Dispersion Monitoring Research Articles

A Pilot-Correlated PMD Monitoring Scheme for Direct Detection Optical OFDM System

A polarization mode dispersion monitoring scheme is proposed and demonstrated for direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) systems. A pair of data-assisted pilot subcarriers is inserted at two spectral edges of the OFDM signal spectrum. Simple data correlation technique is used to estimate the powers of the pilot subcarriers and thus retrieves the DGD value at the monitoring unit, without the need of demodulation of the pilot subcarriers. Experiments show a DGD monitoring range of 0 to 45 ps in a typical radio-frequency tone-assisted DDO-OFDM system. The robustness of the proposed scheme to optical signal-to-noise ratio and accumulated chromatic dispersion is further experimentally investigated. Besides, simulations and experiments are performed to demonstrate the feasibility of using photodiodes with narrow bandwidth. By inserting one more data-assisted pilot subcarrier, the proposed scheme becomes insensitive to the input angle of the state of polarization. The proposed scheme provides an effective monitoring solution for the optical OFDM signals across intermediate nodes in flexible optical network.

Real-time monitoring of carbon nanotube dispersion using dynamic light scattering and UV-vis spectroscopy

A process for continuously monitoring the ultrasonic dispersion process of carbon nanotubes (CNTs) was discovered by integrating dynamic light scattering (DLS) and UV-vis spectroscopy. Through a continuous flow approach adapted to the dispersion system, the CNT suspension could be quantitatively characterized in real time. By continuously monitoring and identifying the evolution of mean particle size distribution and transparency of CNT suspension, the effective dispersion parameters and dispersion quality was quantified. Two types of MWNTs of different diameters and lengths were studied. For longer MWNTs with smaller diameters, the dispersion process achieved at a steady 100 nm of agglomerate size with 40 min of sonication. For shorter and large diameter and less entangled MWNTs, after 60 min of sonication, an agglomerate size of 100 nm was achieved, yet the stability decrease. The results show the potential ability of the system to optimize nanoparticle dispersion process for in-line dispersion quality control.

Simultaneous chromatic dispersion monitoring and optical modulation format identification utilizing four wave mixing

This paper presents a method which is able to monitor the chromatic dispersion (CD) and identify the modulation format (MF) of optical signals simultaneously. This method utilizes the features of the output curve of the highly sensitive all-optical CD monitor based on four wave mixing (FWM). From the symmetric center of the curve CD can be estimated blindly and independently, while from the profile and convergence region of the curve ten commonly used modulation formats can be recognized with simple algorithm based on maximum correlation classifier. This technique does not need any high speed optoelectronics and has no limitation on signal rate. Furthermore it can tolerate large CD distortions and is robust to polarization mode dispersion (PMD) and amplified spontaneous emission (ASE) noise.

Tailoring the orientation of fibres in high performance fibre reinforced cementitious composites: part 2 - correlation to mechanical properties and design implications

Incorporating fibres into a matrix with adapted rheology can lead, thanks to the elimination of vibration and to the rheological stability of the same matrix, to a randomly uniform dispersion of fibres within structural elements. It has also been recently recognised that, through a suitably balanced performance of the fluid mixture, fibres can be effectively aligned along the casting-flow direction. This highlights the need, in promoting high end engineering applications of advanced fibre reinforced cementitious composites, of designing the material for the performance required by the intended structural application. Furthermore, the casting process can be tailored to obtain, e.g., the required, or most suitable, alignment of fibres, e.g., as close as possible with the direction of principal tensile stresses within the element when in service. In part 1 of this paper, the experimental evidence was revision of a flow induced orientation of fibres in highly flowable FRCCs, the mechanisms of orientation of fibres in a yield stress fluid flow and the most recent developments in the field of predictive modelling and non-destructive monitoring of fibre dispersion. This second part of the companion paper will highlight the outcomes of the aforementioned phenomena in terms of structural design of engineering applications.

