Multimode Cavity Research Articles

Microwave-assisted titanium nitride coating processing using nitride powders in ambient atmosphere

The microwave-assisted titanium nitride (TiN) coating method using TiN powders as a raw material was investigated for hard and smooth TiN coatings by decreasing the energy of the exothermic reaction between the raw powder and air. A titanium-aluminum-vanadium alloy (Ti-6Al-4 V) substrate was buried in TiN powders and irradiated with 2.45 GHz microwaves using a multimode cavity. After microwave processing, TiN films were found to be successfully deposited on the Ti-6Al-4 V substrate without atmospheric control. X-ray diffraction results indicated that face-centered cubic (fcc)-TiN phase increased with increasing temperature. TiN coating films synthesized at 900 °C and 800 °C were smoother than those at 1000 °C. Besides, the TiN films synthesized at 900 °C exhibited 697 HV with arithmetic mean roughness (Ra) = 0.29. These results demonstrated that a hard and smooth TiN film can be obtained using TiN powders as raw materials.

Non-Markovian Quantum Dynamics in Strongly Coupled Multimode Cavities Conditioned on Continuous Measurement

A new theory is introduced that describes the conditioned state of a system with continuous measurement undergoing non-Markovian open quantum systems dynamics, opening new perspectives both on a fundamental and practical level.

Complex Permittivity Measurement of Low-Loss Anisotropic Dielectric Materials at Hundreds of Megahertz

Resonant methods are well known for their accuracy in determining the complex permittivity of materials. However, to guarantee the accuracy, interference modes must be suppressed in the measurement band. In this paper, a multi-mode split rectangular cavity is designed and fabricated to measure low-loss anisotropic dielectric materials in the frequency range from 300 to 1000 MHz. Details of the cavity design are presented. Simulation results for a uniaxially anisotropic material validate both the setup and the processing. Moreover, validation measurements on a sheet of polytetrafluoroethylene (PTFE) are in agreement with the literature data, which indicate that the proposed method in this paper is reliable and accurate for low-loss complex permittivity characterization at hundreds of megahertz.

Rapid temperature swing adsorption using microwave regeneration for carbon capture

The use of microwave heating for the thermal regeneration of a porous carbon adsorbent in adsorptive carbon capture was evaluated. In this Microwave Swing Adsorption (MSA) process, a multimode microwave oven has been used to accelerate the desorption of CO2 after the adsorption of a CO2 / N2 (15/85 v/v) mixture. Starting from a commercial activated carbon (AC) material (MSP-20X), sorbent extrudates were prepared and loaded in a Teflon column. The heating of the sorbent bed inside the microwave (MW) cavity was characterised at different locations. Although the adsorption bed is not heated uniformly due to hot spots in the multimode MW cavity, flowing a purge gas reduces the non-uniform heating during the regeneration step. This study also reports that MSA regeneration achieves extremely fast total desorption (in 56 to 79 s), the quickest regeneration reported up to date in MSA, and very rapid desorption rates allowing swift adsorption–desorption cycles. This fast desorption is associated with the extremely high heating rates achieved (100 to 400 °C/min). We show that the desorption rate is faster when using higher powers at practically identical MW energy inputs. Complete CO2 desorption can be achieved at slightly longer durations when using 2-step MW heating. When comparing the MSA results with a reference TSA process, MSA outperforms TSA, due to the higher heating rates achieved by MSA. During eleven adsorption–desorption cycles, it is evidenced that the MSA process can regenerate the adsorption bed at a high reproducibility. The microporosity of the material remained intact during the MSA, revealing that localised heating and the high heating rates are not damaging the sorbent material.

Controlling of spatial modes in multi-mode photonic crystal nanobeam cavity.

