Measurement Of Optical Signals Research Articles

A Multi-Fluorescent DNA/Graphene Oxide Conjugate Sensor for Signature-Based Protein Discrimination.

Signature-based protein sensing has recently emerged as a promising prospective alternative to conventional lock-and-key methods. However, most of the current examples require the measurement of optical signals from spatially-separated materials for the generation of signatures. Herein, we present a new approach for the construction of multi-fluorescent sensing systems with high accessibility and tunability, which allows generating protein fluorescent signatures from a single microplate well. This approach is based on conjugates between nano-graphene oxide (nGO) and three single-stranded DNAs (ssDNAs) that exhibit different sequences and fluorophores. Initially, the three fluorophore-modified ssDNAs were quenched simultaneously by binding to nGO. Subsequent addition of analyte proteins caused a partial recovery in fluorescent intensity of the individual ssDNAs. Based on this scheme, we have succeeded in acquiring fluorescence signatures unique to (i) ten proteins that differ with respect to pI and molecular weight and (ii) biochemical marker proteins in the presence of interferent human serum. Pattern-recognition methods demonstrated high levels of discrimination for this system. The high discriminatory power and simple format of this sensor system should enable an easy and fast evaluation of proteins and protein mixtures.

P366 Multimodal EEG/ECOG and fast optical signal measurements in interictal epileptic spikes

Objectives Although many studies in epilepsy have examined the synaptic mechanisms constituting the basis for most of the current principles of brain activity, relatively less studies have tried to characterize changes in the cellular environment that might predispose a network to pathologic synchronization. Methods In this study, near-infrared optical imaging was used with ECoG and EEG to investigate variations in the optical properties of cortical tissue directly associated with neuronal activity in 15 rats and 3 human epileptic patients. Time-frequency analysis was also used to track variations of (de) synchronization concomitantly with changes in optical signals during IES. Results Changes in Fast optical signals (FOS) occurred 320 ms before to 370 ms after the IES peak. These changes started before any changes in ECoG signal. In addition, time-frequency domain ECoG revealed an alternating decrease-increase-decrease in the ECoG spectral power (pointing to desynchronization-synchronization-desynchronization), which occurred concomitantly with an increase-decrease-increase in relative optical signal (pointing to shrinking-swelling-shrinking of the neuronal assembly) during the IES. Discussion These relationships between electrical and optical changes highlights the complexity of the interplay between the neuronal network activity and its environment around an IES. Conclusions These changes in the neuronal environment around IESs raise new questions about the mechanisms that provides the suitable conditions for the neuronal synchronization during IESs. Significance The multimodal-multiscale FOS-ECoG approach opens new avenues to better analyze the mechanisms of neuronal synchronization in the pathologic epileptic brain, which is applicable in clinic.

Quantum-limited measurements of optical signals from a geostationary satellite

The measurement of quantum signals that traveled through long distances is of fundamental and technological interest. We present quantum-limited coherent measurements of optical signals, sent from a satellite in geostationary Earth orbit to an optical ground station. We bound the excess noise that the quantum states could have acquired after having propagated 38600 km through Earth's gravitational potential as well as its turbulent atmosphere. Our results indicate that quantum communication is feasible in principle in such a scenario, highlighting the possibility of a global quantum key distribution network for secure communication.

Quantitative Fluorescence Quenching on Antibody-conjugated Graphene Oxide as a Platform for Protein Sensing

We created an immunosensing platform for the detection of proteins in a buffer solution. Our sensing platform relies on graphene oxide (GO) nanosheets conjugated with antibodies to provide quantitative binding sites for analyte proteins. When analyte proteins and standard fluorescein-labelled proteins are competing for the binding sites, the assay exhibits quantitative fluorescence quenching by GO for the fluorescein-labelled proteins as determined by the analyte protein concentration. Because of this mechanism, measured fluorescence intensity from unquenched fluorescein-labelled protein was shown to increase with an increasing analyte protein concentration. As an alternative to the conventional enzyme-linked immunosorbent assay (ELISA), our method does not require an enzyme-linked second antibody for protein recognition and the enzyme for optical signal measurement. Thus, it is beneficial with its low cost and fewer systematic errors caused by the series of antigen-antibody recognition steps in ELISA. Immune globulin G (IgG) was introduced as a model protein to test our method and our results showed that the limit of detection for IgG was 4.67 pmol mL−1 in the buffer solution. This sensing mechanism could be developed into a promising biosensor for the detection of proteins, which would broaden the spectrum of GO applications in both analytical biochemistry and clinical diagnosis.

