Delay Calibration Research Articles

Comparative analysis of optical gating time characterization methods for ultrafast gated image intensifiers with sub-nanosecond temporal resolution

Ultrafast gated image intensifiers are crucial for capturing high-resolution images with sub-nanosecond temporal resolution. This study compares two methods for characterizing optical gating time in these intensifiers: Method I, involving a “laser pulse walkthrough,” and Method II, utilizing a fiber optic delay array. Both methods were applied to the same intensifier, with results analyzed for consistency and discrepancies. The findings indicate that both methods yield consistent optical gating times within their standard deviations range, though Method II exhibited greater dispersion at the photocathode edges due to spatial non-uniformity. The study further reveals that while the optical gating time distribution across the photocathode is uniformly consistent, a constant delay exists between different regions. To enhance measurement precision it is recommended to subdivide the photocathode for individual calibration of gating time and delay. These insights are pivotal for improving the precision and reliability of optical gating time measurements in applications requiring sub-nanosecond or even picosecond temporal resolution.

An integrated coupled oscillator network to solve optimization problems

Solving combinatorial optimization problems is essential in scientific, technological, and engineering applications, but can be very time and energy-consuming using classical algorithms executed on digital processors. Oscillator-based Ising machines offer a promising alternative by exploiting the analog coupling between electrical oscillators to solve such optimization problems more efficiently. Here we present the design and the capabilities of our scalable approach to solve Ising and quadratic unconstrained binary optimization problems. This approach includes routable oscillator connections to simplify the time-consuming embedding of the problem into the oscillator network. Our manufactured silicon chip, featuring 1440 oscillators implemented in a 28 nm technology, demonstrates the ability to solve optimization problems in 950 ns while consuming typically 319 μW per node. A frequency, phase, and delay calibration ensures robustness against manufacturing variations. The system is evaluated with multiple sets of benchmark problems to analyze the sensitivity for parameters such as the coupling strength or frequency.

Time delay calibration techniques for receiving arrays in SNSPD-based optical communication systems

Superconducting nanowire single photon detectors (SNSPDs) have attracted considerable attention in the field of free-space optical communications, especially for ultra-long-distance communications. Calibrating the inherent time delay in the optoelectronic circuit of SNSPD arrays is critical to enabling photon detection with high time accuracy. In this paper, we propose two methods for estimating the inherent timing error: Gaussian fitting calibration (GFC) and maximum-likelihood calibration (MLC). In particular, MLC estimates the timing error by taking into account the deadtime and jitter characteristics of SNSPD. Experimental results demonstrate the effectiveness of the proposed methods.

PCO and hardware delay calibration for LEO satellite antenna downlinking navigation signals

Augmentation of the Global Navigation Satellite System by low earth orbit (LEO) satellites is a promising approach benefiting from the advantages of LEO satellites. This, however, requires errors and biases in the satellite downlink navigation signals to be calibrated, modeled, or eliminated. This contribution introduces an approach for in-orbit calibration of the phase center offsets (PCOs) and code hardware delays of the LEO downlink navigation signal transmitter/antenna. Using the satellite geometries of Sentinel-3B and Sentinel-6A as examples, the study analyzed the formal precision and bias influences for potential downlink antenna PCOs and hardware delays of LEO satellites under different ground network distributions, and processing periods. It was found that increasing the number of tracking stations and processing periods can improve the formal precision of PCOs and hardware delay. Less than 3.5 mm and 3 cm, respectively, can be achieved with 10 stations and 6 processing days. The bias projections of the real-time LEO satellite orbital and clock errors can reach below 3 mm in such a case. For near-polar LEO satellites, stations in polar areas are essential for strengthening the observation model.

Dual-oscillator infrared electro-optic sampling with attosecond precision

Electro-optic sampling of infrared electric fields has set sensitivity and dynamic-range records in broadband molecular vibrational spectroscopy. Yet, in these works, the 1-second-scale single-trace acquisition time leads to intra-scan noise accumulation and restricts the throughput in measurements of multiple samples and of dynamic processes. We present a dual-laser-oscillator approach capturing 2800 mid-infrared waveforms per second by scanning the relative delay between the sampled waveform and the gate pulses using a modulated repetition-frequency lock. The new technique of electro-optic delay tracking (EODT) provides delay calibration with down to few-attosecond precision and provides a general route to high-precision dual-oscillator spectroscopy with picosecond delay ranges. Our work has immediate applications in, e.g., precision electric-field metrology and high-speed biosensing.

