Cavity Coupling Research Articles

Whispering gallery mode microsphere resonator based on cylindrical air cavity coupling.

In this Letter, an optical fiber whispering gallery mode microsphere resonator based on cylindrical air cavity coupling is proposed and demonstrated. The cylindrical air cavity is vertical to the axis of a single-mode fiber and in touch with the fiber core, fabricated by using femtosecond laser micromachining together with hydrofluoric acid etching. A microsphere is inserted into the cylindrical air cavity and in tangential contact with the inner cavity wall, which is in touch with or inside the fiber core. The light traveling in the fiber core is coupled into the microsphere via an evanescent wave when the light path is tangential to the contacting point of the microsphere and the inner cavity wall, resulting in whispering gallery mode resonance when the phase-matching condition is satisfied. Such a device is highly integrated, robust in structure, low in cost, stable in operation, and has a good quality factor (Q) of 1.44 × 104.

Highly efficient polaritonic light-emitting diodes with angle-independent narrowband emission

Angle-independent narrowband emission is required for many optoelectronic devices, ranging from high-definition displays to sensors. However, emerging materials for electroluminescent devices, such as organics and perovskites, show spectrally broad emission due to intrinsic disorder. Coupling this emission to an optical resonance reduces the linewidth, but at the cost of inheriting the severe angular dispersion of the resonator. Strongly coupling a dispersionless exciton state to a narrowband optical microcavity could overcome this issue; however, electrically pumped emission from the resulting polaritons is typically hampered by poor efficiencies. Here we present a universal concept for polariton-based emission from organic light-emitting diodes by introducing an assistant strong coupling layer, thereby avoiding quenching-induced efficiency losses. We realize red- and green-emitting, narrowband (full-width at half-maximum of less than 20 nm) and spectrally tunable polaritonic organic light-emitting diodes with up to 10% external quantum efficiency and high luminance (>20,000 cd m−2 at 5 V). By optimizing cavity detuning and coupling strength, we achieve emission with ultralow dispersion (<10 nm spectral shift at 60° tilt). These results may have wide-reaching implications for on-demand polariton emission and demonstrate the practical relevance of strong light–matter coupling for next-generation optoelectronics, particularly display technology.

Evolution of Rényi-2 quantum correlations in a double cavity–magnon system

This work reports on the stationary evolution of three different kinds of quantum correlations between two distant magnon modes. The system at hand consists of two spatially separated cavities, where each cavity has a microwave (MW) cavity and a magnon mode. The two cavities are coupled to each other via the photon-tunneling process, and both are exposed to the output field of a squeezed vacuum MW fields source. By calculating the covariance matrix fully describing the state of the two magnon modes, we give the explicit expressions of the measures of correlations defined via the Rényi-2 entropy, i.e. the Gaussian quantum steering [Formula: see text], Gaussian Rényi-2 entanglement [Formula: see text] and Gaussian Rényi-2 mutual information [Formula: see text]. We find that, the quantum steering is always upper bounded by the entanglement, which is in turn always upper bounded by half of the total correlations. The obtained results are consistent with the hierarchical Rényi-2 quantum correlations established in [L. Lami, C. Hirche, G. Adesso and A. Winter, Phys. Rev. Lett. 117, 220502 (2016)], i.e. they fulfill the hierarchical inequality [Formula: see text]. The influences of the squeezing parameter, the environmental temperature, the cavity–magnon coupling and the cavity–cavity coupling on the correlations are studied in detail.

Simultaneous ground-state cooling of two mechanical modes of a levitated nanoparticle

The quantum ground state of a massive mechanical system is a stepping stone for investigating macroscopic quantum states and building high fidelity sensors. With the recent achievement of ground-state cooling of a single motional mode, levitated nanoparticles have entered the quantum domain. To overcome detrimental cross-coupling and decoherence effects, quantum control needs to be expanded to more system dimensions, but the effect of a decoupled dark mode has so far hindered cavity-based ground-state cooling of multiple mechanical modes. Here, we demonstrate two-dimensional ground-state cooling of an optically levitated nanoparticle. Utilizing coherent scattering into an optical cavity mode, we reduce the occupation numbers of two separate centre-of-mass modes to 0.83 and 0.81, respectively. By controlling the frequency separation and the cavity coupling strengths of the nanoparticle’s mechanical modes, we show the transition from 1D to 2D ground-state cooling. This 2D control lays the foundations for quantum-limited orbital angular momentum states for rotation sensing and, combined with ground-state cooling along the third motional axis shown previously, may allow full 3D ground-state cooling of a massive object.