A high-performance transparent graphene/vertically aligned carbon nanotube (VACNT) hybrid electrode for neural interfacing

Transparent graphene-vertically aligned carbon nanotube (VACNT) electrodes enable the dual function of optical cell monitoring and cell electrical signal measurements with exceptionally high signal amplitude.

An automated approach for real time diagnostics of electrical and optical parameters for ESD events at triple junction

Abstract Environment consisting of charged particles leads to an electrostatic discharge (arcs) on the surface of dielectric material. Simulating such environment in laboratory requires the expertise of plasma physics, vacuum technology and advanced instrumentation. Various electrical and optical discharge parameters are important for understanding arc behavior and developing a mitigation technique against it’s deteriorating effects like change in material properties and decrease in substrate’s life. A real time controller can be used for measuring all these parameters. In order to measure feeble arcs of few microseconds, its voltage and current signals are measured using high speed digitizer. Arc voltage signal is used to trigger a CCD camera for capturing arc image and hence locating its position on the substrate’s surface. Both electrical and optical signals are measured simultaneously with high precision. Gradual rise in surface potential which is responsible for ESD, can be measured by scanning entire substrate’s surface at regular time intervals. A non-contact capacitive Trek probe which is carried by a stage controller is used for this measurement. For these measurements, an advanced data acquisition, logging and analysis system is developed using LabVIEW platform. The scope of this paper is limited to on-line measurement of electrical and optical signals of an ESD event using RT and transferring them to host system. A specific case of discharges on solar panel is considered for experimental validation of the developed algorithm.

The Molecular Bronchoscope: A Tool for Measurement of Spatially Dependent CO2 Concentrations in the Lungs.

Respiratory physicians use bronchoscopy for visual assessment of the lungs' topography and collecting tissue samples for external analysis. We propose a novel bronchoscope tool that would enable spatially dependent measurements of the functioning of the lungs by determining local concentrations of carbon dioxide, which will be produced by healthy parts of the lung at rates that are higher than from portions where gas exchange is impaired. The gas analyzer is based on a compact laser absorption spectrometer making use of fiber optics for delivery and return of low intensity diode laser radiation to and from the measurement chamber at the distal end of a flexible conduit. The appropriate optical wavelength was chosen such that light is selectively absorbed only by gaseous CO2. The optical absorption takes place over a short path (8.8 mm) within a rigid, 12 mm long, perforated probe tip. Wavelength modulation spectroscopy was adopted as the analytical technique to reduce the noise on the optical signal and yield measurements of relative CO2 concentration every 180 ms with a precision as low as 600 part-per-million by volume. The primary objective of such a device is to see if additional spatial information about the lungs functionality can be gathered, which will complement visual observation.

Bidirectional microwave and optical signal dissemination.

We describe a technique to disseminate highly stable microwave and optical signals from physically separated frequency standards to multiple locations. We demonstrate our technique by transferring the frequency stability performance of a microwave frequency reference to the repetition-rate stability of an optical frequency comb in a different location. The stabilized optical frequency comb becomes available in both locations for measurements of both optical and microwave signals. We show a microwave frequency stability of 4×10(-15) in both locations for integration times beyond 100 s. The control system uses only a standard Ethernet connection.

