Phase Jitter Research Articles

Stable Radio Frequency Transmission of Single Optical Source Over Fiber Based on Passive Phase Compensation

In this paper, we propose a stable radio frequency(RF) transmission scheme for optical link based on Dual drive Mach-Zehnder modulator(DDMZM). By frequency mixing, the phase jitter of the output signal caused by environment variation has been automatically compensated. Different from other passive compensation schemes, the reference signal and the pre-compensation signal are modulated on one optical carrier by a DDMZM, and the crosstalk of two RF signals can be depressed by using dispersion compensation and adjusting the bias voltage of DDMZM, without multiple frequency multiplications and divisions. Meanwhile, the noises induced by Rayleigh scattering can be suppressed by using acousto-optic modulator. Our scheme is featured by single laser diode employed and no extra phase jitter induced by wavelength differences, with the advantages of simple structure and cost-effectiveness. In the experiment, we demonstrate 10 GHz RF signal stability transmission over 50 km single mode fiber, the phase jitter mean square error is 0.82 ps during 10 hours.

Clocking Auger electrons

Intense X-ray free-electron lasers (XFELs) can rapidly excite matter, leaving it in inherently unstable states that decay on femtosecond timescales. As the relaxation occurs primarily via Auger emission, excited state observations are constrained by Auger decay. In situ measurement of this process is therefore crucial, yet it has thus far remained elusive at XFELs due to inherent timing and phase jitter, which can be orders of magnitude larger than the timescale of Auger decay. Here, we develop a new approach termed self-referenced attosecond streaking, based upon simultaneous measurements of streaked photo- and Auger electrons. Our technique enables sub-femtosecond resolution in spite of jitter. We exploit this method to make the first XFEL time-domain measurement of the Auger decay lifetime in atomic neon, and, by using a fully quantum-mechanical description, retrieve a lifetime of $2.2^{ + 0.2}_{ - 0.3}$ fs for the KLL decay channel. Importantly, our technique can be generalised to permit the extension of attosecond time-resolved experiments to all current and future FEL facilities.

High-quality 3D shape measurement based on ant colony phase jitter optimization

High-quality 3D shape measurement based on ant colony phase jitter optimization

A dispersion‐free multi‐access RF dissemination link with phase jitter compensation

A dispersion-free scheme for stable multi-access radio frequency dissemination in a fibre loop link is proposed and demonstrated. The phase jitter and dispersion-induced power fading are suppressed simultaneously by transmitting different single-band signals in opposite propagating directions. Experimentally, a 2.5 GHz radio frequency signal is steadily transmitted to different remote sites, with phase deviations less than 0.6 ps over 15,000 s.

Phase-coherent asynchronous optical sampling system.

Mutual phase coherence is the utmost crucial factor in an asynchronous optical sampling system. The enhancement is commonly achieved by phase-locking dual femtosecond lasers to a shared narrow-linewidth cavity-stabilized laser. Here we report such a system with a low residual optical phase jitter at a level of 0.04 rad in a Fourier frequency band from 1 Hz to 5 MHz around 1.55 µm, corresponding to a timing jitter of 30 as. The residual phase jitter reaches 1 rad at a Fourier frequency between 0.06 Hz and 0.1 Hz, from which the phase-coherence time is inferred to be at least 10 s. The multi-heterodyne beats experimentally reveal a hardware-limited phase coherence time of ∼8.155 s throughout the direct lasing spectral band.

A low jitter, low cost optical chopper

An optical chopper is described that has comparable performance to commercially available units. The new chopper is built within the frame of a hard disk drive, and uses the existing motor and its disk for operation. The rotation speed is measured using a photo-interrupter and is adjusted with a microcontroller. Chopping frequencies from 150 Hz to 1650 Hz with phase jitter less than 0.38 degrees per revolution have been demonstrated. The hardware design and control algorithm are described, and results showing the phase jitter characteristics are presented. The performance of this new design is comparable to that of commercial optical choppers, and can be built for a fraction of their cost.

