Detection Bandwidth Research Articles

Label-Free Plasmonic Detection of Untethered Nanometer-Sized Brownian Particles.

Optical detection of individual nanometer-sized analytes, virus particles, and protein molecules holds great promise for understanding and control of biological samples and healthcare applications. As fluorescent labels impose restrictions on detection bandwidth and require lengthy and invasive processes, label-free optical techniques are highly desirable. Here, we introduce an optical technique capable of transforming gold nanorods commonly used as photostable labels into highly localized high-speed probes. Our method detects single untethered 5 nm diameter gold particles as they traverse subattoliter volumes in Brownian motion with a time resolution below microseconds.

Adaptive noise canceling for transient absorption microscopy.

.Significance: Ultrafast fiber lasers are an attractive alternative to bulk lasers for nonlinear optical microscopy for their compactness and low cost. The high relative intensity noise (RIN) of these lasers poses a challenge for pump-probe measurements such as transient absorption and stimulated Raman scattering, along with modalities that provide label-free contrast from the vibrational and electronic structure of molecules.Aim: Digital adaptive filtering was applied to determine the applicability for canceling laser RIN in a transient absorption microscope with an ultrafast fiber laser source.Approach: Digitized signals from the transmitted probe and reference photodetectors were fed to an adaptive filter in MATLAB, running in a noise canceling configuration. This result was then fed to a software lock-in algorithm to demodulate the pump-probe signal. Images were built up one line scan at a time with a 3.5-kHz resonant scanner, with averaging. The imaging target was , which exhibits nondegenerate two-photon absorption at the pump/probe wavelengths used (530-nm pump and 490-nm probe).Results: Without adaptive noise cancellation, the lock-in output primarily passes the laser RIN within its detection bandwidth, resulting in images that closely follow the linear transmissivity and lack sensitivity to pump-probe time delay. With adaptive noise cancellation in front of the lock-in, the RIN rejection is enough to restore the z-sectioning and sensitivity to pump-probe delay, as expected for transient absorption. Results were limited primarily by noise from the photodetector and analog-to-digital converter.Conclusions: Digital adaptive noise cancellation, even when limited by electronics noise, can recover pump-probe signals by removal of laser RIN, under conditions where averaging alone fails.

Optimising micro computed tomography imaging of large animal and human hearts at high resolution

Micro Computed tomography has emerged as a powerful imaging tool to study the micro-structure of cardiac tissue of small mammals. However, conventional techniques in whole organs of large mammals, is compromised due to the use of high molecular weight contrast agents and the relative thickness of samples. To develop a tissue preparation method to optimize microCT imaging of whole hearts with sizes including those of humans. Male pig hearts ( N = 5) were treated by: hydrated samples with conventional contrast agent (iodine, 0.5%) or dehydrated in ethanol and air-dried under hexamethyldisilazane (HMDS). Human hearts ( N = 3) were treated using air-drying method. Hearts were imaged at 21.7 μm isotropic resolution by microCT (SkyScan 1276 Bruker). Images were quantified with Amira software using a 3D cylinder correlation technique. The X-ray attenuation of air-dried samples was better optimized for the bandwidth of the X-ray detector, indicated by reduced x-ray attenuation (pig 65%, human 55), compared to almost complete signal attenuation from hydrated samples (93%). Voxel intensity histograms showed two populations corresponding to the tissue and the background media and sample support structures. Yet, the separating minima of histogram intensities were always observed at lower intensities for air-dried hearts ( Fig. 1 A) than hydrated hearts, increasing the dynamic range for tissue-specific signals ( Fig. 1 B). Imaging air-dried pig or human hearts permitted a simple threshold-based segmentation to isolate microstructures of the heart, including vessels, myocardial fibers and Purkinje from the background (1C). Fiber orientation quantification could be performed directly on unfiltered images. Fiber orientation was validated against subsequent histology of the same samples. Air drying with HMDS enables microCT imaging of human-sized hearts while preserving micro-structure and the identification of individual cardiac muscle fibers.

A submicrometre silicon-on-insulator resonator for ultrasound detection.

