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We study the spectro-temporal characteristics of two repeating fast radio bursts (FRBs), namely, FRB 20180916B and FRB 20180814A, and combine the results with those from our earlier analysis on FRB 20121102A. The relationship between the frequency drift rate, or slope, of individual sub-bursts and their temporal duration is investigated. We consider a broad sample of possible dispersion measure (DM) values for each source to understand the range of valid sub-burst slope and duration measurements for all bursts and to constrain our results. We find good agreement with an inverse scaling law between the two parameters previously predicted using a simple dynamical relativistic model. The remarkably similar behaviour observed in all sources provides strong evidence that a single and common underlying physical phenomenon is responsible for the emission of signals from these three FRBs, despite their associations with different types of host galaxies at various redshifts. It also opens up the possibility that this sub-burst slope law may be a universal property among repeating FRBs, or indicates a distinct subclass among them., 16 pages, 10 figures, accepted MNRAS

The resonant frequency drift caused by the change in mechanical parameters will cause the servo mechanism of CNC machine tools, robots and other equipment to produce mechanical resonance again. To address this problem, we propose a novel identification method of mechanical resonance based on the Fibonacci principle and a novel design method of notch filters based on optimization theory. First, by using a multifrequency sinusoidal signal, we design a fast search algorithm to search for the drift resonance frequency online; then, we optimize the notch filter to achieve fast and real-time resonance suppression by optimization theory. Compared with commonly employed passive resonance suppression methods, the proposed method can rapidly identify the parameters, more accurately suppress the resonance, minimize the phase angle loss and maintain the stability of the system. Finally, we apply the method to a 2-mass system experimental platform. The experimental results show that the proposed method is superior to the conventional passive resonant suppression method under the resonant frequency drift and other states and has strong robust performance.

A 0.8-V Bluetooth 5 (BT5) digitally intensive transceiver with a phase-tracking RX and a digital TX in 40-nm CMOS is presented. For the phase-tracking RX, a hybrid loop filter with a loop-delay compensation is proposed to suppress digitally controlled oscillator (DCO) sidelobe energy, enhancing interference resilience. To facilitate the DCO-based phase-tracking RX for the reception of BT5 signals, a corresponding digital baseband is implemented with a carrier frequency offset (CFO) calibration to remove the initial static CFO error during the preamble, while an automatic frequency calibration tackles the frequency drift during the payload. An all-digital phase-locked loop (ADPLL)-based digital frequency-modulation (FM) interface shared between TX and RX provides a precise deviation frequency control, ensuring the quality of signal transmission and reception. In the RX mode, the chip consumes 2.3 mW from a 0.8-V supply, achieving a figure of merit (FoM) of 180 dB with −91-/−94-dBm sensitivity at 2/1 Mb/s. In the TX mode, it consumes 6.1 mW when delivering a maximum 1.8-dBm output power, resulting in 25% TX system efficiency.

Two ultrastable laser systems for the clock transition spectroscopy in the strontium frequency standard are developed. The high stability of laser radiation frequency is provided by the active loop for frequency referencing to the Fabry–Perot reference cavity. The used cavities are made of glass with ultra-low thermal expansion coefficient and are 48 cm long which provides an extremely low thermal noise limit of 7 × 10–17. The relative frequency drift velocity of laser systems is 216 mHz/s which allows the implementation of high-accuracy spectroscopy of the clock transition in strontium.

In order to improve the scale factor stability of interferometric fiber optic gyroscope (IFOG), laser is considered to be an alternative to traditional broadband light source because of its excellent frequency stability. Although the performance of IFOG driven directly by laser is inspiring, it is still necessary for further improvement. The main limiting factor is its narrow linewidth and errors of coherent backscattering, polarization coupling and Kerr effect will be reintroduced in laser-driven IFOG. At present, one of the best methods is using Gaussian white noise (GWN) to drive an external electro-optic phase modulator (EOM) and broaden the optical spectrum of laser which will not cause additional frequency drift to the laser. This review studies the mechanism of phase modulation comprehensively based on theory and simulation. The process of broadening is described by numerical calculation and OptiSystem platform. The spectrum is also broadened as expected in the experiment observed by optical spectrum analyzer (OSA). Furthermore, by broadening the linewidth before laser enters the IFOG system, its angular random walk noise and drift are improved by more than 60% compared with no modulation. The test results also show that the drift has reached the level of broadband light source. Related work enriches the application of laser as light source in IFOG and the research about external phase modulation.

We demonstrate a laser frequency stabilization method with large tuning range to stabilize a UV laser by installing piezoelectric ceramic actuators into a Fabry–Pérot cavity with an ultra-low expansion spacer. To suppress piezoelectric drift, a two-layer symmetrical structure is adopted for the piezoelectric actuator, and a 14.7 GHz tuning range is achieved. The short-term drift of the piezoelectric ceramics caused by temperature and creep is eliminated, and the long-term drift is 0.268 MHz/h when the Fabry–Pérot cavity is sealed in a chamber without a vacuum environment. The long-term frequency drift is mainly caused by stress release and is eliminated by compensating the cavity voltage with an open loop. Without the need for an external reference or a vacuum environment, the laser frequency stabilization system is greatly simplified, and it can be extended to wavelengths ranging from ultraviolet to infrared. Owing to its simplicity, stability, and large tuning range, it is applicable in cold atom and trapped ion experiments.

