Increase In Q-factor Research Articles

Second harmonic generation in an anisotropic lithium niobate metasurface governed by quasi-BICs

Resonant metasurfaces can greatly trap the light fields, so that they are widely used to enhance light–matter interactions at the nanoscale, such as promoting nonlinear effects of materials. Lithium niobate (LN) is an excellent nonlinear optical material and is often employed to generate harmonic signals. In this Letter, we numerically study the second harmonic generation (SHG) characteristics of the LN metasurface based on the quasi-bound states in the continuum (QBIC). The designed BIC and excited QBIC metasurfaces always hold C4v symmetry, and the BIC is demonstrated to degenerate into two BICs due to the anisotropic characteristics of LN. Moreover, the excited two high Q-factor QBICs can effectively enhance the SHG in LN, although the device maintains C4v symmetry, the SHG signal still shows polarization dependence. In addition, with the increase of Q-factor of quasi-BIC, the power and conversion efficiency (η) of SHG increase significantly. The calculated η can reach 6.04 × 10−3 and can be further improved when the resonance mode is closer to BIC. These results have important implications for high-quality nonlinear light sources based on LN materials.

Characterization of Nano-Structured Magnesium-Aluminum Ferrites Synthesized by Citrate-Gel Auto Combustion Method

An effort is made to find the solution to the new challenges of modification advancements in ferrite technologies. The hypothetical variation in the structural, magnetic, and electrical properties of cubic spinel magnesium aluminum ferrites introduced by the substitution of doping elements has been rationalized and proven. The outcome of aluminum substitution on the magnesium ferrites has been examined and investigated. Spinel ferrites having compositions of MgAlxFe2-xO4 (x = 0.1, 0.2, 0.3, 0.4) were prepared by the sol-gel auto-combustion method. The prepared sample’s characterization, such as scanning electron microscopy (SEM), DC electrical resistivity, AC electrical resistivity, and dielectric properties measurements, were tested using the respective instruments. The grain size and crystal size of all samples were measured from the micrographs of SEM and XRD Data. It is found that the average grain size is within the range of 300 nm - 550 nm for all different series that are formed, keeping the samples at 1100 °C sintering temperatures. A two-probe method experiment with a temperature range of 30 °C to 500 °C gives data on DC electrical resistivity. The Curie temperature depends on the sintering temperature, and it increases with increasing doping concentration. Also, doping influences grain size, which decreases with increasing concentration. Analyzing the SEM micrographs, it is found that the average grain size must decrease in tendency with increasing Al content. DC electrical resistivity exhibits excellent semiconducting behavior. Frequency dependence, dielectric constant, and dielectric loss factors were measured, keeping the frequency range of 75 Hz to 130 MHz at room temperature. The result shows that the dielectric constant (e) and dielectric loss tangent (tan™) decrease with the increase in frequency, while the AC resistivity and Q-factor increase. Comparing the electrical properties of four compositions, it can be suggested that the mixed ferrite, sample-4 (x = 0.3), shows the highest Q-factor of all at 1100 °C.

Light–matter interaction beyond Born–Oppenheimer approximation mediated by stimulated phonon polaritons

For decades, the light-matter interaction (LMI) based on Born-Oppenheimer (BO) approximation has dominated the fields of photonics, materials, and condensed-matter physics. However, in polar crystals, the BO approximation is not applicable when stimulated phonon polaritons are excited. Unlike the studies on topological physics and physical chemistry that go beyond BO approximation, here we unravel a stimulated phonon polariton-mediated LMI mechanism in polar crystals, which is radically different from the traditional LMI interpreted by BO approximation. In the regime of stimulated phonon polariton-mediated LMI, two exemplary experiments were conducted at different wavelengths: Q-factor increase of a LiNbO3 terahertz microcavity, and a five orders-of-magnitude enhancement of second-harmonic generation of infrared laser pulses in a LiNbO3 slab. Our study enhances the understanding of the LMI mechanism and shows potential for applications in the fields of optics/photonics and condensed-matter physics.

