Mode Matching Conditions Research Articles

Output regulation for switched systems via dual distributed event-triggered mechanisms under multiple deception attacks

The secure output regulation (OR) is studied for networked switched systems (NSSs) that exhibit severely unstable dynamics (SUDs) and are vulnerable to multiple deception attacks. The occurrence of some destabilizing switching and unsolvable OR of each individual subsystem is permitted. Dual distributed event-triggered mechanisms (DDETMs) are proposed, incorporating both distributed event detection conditions to tackle the issue of unreliable single-channel data during deception attacks on sensor networks, and mode-matching detection conditions to reduce asynchronous intervals. A dwell time switching rule is developed without consistency constraint, i.e., the sub-controller's stabilizing/destabilizing switching may be inconsistent with that of the subsystem. Judging conditions are introduced for the occurrence of multiple deception attacks on dual-terminal sensor/transmission networks, which adjust the increment coefficients of Lyapunov functions before or after switching instants. Sufficient conditions are provided to ensure secure OR for NSSs under multiple deception attacks. With the aid of a switched RLC circuit, the effectiveness of the presented methodologies is validated.

Nonlinear photonics with metasurfaces

Nonlinear optics is a well-established field of research that traditionally relies on the interaction of light with macroscopic nonlinear media over distances significantly greater than the wavelength of light. However, the recently emerged field of optical metasurfaces provides a novel platform for studying nonlinear phenomena in planar geometries. Nonlinear optical metasurfaces introduce new functionalities to the field of nonlinear optics extending them beyond perturbative regimes of harmonic generation and parametric frequency conversion, being driven by mode-matching, resonances, and relaxed phase-matching conditions. Here we review the very recent advances in the rapidly developing field of nonlinear metasurface photonics, emphasizing multi-frequency and cascading effects, asymmetric and chiral frequency conversion, nonperturbative nonlinear regimes, and nonlinear quantum photonics, empowered by the physics of Mie resonances and optical bound states in the continuum.

Demonstration of length control for a filter cavity with coherent control sidebands

For broadband quantum noise reduction of gravitational-wave detectors, a frequency-dependent squeezed vacuum field realized using a filter cavity is the most promising technique and will be implemented in Advanced LIGO and Advanced Virgo in the fourth observing run. To obtain the benefit of frequency-dependent squeezing, the length and alignment of the filter cavity with respect to the squeezed vacuum field must be accurately controlled. To this purpose, a new length and alignment control scheme for a filter cavity, using coherent control sidebands, was suggested [Phys. Rev. D 102, 042003 (2020)]. The coherent control sidebands are already used to control the squeezing angle in squeezed vacuum sources for gravitational-wave detectors. As both the squeezed vacuum field and coherent control sidebands have the same mode-matching conditions and almost the same frequency, the length and alignment of the filter cavity with respect to the squeezed vacuum field can be accurately controlled with this scheme. In this paper, we experimentally demonstrate the new control scheme for a filter cavity with coherent control sidebands. In addition to the conventional filter cavity control with the green field, we succeed in controlling the length of a 300-m filter cavity with coherent control sidebands and reduce the filter cavity length noise (rms) from 6.8 to 2.1 pm.

Giant Enhancement of Second-Harmonic Generation in Hybrid Metasurface Coupled MoS2 with Fano-Resonance Effect

Plasmonic nanostructures have been regarded as potential candidates for boosting the nonlinear up-conversion rate at the nanoscale level due to their strong near-field enhancement and inherent high design freedom. Here, we design a hybrid metasurface to realize the moderate interaction of Fano resonance and create the dual-resonant mode-matching condition to facilitate the nonlinear process of second harmonic generation (SHG). The hybrid metasurface presents dipolar and octupolar plasmonic modes near the fundamental and doubled-frequency wavelengths, respectively, further utilized to enhance the SHG of low-dimensional MoS2 semiconductors. The maximum intensity of SHG in hybrid metasurface coupled MoS2 is more than ten thousand times larger than that of other structure-units coupled MoS2. The conversion efficiency is reported to be as high as 3.27 × 10−7. This work paves the way to optimize nonlinear light–matter interactions in low-dimensional structures coupled with semiconductors.