We herein report a simultaneous frequency stabilization of two 780-nm external cavity diode lasers using a precision wavelength meter (WLM). The laser lock performance is characterized by the Allan deviation measurement in which we find $\sigma_{y}=10^{-12}$ at an averaging time of 1000 s. We also obtain spectral profiles through a heterodyne spectroscopy, identifying the contribution of white and flicker noises to the laser linewidth. The frequency drift of the WLM is measured to be about 2.0(4) MHz over 36 hours. Utilizing the two lasers as a cooling and repumping field, we demonstrate a magneto-optical trap of $^{87}$Rb atoms near a high-finesse optical cavity. Our laser stabilization technique operates at broad wavelength range without a radio frequency element., Comment: 6 pages, 5 figures

A compact frequency-stabilized laser system at 589 nm is demonstrated for sodium laser guide star and sodium lidar. The 589 nm laser based on all-fiber devices was generated by the sum frequency generation (SFG) of the distributed-feedback laser diodes (DFB-LD) seed lasers of 1064 nm and 1319 nm. The absolute frequency was locked to the D2a line by adopting the method of saturated absorption. The frequency drift of 589 nm can reach to 1.8 MHz (RMS) over 5000 s. The proposed DFB-LD based frequency stabilization scheme of 589 nm laser is a promising solution for applications that require extremely mobile or miniaturized systems.

A quartz crystal resonator (QCR) is an indispensable electronic component in the field of the modern electronics industry. By designing and depositing electrodes of different shapes and thicknesses on a quartz wafer with a certain fundamental frequency, the desired target frequency can be obtained. Affected by factors such as the deposition equipment, mask, wafer size and placement position, it is difficult to accurately obtain the target frequency at a given time, especially for mass-produced QCRs. In this work, a laser with a wavelength of 532 nm was used to thin the electrodes of a QCR with a fundamental frequency of 10 MHz. The electrode surface was etched through a preset processing pattern to form a processing method of local thinning of the electrode surface. At the same time, the effect of laser etching on silicon dioxide and resonator performance was analyzed. Satisfactory trimming frequency-increasing results were achieved, such as a frequency modulation accuracy of 1 ppm, frequency distribution with good consistency and equivalent parameters with small changes, by the laser partial etching of the resonator electrode. However, when the surface electrode was etched into using through-holes, the attenuation amplitude of the equivalent parameter became larger, especially in terms of the quality factor (Q), which decreased from 63 K to 1 K, and some resonators which had a serious frequency drift of &gt, 40%. In this case, a certain number of QCRs were no longer excited to vibrate, which was due to the disappearance of the piezoelectric effect caused by the local thermal phase change in the quartz wafer.

The drift characteristics of well-aged Hydrogen MASERs may be reasonably modeled as linear over periods greater than two weeks. There are several broad strategies used to manage drift: a) quantify and acknowledge drift in a system error budget, b) compensate using post-processing methods, c) apply a linear correction, or d) steer the MASER output frequency to a superior reference. The selection of drift management method greatly depends upon the requirements of a user’s system. Users, such as radio astronomers, may de-emphasize active drift management as their primary concern is 1-to-100 second stability. These users often prefer to compensate for frequency drift after passing a predefined frequency offset threshold. This removal takes the form of a manual frequency adjustment on the MASER. However, time-scale users, who require exact characterization and compensation of drift, will need to intervene using post-processing methods to avoid tampering with a characterized MASER which may be contributing to local UTC. This paper will discuss the underlying processes that may cause linear drift, how this drift is quantified, and then give an overview of the design implications of each drift handling method. For illustration purposes, a MASER’s drift will be characterized, and a linear drift correction will be applied. This illustration covers the use case when a MASER will perform as a standalone standard with moderate long-term stability requirements.

This study reports a portable and economical humidity sensing platform based on the quartz crystal microbalance (QCM). Although QCM sensors have been widely adopted for moisture sensing, the vast majority of such sensors are limited to laboratory tests due to the lack of portability. This work employed a low-cost Arduino microcontroller board and the Pierce oscillator to track the resonance frequency of the QCM sensor, which made the sensing system highly compact and portable. The efficacy of the sensing platform was validated by humidity sensing measurements. Graphene oxide (GO), MXene, and their composite (MXene/GO) were coated on the surface of three QCM sensors to provide oxygen-containing functional groups for interaction with water molecules. The humidity sensing properties of the three sensors were evaluated and compared over the RH range of 0% to 84%. All three sensors showed decent humidity sensing performance in terms of sensitivity, response/recovery time, hysteresis, and accuracy. The QCM-GO sensor exhibited the highest RH sensitivity of 38.5 Hz/%RH, shortest response/recovery time of 15 s/9 s, and lowest hysteresis, while the QCM-MXene/GO sensor revealed the lowest frequency drift of less than 0.7% in a constant RH environment over 30 minutes.

A study using Arase data gives the first observational evidence that the frequency drift of electromagnetic ion cyclotron (EMIC) waves is caused by cyclotron trapping. EMIC emissions play an important role in planetary magnetospheres, causing scattering loss of radiation belt relativistic electrons and energetic protons. EMIC waves frequently show nonlinear signatures that include frequency drift and amplitude enhancements. While nonlinear growth theory has suggested that the frequency change is caused by nonlinear resonant currents owing to cyclotron trapping of the particles, observational evidence for this has been elusive. We survey the wave data observed by Arase from March, 2017 to September 2019, and find the best falling tone emission event, one detected on 11th November, 2017, for the wave particle interaction analysis. Here, we show for the first time direct evidence of the formation of a proton hill in phase space indicating cyclotron trapping. The associated resonance currents and the wave growth of a falling tone EMIC wave are observed coincident with the hill, as theoretically predicted., 宇宙空間で電波を生み出す陽子の集団を発見 --JAXAの人工衛星「あらせ」の観測と解析から--. 京都大学プレスリリース. 2021-07-12.