We numerically and experimentally present the characteristics of disturbed spatial modes (air mode and dielectric mode) in multi-mode photonic crystal nanobeam cavity (PCNC) in the mid-infrared wavelength range. The results show that the resonance wavelength of the spatial modes can be controlled by modifying the size, period and position of the central periodical mirrors in PCNC, achieving better utilization of the spectrum resource. Additionally, side coupling characteristics of PCNC supporting both air and dielectric modes are investigated for the first time. This work serves as a proof of design method that the spatial modes can be controlled flexibly in PCNC, paving the way to achieve integrated multi-function devices in a limited spectrum range.

Effective theory for matter in non-perturbative cavity QED

Starting from a general material system of NN particles coupled to a cavity, we use a coherent-state path integral formulation to produce a effective theory for the material degrees of freedom. We tackle the effects of image charges, the A^2A2 term and a multimode arbitrary-geometry cavity. The resulting (non-local) action has the photonic degrees of freedom replaced by an effective position-dependent interaction between the particles. In the large-NN limit, we discuss how the theory can be cast into an effective Hamiltonian where the cavity induced interactions are made explicit. The theory is applicable, beyond cavity QED, to any system where bulk material is linearly coupled to a diagonalizable bosonic bath. We highlight the differences of the theory with other well-known methods and numerically study its finite-size scaling on the Dicke model. Finally, we showcase its descriptive power with three examples: photon condensation, the 2D free electron gas in a cavity and the modification of magnetic interactions between molecular spins; recovering, condensing and extending some recent results in the literature.

Hybridized Frequency Combs in Multimode Cavity Electromechanical System.

The cavity electromechanical devices with radiation-pressure interaction induced Kerr-like nonlinearity are promising candidates to generate microwave frequency combs. We construct a silicon-nitride membrane based superconducting cavity electromechanical device and study two mechanical modes synergistic frequency combs. Around the threshold of intracavity field instability, we first show independent frequency combs with tooth spacing equal to each mechanical mode frequency. At the overlap boundaries of these two individual mechanical mode mediated instability thresholds, we observe hybridization of frequency combs based on the cavity field mediated indirect coupling between these two mechanical modes. The spectrum lines turn out to be unequally spaced, but can be recognized in combinations of the coexisting frequency combs. Beyond the boundary, the comb reverts to the single mode case, and which mechanical mode frequency will the tooth spacing be depends on the mode competition. Our work demonstrates mechanical mode competition enabled switchability of frequency comb tooth spacing and can be extended to other devices with multiple nonlinearities.

Real-time full-field imaging through scattering media by all-optical feedback

Full-field imaging through scattering media is fraught with many challenges. Despite many achievements in recent years, current imaging methods are too slow to deal with fast dynamics that occur for example in biomedical imaging. Here we present an ultra-fast all-optical method, where the object to be imaged and the scattering medium (diffuser) are inserted into a highly multimode self-imaging laser cavity. We show that the intra-cavity laser light from the object is mainly focused onto specific regions of the scattering medium where the phase variations are low. Thus, round trip loss within the laser cavity is minimized, thereby overcoming most of the scattering effects. The method is exploited to image objects through scattering media whose diffusion angle is lower than the numerical aperture of the laser cavity. As our method is based on optical feedback inside a laser cavity, it can deal with temporal variations that occur on timescales as short as several cavity round trips, with an upper bound of 200 ns.

Hybrid microwave sintering of alumina and 3 mol% Y2O3-stabilized zirconia in a multimode cavity – Influence of the sintering cell