Polarization Dependent Scattering in Cavity Optomagnonics.

The polarization dependence of magnon-photon scattering in an optical microcavity is reported. Because of the short cavity length, the longitudinal mode-matching conditions found in previously explored, large path-length whispering gallery resonators are absent. Nonetheless, for cross-polarized scattering a strong and broadband suppression of one sideband is observed. This arises due to an interference between the Faraday and second-order Cotton-Mouton effects. To fully account for the suppression of the cross-polarized scattering, it is necessary to consider the squeezing of magnon modes intrinsic to thin-film geometry. A copolarized scattering due to Cotton-Mouton effect is also observed. In addition, the magnon modes involved are identified as Damon-Eshbach surface modes, whose nonreciprocal propagation could be exploited in device applications. This Letter experimentally demonstrates the important role of second-order Cotton-Mouton effect for optomagnonic devices.

Engineering gallium phosphide nanostructures for efficient nonlinear photonics and enhanced spectroscopies

Abstract Optical resonances arising from quasi-bound states in the continuum (QBICs) have been recently identified in nanostructured dielectrics, showing ultrahigh quality factors accompanied by very large electromagnetic field enhancements. In this work, we design a periodic array of gallium phosphide (GaP) elliptical cylinders supporting, concurrently, three spectrally separated QBIC resonances with in-plane magnetic dipole, out-of-plane magnetic dipole, and electric quadrupole characters. We numerically explore this system for second-harmonic generation and degenerate four-wave mixing, demonstrating giant per unit cell conversion efficiencies of up to ∼ 2 W−1 and ∼ 60 W−2, respectively, when considering realistic introduced asymmetries in the metasurface, compatible with current fabrication limitations. We find that this configuration outperforms by up to more than four orders of magnitude the response of low-Q Mie or anapole resonances in individual GaP nanoantennas with engineered nonlinear mode-matching conditions. Benefiting from the straight-oriented electric field of one of the examined high-Q resonances, we further propose a novel nanocavity design for enhanced spectroscopies by slotting the meta-atoms of the periodic array. We discover that the optical cavity sustains high-intensity fields homogeneously distributed inside the slot, delivering its best performance when the elliptical cylinders are cut from end to end forming a gap, which represents a convenient model for experimental investigations. When placing an electric point dipole inside the added aperture, we find that the metasurface offers ultrahigh radiative enhancements, exceeding the previously reported slotted dielectric nanodisk at the anapole excitation by more than two orders of magnitude.

Fiber-integrated microcavities for efficient generation of coherent acoustic phonons

Coherent phonon generation by optical pump-probe experiments has enabled the study of acoustic properties at the nanoscale in planar heterostructures, plasmonic resonators, micropillars, and nanowires. Focalizing both the pump and the probe on the same spot of the sample is a critical part of pump-probe experiments. This is particularly relevant in the case of small objects. The main practical challenges for the actual implementation of this technique are stability of the spatiotemporal overlap, reproducibility of the focalization, and optical mode matching conditions. In this work, we solve these three challenges for the case of planar and micropillar optophononic cavities. We integrate the studied samples to single mode fibers lifting the need for focusing optics to excite and detect coherent acoustic phonons. The resulting reflectivity contrast of at least 66% achieved in our samples allows us to observe stable coherent phonon signals over at least a full day and signals at an extremely low excitation power of 1 μW. The monolithic sample structure is transportable and could provide a means to perform reproducible plug-and-play experiments.

