Fundamental Resonator Research Articles

Studies on Dual Helmholtz Resonators and Asymmetric Waveguides for Ventilated Soundproofing.

Achieving the simultaneity of ventilation and soundproofing is a significant challenge in applied acoustics. Ventilated soundproofing relies on the interplay between local resonance and nonlocal coupling of acoustic waves within a sub-wavelength structure. However, previously studied structures possess limited types of fundamental resonators and lack modifications from the basic arrangement. These constraints often force the specified position of each attenuation peak and low absorption performance. Here, we suggest the in-duct-type sound barrier with dual Helmholtz resonators, which are positioned around the symmetry-breaking waveguides. The numerical simulations for curated dimensions and scattered fields show the aperiodic migrations and effective amplifications of the two absorptive domains. Collaborating with the subsequent reflective domains, the designed structure holds two effective attenuation bands under the first Fabry-Pérot resonance frequency. This study would serve as a valuable example for understanding the local and non-local behaviors of sub-wavelength resonating structures. Additionally, it could be applied in selective noise absorption and reflection more flexibly.

Characteristics of high-contrast gratings based spoof surface plasmon polaritons and the application in microwave all-dielectric metamaterial absorbers

High-contrast gratings (HCGs) based spoof surface plasmon polaritons (SSPPs), as a new kind of SSPPs, have been proposed recently. Here, we study their particular mechanism and characteristics by comparing them with traditional metal-type SSPPs. The different fundamental dielectric resonator modes decided by the height–length ratio R of the dielectric element are found to be the key factor of the mechanism, leading to new characteristics and providing more working modes. In low R mode, HCG-based SSPPs can work under deep-subwavelength thickness and can be easily excited by free space wave and, thus, are considered to be applied to all-dielectric metamaterial absorbers (ADMMAs). Simulations and analysis confirm the microwave absorption effect of HCG-based SSPPs as a new mechanism of ADMMAs. Based on this, a carbon black based ADMMA is designed and the simulation and experimental results verify the important role of HCG-based SSPPs in broadband absorption. It is expected that this work can give rise to further and wider studies on the characteristics and applications of HCG-based SSPPs.

Single-longitudinal-mode cascaded crystalline Raman laser at 1.7 µm.

A single-longitudinal-mode crystalline Raman laser in the 1.7 µm wave band was reported for the first time, to the best of our knowledge. The YVO4 Raman laser, which was intracavity-pumped by an actively Q-switched 1314 nm Nd:YLF laser, demonstrated the cascaded Stokes oscillation at 1715 nm. By inserting an etalon in the fundamental resonator, linewidth narrowing and power scaling of the second-Stokes laser were realized based on the spatial-hole-burning-free Raman gain. With an optimal pulse repetition frequency of 4 kHz, the maximum single-longitudinal-mode average output power of 1.8 W was acquired with the spectrum linewidth of ∼340MHz. Further increasing the incident pump power, the second-Stokes laser transitioned to multimode regime, and the maximum average output power reached 2.7 W with the peak power as high as ∼380kW.

High-peak-power narrowband eye-safe intracavity Raman laser.

We demonstrated a narrowband eye-safe intracavity Raman laser by incorporating a fused silica etalon into the fundamental resonator. The KGd(WO4)2 (KGW) Raman laser was pumped by an actively Q-switched Nd:YLF laser at 1314 nm. Thanks to the KGW bi-axial properties, two distinct eye-safe Raman lasers operating at 1461 and 1490 nm were obtained separately by rotation of the KGW crystal. At an optimized pulse repetition frequency of 4 kHz, the maximum average output powers of 3.6 and 4.0 W were achieved with the peak powers up to approximately 330 and 480 kW, respectively. The eye-safe Stokes emissions were narrow linewidth (∼0.05 nm FWHM; measurement limited) and near diffraction limited (M2 < 1.4). The powerful narrowband eye-safe Raman lasers are of interest for applications as diverse as laser range finding, scanning lidar and remote sensing.