Effective handling of nonlinear distortions in CO-OFDM using affinity propagation clustering.

We experimentally demonstrate a system-agnostic and training-data-free nonlinearity compensator, using affinity propagation (AP) clustering in single- and multi-channel coherent optical OFDM (CO-OFDM) for up to 3200 km transmission. We show that AP outperforms benchmark deterministic and clustering algorithms by effectively tackling stochastic nonlinear distortions and inter-channel nonlinearities. AP offers up to almost 4 dB power margin extension over linear equalization in single-channel 16-quadrature amplitude-modulated CO-OFDM and a 1.4 dB increase in Q-factor over digital back-propagation in multi-channel quaternary phase-shift keying CO-OFDM. Simulated results indicate transparency to higher modulation format orders and better efficiency when a multi-carrier structure is considered.

Novel High-Q Partially Air-Filled Pedestal Resonator and Filter Integrated in a Printed Circuit Board (PCB)

In this paper, a resonator and second order filter are fabricated using a novel technological process based on micromachining and thermo-diffusion. The use of this innovative process opens the way to the design of RF components relying on partially air-filled Substrate Integrated Waveguides (SIW). These topologies and particularly the proposed partially air-filled pedestal SIW resonator is suitable to design high-Q, yet compact SIW resonators. In this paper, a study of partially air-filled pedestal SIW resonator is proposed to offer an optimized trade-off between Q-factor and compactness. Then, based on this study, a partially air-filled pedestal resonator working at 5 GHz is designed and manufactured. The measured prototype exhibits a Q-factor of 285, which represents a 53 % increase in Q-factor compared to a fully dielectrically-filled-in pedestal SIW resonator, while the size is kept constant. Finally, a second order filter based on this resonator topology is also designed, measured and discussed.

Artificial Neural Network Symbol Estimator With Enhanced Robustness to Nonlinear Phase Noise

This letter reports a novel approach for nonlinear phase noise mitigation, based on artificial neural networks (ANNs) tailored to classification applications and a pre-processing stage of feature engineering. Starting with a set of proof-of-concept simulations, we verify that the proposed system can achieve optimal performance for the additive white Gaussian noise (AWGN) channel. Then, considering a dispersion-less channel with strong nonlinear phase noise (NLPN) distortion, we demonstrate a Q-factor increase of 0.4dB, comparing with standard carrier-phase estimation (CPE) followed by minimum distance detection. Finally, simulating the propagation of 64Gbaud PM-16QAM over standard single mode fiber (SSMF), we verify that the ANN-based solution is effective on wavelength-division multiplexing (WDM) transmission conditions, enabling to increase the maximum signal reach by approximately 1 fiber span over the legacy CPE-enabled NLPN compensation.

Numerical comparison between DPSK 33, DPSK 66 and duo binary in WOC system

OWC systems have turned into a state-of-the-art technology because of their superior performance uniqueness and its innumerable characteristic as compared to its RF. One of the OWC application is inter-satellite wireless optical communication (Is-WOC), this framework can be improved by using different ways such as advanced modulation formats and aperture diameter. We demonstrate an analysis based on the aperture diameter effect in transmission of single channel with 40 Gb/s Is-WOC system using three different modulation methods, differential phase-shift keying (DPSK) with a duty ratio to 66% and 33% and duobinary. Choosing these three modulations from various modulation format is done depending on the advantage they provide where the DPSK gives to fiber nonlinearity a powerful robustness and less susceptible to SPM and XPM and for system requirements of dispersion compensation in duobinary, it provides higher chromatic dispersion tolerance mitigate. The result shows the effect of different transmitter aperture diameter (from 2 to 20 cm) for a constant distance 200 km accomplished by quality factor and minimum BER. We conclude there is a great loss in the small aperture diameter, even in the presence of best modulation format, therefore as the aperture diameter increase the Q-factor increase, but some increased rise is linear and the other is changing from linear to non-linear in a fixed Q-factor point equal to 5.63.

