Single-frequency Oscillation Research Articles

Periodic Model Containing Coupled Subsystems with Different Types of Oscillations

We consider a periodic model containing coupled subsystems (MCCS), which, when the coupling between subsystems vanishes, decomposes into systems of autonomous ordinary differential equations. We assume that the subsystems admit different types of non-degenerate single-frequency oscillations. We solve the problems of the existence of oscillations in the MCCS, their stability, natural stabilization of MCCS oscillations by smooth time-periodic coupling controls. We also provide an example.

Effect of a Low-Frequency Noise Signal on the Supply Circuit of the Millimeter-Band Generator of Single-Frequency and Chaotic Oscillations Designed on an Avalanche Transit-Time Diode

The effect of a low-frequency noise signal on the supply circuit of a millimeter-band generator of single-frequency and chaotic oscillations designed on an avalanche transit-time diode has been experimentally investigated. Generation of noise oscillations under the action of a low-frequency narrowband (~3 MHz) noise signal on the supply circuit of an avalanche transit-time diode in a single-frequency self-oscillator based on a 7-millimeter-wave avalanche transit-time diode has been obtained for the first time and the possibility of control of the spectral characteristic of a 8-millimeter-band noise generator on an avalanche transit-time diode zusing such an impact has been demonstrated.

Fast and Accurate THz Permittivity Measurement Using a Self-Heterodyne Technique and Multitone Signal With Nonuniform Intervals

A permittivity measurement system operating in the terahertz waveband around 300 GHz achieves fast measurement by using a self-heterodyne technique to measure phase differences. Errors are reduced because a multitone technique with nonuniform frequency intervals enables us to apply a phase-unwrapping method to the self-heterodyne system. For multitone signal generation, just single-frequency oscillators and local oscillator leakage from a modulator are used. The system achieves a measurement time of 0.03 ms at one point, which is 1/200 compared to a conventional system using a vector network analyzer. With the same measurement time, the maximum measurement error can be reduced to less than half compared to the conventional two-tone self-heterodyne system.

Dynamics of Power Pulses in a Research Reactor with Neptunium Nuclear Fuel

The current trend in neutron-aided scientific research presupposes the development of new high-intensity pulsed sources. One variant of such an installation could be a pulsed reactor with a fissile-isotope core – 237Np. The present work is devoted to a study of the dynamics of power pulses of a neptunium reactor taking account of fast temperature feedback during pulse buildup. The problem is reduced to a simple model of a single frequency oscillator combined with the equation of single point kinetics of a reactor neglecting delayed neutrons. It is shown that on the basis of such an approximation, owing to feedback on the temperature of a fuel element the estimated energy of accidental power pulses decreases by almost a factor of 10 compared with a calculation neglecting fast feedback.

Generation & control of chaos in a single loop optoelectronic oscillator

We present a detailed study on the dynamics of a single Loop optoelectronic Oscillator (SLOEO), with the variation of feedback loop delay. The feedback delay can be varied by changing the length of the optical fiber delay line. From the numerical study it is observed that with the variation of the delay the oscillator produces chaotic oscillation following the sequence of Hopf bifurcation, stable periodic and period doubling oscillation. In OEO, incrementing the feedback loop delay increases the number of neighboring modes. The effect of these modes on the dynamics of the OEO is reported through simulation study. It has been seen that due to the generation of additional modes, instability grows in the system and the oscillator changes its state from periodic to chaotic oscillation. Consequently the effect of periodic external synchronizing signal is studied in the chaotic OEO. It is observed that application of an external periodic signal with suitably chosen amplitude and frequency can destroy the chaotic oscillation and produce single frequency oscillation. This mechanism has an additional advantage in the reduction of phase noise with regard to the use of larger delay in the loop. Moreover, the sync. signal increases the effective quality factor (Q) of the circuit thereby reducing the deleterious effect of phase noise.