Time delay and nonadiabatic calibration of the attoclock. Multiphoton process versus tunneling in strong field interaction

The measurement of the tunneling time delay in attosecond experiments, termed attoclock, sparked a heated debate about tunneling time and the role of time in quantum mechanics. We show a model that explains the experimental result of the attoclock in the nonadiabatic field calibration, where we find good agreement with the experimental data of Hofmann et al. (J. Mod. Opt. 66, 1052, 2019). We confirm our result with the numerical integration of the time-dependent Schrödinger equation. We also found that at a field strength F≤Fa (Fa is the atomic field strength), the model always predicts a time delay with respect to the quantum (lower) limit τa at F=Fa. For an adiabatic tunneling, the saturation at the limit (F=Fa) explains the well-known Hartman effect or Hartman paradox.

Synchronous Driving Method for Stitching Pixel Arrays Based on an Adaptive Correction Technique.

With the application of stitching technology in large-pixel-array CMOS image sensors, the problem of non-synchronized output signals from pixel array bilateral driver circuits has become progressively more serious and has led to the DC perforation of bilateral driver circuits, while conventional clock tree synchronization design methodology does not apply to stitching technology. Therefore, this paper analyses reasons for the inconsistency in the output signals of bilateral driving circuits and proposes a synchronous driving method applicable to stitching pixel arrays based on the idea of on-chip output signal delay detection and calibration. This method detects and corrects the non-synchrony of the row driver output signals on both sides according to changes in the operating environment of the chip. This method is characterized by a simple structure and high reliability. Finally, based on the 55 nm stitching process, simulations are carried out in a CMOS image sensor with a chip area of 77 mm × 84 mm to verify that this method is feasible. This large image sensor with a 150 M pixel array has a frame rate of over 10 FPS.

Absolute delay calibration by analytical fitting of attosecond streaking measurements

An accurate temporal characterization of both pump and probe pulses is essential for the correct interpretation of any pump-probe experiment. This is particularly true for attosecond spectroscopy, where the pulses are too short to be directly measured with electronic devices. However, when measuring the absolute timing between a light waveform and the related photoinduced physical phenomenon, such characterization does not suffice. Here, we introduce a new method called rACE (refined Analytical Chirp Evaluation), which retrieves both pump and probe pulses while establishing a direct relation between the reconstructed time axis and the experimental delay. This feature is particularly relevant for the extraction of absolute time delays, a growing field in attosecond spectroscopy. In this work, we prove the robustness of rACE with simulated datasets involving the effect of pulse chirp, distinctive target attributes, and non-isolated attosecond pulses, which normally constitute challenging situations for standard methods. For all the cases reported here, rACE achieves a precise absolute delay calibration with an accuracy better than the atomic unit of time. Its successful application to attosecond experimental measurements makes it a fundamental tool for attaining sub-cycle absolute temporal resolution, enabling new investigations of lightwave-driven ultrafast phenomena.

A Dual-Path Subsampling PLL With Ring VCO Phase Noise Suppression

This article presents a 2-GHz dual-path subsampling phase-locked loop (SSPLL) with ring voltage-controlled oscillator (VCO) phase noise suppression (PNS). In addition to the conventional subsampling charge pump (SSCP), a high-pass path from the subsampling phase detector (SSPD) to the low-pass filter (LPF) is implemented in the proposed SSPLL. Due to this dual-path architecture, a new in-band zero and pole are introduced into the open-loop transfer function (zero frequency is smaller than the pole frequency), which extends the open-loop unit-gain bandwidth without sacrificing the phase margin. Consequently, the phase noise contribution of the ring VCO is suppressed while the loop stability is ensured. Meanwhile, the phase noise contribution of the high-pass path is negligible compared to the reference and ring VCO’s contribution. Measurement results show that the SSPLL’s closed-loop bandwidth is extended to around 6 MHz with a reference of 20 MHz and the jitter is reduced by 1.34 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> (from 3.52 to 2.63 ps) with a maximum noise suppression of 6.5 dB at the 1.1-MHz offset. The PNS path consumes 0.16 mW and no delay line or calibration is needed, which results in a relatively high FoM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm{PNC}}$</tex-math> </inline-formula> value of 40.5 dB.