To enhance the performance of charge detection mass spectrometry, we investigated the behavior of macromolecular single ions on their paths towards and within the Orbitrap analyzer. We discovered that ions in mass beyond one megadalton reach a plateau of stability and can be successfully trapped for seconds, travelling a path length of multiple kilometers, thereby enabling precise mass analysis with an effective resolution of greater than 100,000 at m/z 35,000. Through monitoring the frequency of individual ions, we show that these high mass ions, rather than being lost from the trap, can gradually lose residual solvent molecules and, in rare cases, a single elementary charge. Our observations highlight the importance of efficient desolvation for optimal charge detection mass spectrometry and inspired us to implement multiple improved data acquisition strategies. We demonstrate that the frequency drift of single ions due to desolvation and charge stripping can be corrected, which improves the effective ion sampling 23-fold and gives a two-fold improvement in mass precision and resolution, as demonstrated in the analysis of various viral particles.

A frequency-drift-compensated phase-locked loop (PLL) with an LC voltage-controlled oscillator (VCO) is fabricated in TSMC 40-nm CMOS process. The proposed frequency drift compensator employs an analog-to-digital converter to monitor the control voltage of the PLL in background. The capacitor banks are adjusted to compensate for the frequency drift of the LC-VCO. The measured reference spur is −65.15 dBc. The measured best phase noise of this PLL is −108.32 and −130.26 dBc/Hz at the frequency offset of 1 and 10 MHz, respectively, among five chips. This chip occupies 0.223-mm2 active area. The power dissipation of this PLL is 6.32 mW from a 0.9-V supply voltage. The average temperature coefficient is 2.43 ppm/°C from 20 °C to 100 °C.

This paper examines the frequency drift of sub-synchronous oscillations (SSOs) caused by the DFIG wind farms when the wind speed varies. The examination is carried out by applying the analysis about the open-loop modal coupling, a newly appeared concept to investigate power system oscillations. Analysis is presented in the paper to reveal that when the wind speed varies, the open-loop electromechanical oscillation mode of the DFIG moves on the complex plane. When it moves close to an open-loop SSO mode of the rest of power system, the open-loop modal coupling occurs to lead to the damping degradation of the SSOs caused by the DFIG. Thus, the variation of wind speed may possibly cause the open-loop modal coupling between the DFIG’s electromechanical oscillation mode and different open-loop SSO modes of the power system. Consequently, poorly or even negatively damped SSOs happen at different SSO frequency. Therefore, the paper provides a better understanding on and deeper insight into the mechanism about how the change of wind speed causes the frequency drift of the SSOs from the standpoint of the open-loop modal coupling.

GPS Precision Point Positioning (PPP) has become a standard method for the time and frequency transfer which is especially useful for inter-continental frequency comparisons of atomic clocks. Moreover, the GPS PPP link has been used for the TAI computation for the last decade which provides a direct link to the TAI/UTC for the National Metrology time laboratories. Here we report on a new absolute frequency measurement of the NRC’s strontium ion atomic clock reference transition using the GPS PPP method. We use the GPS PPP link to determine the frequency as well as the drift of the flywheel oscillator, an active hydrogen maser, against TAI/UTC over a period of about 200 days. This frequency drift function was then used to calculate the frequency difference between the Sr+ ion clock and the flywheel oscillator. The low 2 × 10^-16 uncertainty of the PPP link was achieved by using the month-long frequency averaging interval. The NRC’s Sr+ ion clock has a systematic uncertainty of 1.5 × 10^-17 and its reference transition frequency has been recommended as a secondary representation of the SI second by the CIPM [1, 2]. The frequency measurement campaign of the Sr+ ion clock happened in June 2017 and lasted for 13 days with a total up time of 91.73 hours. Two active hydrogen masers (SM1 for the first 3 days and VM1 for the last 10 days) were used as the reference for the optical frequency comb which was used for the Sr+ ion frequency measurement. The data analysis is based on the accurate determination of the absolute frequency of maser VM1, which was used as a flywheel oscillator for the ion clock frequency measurement, through the GPS PPP link over a period of about 200 days. The PPP link was used to transfer the local UTC time, UTC(NRC), to compare to TAI/UTC. On the other hand, the frequency between VM1 and UTC(NRC) was continuously measured and, therefore, could be linked to TAI/UTC. We found that the frequency drift of maser VM1 can be better modeled using a quadratic function instead of just a linear one, indicating the presence of maser settling (or aging). We chose Circular T #354 (MJD 57904 – 57934) as the ion clock frequency evaluation period. The mean frequency difference between the ion clock and maser VM1 was found by the weighted fit of the intermittent frequency measurements using the maser drift function with the measurement durations as the weights. The uncertainty due to the ion clock measurement down times was estimated using the noise model of the VM1. The mean frequency difference between VM1 and TAI/UTC was found using the above mentioned frequency modeling method for the 30 days evaluation period. Traceability to the SI second is completed by taking into account the scale interval d of TAI for the Circular T #354 taken from the BIPM Circular T website. The systematic and statistical uncertainties of each step were carefully calculated. The preliminary absolute frequency of the Sr+ ion reference transition was found to be in excellent agreement with our previous work [3], with a total fractional frequency uncertainty of 3.8 × 10^-16 representing a fourfold improvement over our previous results. The contributions of the statistical uncertainty are from data extrapolation caused by the measurement down times of the Sr+ ion clock (2.4 × 10^-16), the GPS PPP link uncertainty (2.0 × 10^-16), and the statistical uncertainty of the TAI scale interval d (2.0 × 10^-16). The systematic uncertainty is dominated by that of the SI second realization from the primary/secondary frequency standards (1.0 × 10^-16). This accurate measurement of the reference transition frequency is critical for the NRC’s Sr+ ion atomic clock as a candidate for a future re-definition of the SI second., 52nd Annual Precise Time and Time Interval Systems and Applications Meeting, Jan. 25-28, 2021, Held Online, Series: The Precise Time and Time Interval Systems and Applications Meeting

