Nonlinear microwave spin wave interferometer

The characteristics of a nonlinear microwave spin wave interferometer were experimentally studied for the first time. The interferometer was implemented according to a bridge scheme with a nonlinear spin wave phase shifter based on an yttrium-iron garnet film. The maximum sensitivity of the nonlinear interferometer with respect to the input signal level was reached with a phase shifter operating on the forward volume spin waves. In the GHz frequency range, an increase in the microwave power up to a few mW led to a signal phase shift exceeding 180 °.     

Amplitude-frequency characteristic of a nonlinear spin wave interferometer operating in a quasi-nonlinear regime

A thin-film nonlinear spin wave interferometer has been experimentally studied. The concept of a quasi-nonlinear operation regime is introduced for the first time and the boundaries of the quasi-nonlinear dynamic range of the interferometer are experimentally determined. It is shown that the nonlinear spin wave interferometer operating in the quasi-nonlinear regime can be characterized, like linear devices, by the amplitude-frequency characteristic (AFC). However, an increase in the signal power level within the quasi-nonlinear dynamic range at the input of the nonlinear interferometer leads, in contrast to the case of a linear device, to a frequency shift of the AFC. An analysis of the AFC shift indicates that a 180° change in the phase difference between the interfering signals at each separate frequency is achieved for the input power varied within the limits of the quasi-nonlinear dynamic range. This behavior shows the possibility of using the nonlinear interferometer for the processing of microwave signals without undesired distortion of the signal waveform.     

Generation of chaotic microwave pulses with the help of passive synchronization of spin wave self-modulation frequencies in self-oscillatory ring systems

Passive synchronization (PS) of spin wave self-modulation frequencies of a chaotic microwave signal has been observed for the first time in a self-oscillatory ring system involving a nonlinear passive element with saturable absorption. The development of PS led to the generation of a periodic train of chaotic microwave pulses with an off/duty ratio exceeding 20. It is established that the repetition period of chaotic microwave pulses can be controlled by changing gain in the ring system.     

Microwave nonlinear spin wave directional coupler

A nonlinear spin-wave directional coupler for the microwave range has been designed, constructed, and studied for the first time. Each of the four ports of the device can be used as the input or output for a microwave signal. The role of a control element in the coupler is played by a nonlinear spin wave shifter based on a thin ferromagnetic film. A distinctive feature of the proposed device is that an increase in the input power level leads to the signal switching from one to another output, which is caused by a power-dependent variation in the spin wave phase shift.     

Generation of single chaotic microwave pulses in a self-oscillating ring system with ferromagnetic film under the action of external noise

The generation of single chaotic microwave pulses in a self-oscillating ring system with ferromagnetic film under the action of external narrow-band noise microwave signal occurring outside the band of frequencies of the chaotic microwave signal was observed. Chaotic generation emerged due to the parametric instability of the magnetostatic surface wave in the ferromagnetic film, whereas formation of single chaotic microwave pulses was caused by the absence of complete suppression of chaos under the action of narrowband noise.     

Generation of chaotic microwave pulses in broadband self-oscillating ring system with ferromagnetic film under the action of external pulse-modulated microwave signal

We have experimentally studied specific features of the generation of chaotic microwave pulse trains in a self-oscillating ring system with nonlinear delay line on surface magnetostatic waves, bandpass filter, and power amplifier on GaAs field-effect transistors under the action of an external pulse-modulated microwave signal occurring outside the band of the generated chaotic signal. It is established that a decrease in the off/duty ratio in the external pulse-modulated microwave signal leads to an increase in this ratio for the chaotic microwave pulses. The integral power of the chaotic microwave signal generated under the pulsed external signal action is increased as compared to the power of signal generated in the autonomous regime.     

Synchronizing pulsations of a saturating absorber injection laser

Radiation pulses of an injection laser with a saturating absorber layer have been synchronized using a harmonic microwave (0.8–2.6 GHz) current with a power below 1 mW. The synchronization leads to a sharp decrease in instability of the laser pulse repetition period. The dependence of the synchronization frequency band on the pumping current, the synchronizing signal amplitude, and the temperature has been studied.     

