Low-noise Source Research Articles

Gaussian-weighted crosscorrelation imaging condition for microseismic source localization

Time-reversal imaging is a powerful method for the localization of microseismic events. Conventional time-reversal imaging methods such as autocorrelation imaging or grouped crosscorrelation imaging may suffer from imaging artifacts, e.g., caused by less refined velocity models, noise-contaminated data, and data acquired from sparse receiver networks. These artifacts typically reduce imaging quality and may cause subsequent misinterpretations leading to false positives. To address these issues, we develop a new imaging condition that comprises three steps for each time step. First, we divide the back-propagated wavefield into parts according to their maximum absolute amplitudes. Second, the amplitudes of the back-propagated wavefield are weighted by a Gaussian function with the spatial extent of the prevailing wavelength of the event, centered at the absolute maximum of that part of the wavefield. Finally, we zero-lag crosscorrelate these weighted wavefields at each space point to obtain an image for this time step. The final image is gained by summing the images for each time step. This process collects all energy concentrations along the back projection process, and the energy on the wavefront overlaps and collapses at the hypocenter leading to high-resolution images displaying little to no imaging artifacts. Numerical examples using the Marmousi-II and the 3D SEG overthrust models and a 3D field data example indicate the performance of our method. High-resolution low-noise source images allow unique identification of sources even for source clusters, noisy data, and sparse acquisitions. The source localization errors are smaller than the dominant wavelength of the signal, where a smooth model with a mean velocity error of approximately 5% was considered in the synthetic examples, and a homogeneous model was used in the field data example.

Optical noise characteristics of injection-locked epitaxial quantum dot lasers on silicon.

This work theoretically investigates the relative intensity noise (RIN) and spectral linewidth characteristics of epitaxial quantum dot (QD) lasers on silicon subject to optical injection. The results show that the RIN of QD lasers can be reduced by optical injection, hence a reduction of 10 dB is achieved which leads to a RIN as low as -167.5 dB/Hz in the stable injection-locked area. Furthermore, the spectral linewidth of the QD laser can be greatly improved through the optical injection locked scheme. It is reduced from 556.5 kHz to 9 kHz with injection ratio of -60 dB and can be further reduced down to 1.5 Hz with injection ratio of 0 dB. This work provides an effective method for designing low intensity noise and ultra-narrow linewidth QD laser sources for photonics integrated circuits on silicon.

60 Gbps real-time wireless communications at 300 GHz carrier using a Kerr microcomb-based source

Future wireless communication infrastructure will rely on terahertz systems that can support an increasing demand for large-bandwidth, ultra-fast wireless data transfer. In order to satisfy this demand, compact, low-power, and low noise sources of terahertz radiation are being developed. A promising route to achieving this goal is combining photonic-integrated optical frequency combs with fast photodiodes for difference frequency generation in the THz. Here, we demonstrate wireless communications using a 300 GHz carrier wave generated via photomixing of two optical tones originating from diode lasers that are injection locked to a dissipative Kerr soliton frequency microcomb. We achieve transfer rates of 80 Gbps using homodyne detection and 60 Gbps transmitting simultaneously both data and clock signals in a dual-path wireless link. This experimental demonstration paves a path toward low-noise and integrated photonic millimeter-wave transceivers for future wireless communication systems.

Broadband sound source hologram formation and application in oceanic waveguides

The physical and mathematical basics of holographic interferometry of broadband signal processing in oceanic waveguides are presented. The application of holographic processing for localization of low-noise sources is considered.

Experimental investigation of possible improvements of ISO 9614

Sound power level is the key quantity to describe the noise emission of products and is needed to reduce noise at work, at home, and in the environment, e.g. for promoting and selecting low noise products (Sell and Buy Quiet). Sound power determination based on sound intensity measurements has advantages in non-ideal acoustic environments, e.g. indoors, but outside of acoustic test rooms, and is standardized in the ISO 9614 series. The current version of all three parts of ISO 9614 is their first edition. The advances of technology and knowledge indicate that the whole series should be revised. The improvement of the sound intensity method was investigated regarding a number of aspects. The use of a single spacer up to frequencies, which are outside of the currently usable frequency range, was studied. The effect of electrical noise was investigated to extend the applicability of the method to low noise sources. The discretization of the enveloping surface is discussed in relation to the accuracy grade of the measurements. The possibility to measure with more than one probes is also presented. The results indicate that there is the possibility for a substantial improvement of the ISO 9614 series.