A difference-fitting method is proposed to mitigate the low frequency drift of a phase-sensitive optical time domain reflectometry ( Φ -OTDR) system caused by laser phase noise. The effective difference region for phase demodulation is theoretically analyzed and experimentally verified, which should be greater than the convolution of the spatial resolution and the length of disturbed optical fiber. Then, a median-fitting algorithm is used to obtain the phase noise of the differential region. The vibration signal of 0.2 Hz is first demodulated with the SNR of 41.79 dB on the optical fiber of 11 km. The low-frequency vibration signals of 0.05 Hz and 0.02 Hz are then successfully restored by using the difference-fitting method, which can effectively eliminate the influence of low frequency drift.

We present an electro-optic technique that generates an independent readout of optical cavity mode frequency spacing. We demonstrate a fractional frequency drift resolution of 1 ppb, sufficient to meet expected future mass change mission requirements.

We suggest that pairing of bouncing medium-energy electrons in the auroral upward current region close to the mirror points may play a role in driving the electron cyclotron maser instability to generate an escaping narrow band fine structure in the auroral kilometric radiation. We treat this mechanism in the gyrotron approximation, for simplicity using the extreme case of a weakly relativistic Dirac distribution instead the more realistic anisotropic Juettner distribution. Promising estimates of bandwidth, frequency drift and spatial location are given.

We introduce a new, to the best of our knowledge, passive technique of mitigating the phase noise in optical frequency combs (FC) by reducing the drift of offset frequency. This can be achieved by customizing the dispersion to attain a power law dependence of the wave vector on frequency, k ( ω ) ∼ ω α , ensuring a constant ratio between group and phase velocities. When this condition is maintained, the drift offset frequency is passively mitigated, and phase noise is reduced. Using quantum cascade laser (QCL) FCs as an example, we demonstrate, analytically and numerically, that the desired dispersion can be easily engineered by properly adjusting the thickness of the QCL active region and that stable offset frequency can be combined with low residual group dispersion.

The paper describes a Raman-laser system with high performance for an absolute gravimeter that was based on 87Rb atom interferometer. As our gravimeter is a part of the standard acceleration of gravity of China, the Raman lasers&rsquo, characteristics should be considered. This laser system includes two diode lasers. The master laser is frequency locked through the frequency-modulation (FM) spectroscopy technology. Its maximum frequency drift is better than 50 kHz in 11 h, which is measured by home-made optical frequency comb. The slave laser is phase locked to the master laser with a frequency difference of 6.8346 GHz while using an optical phase lock loop (OPLL). The phase noise is lower than &minus, 105 dBc/Hz at the Fourier frequency from 200 Hz to 42 kHz. It is limited by the measurement sensitivity of the signal source analyzer in low Fourier frequency. Furthermore, the power fluctuation of Raman lasers&rsquo, pulses is also suppressed by a fast power servo system. While using this servo system, Raman lasers&rsquo, pulses could be fast re-locked while its fast turning on again in the pulse sequence. The peak value fluctuation of the laser power pulses is decreased from 25% to 0.7%, which is improved over 35 times. This Raman-laser system can stably operate over 500 h, which is suited for long-term highly precise and accurate gravity measurements.

We propose and experimentally demonstrate a continuous-wave (CW) terahertz (THz) imaging system based on microwave photonic signal generation scheme. Compared to the traditional opto-electronic THz imaging by using unmodulated lasers, our proposed system obtains the amplitude information by using microwave photonic optical double sideband modulation (DSB). As a result, the phase noise and frequency drift of the free-running laser sources are negligible. We experimentally demonstrate a THz imaging system for measuring various 3D-printed samples by using a 300 GHz DSB signal. In the experiment, the optical DSB modulation is realized with an in-phase and quadrature Mach-Zehnder modulator, and THz signals are generated by photo-mixing at a uni-traveling-carrier photodiode. The THz signals passing through the sample is received by a self-mixing-based Schottky barrier diode. The experimental results show signal-tonoise ratio (SNR) a ~25 dB . In addition, we verify that the optical DSB system operating in the linear regime is superior to the carrier-suppressed scheme, which is attributed to higher THz power and higher SNR. Therefore, the proposed scheme based on microwave photonic double sideband modulation is potentially promising in high-resolution object recognition.

Fabrication of microwave slot array antennas and waveguide bandpass and notch filters using 3D printing has significant advantages in terms of speed and cost even for parts with high mechanical complexity. One disadvantage of Stereolithography (SLA) 3D printed, copper plated microwave components is that some SLA resins have a high Coefficient of Thermal Expansion (CTE), quoted in micrometers per meter per degree or 10&minus, 6 per degree. Compared to typically used metals such as aluminum (CTE 24 &times, 10&minus, 6&middot, K&minus, 1) and copper (CTE 17 &times, 1), SLA resin can have CTE above 100 &times, 1. Resonant structures experience significant frequency drift with temperature changes on the order of 10&ndash, 50 &deg, C. The issue of 3D printed microwave structures changing frequency characteristics significantly with temperature shift has not been addressed or reviewed in current literature. We measured and simulated the effect of temperature change on a slot array, cavity notch filters, and post loaded waveguide bandpass filters. We tested several types of SLA resin, different plating techniques, and also Direct Metal Laser Sintering (DMLS) and Binder Infusion metal 3D printing. Performance as a function of temperature is presented for these alternatives.