A Harmonic-Tuned VCO With an Intrinsic-High-Q F23 Inductor in 65-nm CMOS

A harmonic-tuned (HT) voltage-controlled oscillator in a 65-nm CMOS process is demonstrated in this letter. The oscillation frequency and harmonics are tuned independently by two separated high- $Q$ resonators. A novel F23 inductor–capacitor resonator resonating at the second and third harmonics simultaneously is introduced. The proposed F23 inductor has a high-quality factor of 15 and 24 in common-mode (CM) and differential-mode (DM), respectively. The simulation results show that a 4.3-dB phase noise (PN) improvement is achieved in the thermal noise region due to the high- $Q$ HT method. Meanwhile, less harmonic currents are injected into the fundamental resonator due to the source-degeneration principle, hence decreasing the Groszkowski effect and suppressing the flicker noise. The measured PN is −117.5 dBc/Hz at the 1-MHz offset, and the tuning range is 12% from 6.80 to 7.66 GHz. The flicker noise corner is around 220 kHz and the figure-of-merit is 187.2 dBc/Hz. The power consumption is 5 mW under a 0.55-V supply.

Waveguide Filters With Central-Post Resonators

In this letter, a class of rectangular waveguide filters with central-post resonators is introduced. By introducing a central post in an oversized rectangular cavity, the resonant frequency of TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">301</sub> -mode can be brought close to that of TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">201</sub> -mode. The two resonant modes are coupled to adjacent fundamental mode resonators by inductive irises. A doublet coupling topology can be used to model the physical configuration, and flexible filter responses with finite-position transmission zeros (TZs) can be realized. Four 4-pole filters with different TZ positions are designed and simulated. A seven-pole filter with two cascaded central-post resonators is fabricated and measured. In the seven-pole filter, each central-post resonator independently controls one TZ on the lower side and very close to the passband. The measurement results of the seven-pole filter agree with the simulated counterparts very well, thus validating this filter design technique.

Enhancement of Intracavity-Pumped Terahertz Parametric Oscillator Power by Adopting Diode-Side Pumped Configuration Based on KTiOPO4 Crystal

In this paper, a KTiOPO4 (KTP) crystal is used as the nonlinear medium in an intracavity-pumped terahertz parametric oscillator (TPO) based on stimulated polariton scattering (SPS). Almost all the reported intracavity SPS sources adopt the diode-end pumped configuration, and the THz output power is limited by the serious thermal effect and small fundamental beam size. For improving the THz output power, we propose diode-side pumping for the laser medium to get a higher fundamental power and a larger fundamental beam size. A convex–plane fundamental laser resonator is used to further offset the thermal effect and increase the fundamental beam size. The THz frequency of the intracavity-pumped KTP terahertz parametric oscillator can be discontinuously tuned from 3.19 THz to 5.94 THz with three gaps. The fundamental beam diameter in the KTP crystal is about 1.3 mm. The maximum average THz power is 166 μW at 5.74 THz under a pulse repetition frequency (PRF) of 6 kHz and a diode pump power of 98 W. By means of the diode-side pumped configuration, the maximum THz output power is more than two-fold higher compared to the diode-end pumped configuration reported using the KTP crystal.

A design of ± 0.28 ppm temperature-compensated crystal oscillator in a 0.35 μm CMOS process

A high-performance temperature-compensated crystal oscillator (TCXO) is presented. This paper proposes a new temperature sensor with a Σ–Δ analog to digital converter, and a voltage-controlled crystal oscillator, respectively, using two sets of independent power supply. The presented TCXO is implemented in a 0.35 μm 2P3 M standard complementary metal-oxide semiconductor process at a power supply of 3.3 V, and the total power dissipation is 21 mW. Measurement results indicate that the designed TCXO achieves ± 16 ppm output frequency tuning range and 135, − 141 dBc/Hz phase noise at 1, 10 kHz frequency offset, respectively, by using a 40 MHz fundamental AT-cut crystal resonator. With the temperature compensation, the frequency deviation is within ± 0.28 ppm over − 40 °C to 85 °C.

