Large Quality Factor Research Articles

High-Q nanobeam cavities on a silicon nitride platform enabled by slow light

Silicon nitride integrated photonic devices benefit from a wide working spectral range covering the visible and near-infrared spectra, which in turn enables important applications in bio-photonics, optical communications, and sensing. High-quality factor optical resonators are essential photonic devices for such applications. However, implementing such resonators on a silicon nitride platform is quite challenging due to the low refractive index contrast attainable with this material. Here, we demonstrate that silicon nitride photonic cavities comprising a slow-light waveguide bounded by mirrors can in principle exhibit quality factors in the order of several millions despite a relatively low refractive index contrast. We show that the energy stored in such a slow-light cavity exhibits a cubic dependence on the cavity length, which can enable extremely large quality factors with modest-length cavities. We present the design and experimental characterization of silicon nitride slow-light nanobeam-type cavities. Two sets of nanobeam cavities were fabricated to experimentally verify the cubic dependence of the Q factor on the cavity length. The highest measured Q factor in our devices is 4.42 × 105, which is limited by fabrication imperfections.

High Fill Factor Array of Piezoelectric Micromachined Ultrasonic Transducers with Large Quality Factor

High Fill Factor Array of Piezoelectric Micromachined Ultrasonic Transducers with Large Quality Factor

Effect of structural design on the electrical, optical and mechanical properties of flexible BaSnO3–Ag composite thin films

Barium stannate (BaSnO3, BS) and silver composite thin films are deposited on flexible polyethylene terephthalate (PET) substrates by magnetron sputtering. The effects of structural design on electrical and optical properties of the BS/Ag/BS tri-layer flexible thin films are investigated systematically. The BS layers can enhance the transmittance significantly, due to the fact that reflection of light from the Ag layer and PET substrate can be suppressed by BS layers. The tri-layer thin films show the high figure of merit of 16.66 × 10−3 Ω−1 and the large commutation quality factor of 197, while the average optical transmittance in the visible light range is above 84% and the sheet resistance is 10.52 Ω/sq. In addition, the flexible tri-layer thin films show outstanding mechanical flexibility, adhesion to PET substrate and stability at high temperature.

Magic-intensity trapping of the Mg lattice clock with light shift suppressed below 10−19

Progress in atomic optical clocks with total uncertainty of $10^{-18}$ or below requires a precise estimation of multipolar and higher-order effects due to atom-field interactions. Magnesium is an attractive candidate for optical lattice clocks because it is insensitive to blackbody radiation and has a large quality factor. We employ a combined method of the Dirac-Fock plus core polarization and the relativistic configuration interaction to calculate the dynamic multipolar polarizabilities and the hyperpolarizabilities of the atomic Mg clock. The lattice light shift against variation of the laser detuning and trap depth is also investigated. We find that there exists a distinctive operational magic lattice intensity of $5.33(2)E_R$ ($E_R$ is the lattice photon recoil energy) that reduces the total light shift below $1\times 10^{-19}$ over 14\% of the trap depth variation, which will pave the way for the development of a new time-frequency standard of the Mg lattice clock.

High coherence collapse of a hybrid III–V/Si semiconductor laser with a large quality factor

The high-speed dynamics of a hybrid distributed feedback semiconductor laser heterogeneously integrated onto silicon is experimentally investigated in the presence of external optical feedback. The laser fabrication relies on a proper modal engineering in which light is generated in the III–V material and stored in the low-loss silicon region in order to substantially enhance the quality factor of the cavity resonator. In this work, the hybrid laser is found to be insensitive to parasitic reflections leading to a 10 Gbps floor-free transmission with a power penalty no greater than 1.5 dB at room temperature. As a conclusion, owing to the large quality factor, a high coherence collapse level is unveiled in such laser indicating its vast potential to serve as an alternative solution for the development of isolator-free applications in future photonics integrated circuits. A qualitative interpretation is also provided by linking the standard feedback equations to the quality factor of the resonator.