Using centimeter wave and decimeter wave solar radio spectral observations of the flares of November 18, 2003 and September 12, 2004, we have discussed two type II like bursts at the meter waves. The radio bursts show that the ordinary frequency drift from high to low frequencies slows down and stops, and a frequency drift from low to high frequencies appears. An analysis of all data on the corresponding flares provides evidence of formation of quasi standing fast mode shocks (termination shocks, TS). TS are able to generate energetic electrons, responsible for the appearance of new sources of hard X ray radiation and generation of fast radio bursts (spikes), fibers and zebra structures. The sources of the radio emission bands with the unusual frequency drift are situated above the top of the post flare loops (lower TS) or are connected with the erupting prominence or coronal mass ejection (CME, upper TS). Estimations of the critical Mach numbers for the ordinary plasma parameters in the solar flares give the values 1.3 easily realized in the flare events. The conditions necessary for generation of unusual radio bursts are likely to occur in the helmet shaped magnetic structures in the solar corona., Comment: 19 pages, 4 figures

A system providing an optical frequency with an instability comparable to that of a hydrogen maser is presented. It consists of a $5$ $\mathrm{cm}$ long, vertically oriented silicon optical resonator operated at temperatures between $1.5$ $\mathrm{K}$ and $3.6$ $\mathrm{K}$ in a closed-cycle cryostat with low-temperature Joule-Thomson stage. We show that with a standard cryostat, a simple cryogenic optomechanical setup, no active or passive vibration isolation, a minimum frequency instability of $2.5\times10^{-15}$ at $\tau=1500$ $\mathrm{s}$ integration time can be reached. The influence of pulse-tube vibrations was minimized by using a resonator designed for low acceleration sensitivity. With reduced optical laser power and interrogation duty cycle an ultra-low fractional frequency drift of $-2.6\times10^{-19}$/$\mathrm{s}$ is reached. At $3.5$ $\mathrm{K}$ the resonator frequency exhibits a vanishing thermal sensitivity and an ultra-small temperature derivative $8.5\times10^{-12}/\mathrm{K}^{2}$. These are favorable properties that should lead to high performance also in simpler cryostats not equipped with a Joule-Thomson stage.

© 2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. In optical networks, degradation of the Quality of Transmission (QoT) can be the outcome of soft-failures in optical devices, like Optical Transponders, Wavelength Selective Switches (WSS) and Optical Amplifiers (OA). In this paper, we assume time-dependent degradations on ROADMs and OAs. Specifically, several degradations are considered: i) the noise figure can increase linearly over time due to the aging of the components; ii) the maximum of optical output power of the amplifiers can decrease because of the degradation in the pump lasers of the EDFAs; iii) aging effects, e.g., due to fiber splices; and iv) the OSNR can vary caused by frequency drift of WSSs due to temperature variations. Our proposal for degradation detection and soft-failure localization includes algorithms that are able to detect and localize the degradation in early stages and facilitate network diagnosis.In addition, we propose an architecture where the control plane consist of a network controller, a Monitoring and Data Analytics system and a QoT tool based on GNPy that are interconnected with each other. The research leading to these results has received funding from the Spanish MINECO TWINS project (TEC2017-90097-R), and from the Catalan Institution for Research and Advanced Studies (ICREA).

We investigate the effect of third order dispersion on the WDM signal generated by optical Fourier transformation. Compared to FBGs, SMF is experimentally shown to result in a channel frequency drift exceeding the channel spacing.

A low-power relaxation oscillator with a high frequency stability is presented for radio frequency identification (RFID). This oscillator implements an improved self-biased and a comparator multiplexing techniques to reduce the power consumption and chip area. A capacitor resetting delay cancellation technique based on a two-phase operation and a proportional to absolute temperature (PTAT) current with an upward curvature versus the temperature are adopted to maintain the frequency stability. The oscillator is designed in a 65 nm standard CMOS process and occupies a small area of 0.0216 mm2. The post-layout simulation results show that a frequency drift of 0.95% from 0.7 to 1.7 V and a temperature stability of 27 ppm/°C as the temperature varies from − 40 to 85 °C at a typical working frequency of 1.92 MHz. Under a supply voltage of 0.7 V, the maximum power consumption is only 15.4 μW at − 40 °C. At room temperature, the figure of merit (FOM1 and FOM2) are 8 nW/kHz and 89.5 dB, respectively, which makes it more efficient than relaxation oscillators reported to date.

We demonstrate a robust, stable and compact spectral filter for use in quantum optics experiments by implementing Fabry-Perot resonators within optical fibre using pairs of fibre Bragg gratings. With only temperature stabilisation, these devices show less than 20 MHz frequency drift over 12 hours with a maximum suppression of roughly 35 dB and overall transmission of 75%. These characteristics make fibre Bragg grating Fabry-Perot resonators ideal for quantum optics experiments where single photon-level signals must be efficiently filtered from large optical fields.

International audience; Burst-mode operation of laser arrays suitable for next generation passive optical networks (NG-PON2) employing time and wavelength division multiplexing (TWDM) is impaired by frequency drifts under variable burst duration. In this work, the issue of frequency drifts under burst and wavelength switching operation is addressed in a four-laser array integrated with a multimode interference coupler using a regrowth-free technology. Frequency drifts are shown to be significantly reduced in a TWDM-PON configuration thanks to the introduction of a thermal management technique based on the use of inactive lasers in the array. Thanks to this method, up to 22% drift reduction is obtained under burst and wavelength switching operation.