Stabilization of oscillations in a coupled periodic system

Consideration was given to a model containing two coupled autonomous planar subsystems of differential equations. It was assumed that the subsystems admitted families of nondegenerate single-frequency oscillations, and coupling was described by time-periodic functions. Solved was the problem of natural stabilization of system oscillations, where by natural stabilization was meant construction of an isolated oscillation and its concurrent stabilization. Constructive conditions for smooth periodic coupling controls providing problem solution were derived. Specific control was proposed for coupled conservative systems with one degree of freedom.

The effect of a low-frequency noise signal on a single-frequency millimeter-band oscillator based on an avalanche-transit diode

Noise-wave generation in a single-frequency oscillator based on a 7-mm-band avalanche-transit diode has been implemented for the first time under the action of a low-frequency narrow-band (~3 MHz) noise signal on an avalanche-transit-diode feed circuit.

Single-frequency oscillation of thin-disk lasers due to phase-matched pumping.

We present a novel pump concept that should lead to single-frequency operation of thin-disk lasers without the need for etalons or other spectral filters. The single-frequency operation is due to matching the standing wave pattern of partially coherent pump light to the standing wave pattern of the laser light inside the disk. The output power and the optical efficiency of our novel pump concept are compared with conventional pumping. The feasibility of our pump concept was shown in previous experiments.

Model containing coupled subsystems with oscillations of different types

Consideration was given to an autonomous model containing coupled subsystems (MCCS) and, in the absence of couplings between the subsystems, falling down into systems of ordinary differential equations. It is assumed that the subsystems admit different types of nondegenerate single-frequency oscillations. Solved were the problems of oscillations in MCCS, their stability, and stabilization of MCCS oscillation by smooth autonomous coupling controls. It was shown how the developed theory is applied to the coupled Duffing and Van der Pol oscillators.

ЭФФЕКТИВНАЯ СХЕМА НАКАЧКИ ЭРБИЕВОГО ВОЛОКОННОГО ЛАЗЕРА С РАСПРЕДЕЛЕННОЙ ОБРАТНОЙ СВЯЗЬЮ ДЛЯ ПОДАВЛЕНИЯ РЕЛАКСАЦИОННЫХ КОЛЕБАНИЙ

The scheme of erbium-doped distributed feedback fiber laser is proposed, which combines pumping schemes of the single frequency oscillator and optical signal amplifier. The scheme provides maximum efficiency of pump to signal conversion while minimizing the effect of relaxation oscillations on the output radiation parameters. In this scheme single-frequency fiber laser radiation power up to 30 mW achieved at the pump power of 600 mW at 980 nm. Amplified spontaneous emission was at the level of 0.08%. The magnitude of the relative intensity noise is — 140dB/Hz at frequencies more than 10 MHz and — 100dB/Hz at the peak of relaxation oscillations. The linewidth of the laser radiation is less than 1 kHz.

Tunable single-frequency fiber laser based on the spectral narrowing effect in a nonlinear semiconductor optical amplifier.

A wavelength-tunable single-frequency fiber laser based on the spectral narrowing effect in a nonlinear semiconductor optical amplifier (NL-SOA) is proposed and experimentally demonstrated. The single-frequency operation is achieved based on the spectral narrowing effect resulted from the inverse four-wave mixing in a NL-SOA. By incorporating the NL-SOA in the fiber laser cavity, single-frequency lasing is achieved. The lasing frequency can be tuned by tuning the center wavelength of a tunable filter (TF) incorporated in the laser cavity. The proposed wavelength-tunable single-frequency fiber laser is experimentally evaluated. Stable single-frequency oscillation with a side-mode suppression ratio (SMSR) as high as 55 dB and a spectral linewidth of less than 10.1 kHz over a wavelength tuning range of as wide as 48 nm is demonstrated.

Regional gas transport in the heterogeneous lung during oscillatory ventilation.

