Fundamental Cavity Mode Research Articles

Cavity fundamental mode and beam interaction in CEPC main ring

CEPC is a 100-kilometer-long electron-position collider, aiming to produce Higgs, W and Z-pole. Double ring (DR) is the baseline design of its main ring, and advanced partial double ring (APDR) is the alternative one. The purpose of this paper is to study the beam loading effects and the corresponding longitudinal beam dynamics of CEPC DR and APDR. The phase shift of the bunches modulated by the bunch gap is calculated with the approximation formulas and simulated with the program. All these methods are compared, and the application conditions of them are also elaborated. In addition, the longitudinal coupled-bunch instability in CEPC main ring is calculated by analytical formulas. In CEPC DR high-lumi Z, the phase shift can be reduced to 0.51 deg( $$^\circ $$ ). Besides, the total number of unstable longitudinal modes is 15 in CEPC DR high-lumi Z when no feedback system is added. The phase shift of the bunches in CEPC can be reduced to an acceptable value if the optimal filling pattern is chosen. For CEPC APDR, the RF parameters are calculated and the beam loading effects are tolerable.

Benchmarking five numerical simulation techniques for computing resonance wavelengths and quality factors in photonic crystal membrane line defect cavities.

We present numerical studies of two photonic crystal membrane microcavities, a short line-defect cavity with a relatively low quality (Q) factor and a longer cavity with a high Q. We use five state-of-the-art numerical simulation techniques to compute the cavity Q factor and the resonance wavelength λ for the fundamental cavity mode in both structures. For each method, the relevant computational parameters are systematically varied to estimate the computational uncertainty. We show that some methods are more suitable than others for treating these challenging geometries.

Influence of mode-beating pulse on laser-induced plasma

This paper addresses the influence of mode-beating pulse on laser-induced plasma. The second harmonic of a Nd:YAG laser, operated either with the single mode or multimode, was used for non-resonant optical breakdown, and subsequent plasma development was visualized using a streak imaging system. The single mode lasing leads to a stable breakdown location and smooth envelopment of the plasma boundary, while the multimode lasing, with the dominant mode-beating frequency of 500–800 MHz, leads to fluctuations in the breakdown location, a globally modulated plasma surface, and growth of local microstructures at the plasma boundary. The distribution of the local inhomogeneity was measured from the elastic scattering signals on the streak image. The distance between the local structures agreed with the expected wavelength of hydrodynamic instability development due to the interference between the surface excited wave and transmitted wave. A numerical simulation, however, indicates that the local microstructure could also be directly generated at the peaks of the higher harmonic components if the multimode pulse contains up to the eighth harmonic of the fundamental cavity mode.

Experimental demonstration on air cavity mode of violin using holed sheets of paper

The fundamental air cavity mode (A0) of a violin was investigated from the viewpoint of its dependence on the opening area and shape by using holed sheets of paper. The dependences of the frequency response of the A0 cavity mode on the shape, opening area, and orientation of the openings were observed. It was also demonstrated that the change of the opening area of f-holes affects to the performed tone with an actual violin.

Thermal analysis of high-bandwidth and energy-efficient 980 nm VCSELs with optimized quantum well gain peak-to-cavity resonance wavelength offset

The static and dynamic performance of vertical-cavity surface-emitting lasers (VCSELs) used as light-sources for optical interconnects is highly influenced by temperature. We study the effect of temperature on the performance of high-speed energy-efficient 980 nm VCSELs with a peak wavelength of the quantum well offset to the wavelength of the fundamental longitudinal device cavity mode so that they are aligned at around 60 °C. A simple method to obtain the thermal resistance of the VCSELs as a function of ambient temperature is described, allowing us to extract the active region temperature and the temperature dependence of the dynamic and static parameters. At low bias currents, we can see an increase of the −3 dB modulation bandwidth f−3dB with increasing active region temperature, which is different from the classically known situation. From the detailed analysis of f−3dB versus the active region temperature, we obtain a better understanding of the thermal limitations of VCSELs, giving a basis for next generation device designs with improved temperature stability.