From edge to bulk: Cavity-induced displacement of topological nonlocal qubits

We investigate the ability of selective cavity coupling to a topological chain for tailoring the connectivity of Majorana fermions. We show how topological qubits (TQs), associated with nonlocal Majorana fermion pairing, can be displaced from the edges to the bulk of a topological chain through selective access to light-matter interaction with specific physical sites. In particular, we present a comprehensive density matrix renormalization group study of ground-state features in different chain-cavity coupling geometries, and we validate analytical insights in the strong-coupling regime. This type of Majorana fermion correlation generation process comes with emergent cavity photon features. Moreover, by considering the time evolution after a sudden quench of the cavity-matter coupling strength, we show that the development of high nontrivial matter (Majorana) correlations leaves behind measurable nonclassical photon imprints in the cavity. Innovative ways to dynamically generate TQ nonlocal correlations in topological chains of arbitrary length are thus provided, opening alternative routes to controllable long-range entanglement in hybrid photonic solid-state systems.

A novel architecture for room temperature microwave optomechanical experiments

We have developed a novel architecture for room temperature microwave cavity optomechanics, which is based on the coupling of a 3D microwave re-entrant cavity to a compliant membrane. Device parameters have enabled resolving the thermomechanical motion of the membrane and observing optomechanically induced transparency/absorption in the linear regime for the first time in a microwave optomechanical system operated at room temperature. We have extracted the single-photon coupling rate (g0) using four independent measurement techniques and, hence, obtained a full characterization of the proposed cavity optomechanical system.

A W-Band E-Plane Waveguide In-Phase Power Divider With Full Bandwidth and High Isolation

In this letter, a new two-way E-plane waveguide in-phase power divider (PD) with high port-port isolation operating in full W-band is proposed. This architecture is based on the classical six-port branch guide coupling principle, and consists of one input port, two output ports, and three isolation ports. To overcome the inherent tradeoff between fractional bandwidth and processing difficulty, a novel rectangular cavity coupling structure with greater waveguide width has been proposed. By analyzing, it is found that this novel layout allows broadband isolation and larger branch height which greatly eases the fabrication. Finally, an eight-branch prototype at W-band is designed, fabricated, and measured. In full W-band, the return loss is better than 20 dB and the isolation is better than 25 dB. The amplitude and phase imbalance between two output ports are less than ±0.4 dB and ±3.6°, respectively. The simulated and measured results are in good agreement.

Antibunching Effects in the Hybrid Cavity–Bose–Einstein Condensates System

We theoretically study the model of a hybrid cavity–Bose–Einstein condensates (BEC) system that consists of a two-level impurity atom coupled to a cavity–BEC system with radiation pressure coupling, where the system is weakly driven by a monochromatic laser field. The steady-states behavior of the entire system is researched in the framework of the impurity–cavity coupling dispersive limit. We find that the multiple types of photon steady-state antibunching effects can be obtained when only the dissipation of the cavity is included. Moreover, the strength and frequency range of conventional steady-state antibunching effects of the cavity can be significantly modified by the impurity atom and intrinsic non-linearity of BEC. This result shows that our study can provide a method to tune the antibunching effects of the cavity field. In addition, the non-standard photon blockade or superbunching effect with the suppression of two-photon correlation and enhancement of three-photon correlation can be realized. The frequency range of the superbunching effect also can be changed by the impurity atom and intrinsic non-linearity of BEC. Therefore, our study shows many quantum statistical characteristics in a hybrid cavity–BEC quantum system and its manipulation.

Integrating a fiber cavity into a wheel trap for strong ion–cavity coupling

We present an ion trap with an integrated fiber cavity, designed for strong coupling at the level of single ions and photons. The cavity is aligned to the axis of a miniature linear Paul trap, enabling simultaneous coupling of multiple ions to the cavity field. We simulate how charges on the fiber mirrors affect the trap potential, and we test these predictions with an ion trapped in the cavity. Furthermore, we measure micromotion and heating rates in the setup.

MECHANICAL JOINTS IN ROLLED SCREW-THREADED REINFORCING BARS

Introduction. Russian manufacturers currently produce screw-threaded reinforcing bars (rebars) and couplers to join them. However, the application of such reinforcement in the construction industry is hindered by a high compliance in screw couplings.Aim: to assess the compliance of coupling joints reinforced with adhesives.Materials and methods. The study used Av500P screw-threaded rebars, couplers, as well as adhesive compounds containing a cement binder and epoxy resin. The compounds were injected into the coupling cavity by means of hand pumps, followed by their natural hardening. The tests were conducted using universal testing machines.Results. In terms of strength, yield, and delaminatability, the compounds were found to meet the required stress-strain properties of couplers. Recommendations for assembling joints are provided.Conclusions. The conducted studies show that Av500P screw-threaded rebars can be joined by means of couplers in construction.

