Jitter Characterization Research Articles

Observation of subfemtosecond fluctuations of the pulse separation in a soliton molecule.

In this work, we study the timing instability of a scalar twin-pulse soliton molecule generated by a passively mode-locked Er-fiber laser. Subfemtosecond precision relative timing jitter characterization between the two solitons composing the molecule is enabled by the balanced optical cross-correlation (BOC) method. Jitter spectral density reveals a short-term (on the microsecond to millisecond timescale) random fluctuation of the pulse separation even in the robust stationary soliton molecules. The root-mean-square (rms) timing jitter is on the order of femtoseconds depending on the pulse separation and the mode-locking regime. The lowest rms timing jitter is 0.83fs, which is observed in the dispersion managed mode-locking regime. Moreover, the BOC method has proved to be capable of resolving the soliton interaction dynamics in various vibrating soliton molecules.

Stabilizing isolated attosecond pulse formation by dispersion tuning

The carrier envelop phase (CEP) of isolated attosecond pulses (IAPs) is theoretically and experimentally investigated based on the assumption that a significant contribution originates from the measurable CEP jitter of the driving laser. By solving the timedependent Schr\"odinger equation, it is demonstrated that the attosecond CEP jitter of IAPs is minimized when the driving pulse is near its Fourier limit but with slightly negative chirp. Although, at present the utilization of the CEP of IAPs has limited applications, understanding and characterization of the CEP jitter of IAPs is the first step towards exact control of the electric field of extreme ultraviolet (XUV) pulses

Sub-femtosecond precision timing synchronization systems

We present a timing synchronization system that can synchronize optical and microwave signals with attosecond-level precision across kilometer distances. With this technique, the next-generation photon science facilities like X-ray free-electron lasers and intense laser beamlines can be enabled to observe ultra-fast dynamics in atoms, molecules and condensed matter taking place on an attosecond time scale. We discuss some key technologies including master-laser jitter characterization, local one-color laser synchronization, remote two-color laser synchronization, and analyze technical noise contributions in the system. A 4.7-km laser–microwave network with 950-attosecond timing jitter is realized over tens of hours of continuous operation. Finally, an integrated balanced optical cross correlator is introduced. With the same input power level, the required operational power for each timing link is significantly reduced.

Breaking the Femtosecond Barrier in Multi-Kilometer Timing Synchronization Systems

To observe electronic dynamics in atoms, molecules, and condensed matter taking place on an attosecond time scale, next-generation photon science facilities like X-ray free-electron lasers and intense laser beamlines require system-wide attosecond-level synchronization of dozens of optical and microwave signals up to kilometer distances. Here, we present for the first time a timing synchronization system that can meet the strict timing requirements of such large-scale facilities. We discuss some key enabling technologies including master-laser jitter characterization, local timing synchronization, new designs of attosecond-precision timing/phase detectors, and analyze fundamental noise contributions in nonlinear pulse propagation in fiber links. Finally, a complete 4.7-km laser-microwave network with 950-as timing jitter is realized over tens of hours of continuous operation.

Quantum-limited timing jitter characterization of mode-locked lasers by asynchronous optical sampling.

We demonstrate a novel time domain timing jitter characterization method for ultra-low noise mode-locked lasers. An asynchronous optical sampling (ASOPS) technique is employed, allowing timing jitter statistics on a magnified timescale. As a result, sub femtosecond period jitter of an optical pulse train can be readily accessible to slow detectors and electronics (~100 MHz). The concept is applied to determine the quantum-limited timing jitter for a passively mode-locked Er-fiber laser. Period jitter histogram is acquired following an eye diagram analysis routinely used in electronics. The identified diffusion constant for pulse timing agrees well with analytical solution of perturbed master equation.

Temporal jitter in free-running InGaAs/InP single-photon avalanche detectors.

Negative-feedback avalanche diodes (NFADs) provide a practical solution for different single-photon counting applications requiring free-running mode operation with low afterpulsing probability. Unfortunately, the timing jitter has never been as good as for gated InGaAs/InP single-photon avalanche diodes. Here we report on the timing jitter characterization of InGaAs/InP based NFADs with particular focus on the temperature dependence and the effect of carrier transport between the absorption and multiplication regions. Values as low as 52 ps full-width at half-maximum were obtained at an excess bias voltage of 3.5 V and an operating temperature of around -100°C.