Chirped and apodized grating couplers on lithium niobate thin film

Chirped and apodized grating couplers were designed, fabricated and characterized in lithium niobate thin film for fiber-to-chip coupling. The maximum coupling efficiency of -1.8 dB and -6.9 dB for TE mode at a wavelength of 1550 nm was simulated and measured, respectively. The discrepancies were mainly attributed to the different fabrication errors of local periods and groove widths, which hampered the mode matching condition heavily. In addition, when a metal bottom reflector was added, the simulated and measured coupling efficiency were improved to -0.8 dB and -5.5 dB, respectively.

Control of a filter cavity with coherent control sidebands

For broadband quantum noise reduction of gravitational-wave detectors, frequency-dependent squeezed vacuum states realized using a filter cavity is a mature technique and will be implemented in Advanced LIGO and Advanced Virgo from the fourth observation run. To obtain the benefit of frequency-dependent squeezing, detuning and alignment of the filter cavity with respect to squeezed vacuum states must be controlled accurately. To this purpose, we suggest a new length and alignment control scheme, using coherent control sidebands which are already used to control the squeezing angle. Since both squeezed vacuum states and coherent control sidebands have the same mode matching conditions and almost the same frequency, detuning and alignment of the filter cavity can be controlled accurately with this scheme. In this paper, we show the principle of this scheme and its application to a gravitational-wave detector.

Second-harmonic generation with metal/dielectric/metal hybridized nanoantennas: enhanced efficiency, reduced mode volume and ideal magnetic/electric dipole scattering

Although nonlinear optical responses with high refractive index dielectric nanostructures benefit from the large mode volume of the Mie resonances, it is an obstacle to achieve ultra-compact devices compared with plasmonic nanostructures. Besides that, the nonlinear emissions for dielectric nanoparticles often possess complex multipolar contributions, which is not favorable for nonlinear far-field manipulating such as beam steering. This study numerically demonstrates that with the formation of mode-matching condition, the efficiency of second-harmonic generation with an Au/AlGaAs/Au hybridized sandwich nanodisk can be enhanced by two orders compared with a same size AlGaAs nanoparticle, and the mode volume is reduced by about two orders at the same time. What is more interesting is that the nonlinear sources and far-field scattering are tailored by the hybridized resonances, where an ideal magnetic (or electric) dipole scattering around a broadband spectral range is observed for the second-harmonic generation, which provides a reliable way to generate pure magnetic light and to manipulate the nonlinear far-field emissions. The realization of enhanced nonlinear efficiency, the reduced mode volume, the background-free responses, and the ideal magnetic/electric dipole scattering make the sandwich hybridized nanoparticle a promising platform for nonlinear nanophotonics.

Acoustic Plane Wave Diffraction from a Circular Soft Ring

The paper presents the implementation of the rigorous method of analytical regularization to the canonical problem of axially-symmetric diff raction from a soft ring. The series equations of the problem are reduced to an infinite series of linear algebraic equations (ISLAE) and the technique of analytical regularization is applied. Finally, the resulting matrix equation is the ISLAE of the second kind and can be solved numerically by the truncation method with any desired accuracy. The near field in the vicinity of the aperture of the ring is presented in the form of maps of the normalised total field. The far field features of the ring are obtained and discussed. The validation of our calculation is confirmed by testing of the mode matching conditions and through the comparison of the results with those for a disc.

Surface second-harmonic generation from metallic-nanoparticle configurations: A transformation-optics approach

We study surface second-harmonic generation (SHG) from a singular plasmonic structure consisting of touching metallic wires. We use the technique of transformation optics and relate the structure to a rather simpler geometry, a slab waveguide. This allows us to obtain an analytical solution to the problem, revealing rich physical insights. We identify various conditions that govern the SHG efficiency. Importantly, our analysis demonstrates that apart from the mode-matching condition, phase-matching condition is relevant even for this sub-wavelength structure. Furthermore, we identify a geometric factor which was not identified before. We support our analysis with numerical simulations.

