating strength (number of periods). We show that coupling efficiencies as high as 87% and 83% can be realized for a dipole emitter placed at the center of the nanofiber with polarization perpendicular ( x -pol) and parallel ( y -pol) to the hole-axis, respectively. This system may attract various quantum photonic applications based on single-photon sources.
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.
Optical nanofiber-based single-photon source has attracted considerable interest due to its property of seamless integration with a single-mode fiber. With nanostructure engraved in the nanofiber, the single-photon collection efficiency can be greatly boosted with enhanced interaction between the single quantum emitter and the guided light. However, the prerequisite nanofabrication processes introduce complexities and extra loss. Here, we demonstrate that by simply placing a quantum emitter in the gap of two parallel nanofibers, single-photon coupling efficiency may reach 54.2%. Our numerical simulation results indicate that photon coupling efficiency of such simple structure is insensitive to the discrepancy in nanofiber radii, which further reduces the difficulties in device fabrication.
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.
We propose a geometry-driven strategy for achieving tunable single-photon coupling in an optical nanofiber cavity (ONFC), where the resonance wavelength is controlled by tailoring the optical nanofiber (ONF) diameter and the grating pitch. By adjusting these structural parameters, the cavity response can be systematically tuned without modifying the material platform or by using any external control schemes. There is a wide spectral resonance wavelength variation of 60, 106, and 70 nm that can be achieved by varying the ONF diameter in the range of 150 nm, the grating pitch of 60 nm, and the elongation of 400 µm, respectively. The integration of a quantum emitter (QE) within the cavity region retains the geometry-dependent tunability of the system. This enables controlled spectral alignment between the QE emission wavelength and the cavity resonance. For a typical QE placed on the ONFC operating around 640 nm, it facilitates a strong spontaneous emission enhancement with a Purcell factor of ∼20 and a coupling efficiency of ∼94% into the ONF-guided mode. The scattering-limited cavity performance yields a quality factor, finesse, and one-pass power loss of 2930, 104, and 2.9%. Owing to its geometry-controlled design, the proposed device can be readily adapted to different QE wavelengths through appropriate structural optimization, offering a compact and fiber-integrated platform for quantum information and communication applications.
We demonstrate cavity QED conditions in the Purcell regime for single quantum emitters on the surface of an optical nanofiber. The cavity is formed by combining an optical nanofiber and a nanofabricated grating to create a composite photonic crystal cavity. By using this technique, significant enhancement of the spontaneous emission rate into the nanofiber guided modes is observed for single quantum dots. Our results pave the way for enhanced on-fiber light-matter interfaces with clear applications to quantum networks.