Detection Bandwidth Research Articles

Miniature all-optical flexible forward-viewing photoacoustic endoscopy probe for surgical guidance.

A miniature flexible photoacoustic endoscopy probe that provides high-resolution 3D images of vascular structures in the forward-viewing configuration is described. A planar Fabry–Perot ultrasound sensor with a bandwidth of 53 MHz located at the tip of the probe is interrogated via a flexible fiber bundle and a miniature optical relay system to realize an all-optical probe measuring 7.4 mm in outer diameter at the tip. This approach to photoacoustic endoscopy offers advantages over previous piezoelectric based distal-end scanning probes. These include a forward-viewing configuration in widefield photoacoustic tomography mode, finer spatial sampling (87 µm spatial sampling interval), and wider detection bandwidth (53 MHz) than has been achievable with conventional ultrasound detection technology and an all-optical passive imaging head for safe endoscopic use.

A Seismological Study of the Sos Enattos Area—the Sardinia Candidate Site for the Einstein Telescope

AbstractThe recent discovery of gravitational waves (GWs) and their potential for cosmic observations prompted the design of the future third-generation GW interferometers, able to extend the observation distance for sources up to the frontier of the Universe. In particular, the European detector Einstein Telescope (ET) has been proposed to reach peak strain sensitivities of about 3×10−25 Hz−1/2 in the 100 Hz frequency region and to extend the detection band down to 1 Hz. In the bandwidth [1,10] Hz, the seismic ambient noise is expected to represent the major perturbation to interferometric measurements, and the site that will host the future detectors must fulfill stringent requirements on seismic disturbances. In this article, we conduct a seismological study at the Italian ET candidate site, the dismissed mine of Sos Enattos in Sardinia. In the range between few mHz to hundreds of mHz, out of the detection bandwidth for ET, the seismic noise is compatible with the new low-noise model (Peterson, 1993); in the [0.1,1] Hz bandwidth, we found that seismic noise is correlated with sea wave height in the northwestern Mediterranean Sea. In the [1,10] Hz frequency band, noise is mainly due to anthropic activities; within the mine tunnels (≃100 m underground), its spectrum is compliant with the requirements of the ET design. Noise amplitude decay with depth is consistent with a dominance of Rayleigh waves, as suggested by synthetic seismograms calculated for a realistic velocity structure obtained from the inversion of phase- and group-velocity dispersion data from array recording of a mine blasting. Further investigations are planned for a quantitative assessment of the principal noise sources and their spatiotemporal variations.

All-optical phase-sensitive detection for ultra-fast quantum computation.

Phase-sensitive detection is the essential projective measurement for measurement-based continuous-variable quantum information processing. The bandwidth of conventional electrical phase-sensitive detectors is up to several gigahertz, which would limit the speed of quantum computation. It is theoretically proposed to realize terahertz-order detection bandwidth by using all-optical phase-sensitive detection with an optical parametric amplifier (OPA). However, there have been experimental obstacles to achieve large parametric gain for continuous waves, which is required for use in quantum computation. Here, we adopt a fiber-coupled χ(2) OPA made of a periodically poled LiNbO3 waveguide with high durability for intense continuous-wave pump light. Thanks to that, we manage to detect quadrature amplitudes of broadband continuous-wave squeezed light. 3 dB of squeezing is measured up to 3 THz of sideband frequency with an optical spectrum analyzer. Furthermore, we demonstrate the phase-locking and dispersion compensation of the broadband continuous-wave squeezed light, so that the phase of the squeezed light is maintained over 1 THz. The ultra-broadband continuous-wave detection method and dispersion compensation would help to realize all-optical quantum computation with over-THz clock frequency.

Bandwidth-Enhanced Quasi-Distributed Acoustic Sensing With Interleaved Chirped Pulses

In this letter, to break through the response bandwidth limit of quasi-distributed acoustic sensing system, a novel interleaved chirped pulses (ICP) approach is proposed on the basis of pulse compression ${\Phi }$ -OTDR with coherent detection. As shown in the theoretical analysis, for ultra-weak fiber Bragg grating (UWFBG) array with fixed positions and intervals, the space between any two FBGs can be used to multiplex probing pulses, without occupying extra detection bandwidth. The cross-correlation peak of probe pulses can be separated from each other in the time domain with matched filtering. By injecting probe pulses which are evenly interleaved as positive-chirped and negative-chirped, crosstalk of the cross-correlation peaks can be suppressed. In the proof-of-principle experiment, the response bandwidth is 3 times as that of the traditional single pulse probing scheme, all with the same detection bandwidth; 860 m sensing range with 166.4 kHz response bandwidth has been achieved, with 5 m spatial resolution and 1.8 p ${\varepsilon /\sqrt {Hz}}$ strain sensitivity.

Deep-Learning Image Reconstruction for Real-Time Photoacoustic System.

Recent advances in photoacoustic (PA) imaging have enabled detailed images of microvascular structure and quantitative measurement of blood oxygenation or perfusion. Standard reconstruction methods for PA imaging are based on solving an inverse problem using appropriate signal and system models. For handheld scanners, however, the ill-posed conditions of limited detection view and bandwidth yield low image contrast and severe structure loss in most instances. In this paper, we propose a practical reconstruction method based on a deep convolutional neural network (CNN) to overcome those problems. It is designed for real-time clinical applications and trained by large-scale synthetic data mimicking typical microvessel networks. Experimental results using synthetic and real datasets confirm that the deep-learning approach provides superior reconstructions compared to conventional methods.

ELGAR—a European Laboratory for Gravitation and Atom-interferometric Research

Gravitational waves (GWs) were observed for the first time in 2015, one century after Einstein predicted their existence. There is now growing interest to extend the detection bandwidth to low frequency. The scientific potential of multi-frequency GW astronomy is enormous as it would enable to obtain a more complete picture of cosmic events and mechanisms. This is a unique and entirely new opportunity for the future of astronomy, the success of which depends upon the decisions being made on existing and new infrastructures. The prospect of combining observations from the future space-based instrument LISA together with third generation ground based detectors will open the way toward multi-band GW astronomy, but will leave the infrasound (0.1–10 Hz) band uncovered. GW detectors based on matter wave interferometry promise to fill such a sensitivity gap. We propose the European Laboratory for Gravitation and Atom-interferometric Research (ELGAR), an underground infrastructure based on the latest progress in atomic physics, to study space–time and gravitation with the primary goal of detecting GWs in the infrasound band. ELGAR will directly inherit from large research facilities now being built in Europe for the study of large scale atom interferometry and will drive new pan-European synergies from top research centers developing quantum sensors. ELGAR will measure GW radiation in the infrasound band with a peak strain sensitivity of at 1.7 Hz. The antenna will have an impact on diverse fundamental and applied research fields beyond GW astronomy, including gravitation, general relativity, and geology.

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.