Fiber cavities with integrated mode matching optics

In fiber based Fabry-Pérot Cavities (FFPCs), limited spatial mode matching between the cavity mode and input/output modes has been the main hindrance for many applications. We have demonstrated a versatile mode matching method for FFPCs. Our novel design employs an assembly of a graded-index and large core multimode fiber directly spliced to a single mode fiber. This all-fiber assembly transforms the propagating mode of the single mode fiber to match with the mode of a FFPC. As a result, we have measured a mode matching of 90% for a cavity length of ~400 μm. This is a significant improvement compared to conventional FFPCs coupled with just a single mode fiber, especially at long cavity lengths. Adjusting the parameters of the assembly, the fundamental cavity mode can be matched with the mode of almost any single mode fiber, making this approach highly versatile and integrable.

Transition From Surface Cavity Mode to Cavity Mode in Deep-Grooved Parallel Plate Waveguide

The parallel plate waveguide (PPWG) is an excellent device for guiding and controlling at terahertz wave. When a deep groove is integrated into a PPWG, only the surface cavity mode is excited, which limits its applications in filtering and sensing. In this paper, we demonstrated that in a double deep-grooved PPWG, both fundamental and higher-order cavity modes can be observed. Our experimental and simulation results show that the effective groove depth of the fundamental cavity mode in the bottom deep groove can be efficiently increased by cutting another shallow groove in the top metal plate, facing the bottom deep groove. In addition, the transition from the so-called surface cavity mode to traditional cavity mode can be observed with increasing depth of the shallow groove. These results may have applications in the multichannel filtering and sensing field.

Deterministic radiative coupling of two semiconductor quantum dots to the optical mode of a photonic crystal nanocavity

A system of two site-controlled semiconductor quantum dots (QDs) is deterministically integrated with a photonic crystal membrane nano-cavity. The two QDs are identified via their reproducible emission spectral features, and their coupling to the fundamental cavity mode is established by emission co-polarization and cavity feeding features. A theoretical model accounting for phonon interaction and pure dephasing reproduces the observed results and permits extraction of the light-matter coupling constant for this system. The demonstrated approach offers a platform for scaling up the integration of QD systems and nano-photonic elements for integrated quantum photonics applications.

Active coherent control of nanoscale light confinement: Modulation of plasmonic modes and position of hotspots for surface-enhanced Raman scattering detection

Multistep plasmonic nanostructures can induce the deep modulation of electromagnetic-field interactions on the nanoscale for positioning hotspots, and this generation of enhanced fields is important in many optical applications. In this article, a new strategy is proposed for fabricating a plasmonic doublestacked nanocone (DSC) nanostructure. In the DSC structure, a tunable plasmonic hybrid mode proceeds from the strong coupling of the plasmonic resonance of a fundamental cavity mode with a localized surface plasmon gap mode. In the nanostructure, the far-field response is deeply modulated and the hottest spots can be effectively positioned on the top surface of the DSC nanostructure. A controllable and cost-effective mask-reconfiguration technique for manufacturing the multiscale nanostructure is developed, which guarantees the generation of the introduced crucial stage on the DSC nanostructure. To evaluate the features of the plasmonic resonance, the DSC nanostructure is used as a surface-enhanced Raman scattering (SERS) substrate for detecting 4-mercaptopyridine molecules under specific excitation conditions. Its good performance, with an average measured SERS enhancement factor as high as 108, demonstrates its strong plasmonic-mode hybridization and extreme field enhancement.

Semiconductor meta-surface based perfect light absorber

We numerically proposed and demonstrated a semiconductor meta-surface light absorber, which consists of a silicon patches array on a silicon thin-film and an opaque silver substrate. The Mie resonances of the silicon patches and the fundamental cavity mode of the ultra-thin silicon film couple strongly to the incident optical field, leading to a multi-band perfect absorption. The maximal absorption is above 99.5% and the absorption is polarization-independent. Moreover, the absorption behavior is scalable in the frequency region via tuning the structural parameters. These features hold the absorber platform with wide applications in optoelectronics such as hot-electron excitation and photo-detection.