Використання резонансного короткозамикаючого поршня у перестроюваних хвилевідно-діелектричних та хвилевідно-коаксіальних резонаторах на циліндричних позамежних хвилеводах

Subject and Purpose. Tunable resonant structures make numerous microwave devices, among which are waveguide-dielectric and waveguide-coaxial resonators (WDR and WCR) built around cylindrical evanescent waveguides and involving a resonant short-circuit (RSC) plunger for tuning purposes. The present paper seeks to study specific features of the RSC-plunger operation in the evanescent waveguide and estimate the RSC-plunger efficiency. Method and Methodology. The RSC-plunger efficiency is approximately estimated in terms of the transmission line theory. Comparative experimental verification of the Q-factor increase is provided by an example of a 3 cm WDR resonator equipped with a RSC-plunger. Results. It has been shown that relevant formulae of the transmission line theory can be extended for the RSC-plunger efficiency estimation on the TEM and H11 oscillations. A possibility has been studied of the TEM type transformation to the H11 oscillation and back when the spurious resonance of the RSC-plunger falls within the WDR (WCR) tuning range. Conclusion. Insignificance of the effect that small deviations from the numerically predicted dimensions of the RSC-plunger exert on the RSC-plunger operation efficiency has been demonstrated. The RSC-plunger efficiency and a possibility to remove the spurious resonances from the resonator tuning range have been experimentally confirmed.

Propagation of longitudinal waves in a single‐walled carbon nanotube under thermoelastic damping

The propagation of the longitudinal waves in a single-walled carbon nanotube (SWCNT) considering the effects of thermoelastic damping is investigated in this Letter. The cylindrical shell is considered and the Donnell–Mushtari–Vlasov approach is utilised. The thermoelasticity governing equations are derived based on thin shell theory. Analytical expressions for the quality factor (Q-factor) of thermoelastic damping are presented for plane stress and strain conditions. The numerical results are presented to investigate the influence of some parameters on Q-factor of thermoelastic damping, such as the length of a nanotube, nanotube thickness and the ambient temperature. In addition, the dispersion curve of the longitudinal waves propagation in the SWCNT under the effects of thermoelastic damping is plotted. It can be seen that the Q-factor is proportional to the length and thickness of the SWCNT. It means that the increase in both length and radial thickness of the nanotube makes the Q-factor increase. For the final observation, it should be noted that the ambient temperature has an inverse effect on the Q-factor for the SWCNT. It means that the increase in ambient temperature makes the Q-factor decrease. These results can be helpful in the design of resonators and nanodevices.

Effect of Q-factor manipulation via pedal spacers on lower limb frontal plane kinematics during cycling

Anecdotal evidence suggests that frontal plane kinematics of the lower extremity are an important aspect of bicycle fit, however, frontal plane adjustments are often overlooked during common fitting procedures. The purpose of this study was to manipulate Q-factor width via pedal spacers to determine their influence on frontal plane kinematics of the hip, knee, and ankle during cycling. Twenty-four young healthy recreational cyclists (12 female) completed five minutes of pedaling at their preferred cadence and power output under three stance widths conditions: no spacer, 20 mm spacer, and 30 mm spacer. For each participant, the pedaling cadence and power output were kept identical for all experimental conditions. Lower extremity marker position data were captured at 250 Hz for the last two minutes of each condition. Sixty consecutive crank cycles were analyzed to identify maximum and minimum hip, knee, and ankle angles in the frontal plane. With an increase in Q-factor, hip and knee maximum abduction angles increased and maximum adduction angles decreased. With increase in Q-factor from no spacer to 20 mm spacer condition, hip abduction increased by 0.8o (∆10%; p<0.001) whereas hip abduction decreased by 0.9o (∆23%; p<0.001) and similarly, knee abduction increased by 1.2o (∆60%; p=0.002) whereas knee abduction decreased by 1.1o (∆18%; p=0.003). And with increase in Q-factor from no spacer to 30 mm spacer condition, hip abduction increased by 1.4o (∆18%; p<0.001) and hip adduction decreased by 1.6o (∆40%; p<0.001) and similarly, knee abduction increased by 1.8o (∆86%; p<0.001) and knee adduction decreased by 2.1o (∆35%; p<0.001). Maximum and minimum ankle angles were not affected by the stance width conditions (p>0.05). Pedal spacers are an effective way of manipulating Q-factor and frontal plane kinematics of the hip and knee and could help cyclists experiencing medial or lateral knee pain.