Ultracompact metasurface in-line polarimeter

In-line polarimeters perform nondestructive polarization measurements of optical signals, and play a critical role in monitoring and controlling the polarization environment in, for example, optical networks. While current in-line polarimeters are constructed with multiple optical components, either fabricated into an optical fiber or using free-space optics, we present here a novel architecture conducive to monolithic on-chip integration. This enables the scalable fabrication of high-performance polarization sensors with exceptional stability, compactness, and speed. The method relies on the detection of the highly polarization-dependent scattered field of a subwavelength antenna array known as a metasurface, and is shown here to provide polarization state measurements matching those of a state-of-the-art commercial polarimeter.

A Fully Analog High Performances Automatic System for Phase Measurement of Electrical and Optical Signals

In this paper, we present a high performance, automatic fully analog phase-to-voltage converter (PVC) circuit for phase shift measurements of periodic waveforms and repeated pulsed signals with zero and nonzero mean values. The PVC operation is fully automatic because an internal closed feedback loop guarantees the self-phase alignment (self-locking) between the reference and input signals. The system has been tested by measuring the phase shifts between the electrical signals generated by digital waveform generators and by photodiodes. The PVC output voltage dynamic range is ±10 V, independently from the phase-shift full-scales equal to ±10°, ±1°, and ±0.1°. The increase of the PVC sensitivity, expressed in volts/degree, which can be easily set to about 1, 10, and 100 V/°, is achieved without any amplification of the signal so avoiding the increasing and/or introduction of additional electronic noise to the measurements. As a consequence, for the smallest phase-shift full-scale equal to ±0.1°, the proposed PVC circuit is capable to achieve phase resolutions in the order of 0.0001°, a value one order of magnitude better than that one of commercial lock-in amplifiers. In the case of optical applications, the PVC is able to detect laser power variations with sensitivity values settable to about 6, 60, and 600 V/ $\mu \!$ W so achieving the best resolution of 16 pW.

Global observations of aerosol-cloud-precipitation-climate interactions

Cloud drop condensation nuclei (CCN) and ice nuclei (IN) particles determine to a large extent cloud microstructure and, consequently, cloud albedo and the dynamic response of clouds to aerosol-induced changes to precipitation. This can modify the reflected solar radiation and the thermal radiation emitted to space. Measurements of tropospheric CCN and IN over large areas have not been possible and can be only roughly approximated from satellite-sensor-based estimates of optical properties of aerosols. Our lack of ability to measure both CCN and cloud updrafts precludes disentangling the effects of meteorology from those of aerosols and represents the largest component in our uncertainty in anthropogenic climate forcing. Ways to improve the retrieval accuracy include multiangle and multipolarimetric passive measurements of the optical signal and multispectral lidar polarimetric measurements. Indirect methods include proxies of trace gases, as retrieved by hyperspectral sensors. Perhaps the most promising emerging direction is retrieving the CCN properties by simultaneously retrieving convective cloud drop number concentrations and updraft speeds, which amounts to using clouds as natural CCN chambers. These satellite observations have to be constrained by in situ observations of aerosol-cloud-precipitation-climate (ACPC) interactions, which in turn constrain a hierarchy of model simulations of ACPC. Since the essence of a general circulation model is an accurate quantification of the energy and mass fluxes in all forms between the surface, atmosphere and outer space, a route to progress is proposed here in the form of a series of box flux closure experiments in the various climate regimes. A roadmap is provided for quantifying the ACPC interactions and thereby reducing the uncertainty in anthropogenic climate forcing.

Measurement of optical signals as a plasma propagation in the atmospheric pressure plasma jet columns

The propagation of plasma jets with argon gas is characterized in terms of two factors, the effect of electric field distribution along the tube and the effect of voltage polarity, from the observed results of optical signals along the entire column of plasma. The optical signal of plasma propagates from the high electric-field region of high-voltage electrode toward the low field region of the open air-space, regardless of the polarity of the voltage. The optical intensity and the propagation velocity are higher for the positive voltage than for the negative voltage. Moreover, the length of plasma plume exited from the end of the glass tube into the open air is shorter for the negative voltage. When the optical intensity is strong enough, a secondary peak signal follows the primary peak. In the plasma column on the inside of the glass tube, the optical intensity and the propagation velocity depend on the strength of the electric field; they are both high at the high-field region of voltage terminal and decay toward the end of the tube. The velocity is as fast as 104 m/s at the high-field region and slows down to 103 m/s at the low-field region of the glass-tube end. However, the plasma accelerates drastically to be (104–105) m/s after exiting the glass tube toward open air, even though the electric field is a quite low and thus the optical signal decays low before fading out. The experimental observations present in this report are explained with the propagation of the plasma diffusion waves.