High power, microjoule-level diffraction-limited picosecond oscillator based on Nd:GdVO4 bulk crystal

1.2 μJ pulses with average power of 9 W were directly generated from a passively mode-locked picosecond oscillator based on a Nd:GdVO4 bulk crystal. Short cavity operation in continuous wave and mode-locking regimes was conducted first to confirm the resonator performance and proper alignment. With a carefully calibrated q-preserving multi-pass cell inserted into the laser cavity, the cavity length of the original short cavity was extended while the mode-matching condition was maintained fairly well. Compared with the short cavity, nearly fivefold energy enhancement was achieved while the diffraction-limited beam quality was undisturbed. To the best of our knowledge, this is the highest output power ever produced from a mode-locked oscillator based on a single bulk crystal at a repetition rate below 10 MHz without cavity dumping.

Scattering of the plane acoustic wave from a finite hollow rigid cone at oblique incidence

AbstractThe paper deals with solving of the diffraction plane wave problem from a finite rigid hollow cone at oblique incidence. The diffraction problem is treated in terms of the scattering velocity potential by means of the mode matching technique and the analytical regularization procedure. The unknown expansion coefficients are found from an infinite system of linear algebraic equations of the second kind which allows us to obtain a solution with a desired accuracy. The influence of the cone parameters and angles of plane wave incidence on scattering characteristics of the cone is discussed. The obtained numerical results are verified by testing the satisfaction of the mode matching conditions and by comparing our calculations with those known for the rigid disc.

Design of a Dual Quantization Electromechanical Sigma–Delta Modulator MEMS Vibratory Wheel Gyroscope

This paper presents a dual quantization lateral-axis capacitive electromechanical sigma–delta modulator (EM- $\Sigma \Delta {\mathrm{ M}}$ ) vibratory wheel gyroscope under mode-matched condition. A symmetric wheel gyroscope structure was designed, fabricated, and wafer-level packaged under vacuum. The EM- $\Sigma \Delta {\mathrm{ M}}$ interface loop adopts a fourth-order multifeedback and local resonator $\Sigma \Delta {\mathrm{ M}}$ noise shaping structure, taking advantage of single-bit and multibit quantization in a single-loop modulator. To evaluate the influence of quantization noise, various numbers of bits of the multibit quantizator were compared and the optimal number of bits was calculated. The interface circuit system was implemented in hardware based on a low-noise front-end application-specified integrated circuit and a back-end discrete-time EM- $\Sigma \Delta {\mathrm{ M}}$ realized in a field-programmable gate array chip. The system clock was generated using a self-clocking scheme, which allows interfacing to gyroscope with a wide range of drive frequencies. Experimental evaluation indicated that the digital gyroscope system achieved a scale factor of 2073LSB(4.1 mV)/deg/s, with a nonlinearity of 0.046%, a noise floor of 3.1 m°/s/ $\surd $ Hz within a bandwidth of 100 Hz, and a bias instability of 1.3 deg/hr. [2017-0081]

Enhanced Second Harmonic Generation by Mode Matching in Gain-assisted Double-plasmonic Resonance Nanostructure

We theoretically study the gain-assisted double plasmonic resonances to enhance second harmonic generation (SHG) in a centrosymmetric multilayered silver-dielectric-gold-dielectric (SDGD) nanostructure. Introducing gain media into the dielectric layers can not only compensate the dissipation and lead to giant amplification of surface plasmons (SPs), but also excite local quadrupolar plasmon which can boost SHG by mode matching. Specifically, as the quadrupolar mode dominates SHG in our nanostructure, under the mode matching condition, the intensity of second harmonic near-field can be enhanced by 4.43 × 102 and 1.21 × 105 times when the super-resonance is matched only at the second harmonic (SH) frequency or fundamental frequency, respectively. Moreover, the intensity of SHG near-field is enhanced by as high as 6.55 × 107 times when the nanostructure is tuned to double super-resonances at both fundamental and SH frequencies. The findings in this work have potential applications in the design of nanosensors and nanolasers.

Triple-Resonant Brillouin Light Scattering in Magneto-Optical Cavities.