Quantification of scattering loss of III-nitride photonic crystal cavities in the blue spectral range

The mechanisms contributing to experimental quality factors of short wavelength ($\ensuremath{\lambda}=440--480$ nm) III-nitride on silicon one-dimensional photonic crystal cavities were quantified. Fluctuations in fundamental and first-order cavity mode wavelength and quality factor were compared over sets of nominally identical cavities. Unlike at $\ensuremath{\lambda}=1.5\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$, experimental quality factors were not limited by fabrication disorder modeled as smooth, normally distributed hole size and position variations; after ruling out absorption losses, additional scattering losses were found to predominate at short wavelengths. Experimental quality factors were sensitive to conformal deposition of few nanometer thin films on the photonic crystal surface, suggesting that the additional scattering losses were linked to the surface.

Superharmonic resonances in a strongly coupled cavity-atom system

We study a system consisting of a superconducting flux qubit strongly coupled to a microwave cavity. The fundamental cavity mode is externally driven and the response is investigated in the weak nonlinear regime. We find that near the crossing point, at which the resonance frequencies of the cavity mode and qubit coincide, the sign of the Kerr coefficient changes, and consequently the type of nonlinear response changes from softening to hardening. Furthermore, the cavity response exhibits superharmonic resonances when the ratio between the qubit frequency and the cavity fundamental mode frequency is tuned close to an integer value. The nonlinear response is characterized by the method of intermodulation and both signal and idler gains are measured. The experimental results are compared with theoretical predictions and good qualitative agreement is obtained. The superharmonic resonances have potential for applications in quantum amplification and generation of entangled states of light.

Coupling of Surface-Plasmon-Polariton-Hybridized Cavity Modes between Submicron Slits in a Thin Gold Film

Electron energy loss spectroscopy (EELS) in a monochromated transmission electron microscope is applied to probe standing-wave-like cavity modes hybridized with surface plasmon polaritons (SPP) in rectangular submicron slits in a thin gold film. Coupling of hybridized SPP-cavity modes between two adjacent slits is studied by systematically varying the width of the metal bar d that separates the identical slits in a two-slit system. Measurements on two-slit systems with different slit lengths L and fixed width reveal energy shifts and mode splitting of the fundamental SPP cavity mode which can be generally described as a function of a dimensionless scaling parameter L/d. Numerical simulations with the Discontinuous Galerkin Time-Domain (DGTD) method confirm the experimental data and reveal insights into the underlying complex coupling mechanisms.

Gain Spectroscopy of Solution‐Based Semiconductor Nanocrystals in Tunable Optical Microcavities

The lasing behavior of solution‐based colloidal quantum dots within an open microcavity is reported. The small size and wide tunability of the cavity provide single mode lasing over a wavelength range in excess of 25 nm. By extracting the lasing threshold and differential gain for the fundamental cavity mode over this spectral range, gain spectroscopy of the quantum dot solution is demonstrated. This new approach could help in the optimization of laser gain media and provides a way of constructing miniature laser arrays for on‐chip integration.

Dual-Band Textile MIMO Antenna Based on Substrate-Integrated Waveguide (SIW) Technology

A dual-band textile antenna for multiple-input–multiple-output (MIMO) applications, based on substrate-integrated waveguide (SIW) technology, is designed. The fundamental SIW cavity mode is designed to resonate at 2.4 GHz. Meanwhile, the second and third modes are modified and combined by careful placement of a via within the cavity to enable wideband coverage in the 5-GHz WLAN band. The simple antenna topology can be fabricated fully using textiles in a planar form, ensuring reliability and comfort. Numerical and experimental results indicate satisfactory antenna performance when worn on body in terms of impedance bandwidth, radiation efficiency, and specific absorption ratio (SAR). In order to validate its potential for MIMO applications, two elements of the proposed SIW antenna are arranged in six configurations to study the performance in terms of mutual coupling and envelope correlation. It is observed that the placement of the shorted edges of the two elements adjacent to each other produces the lowest mutual coupling and consequently the best envelope correlation.

