Power Detection Scheme Research Articles

Recent Advances in Rational Design and Engineering of Signal-Amplifying Substrates for Surface-Enhanced Raman Scattering-Based Bioassays

In recent decades, surface-enhanced Raman spectroscopy (SERS) has become a powerful detection scheme for many applications, particularly bioassays, due to its unique strengths, such as its ultrasensitive performance. Due to the development of various SERS substrates, more SERS-based bioassays with improved sensitivity and reproducibility have been designed and manufactured. SERS is able to provide the intrinsic vibration information of molecules through the unique Raman fingerprint to enable direct detection and quantitation. Meanwhile, with the assistance of Raman-active labels, biomolecules, like proteins and nucleic acids, can be detected by the immunosandwich assay. In this review, we focus on the rational design and engineering of signal-enhancing substrates for SERS-based bioassays. Those substrates are classified into two categories, i.e., nanoparticles in colloidal suspension and nanostructures on a solid support. Each category is discussed in detail with stress on their biomedical application potential. Afterward, we summarize the SERS-based assays of proteins, nucleic acids, and viruses, for which both label-free and labeled approaches play important roles. Finally, we present the remaining challenges in the field of SERS-based bioassays and sketch out promising directions for future development.

Research and Application of Power Detection Technology on Photovoltaic Module Array

Based on the principle of photovoltaic module power detection, an intelligent module array power detection scheme is proposed, and a photovoltaic module array power detection device is designed. It consists of a master and multiple slaves. The voltage, current, temperature, and irradiation signals are synchronously collected and processed by acquisition module CC2530, and then wirelessly transmitted to the host for processing through zigbee communication protocol. These signals are calculated and displayed by the host software. Photovoltaic module array power detection device adopts modular design and experience experimental test. The measurement error meets the needs of field test. The device has the advantages of convenient portability, simple operation, high informatization, large test range, and good safety.

RF pilot tone phase noise cancellation based on DD-MZM SSB modulation for optical heterodyne RoF link

The optical heterodyne radio over fiber (RoF) link using single-sideband (SSB) modulation has advantage in system scalability, tunability, as well as resistance to chromatic dispersion induced frequency selective fading. However, the phase noise which seriously degrades system performance, is a major obstacle to employ low-cost free-running lasers in the aforementioned link. In this paper, the RF pilot tone (RFP) phase noise cancellation (PNC) based on dual drive Mach–Zehnder modulator SSB modulation for optical heterodyne RoF link is investigated and demonstrated. Two kinds of RFP PNC schemes, carrier whole multiplication (CWM) and carrier signal multiplication (CSM), are both derived theoretically and verified experimentally. The impacts of carrier signal power ratio, carrier filter bandwidth and guard band on system performance are studied in detail. The results show that, the RFP-CSM scheme can improve the spectral efficiency by 62.5% and receiver sensitivity of 1.2 dB for 1.25 Gbps quadrature phase shift keying signal at a BER of 3.8 ×10−3, as compared with the RFP-CWM scheme and power detection scheme, mainly attributed to the absence of the second-order nonlinear intermodulation distortion. Furthermore, the RFP-CSM scheme demonstrates good phase noise robustness with different high-order modulation formats under two kinds of linewidth local oscillator lasers.

Power-efficient heterodyne radio over fiber link with laser phase noise robustness

A pre-coding-assisted power detection scheme for radio over fiber downlink is presented. This scheme can eliminate laser phase noise while avoiding high energy-consuming electrical carrier required in conventional power and/or envelope detection schemes. Theoretical analysis and experimental verification are performed. 0.625 Gbaud pre-coded quadrature phase-shift keying or 16 quadrature amplitude modulation signals can both be recovered by power detection without electrical carrier assistance at the receiver after 75 km fiber transmission. Not only robust against the laser phase noise, an improvement of about 5 dB in receiver sensitivity can also be achieved, as compared with the conventional power detection scheme.