Regional ventilation in the injured lung is heterogeneous and frequency dependent, making it difficult to predict how an oscillatory flow waveform at a specified frequency will be distributed throughout the periphery. To predict the impact of mechanical heterogeneity on regional ventilation distribution and gas transport, we developed a computational model of distributed gas flow and CO2 elimination during oscillatory ventilation from 0.1 to 30 Hz. The model consists of a three-dimensional airway network of a canine lung, with heterogeneous parenchymal tissues to mimic effects of gravity and injury. Model CO2 elimination during single frequency oscillation was validated against previously published experimental data (Venegas JG, Hales CA, Strieder DJ, J Appl Physiol 60: 1025-1030, 1986). Simulations of gas transport demonstrated a critical transition in flow distribution at the resonant frequency, where the reactive components of mechanical impedance due to airway inertia and parenchymal elastance were equal. For frequencies above resonance, the distribution of ventilation became spatially clustered and frequency dependent. These results highlight the importance of oscillatory frequency in managing the regional distribution of ventilation and gas exchange in the heterogeneous lung.

Investigation on multi-frequency oscillations in InGaAs planar Gunn diode with multiple anode-cathode spacings

Abstract Current oscillations in an AlGaAs/InGaAs/AlGaAs-based two-dimensional electron gas (2DEG)-based hetero-structure have been investigated by means of semiconductor device simulation software SILVACO, with an interest on the charge domain formation at large biases. Single-frequency oscillations are generated in planar Gunn diodes with uniform anode and cathode contacts. The oscillation frequency reduces as the applied bias voltage increases. We show that it is possible to create multiple, independent charge domains in a novel Gunn diode structure with designed multiple anode-cathode spacings. This enables simultaneous generation of multiple frequency oscillations in a single planar device, in contrast to traditional vertical Gunn diodes where only single-frequency oscillations can be achieved. More interestingly, frequency mixing in multiple-channel configured Gunn diodes appeared. This proof-of-concept opens up the possibility for realizing compact self-oscillating mixer at millimeter-wave applications.

295 mW output, frequency-stabilized erbium silica fiber laser with a linewidth of 5 kHz and a RIN of -120 dB/Hz.

We demonstrate the frequency stabilization of a high output power, erbium silica fiber laser by utilizing a (13)C2H2 (acetylene) absorption line at 1538.8 nm and a H(13)C(14)N (hydrogen cyanide) absorption line at 1549.73 nm. We introduced a novel short ring cavity configuration and pump power feedback control to suppress the intensity noise of the laser output, which is caused by the relaxation oscillation of erbium ions. As a result, we succeeded in simultaneously obtaining a stable single-frequency oscillation with an output power of over 290 mW, a linewidth of 5 kHz, and a low relative intensity noise (RIN) of -120 dB/Hz. The frequency stabilities reached 2.8 × 10(-11) and 6.9 × 10(-11) for an integration time of 1 s with a (13)C2H2 and a H(13)C(14)N absorption line, respectively.

MoS2 saturable absorber for single frequency oscillation of highly Yb-doped fiber laser

In this Letter, a single-frequency fiber laser using a molybdenum disulfide (MoS2) thin film as a saturable absorber is demonstrated. We use a short length of highly Yb-doped fiber as the gain medium and a fiber ferrule with MoS2 film adhered to it by index matching gel (IMG) that acts as the saturable absorber. The saturable absorber can be used to discriminate and select the single longitudinal modes. The maximum output power of the single-frequency fiber laser is 15.3 mW at a pump power of 130 mW and the slope efficiency is 15.3%. The optical signal-to-noise ratio and the laser linewidths are ～60 dB and 5.89 kHz, respectively.

