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Improving photon antibunching with two dipole-coupled atoms in whispering-gallery-mode microresonators
摘要： In the two-atom or multiatom system, the atoms can interact with each other through exchange of virtual photon. This kind of energy exchange is often referred as the dipole-dipole interaction (DDI). Here we consider this DDI system consisting of a pair of two-level atoms strongly coupled with a bimodal whispering-gallery-mode (WGM) microresonator which is driven by an external laser field. Our aim is to explore the photon correlation characteristics of the proposed architecture using realistic experimental parameter values. We compare in detail the quality of photon antibunching (i.e., the smallness of the second-order correlation function) from three involved configurations in cavity quantum electrodynamics (QED): (i) only one two-level atom, (ii) two far apart two-level atoms without DDI, and (iii) two DDI (dipole-coupled) two-level atoms are respectively coupled to the driven WGM microresonator through the evanescent field. We clearly show that the DDI between both atoms can distinctly enhance the photon antibunching even in the weak-coupling regime in configuration (iii) with feature-rich line shapes. We also find that the photon antibunching can be modulated by properly adjusting the atom-cavity coupling strength. In addition, we display that this strong photon antibunching is robust against the cooperative atomic decay. Our DDI-based cavity QED scheme may provide an alternative way to the construction of integrated on-chip single-photon sources.
关键词： photon antibunching,whispering-gallery-mode microresonators,single-photon sources,dipole-dipole interaction,cavity quantum electrodynamics
更新于2025-09-19 17:13:59
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Saturable Absorption with CNT Coupled WGM and Fabrication of Er-Doped Microresonator for on-Chip Mode-Locked Laser
摘要： Mode-locked (ML) fiber lasers are becoming key components in industry, because they provide high performance while being relatively inexpensive. The generation of high-repetition rate pulses is gaining interest but it remains a challenge to achieve a GHz repetition rate with fiber lasers. On the other hand, whispering-gallery-mode (WGM) microresonators allow the strong confinement of light and miniaturizing an ML laser into a WGM microresonator will enable us to achieve a high pulse repetition rate, a small footprint and on-chip integrability. In this work, we explore the possibility of a passive ML laser with the system shown in Fig. 1(a). There are two key technologies involved; one is saturable absorption (SA) and the other is laser gain in a microresonator. First, we verified numerically that we could realize an ML laser with our proposed carbon nanotube (CNT) coupled erbium (Er) doped microresonator, and the result is shown in Fig. 1(b). We modelled our system with a nonlinear Schr?dinger equation, where we took gain and SA (also loss (Q), Kerr effect, and dispersion) into account [2]. The result shows that a self-starting ML is possible with microresonator parameters. Next, encouraged by the numerical result, we experimentally demonstrated SA in a microtoroid. We grew CNTs selectively on a silica microtoroid by chemical vapor deposition and investigated the SA behavior (Fig. 1(c)). By performing a pump-probe like experiment we successfully characterized the SA behavior in a microresonator system. This is the first demonstration of SA in a WGM microcavity system [1]. We then fabricated an Er-doped active microtoroid by using the sol-gel method. The sol-gel method is one way of forming silica from a metal alkoxide precursor. Although sol-gel has been widely used, it is still a challenge to fabricate high-quality defect-free film on a Si wafer that allows us to fabricate an ultrahigh-Q WGM microresonator. Figure 1(d)-(f) shows the fabricated films. We found optimum parameters and obtained a clean film as shown in Fig. 1(g). By using this film, we fabricated an Er-doped WGM microresonator, where the Q was 1.2×106 at 1480 nm (Fig. 1(h)). We obtained clear up-conversion luminescence when we pumped the cavity at 1480 nm, which constitutes the first step towards ML lasing in such a WGM microresonator. In summary, these results provide a promising approach for realizing an on-chip high repetition rate ML WGM microresonator.
关键词： saturable absorption,sol-gel method,carbon nanotube,whispering-gallery-mode microresonators,erbium-doped microresonator,Mode-locked fiber lasers
更新于2025-09-11 14:15:04