A Long-Distance Millimeter-Wave RoF System With a Low-Cost Directly Modulated Laser

We have experimentally demonstrated a world record of transmitting 60-GHz radio frequency signals over 200-km standard single-mode fiber (SSMF) through a novel end-to-end fiber-wireless integration and transport scheme using a low-cost directly modulated laser without requiring expensive optical dispersion compensation component and an external modulator. We designed a special dual-stage single-sideband (SSB) modulation and power-detection scheme to overcome the power fading caused by severe chromatic dispersion. The SSB signals are generated by the operations in both optical and electrical domains to avoid any possible beating between the two sidebands. In the experiment, QPSK wireless signals at 14 Gb/s are successfully transmitted through a 200-km SSMF and 1-m 60-GHz wireless channel with a bit error rate less than $3.8\times 10^{-3}$ . The proposed dual-stage SSB modulation and power-detection scheme are free of expensive devices, such as microwave sources, dispersion compensation components, narrow-linewidth laser sources, or external optical modulators.

Liquid crystal-based detection of DNA hybridization using surface immobilized single-stranded DNA

The authors have investigated (a) the self-assembly of single-stranded DNA (ssDNA) on glass surfaces, and (b) the interaction of DNA with liquid crystals (LCs) on solid surfaces. The results suggest that ssDNA (compared to dsDNA) on the solid interface causes particularly different orientations in LCs. The LC molecules assume a uniform homeotropic orientation on the surface with a typical surface ssDNA coverage of ~2.4 × 1012 molecules per square cm. Once complementary DNA is hybridized on the surface, the homotropic orientation of the LCs becomes disrupted. This orientation transition can be visually observed by using a crossed polarizer. The findings were exploiting to design an assay for target DNA (= analyte DNA) that has an ~0.1 nM detection limit. The assay is highly selective and can easily differentiate target DNA from single-base mismatch and non-complementary DNA. In our perception, it represents a powerful, label-free and portable DNA detection scheme.

High resolution fiber optic surface plasmon resonance sensors with single-sided gold coatings.

The surface plasmon resonance (SPR) performance of gold coated tilted fiber Bragg gratings (TFBG) at near infrared wavelengths is evaluated as a function of the angle between the tilt plane orientation and the direction of single- and double-sided, nominally 50 nm-thick gold metal depositions. Scanning electron microscope images show that the coating are highly non-uniform around the fiber circumference, varying between near zero and 50 nm. In spite of these variations, the experimental results show that the spectral signature of the TFBG-SPR sensors is similar to that of simulations based on perfectly uniform coatings, provided that the depositions are suitably oriented along the tilt plane direction. Furthermore, it is shown that even a (properly oriented) single-sided coating (over only half of the fiber circumference) is sufficient to provide a theoretically perfect SPR response with a bandwidth under 5 nm, and 90% attenuation. Finally, using a pair of adjacent TFBG resonances within the SPR response envelope, a power detection scheme is used to demonstrate a limit of detection of 3 × 10-6 refractive index units.

Dynamic Spectrum Tracking Using Energy and Cyclostationarity-Based Multi-Variate Non-Parametric Quickest Detection for Cognitive Radios

A novel non-parametric, multi-variate quickest detection method is proposed for cognitive radios (CRs) using both energy and cyclostationary features. The proposed approach can be used to track state dynamics of communication channels. This capability can be useful for both dynamic spectrum sharing (DSS) and future CRs, as in practice, centralized channel synchronization is unrealistic and the prior information of the statistics of channel usage is, in general, hard to obtain. The proposed multi-variate non-parametric average sample power and cyclostationarity-based quickest detection scheme is shown to achieve better performance compared to traditional energy-based schemes. We also develop a parallel on-line quickest detection/off-line change-point detection algorithm to achieve self-awareness of detection delays and false alarms for future automation. Compared to traditional energy-based quickest detection schemes, the proposed multi-variate non-parametric quickest detection scheme has comparable computational complexity. The simulated performance shows improvements in terms of small detection delays and significantly higher percentage of spectrum utilization.