Technology and System for Noninvasive Spectrophotometric Assessment of Hematocrit Level

The technology and a system for rapid noninvasive assessment of hematocrit level for disaster medicine are con-sidered. The method is based on blood spectrophotometry using a package of pulsed optical radiation sources. A mathematical model of the process of optical signal measurement at the wavelengths of the radiation sources is described. The model takes into account absorption of radiation by structural elements of blood. Analytical rela-tionships for determination of concentration of structural elements of blood and hematocrit level are presented. Some practical implementation aspects of the proposed research methodology and system operation principle are also considered.

Detection of optical neuronal signals in the visual cortex using continuous wave near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) measures slow hemodynamic signals noninvasively to indirectly infer the neuronal activity in the brain. However, it remains a controversy on whether this optical measurement technique can detect the optical neuronal signal, which reflects the optical changes directly associated with neuronal activity, within the visual cortex of human and non-human primates. By carefully reviewing the important factors in the detection of optical neuronal signals, we aim to investigate the feasibility of performing NIRS measurements of optical neuronal signals within the visual cortex in humans. To ensure a strong optical neuronal response, a full-field circular black and white reversing checkerboard stimulus was presented, and the reversal frequency was carefully chosen. We used a homemade continuous wave (CW) NIRS system with high detection sensitivity (of the order of 0.1pW) to record a large area of the visual cortex (approximately 6×14cm2). EEG was simultaneously acquired with the optical signal. Based on the mathematical morphology, we adapted the filter proposed by Gratton et al. to remove the influence of arterial pulsation and facilitate the detection and elimination of unknown artifacts from the data. We obtained reliable optical neuronal signals in 77% of the participants (10 out of 13). The amplitudes (latencies) of the obtained optical neuronal signals corresponding to the 785 and 850nm wavelengths were 0.017±0.003% (94.7±8.4ms) and 0.025±0.006% (99.0±7.7ms), respectively. There were no significant differences between the latencies of the N75 component of the visual evoked potential (VEP) and optical neuronal signals at either wavelength. This is the first study to report optical neuronal signals within the visual cortex in the intact human brain using a CW NIRS system. These results indicate the feasibility of measuring noninvasive optical neuronal signals using a CW NIRS system with high detection sensitivity.

Measurement of optical signals emitted by surface discharges on bushing and post insulator

The paper presents the measurement methodology and result analyses of optical signals emitted by surface discharges occurring on bushing and post insulators, recorded using camera during tests under laboratory conditions. The performer analyses were carried out to determine the impact of the supply voltage on the intensity of the optical radiation emitted by partial discharges according to red, green and blue colors.

In-vivo Optical Measurement of Neural Activity in the Brain

The optical neural recording techniques are promising tools in recent years. Compared to the traditional electrophysiological recording, the optical means offer several advantages including no inclusion of electrical noise, simultaneous imaging of a large number of neurons, or selective recording from genetically-targeted neurons. Overall the optical neural recording technique comprises the intrinsic and the extrinsic optical recordings. The methods for intrinsic neural recording employ the change of optical properties in brains such as blood flow/oxygenation, cellular volume change, or refractive index change without addition of external indicators. Those properties can be detected using various optical techniques including laser Doppler flowmetry (LDF), near-infrared (NIR) spectrometer, functional optical coherence tomography (fOCT), and surface plasmon resonance (SPR). The extrinsic monitoring techniques use fluorescence signals reflecting neuronal activity via chemical or genetic modification of the neuronal cells. Two most popular activity-dependent fluorescent probes, calcium indicators and voltage-sensitive fluorescent proteins will be examined in this review. The principles, the instrumentations and in vivo applications of those optical signal measurements are described.