Concurrent Multi-Channel Crosstalk Jitter Characterization Using Coprime Period Channel Stimulus

In recent years, the use of highly parallelized and high-speed data links has exacerbated the problem of crosstalk coupling. Signals with high frequency components couple to and degrade the quality of signals in adjacent lines aggressively with reduced device dimensions. In this paper, we propose a methodology for characterizing multiple crosstalk jitter effects in the time domain using a single data capture without the use of any channel models. The method uses repetitive data patterns across different signal lines with coprime periods. Each signal with crosstalk effects is digitized using sub-Nyquist sampling, and after back-end digital signal processing, the original transmitted signal on each line is isolated from its crosstalk components. Mathematical analysis shows that only by using patterns with coprime lengths, unbiased crosstalk characterization is possible. Hardware measurements support the proposed test methodology.

Ultrafast amplifier additive timing jitter characterization and control.

We report on the characterization and long-term compensation of additive timing jitter introduced by a femtosecond ytterbium regenerative amplifier with a 100 kHz repetition rate. A balanced optical cross-correlation technique is used to generate a jitter error signal. This approach is well suited to characterize the additive timing jitter of Yb amplifiers seeded by narrow spectrum Yb oscillators. The balanced optical cross-correlator is in a noncollinear configuration allowing a background free coindence detection. This setup enables the measurement of additive timing jitter from the amplifier, with a noise floor of 300 as integrated from 10 Hz to 10 kHz. The measured additive timing jitter level is about 5 fs, integrated from 0.1 Hz to 10 kHz. The amplifier timing drift characterization and control are performed for more than an hour.

Characterization and analysis of timing jitter in normal-dispersion mode-locked Er-fiber lasers with intra-cavity filtering.

We characterize and analyze the timing jitter of normal-dispersion mode-locked Er-fiber lasers with intra-cavity filtering. The timing jitter of Er-fiber lasers with 9-nm bandpass filters operating at + 0.0084 ps(2) is measured to be 3.46 fs (rms) when integrated from 10 kHz to 10 MHz offset frequency, which is similar to the jitter level of typical stretched-pulse or soliton Er-fiber lasers. The numerical simulation based on split-step Fourier transform method shows that the measured high-frequency jitter is quantum noise-limited performance. We also develop an analytical model for filtered normal-dispersion fiber lasers by modifying the well-established noise model of stretched-pulse fiber lasers. The analytical modeling reveals that the jitter performance is improved mostly by reducing the chirp parameter by intra-cavity filtering. Both numerical simulation and analytical model fit fairly well with the measured timing jitter result.

New Methods to Characterize Deterministic Jitter and Crosstalk-Induced Jitter From Measurements

A small amount of jitter can quickly eat up timing budgets and create timing issues. Precise characterization of deterministic and crosstalk-induced jitter can help isolate and solve issues within high-speed links. Characterizing deterministic and crosstalk-induced jitter is challenging, however, because many types of jitter work together to create the overall jitter profile. Methods are presented in this paper to characterize the deterministic and crosstalk-induced jitter from measurements of total jitter. An improved tail-fit deconvolution method is proposed for characterizing the impact of deterministic jitter in the presence of random jitter. The contribution of random jitter to total jitter is found first, and then that contribution is accounted for to find deterministic jitter. A Wiener filter deconvolution method is also presented for extracting the characteristics of crosstalk-induced jitter from measurements of total jitter made when the crosstalk sources were and were not present. The Wiener filter allows for accurate deconvolution of the measured histograms for total jitter even in the presence of the measurement noise. The proposed techniques are shown to work well both in simulations and in measurements of a high-speed link.

Timing jitter characterization of mode-locked lasers with

Timing jitter characterization of free-running mode-locked lasers with an unprecedented resolution is demonstrated using an optical heterodyne technique. A highly sensitive timing jitter phase-discrimination signal with low-parasitic-amplitude sensitivity is achieved. Analytical and numerical methods are used to analyze the properties of the discrimination signal. For an experimental demonstration, we measure the timing jitter between two loosely synchronized mode-locked Er:Yb:glass lasers with 500-MHz fundamental repetition rates. The timing jitter-detection noise floor for a single mode-locked laser reaches 2.8×10(-13) fs(2)/Hz (∼530 ys/√Hz), and the integrated timing jitter is 16.3 as from 10 kHz to the Nyquist frequency (250 MHz). These results show that this approach can be a simpler alternative to the well-established balanced optical cross-correlation technique.

All fiber-coupled, long-term stable timing distribution for free-electron lasers with few-femtosecond jitter.