Homogeneous quantum cascade lasers operating as terahertz frequency combs over their entire operational regime

AbstractWe report a homogeneous quantum cascade laser (QCL) emitting at terahertz (THz) frequencies, with a total spectral emission of about 0.6 THz, centered around 3.3 THz, a current density dynamic range Jdr = 1.53, and a continuous wave output power of 7 mW. The analysis of the intermode beatnote unveils that the devised laser operates as an optical frequency comb (FC) synthesizer over the whole laser operational regime, with up to 36 optically active laser modes delivering ∼200 µW of optical power per optical mode, a power level unreached so far in any THz QCL FC. A stable and narrow single beatnote, reaching a minimum linewidth of about 500 Hz, is observed over a current density range of 240 A/cm2 and even across the negative differential resistance region. We further prove that the QCL FC can be injection locked with moderate radio frequency power at the intermode beatnote frequency, covering a locking range of 1.2 MHz. The demonstration of stable FC operation, in a QCL, over the full current density dynamic range, and without any external dispersion compensation mechanism, makes our proposed homogenous THz QCL an ideal tool for metrological applications requiring mode-hop electrical tunability and a tight control of the frequency and phase jitter.

DEVELOPMENT OF A MATHEMATICAL MODEL OF THE FUNCTIONING OF MULTI-ANTENNA RADIO COMMUNICATIONS WITH SPECTRALLY EFFECTIVE SIGNALS UNDER THE INFLUENCE OF DESTABILIZING FACTORS

The necessity of developing a mathematical model for the functioning of multi-antenna radio communication facilities with spectrally effective signals under the influence of destabilizing factors has been substantiated. The results of the study of the influence of destabilizing factors on the multi-antenna systems with spectrally effective signals are presented. New analytical dependences have been obtained, which make it possible to calculate the effect of destabilizing factors on the efficiency of multi-antenna system with spectrally effective signals. Object of research: development of a mathematical model of the functioning of multi-antenna radio communication facilities with spectrally effective signals under the influence of destabilizing factors. Investigated problem: taking into account additional destabilizing factors on the multi-antenna of a radio communication facility with spectrally effective signals. Main scientific results: when transmitting information in multi-antenna radio communication systems with spectrally effective signals, the following are taken into account: Type of parameters of deliberate interference, type and parameters of deliberate fading, type and parameters of security code structures, phase jitter, slope of the constellation matrix, Intersymbol interference, high mobility of objects (transmitter and receiver), the number of receiving and transmitting antennas, the number of subcarriers in the antenna channel. It has been established that taking into account all the parameters in the system makes it possible to assess the state of the channel, to develop measures to reduce the negative influence of destabilizing factors on the noise immunity of multi-antenna systems. A review of the practical use of research results: radio communication facilities with programmable architecture. Innovative technologies product: technology for substantiating the architecture of transceivers, software for programmable radio equipment, which can increase the noise immunity of radio communications, taking into account additional destabilizing factors and software for radio monitoring equipment. Overview of an innovative technological product: programmable radios, software for radio communications.

Upgrade of low level RF system based on Micro Telecom Computing Architecture (MTCA) for HLS-II LINAC

The performance of Hefei Light Source II (HLS-II) has improved a lot after major maintenance and reconstruction. To further provide continuous and stable light, the RF system of the HLS-II LINAC needs to be upgraded for top-off mode. It is required that the RF power source have long-time stability and reliability, but the old analog low level RF system(LLRF) can’t meet the requirement. Hence a digital low level RF control system based on Micro Telecom Computing Architecture(MTCA) is designed and implemented to control the amplitude and phase of the RF power source. This system is composed of digital board cards based on FPGA, RF board cards, MTCA chassis and a frequency synthesis system. It works at 2856 MHz of S band, with phase and amplitude stability up to 0.2° and 0.04% respectively, which meets the top-off mode requirement of 0.25° RMS phase jitter of the digital low-level RF system in the HLS-II LINAC.

Multipoint stable radio frequency long distance transmission over fiber based on tree topology, with user fairness and deployment flexibility.

In this paper, we propose a multipoint stable radio frequency (RF) optical transmission system with tree structure. Based on the principle of phase conjugation, the phase jitter induced by environment variation can be compensated by frequency mixing. Different from other schemes, the RF signal is modulated on a optical comb at local and each tooth is grouped with a near subcarrier for a user. By using wavelength division multiplexer, these groups are separated and transmitted to the multiple points over fiber. Therefore, the degradation of compensation performance caused by the wavelength difference between the common main carrier and farther subcarrier can be avoided, and the accumulated power loss induced by the branch points will be significantly reduced. In addition, an acousto-optic modulator is used at the local station to depress the impact of Rayleigh scattering. Experimentally, we demonstrate 2.4 GHz RF signal transmission to the two users over 25 and 100 km fiber during 1 × 104 seconds, and the phase jitter mean square errors are 2.50 × 10-2 and 4.27 × 10-2 rad, respectively.