This paper studies a new dual-band CMOS class-C voltage-controlled oscillator (VCO). The oscillator consists of a dual-resonance LC resonator in shunt with two pairs of capacitive cross-coupled nMOSFETs. The proposed oscillator has been implemented with the TSMC 0.18 μm CMOS technology, and it shows a frequency tuning range with two frequency bands and a small tuning hysteresis is measured. The oscillator can generate differential signals at 2.4 GHz and 6.9 GHz and it also can generate concurrent frequency oscillation while the circuit is biased around the bias with frequency tuning hysteresis. With the supply voltage of VDD = 1.1 V, the VCO-core current and power consumption of the oscillator are 2.90 mA and 3.19 mW, respectively. The die area of the class-C oscillator is 0.9 × 0.97 mm2. Overvoltage stress is applied to the oscillator, measurement indicates the concurrent oscillation is sensitive to overvoltage stress.

For emerging TWDM-PON systems, based on burst-mode operation over WDM channels, a main challenge is the laser self-heating during bursts. This effect creates a drift of the emission frequency, leading to degraded transmission performances, and perturbation of adjacent channels. We explain an accurate method for characterization of wavelength drift during bursts at a bit time level, and use this method along the paper to characterize frequency drifts in burst-mode operation. First, we present an optimized directly modulated laser design for reduced self-heating, compatible for 100 GHz-spaced systems. Then, we propose a new solution based on counter-heating of the laser with a side heater, enabling to reduce self-heating induced frequency drift. This counter-heating scheme is applied to a standard laser, demonstrating a stringent reduction of frequency drift, and making it compatible for 100-GHz-spaced TWDM-PON transmissions. This simple method opens the way for simple low-cost transmitters in dense and high power TWDM-PON systems.

True random number generator (TRNG) is a critical component in hardware security that is increasingly important in the era of mobile computing and internet of things. A memristor is a promising candidate to construct a TRNG due to its intrinsic variability of switching behavior and high-density integration. Here, we present a 1T1R oscillation structure with a TiN/NbOx/Pt memristor for constructing a rate-adjustable TRNG. The randomness of the oscillation comes from the stochastic switch latency of the memristor. The experimental results demonstrate that the oscillation rate can be modulated by changing the gate bias of the transistor in series. Furthermore, a TRNG circuit with adjustable rates is constructed based on the 1T1R oscillation, and the simulated results revealed that the proposed TRNG output can pass eight NIST tests, indicating the true randomness of the circuit. Finally, the randomness in the memristor, the adjustable rate of the 1T1R oscillation, and the NIST test result of RNG are proved in turn. These results demonstrate the feasibility of the circuit, which can minimize the power consumption by adjusting the random number generation rate to correct the frequency drift caused by extrinsic factors, such as environment temperature and humidity.

New realisation scheme of linear voltage-controlled quadrature oscillator (QO) is proposed. The active building block is electronically tunable (ET) differential voltage current conveyor transconductance (gm ) amplifier configured with current feedback amplifier and multiplication mode current conveyor devices. The designs are essentially tuned-inductor–capacitor oscillator, wherein the electronically variable lossless grounded inductor (L) had been simulated at suitable nodes of the active building block. Subsequently, with slight modification of the block, an ET floating-lossless immittance function generation is presented. Effects of device port mismatch error and parasitic capacitances are analysed. Albeit sensitivity relative to port mismatch error is negligible, the parasitic components tend to limit the higher-usable frequency range; appropriate design equations are derived for a true bilinear admittance function realisation and their applications to filter and sinusoid oscillator design are included. Experimental results on the QO with linear fo -tuning law are satisfactorily verified up to 8.7 MHz at low total harmonic distortion.

We have studied a complex metric radio event which originated in a compact flare, observed with the ARTEMIS-JLS radiospectro-graph on February 12, 2010. The event was associated with a surge observed at 195 and 304 {\AA} and with a coronal mass ejection observed by instruments on-board STEREO A and B near the East and West limbs respectively. On the disk the event was observed at 10 frequencies by the Nancay Radioheliograph, in Ha by the Catania observatory, in soft x-rays by GOES SXI and Hinode XRT and in hard x-rays by RHESSI. We combined these data, together with MDI longitudinal magnetograms, to get as complete a picture of the event as possible. Our emphasis is on two type-II bursts that occurred near respective maxima in the GOES light curves. The first, associated with the main peak of the event, showed an impressive F-H structure, while the emission of the second consisted of three well-separated bands with superposed pulsations. Using positional information for the type-IIs from the NRH and triangulation from STEREO A and B, we found that the type IIs were associated neither with the surge nor with the disruption of a nearby streamer, but rather with an EUV wave probably initiated by the surge. The fundamental-harmonic structure of the first type II showed a band split corresponding to a magnetic field strength of 18G, a frequency ratio of 1.95 and a delay of 0.23-0.65s of the fundamental with respect to the harmonic; moreover it became stationary shortly after its start and then drifted again. The pulsations superposed on the second type II were broadband and had started before the burst. In addition, we detected another pulsating source, also before the second type II, polarized in the opposite sense; the pulsations in the two sources were out of phase and hence hardly detectable in the dynamic spectrum. The pulsations had a measurable reverse frequency drift of about 2/s., Comment: Accepted for Publication in A&A, Article Number: aa41672-21