An electroacoustic method for measuring the intensity of high-powermicrowave pulses

A microwave electric field intensity meter for single high-power radiowave pulses is described. A surface acoustic wave (SAW) dielectric acoustic line is used which has nonlinear electroacoustic properties and is comprised of two transducers. The first (nonlinear) transducer is affected by a microwave electric field and provides the SAW excitation due to nonlinear effects. A delayed SAW signal, carrying information about the electric field strength, is received by a linear interdigital transducer     

An electron spin resonance (ESR) investigation of the dosimetric potential of potassium tartrate

While unirradiated potassium tartrate (PT) samples do not exhibit any electron spin resonance signal, irradiated ones contain many resonance signals. A power function of the radiation dose was found to describe well the dose-response curve of the central resonance signal, and adjusting the microwave power and modulation amplitude to be 2 mW and 1 mT, respectively, was found to increase the sensitivity of PT. The radiation sensitivity of PT and the accuracy of the measured radiation dose were found to be G = 0.42 and 6 %, respectively.     

Nonlinear suppression of microwave signals in a resonant magnetostatic wave transmission line

We have studied the phenomenon of suppression of a microwave signal in a magnetostatic wave (MSW) resonant transmission line comprising a microstrip resonator with a tangentially magnetized ferromagnetic film. Distinctions are revealed between the observed effects and those reported for a matched MSW line transmitting one microwave signal or two signals with different power levels.     

Interferometric all-optical switches for ultrafast signal processing

All-optical switches find applications in ultrahigh-speed network-user interfaces and in specialized high-speed processors, such as data regenerators and encryptors and microwave signal generators. We describe a semiconductor optical-amplifier-based single-arm interferometric switch called the ultrafast nonlinear interferometer. We discuss how the gain and the refractive-index nonlinearities in semiconductor optical amplifiers have an impact on the all-optical switch design, and we review experimental results obtained with the ultrafast nonlinear interferometer.     

The effect of a pulsed magnetic field on the nuclear spin echo signal in ferrite

A pulsed magnetic field produces shifts of domain walls in a magnetically ordered material (ferrite) and thus affects the nuclear spin echo signal in this material. The suppression and restoration of a response signal have been observed using exciting sequences with pulses of different polarities. The established dependence of the spin echo suppression coefficient on the external constant magnetic field confirms the hypothesis that the observed phenomena are related to the domain walls.     

Supercontinuum generation from a sub-megahertz repetition rate femtosecond pulses based on nonlinear polarization rotation technique

A means of supercontinuum (SC) generation is proposed and demonstrated, using femtosecond mode-locked pulses with sub-megahertz repetition rate based on the nonlinear polarization rotation technique. Total cavity length is approximately 522?m, which includes an additional 500?m single mode fiber (SMF) and the fundamental repetition rate obtained is 404.5?kHz. The mode-locked spectrum has a central wavelength of approximately 1600?nm and a 3?dB bandwidth of 16?nm, which falls within the L-band region. The threshold power for the mode-locked operation is achieved at approximately 52?mW. At pump power of 74?mW, the measured pulse width, pulse energy, and average output power are 70?fs, 18.3?nJ and 7.4?mW respectively. The generated pulses are amplified by a 72.44?mW erbium-doped fiber amplifier before being injected into a 100?m long highly non-linear fiber as the nonlinear medium to generate the SC spectrum. The obtained SC spectrum spans from 1250?nm to more than 1700?nm, with bandwidths of 450?nm at a ?70?dBm output power level. For comparison purpose, the 500?m SMF is removed from the setup and similar measurements are then repeated for this case.     

Chirp signal matching and signal power optimization in pulse-echomode ultrasonic nondestructive testing

Chirp pulse compression is a signal correlation technique that uses frequency modulated pulses as transmitted signals. Usually, signals with linear frequency modulation are applied. They can be generated rather easily, but their spectra are not totally matched to the transfer function of ultrasonic systems. In pulse-echo mode operation, with signal duration and consequently the time-bandwidth product being critical parameters, waveforms should be applied which make full use of the available power and bandwidth resources. We report here two methods to improve the overall efficiency of an ultrasonic pulse-echo system. Transmitter signals with constant amplitude level and nonlinear frequency modulation can be generated in such a way that they are spectrally matched to the system. A formula for the calculation of such a matched nonlinear chirp signal is presented. This modulation scheme also leads to a side-lobe level reduction of the compressed pulses. The application of square wave chirps derived from sine type chirps yields an additional gain of echo signal amplitude. Moreover, the complexity of the signal generation hardware is reduced. The methods are illustrated by an example     