A Comparative Performance Analysis of GPS L1 C/A, L5 Acquisition and Tracking Stages Under Polar and Equatorial Scintillations

This article provides a comparative performance analysis of different acquisition and tracking methods of GPS L1 C/A and GPS L5 signals testing their robustness to the presence of scintillations in the propagation environment. This article compares the different acquisition methods in terms of probabilities of detection/false alarm, peak-to-noise floor ratios for the acquired signal and execution time, assessing the performance loss in the presence of scintillations. Moreover, robust tracking architectures that are optimized to operate in a harsh ionospheric environment have been employed. The performance of the carrier tracking methods, namely, traditional phase-locked loop (PLL) and Kalman filter based-PLL, have been compared in terms of the standard deviation of Doppler estimation, phase error, phase lock indicator (PLI), and phase jitter. The article is based on real global navigation satellite systems (GNSS) signals affected by significant phase and amplitude scintillation effects, collected at the South African Antarctic research base (SANAE IV) and Brazilian Centro de Radioastronomia e Astrofisica Mackenzie (CRAAM) monitoring stations. Performance is assessed exploiting a fully software GNSS receiver, which implements the different architectures. The comparative analysis allows to choose the best setting of the acquisition and tracking parameters, in order to allow the operation of signal acquisition and tracking at a required performance level under scintillation conditions.

Effects of Dynamic Plasma Sheath on Electromagnetic Wave Propagation and Bit Error Rate Under External Magnetic Field

The “magnetic window” is considered to be an effective technique for alleviating a vehicle’s atmospheric reentry blackout, whereas the dynamic variation characteristic of the plasma sheath is critical for the vehicle’s communication. In this article, the effects of dynamic plasma sheath on electromagnetic wave propagation and the bit error rate (BER) of two typical modulation signals under an external magnetic field are investigated. First, the hybrid matrix method is used to calculate the transmission coefficients of right-handed circularly polarized (RHCP) waves with different magnetic fields and plasma electron density fluctuation. Then, the average BER of two typical modulations signals, namely M-ary phase-shift keying (MPSK) and noncoherent M-ary frequency shift keying modulation (NC-MFSK) is numerically simulated based on the magnetized plasma sheath channel response. The results show that the magnitude in dB scale and phase of the RHCP transmission coefficient follow Gaussian distribution when the probability density function of the electron density is a Gaussian distribution. The BER performance of binary phase-shift keying (BPSK) and NC-MFSK is relevant to the incident wave frequency, the plasma stopband, and the intensity of electron density variation. Owing to the insensitivity of phase jitter, the NC-8FSK has a better performance than BPSK, followed by NC-4FSK and NC-2FSK.

A fully stabilized low-phase-noise Kerr-lens mode-locked Yb:CYA laser frequency comb with an average power of 1.5 W

We report a fully stabilized self-referenced all-solid-state-laser frequency comb based on a home-built Kerr-lens mode-locked Yb:CaYAlO4 oscillator, which delivers ultrafast pulses with a pulse duration of 54 fs and an average power of 1.5 W. Free running carrier-envelope phase offset frequency (fceo) is observed with a signal to noise ratio of 40 dB at 100 kHz resolution bandwidth, which is phase-locked to a microwave frequency synthesizer with a residual phase jitter of 370 mrad [1 Hz–1 MHz] and with a standard frequency deviation of 0.8 mHz at 1-s gate time within 3-h, corresponding to the relative frequency instability of 2.9 × 10−18 at 1-s average time. It is the lowest phase noise and the highest frequency stability of fceo obtained in a watt-level all-solid-state bulk laser frequency comb to the best of our knowledge. A 13th repetition rate is simultaneously phase-locked to the same microwave standard with a frequency instability level of 10−12 at 1 s average time. Such fully stabilized power scaling Yb: CaYAlO4 laser frequency combs have great potential for applications in broadband dual comb spectroscopy as well as high loss cases such as long-distance time and frequency transfer.

