Measurement Bandwidth Research Articles

Measuring complex field waveforms of quadrature amplitude modulation optical signals using a spectrally slicing-and-synthesizing coherent optical spectrum analyzer.

We propose a spectrally slicing-and-synthesizing coherent optical spectrum analyzer to measure complex field waveforms of quadrature amplitude modulation (QAM) optical signals with ultralong periods. The optical spectrum of a measured optical signal is divided into multiple narrowband spectral components, called slices. The slices are sequentially measured using low-speed coherent detection. After phase noise suppression and frequency fluctuation compensation on each slice, the measured slices are synthesized to recover the original signal spectrum. Our numerical and experimental results confirm that the proposed method can overcome the limitation of the measurement bandwidth because the signal spectrum can synthesize more than 100 slices. We experimentally demonstrate complex field measurements of 16QAM optical signals. Our method can measure high-speed optical complex field waveforms with no bandwidth limitation.

Methods for dynamic behavior improvement of tachometric and thermal anemometers by active control

Tachometric and thermal anemometers are two types of instruments mainly used in typical standard measurements in meteorology, ventilation, air conditioning, technical and industrial measurements. Both types of these instruments have many beneficial metrological properties, which causes their widespread use in many measurement issues. However, the sensors of mechanical anemometers have large dimensions and considerable high mechanical inertia. This is the reason for their poor dynamic properties. This results in dynamic measurement errors that are the cause of the measured average value being normally overstated. Thermal anemometers are dedicated for measurements in fast-changing flows. Hot-wire constant-temperature anemometers due to the low thermal inertia of the sensor and the applied feedback, have a wide frequency bandwidth for velocity fluctuations measurement, reaching hundreds of kilohertz. For standard constant-temperature anemometers this bandwidth strongly depends on flow velocity. In high-amplitude fast-changing flows, this can cause significant dynamic measurement errors. This paper presents two methods for improving the dynamic behavior of respectively rotary and thermal anemometers by active control. These methods are based on the introduction of additional feedback loop to the instruments.

Second‐order matrix pencil‐based phasor measurement algorithm for P‐class PMUs

Phasor measurement units (PMUs) have made real-time monitoring and control of power systems possible, thanks to their time synchronisation and fast reporting rate. It is critical that the PMUs can track the dynamics of complex power systems accurately. In this study, a measurement bandwidth extraction method based on signal reconstruction is proposed to filter the out-of-band signals without extra response time. The synthetic phasor is modelled by the second-order Taylor's series expansion. A matrix pencil-based fast phasor measurement algorithm is proposed for P-class PMUs. Simulation and experiment results show that the accuracy and the response time of the proposed algorithm meet the requirements of the IEEE standard. Field data test shows that out-of-band signals have been reduced and the dynamic change of power system can be accurately reflected by phasor estimations. All results demonstrate that the proposed algorithm is suitable for P-class PMUs in complex power systems.

Effects of Kerr medium on force sensing in a dissipative optomechanical system

In this paper, we study the effects of the Kerr medium on the detection of a weak classical force acting on an optomechanical oscillator which is coupled purely dissipatively. We find that force sensing better than the standard quantum limit (SQL) of the mechanical oscillator can be achieved in the presence of Kerr medium. We show that increasing the strength of Kerr nonlinearity not only improves the force sensitivity but also increases the measurement bandwidth. Moreover, our results also show that the influence of thermal noise on force sensing is smaller in the presence of optical Kerr medium, thus making the system more robust against thermal fluctuations.

Quantum hybrid optomechanical inertial sensing.

We discuss the design of quantum hybrid inertial sensor that combines an optomechanical inertial sensor with the retroreflector of a cold atom interferometer. This sensor fusion approach provides absolute and high-accuracy measurements with cold atom interferometers, while utilizing the optomechanical inertial sensor at frequencies above the repetition rate of the atom interferometer. This improves the overall measurement bandwidth as well as the robustness and field deployment capabilities of these systems. We evaluate which parameters yield an optimal acceleration sensitivity, from which we anticipate a noise floor at nano-g levels from DC to 1 kHz.