We report recent progress made in a complete fiber-optic, high-precision, long-term stable timing distribution system for synchronization of next generation X-ray free-electron lasers. Timing jitter characterization of the master laser shows less than 170-as RMS integrated jitter for frequencies above 10 kHz, limited by the detection noise floor. Timing stabilization of a 3.5-km polarization-maintaining fiber link is successfully achieved with an RMS drift of 3.3 fs over 200 h of operation using all fiber-coupled elements. This all fiber-optic implementation will greatly reduce the complexity of optical alignment in timing distribution systems and improve the overall mechanical and timing stability of the system.

Timing Noise Characterization of High-Speed Digital Bit Sequences Using Incoherent Subsampling and Algorithmic Clock Recovery

In this paper, we exploit a software-based nonreal-time signal acquisition technique to enable high-precision jitter characterization of multi-Gb/s pseudorandom bit sequences (PRBSs) with minimal hardware support. For signal acquisition, incoherent subsampling is employed to increase the effective sampling rate of a digitizer and to simplify its signal acquisition architecture by removing the need for timing synchronization circuits. As a substitute for hardware synchronization circuits, the multiple stages of discrete frequency estimation algorithm, called algorithmic clock recovery (CR), are used. Using the frequency estimate obtained from the proposed algorithmic CR allows us to digitally reconstruct an incoherently subsampled PRBS into a single period of the signal in the discrete-time-domain. The proposed algorithmic CR is accurate and robust, especially in the presence of signal noise and multiple aliased distortions as compared with previously published approaches. In addition, the proposed all-digital jitter characterization technique (including self-reference signal extraction) enables data-dependent jitter separation without using the tail-fitting of a jitter histogram.

Reduction of timing jitter and intensity noise in normal-dispersion passively mode-locked fiber lasers by narrow band-pass filtering.

Fiber lasers mode-locked with normal cavity dispersion have recently attracted great attention due to large output pulse energy and femtosecond pulse duration. Here we accurately characterized the timing jitter of normal-dispersion fiber lasers using a balanced cross-correlation method. The timing jitter characterization experiments show that the timing jitter of normal-dispersion mode-locked fiber lasers can be significantly reduced by using narrow band-pass filtering (e.g., 7-nm bandwidth filtering in this work). We further identify that the timing jitter of the fiber laser is confined in a limited range, which is almost independent of cavity dispersion map due to the amplifier-similariton formation by insertion of the narrow bandpass filter. The lowest observed timing jitter reaches 0.57 fs (rms) integrated from 10 kHz to 10 MHz Fourier frequency. The rms relative intensity noise (RIN) is also reduced from 0.37% to 0.02% (integrated from 1 kHz to 5 MHz Fourier frequency) by the insertion of narrow band-pass filter.

Few-femtosecond-resolution characterization and suppression of excess timing jitter and drift in indoor atmospheric frequency comb transfer

We characterize the timing jitter spectral density of the time-of-flight (TOF) in the indoor atmospheric transfer of optical pulse train over 10 decades of Fourier frequency range (10 μHz - 100 kHz) with sub-100-as resolution using a balanced optical cross-correlator (BOC). Based on the well-known theory for atmospheric transfer of a laser beam, we could fit the measured timing jitter power spectral density to the theory and analyze it with a fairly good agreement from 20 mHz to 10 Hz Fourier frequency range. Moreover, we demonstrate that the BOC-based timing stabilization method can suppress the excess fluctuations in timing from >200 fs (rms) to 2.6 fs (rms) maintained over 130 hours when an optical pulse train is transferred over a 76.2-m long free-space beam path in laboratory environment. The demonstrated stabilization result corresponds to 4 × 10(-20) overlapping Allan deviation at 117,000 s averaging time.

Emitter identification of electronic intelligence system using type-2 fuzzy classifier

Emitter signal recognition is one of the key procedures in signal processing of electronic intelligence (ELINT). In particular, the identification of radar emitters has been important with the advances in radio frequency, electronics and control technologies. Jitter is an unintentional form of modulation that can have a wide variety of sources. Timing-related data errors will occur if jitter is beyond acceptable limits. Designers need a fast and easy way to obtain a complete characterization of clock jitter in the microprocessor controlled. To enhance the ability of specific emitter identification (SEI) to meet the requirement of modern ELINT, a novel identification approach for radar emitter signals based on type-2 fuzzy classifier is presented in this paper. In fuzzy type-2 sets, the uncertainty is represented as an extra dimension. In this article, we show how it is possible to reduce the effect of SEI-induced highly jittered radar emitters in ELINT, with the classifiers of type-1 and type-2 fuzzy logic. This work discusses the impact of unknown jitter sampling on signal estimation. Based on the ELINT feature extraction of radar emitter signals, the type-2 fuzzy classifier is applied to identification of radar emitters effectively. Experiment results shows that the approach can achieve high accurate classification even at higher error deviation level and has good characteristics of identification.