An enhancement in Brillouin light scattering of optical photons with magnons is demonstrated in magneto-optical whispering gallery mode resonators tuned to a triple-resonance point. This occurs when both the input and output optical modes are resonant with those of the whispering gallery resonator, with a separation given by the ferromagnetic resonance frequency. The identification and excitation of specific optical modes allows us to gain a clear understanding of the mode-matching conditions. A selection rule due to wave vector matching leads to an intrinsic single-sideband excitation. Strong suppression of one sideband is essential for one-to-one frequency mapping in coherent optical-to-microwave conversion.

Shaping propagation invariant laser beams

Propagation-invariant structured laser beams possess several unique properties and play an important role in various photonics applications. The majority of propagation invariant beams are produced in the form of laser modes emanating from stable laser cavities. Therefore, their spatial structure is limited by the intracavity mode formation. We show that several types of anamorphic optical systems (AOSs) can be effectively employed to shape laser beams into a variety of propagation invariant structured fields with different shapes and phase distributions. We present a propagation matrix approach for designing AOSs and defining mode-matching conditions required for preserving propagation invariance of the output shaped fields. The propagation matrix approach was selected, as it provides a more straightforward approach in designing AOSs for shaping propagation-invariant laser beams than the alternative technique based on the Gouy phase evolution, especially in the case of multielement AOSs. Several practical configurations of optical systems that are suitable for shaping input laser beams into a diverse variety of structured propagation invariant laser beams are also presented. The laser beam shaping approach was applied by modeling propagation characteristics of several input laser beam types, including Hermite–Gaussian, Laguerre–Gaussian, and Ince–Gaussian structured field distributions. The influence of the Ince–Gaussian beam semifocal separation parameter and the azimuthal orientation between the input laser beams and the AOSs onto the resulting shape of the propagation invariant laser beams is presented as well.

Ho:KLuW microchip laser intracavity pumped by a diode-pumped Tm:KLuW laser

A compact intracavity-pumped microchip Ho laser is realized using stacked Tm:KLuW/Ho:KLuW crystals pumped by a laser diode at 805 nm; both crystals are cut for light propagation along the N g optical indicatrix axis and emit with polarization along the N m axis. Maximum CW output power of 285 mW is achieved at a wavelength of 2080 nm for 5.6 W absorbed pump power in the Tm:KLuW crystal with a maximum slope efficiency of 8.3 %. Maximum total (Tm3+ and Ho3+ emission) output of 887 mW with a slope efficiency of 23 % is achieved. Laser operation is obtained in the 1867–1900 nm spectral range corresponding to the Tm emission, while Ho emits at 2078–2100 nm, depending on the output coupling. The microchip Ho laser generates a near-circular output beam with M 2 < 1.1. The compact laser setup with plane–plane cavity provides automatic mode-matching condition for the Tm and Ho laser modes.

Mapping the Influence of Acoustic Resonators on Rocket Engine Combustion Stability

A mode-based, acoustic low-order network model for rocket chambers with resonator ring is introduced. This model involves effects of dissipation as well as scattering and mode coupling associated with a resonator ring. Discontinuities at the interface between acoustic elements are treated with integral mode-matching conditions. Eigenfrequencies and accordingly the linear system stability can be determined with the generalized Nyquist plot method based on the network model. Because of low computational cost, parameter studies can be performed in a reasonable time. An additional chamber eigenmode is observed for well-tuned resonators. Both the original and the additional mode show favorable stability properties for a generic test chamber. The optimal length and number of cavities are identified for that chamber. The need for analyzing the coupled system of resonators and combustion chamber in the design process is made evident by the discrepancy between detected values and those of an a priori consideration. Derived stability maps demonstrate that the region of stable operation is increased considerably by inserting well-tuned resonators. The destabilizing influence of temperature deviations in the cavities is quantified. Such sensitivities to modifications of design conditions can be extenuated by a ring configuration with several nonidentical resonator types. Moreover, the strong impact of the nonlinear correlation factor in the resonator modeling on the overall system stability is worked out.