Passive Optical Phase Stabilization on a Ring Fiber Network

Optical frequency transfer provides the means for high-fidelity frequency transfer across thousands of kilometers. A critical step in the further developing optical frequency transfer is its capability to transfer a high spectral purity feature from ultrastable lasers or optical clocks to any remote locations and, at the same time, its adaptability to incorporate the optical frequency transfer technique into any existing communication networks with different topologies. Here we for the first time report a technique that delivers optical-frequency signals to multiple independent remote hubs along a ring optical-fiber network with passive phase stabilization. The technique automatically corrects optical-fiber length fluctuations of arbitrary hubs along the loop by mixing and shifting optical signals. Without the help of an active phase tracker and a compensator, it could significantly mitigate some technical problems such as the limited compensation speed and phase recovery time, the phase jitter contamination caused by the servo bump in conventional phase noise cancellation. Moreover, by transmitting optical signals along both directions using the same optical source, it can improve the signal-to-noise ratio at each hub. This technique maintains the same delay-limited phase noise correction capability as in conventional techniques and, furthermore, improves the phase jitter by a factor of 3, opening a way to a broad distribution of an ultrastable frequency reference with high spectral purity and enabling a wide range of applications beyond metrology over a ring fiber network with the naturally impressive reliability and scalability.

The PSK Channel Capacity Estimation under Dynamic Plasma Sheath Channel

During the reentry process, the plasma sheath covering the surface of the hypersonic aircraft will cause the amplitude attenuation and phase jitter of the communication electromagnetic waves. Channel parameters such as the electron density and collision frequency of the plasma sheath reflect the changing trend of the plasma sheath, and these parameters can be measured by physical means. However, these parameters cannot directly reflect the change of the channel communication ability and cannot directly serve the design of communication methods in the plasma sheath. Due to the particularity of the plasma sheath, the traditional channel estimation method for Additive White Gaussian Noise channels will no longer be applicable. This paper presents a channel capacity estimation method for dynamic plasma sheath. First, the plasma sheath is equivalent to a discrete input continuous output memoryless channel, and then the channel capacity expression is derived according to Shannon formula. Finally, the channel capacity of the dynamic plasma sheath is estimated by calculating the transition probability density function. The simulation results show that the channel capacity of the dynamic plasma sheath is affected by both the signal-to-noise ratio (SNR) and the dynamic parameters of the plasma sheath. When the electron density is small, the channel capacity is mainly affected by the SNR. As the electron density increases, the dynamic parameters of the plasma sheath gradually become the main factor affecting the channel capacity. This method is a theoretical analysis of the channel capacity when the channel parameters of the plasma channel are known, and it is meaningful for conducting the work of communication methods design.

Unveiling delay-time-resolved phase noise statistics of narrow-linewidth laser via coherent optical time domain reflectometry.

Laser with high spectral purity plays a crucial role in high-precision optical metrology and coherent communication. Thanks to the rapid development of laser frequency stabilization, the laser phase noise can be remarkably compensated, allowing its ultra-narrow linewidth subject to mostly quantum limit. Nevertheless, the accurate characterization of phase noise statistics and its linewidth of a highly coherent laser remains ambiguous and challenging. Here, we present an approach capable of revealing delay-time-resolved phase noise statistics of a coherent laser based on coherent optical time domain reflectometry (COTDR), in which distributed Rayleigh scattering along a delay fiber essentially allows a time-of-flight mapping of a heterodyne beating signal associated with delay-time-dependent phase information from a single laser source. Ultimately, this novel technique facilitates precise measurement of ultra-narrow laser linewidth by exploiting its delay-time-resolved phase jitter statistics of random fiber laser with pump lasers of various linewidths, confirmed with the analytical modeling and numerical simulations.