Galileo E3 Total Time Delay Calibration in NTSC Time and Frequency Comparison

In order to improve the reliability of the time transfer link, Bureau International des Poids et Mesures (BIPM) has offcially taken the Galileo time comparison as the backup link for UTC calculation since 2020. Therefore, Galileo calibration of receiver is a necessary work for all timekeeping labs around the world to participate in the UTC link. Taking the GPS link calibrated by Physikalisch-Technische Bundesanstalt (PTB) and the National Time Service Center (NTSC) as reference, this paper sets PT09 as reference station to calibrate and verify the Galileo E3 (E1&E5a) total delay of NT02 and NT05 receivers from NTSC. The results show that the Galileo E3 total delay of NT02 and NT05 are 74.6 ns and 46.5 ns, respectively, the calibration uncertainty is 3.5 ns, and the calibration delay is relatively stable. After calibration, GPS P3 and Galileo E3 Common View results between NT02/NT05 and calibrated receivers of other timekeeping labs are basically consistent. Taking the GPS P3 links comparison results as reference between NTP3 and receivers from other labs, the average deviation is less than 1.5 ns, which is within the calibration uncertainty range.

Data-Driven Antenna Delay Calibration for UWB Devices for Network Positioning

Data-Driven Antenna Delay Calibration for UWB Devices for Network Positioning

Revealing regolith substructure by Chang’E-5 LRPR with optimized cable delay calibration method

The Lunar Regolith Penetrating Radar (LRPR) onboard the Chang’E 5 lander is the first antenna-array radar deployed for the exploration of an extraterrestrial object. It is able to measure the subsurface structure of the moon at a resolution of ∼10 cm. This work presents a method for calibrating the variable cable delay of the LRPR and an imaging method based on synthesis imaging from Radio Astronomy. The cable delay calibration method effectively calibrates the cable delay shift of the LRPR with a nanosecond-level precision. To validate the accuracy of the cable delay method, we use the data obtained from both the ground experiment and the moon-exploration mission of the LRPR. The imaging method is used to visualize the subsurface structure of the Chang’E-5 (CE-5) landing site. Moreover, Finite-Difference Time-Domain (FDTD) simulation is carried out to help interpret the imaging results. The radar images derived from the LRPR observations show consistency with each other and match the bit force record during the drilling process. The results suggest that the rocks interacted with the CE-5 drill feature a size of 15 to 20 cm.

A Precise Zenith Hydrostatic Delay Calibration Model in China Based on the Nonlinear Least Square Method