Terahertz monolithic integrated narrow-band filter based on the silicon carbide substrate

This paper presented a narrow-band terahertz integrated cavity filter based on the silicon carbide (SiC) substrate. By introducing two metalized via-holes in a rectangular integrated cavity, an integrated coupling cavity was built, on the one hand, to operate as a coupling structure; on the other hand, to control the direct coupling between input and output feeding lines, further to control the frequency of the transmission zero. This novel approach was thoroughly investigated with attention paid to the position of the via-holes. Based on this approach, a terahertz narrow-band filter was realized on the semi-insulating SiC substrate, demonstrated good filtering performance, especially the stopband rejection characteristic, and established the groundwork for the production of the terahertz monolithic integrated circuit.

Analysis of physical mechanism of beam crosstalk in semiconductor laser array spectral-beam-combined system

In spectral beam combining systems based on a grating-external cavity, due to some factors such as the “smile” effect of the semiconductor laser array and the error of the optical components in the external cavity, the beam from one emitter transmits into the external cavity and then can return to other emitters, thereby forming beam crosstalk between the two emitters. In this work, in order to investigate the physical mechanism of beam crosstalk and the influence of beam crosstalk on beam properties such as locked spectra and beam combining efficiency, based on the optical feedback semiconductor rate equation, the beam modes that can stably oscillate in the coupling cavity are derived, and the coupling cavity oscillating model is built. With the consideration of the mode competition mechanism in the coupling cavity, the effects of different crosstalk between two emitters with different intervals on the locked spectra are analyzed in detail. The results show that crosstalk leads to the shift of the peak of locked spectrum and the generation of sub-peak. The crosstalk between two closer emitters has a more serious influence on the beam spectrum structure, combined beam spot, and combining efficiency. The combining efficiencies influencing the 1&lt;sup&gt;st&lt;/sup&gt;, 2&lt;sup&gt;nd&lt;/sup&gt; and 3&lt;sup&gt;rd&lt;/sup&gt; crosstalk are 45.5%, 50.2%, and 63.8%, respectively (When there is no crosstalk, the efficiency is 80.1%). Finally, the results of the theoretical analysis are verified experimentally, and the experimentally observed spectra under the influence of crosstalk show phenomena such as peak degradation, peak shift, edge burrs, and side lobes in spectra, which are consistent with the theoretical predictions. Moreover, according to the simulation results and experimental observations, it is found that the crosstalk can be suppressed to a certain extent by increasing the spacing between emitters, and the Galileo telescope system is suggested to suppress crosstalk and optimize the spectral structure and beam combining efficiency. Compared with the Kepler telescope structure, the Galileo telescope does not have a real focal point, which can prevent the local power from being too high, thereby damaging the optical components.

Optomechanically Induced Amplification and Slow Light in Coupled Cavities

Optomechanically Induced Amplification and Slow Light in Coupled Cavities

High-power Ka-band Extended Interaction Klystron Design Based on Internal Coupling Cavity

High-power Ka-band Extended Interaction Klystron Design Based on Internal Coupling Cavity

Cat-eye retroreflectors based large-dynamic-range alignment-free laser

Lasers with cavities consisting of retroreflecting elements can give the potential for large-dynamic-range alignment-free operation, which makes the important applications in adaptive wireless laser power transfer/communication possible. In such an emerging approach based on resonant laser beam in the cavity, the laser is delivered to the photovoltaic cell for charging application (or photodiode for communication application) at the receiver automatically, without the necessity of positioning and aiming the receiver in conventional laser wireless power transfer techniques. The laser capable of operating alignment-free efficiently across large-dynamic-range is essential for the application. In this work, the requirements for the dynamic range of alignment-free operation are summarized. An alignment-free laser with a cavity consisting of cat-eye retroreflectors is designed, and a large alignment-free dynamic range as never before is experimentally demonstrated. Telescope system in the laser cavity is adopted to suppress the beam expansion to enhance the working distance between the laser transmitter and the receiver. Coupled cavity scheme is used to reduce the laser intensity between the transmitter and the receiver for laser safety. By calculating the stability zone of the laser cavity, it is found that the stability zone of the receiver cat-eye distance is quite narrow. Hence, the laser operation is very sensitive to the defocusing of the cat eye defocusing. Moreover, the cat eye defocusing induced by optical aberrations of spherical aberration and field curvature can be rather serious, when the long working distance results in a large beam size and the angle of incidence is large, hence limiting the effective working distance and the field of view of the alignment-free laser significantly. In the experiment, the improved optical designs with the aberrations compensation are adopted for large-dynamic-range alignment-free operation. The end-pumped Nd:GdVO&lt;sub&gt;4&lt;/sub&gt; laser at 1063 nm can deliver over 5-W output within a working distance range of 1–5 m, and a receiver field of view of ±30°, without cavity realignment. The transmitter field of view reaching 4.6° (full width at half maximum) at a working distance of 5 m is also realized, with a corresponding receiver transverse movement range of 40 cm. Our work clarifies the optimizing criteria of the large-dynamic-range alignment-free laser based on cat-eye retroreflectors.