Broadband Lamb shift in an engineered quantum system

The shift of energy levels owing to broadband electromagnetic vacuum fluctuations, the Lamb shift, has been pivotal in the development of quantum electrodynamics and in understanding atomic spectra. Currently, small energy shifts in engineered quantum systems are of paramount importance owing to the extreme precision requirements in applications such as quantum computing. However, without a tunable environment it is challenging to resolve the Lamb shift in its original broadband case. Consequently, the observations in other than atomic systems are limited to environments comprised of narrow-band modes. Here, we observe a broadband Lamb shift in high-quality superconducting resonators, a scenario also accessing static shifts inaccessible in Lamb's experiment. We measure a continuous change of several megahertz in the fundamental resonator frequency by externally tuning the coupling strength of the engineered broadband environment which is based on hybrid normal-metal--superconductor tunnel junctions. Our results may lead to improved control of dissipation in high-quality engineered quantum systems and open new possibilities for studying synthetic open quantum matter using this hybrid experimental platform.

Wavelength tuning and power enhancement of an intracavity Nd:GdVO4-BaWO4 Raman laser using an etalon.

We report the wavelength tuning, linewidth narrowing and power enhancement of a continuous-wave intracavity Raman laser by incorporating solid etalons in the high-Q fundamental resonator. With a-cut Nd:GdVO4 and a-cut BaWO4 serving as the laser and Raman crystals respectively, tilting of a 50 μm-thick etalon in the high-Q fundamental cavity enabled the fundamental to be tuned from 1061.00 nm to 1065.20 nm. This gave rise to Stokes output which was tunable from 1176.46 nm to 1181.63 nm whilst the narrowed fundamental linewidth resulted in higher effective Raman gain and as a consequence enhanced output power, as well as the narrow-linewidth Stokes output. Frequency-doubling of the Stokes field resulted in yellow output tunable from 588.23 nm to 590.81 nm, which covers the guide star wavelength of 589.16 nm.

Cascaded crystalline Raman lasers for extended wavelength coverage: continuous-wave, third-Stokes operation

The development of high-power laser sources with narrow emission, tunable within the water transmission window around 1.7 μm, is of interest for applications as diverse as medical imaging and atmospheric sensing. Where suitable laser gain media are not available, operation in this spectral region is often achieved via nonlinear frequency conversion, and optical parametric oscillators (OPOs) are a common solution. A practical alternative to OPOs, to avoid birefringent- or quasi-phase-matching requirements, is the use of stimulated Raman scattering within a suitable material to convert a pump source to longer wavelengths via one or more Stokes shifts; however, as this is a χ(3) nonlinear process, such frequency conversion is usually the preserve of high-energy pulsed lasers. Semiconductor disk lasers (SDLs), on the other hand, have very high-finesse external resonators, suitable for efficient intracavity nonlinear conversion even in continuous-wave (CW) operation. Here we report, to the best of our knowledge, the first continuous-wave third-Stokes crystalline Raman laser and the longest emission wavelength from an SDL-pumped Raman laser, achieving high power, CW output, and broad wavelength tuning around 1.73 μm. The KGd(WO4)2 (KGW) Raman laser, which was intracavity-pumped by a 1.18 μm InGaAs-based SDL, demonstrated cascaded CW Stokes oscillation at 1.32 μm, 1.50 μm, and 1.73 μm with watt-level output achievable at each wavelength. The 1.73 μm Stokes emission was diffraction limited (M2<1.01) and narrow linewidth (<46 pm FWHM; measurement limited). By rotation of a birefringent filter placed within the fundamental resonator, we attained three tunable emission wavelength bands, one centred at each Stokes component, and achieved up to 65 nm tuning for the third-Stokes Raman laser from 1696 nm to 1761 nm. We have thus demonstrated a platform laser technology that takes well-developed InGaAs-based SDLs and provides spectral coverage and high performance in the near-infrared water transmission windows using commercially available components.