Magnetic resonant wireless power transfer (MR-WPT) has several advantages over conventional wired underground power supply methods. However, MR-WPT inevitably encounters metal conductors, which reduce the system efficiency through the eddy loss induced in the conductor by high-frequency electromagnetic waves. In this paper, the effect of resonant frequency variations caused by metal tube interference with the aim of maximizing the system efficiency is studied. According to the variation in the resonant frequency, the system efficiency is analytically derived by an equivalent circuit model. Electromagnetic simulations are carried out to further analyze the metal tube interference on the system. The results demonstrate the existence of an optimal resonant frequency that maximizes the system efficiency. Aluminum tube interference produces a lower optimal resonant frequency and higher efficiency than a 304 stainless-steel tube. When the metal tube is slotted, the optimal slot width and number of slots enhance the maximum efficiency and reduce the optimal resonant frequency and frequency drift. With slot widths of 2 and 8 mm, the system efficiency reaches ∼67% at 40.1 kHz and 55% at 48 kHz, respectively. Finally, different types of slotted tubes are fabricated, and the theoretical results are experimentally verified.

A novel triple-path PLL (TPPLL) is presented to compensate the VCO frequency drift caused by the large temperature variations meanwhile maintaining a stable bandwidth and good jitter performance. The proposed PLL architecture splits the VCO tuning loop into three paths as the proportional, the integral, and the temperature compensation (TC) path, respectively. The feed-forward TC path with a large VCO gain but a small bandwidth is adopted to realize the compensation for the VCO frequency temperature drift in a closed-loop manner without affecting the high-frequency performance of the VCO. The fixed control voltage on the proportional path and limited control-voltage variation on the integral path desensitize the VCO gain ( $K_{\mathrm {VCO}}$ ) non-linearity and stabilizes the loop bandwidth over large temperature range. The small VCO gain on the proportional and integral paths contributes to low phase noise and spurs. In addition, the different gain settings for the separate proportional and integral paths work as a capacitor multiplier, leading to saving on the silicon area of the loop filter. A prototype TPPLL at 2.56 GHz using a 65-nm CMOS process has been implemented and measured. The core circuits occupy an area of 0.08 mm2, and consume 8.5 mW. The silicon measurement results show that this PLL can continuously work (without calibration) when the temperature changes from 300 K down to 77 K, and has a frequency drift reduction by 99%, while keeping good jitter performance across the entire temperature range.

One-chip measurements without modifying the physical structure of packaged integrated circuits such as field-programmable gate arrays (FPGA) is challenging. This paper proposes a sensor for detecting the radio frequency interference (RFI) on the supply inside the FPGA chip. The core of the sensor is a ring oscillator built with FPGA look-up tables. The paper proposes a model to predict the response of the ring oscillator to power supply RFI, and shows that the normalized frequency shift of the ring oscillator resulting from the interference is determined by the amplitude of the interference. This relationship is independent of the interference frequency and the size of the ring oscillator. To verify the model, simulations on transistor-level look-up tables of 130-nm and 40-nm technologies were performed. The simulation results matched well with the model. In addition to simulation, an FPGA test board was fabricated. Measurements of FPGA RFI response were performed and the results were consistent with the theoretical model. The effect of the interference on the ring oscillator provided a mechanism to detect the amplitude of the supply interference on the FPGA chip. The frequency of the ring oscillator was monitored through the supply pin by measuring the spectrum of the supply noise. The properties of the sensor, such as constant response in a wide frequency range, insensitiveness to the oscillator size, ease of implementation, and minimal modification requirement of the physical structure, made it suitable for performing on-chip FPGA measurements.

A 51.3-MHz 18- $\mu\text{W}$ 21.8-ppm/°C relaxation oscillator is presented in 90-nm CMOS. The proposed oscillator employs an integrated error feedback and composite resistors to minimize its sensitivity to temperature variations. For a temperature range from −20 °C to 100 °C, the fabricated circuit demonstrates a frequency variation less than ±0.13%, leading to an average frequency drift of 21.8 ppm/°C. As the supply voltage changes from 0.8 to 1.2 V, the frequency variation is ±0.53%. The measured rms jitter and phase noise at 1-MHz offset are 89.27 ps and −83.29 dBc/Hz, respectively.

By using numerical simulations we generalize certain relationships between the parameters of quasimonochromatic whistler-mode waves generated at the linear and nonlinear stages of the cyclotron instability in the backward-wave oscillator regime. One of these relationships is between the wave amplitude at the nonlinear stage and the linear growth rate of the cyclotron instability. It was obtained analytically by V.Yu.Trakhtengerts (1984) for a uniform medium under the assumption of constant frequency and amplitude of the generated wave. We show that a similar relationship also holds for the signals generated in a nonuniform magnetic field and having a discrete structure in the form of short wave packets (elements) with fast frequency drift inside each element. We also generalize the formula for the linear growth rate of absolute cyclotron instability in a nonuniform medium and analyze the relationship between the frequency drift rate in the discrete elements and the wave amplitude. These relationships are important for analyzing the links between the parameters of chorus emissions in the Earth’s and planetary magnetospheres and the characteristics of the energetic charged particles generating these signals.

In this brief, a cross-coupled oscillator is analyzed based on the two-port network theory and the $Y$ - parameter model for a transistor. Contrary to the previous works, the proposed analysis shows that LC cross-coupled oscillators have an additional and higher pure imaginary natural frequency at which the circuit cannot oscillate. The analysis investigates the sufficient condition at which the circuit is able to oscillate at this higher frequency. For the oscillation at the higher frequency mode, we propose adding an extra stage and making a three-stage ring oscillator. The equations obtained from this analysis indicate that the oscillation start-up condition depends on the oscillation frequency. Hence, increasing the speed of the oscillator does not satisfy the start-up condition of oscillators. Our analysis shows that the maximum frequency, in which the circuit stops oscillation in the ring oscillator, is higher than the cross-coupled oscillator and this maximum frequency is very close to the maximum frequency of the transistor.