Universal single-frequency oscillations in a quantum impurity system after a local quench

Long-lived single-frequency oscillations in the local non-equilibrium dynamics of a quantum many-body system is an exceptional phenomenon. In fact, till now, it has never been observed, nor predicted, for the physically relevant case where a system is prepared to be quenched from one quantum phase to another. Here we show how the quench dynamics of the entanglement spectrum may reveal the emergence of such oscillations in a correlated quantum system with Kondo impurities. The oscillations we find are characterized by a single frequency. This frequency is independent of the amount of energy released by the local quench, and scales with the inverse system size. Importantly, the quench-independent frequency manifests itself also in local observables, such as the spin-spin correlation function of the impurities.

Asymmetric Interaction of a Pair FitzHugh–Nagumo Oscillators

A pair of diffusion connected FitzHugh–Nagumo oscillators with an asymmetric interaction are considered. The problem is investigated in the close to critical case, where the matrix of the linear part of the system has a pair of purely imaginary eigenvalues. The normal form is constructed and its coefficients are determined depending on the initial parameters. The source system may be in two different situations: stable singlefrequency oscillations with two different frequencies coexist or a single-frequency mode branches from the equilibrium. The obtained asymptotic results are supplemented by the numerical analysis.

Automatic Detection and Frequency Estimation of Oscillatory Variables in the Presence of Multiple Oscillations

Automatic detection of oscillatory variables in the presence of multiple oscillations is still a challenging problem in the literature, despite the fact that there are several methods for detection and estimation of single-frequency oscillation. A method is proposed that utilizes the autocorrelation function (ACF) to detect the oscillatory variables and estimate the oscillation periods in the presence of multiple oscillations. The advantage of the developed method is that it requires no or little human interference in the detection process. It is also capable of estimation of the decay rate for decaying oscillations and is advantageous over methods based on analyzing the power spectrum for oscillation detection in case of nonsinusoidal oscillations. The proposed method is verified through a case study.

Quantum phase transition of light in coupled optical cavity arrays: A renormalization group study

We study the quantum phase transition of light of a system when atom trapped in microcavities and interacting through the exchange of virtual photons. We predict the quantum phase transition between the photonic Coulomb blocked induce insulating phase and anisotropic exchange induced photonic superfluid phase in the system due to the existence of two Rabi frequency oscillations. The renormalization group equation shows explicitly that for this system there is no self-duality. The system also shows two Berezinskii-Kosterlitz-Thouless (BKT) transitions for the different physical situation of the system. The presence of single Rabi frequency oscillation in the system leads to the BKT transition where system shows the quantum phase transition from photonic metallic state to the Coulomb blocked induced insulating phase. For the other BKT transition when the z-component of exchange interaction is absent, the system shows the transition from the photonic metallic state to the photonic superfluid phase. We also predict the commensurate to incommensurate transition under the laser field detuning.

Control approaches for robotic knee exoskeleton and their effects on human motion

In this paper we compare three noninvasive control methods for a robotic knee exoskeleton and asses their kinematic influences on the repetitive squatting motions of able-bodied human subjects. The motion of the subjects wearing the knee exoskeleton was also compared to the motion of the subjects performing the same task without using the assistance of the knee exoskeleton. We chose the squatting motion because it approximates common movements with high metabolic cost, such as standing up from a chair and ascending or descending the stairs. Beside the two classical robotic control approaches, i.e. the position control and the gravity compensation, we propose a method that is based on a single adaptive frequency oscillator combined with an adaptive Fourier series in a feedback loop. The method can extract frequency and phase of an arbitrary periodic signal in real-time. This method is particularly appropriate for controlling novel robotic assisting devices since it does not require complex signal sensing or user calibration. The results show that the total knee torque was increased while using the exoskeleton device compared to the squatting without the assistance of the exoskeleton device. In effect, there were significant kinematic adaptations observed when the exoskleton device assisted the motion of the subjects. However, no significant kinematic differences were found between different control methods. We conclude that an assistive device can augment the abilities of the able-bodied humans in the targeted joints (i.e. the joints provided with additional mechanical power) but, on the other hand, significantly alters whole body kinematics.