Potential noise annoyance from ambient air quality measurement using high volume air sampler (HVAS)

One of the benchmarks in air pollution is the quality of ambient air consisting of gas and particulate matter. Measurement of particulates in ambient air can be done using a High-Volume Air Sampler (HVAS). However, in the measurement process it sometimes causes noise annoyance to the community where the measuring instrument is operated, considering that the operating time of the instrument is 24 consecutive hours. This research identifies the value of the sound power level emitted from the several types of HVAS to the surrounding environment. There are two types of HVAS measured in this study consisting of one unit of HVAS with analogue flow control made by Indonesian manufacturer and two units of HVAS with digital flow control made by Japan and United States of America manufacturers. Sound power level is determined using ISO 9614 method with a sound intensity analyzer as the main instrument. The sound power level data for each HVAS were than compared and frequency spectrum distributions are evaluated. Based on the research results, it was found that some sample units emitted sound power levels of more than 90 dBA with dominant noise being at high frequencies starting from 4000 Hz. The results of the research can be used as an early information in the development of the HVAS regarding noise mitigation, because there is different approach for controlling noise specifics in low, mid and high frequencies noise source.

High-energy normal-dispersion fiber optical parametric chirped-pulse oscillator.

We demonstrate a fiber optical parametric chirped-pulse oscillator (FOPCPO) pumped in the normal-dispersion regime by chirped pulses at 1.036 µm. Highly chirped idler pulses tunable from 1210 nm to 1270 nm with energies higher than 250 nJ are generated from our system, along with signal pulses tunable from 870 nm to 910 nm. Numerical simulations demonstrate that further energy scaling is possible and paves the way for the use of such FOPCPOs for applications requiring high-energy, compact, and low-noise sources, such as in biophotonics or spectroscopy.

Nonlinear pulse compression of an all-normal-dispersion Yb-fiber laser by a single-mode fiber amplifier

We have successfully compressed the pulse duration of an all-normal-dispersion (ANDi) Yb-fiber laser to sub-100 fs by a single-mode nonlinear fiber amplifier. Through optimizing the input power, prechirp, and the pump power of the amplifier, the pulse duration of the ANDi Yb-fiber laser is compressed to 68 fs when a 2.5-m active fiber is used, although for a 3.5-m active fiber, the pulse duration of the laser can be compressed to 58 fs. We have also shown that a low relative intensity noise is maintained within the nonlinear amplification process. The experimental results prove this ultrashort-pulse-duration and low-noise laser source with moderate output power can be a good candidate for frequency comb, multiphoton imaging, coherent Raman spectroscopy, and other applications.

Adaptive Algorithms for Interferometric Processing

A numerical experiment on approving adaptive sound-source localization algorithms making it possible to solve the inverse problem in the absence of data on the hydroacoustic characteristics of ocean medium has been performed. These results may be useful for identifying low-noise sources in water areas where acoustic calibration is impossible and there is no a priori information about the transfer function. The conditions for the few- and multimode regimes of sound propagation are discussed.

Two-Stage Reduction in the Output Noise Level of Voltage Sources

The development of digital technologies that are widely used in industry and agriculture places high demands on voltage reference sources for a number of parameters, each of which is important in its own way. However, a further increase in the resolution of analog-to-digital and digital-to-analog converters and, therefore, of all digital signal processing is impossible without an improvement in such a quality indicator of reference voltage sources as the noise level. In this paper, we discuss the method and schematic solution of designing a low-noise source of stable dc voltage base on standard integrated circuits of voltage stabilizers. The schematic solution provides an ability to reduce the output noise level of the corresponding reference voltage sources to a level slightly higher than the intrinsic noise level of operational amplifiers used as a part of the device block circuits, maintaining the polarity and stability of the device output voltage relative to the output voltage of the used integrated circuit of a voltage stabilizer, and reduction in capacitance of used capacitors compared with known circuit solutions.

