In this paper, we analyze a chain-linked triple-cavity photonic molecule (TCPM) with controllable coupling strengths between the cavities on their spectral properties and field (energy) distributions by solving eigenvalues and eigenvectors of the Hamiltonian matrix based on coupled-mode theory. Phase transition is extended from double-cavity photonic molecules (DCPMs) to TCPMs, and evolutions of the supermode frequencies and linewidths are analyzed, which have synchronous relations with the degree of coherence between adjacent optical microcavities and energy distributions in the three cavities, respectively. We develop a superposition picture for the three supermodes of the TCPM, as interferences between supermodes of sub-DCPMs. In particular, we demonstrate the abnormal properties of the central supermode in TCPMs, such as the dark state in the middle cavity and phase shift when energy is flowing between the side cavities; these are promising for information processing and remote control of energy. General properties of TCPMs are summarized and limitations on linewidths are given. Finally, we make an interesting analog to intracavity electromagnetically induced transparency in multilevel atomic systems using the flexible TCPM platform under appropriate conditions.
In this paper, we analyze a chain-linked triple-cavity photonic molecule (TCPM) with controllable coupling strengths between the cavities on their spectral properties and field (energy) distributions by solving eigenvalues and eigenvectors of the Hamiltonian matrix based on coupled-mode theory. Phase transition is extended from double-cavity photonic molecules (DCPMs) to TCPMs, and evolutions of the supermode frequencies and linewidths are analyzed, which have synchronous relations with the degree of coherence between adjacent optical microcavities and energy distributions in the three cavities, respectively. We develop a superposition picture for the three supermodes of the TCPM, as interferences between supermodes of sub-DCPMs. In particular, we demonstrate the abnormal properties of the central supermode in TCPMs, such as the dark state in the middle cavity and phase shift when energy is flowing between the side cavities; these are promising for information processing and remote control of energy. General properties of TCPMs are summarized and limitations on linewidths are given. Finally, we make an interesting analog to intracavity electromagnetically induced transparency in multilevel atomic systems using the flexible TCPM platform under appropriate conditions.
Photonic molecules have been shown to be a very useful platform for studying fundamental physics and practical applications. In recent years, double-cavity photonic molecules have been used in many important applications. Here, an approach to realize the fully-controlled triple-cavity photonic molecules, based on three ultrahigh-Q microtoroids with two different configurations, is experimentally demonstrated. By controlling the coupling strengths and resonant frequencies of the high-Q microcavities, interesting phenomena, such as super-mode evolution, dark state, double anti-crossing, as well as transition from double-EIT to double-EIA, are observed. This fully-controllable triple-cavity photonic molecule sets a unique stage for future investigations of photonic devices and cavity-QED effects. (Picture: Chao Yang et al., article number 1600178, in this issue)
All-optical analogs of electromagnetically induced absorption (EIA) and electromagnetically induced transparency (EIT) are important for light storage, sensing, and optical communication. Here, we report results of a computational study focusing on the EIA and EIT characteristics of triple-microcavity hosting one-dimensional photonic crystals (PHCs). In contrast to previous experimental investigation of dual PHC cavities, realization EIA and EIT in the triple-cavity PHC is not restricted to reflection and transmission, respectively. In addition, the dispersive response of the triple-cavity is also distinct since EIA in the triple-cavity may lead to the generation of both sub- and superluminal light pulses. Furthermore, the dispersion of the system at either output may be reversed by altering the distribution of the coupled light among the three cavities. Finally, we discuss the experimental implementation of these features based on a single monolithic PHC and show tuning of the EIA and EIT phenomenon over a broad spectral range by using strain-tunable polymer-based PHC microcavities. Among others, these findings are advantageous for realizing ultra-narrow bandwidth optical filters, all-optical switching, temporal control of cavity quantum electrodynamics effects, and on-chip dispersion control.