Definition and evaluation of topography measurement noise in optical instruments

The pursuit of low noise in optical instruments for areal surface topography measurement is relevant to many surface types, ranging from super-polished optical surfaces to weakly reflecting or scattering textures that require enhanced signal sensitivity. We clarify the definition and experimental methods for quantifying random noise in areal surface topography measurements. We also propose a parameter, the topographical noise density, that concisely summarizes the effects of measurement bandwidth. To illustrate these ideas, we present results from a commercial phase-shifting interference microscope showing an RMS measurement noise of 0.03 nm for a 1-s data acquisition of 1 million surface topography image points, after application of a 3 × 3-pixel convolution filter. The results follow the expected inverse square root dependence on the data acquisition time for fast averaging of topography maps, resulting in a measurement noise of <0.01 nm for a 10-s data acquisition.

Time-resolved ion velocity measurements in a high-power Hall thruster using laser-induced fluorescence with transfer function averaging

We present time-resolved laser-induced fluorescence measurements of ion velocity distributions in a 12.5 kW Hall Effect Rocket with Magnetic Shielding (HERMeS) operating in both quasi-periodic and aperiodic oscillation regimes. Transfer function averaging in Fourier space is used to obtain useable signal-to-noise ratios and synchronize data traces taken at different laser wavelengths, measurement axes, and positions in the plasma, achieving a measurement bandwidth of ∼100 kHz. For breathing-mode like global oscillations, the results are shown to be robust to the choice of either discharge current Id(t) or cathode-to-ground voltage Vcg(t) as the reference waveform input to the transfer function. At discharge voltage Vd=600 V, a nearly periodic, impulsive oscillation in the acceleration zone position was accompanied by a ≳100 V peak-to-peak oscillation in the near-plume plasma potential. Smaller amplitude, aperiodic oscillations in the mean ion velocities were detected at Vd=300 V.

In-Plane-Sense Magnetometer Based on Torsional MEMS With Vertically-Interlaced Combs via Self-Alignment Technique

We present a MEMS magnetometer based on the Faraday electromagnetic induction principle that works in the torsional resonance mode to sense in-plane magnetic fields. As for the device design and fabrication, a self-alignment technique is introduced to realize vertically-interlaced combs used for electrostatic driving for a torsional frame structure. In order to directly acquire relatively pure resonance characteristics of devices, an electromagnetic detection means with differential outputs is proposed to suppress the parasitic feed-through effect existing in the normal electrostatic-detection. Based on magnetic response tests, the proposed device has the measured sensitivity of 491 mV/mT with the non-linearity of 0.40% and the resolution of 6 μT under atmospheric pressure. Featured with the quasi-zero power consumption (75 nW), the measurement bandwidth without mechanical bandwidth limits, and the wide dynamic range (98 dB), this in-plane-sense device constituting as an essential for a 3-axis MEMS magnetometer has wide application prospects in automotive and portable electronics.

Impact of bilayered oxide stacks on the breakdown transients of metal–oxide–semiconductor devices: An experimental study

The role of the bilayered structure of the gate oxide on the dynamics of progressive breakdown is systematically studied on Au/Cr/HfO2/Al2O3/InGaAs metal–oxide–semiconductor stacks. Samples with bilayered oxides of 100 Å total thickness were fabricated using different Al2O3 interfacial layer thicknesses to investigate the effects of combining insulator materials with largely different electrical and thermal properties. The breakdown current growth rate dIBD/dt was captured by means of low and high bandwidth measurement setups, and the results were compared in the framework of an electromigration-based progressive breakdown model, originally derived for single-layered oxides. Experimental results show that as the interfacial layer is thicker, a clear increase is observed on the applied voltage required to obtain dIBD/dt values in the same range. However, this effect is not observed for thicknesses above 10 Å for the Al2O3 layer. This is linked to both the electrical stress distribution across the bilayered structure and to the thermal characteristics of Al2O3 that contribute to reduce the temperature of the breakdown spot. The progressive breakdown model is modified to account for these features, showing good agreement with experimental results, behavior that cannot be explained by the model considering one of the layers as already broken during progressive breakdown.

Performance Analysis of ACTE

HTTP adaptive streaming with chunked transfer encoding can offer low-latency streaming without sacrificing the coding efficiency. This allows media segments to be delivered while still being packaged. However, conventional schemes often make widely inaccurate bandwidth measurements due to the presence of idle periods between the chunks and hence this is causing sub-optimal adaptation decisions. To address this issue, we earlier proposed ACTE (ABR for Chunked Transfer Encoding) [6], a bandwidth prediction scheme for low-latency chunked streaming. While ACTE was a significant step forward, in this study we focus on two still remaining open areas, namely, (i) quantifying the impact of encoding parameters, including chunk and segment durations, bitrate levels, minimum interval between IDR-frames and frame rate on ACTE, and (ii) exploring the impact of video content complexity on ACTE. We thoroughly investigate these questions and report on our findings. We also discuss some additional issues that arise in the context of pursuing very low latency HTTP video streaming.