In microwave (MW) sintering, samples directly heat by absorption of the electromagnetic field, leading to a fast volumetric heating. Thus, the materials are heated thanks to their own dielectric properties. In multimode cavities, samples are always heated with a sintering cell in order to get an insulation of the samples and a heating homogeneity. However, to date, very limited research has been carried out to study the effects of materials used in the sintering cell. In this paper the microstructure and densification of Al2O3 and 3Y-TZP were investigated and compared between three different sintering cells. The used sintering cell contains three main elements: thermal insulators, a SiC susceptor and a protective mullite tube. Higher final densities (98.3 ± 0.6% and 98.6 ± 0.6% of T.D. for Al2O3 and 3Y-TZP respectively), lower densification temperatures and better microstructure homogeneity were obtained by using the sintering cell containing both mullite tube and SiC susceptor. But, sintering using the sintering cell without the SiC susceptor was also possible, especially for the lowest lossy material,i.e., Al2O3. This can be explained by a possible susceptor effect of the mullite tube. However, the microstructural observations showed a difference of homogeneity in the microstructure for Al2O3 and 3Y-TZP with some sintering cells. It can be linked to the difference of dielectric properties of the two materials. The influence of the sintering cell is less critical for 3Y-TZP, which couples better with MW than Al2O3. It was also observed that densification curves were switched to higher temperatures during sintering with the presence of SiC susceptor and without mullite tube. These results were justified by an error in the temperature measurement of the IR-pyrometer.

Light-Induced Quantum Droplet Phases of Lattice Bosons in Multimode Cavities.

Multimode optical cavities can be used to implement interatomic interactions which are highly tunable in strength and range. For bosonic atoms trapped in an optical lattice we show that, for any finite range of the cavity-mediated interaction, quantum self-bound droplets dominate the ground state phase diagram. Their size and in turn density is not externally fixed but rather emerges from the competition between local repulsion and finite-range cavity-mediated attraction. We identify two different regimes of the phase diagram. In the strongly glued regime, the interaction range exceeds the droplet size and the physics resembles the one of the standard Bose-Hubbard model in a (self-consistent) external potential, where in the phase diagram two incompressible droplet phases with different filling are separated by one with a superfluid core. In the opposite weakly glued regime, we find instead direct first order transitions between the two incompressible phases, as well as pronounced metastability. The cavity field leaking out of the mirrors can be measured to distinguish between the various types of droplets.

High-Efficiency Continuous-Flow Microwave Heating System Based on Asymmetric Propagation Waveguide

Continuous-flow microwave heating is widely used in chemical engineering and other fields. However, during microwave heating, the load’s electrical permittivity change will affect microwave heating efficiency. In this article, a WR430 asymmetric propagation waveguide is proposed based on gradient-index metasurfaces (GIMs), which can achieve high-efficiency continuous-flow heating with a large range of permittivity. First, asymmetric microwave propagation is realized in a WR430 3-D waveguide model, and the influence of metasurfaces index, thickness, and discrete element size is analyzed. Second, the asymmetric propagation waveguide is realized by fluted medium based on the permittivity equivalent method. The results show that the microwave inside the waveguide can only propagate along one direction at 2.4–2.6 GHz. Finally, the proposed waveguide is applied to a continuous-flow heating system. Compared with the single-mode cavity, multimode cavity, and waveguide water load, the proposed method can improve heating robustness and efficiency with different loads. Experiments show that the microwave absorption efficiency is stable and greater than 90% in the proposed system when the permittivity of the load changes drastically. The proposed system has a simple structure and strong applicability, which can replace the three-stub tuner and get rid of the circulator and water load for continuous-flow heating.

A parametric study of conventional and high-speed microwave sintering of robocast porcelain

The combination of three-dimensional (3D) printing technologies and microwave (MW) sintering offers new perspectives for minimizing material, energy and time waste. This study aimed at conducting a parametric study on the sintering of robocast porcelain by conventional and MW heating in a multimode cavity (2.45 GHz, 3 kW). The effect of heating rate, dwell temperature and dwell duration on sample density, shrinkage and microstructure was investigated on small pellets. With conventional heating, a good densification was achieved with a 2 h dwell at 1250 °C, independent of heating rate (1–20 °C/min). A similar density was reached using microwave hybrid heating at a much higher heating rate (100 °C/min), shorter dwell (30 min) and slightly higher sintering temperature (1300 °C). Without susceptor, a longer pre-heating step was required to initiate the sample heating, thus extending the heat treatment duration. This study provides seeding data for the development of greener processes for aluminosilicate ceramic manufacturing.