Ultrasound detectors use high-frequency sound waves to image objects and measure distances, but the resolution of these readings is limited by the physical dimensions of the detecting element. Point-like broadband ultrasound detection can greatly increase the resolution of ultrasonography and optoacoustic (photoacoustic) imaging1,2, but current ultrasound detectors, such as those used for medical imaging, cannot be miniaturized sufficiently. Piezoelectric transducers lose sensitivity quadratically with size reduction3, and optical microring resonators4 and Fabry-Pérot etalons5 cannot adequately confine light to dimensions smaller than about 50 micrometres. Micromachining methods have been used to generate arrays of capacitive6 and piezoelectric7 transducers, but with bandwidths of only a few megahertz and dimensions exceeding 70 micrometres. Here we use the widely available silicon-on-insulator technology to develop a miniaturized ultrasound detector, with a sensing area of only 220 nanometres by 500 nanometres. The silicon-on-insulator-based optical resonator design provides per-area sensitivity that is 1,000 times higher than that of microring resonators and 100,000,000 times better than that of piezoelectric detectors. Our design also enables an ultrawide detection bandwidth, reaching 230 megahertz at -6 decibels. In addition to making the detectors suitable for manufacture in very dense arrays, we show that the submicrometre sensing area enables super-resolution detection and imaging performance. We demonstrate imaging of features 50 times smaller than the wavelength of ultrasound detected. Our detector enables ultra-miniaturization of ultrasound readings, enabling ultrasound imaging at a resolution comparable to that achieved with optical microscopy, and potentially enabling the development of very dense ultrasound arrays on a silicon chip.

Modeling of MIMO Less Mode Division Multiplexed Systems

A transmission model for a mode group division multiplexing system is presented. The model is used to model a two mode group system with either 10 Gbit/s NRZ modulation or 25 Gbit/s PAM4 modulation. Influence of wavelength separation between the channels, detector bandwidth and component crosstalk is examined.

A Deep Convolutional Network for Multitype Signal Detection and Classification in Spectrogram

Wideband signal detection is an important problem in wireless communication. With the rapid development of deep learning (DL) technology, some DL-based methods are applied to wireless communication and have shown great potential. In this paper, we present a novel neural network for detecting signals and classifying signal types in wideband spectrograms. Our network utilizes the key point estimation to locate the rough centerline of the signal region and recognize its class. Then, several regressions are carried out to obtain properties, including the local offset and the border offsets of a bounding box, which are further synthesized for a more fine location. Experimental results demonstrate that our method performs more accurate than other DL-based object detection methods previously employed for the same task. In addition, our method runs obviously faster than existing methods, and it abandons the candidate anchors, which make it more favorable for real-time applications.

Colorimetry of Luminescent Lanthanide Complexes.

Europium, terbium, dysprosium, and samarium are the main trivalent lanthanide ions emitting in the visible spectrum. In this work, the potential of these ions for colorimetric applications and colour reproduction was studied. The conversion of spectral data to colour coordinates was undertaken for three sets of Ln complexes composed of different ligands. We showed that Eu is the most sensitive of the visible Ln ions, regarding ligand-induced colour shifts, due to its hypersensitive transition. Further investigation on the spectral bandwidth of the emission detector, on the wavelengths’ accuracy, on the instrumental correction function, and on the use of incorrect intensity units confirm that the instrumental correction function is the most important spectrophotometric parameter to take into account in order to produce accurate colour values. Finally, we established and discussed the entire colour range (gamut) that can be generated by combining a red-emitting Eu complex with a green-emitting Tb complex and a blue fluorescent compound. The importance of choosing a proper white point is demonstrated. The potential of using different sets of complexes with different spectral fingerprints in order to obtain metameric colours suitable for anti-counterfeiting is also highlighted. This work answers many questions that could arise during a colorimetric analysis of luminescent probes.

MDM Transmission Using Air-Clad Photonic Lanterns

MIMO less few mode transmission is performed using two spatial channels transmitted through 1 km of two mode graded index fiber at 10 Gb/s modulation rate. The multiplexing and de-multiplexing of the spatial channels are done using air clad photonic lanterns. The power in the two degenerate LP11 modes are added electrically and counted as a single channel. The Q values calculated for the LP01 and LP11 channels are 5.4 and 4.7 respectively. We also show that, the signal degradation due to modal interference can be mitigated by using different laser sources for different spatial channels with some wavelength spacing. The wavelength separation increases the modal beat frequency beyond the detector bandwidth, thus improving the transmission performance. Using two laser sources with a wavelength spacing of 0.2 nm between the spatial modes could improve the Q compared to the case where a single laser source is split between the spatial channels with some extra length of fiber in one of the paths for optical decorrelation.