A power efficient low-noise source degenerated bio-potential amplifier

In literature double recycling folded cascode operational transconductance amplifier (DRFC-OTA) is realized to achieve higher transconductance. To realize preamplifier for bio-medical applications, it is necessary to design an OTA with lower noise. In this paper source degeneration is adopted for DRFC-OTA for further reduction of noise and is proposed. To access the efficacy of this technique, the preamplifier using DRFC-OTA with source degeneration (DRFCSD) is realized in UMC 180 nm technology and is studied through simulations. For sizing the transistors of DRFCSD, $$g_{m}/I_{D}$$ methodology is adopted. From the simulation results it is observed that, the preamplifier exhibits a mid-band gain of 40.02 dB at − 3 dB bandwidth of 5.69 Hz–5.45 kHz. The total input referred noise of amplifier is found to be $$3.27\ \upmu V_{rms}$$ for 5.69 Hz–5.45 kHz for a power consumption of $$1.53\ \upmu {\mathrm{W}}$$. The noise efficiency factor is found to be 1.58 and provides an output swing of 1.2 $$V_{pp}$$ at THD of 1 %. CMRR and PSRR of the preamplifier are simulated and found to be 66.55 dB and 54.99 dB respectively. The amplifier occupies an area of $$0.16\ {\mathrm{mm}}^{2}$$.

Reduction of the Output Noise Level of Reference Voltage Sources

The development of digital technologies that are widely used in industry and agriculture imposes increased requirements on the reference voltage sources for a variety of parameters, each of which is important. However, further enhancement of the resolution of analog–digital and digital–analog converters and, hence, the digital signal processing as a whole, is impossible without improving such the noise level quality index of reference voltage sources. This work describes a method and circuit design for constructing a low-noise source of stable dc voltage on the basis of typical microelectronic circuits of voltage stabilizers. The developed circuit design provides a reduction in the output noise level of the reference voltage sources made based on such microelectronic circuits of voltage stabilizers up to the level of intrinsic noise of the operational amplifiers used in the developed device. The developed source of stable dc voltage is characterized by inversion of the output voltage polarity relative to the output voltage polarity of the microelectronic circuit of the voltage stabilizer that is used.

Simultaneous multi-element determination in electrothermal atomic-absorption spectrometry with electrothermal atomization

A discussion of the prospects for creating a multi-element atomic absorption (AA) spectrometer leads to the conclusion regarding the expediency of using spectral devices of relatively low resolution. Previous studies showed that the spectrometer with instrumental bandwidth 0.12 nm equipped with a CCD detector could provide the absorption measurements within a wavelength range of 200 – 400 nm using low-noise radiation sources, e.g., deuterium or low current xenon lamps. The rate of data acquisition was sufficient for vapour spectra monitoring during the pulse atomisation in graphite furnace atomizer. The loss in sensitivity due to low resolution is compensated by the possibility of direct determination of several elements in a single liquid or powder sample. Feasibility of multi-element simultaneous AA spectrometry depends on the efficiency of atomization technique and technology of data processing. The concurrent problems are discussed by the example of new calculation algorithm and its application to the analysis of multi-element nitrate and halogen containing reference materials. It is shown that linearization of the calibration curves for about 10 – 15 elements, which are not subject to chemical impacts, can be carried out automatically in a concentration range up to 4 – 5 orders of magnitude with 5 – 10 % deviation from the linearity at the ends of the interval. For the elements forming stable molecular compounds further improvement of the atomization technique is required.

Measurement Capability of the Interferometric Method of Sound Source Localization in the Absence of Data on the Waveguide Transfer Function

The resolution of interferometric method of a sound source localization is analyzed. Two realizations of this method are presented, which do not call for the knowledge of the propagation medium characteristics for determining the source coordinates. These realizations solve the problem of identifying a low-noise source in water areas where acoustic calibration cannot be performed. The maximum applicability range of the method is estimated; this estimate makes it possible to optimize the source signal processing.

Level Reduction of Output Noise of Reference Voltage Sources

Abstract Technologies for processing of digital signals find broad application in all spheres of the human activity, including agriculture. Further perfecting of these technologies is related to increasing of resolving power in analogue-to-digital and digital-to-analogue converters, requiring the improvement of quality indicator of the reference voltage sources such as noise level. This paper presents the possibilities for level reduction of output noise of the reference voltage sources. Circuit solutions of the single-stage and twostage, unipolar and bipolar low-noise sources of stable voltage of direct current produced on the basis of standard integral chips of voltage stabilizers are observed. The proposed circuit solutions provide reduction of output noise level of the reference voltage sources to the level of intrinsic noise of the operational amplifiers, which are part of the developed devices. It should be emphasized that single-stage unipolar low-noise sources of stable voltage of direct current are characteristic by the inversion of output voltage polarity that takes place in accordance with the polarity of output voltage of voltage stabilizer integral chip.