Upper bound of efficiency for Smith-Purcell emission and evanescent-to-propagating wave conversion in metal-groove metasurfaces

When a charged particle moves parallel and close to the surface of a metasurface, intense Smith-Purcell radiation can be observed at resonant frequencies. Here, we present a systematic investigation on the Smith-Purcell radiation and evanescent-to-propagating wave conversion in metal-groove metasurfaces. Based on a coupled mode theory, analytic formulas are derived for the resonant frequency, Q-factor, and wave conversion efficiency at resonant frequency. The accuracy of the formulas is verified by numerical simulations. It is found that the resonant frequency and Q-factor depend on the depth and filling ratio of the grooves, respectively. A high Q-factor can be obtained by decreasing the filling ratio of the grooves. As the Q-factor increases, the wave conversion efficiency at resonant frequency increase but exhibits an upper limit. Such an upper bound of efficiency (Cr,max = 4) can be approached at a moderate Q-factor (Q = 16) or an optimal filling ratio of the grooves (fs = 0.05). Our results may benefit the construction of compact high-power free-electron light sources.

Transmitter Aperture Diameter Effect in 40 Gb/s Inter-Satellite Optical Wireless Communication System

Optical wireless communication systems have turned into a state-of-the-art technology because of their superior performance uniqueness and innumerable characteristics, as compared to radio frequency. One optical wireless communication application is Inter-Satellite Optical Wireless Communication. Inter-Satellite Optical Wireless Communication systems can be improved by using, for example, advanced modulation formats and adjusting the aperture diameters. We demonstrate an analysis based on the aperture diameter effect in the transmission of a single channel using a 40 Gb/s Inter-Satellite Optical Wireless Communication system and three different modulation methods, specifically differential phase-shift keying with a duty ratio of 66% or 33% and duobinary. These three modulations were chosen among various modulation formats due to the advantages they provide, i.e., the differential phase-shift keying provides stronger robustness to fiber nonlinearity and duobinary provides higher chromatic dispersion tolerance to mitigate the system requirements for dispersion compensation. The results show the effect of different transmitter aperture diameters (from 2 to 20 cm) at a constant distance (200 km) in terms of the quality factor and minimum Bit Error Rate. We conclude there is a great loss in the small aperture diameter, even in the presence of the best modulation format; therefore, as the aperture diameter increases the Q-factor increases, but some of the increased rise is linear and some changes from linear to non-linear at a fixed Q-factor point equal to 5.63.

Bidirectional Network in Hybrid Coarse Wavelength Division Multiplexing/Time Division Multiplexing (CWDM/TDM) on NG-PON2 for 40 Gbps

In this research, we propose hybrid Coarse Wavelength Division Multiplexing/Time Division Multiplexing (CWDM/TDM)-Passive Optical Networks (PON) scheme for optimizing the new technology of Gigabit-PON (GPON) called Next Generation-PON Stage 2 (NG-PON2). The simulation of using this scheme proved that Q-Factor increase and Bit Error Rate (BER) decreased, significantly. We use CWDM scheme for downstream while TDM is used for upstream, and we assimilate both of them with new configuration in bidirectional cable setting. CWDM is used due to low nonlinearity effect like Kerr effects. It has the same working principle based on (Time Wavelength Division Multiplexing-PON) TWDM-PON by differentiating the use of wavelength, it can be easily implemented on existing PON technology, and can be used in single-mode optical fiber (SMF) with greater bandwidth and much cheaper operational costs. From the calculations and simulations, it can be analyzed that the network Hybrid of CWDM / TDM-PON able to work on bit rate of 40/10 Gbps on the number of users 32, 64, and 128, with Q-Factor value is above 6 equal to International Telecommunication Union of Telecommunication (ITU-T) standard. The number of users 32 with two cable lengths of 10 and 20 km have value of Q-Factor 25.960 and 14.815 respectively, while64 users with the same cable length have Q-Factor value of 15.808 and 13.046 respectively. In addition, 128 users with the same cable length have BER value of 17.778 and 12.944 respectively.