Abstract Zenith hydrostatic delay (ZHD) is a crucial parameter in Global Navigation Satellite System (GNSS) navigation and positioning and GNSS meteorology. Since the Saastamoinen ZHD model has a larger error in China, it is significant to improve the Saastamoinen ZHD model. This work first estimated the Saastamoinen model using the integrated ZHD as reference values obtained from radiosonde data collected at 73 stations in China from 2012 to 2016. Then, the residuals between the reference values and the Saastamoinen modeled ZHDs were calculated, and the correlations between the residuals and meteorological parameters were explored. The continuous wavelet transform method was used to recognize the annual and semiannual characteristics of the residuals. Because of the nonlinear variation characteristics of residuals, the nonlinear least squares estimation method was introduced to establish an improved ZHD model—China Revised Zenith Hydrostatic Delay (CRZHD)—adapted for China. The accuracy of the CRZHD model was assessed using radiosonde data and International GNSS Service (IGS) data in 2017; the radiosonde data results show that the CRZHD model is superior to the Saastamoinen model with a 69.6% improvement. The three IGS stations with continuous meteorological data present that the BIAS and RMSE are decreased by 2.7 and 1.5 (URUM), 5.9 and 5.3 (BJFS), and 9.6 and 8.8 mm (TCMS), respectively. The performance of the CRZHD model retrieving PWV was discussed using radiosonde data in 2017. It is shown that the CRZHD model retrieving PWV (CRZHD-PWV) outperforms the Saastamoinen model (SAAS-PWV), in which the precision is improved by 44.4%. The BIAS ranged from −1 to 1 mm and RMSE ranged from 0 to 2 mm in CRZHD-PWV account for 89.0% and 95.9%, while SAAS-PWV account for 46.6% and 58.9%. Significance Statement Zenith hydrostatic delay (ZHD) is one of the most important parameters in Global Navigation Satellite System (GNSS) navigation and positioning and GNSS meteorology, which can be derived from a precise ZHD model due to its stability. This research established an improved ZHD model for China to obtain accurate ZHD, which is a prerequisite for pinpoint precipitable water vapor (PWV) retrieval. And the PWV value is beneficial to analyze the change in precipitation in some regions, forecast the short-term rainfall, and monitor the climate.

Tropospheric Delay Calibration System Performance During the First Two BepiColombo Solar Conjunctions

AbstractMedia propagation delay and delay‐rate induced by the water vapor within the Earth's troposphere represent one of the main error sources for radiometric measurements in deep space. In preparation for the BepiColombo and JUICE missions, the European Space Agency has installed and operates the prototype of a tropospheric delay calibration system (TDCS) at the DSA‐3 ground station located in Malargüe, Argentina. An initial characterization of the TDCS performance was realized using two‐way Doppler measurements at X‐band to perform the orbit determination of the Gaia spacecraft. This work will further characterize the system by analyzing two‐way Doppler and range data at X‐ and Ka‐band for 31 tracking passes of the BepiColombo spacecraft, which were recorded between March 2021 and February 2022 during the first two solar conjunction experiments. The performance exceeds the expectations based on the previous analysis, with a reduction of the Doppler noise of 51% on average and up to 73% when using the TDCS measurements in place of standard calibrations based on global navigation satellite system data. Furthermore, the campaign serves as validation of the TDCS operations during superior solar conjunctions, with most of the tracking passes at low elongation now satisfying the Mercury orbiter radioscience experiment requirements on two‐way Doppler stability. These results, which are in line with those of similar instruments installed at other Deep Space Network antennas, are obtained using a commercial microwave radiometer with significantly lower installation and maintenance costs.

High-flexibility and high-accuracy phase delay calibration method for MEMS-based fringe projection systems.

Microelectromechanical system (MEMS) mirror based laser beam scanning (LBS) projectors for fringe projection profilometry (FPP) are becoming increasingly popular attributing to their small size and low cost. However, the initial phase of the scanning MEMS mirror employed in an LBS projector may vary over time, resulting in unstable and distorted fringe patterns. The distorted fringe patterns will largely decrease the accuracy of the three-dimensional (3D) topographic reconstruction. In this paper, an efficient phase delay calibration method based on a unique fringe projection sequence and a corresponding image processing algorithm is proposed. The proposed method can compensate the phase uncertainty and variation with no need to add any extra components. One LBS projector has been constructed using a uniaxial electrostatic MEMS mirror that has a mirror size of 2.5 mm × 2.5 mm and a scanning field of view of 60 ∘ at its resonance of 1523 Hz. 3D reconstruction experiments are conducted to study how the 3D reconstruction results are affected by the phase delay. The standard deviation of a sphere reconstruction is improved from 2.05 mm to 0.20 mm after the positive phase delay deviation of 5 μs is compensated using this new calibration method.