We study the tunable photonic distribution in an optical molecule consisting of two linearly coupled single-mode cavities. With the intercavity coupling and two driving fields, the energy levels of the optical-molecule system form a closed cyclic energy-level diagram, and the phase difference between the driving fields serves as a sensitive controller on the dynamics of the system. Due to the quantum interference effect, we can realize a partially dark optical molecule, where the steady-state mean photon number in one of the cavities achieves zero even under the external driving. And the dark cavity can be changed from one of the cavities to the other by only adjusting the phase difference. We also show that our proposal is robust to the noise at zero temperature. Furthermore, we show that when one of the cavities couples with an atomic ensemble, it will be dark under the same condition as that in the case without atoms, but the condition for the other cavity to be dark is modified.
We present a theoretical study of an optical cavity coupled with single four-level atoms in closed loop formed via applied control lasers. The transmitted probe field from the cavity is analyzed. We show that the electromagnetically induced transparency (EIT) in the cavity and the normal mode splitting will be very different with changing the closed interaction phase and the intensity of the free-space control laser. This coupled cavity–atom system presents a variational double-EIT that comes from modulating the splitting of the dark state, which means that we could realize the gradual transfer between one EIT peak and two EIT peaks by adjusting the applied control lasers, and the normal mode splitting sidebands will shift slightly by changing the free-space control laser. This means that we could control the output cavity probe field more freely and it is easer to realize optical switch controlled by more parameters. We also depict the angular dispersion of the intracavity probe field in different free-space control laser. The large phase shift ( ) of the reflected intracavity probe field will be very useful for optical temporal differentiation and quantum phase gate.
Abstract Harnessing optical supermode interaction to construct artificial photonic molecules has uncovered a series of fundamental optical phenomena analogous to atomic physics. Previously, the distinct energy levels and interactions in such two-level systems were provided by coupled microresonators. The reconfigurability is limited, as they often require delicate external field stimuli or mechanically altering the geometric factors. These highly specific approaches also limit potential applications. Here, we propose a versatile on-chip photonic molecule in a multimode microring, utilizing a flexible regulation methodology to dynamically control the existence and interaction strength of spatial modes. The transition between single/multi-mode states enables the “switched-off/on” functionality of the photonic molecule, supporting wider generalized applications scenarios. In particular, “switched-on” state shows flexible and multidimensional mode splitting control in aspects of both coupling strength and phase difference, equivalent to the a.c. and d.c. Stark effect. “Switched-off” state allows for perfect low-loss single-mode transition (Q i ~ 10 million) under an ultra-compact bend size (FSR ~ 115 GHz) in a foundry-based silicon microring. It breaks the stereotyped image of the FSR-Q factor trade-off, enabling ultra-wideband and high-resolution millimeter-wave photonic operations. Our demonstration provides a flexible and portable solution for the integrated photonic molecule system, extending its research scope from fundamental physics to real-world applications such as nonlinear optical signal processing and sixth-generation wireless communication.
This thesis mainly focuses on the experimental investigations of electromagnetically induced transparency (EIT) related phenomena in various systems involving multilevel atoms inside an optical ring cavity. Semiclassical methods, e.g. density-matrix equations, are used through out this thesis to simulate the experimental results. First, the cavity transmission spectrum can be significantly modified when multilevel atoms are placed inside an optical ring cavity. Such coupled atom-cavity systems are well explained by the intracavity dispersion/absorption properties. Specifically, three-level lambda-type, four-level N-type and double-lambda-type atoms inside an optical ring cavity are investigated by examining their cavity transmission spectra. Second, optical multistability (OM) has been demonstrated with EIT atoms inside an optical ring cavity. Such OM has been utilized to realize a controllable optical multistate switch, which can be modeled as a triple-well system. Third, self-Kerr nonlinearities of multilevel atoms are measured in an optical ring cavity by scanning the cavity length. Fourth, bright Stokes and anti-Stokes fields are generated simultaneously in a doubly-resonant atomic optical parametric oscillator (AOPO). In addition, vacuum-induced absorption and noise correlations are studied in the AOPO system. Last, a theoretical model is proposed to realize parity-time (PT) symmetry in a four-level N-type atomic system by spatially modifying the complex refractive index in free space. Moreover, the experimental progress is made to observe discrete diffraction pattern in an optically induced lattice by interfering with plane waves in a coherent atomic medium.