Tunable microwave frequency comb generation based on double-loop mixing-frequency optoelectronic oscillator

With the development of wireless communication technology and micro-cell technology, optical-borne microwave technology, specially optical-borne multi-carrier technology has become one of the most important trends for generating high-quality sources. Therefore, the efficient generation of high-quality microwave signals has always been a requirement in wireless communication systems. Due to its low-noise and high-frequency output characteristics, photoelectric oscillator is widely used to generate high-quality microwave frequency sources in communication systems. Combining the advantages of photoelectric oscillator's low-noise output and direct-modulated laser's gain-switching state characteristics, a tunable optical-borne microwave frequency comb scheme based on dual-loop mixing-frequency photoelectric oscillator is proposed in this paper. And a direct-modulated laser operating in a gain-switching state is used to generate the original optical-borne microwave frequency comb signals. The dual-loop adjacent resonant frequencies are separated by two different high-frequency microwave bandpass filters. The beat frequency of adjacent frequencies mentioned above is injected back into laser to form photoelectric resonance, and thus enhancing the generated original optical-borne microwave frequency comb signals. To suppress the side modes caused by long resonant cavity, a polarized dual-loop structure is used in the system, and thus improving the noise characteristics of output signals. After experimental analysis, the dual-loop filtered resonant microwave signals and low-phase-noise microwave comb signals with a frequency interval of 797.4 MHz are all obtained. The microwave output side-mode suppression ratio after polarized dual-loop adjustment is improved to 47 dB. And microwave comb signal's first-order carrier phase noise is lower than-101.7 dBc/Hz at 10 kHz,-115.2 dBc/Hz at 50 kHz. In addition, higher-order carriers all come from the light multiplication of first-order carrier, they share the same low noise characteristics with first-order microwave comb signal. The output power of first-to-fourth, fifth-to-thirteenth order carriers are balanced to 10 dB by photoelectric resonance injection. And their side-mode suppression ratios are all better than 40 dB. Furthermore, theoretically, the comb interval can be adjusted to any frequencies by changing the center frequencies of two high-frequency bandpass microwave filters. Therefore, optical-borne multi-carrier microwave signals are generated efficiently and cost-effectively by this tunable optical-borne microwave frequency comb scheme, and the generated low-noise multi-carrier frequency sources meet the demand of an optical-borne microwave wireless communication system.

Precision spectroscopy on the 2 3S-2 3P transition of atomic helium

Precision measurement in few-electron atomic systems played an important role in testing fundamental physics and determination of the fundamental physical constants throughout the past few decades.Atomic helium,as the simplest multi-electron system,its energy levels can be calculated with a very high precision by means of ab-initio calculations, and can be accurately determined using precision spectroscopy.Test of quantum theories can be achieved by comparing theoretical predictions with experimental results.In case of any disagreement,it might imply that there are some undiscovered systematic effects,or might signal physics beyond the standard model.Particularly,the 2 3PJ energy level in atomic helium is considered as one of the best atomic systems for determining the fine-structure constant α.High precision helium spectroscopy can also be used for setting constraints on exotic spin-dependent interactions,and may provide an accurate determination of the helium nuclear charge radius.Comparison of results from electronic and muonic helium may provide a sensitive test of universality in electromagnetic interactions of leptons,and may help solve the socalled “proton size puzzle”.In this paper,we summarize our recent progress on precision spectroscopy of atomic helium. By using transverse cooling and deflection,we are able to prepare a low-noise bright source of atoms in the metastable state 2 3S1.The initial state preparation is completed by optical pumping,followed by laser spectroscopy in the 2 3S-2 3P transition.The 2 3P0-2 3P2 and 2 3P1-2 3P2 fine-structure intervals are determined to be (31908130.98 ±0.13) kHz and (2291177.56 ±0.19) kHz,respectively.Compared with calculations including terms up to α7m,the deviation for the α-sensitive interval 2 3P0-2 3P2 is only 0.22 kHz,which paths way for further improvement of theoretical predictions and independent determination of α with a 2-ppb precision.The 2 3S-2 3P transition frequency is determined with an accuracy of 1.4 kHz by utilizing comb-linked spectroscopy and first-order Doppler cancellation technique.Our result is not only more accurate but also differs by as much as 50 kHz (20 σ) from the previously reported result.This discrepancy remains unsolved and indicates the need for further independent measurements.In combination with ongoing theoretical calculations,this new result may provide the most accurate determination of helium nuclear charge radius.Prospects for future improvements in relevant precision measurements,including simple molecules,are also discussed.