MRI in Neurosciences

MRI in Neurosciences

Single-atom detection with optical cavities

We present a thorough analysis of single-atom detection using optical cavities. The large set of parameters that influence the signal-to-noise ratio for cavity detection is considered, with an emphasis on detunings, probe power, cavity finesse, and photon detection schemes. Real device operating restrictions for single photon counting modules and standard photodiodes are included in our discussion, with heterodyne detection emerging as the clearly favorable technique, particularly for detuned detection at high power.

New structure for multipoint temperature-independent strain sensing system employing optical power detection scheme

A new structure of multipoint temperature-independent strain sensing system with dual fiber Bragg gratings as sensors is proposed. An optical switch is employed to bridge between the detection site and multiple far ends where fiber Bragg grating sensors are located. A voltage divider is used in the proposed optical power detection scheme to resolve the measurement instability caused by the power fluctuation of the light source in a long term and the nonflat spectrum of the light source. This new detection scheme is demonstrated to have a measurement linearity and resolution of ± 0.25 % and 0.4 μS, respectively.

Temperature-insensitive multipoint strain-sensing system based on fiber Bragg gratings and optical power detection scheme

This work presents a new temperature-insensitive multipoint strain sensor based on fiber Bragg gratings. A divider circuit at the post detection port compensates for optical power variation and thermal instability induced by the nonflatness of the source spectrum. Experimental results show a measurement resolution of /spl plusmn/0.35 /spl mu/S and a temperature stability of /spl plusmn/0.005% for no strain (/spl plusmn/0.48% for a strain of <400 /spl mu/S) in an example with two sensing points. A measurement linearity of /spl plusmn/0.17% is estimated in the range 0 to 350 /spl mu/S with no crosstalk.

New image tampering detection and recovery system of JPEG2000 region of interest area

This paper describes a scheme for extracting coefficient values from the region of interest (ROI) of an image in JPEG2000. Three copies of the extracted data were hidden in three different complex processes in the non-ROI (NROI) of the frequency domain before the entropy coding stage. This scheme is robust. Experimental results showed that tamper can be detected and the tampered areas identified. The original image can be recovered from tampering with a high peak signal-to-noise ratio and no visually detectable distortions. This is a powerful tamper detection and recovery scheme. It is suitable for applications where only specific areas of an image needed protection. For example, to protect license plates, stamps and medical records.

A dual noise-predictive partial response decision-feedback equalizer for RLL(1,x) coded perpendicular magnetic recording channels

Partial response maximum likelihood (PRML) is a powerful and indispensable detection scheme for perpendicular magnetic recording channels. The performance of PRML can be improved by incorporating a noise prediction scheme into branch metric computations of the Viterbi algorithm (VA). However, the systems constructed by VA have shortcomings in the form of high complexity and cost. In this connection, a new simple detection scheme is proposed by exploiting the minimum run-length parameter d=1 and is extended to dual-detection scheme for improving the bit-error rate (BER) performance. Simulation results show that the proposed scheme has a comparable performance to noise-predictive maximum likelihood detector with less complexity when the partial response (PR) target is (1,2,1).

Long period gratings in multimode optical fibers: application in chemical sensing

We propose and demonstrate a new technique for evanescent wave chemical sensing by writing long period gratings in a bare multimode plastic clad silica fiber. The sensing length of the present sensor is only 10 mm, but is as sensitive as a conventional unclad evanescent wave sensor having about 100 mm sensing length. The minimum measurable concentration of the sensor reported here is 10 nmol/l and the operating range is more than 4 orders of magnitude. Moreover, the detection is carried out in two independent detection configurations viz., bright field detection scheme that detects the core-mode power and dark field detection scheme that detects the cladding mode power. The use of such a double detection scheme definitely enhances the reliability and accuracy of the results. Furthermore, the cladding of the present fiber need not be removed as done in conventional evanescent wave fiber sensors.