A Fast Deep-Learning Signal Detection Architecture for the Short-wave Band

Wideband signal detection plays an important role in wireless communication systems. In recent years, deep learning (DL) has been introduced, and many trial efforts have been posed. In this paper, a fast deep-learning signal detection architecture is proposed for the short-wave band, which consists of the GPU-based Down Digital Converter (DDC), the DL-based signal detector, and the signal data viewer & recorder. Wideband signal data are taken directly as the input, and detected signals are automatically recorded as the output of the architecture. Experimental results suggest that our architecture is capable of detecting signals in the whole short-wave band in quasi-real-time, and specifically, with single GPU device.

Photonics-Based Real-Time Spectrogram Analysis of Broadband Waveforms

This article provides a review and deeper insight on the fundamentals and main design trade-offs of a new method for joint time-frequency analysis of broadband signals, namely, the time-mapped spectrogram (TM-SP). This method involves a temporal periodic sampling of the signal under test (SUT) followed by chromatic dispersion under a Talbot condition. Through this scheme, the time-changing spectrum of the input SUT, namely, its short-time Fourier transform (or SP), is continuously mapped along the time domain, at the sampling rate. The time and frequency resolutions of the resulting SP are respectively dependent on the spectral and temporal width of the sampling pulses, though the latest may be limited by the detection bandwidth. Additionally, the obtained spectrogram is heavily oversampled, ensuring a gap-free spectral analysis, and providing additional opportunities to relax the detection device specifications. A photonic implementation of the concept is discussed, and numerically and experimentally demonstrated, validating our central theoretical findings and predictions. The method enables real-time spectral analysis of GHz-bandwidth arbitrary microwave signals with nanosecond resolutions, fulfilling the performance requirements across many scientific and technology applications.

Reverse contrast laser Doppler holography for lower frame rate retinal and choroidal blood flow imaging.

Laser Doppler holography (LDH) is an interferometric blood flow imaging technique based on full-field measurements of the Doppler spectrum. LDH has so far been demonstrated in the retina with ultrafast cameras, typically at 75 kHz. We show here that a similar method can be implemented with camera frame rates 10 times slower than before. Due to energy conservation, low and high frequency local power Doppler signals have opposite variations, and a simple contrast inversion of the low frequency power Doppler reveals fast blood flow beyond the camera detection bandwidth for conventional laser Doppler measurements. Relevant blood flow variations and color composite power Doppler images can be obtained with camera frame rates down to a few kHz.

Sensitive terahertz-wave detector responses originated by negative differential conductance of resonant-tunneling-diode oscillator

We present an experimental characterization of frequency- and bias-dependent detector responses in a resonant-tunneling-diode (RTD) terahertz (THz)-wave oscillator. By tuning the incident THz-wave frequency and the bias voltage applied to the RTD device, the origins of detection signals are identified to be two distinct detection modes. One is based on square-law detection near the peak and valley points of the negative differential conductance (NDC) region, with the detection bandwidth determined by an integrated slot antenna. The other is based on detectable current changes induced by injection locking within the NDC region when the frequency of the incident THz-wave radiation to be detected is coincident with that of the bias-dependent RTD self-oscillation between 0.74 and 0.81 THz, resulting in a minimum noise equivalent power (NEP) of 7.7 pW/√Hz at 0.78 THz at room temperature. Our conclusions demonstrate that an RTD oscillator can be used as a sensitive THz-wave detector within and around the NDC region.

Colorimetric fiber-optic sensor based on reflectance spectrum estimation for determining color of printed samples

A new colorimetric method for determining the color of a printed sample using electrophotography is presented. As a trade-off solution between colorimeter and spectrophotometer, this method aims to increase accuracy with respect to the colorimeter and simplify the system with respect to the spectrophotometer. The method is based on estimation of the spectrum of electromagnetic radiation in the visible range. This was performed by interpolating over the measured values of the spectral power radiation of proposed LED sources. Six LED sources were used, with dominant wavelengths at 400 nm, 457 nm, 517 nm, 572 nm, 632 nm and 700 nm at the transmitting side. On the receiving side there is a wideband detector in charge of recording the optical power at the above-mentioned wavelengths. Colorimetric capabilities of the proposed method were compared with spectrophotometric results, and good match was achieved. Reflectance spectrums obtained by the proposed method for printed samples doesn’t deviate significantly from those recorded by a commercial spectrophotometer. Also, the calculations of color differences don’t deviate from the tolerance threshold.