Fiber-Optic Sensing of Coal Mine Gas Based on Fabry - Perot Interferometer

In this paper, According to mine gas accident frequent and the shortages of traditional gas monitoring system, puts forward some eigenvalue fabry-perot interference (EFPI) technology, its spectrum domain to study the mechanism of white light interference demodulation . establishing the wavelength fiber methane sensor system, realized the sensing information high resolution, wide measuring range and do not suffer light wave, the spectrum domain influence of disturbance synthesis technology. Experimental results show that have an accurate measurement results, it can be applied in underground bad environment method of measuring gas concentration, the research may realize all fiber optical signal measurement, underground only, no electrical signals, strong anti-jamming capability, suitable for inflammable, explosive and other environmental.

Sub-picosecond phase-sensitive optical pulse characterization on a chip

The recent introduction of coherent optical communications has created a compelling need for ultra-fast phase-sensitive measurement techniques operating at milliwatt peak power levels and in time scales ranging from sub-picoseconds to nanoseconds. Previous reports of ultrafast optical signal measurements in integrated platforms[8-10] include time-lens temporal imaging on a silicon chip[8,9] and waveguide-based Frequency-Resolved Optical Gating (FROG). Time-lens imaging is phase insensitive while waveguide-based FROG methods require the integration of long tuneable delay lines - still an unsolved challenge. Here, we report a device capable of characterizing both the amplitude and phase of ultrafast optical pulses with the aid of a synchronized incoherently-related clock pulse. It is based on a novel variation of Spectral Phase Interferometry for Direct Electric-Field Reconstruction (SPIDER)that exploits degenerate four-wave-mixing (FWM) in a CMOS compatible chip. We measure pulses with <100mW peak power, a frequency bandwidth >1THz, and up to 100ps pulsewidths, yielding a time-bandwidth product (TBP)>100.

Performance Analysis of Location Tracking System for Multiple Levels

Location tracking in an indoor environment is possible with various techniques based on mechanical, acoustical, ultrasonic, optical, infrared, inertial or radio signal measurements. Global Positioning System (GPS) is one of famous tracking system as a feasible and effective outdoor tracking system. Nowadays, location tracking information and visualization of 3D graphics either in outdoor or indoor environment had been presented as one of research issues. Traditional tracking system with 2D-image standard presents only few and dull information to users. In addition 2D localization only supports one level platform (i.e. horizontally). Thus, the 3D location tracking system had been developed to support multilevel network. In this paper we developed a real-time indoor tracking system with 3D locations which are able to provide more useful location tracking information to user using radio signals. This system had been developed for multiple levels building. For this project we used the existing Wireless Local Area Network (WLANs) attached devices called the access point (AP) to the edge of the wired network. Nodes communicate with the AP using a wireless network adapter similar in function to a traditional Ethernet adapter. The signal from the nodes or the APs that using WLAN can be read or calculated using Received Signal Strength Indication (RSSI) due to its low-cost solutions. Besides that, the system operates in the IPv6 network to provide more reliable system. The localization algorithm use is triangulation method which is suitable for indoor environment. In this paper we present the results of the 3D location tracking for one level as well as two level building. The results are comparing in terms of experimental and calculated.

Circular polarization intrinsic optical signal recording of stimulus-evoked neural activity

Linear polarization intrinsic optical signal (LP-IOS) measurement can provide sensitive detection of neural activities in stimulus-activated neural tissues. However, the LP-IOS magnitude and signal-to-noise ratio (SNR) are highly correlated with the nerve orientation relative to the polarization plane of the incident light. Because of the complexity of orientation dependency, LP-IOS optimization and outcome interpretation are time consuming and complicated. In this study, we demonstrate the feasibility of circular polarization intrinsic optical signal (CP-IOS) measurement. Our theoretical modeling and experimental investigation indicate that CP-IOS magnitude and SNR are independent from the nerve orientation. Therefore, CP-IOS promises a practical method for polarization IOS imaging of complex neural systems.