Integration of an anti-resonant hollow-core fiber with a multimode Yb-doped fiber for high power near-diffraction-limited laser operation.

We proposed and demonstrated mode cleaning in a high-power fiber laser by integrating an anti-resonant hollow-core fiber (AR-HCF) into a multimode laser cavity of an ytterbium (Yb)-doped fiber (YDF). An in-house mode-matched AR-HCF was fusion-spliced to a commercial multimode LMA-YDF, ensuring efficient fundamental mode coupling. The AR-HCF inflicts a high propagation loss selectively on higher-order modes, facilitating fundamental mode operation. Thus, the AR-HCF works as an efficient spatial mode filter embedded in the multimode fiber laser cavity and reinforces preferential amplification of the fundamental mode. Beam quality factor enhancement was achieved from M2 = 2.09 to 1.39 at an output power of 57.7 W (pump-power limited). The beam quality can be further improved by refining the AR-HCF fabrication. The proposed technique has a great potential to be exploited in other multimode fiber laser cavities involving erbium- or thulium-doped fibers and obviates the need for complicated specialty active fiber designs. Compared with the commonly used fiber bending technique, our method can achieve an efficient higher-order mode suppression without inducing mode-field deterioration.

Few-photon transport via a multimode nonlinear cavity: Theory and applications

Few-photon transport via waveguide-coupled local quantum systems has attracted extensive theoretical and experimental studies. Most of the study has focused on atomic or atomic-like local quantum systems due to their strong light-matter interaction useful for quantum applications. Here, we study few-photon transport via a waveguide-coupled multimode optical cavity with second-order bulk nonlinearity. We develop a Feynman diagram approach and compute the scattering matrix of the one- and two-photon transport. Based on the calculated scattering matrix, we show highly nonclassical photonic effects, including photon blockade and $\pi-$conditional phase shift, are achievable in the waveguide-coupled multimode optical cavity system via quantum interference and linear response engineering. Our results might lead to significant applications of quantum photonic circuits in all-optical quantum information processing and quantum network protocols.

Crosstalk-free all-optical switching enabled by Fano resonance in a multi-mode photonic crystal nanocavity.

We demonstrate all-optical switching using a multi-mode membranized photonic crystal nanocavity exploiting the free-carrier induced dispersion in InP and the sharp asymmetric lineshape of Fano resonances. A multi-mode cavity is designed to sustain two spatially overlapping modes with a spectral spacing of 18 nm. The measured transmission spectrum of the fabricated device shows multiple asymmetric Fano resonances as predicted by optical simulations. The capabilities of the device are benchmarked by comparing a wavelength conversion from 1538.2 nm to 1565.2 nm with a single-mode wavelength conversion at 1566.2 nm on the same device. The results show an improvement in signal quality with a 5.6 dB power penalty reduction at the receiver as well as in energy efficiency with a reduction of the pump power from 534 fJ/bit to 445 fJ/bit.

Cavity Backed Slot Antenna Fed by a Stripline with SIW Structure and Vertical Coaxial Transition for Microwave Solid-State Heating Applications

This paper presents a new approach to feed multimode cavities used as microwave applicators for industrial and domestic microwave ovens using solid-state sources operating in the 2.45 GHz ISM (Industrial, Scientific and Medical) band (commonly used for industrial microwave applications). The feeding structure consists of a slot on the top side of the applicator cavity. The slot is fed by a shielded asymmetric stripline with a Substrate Integrated Waveguide structure (to preserve the stripline Transversal Electro-Magnetic (TEM) operation within the shield) and is N-connectorized. A first design of the antenna was obtained using state-of-the-art antenna theory assuming free-space radiation. Then, it was refined using a commercial simulation tool based on the Finite Element Method in the frequency domain to achieve VSWR values lower than 1.5 in the source bandwidth (from 2.42 to 2.48 GHz) when the antenna radiates into the applicator cavity. The design parameters of all the components making up this feeding structure are discussed throughout the paper. A prototype was built and measured in the laboratory. The experimental results are presented at the end of the paper along with the simulated ones, showing a very good agreement.