Time-domain Measurement and Analysis of Differential Mode Delay and Modal Bandwidth of Graded-Index Multimode Fiber in SDM Networks

Abstract A novel differential mode delay (DMD) and modal bandwidth measurement technique for a multi-mode optical fiber based on time-domain method has been proposed and analyzed. Mode-dependent loss (MDL) is known to have a detrimental impact on the capacity of multi-mode fiber systems. The bandwidth behavior of 50 μm/62.5 μm graded-index multimode fibers (GI-MMFs) is investigated by launching a temporal pulse into the fiber and measuring the output time-domain waveform to understand and characterize the effect of DMD. The baseband response is measured by observing the broadening of a narrow input pulse (time-domain measurement). This paper verifies the degradation in bandwidth due to profile distortion by the maximum radial shift (starting from the center of the fiber) and the number of steps. The impact due to DMD on GI-MMF performance has been analyzed through fiber transfer function, pulse width and phase changes.

Slightly off-axis digital holographic microscopy with a divided aperture

Divided aperture (DA) technology enhances the depth and anti-scattering capability in microscopy while slightly off-axis digital holographic microscopy improves the input-plane field of view (FOV) utilisation and optimises the detector measurement bandwidth. In this work, we propose a micro-imaging system utilising these two methods to perform full-field 3D topography measurements without any scanning. The DA eliminates the need for element tilts, pinholes, and gratings to produce an angle between the sample and reference beams. Two π/2-phase-shifted interferograms are obtained with polarising elements in one shot. Experiments are performed to prove the feasibility and validity of the proposed method.

Differentiator-Based Photonic Instantaneous Frequency Measurement for Radar Warning Receiver

Radar warning receiver (RWR) plays a significant role in detecting weapon radar. The instantaneous frequency measurement (IFM) section with fast measuring response, large measurement bandwidth, moderate accuracy, and sensitivity is important for an all-threat-covered RWR. In this IFM method, a phase modulator (PM) in combination with a differentiation structure is employed to get rid of the DC drifting and makes the power response is a strict monotonous function of the input frequency. Therefore, the unambiguous determination can be made in a very large range, which guarantees the fast measuring response. According to the theoretical analysis, a strict monotonous amplitude comparison function (ACF) with the covering range higher than 40 GHz can be achieved. Besides, no filter or dispersion elements (DE) such as optical fibers are required, which makes the structure be very concise to meet the potential of integrating in any receiving systems. Due to the limit operation range of the PM, only the range from 0.1 GHz to 25 GHz is demonstrated. The measurement error can be lower than 3%. Especially, benefited by the balance photo-diode (BPD), the sensitivity is good without any noise cancellation processing. The error of lower than 10% will be promised when the RF power level is −40 dBm.

Metrological Support for Measurements of Speed and Bandwidth of Packet Data Networks: Problems and Prospects for Development

We consider the main problems of metrological support for measurements of speed and bandwidth in digital packet data networks. We enumerate the methods for performing data rate measurements. We propose various ways of providing traceability of digital data rate meters such as upgrades to the existing standard GET 200-2012, development of a primary reference method for measuring speed, and the creation of a local verification procedure for measuring the transmission speed of digital information. Recommendations are given for the implementation of the selected method for ensuring traceability of meters for data transfer rate and bandwidth of communication channels. Suggested approaches can apply in metrology for digital communication systems.

Underwater Wireless Information Transfer with Compressive Sensing for Energy Efficiency

Acquisition of sensor data in wireless sensor networks with compressive sensing reduces the cost involved with sensing and communication. The challenge behind this work in underwater environment is exploring the fact of transfer capability of sensor nodes and underwater channel. The robustness of compressive sensing scheme in underwater environment is further augmented by recovery and transfer path. Two algorithms have been proposed. The first which uses compressive sensing at source and reconstruct using orthogonal matching pursuit at sink named as Underwater Wireless Information Transfer with Compressive sensing. Second algorithm exploits bandwidth estimation exploiting the cross traffic at intermediate forwarders for each source sensors to its associated sink named as: Underwater Wireless Information Transfer with Compressive sensing Bandwidth Measurements. Performance metrics of both protocols are interpreted through simulations.