Direct excitation of a series resonant circuit by rectangular voltage pulses. Analysis, numerical evaluation

Expansion of the use of resonance phenomena in high-effective electrical devices requires detailed consideration of the processes occurring in them. Devices that include a sequential active-reactive circuit are particularly interesting. Such devices allow obtaining multiple power amplification when selecting the appropriate parameters. The purpose of this work is to analyze the direct resonant excitation of a sequential active-reactive circuit with periodic series of rectangular unipolar or oscillating voltage pulses with a resonant frequency of their repetition and, accordingly, to determine its response to excitation. As a result of solving the corresponding problem, differential equations are formulated. Their solution was carried out using an operator method and expressions for currents excited in the circuit were obtained. It is shown that the first harmonic in the amplitude-frequency decomposition, both in the case of unipolar and in the case of oscillating excitation, determines the harmonic component of the excited current with a frequency equal to the resonant frequency and an amplitude equal to the ratio of the amplitude of the first harmonic of the exciting voltage and active resistance of the series resonant circuit. A slightly higher efficiency of unipolar excitation of harmonic processes is noted in comparison with excitation by oscillating sequences of periodic voltage pulses. It is shown that, both in the case of unipolar and oscillating excitation, the contribution of higher spectral components, regardless of the type of input voltage, decreases significantly with increasing Q-factor of the resonant circuit, and with a significant increase in Q-factor, the excited current becomes strictly harmonic.

Tunable Supermode Dielectric Resonators for Axion Dark-Matter Haloscopes

We present frequency tuning mechanisms for dielectric resonators, which undergo "super-mode" interactions as they tune. The tunable schemes are based on dielectric materials strategically placed inside traditional cylindrical resonant cavities, necessarily operating in Transverse Magnetic modes for use in axion haloscopes. The first technique is based on multiple dielectric disks with radii smaller than that of the cavity. The second scheme relies on hollow dielectric cylinders similar to a Bragg resonator, but of different location and dimension. In particular we engineer a significant increase in form factor for the TM030 mode utilising a variation of a Distributed Bragg Reflector Resonator. Additionally, we demonstrate application of traditional Distributed Bragg Reflectors in TM modes, which may be applied to a haloscope. This is the first demonstration of Bragg resonators applied to TM modes, as well as the first application of super-modes to tune Bragg resonators, or haloscope resonators. Theory and experimental results are presented showing an increase in Q-factor and tunability due to the super-mode effect. The TM030 ring resonator mode offers between 1 and 2-orders-of-magnitude improvement in axion sensitivity over current conventional cavity systems and will be employed in the forthcoming ORGAN experiment.

Q-factor enhancement of piezoelectric MEMS resonators in liquids with active feedback

For a precise determination of the density and viscosity of liquids with MEMS resonators, a high Q-factor is of utmost importance. In such environments, in-plane resonant modes offer a lower damping compared to out-of-plane modes, thus allowing to quantify the increase in Q-factor with and without electrical feedback directly. To stimulate an in-plane oscillation, a sputter deposited aluminum nitride layer on a silicon cantilever is driven by a Lock-In amplifier which is adjusted by the feedback signal originating from the piezoelectric thin film. The exposure to selected liquids, ranging from ethanol to N35 with a dynamic viscosity from 1.2mPas up to 73.2mPas, features at room temperature intrinsic Q-factors of about 40 and 8, respectively. With a carefully designed amplification circuit, the Q-factors are increased by a factor of 1.4 up to 9.3, which represents Q-factors of 374–12, demonstrating the high potential especially at low viscous liquids.