Shape anisotropy effects on spin-torque oscillators

Spin-torque oscillators are promising candidates for hard disk drive read head sensors, neuromorphic computing, and telecommunications due to their frequency tunability by a direct current or a magnetic field. A narrow linewidth and a large quality factor are of great importance for these applications. Previous studies have indicated that the spin-torque oscillation linewidth depends on the temperature, current, and in-plane field angle. Here, we have investigated the spin-torque oscillations in MgO-based magnetic tunnel junctions (MTJs) and demonstrated the impact of the MTJ shape anisotropy on the threshold current. Our experimental results suggest that due to different threshold currents, the linewidth is different in the MTJs with different shape anisotropy, which might be significant for device optimization.

Monolithic high-contrast grating planar microcavities

Abstract Semiconductor planar microcavities significantly enhance the interaction between light and matter and are thus crucial as a fundamental research platform for investigations of quantum information processing, quantum dynamics, and exciton-polariton observations. Microcavities also serve as a very agile basis for modern resonant-cavity light-emitting and detecting devices now in large-scale production for applications in sensing and communication. The fabrication of microcavity devices composed of both common materials now used in photonics and uncommon or arbitrary materials that are new to photonics offers great freedom in the exploration of the functionalities of novel microcavity device concepts. Here we propose and carefully investigate two unique microcavity designs. The first design uses a monolithic high-index-contrast grating (MHCG) and a distributed Bragg reflector (DBR) as the microcavity mirrors. The second design uses two MHCGs as the microcavity mirrors. We demonstrate by numerical analysis that MHCG-DBR and MHCG-MHCG microcavities, whose lateral radial dimension is 16 μm, reach very large quality factors at the level of 104 and nearly 106, as well as purposely designed wavelength tuning ranges of 8 and 60 nm in both configurations, respectively. Our MHCG-MHCG microcavities with a very small size of 600 nm in the vertical dimension show extremely large quality factors, which can be explained by treating the optical modes as quasi-bound states in a continuum (BICs). Moreover, we verify our theoretical analysis and calibrate our simulation parameters by comparing to the experimental characteristics of an electrically injected MHCG-DBR microcavity vertical-cavity surface-emitting laser (VCSEL) emitting at a peak wavelength of about 980 nm. We use the calibrated parameters to simulate the emission characteristics of electrically injected VCSELs in various MHCG-DBR and MHCG-MHCG microcavity configurations to illustrate the influence of microcavity designs and their quality factors on the predicted lasing properties of the devices.

Echoes in brane worlds: Ringing at a black hole-wormhole transition

Echoes are known as modifications of the usual quasinormal ringing of a black hole at late times because of the deviation of space-time from the initial black-hole geometry in a small region near its event horizon. We consider a class of brane-world model solutions of the Shiromizu-Maeda-Sasaki equations, which describe both black holes and wormholes and interpolate between them via a continuous parameter. In this way the brane-world scenario provides a natural model for wormholes mimicking the black hole behavior if the continuous parameter is chosen near the threshold with a black-hole solution. We show that in the vicinity of this threshold interpolating between black holes and wormholes, quasinormal ringing of the wormholes at the initial stage is indistinguishable from that of the black holes with nearby values of the above parameter, but at later times the signal is modified by intensive echoes. We notice that the black-hole mimickers that are wormholes near the threshold have the largest quality factor and are therefore the best oscillators among the considered examples.

Toroidal metasurfaces in a 2D flatland

A toroidal dipole is a new class of electromagnetic excitations and are different from traditional electric and magnetic dipoles. Toroidal dipoles are described by the poloidal currents flowing on the surface of torus and have opened a new route to control radiative losses via near field coupling mechanism or radiation cancellation approach in the unit cell of metasurface. Radiative loss engineering in metamaterials is one of the most fundamental requirements to gauge the suitability of a metaphotonic device for a specific on-demand application. Here, we discuss strategies to excite toroidal dipolar modes in a planar metasurface which were initially thought to exist only in three-dimensional (3D) arrangements. Two dimensional (2D) toroidal metasurfaces are conceptual simplification of 3D toroid configurations, which pose fabrication challenges at micro-nanoscales. We further discuss the destructive interference between electric and toroidal dipoles to realize non-radiating modes in the form of an anapole excitation that fulfills the requirement for the excitation of extremely large quality factor resonances. Overall, the intriguing features of a toroidal dipole could have significant implications on the design of resonant metamaterials that are important for the development of low-loss sensors, modulators, filters, and efficient cavities for strong light matter interactions.