Analysis of Multi-hour Continuous Observations of Seven Millisecond Pulsars

Abstract Precision pulsar timing can be used for a variety of astrophysical tests, from the detection of gravitational waves to probing the properties of the interstellar medium. Here we analyze various noise contributions to pulsar timing residuals from continuous multi-hour observations of seven millisecond pulsars (MSPs). We present scintillation bandwidth measurements for all MSPs in the sample, some for the first time. We also present scintillation timescale measurements and lower limits for all MSPs for the first time. In addition, we present upper limits on the contribution of pulse phase jitter to the timing residual error for all MSPs. These long observations also allow us to constrain variations in dispersion measures (DMs) on hour-long timescales for several millisecond pulsars. We find that there are no apparent DM variations in any of the MSPs studied on these timescales, as expected. In light of new radio telescopes, such as the Canadian Hydrogen Intensity Mapping Experiment, which will be able to time many pulsars for a short time each day, we search for differences in timing precisions from continuous pulse times of arrival (TOAs) and from equivalent length time-discontinuous TOAs. We find no differences in the precision for any of the MSPs in our sample, as expected. We conclude that the TOA variations are consistent with the expected breakdown into template-fitting, jitter, and scintillation errors.

Hitting a ball on a spring: a simple model for understanding decoherence with wavefunctions

The typical approach to studying decoherence begins by examining a combined system and interacting environment (termed bath), and then deriving a master equation to examine the behaviour of the density matrix after tracing over the bath, typically by invoking the Markovian approximation. This approach is quite successful for a large variety of systems however is frequently a non-intuitive picture that can mask the fundamental behaviour of the system. We examine here a simple model that captures the essence of decoherence and study it using the wavefunction picture, invoking the analytic concepts of the correspondence principle, the method of images, the phase jitter concept, and the scattering matrix formalism. We complement this with a numerical study using the split-operator FFT method, the forced harmonic oscillator method, and the thawed Gaussian approximation.

Improvements in a 20-kW Phase-Locked Magnetron by Anode Voltage Ripple Suppression

Microwave devices based on high-power magnetrons are currently used widely and there is a strong demand for phase-controlled magnetrons. In this work, the performance of a 20-kW $S$ -band continuous-wave magnetron with varied anode voltage ripple is studied. The anode voltage ripple is introduced to an equivalent model of the magnetron to evaluate the system’s performance theoretically. The effects of the anode voltage ripple and the injection parameters on the magnetron’s output are thus analyzed numerically. Furthermore, experiments are performed while the anode voltage ripple is varied from 4.2% to 0.6% using a shunt capacitance-adjustable ripple filter module. A nearly tripled locking bandwidth is observed under a constant injection ratio at 0.1 with decreasing ripple. The ripple-suppressed system pulls its sideband energy to the locking frequency and thus achieves a spectral intensity increment of 0.9 dB, phase noise reduction of 13 dB at an offset of 100 kHz, and phase jitter convergence from ±1.8° to ±0.9°. The experimental features validate the results obtained from the theoretical analyses. The results of this investigation also provide guidance for future industrial applications of phase-locked magnetron arrays.

Hardware implementation of phased locked loop in biomedical diagnostics devices

ABSTRACT. This paper is devoted to the implementation of synchronous demodulator of amplitude-modulated signals by means of digital signal processing to increase the amount of diagnostic information of biomedical devices. A feature of the implemented demo- dulator is the usage of a phase-locked loop system, which, while ensuring high sensitivity of the demodulator, allows processing signals with low power. To create a mathematical model of the demodulator being developed, a phase-locked loop structure chart was drawn up. When drawing up a block diagram of the PLL model, which in this case consists of a numerically controlled cosine-sine oscillator and a loop filter, it was taken into account that they operate in discrete time, i.e. the implementation of these schemes will be performed entirely in digital form. As a result of the calculation, the transfer characteristic and difference equation of the loop filter (proportional-integrating type) for second-order of phase-locked loop were obtained, and then the simulation of the calculated phase-locked loop system was carried out in the Simulink application in MatLab. Using the formulas obtained, a program was written to determine such loop transfer coefficients that can ensure the nominal operation of the phase-locked loop. The obtained simulation results confirmed that the developed version of the loop filter provides a wide capture band while simultaneously suppressing phase jitter. At the next step, a computer program was compiled in the Verilog language with the purpose of the full-scale implementation of the designed demodulator based on the field-programmable gate arrayt debugging board such as Spartan 6 Xilinx with the Xilinx ISE design system. In order to verify the developed software code for the hardware implementation of the demodulator in the Xilinx ISE design system, a software simulation of the input signal in Testbench with simultaneous use of the ISIM application was performed, and the simulation results were visualized in GTKWave. The obtained experimental results of the synthesized demodulator confirmed the results of simulation modeling