Design of an ultracompact low-power all-optical modulator by means of dispersion engineered slow light regime in a photonic crystal Mach-Zehnder interferometer

We present the design procedure for an ultracompact low-power all-optical modulator based on a dispersion-engineered slow-light regime in a photonic crystal Mach-Zehnder interferometer (PhC MZI), selectively infiltrated by nonlinear optical fluids. The dispersionless slow-light regime enhancing the nonlinearities enabled a 22 μm long PhC MZI to operate as a modulator with an input power as low as 3 mW/μm. Simulations reveal that the switching threshold can be controlled by varying the optofluidic infiltration.     

Amplitude-stabilized frequency-modulated laser diode and its interferometric sensing applications

A direct frequency-modulated (FM) laser diode light source without light power variation is developed. The amplitude variation of the FM laser diode is compensated by means of a feedback system with use of a superluminescent diode as an external light power controller. Output power greater than 1 mW is obtained at the modulation frequency to 5 kHz with a >10 stabilization factor. By use of the amplitude-stabilized FM laser diode, we measured subfringes with high accuracy in FM continuous wave interferometry, increased the dynamic range of the displacement measurement, and improved the stabilization factor in the laser diode feedback interferometer.     

Generation of gigawatt 10-GHz pulses with stable phase

The generation of microwave pulses in a 10-GHz range has been studied in a nonstationary relativistic backward wave oscillator (BWO) operating at a pulse train repetition rate of up to 300 Hz. Regimes with a stabilized phase of the high-frequency filling of pulses with respect to the accelerating voltage pulse front have been observed at a BWO peak output power of ～1 and 3 GW. In pulse trains with a length of 10–100 s, the average output microwave power reached ～1 kW.     

High-power pumping wave influence on the volume spin wave propagation in a ferrite film

The influence of a high-power pumping wave on the propagation of backward volume spin waves in a longitudinally magnetized ferrite film was experimentally studied. Narrowing of the frequency band of propagation and the subsequent complete suppression of the volume spin waves with an increase of the pumping power were observed for the magnetic fields and frequencies allowing three-wave processes of the volume wave splitting.     

空间引力波探测干涉仪探测模式比较研究

为了实现毫赫兹频段的引力波信号测量,基于激光干涉体制的空间引力波探测计划要求干涉系统硬件本底噪声低于星间散粒噪声极限,这对光机设计及相应干涉载荷提出了严苛的工程指标。本文从探测模式选择的角度出发,推导了在单探测器模式和平衡模式下读出噪声和杂散光噪声在干涉信号中的表达形式,并就科学干涉仪的弱光干涉过程进行了详细讨论。结果表明,平衡模式可以跨量级的抑制激光功率涨落和后向杂散光引起的干涉相位噪声,但其抑制能力受限于合束器的不等比分光性质。为此引入相对增益因子来补偿合束器的不等比分光特性,进一步的分析表明,电子学手段的增益补偿只能消除不等比分光对两者之一的影响,不能同时兼顾,需要在激光功率涨落噪声和杂散光噪声的抑制之间平衡选择增益补偿。即便如此,平衡模式下的跨量级的噪声抑制能力,仍然可望降低对激光功率涨落和望远镜杂散光的工程指标要求。

     

Measurements of femtosecond pulse temporal profile by means of a Michelson interferometer with a Schottky junction

We introduce a new method for femtosecond pulse shape measurement. The interference of two pulses is employed rather than the second-harmonic generation (SHG). Usually, the measurements of the femtosecond pulse is realized by an interferometer in combination with a nonlinear optical material, while the measurement that we describe is realized by means of a Michelson interferometer with a Schottky junction. Only a metal-semiconductor junction (Schottky junction) is needed, and neither the nonlinear optical material nor a photodetector is included. The two-photon absorption arises when the light is strong enough, while there is only a one-photon absorption when the light is weak. And the calculations are in good agreement with the experimental results. In principle, the new technique could be used for the measuring of pulses with any duration and with very low power. Unlike the SHG scheme, in the new method the quality of optics, mechanics, and other elements of the scheme are not essential, and the measurement is easily realized, but the results are quite precise and very sensitive to the light.