3D-Printed Low-Cost Dielectric-Resonator-Based Ultra-Broadband Microwave Absorber Using Carbon-Loaded Acrylonitrile Butadiene Styrene Polymer.

In this study, an ultra-broadband dielectric-resonator-based absorber for microwave absorption is numerically and experimentally investigated. The designed absorber is made of the carbon-loaded Acrylonitrile Butadiene Styrene (ABS) polymer and fabricated using the 3D printing technology based on fused deposition modeling with a quite low cost. Profiting from the fundamental dielectric resonator (DR) mode, the higher order DR mode and the grating mode of the dielectric resonator, the absorber shows an absorptivity higher than 90% over the whole ultra-broad operating band from 3.9 to 12 GHz. The relative bandwidth can reach over 100% and cover the whole C-band (4–8 GHz) and X-band (8–12 GHz). Utilizing the numerical simulation, we have discussed the working principle of the absorber in detail. What is more, the absorption performance under different incident angles is also simulated, and the results indicate that the absorber exhibits a high absorptivity at a wide angle of incidence. The advantages of low cost, ultra-broad operating band and a wide-angle feature make the absorber promising in the areas of microwave measurement, stealth technology and energy harvesting.

Performance Evaluation of Integrated Semiconductor Ring Laser Gyroscope

We present a mathematical analysis and comparison of the performance of integrated on-chip semiconductor ring laser gyroscope (SRLG) fabricated using GaAs/AlGaAs and InP/InGaAsP technologies. The performance parameters of the gyro are modeled in terms of fundamental material, waveguide, and resonator parameters. In addition to this, influence of phenomena specific to semiconductor lasers such as nonlinear coupling, spatial hole burning, gain grating formation, and carrier induced index change on the gyro performance is also included. The analysis helps in identifying critical parameters, which must be optimized to improve the gyro performance.Best achievable performance of integrated SRLG is calculated, and design modifications are suggested to enhance it for high-performance military applications.

Intracavity CH 4 Raman laser using negative-branch unstable resonator

An intracavity Q-switched Nd:YAG/CH4 Raman laser is realized based on the configuration of a negative-branch confocal unstable resonator. A numerical model of the bare resonator was introduced to simulate the fundamental transverse mode and calculate the loss of the fundamental resonator. With different magnifications of the fundamental resonator, the first Stokes output energy was presented as a function of the discharge voltage. The influence of the Stokes resonator on Raman conversion was analyzed. With a fundamental resonator magnification of 1.1, a maximum output energy of 58 mJ was obtained, and the corresponding photon conversion efficiency was 48%.

Wavelength shifting of intra-cavity photons: Adiabatic wavelength tuning in rapidly wavelength-swept lasers.

We analyze the physics behind the newest generation of rapidly wavelength tunable sources for optical coherence tomography (OCT), retaining a single longitudinal cavity mode during operation without repeated build up of lasing. In this context, we theoretically investigate the currently existing concepts of rapidly wavelength-swept lasers based on tuning of the cavity length or refractive index, leading to an altered optical path length inside the resonator. Specifically, we consider vertical-cavity surface-emitting lasers (VCSELs) with microelectromechanical system (MEMS) mirrors as well as Fourier domain mode-locked (FDML) and Vernier-tuned distributed Bragg reflector (VT-DBR) lasers. Based on heuristic arguments and exact analytical solutions of Maxwell's equations for a fundamental laser resonator model, we show that adiabatic wavelength tuning is achieved, i.e., hopping between cavity modes associated with a repeated build up of lasing is avoided, and the photon number is conserved. As a consequence, no fundamental limit exists for the wavelength tuning speed, in principle enabling wide-range wavelength sweeps at arbitrary tuning speeds with narrow instantaneous linewidth.