Single layer diamond - A new ultrathin 2D carbon nanostructure for mechanical resonator

The single layer diamond – diamane, a two-dimensional (2D) form of diamond with a bilayer sp3 carbon nanostructure, has been initially predicted in 2009, while its experimental synthesis has only been reported very recently. This work carries out a comprehensive study on the vibrational properties of diamane nanoribbon (DNR) targeting the ultra-sensitive sensing applications. Based on in silico studies, it is found that the DNR resonator possesses a higher natural frequency and a large quality factor (Q-factor) on the order of 105 higher than those of a bilayer nanoribbon resonator. Under pre-tensile strain, the natural frequency of the DNR resonator receives a remarkable increase and its Q-factor maintains a high magnitude yielding to an extremely high figure of merit on the order of 1015. It is further found that the randomly distributed surface hydrogenation exerts negligible influence on the vibrational properties of the DNR resonator. However, an unevenly distributed hydrogenation results in out-of-plane deformation and significantly changes its vibrational properties. It is additionally found that the stacking configuration of the diamane leads to negligible influence on its vibrational properties. This study reveals that the DNR resonator has excellent vibrational properties, which are promising for the construction of ultra-sensitive resonator-based sensors.

Graphene hybridized ultrahigh-Q high-order Fano resonance for nanoscale optical sensing

We propose an ultranarrow high-order Fano resonance generated by the plasmonic coupling between a hybridized quadrupole mode formed by plasmon hybridization of graphene nanoribbon dimer and a broad magnetic dipole mode from metallic split rings in a hybrid metamaterial. The results reveal that the high-order Fano curve is very narrow and indicates a large quality (Q) factor of 110. The ultrahigh-Q high-order Fano resonance can be convenient tailored by tuning Fermi levels and structural parameters. Our designed ultrahigh-Q hybrid metamaterial exhibits a high optical sensitivity of 4 μm/RIU and figure of merit (FOM) of 44, which is very helpful to design high-sensitive sensors.

Cavity QED based on room temperature atoms interacting with a photonic crystal cavity: a feasibility study

The paradigm of cavity QED is a two-level emitter interacting with a high-quality factor single-mode optical resonator. The hybridization of the emitter and photon wave functions mandates large vacuum Rabi frequencies and long coherence times; features that so far have been successfully realized with trapped cold atoms and ions, and localized solid-state quantum emitters such as superconducting circuits, quantum dots, and color centers Reiserer and Rempe (Rev Modern Phys 87:1379, 2015), Faraon et al. (Phys Rev 81:033838, 2010). Thermal atoms, on the other hand, provide us with a dense emitter ensemble and in comparison to the cold systems are more compatible with integration, hence enabling large-scale quantum systems. However, their thermal motion and large transit-time broadening is a major bottleneck that has to be circumvented. A promising remedy could benefit from the highly controllable and tunable electromagnetic fields of a nano-photonic cavity with strong local electric-field enhancements. Utilizing this feature, here we investigate the interaction between fast moving thermal atoms and a nano-beam photonic crystal cavity (PCC) with large quality factor and small mode volume. Through fully quantum mechanical calculations, including Casimir–Polder potential (i.e. the effect of the surface on radiation properties of an atom), we show, when designed properly, the achievable coupling between the flying atom and the cavity photon would be strong enough to lead to quantum interference effects in spite of short interaction times. In addition, the time-resolved detection of different trajectories can be used to identify single and multiple atom counts. This probabilistic approach will find applications in cavity QED studies in dense atomic media and paves the way towards realizing large-scale, room-temperature macroscopic quantum systems aimed at out of the lab quantum devices.