On the flow characteristics of two supercavitating projectiles moving in water side-by-side

Multiple projectiles moving in water often encounter problems such as motion disturbance from adjacent body and unsteady cavity coupling, making the flow structure and motion characteristics very complex. In this study, a computational fluid dynamics (CFD) method is employed to model two parallel supercavitating projectiles moving in water side-by-side. The cavity characteristics and flow details around the two projectiles are presented, and the variation of mutual disturbance with axis distance and flow velocity are analyzed. Numerical results show that the two cavities feature good mirror symmetry, and the influence of axis distance and flow velocity on the cavity contour is mainly reflected in the varying cavity diameter and length. It is found that the parallel projectiles repel each other at different axis distances and flow velocities. It is more easily for the parallel projectiles to achieve supercavitating motion state than a single projectile due to the flow interaction between the twin projectiles.

Tunable magnomechanically induced transparency and fast-slow light in a hybrid cavity magnomechanical system

We theoretically explore the tunability of magnomechanically induced transparency (MMIT) phenomenon and fast-slow light effect in a hybrid cavity magnomechanical system in which a high-quality yttrium iron garnet (YIG) sphere and an atomic ensemble are placed inside a microwave cavity. In the probe output spectrum, we can observe magnon-induced transparency (MIT) and MMIT due to the photon-magnon and phonon-magnon couplings. We further investigate the effect of atomic ensemble on the absorption spectrum. The results show that better transparency can be obtained by choosing appropriate atomic ensemble parameters. We give an explicit explanation for the mechanism of the Fano resonance phenomenon. Moreover, we discuss phenomena of slow-light propagation. The maximum group delay increases significantly with the increasing atom–cavity coupling strength, and the conversion between slow light and fast light can also be achieved by adjusting the atom–cavity coupling strength. These results may have potential applications for quantum information processing and high precision measurements.

Emission spectral non-Markovianity in qubit-cavity systems in the ultrastrong coupling regime.

We study the emission spectra of the dissipative Rabi and Jaynes-Cummings models in the non-Markovian and ultrastrong coupling regimes. We have derived a polaron-transformed Nakajima-Zwanzig master equation (PTNZE) to calculate the emission spectra, which eliminates the well-known limitations of the Markovian approximation and the standard second-order perturbation. Using the time-dependent variational approach with the multiple Davydov ansatz as a benchmark, the PTNZE is found to yield accurate emission spectra in certain ultrastrong coupling regimes where the standard second-order Nakajima-Zwanzig master equation breaks down. It is shown that the emission spectra of the dissipative Rabi and Jaynes-Cummings models are, in general, asymmetric under various initial conditions. Direct comparisons of spectra for the two models illustrate the essential role of the qubit-cavity counter-rotating term and the spectral features under different qubit-cavity coupling strengths and system initial conditions.

Phase-Difference-Dependent Surface Plasmon Polariton Waveguide Coupling in a Symmetrical Dual-Channel Metal-Insulator-Metal Structure

This work reports a phase difference modulated coupling of two surface plasmon polariton (SPP) sources in a symmetrical two-channel metal-insulator-metal (MIM) waveguide device. In the device, two sources with different initial phases interact indirectly through the function of a rectangular cavity. With the phase difference varying, we have achieved tunable SPP coupling followed by continuously adjustable filtering property and Fano resonance. Further results show that the tunable SPP coupling in the resonance cavity can be well described by the electromagnetic wave interference theory. Moreover, we have also demonstrated the excellent performance of this phase-difference-dependent MIM waveguide in refractive-index sensing and have achieved considerable sensitivity as high as 818.8 nm/RIU. This research has great significance for tunable filtering and signal compensation in MIM waveguide-based photonic chips and also provides a device with high potential in refractive-index sensing.

Modeling and Vibro-acoustic Characterization of Elastic Plate-Irregular Hexahedral Acoustic Cavity Coupling Systems

Modeling and Vibro-acoustic Characterization of Elastic Plate-Irregular Hexahedral Acoustic Cavity Coupling Systems