A 5x16 Gbps DWDM system for ground-to-satellite using RZ signaling scheme under different turbulences

Dense Wavelength Division Multiplexing (DWDM) is one of the hopeful and ultimate solution using an eye safety wavelength for proper utilization of bandwidth and increasing capacity. In this paper, we demonstrate a 5×16 GB/s DWDM system with frequency spacing of 100 GHz is done in case of clear weather conditions and turbulence incorporated in the channel for a distance of 38500 km. Our studies show that Q-factor increase with increase in transmitted optical power and decreases with increase in increasing turbulence effects.

The influence of the Goos–Hänchen effect on seismic data processing and AVO in attenuating media

The Goos–Hänchen (GH) effect induced by the total reflection of an incident beam of P-wave from a low-impedance medium to a high-impedance medium at near- and post-critical angles was theoretically simulated and discussed. For both PP- and PSV-waves, there may be large GH shifts (GHS) and penetration depths (PD) for both lossless and attenuating media. As the Q-factor increases, or the frequency of the seismic wave decreases, the GH effect is increased. However, in attenuating media, there may be non-zero GHS and PD at all non-zero incident angles, not just post-critical angles. GHS may be either positive or negative, while PD is positive only. Compared to the Q-factor in the incident medium, the Q-factor in the transmission medium may play a more dominant role in the determination of reflection coefficients, GHS, and PD. The GH-induced normal moveout (NMO) discrepancy of the PSV-wave may be larger than that of the PP-wave. Due to the GH effect, there may be an angle discrepancy (at fixed offset) between the GH-modified incident angle and the traditional incident angle. In addition, the GH effect at a given offset may produce two or three reflected waves, from different incident angles. These results suggest that, within their assumptions, the GH effect may lead to errors in NMO estimates and the vertical location of the reflector. Furthermore, there may be errors in offsets, incident angles, and reflection amplitudes, in the analyses of the amplitude variation with offset (AVO). These GH effects might be more important for seismic data at fixed offsets and shallow layers, and for sonic log data, which might fall into the post-critical angle regime. Therefore, there may be a necessity to take into account the GH effect in the interpretation of wide-angle reflection data in NMO and AVO analyses.

Improvement in inductance and Q-factor by laser microstructuring of ferromagnetic on-chip thin film inductors

In this work, we examine the potential improvement in inductance (L) and quality factor (Q) of on-chip ferromagnetic thin film inductors through the formation of conical microstructures by localized ultraviolet laser irradiation on ferromagnetic thin film. Parameters affecting L and Q, and arising from the surface modification upon laser irradiation include thickness of the film, size, and density of the structures. The thickness of the film is optimized to 0.2 μm, and at least 18% increase in inductance and 25% increase in Q-factor for NiFe thin film in comparison to the conventional spiral inductor is expected. L and Q values of NiFe films with and without microstructuring are compared, and a 7% increase is predicted for the microstrucired film. The proposed fabrication process, including the laser microstructuring technique, is likely to provide a significant flexibility, cost effectiveness and even better parameters, if other material systems are considered.

Study of thermally-induced optical bistability and the role of surface treatments in Si-based mid-infrared photonic crystal cavities

We report the observation of optical bistability in Si-based photonic crystal cavities operating around 4.5 µm. Time domain measurements indicate that the source of this optical bistability is thermal, with a time constant on the order of 5 µs. Quality (Q) factor improvement is shown by the use of surface treatments (wet processes and annealing), resulting in a significant increase in Q-factor, which in our best devices is on the order of ~45,000 at 4.48 µm. After annealing in a N(2) environment, optical bistability is no longer seen in our cavities.