Strong light-matter coupling in dielectric metasurfaces

We demonstrate the strong coupling between excitons in organic molecules and all-dielectric metasurfaces formed by arrays of silicon nanoparticles supporting Mie surface lattice resonances (MSLRs). Compared to Mie resonances in individual nanoparticles, MSLRs have extended mode volumes and much larger quality factors, which enables to achieve collective strong coupling with very large coupling strengths and Rabi energies. Moreover, due to the electric and magnetic character of the MSLR given by the Mie resonance, we show that the hybridization of the exciton with the MSLR results in exciton-polaritons that inherit this character as well. Our results demonstrate the potential of all-dielectric metasurfaces as novel platform to investigate and manipulate exciton-polaritons in low-loss polaritonic devices.

Near‐Unity and Narrowband Thermal Emissivity in Balanced Dielectric Metasurfaces

AbstractNanostructured materials have provided new freedoms for tailoring thermal emissivity in an ultracompact footprint. However, while many designs have demonstrated large absorption amplitude, this often comes at the expense of angular dispersion or the need for a reflective backplane. Furthermore, metal‐based designs generally have broad linewidths due to large nonradiative damping. Here, a unique approach is outlined for obtaining narrowband near‐unity thermal emissivity through spectrally overlapping two orthogonal lossy Mie‐type modes in dielectric metasurfaces operating in the long‐wave infrared. Operating near the transverse optic phonon frequency of a polar dielectric provides a suitably lossy environment, but also one featuring extremely large permittivity, enabling deeply subwavelength resonator sizes, insensitivity to the angle of incidence, and large quality factors even while operating in the long‐wave infrared. Balancing the oscillator strengths and optical losses of the two overlapped resonances maximizes the absorption, resulting in a 3C‐SiC metasurface with 78% absorptance and a quality factor of 170. This balanced metasurface possesses a quality factor on par with some of the narrowest band thermal emitters in the long‐wave infrared, while possessing a simple architecture and prospects for unity emissivity.

Novel terahertz metasurfaces based on complementary coupled split ring resonators

In this paper, we propose a terahertz metasurface unit cell based on an efficient coupling between two completely symmetric complementary split-ring resonators via a coupling slot. This coupling allows the excitation of a dark eigenmode resonance that is otherwise forbidden. In turn, the radiation losses are highly suppressed and the excited eigenmode features a quite large quality factor. Interestingly, this kind of coupling leads to the restoration of the symmetry of the unit cell of the coupled resonators with respect to the terahertz field illumination. More importantly, we show that the quality factor of this dark mode resonance can be tuned by modifying the coupling slot length and reach a high value of 67.4. Furthermore, a laser beam machining technique can be easily exploited during the fabrication process of this design. Besides using this design as a sharp bandpass filter, it can be utilized as an efficient biosensor. We show that a sensitivity level of 6.3 × 104 nm/RIU is indeed doable using the proposed structure. This design may emerge as a potential candidate for future biosensors and hence utilized during the development of new cancer biomarkers.

Graphene enabled dynamic tuning of the surface lattice mode for broadband infrared light modulation

Narrowband perfect absorbers based on surface plasmon polariton resonance have been mainly used in label free sensing due to large quality factors and high surface sensitivities. In this work, it is proposed and theoretically demonstrated that narrowband perfect absorbers combined with graphene are capable of broadband mid-IR light modulation. A large intensity modulation depth over 90% can be obtained in the wavelength range from 5µm to 6µm, which is 2.5-fold enhanced compared with that of a broadband perfect absorber. Phase modulation application has also been demonstrated, and a tuning range of 180° is achievable. The influences of structure parameters on modulation performance are discussed at last using coupled mode theory.