Toward a large bandwidth photonic correlator for infrared heterodyne interferometry

Context. Infrared heterodyne interferometry has been proposed as a practical alternative for recombining a large number of telescopes over kilometric baselines in the mid-infrared. However, the current limited correlation capacities impose strong restrictions on the sensitivity of this appealing technique. Aims. In this paper, we propose to address the problem of transport and correlation of wide-bandwidth signals over kilometric distances by introducing photonic processing in infrared heterodyne interferometry. Methods. We describe the architecture of a photonic double-sideband correlator for two telescopes, along with the experimental demonstration of this concept on a proof-of-principle test bed. Results. We demonstrate the a posteriori correlation of two infrared signals previously generated on a two-telescope simulator in a double-sideband photonic correlator. A degradation of the signal-to-noise ratio of 13%, equivalent to a noise factor NF = 1.15, is obtained through the correlator, and the temporal coherence properties of our input signals are retrieved from these measurements. Conclusions. Our results demonstrate that photonic processing can be used to correlate heterodyne signals with a potentially large increase of detection bandwidth. These developments open the way to photonic processing of wide bandwidth signals for mid-infrared heterodyne interferometry, in particular for a large number of telescopes and for direct imager recombiners.

Investigation on response function of terahertz air coherent detection technique

Terahertz (THz) air coherent detection is a broadband coherent detection technique, which has been used widely in the THz science and technology. In this paper, a frequency-dependent response function of THz air coherent detection is defined based on the nonlinear polarization of gas molecules induced by the ultrashort laser pulses and the THz pulses. Calculations show that the response function of this technique has a half of Gaussian-like profile, which has a high sensitivity in the low frequency range and low sensitivity in the high frequency range of THz waves. Two fitted functions are given based on the calculated results, which can provide a good reference bandwidth when using the air coherent detection with a given probe laser pulse. The distortions of THz pulses induced by the air coherent detection in the detection process are discussed as well. This study will help to understand the response bandwidth and the limitation of detection bandwidth of the air coherent detection technique.

FRF-based transient wave analysis for the viscoelastic parameters identification and leak detection in water-filled plastic pipes

Plastic/viscoelastic pipes, such as polyvinyl chloride (PVC), polyethylene (PE) and high-density polyethylene (HDPE), have been increasingly used in water piping systems, which has stimulated the study of viscoelastic hydrodynamics in these pipe systems. An in-depth understanding of the pipe-wall viscoelasticity features is beneficial and necessary to the effective application and management of plastic pipes such as leak detection in urban water supply systems. This paper presents a frequency response function (FRF)-based transient wave analysis method (TWAM) for the identification of viscoelastic pipe properties as well as the detection of leaks in water filled plastic pipes. To this end, an analytical FRF expression is firstly derived for the interaction of transients with pipe-wall elasticity and leaks in plastic pipes, which is thereafter used for the identification of viscoelastic parameters and potential leaks in plastic pipes. Laboratory experiments are performed to validate the proposed FRF-based TWAM and thereby examining the effective range of injected wave bandwidth for accurate leak detection with existence of pipe-wall viscoelasticity. The validated method is further analyzed through extensive numerical applications to systematically examine the influences of different system and flow conditions. Application results confirm the feasibility and accuracy of the developed FRF-based TWAM method for the identification of viscoelastic parameters as well as the detection of plastic pipe leaks. The results also indicate that the proposed method in this study is more accurate to locate leaks than to size leaks in plastic pipes, which requires more attention to the future applications.