Lunar Orbit VLBI Experiment Ground Validation System

China is planning to launch a relay satellite in the coming years with a payload for the Earth-Moon Very-Long-Baseline Interferometer (VLBI) observation research and scientific applications, known as the Lunar Orbit VLBI Experiment (LOVEX) system. This system will perform the lunar orbit VLBI experiments for in the world, and will improve the accuracy of planetary spacecraft orbit determination and the scientific observation capabilities of astrophysics and astrometry. Prior to launch, key technologies of the system must be verified, so we have established a LOVEX ground validation system with similar performance to the LOVEX system. The LOVEX ground validation system consists of a 4.5-meter ring-focus antenna, X-band receiver, frequency converter and digital backend, hydrogen maser, and monitoring and control software. Using this system, we have successfully conducted VLBI differential observation experiments with the Shanghai 65m radio telescope and Beijing 50m radio telescope. The experimental results show that, after calibration with NRAO150, the standard deviations of delay error of Tianwen-1 is within 0.5 ns, consistent with the theoretical timing accuracy, verifying the feasibility of the LOVEX time delay calibration.

Research and application of picosecond accuracy time delay calibration for satellite laser ranging system

Research and application of picosecond accuracy time delay calibration for satellite laser ranging system

Low-Cost GNSS Simulators With Wireless Clock Synchronization for Indoor Positioning

In regions where global navigation satellite systems (GNSS) signals are unavailable, such as underground areas and tunnels, GNSS simulators can be deployed for transmitting simulated GNSS signals. Then, a GNSS receiver in the simulator coverage outputs the position based on the received GNSS signals (e.g., Global Positioning System (GPS) L1 signals in this study) transmitted by the corresponding simulator. This approach provides periodic position updates to GNSS users while deploying a small number of simulators without modifying the hardware and software of user receivers. However, the simulator clock should be synchronized to the GNSS satellite clock to generate almost identical signals to the live-sky GNSS signals, which is necessary for seamless indoor and outdoor positioning handover. The conventional clock synchronization method based on the wired connection between each simulator and an outdoor GNSS antenna causes practical difficulty and increases the cost of deploying the simulators. This study proposes a wireless clock synchronization method based on a private time server and time delay calibration. Additionally, we derived the constraints for determining the optimal simulator coverage and separation between adjacent simulators. The positioning performance of the proposed GPS simulator-based indoor positioning system was demonstrated in the underground testbed for a driving vehicle with a GPS receiver and a pedestrian with a smartphone. The average position errors were 3.7 m for the vehicle and 9.6 m for the pedestrian during the field tests with successful indoor and outdoor positioning handovers. Since those errors are within the coverage of each deployed simulator, it is confirmed that the proposed system with wireless clock synchronization can effectively provide periodic position updates to users where live-sky GNSS signals are unavailable.

A Fractional-N CP-PLL with fast two-point modulation calibration using duty-cycle and polarity tracking technique in 110-nm CMOS

This article proposes a fractional-N charge pump phase-locked loop (CP-PLL) with fast two-point modulation calibration using Duty-Cycle and Polarity Tracking technique. The proposed calibration method can perform delay and gain calibration within 15 μs, respectively. A DTC-assisted Polarity Detector is used to track and countervail the propagation delay of two modulation paths. A TDC-based Duty-Cycle Detector is used to monitor and compensate the two paths gain mismatch. By comparing the code with the threshold set in the look-up table (LUT), a quick calibration can be achieved. To maintain high out-band phase noise performance and stronger robustness, a Class-C oscillator using Capacitance Desensitization technique and Cross-Bias technique is adopted in the design. The proposed CP-PLL is implemented in a standard 110-nm CMOS technology, occupying 2.7 mm2 silicon area. The post-simulation results show the proposed calibration method can calibrate the delay/gain mismatch within 30 μs. Fast calibration mode supports calibration time within 62.5 ns. The phase noise performance is −91-dBc/Hz@100 kHz, −119-dBc/Hz@1 MHz. The entire CP-PLL dissipates 20.9-mW and achieves an RMS jitter of 6.2 ps, corresponding to a figure of merit (FOM) of −211-dB.

Development of 38GHz-band wireless communication system using high altitude platform station (HAPS) for 5G network--study on delay calibration of full digital beamforming for HAPS with base station on-board--

Development of 38GHz-band wireless communication system using high altitude platform station (HAPS) for 5G network--study on delay calibration of full digital beamforming for HAPS with base station on-board--