High temperature stability and mechanical quality factor of donor-acceptor co-doped BaTiO3 piezoelectrics

Low temperature stability has limited the applications at elevated temperature for ABO3-type lead-free ceramics. And multi-grade resonances of piezoelectric ceramics are hardly obtained although the resonances are very important in some applications such as filter and resonator. High piezoelectric properties and large mechanical quality factors with multi-grade resonances can be obtained in (Li+-La3+) co-doped BaTiO3 ceramics, and excellent temperature stabilities are achieved in the ceramics. It has been shown that the thermal treatments both with and without electric field at 200 °C improve the piezoelectric properties and thermal stability further. Large piezoelectric constant (272 pC N1) and huge mechanical quality factor (2010) was obtained after thermal-electrical treatment, which is caused by Li+-La3+ ionic pair aligning along the external electric filed during thermal-electrical treatment. Moreover, the present study provides an effective method to design combination properties with high temperature stability for ABO3 perovskite ferroelectric ceramics.

All‐Dielectric Active Terahertz Photonics Driven by Bound States in the Continuum

The remarkable emergence of all-dielectric meta-photonics governed by the physics of high-index dielectric materials offers a low-loss platform for efficient manipulation and subwavelength control of electromagnetic waves from microwaves to visible frequencies. Dielectric metasurfaces can focus electromagnetic waves, generate structured beams and vortices, enhance local fields for advanced sensing, and provide novel functionalities for classical and quantum technologies. Recent advances in meta-photonics are associated with the exploration of exotic electromagnetic modes called the bound states in the continuum (BICs), which offer a simple interference mechanism to achieve large quality factors (Q) through excitation of supercavity modes in dielectric nanostructures and resonant metasurfaces. Here, a BIC-driven terahertz metasurface with dynamic control of high-Q silicon supercavities that are reconfigurable at a nanosecond timescale is experimentally demonstrated. It is revealed that such supercavities enable low-power, optically induced terahertz switching and modulation of sharp resonances for potential applications in lasing, mode multiplexing, and biosensing.

Large Q Factor with Very Small Whispering-Gallery-Mode Resonators

Efficient micro-resonators simultaneously require a large quality factor $Q$ and a small volume $V$. However, the former is ultimately limited by bending losses, the unavoidable radiation of energy of a wave upon changing direction of propagation. Such bending losses increase exponentially as $V$ decreases and eventually result in a drop of $Q$. Therefore, circular cavities are generally designed with radii that are much larger than the optical wavelength. The same leakage of energy by radiation limits the sharpness of bends in photonic integrated circuits. In this article, we present a way to reduce bending losses in circular micro-resonators. The proposed scheme consists of one or more external dielectric rings that are concentric with the cavity. These rings alter the field outside the cavity where radial oscillations set in, and thus control the far field radiation. As a result, the $Q$ factor can be increased by several orders of magnitude while keeping a small cavity volume.

Air-Coupled and Resonant Pulse-Echo Ultrasonic Technique.

An ultrasonic, resonant, pulse-echo, and air-coupled nondestructive testing (NDT) technique is presented. It is intended for components, with regular geometries where it is possible to excite resonant modes, made of materials that have a high acoustic impedance (Z) and low attenuation coefficient (α). Under these conditions, these resonances will present a very large quality factor (Q) and decay time (τ). This feature is used to avoid the dead zone, produced by the echo coming from the first wall, by receiving the resonant echo from the whole specimen over a longer period of time. This echo is analyzed in the frequency domain to determine specimen resonant frequency, which can be further used to determine either velocity or thickness. Using wideband air-coupled transducers, we tested the technique on plates (steel, aluminum, and silicone rubber) by exciting the mode of the first thickness. As expected, the higher the Z and the lower the α, the better the technique performed. Sensitivity to deviations of the angle of incidence away from normal (±2°) and the possibility to generate shear waves were also studied. Then, it was tested on steel cylindrical pipes that had different wall thicknesses and diameters. Finally, the use of this technique to generate C-Scan images of steel plates with different thicknesses was demonstrated.