Sensitivity and noise in THz electro-optic upconversion radiometers

This paper presents a study of noise in room-temperature THz radiometers that use THz-to-optical upconversion followed by optical detection of thermal radiation. Despite some undesired upconverted thermal noise, no noise is intrinsically introduced by efficient electro-optic modulation via a sum-frequency-generation process in high quality factor (Q) whispering-gallery mode (WGM) resonators. However, coherent and incoherent optical detection results in fundamentally different noise characteristics. The analysis shows that the upconversion receiver is quantum limited like conventional amplifiers and mixers, only when optical homodyne or heterodyne detection is performed. However, this type of receiver shows advantages as a THz photon counter, where counting is in the optical domain. Theoretical predictions show that upconversion-based room-temperature receivers can outperform state-of-the-art cooled and room-temperature THz receivers based on low-noise amplifiers and mixers, provided that a photon conversion efficiency greater than 1% is realized. Although the detection bandwidth is naturally narrow due to the highly resonant electro-optic modulator, it is not fundamentally limited and can be broadened by engineering selective optical coupling mechanisms to the resonator.

Amplitude Integrated Electroencephalogram Study of the Effect of Caffeine Citrate on Brain Development in Low Weight Infants with Apnea

To investigate the effect of caffeine citrate on the integrated brain electroencephalogram (EEG) of apnea and low birth weight infants. Overall, 212 infants with apnea and low birth weight admitted to Xuzhou Central Hospital from June 2016 to June 2018 were enrolled. The infants were divided into control group and observation group according to the random number table method, 106 cases in each group. Infants in control group were treated with aminophylline, and infants in the observation group were given caffeine citrate. All children were continuously tested by digital amplitude integrated brain function monitor. The amplitude-integrated electroencephalogram (aEEG) was used to detect sleep arousal cycle (Cy), graphic continuity (Co), lower edge amplitude value (LB) scores, aEEG continuous voltage and periodic occurrence rate, narrowband voltage and bandwidth. After treatment, scores of Cy, Co and LB increased in both groups, and the scores were significantly higher in observation group than in control group (P=0.029, 0.017, 0.047). After treatment, continuous voltage positive rate, sleep-wake cycle occurrence rate, and narrow-band lower boundary voltage increased in both groups, and the values were significantly higher in observation group than in control group (P=0.011, 0.042). After treatment, aEEG detection bandwidth and the upper boundary voltage of the narrow band decreased in both groups, and the values were significantly lower in observation group than in control group (P=0.007, 0.020, 0.032). Citrate caffeine can alleviate the brain development of low-weight infants with apnea, improve brain electrical activity and promote brain function and maturity.

Simultaneous ranging and velocimetry with multi-tone continuous wave lidar.

In this paper, we demonstrate analytical modeling and experimental verification of simultaneous ranging and velocimetry measurements in multi-tone continuous wave lidars. To assess the ranging performance of the proposed lidar, a comparative experiment of the multi-tone continuous wave and time-of-flight techniques is performed. The average deviation in ranging is ∼0.75cm with >90% fitting accuracy, which corresponds to the uncertainty of the time-of-flight measurements due to the detector bandwidth. Simultaneous ranging and velocimetry are performed on a moving target. The velocimetry accuracy of the multi-tone continuous wave lidar is dictated by the frequency resolution of the Doppler shift, which is measured as ± 0.8cm/s. The results indicate that multi-tone continuous wave lidars can be improved to perform remote sensing for oceanography and atmospheric sciences and for autonomous vehicles without using any amplitude, frequency or phase sweeping.

Distributed fiber vibration sensing with single-shot measurement and moving time-gating method

The single-shot measurement method is proposed to improve measurement accuracy in distributed dynamic strain sensing by using time-resolved optical frequency domain reflectometry (OFDR). Time-domain information can be obtained without reference scan by single-shot measurement with standard polarization-maintaining fiber as the sensing fiber via auto-correlation calculation to measure Rayleigh backscatter spectrum in different wavelength ranges. Experimental results verify that the information of vibrated and non-vibrated state can be determined by monitoring the side peak shifts in the local Rayleigh backscatter spectrum along the sensing fiber. Furthermore, moving time-gating method is illustrated and used to broaden the detection bandwidth. The effective sampling rate can be increased so that the measurable frequency range can be further increased. In the further proof of concept experiment, for a conventional OFDR system, the measurable frequency of vibration event can be achieved up to 30Hz along the polarization-maintaining fiber with a tunable laser sweeping rate of 40nm/s by single-shot measurement and moving time-gating method. The measurable frequency range could be further broadened by using tunable laser sources with higher sweeping speeds. The proposed schemes provide new approach to enhance the measurement accuracy via single-shot measurement in the OFDR system which is of great significance in distributed dynamic signal detection system.