A differential coupled frequency doubling voltage-controlled crystal oscillator in a 0.35 μm CMOS process

This paper presents a high-performance differential coupled frequency doubling voltage-controlled crystal oscillator (VCXO). Frequency doubling and low phase noise are realized through a novel gm-boosted differential Colpitts oscillator. Distributed varactor arrays are used to obtain wide frequency tuning range and high tuning linearity simultaneously. The proposed VCXO is fabricated in a 0.35 μm 2P3M standard complementary metal-oxide semiconductor process at a supply voltage of 3.3 V, and the power dissipation is 7 mW. Measurement results show that the designed VCXO achieves ±135 ppm output frequency variation range with 5 % linearity and ?133 dBc/Hz phase noise at 1 kHz frequency offset by using a 40 MHz fundamental AT-cut crystal resonator.

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.

LD-side-pumped Nd:YAG/BaWO4 intracavity Raman laser for anti-Stokes generation

A diode-side-pumped actively Q-switched Nd:YAG/BaWO4 intracavity anti-Stokes Raman laser is demonstrated for the first time. The oscillation directions of the fundamental and the Stokes beams are separated at a phase-matching angle by introducing an additional coupled Raman cavity in the fundamental resonator. The highest 968nm anti-Stokes output power of 0.94mW is obtained with a 170W 808nm pumping power and a 7.5kHz pulse repetition frequency. Meanwhile, the Stokes power obtained is 4.2W.

A high electromechanical coupling coefficient SH0 Lamb wave lithium niobate micromechanical resonator and a method for fabrication

We present a high coupling coefficient, keff2, micromechanical resonator based on the propagation of SH0 Lamb waves in thin, suspended plates of single crystal X-cut lithium niobate (LiNbO3). The thin plates are fabricated using ion implantation of He to create a damaged layer of LiNbO3 below the wafer surface. This damaged layer is selectively wet etched in a hydrofluoric (HF) acid based chemistry to form thin, suspended plates of LiNbO3 without the wafer bonding, layer fracturing and chemical mechanical polishing in previously reported LiNbO3 microfabrication approaches. The highest coupling coefficient is found for resonators with acoustic propagation rotated 170° from the y-axis, where a fundamental mode SH0 Lamb wave resonator with a plate width of 20μm and a corresponding resonant frequency of 101MHz achieves a keff2 of 12.4%, a quality factor of 1300 and a resonator figure of merit (M) of 185. The keff2 and M are among the highest reported for micromechanical resonators.

Practical Strategies for Stable Operation of HFF-QCM in Continuous Air Flow

Currently there are a few fields of application using quartz crystal microbalances (QCM). Because of environmental conditions and insufficient resolution of the microbalance, chemical sensing of volatile organic compounds in an open system was as yet not possible. In this study we present strategies on how to use 195 MHz fundamental quartz resonators for a mobile sensor platform to detect airborne analytes. Commonly the use of devices with a resonant frequency of about 10 MHz is standard. By increasing the frequency to 195 MHz the frequency shift increases by a factor of almost 400. Unfortunately, such kinds of quartz crystals tend to exhibit some challenges to obtain a reasonable signal-to-noise ratio. It was possible to reduce the noise in frequency in a continuous air flow of 7.5 m/s to 0.4 Hz [i.e., σ(τ) = 2 × 10−9] by elucidating the major source of noise. The air flow in the vicinity of the quartz was analyzed to reduce turbulences. Furthermore, we found a dependency between the acceleration sensitivity and mechanical stress induced by an internal thermal gradient. By reducing this gradient, we achieved reduction of the sensitivity to acceleration by more than one decade. Hence, the resulting sensor is more robust to environmental conditions such as temperature, acceleration and air flow.