An optoelectronic oscillator based on series resonance cavity

Commercial and military applications of microwave and millimeter-wave sources in aerospace, radar, navigation, and communication system require high spectrum purity and low phase-noise oscillators. The optoelectronic oscillator (OEO) emerges as an excellent low noise source that has attracted great attention in recent years. In this paper, a novel technique is proposed for single-mode selection in an optoelectronic oscillator, which uses a microwave cavity as the mode selector. It consists of a pump laser and a feedback circuit including an intensity modulator, an optical fiber delay lines, a photodetector, an amplifier, a filter and two drilling cables. The drilling cable is fabricated by drilling open holes on a coaxial cable using a drilling machine. By changing the radius of the drilling holes, the designed reflection coefficient can be obtained. By simulation, the constructed microwave resonator that consists of a filter and two drilling cables has a higher Q value and only the modes that satisfy the oscillation conditions of the loop will be selected. The basic principle is analyzed theoretically and experimentally. By comparing with traditional structure of OEO, it is shown that the novel structure can effectively improve the side-mode suppression ratio. In addition, the stability of the oscillation frequency is easier to control than the parallel structure. In this experiment, the output of a 10 GHz single-mode signal with a side-mode suppression ratio of 72 dB and a phase noise of -122 dBc/Hz@10 kHz from the carrier is obtained. Meanwhile, phase-lock techniques are used to compensate the drift of cavity length. Then the radio frequency (RF) stability of the oscillation frequency is measured using an RF spectrum analyzer, and the RF stability over 3 hours for the OEO is less than 4 Hz. This scheme has the advantages of traditional OEO with low noise since no extra active devices are needed, and it suppresses the side-mode noise also effectively. In addition, this system is promising for the development of compact, high frequency, low cost and low noise OEOs.

A step-wise steerable source of illumination for low-noise "Violin-Mode" shadow sensors, intended for use in interferometric gravitational wave detectors.

A steerable low-noise source of illumination is described for shadow-sensors having a displacement sensitivity of ∼100 pm (rms)/√Hz, at 500 Hz, over a measuring span of at least ±0.5 mm. These sensors were designed to detect lateral "Violin-Mode" resonances in the highly tensioned fused-silica suspension fibres of the test-masses/mirrors for the Advanced Laser Interferometer Gravitational Wave Observatory gravitational wave detectors. The shadow sensors-one intended for each of the four fibres in a suspension-comprised a source of Near InfraRed (NIR) radiation (emitter) and a differential shadow-displacement sensor (detector), these bracketing the fibre under test. The suspension fibres themselves were approximately 600 mm long by 0.4 mm in diameter, and when illuminated from the side, they cast narrow, vertical, shadows onto their respective detectors-these being located at an effective distance of 50 fibre diameters behind the axes of the fibres themselves. The emitter described here was designed to compensate for a significant degree of mechanical drift or creep over time in the mean position of its suspension fibre. This was achieved by employing five adjacent columns of 8 × miniature NIR LEDs (Light Emitting Diodes, λ = 890 nm), with one column being activated at a time. When used in conjunction with a "reverse Galilean" telescope, the LED sources allowed the collimated beam from the emitter to be steered azimuthally in fine angular increments (0.65°), causing the fibre's shadow to move laterally, in a step-wise manner, across the plane of its facing detector. Each step in shadow position was approximately 0.23 mm in size, and this allowed the fibre's shadow to be re-centred, so as to bridge once again both elements of its photodiode detector-even if the fibre was off-centred by as much as ±0.5 mm. Re-centring allowed Violin-Mode vibrations of the fibre to be sensed once again as differential AC photocurrents, these flowing in anti-phase in the two elements of the "split-photodiode" detector.

Pareto optimization of radar receiver low-noise amplifier source impedance for low noise and high gain

In radar receivers, the low noise amplifier(LNA)must provide very low noise figure and high gain to successfully receive very low signals reflected off of illuminated targets. Obtaining low noise figure and high gain, unfortunately, is a well-known trade-off that has been carefully negotiated by design engineers for years. This paper presents a fundamental solution method for the source reflection coefficient providing the maximum available gain under a given noise figure constraint, and also for the lowest possible noise figure under a gain constraint. The design approach is based solely on the small-signal S-parameters and noise parameters of the device; no additional measurements or information are required. This method is demonstrated through examples. The results are expected to find application in design of LNAs and in real-time reconfigurable amplifiers for microwave communication and radar receivers.