Fast obstacle detection for urban traffic situations

The early recognition of potentially harmful traffic situations is an important goal of vision-based driver assistance systems. Pedestrians, in particular children, are highly endangered in inner city traffic. Within the DaimlerChrysler urban traffic assistance (UTA) project, we are using stereo vision and motion analysis in order to manage those situations. The flow/depth constraint combines both methods in an elegant way and leads to a robust and powerful detection scheme. A ball bouncing on the road often implies a child crossing the street. Since balls appear very small in the images of our cameras and can move considerably fast, a special algorithm has been developed to achieve maximum recognition reliability.

Temperature-insensitive linear strain measurement using two fiber Bragg gratings in a power detection scheme

Two optical fiber Bragg gratings (FBGs) of slightly separated Bragg wavelengths were tandem spliced for temperature-insensitive strain sensing. The two FBGs, one used for sensing and the other used for reference, were placed side by side in parallel to assure that they had the same thermal condition. Strain was calibrated simply through reflected power measurement of the system, which was determined by the union of the spectra of the two FBGs. Linear strain measurement up to 740 μS with strain accuracy of ±1.1 μs and thermal stability of <0.7% in detected power in the temperature range from 19 to 103 °C was obtained.

Capillary electrophoresis in clinical toxicology

During the past decade, capillary electrophoresis (CE) emerged as a promising, effective and economic approach for separation of a large variety of substances, including those encountered in clinical toxicology. Reliable and automated CE instruments became commercially available and promoted the exploration of an increasing number of CE methods for illicit and licit drugs in body fluids. The widespread applicability of CE, its enormous separation power and high-sensitivity detection schemes make this technology an attractive and promising tool. This review provides an overview of the key achievements encountered with CE in clinical toxicology, including (i) the rapid assessment of drug intoxications via direct sample injection, (ii) the screening for and determination of illicit and licit drugs in body fluids with drug extraction, drug concentration (stacking) and chiral discrimination, (iii) the application of immunological single and multianalyte assays in the capillary format to the screening for drugs in body fluids, and (iv) drug confirmation by on-column multiwavelength absorbance and fluorescence detection and/or CE coupled to mass spectrometry. With its distinct features (automation, small sample size, minimal sample preparation, requirement of almost no organic solvents, ease of buffer change and method development, speed of analysis, low cost of capillaries and chemicals) CE has a bright future and the twenty-first century will witness the widespread use of a large number of simple and reliable CE based assays for drugs, methods that will be employed in clinical toxicology, therapeutic drug monitoring and forensic science.

Capillary electrophoresis in clinical and forensic analysis.

During the past decade, capillary electrophoresis (CE) emerged as a promising, effective and economic approach for separation of a large variety of substances, including those encountered in clinical and forensic analysis. Reliable and automated CE instruments became commercially available and promoted the exploration of an increasing number of CE methods and fields of application. The widespread applicability of CE, its enormous separation power and high-sensitivity detection schemes make this technology an attractive and promising tool. This review discusses the principles and important aspects of CE-based assays and provides an overview of the key achievements encountered with CE in clinical and forensic analysis, including those associated with the analysis of serum proteins, hemoglobin variants, drugs and nucleic acids. Validated assays, interesting applications and future trends in clinical and forensic analysis are also discussed.

Sensitive detection of IR photons with picosecond time resolution

Parametric upconversion is shown to be a powerful detection scheme for picosecond pulses in the IR. Tuning characteristics, spectral bandwidth, and solid angle of acceptance of the process are discussed. The linear response of the setup is demonstrated over a large range of 8 orders of ten in agreement with theoretical arguments. Using pump pulses of 1 x 10(-5) J, IR signals with 1 x 10(-15) are detected with a time resolution of approximately ~10 psec.