A frequency-stabilized laser system at 1572 nm for space-borne carbon dioxide (CO2) detection LIDAR to realize the precise measurement of the global atmospheric CO2 concentration is presented in this Letter. A distributed-feedback laser diode serves as the master laser (ML) and is wavelength locked to the CO2 line center at 1572.0179 nm using the external frequency modulation technique. The root mean square frequency drift is suppressed to about 50 kHz at an average time of 0.1 s over 8 h. Based on optical phase-locked loops, an online seeder and an offline seeder are offset locked to the reference laser at 1572.024 and 1572.081 nm, respectively, retaining virtually the same frequency stability as the ML.

This paper shows the effect of the harmonics signals and frequency drift in the power factor correction systems. The phase induced concept is introduced as a key to understanding the dynamics of the power factor parameter. Results shown are related to real and reactive power considering the four first harmonics signal in an electrical network with a nominal frequency at 60 Hz. In addition, the bandwidth for correct the phase induced by harmonics is proposed based on integration time uses for analysis the frequency drift.

A micro-Doppler radar system has recently introduced using the Frequency-Group function as well as using the CW, which requires to set accurately frequency should consider the frequency drift due to temperature variations from the environment. This paper defines the three challenges, proves the experimental result with the test model and proposes the method for resolving issues with three points for observation as follows; Frequency drift, I/Q DC-bias drift, and the full-scale input voltage range of ADC. Finally, we confirmed that the compensation of frequency and DC-bias drift is essential.

Thermal and acoustic noises are crucial to the long-term stability of fiber lasers, as it introduces the fluctuation of optical path length on laser cavity, and hence imposing undesirable intensity noise and frequency drift, particularly for a random fiber laser with distributed Rayleigh scattering feedback from a long length fiber. In this Letter, we propose and demonstrate a thermal and acoustic noise insensitive Brillouin random fiber laser by utilizing the random feedback from a polarization-maintaining (PM) fiber-based random grating. A theoretical model is developed for the first time, to the best of our knowledge, to analyze environmental perturbation on the randomly induced refractive index modulation via a PM random grating. Both the theory and experiments show that the scattered optical intensity of the PM random fiber grating exhibits a weak dependence on the temperature fluctuation and the acoustic noise perturbation compared to that of the Rayleigh scattering from hundreds of meters of PM fibers, leading to the Brillouin random lasing radiation with a 20 dB relative intensity noise suppression in the frequency range from 10 Hz to 1 kHz.

A low-power ring-oscillator-based injection-locked frequency multiplier with a continuous frequency-tracking loop (FTL) that generates 2.4 GHz frequency is proposed. This clock multiplier is designed for wireless local area network (WLAN) applications. A low-power delay cell is used to enhance the efficiency of the system. The FTL is used for continuous calibration of the ring voltage-controlled oscillator (VCO) frequency drift across process, supply, and temperature variations. The proposed architecture is designed using 130-nm CMOS process. The integrated RMS-jitter achieved is 272 fsec in the range from 12 kHz to 20 MHz of the 2.4-GHz output signal with total power consumption of 2.8 mW.

The proposed work is a fully-integrated temperature sensor with low power consumption. The frequency drift of the oscillator will be compensated by this designed CMOS temperature sensor. The bandgap reference circuit was implemented to generated required control voltage and slope. The work demonstrated required control voltage and slope can be generated by changing variable resistors. The deigned CMOS temperature sensor dissipate 302uW while exhibiting inaccuracy of -$0.001^{\mathrm {o}}\text{C}$ and +$0.032^{\mathrm {o}}\text{C}$ over a temperature range between -10 to 90 0C and voltage supply variations of 10%130

Continuous-wave, single-frequency, solid-state lasers with long-term frequency stability and low-intensity noise are an essential resource to generate squeezed and entangled states of light. In order to obtain the stable, nonclassical states of light, the frequency of the laser has to be stabilized with a stable reference. Due to the zero expansion property at a certain temperature, an ultra-low expansion (ULE) Fabry-Perot (F-P) cavity with a high finesse can be used as one of the best candidates of the frequency reference. We perform a detailed analysis of an extraordinarily high-frequency stability and ultra-low-intensity noise laser based on an improved cascade Pound-Drever-Hall frequency stabilization to a ULE F-P cavity. The frequency drift of the laser is suppressed to 7.72 MHz in 4 hours, and the noise level of the laser is simultaneously reduced to the quantum noise limit in the frequency below 300 kHz, which provides the possibility for the direct generation of a stable, high-level squeezed state in a lower-frequency region.

To eliminate the mechanical coupling error caused between the driving fork and the picking up fork, the mass balancing method was used to decrease the mechanical coupling error by the laser etching frequency trimming technique on tuning forks. In order to get high-quality quartz tuning forks, the mechanical coupling error and frequency drift caused by machining must be resolved. The mechanical coupling error was eliminated effectively by the mass balancing method that could compensate the machining error and realize the control of the quartz tuning fork gyroscope at the best resonant frequency. Experimental results showed that, by the mass balancing method, when the symmetry of driving tuning forks and readout tuning forks was amended, the quality factor of driving forks was obviously increased, the driving voltage descended, the mechanical coupling error decreased and the impedance characteristics of quartz tuning fork was improved obviously.