Generation of Rabi-frequency radiation using exciton-polaritons

We study the use of exciton-polaritons in semiconductor microcavities to generate radiation spanning the infrared to terahertz regions of the spectrum by exploiting transitions between upper and lower polariton branches. The process, which is analogous to difference-frequency generation (DFG), relies on the use of semiconductors with a nonvanishing second-order susceptibility. For an organic microcavity composed of a nonlinear optical polymer, we predict a DFG irradiance enhancement of $2.8\cdot10^2$, as compared to a bare nonlinear polymer film, when triple resonance with the fundamental cavity mode is satisfied. In the case of an inorganic microcavity composed of (111) GaAs, an enhancement of $8.8\cdot10^3$ is found, as compared to a bare GaAs slab. Both structures show high wavelength tunability and relaxed design constraints due to the high modal overlap of polariton modes.

Beyond Strong Coupling in a Multimode Cavity

The study of light-matter interaction has seen a resurgence in recent years, stimulated by highly controllable, precise, and modular experiments in cavity quantum electrodynamics (QED). The achievement of strong coupling, where the coupling between a single atom and fundamental cavity mode exceeds the decay rates, was a major milestone that opened the doors to a multitude of new investigations. Here we introduce multimode strong coupling (MMSC), where the coupling is comparable to the free spectral range (FSR) of the cavity, i.e. the rate at which a qubit can absorb a photon from the cavity is comparable to the round trip transit rate of a photon in the cavity. We realize, via the circuit QED architecture, the first experiment accessing the MMSC regime, and report remarkably widespread and structured resonance fluorescence, whose origin extends beyond cavity enhancement of sidebands. Our results capture complex multimode, multiphoton processes, and the emergence of ultranarrow linewidths. Beyond the novel phenomena presented here, MMSC opens a major new direction in the exploration of light-matter interactions.

Resonant second harmonic generation in a gallium nitride two-dimensional photonic crystal on silicon

We demonstrate second harmonic generation in a gallium nitride photonic crystal cavity embedded in a two-dimensional free-standing photonic crystal platform on silicon. The photonic crystal nanocavity is optically pumped with a continuous-wave laser at telecom wavelengths in the transparency window of the nitride material. The harmonic generation is evidenced by the spectral range of the emitted signal, the quadratic power dependence vs. input power, and the spectral dependence of second harmonic signal. The harmonic emission pattern is correlated to the harmonic polarization generated by the second-order nonlinear susceptibilities χzxx(2), χzyy(2) and the electric fields of the fundamental cavity mode.

Analysis and alignment of the light path of Gauss beam matched to the fundamental mode ofan optical resonator

In order to reduce the influences of misalignment parameter and mismatch parameter on measurement based on optical resonator, the influence on the coupling efficiency of a source laser is stabilized to a fundamental cavity mode, and two limiting cases are analyzed and derived by using conversion of Gaussian beam, mode coupling theory and coordinate transformation theory, including the expression of coupling efficiency of fundamental cavity mode as two limiting cases emerge simultaneously. Analyses show that for mismatch parameter, only even-indexed Hermite-Gaussians beam is excited; for misalignment parameter, there exists an effect on the proportion of Hermite-Gaussians beam, which should bring about serious measurement error. These optical signals provide the error signals which are minimized. By taking the laser line width into account, we propose two methods for real time alignment of a Gaussian beam for an optical resonator perfectly coupled system: Fabry-Perot electro-optic sensors of a misadjusted system and control loops system depends on detecting emergent light of cavity via multi-dimensional quadrant detector. All of these will provide a theoretical direction for analyzing the measurement error and improving the measurement accuracy.

Diffraction-limited Fabry–Perot cavity in the near concentric regime

Nearly concentric optical cavities can be used to prepare optical fields with a very small mode volume. We implement an anaclastic design of such a cavity that significantly simplifies mode matching to the fundamental cavity mode. The cavity is shown to have diffraction-limited performance for a mode volume of . This is in sharp contrast with the behavior of cavities with plano-concave mirrors, where aberrations significantly decrease the coupling of the input mode to the fundamental mode of the cavity and increase the coupling to the higher-order modes. We estimate the related cavity quantum electrodynamics parameters and show that the proposed cavity design allows for strong coupling without a need for high finesse or small physical-cavity volume.