Compact Substrate Integrated Waveguide Filtering Antennas: A Review

In recent years, with the rapid development of integrated circuits, the filtering antenna (FA) circuit of the substrate integrated waveguide (SIW) has attracted widespread attention in wireless communications. Numerous structures have been proposed to improve the performance of SIW FA. Hence, this paper presents the development and miniaturization trend of the SIW FA, and briefly introduces the structure and historical development of the SIW FA. In terms of the mode, multi-mode cavities and incomplete mode cavities are constructed. Multi-layer structures, special structures and the slow-wave technology are constructed in physical structure. Several methods and design examples of the SIW FA miniaturization are introduced from these two aspects. Based on the combination of the filter and antenna, the FA remains the advantages of the SIW structure, mainly including small size, low insertion loss, high quality-factors, and easy integration in planar radio frequency components. Therefore, it can further reduce the circuit, allowing SIW FAs to be applied in many aspects such as the 5G (5th generation mobile communication technology) and wireless local area network communications.

Mode-Manipulated Multimode Cavity for Quantum Memory

In this study, a quasi-elliptical geometry and the iris technique are applied to a multimode cavity to manipulate the resonant mode in the desired direction for quantum memories. By applying quasi-elliptical geometry, the characteristics of monotonically increasing, equally spaced, and monotonically decreasing frequency intervals between the modes are realized. To manipulate a certain mode, an iris is applied to the multimode storage cavity. As an example, the entire mode, including the readout cavity, is implemented at equal intervals to minimize the interference and maximize the mode number from adjacent modes for the 5–8 GHz frequency band.

An optical lattice with sound.

Quantized sound waves-phonons-govern the elastic response of crystalline materials, and also play an integral part in determining their thermodynamic properties and electrical response (for example, by binding electrons into superconducting Cooper pairs)1-3. The physics of lattice phonons and elasticity is absent in simulators of quantum solids constructed of neutral atoms in periodic light potentials: unlike real solids, traditional optical lattices are silent because they are infinitely stiff4. Optical-lattice realizations of crystals therefore lack some of the central dynamical degrees of freedom that determine the low-temperature properties of real materials. Here, we create an optical lattice with phonon modes using a Bose-Einstein condensate (BEC) coupled to a confocal optical resonator. Playing the role of an active quantum gas microscope, the multimode cavity QED system both images the phonons and induces the crystallization that supports phonons via short-range, photon-mediated atom-atom interactions. Dynamical susceptibility measurements reveal the phonon dispersion relation, showing that these collective excitations exhibit a sound speed dependent on the BEC-photon coupling strength. Our results pave the way for exploring the rich physics of elasticity in quantum solids, ranging from quantum melting transitions5 to exotic 'fractonic' topological defects6 in the quantum regime.

Seamless High- Q Microwave Cavities for Multimode Circuit Quantum Electrodynamics

Multimode cavity quantum electrodynamics-where a two-level system interacts simultaneously with many cavity modes-provides a versatile framework for quantum information processing and quantum optics. Because of the combination of long coherence times and large interaction strengths, one of the leading experimental platforms for cavity QED involves coupling a superconducting circuit to a 3D microwave cavity. In this work, we realize a 3D multimode circuit QED system with single photon lifetimes of 2ms across 9 modes of a novel seamless cavity. We demonstrate a variety of protocols for universal single-mode quantum control applicable across all cavity modes, using only a single drive line. We achieve this by developing a straightforward flute method for creating monolithic superconducting microwave cavities that reduces loss while simultaneously allowing control of the mode spectrum and mode-qubit interaction. We highlight the flexibility and ease of implementation of this technique by using it to fabricate a variety of 3D cavity geometries, providing a template for engineering multimode quantum systems with exceptionally low dissipation. This work is an important step towards realizing hardware efficient random access quantum memories and processors, and for exploring quantum many-body physics with photons.