Delay and Jitter Characterization for Software-Based Clock Synchronization Over WLAN Using PTP

In distributed systems, clock synchronization performance is hampered by delays and jitter accumulated not only in the network, but also in the timestamping procedures of the devices being synchronized. This is particularly critical in software timestamp-based synchronization where both software- and hardware-related sources contribute to this behavior. Usually, these synchronization impairments are collapsed into a black-box performance figure without quantifying the impact of each individual source, which obscures the picture and reduces the possibility to find optimized remedies. In this study, for the first time, the individual sources of delay and jitter are investigated for an IEEE 802.11 wireless local area network (WLAN) synchronization system using the IEEE 1588 protocol and software timestamps. Novel measurement techniques are proposed to quantify the hardware- and software-related delay and jitter mechanisms. It is shown that the delays and their associated jitter originate from both the WLAN chipset and the host computer. Moreover, the delay from the chipset cannot be considered symmetric and any such assumption inevitably leads to a residual offset, and thus to synchronization inaccuracy. Therefore, a calibration-based approach is proposed to compensate for these delays and to improve the performance of WLAN synchronization. Experimental results show that with optimal error compensation, a similar synchronization performance as software-based synchronization in Ethernet networks can be achieved.

Amplitude Noise and Timing Jitter Characterization of a High-Power Mode-Locked Integrated External-Cavity Surface Emitting Laser

We present a timing jitter and amplitude noise characterization of a high-power mode-locked integrated external-cavity surface emitting laser (MIXSEL). In the MIXSEL, the semiconductor saturable absorber of a SESAM is integrated into the structure of a VECSEL to start and stabilize passive mode-locking. In comparison to previous noise characterization of SESAM-mode-locked VECSELs, this first noise characterization of a MIXSEL is performed at a much higher average output power. In a free-running operation, the laser generates 14.3-ps pulses at an average output power of 645 mW at a 2-GHz pulse repetition rate and an RMS amplitude noise of 0.15% [1 Hz, 10 MHz]. We measured an RMS timing jitter of 129 fs [100 Hz, 10 MHz], which represents the lowest value for a free-running passively mode-locked semiconductor disk laser to date. Additionally, we stabilized the pulse repetition rate with a piezo actuator to control the cavity length. With the laser generating 16.7-ps pulses at an average output power of 701 mW, the repetition frequency was phase-locked to a low-noise electronic reference using a feedback loop. In actively stabilized operation, the RMS timing jitter was reduced to less than 70 fs [1 Hz, 100 MHz]. In the 100-Hz to 10-MHz bandwidth, we report the lowest timing jitter measured from a passively mode-locked semiconductor disk laser to date with a value of 31 fs. These results show that the MIXSEL technology provides compact ultrafast laser sources combining high-power and low-noise performance similar to diode-pumped solid-state lasers, which enable world-record optical communication rates and low-noise frequency combs.

Advanced Test Solution for Data Dependent Jitter Characterization of Hsio on ATE

Jitter is the core testing spec in HSIO device characterization phase. Normally peak-to-peak jitter is measured with spec search method on ATE. But it is not sufficient due to some advanced processors require to get the knowledge of sources of deterministic jitter, especially the Data dependent jitter. In this paper, an approach for measuring the DDJ on Advantest 93K test platform is introduced, and the correlation data with bench instrumentation is shown.

Laser Scanner Jitter Characterization

The electrophotographic (EP) process is widely used in imaging systems such as laser printers and office copiers. In the EP process, laser scanner jitter is a common artifact that mainly appears along the scan direction due to the condition of polygon facets. Prior studies have not focused on the periodic characteristic of laser scanner jitter in terms of the modeling and analysis. This paper addresses the periodic characteristic of laser scanner jitter in the mathematical model. In the Fourier domain, we derive an analytic expression for laser scanner jitter in general, and extend the expression assuming a sinusoidal displacement. This leads to a simple closed-form expression in terms of Bessel functions of the first kind. We further examine the relationship between the continuous-space halftone image and the periodic laser scanner jitter. The simulation results show that our proposed mathematical model predicts the phenomenon of laser scanner jitter effectively, when compared to the characterization using a test pattern, which consists of a flat field with 25% dot coverage.