Crosstalk reduction for multi-channel optical phase metrology.

Digitally enhanced heterodyne interferometry (DEHI) combines the sub-wavelength displacement measurements of conventional laser interferometry with the multiplexing capabilities of spread-spectrum modulation techniques to discriminate between multiple electric fields at a single photodetector. Technologies that benefit from DEHI include optical phased arrays, which require the simultaneous phase measurement of a large number of electric fields. A consequence of measuring the phase of multiple electric fields is the introduction of crosstalk, which can degrade measurement precision. This work analytically and experimentally investigates the crosstalk when using DEHI to measure the phase of an arbitrarily large number of electric fields at a single photodetector. Also considered is the practical limit the dynamic range of the photodetector and shot noise imposes on the number of electric fields that can be discriminated. We describe how to minimize crosstalk by design. Experimental results demonstrate up to 55 dB suppression of crosstalk between two electric fields with a phase measurement bandwidth of 20 kHz and 1-10 pm/Hz displacement sensitivity for audio frequencies. Additionally, we demonstrate scaling of crosstalk proportional to the square-root of the number of electric fields when using an M-sequence modulation. Based on this analysis, we estimate that digitally enhanced heterodyne interferometry should be capable of measuring the phase of several hundreds of electric fields at a single photodetector while maintaining the same measurement bandwidth.

Modification of Hot-Wire Anemometers Frequency Bandwidth Measurement Method.

In measurements of fast-changing flows, one of the key issues is knowledge of the anemometer frequency bandwidth. In such measurements, the measurement technique often used is hot-wire anemometry. The determination and optimization of the measurement bandwidth of the hot-wire system is very important for the quality of the measurements carried out. One of the methods used is square-wave or sine-wave electrical testing. The article proposes modification of this method, which involves applying an electrical test signal wirelessly directly to the sensor, using transformer inductive coupling. This modification may in some cases be beneficial and find application in selected metrological problems. The article describes the modified method and its example application.

Analysis of Multi-hour Continuous Observations of Seven Millisecond Pulsars

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

Dynamic compensation method based on system identification and error-overrun mode correction for strain force sensor

To improve the dynamic performance of strain force sensor, a new dynamic compensation method based on system identification and error-overrun (EOV) mode correction is proposed to solve the problem that the existing methods though can improve the time-domain tracking performance but sometimes fail to widen the frequency-domain measurement bandwidth of the sensor simultaneously. For the new method, sensor dynamic compensation is divided into primary and secondary compensations. Primary compensator is obtained by system identification method for correcting the overall frequency response of the sensor, secondary compensators are constructed in a unified structure of 2nd-order system for purposely correcting the remaining EOV modes that limit the sensor measurement bandwidth. Specifically, construction methods of four categories of secondary compensators are discussed; circular construction of multiple secondary compensators and sequential dynamic compensation of sensor output are presented; last, an ATI Mini45 force/torque sensor is employed for verification. The results show that, the proposed method can shorten the step adjust times of the sensor six channels from up to hundreds of millisecond to within 3 ms and widen the bandwidths from around 30 Hz to over 100 Hz; and that, re-identifying a wideband primary compensator and constructing more secondary compensators can further improve the former indices to 0.45 ms and over 287 Hz for a channel. Consequently, the proposed method can effectively improve the time-domain tracking performance and measurement bandwidth of the sensor simultaneously, and it is proven to be effective, practical, and robust for sensor dynamic compensation.

Modal delay and modal bandwidth measurements of bi-modal optical fibers through a frequency domain method

Abstract We propose a simple and robust frequency domain method for measuring modal delay and bandwidth of bi-modal optical fibers. An analytical transfer function model is formulated showing excellent agreement with experimental results for relatively short fibers. Using the model, a full set of information can be extracted, including modal delay and modal bandwidth under any launch conditions. As a result, one can obtain a worst-case modal bandwidth that can gauge the fiber modal bandwidth under general conditions. In addition, the frequency domain measurement method and the analytical model are validated through the excellent agreements with the time domain measurement results. The analytical model is also generalized for longer fiber lengths when additional degradation effects become significant to alter the behavior of the transfer function. Through the detailed study, we show that the simple frequency domain measurement method as facilitated by the analytical model can deliver a full set of modal delay and modal bandwidth information that otherwise requires more complex method of differential mode delay measurements.