Monitoring of Aqueous Fullerene Dispersions by Thermal-Lens Spectrometry

Aqueous fullerene solutions (dispersions) are very promising materials of biomedicine and biotechnology. Of importance are the traceability of their production and characterization of their optical and colloidal properties. Thermal-lens spectrometry, as a method suitable for both optical and thermophysical studies, was used to elucidate the forms of non-modified fullerenes in their aqueous dispersions and to determine low concentrations of $$\hbox {C}_{60}$$ and $$\hbox {C}_{70}$$ fullerenes. It was shown that the residual amounts of toluene in aqueous fullerene dispersions made according to the solvent-exchange protocol could be detected by thermal lensing. As a result, the technique for the production of aqueous fullerene dispersions was improved compared to the existing data providing higher fullerene concentrations. The limits of detection of $$\hbox {C}_{60}$$ and $$\hbox {C}_{70}$$ fullerenes are approximately $$100\,\hbox {ng}{\cdot }\hbox {mL}^{-1}$$ , which are 20-fold lower compared to conventional spectrophotometry. The distinction between aqueous fullerene dispersions in comparison with organic solutions of fullerenes caused by the formation of large clusters is shown by the comparison of transient and steady-state calibration curves for aqueous and organic fullerene solutions and model reference systems under various thermal-lens excitation conditions. The advantages of thermal lensing for such colloidal systems are discussed.

A novel dispersion monitoring technique in W-band radio-over-fiber signals using clustering on asynchronous histograms

Radio over Fiber (RoF) systems have been proposed as a promising solution for transmitting radiofrequency signals at high data rates over long distances. To reach data rates in the Gbps range, studies indicate using the W-Band (75 -110 GHz). However, in this frequency band, chromatic dispersion becomes an issue that increases the bit-error-rate. This paper presents a novel digital dispersion monitoring technique for RoF systems based on asynchronous histogram analysis. This method quantifies the intensity level of the distortion of a radiofrequency demodulated signal by a dispersion factor. This dispersion factor is calculated using an enhanced clustering approach, which carries out a Gaussian fitting technique through the expectation-maximization algorithm. Dispersion monitoring was performed on radiofrequency transmission simulations using non-return-to-zero and binary phase-shift keying modulated signals over 80 km of optical fiber at 60, 75 and 100 GHz. The bit error rate is estimated and compared to the dispersion factor, showing that the behavior of the dispersion effects are not proportional to the increase of carrier frequency, bit rate and distances. This novel monitoring method can be used to estimate the feasibility of RoF systems for future hybrid networks under specific transmission parameters such as fiber length, modulation format, and carrier frequency.

Monitoring the dominance of higher-order chromatic dispersion with spectral interferometry using the stationary phase point method

Simulations were performed in order to investigate whether the stationary phase point method can be used to estimate the dominance of higher-order dispersion of the optical element under study. It was shown that different higher-order dispersion terms may result in the appearance of more than one stationary phase point on the interferogram in contrast to common glasses having group-delay dispersion as the highest decisive term in their spectral phase. The results obtained by simulations were demonstrated experimentally with spectral interferometric measurements conducted on a photonic bandgap fiber sample and a prism pair. We concluded that from the shape, movement and number of the stationary phase points it is generally possible to predict which dispersion terms are the most significant, however, in some cases the retrieval of the coefficients is also necessary in order to rule out any ambiguity. The method can offer a dispersion monitoring possibility which is useful in quality testing of specialty fibers and when adjusting stretcher-compressor systems, for example.

A systematic study on dispersion stability of carbon nanotube-modified epoxy resins

It is well accepted that the state of dispersion of carbon nanotubes (CNTs) considerably influences the performance of epoxy nanocomposites. Previous studies suggest that CNTs might reagglomerate during the processing of epoxy nanocomposites. Shear forces, resin viscosity, thermal excitation, curing reaction, and CNTs concentration are among the main factors suggested to influence the dispersion stability. The present work focuses on understanding the important role of each parameter on the dispersion stability and explaining the mechanisms by which the dispersion evolves during processing. In this regard, an in-situ dispersion monitoring technique was utilized to acquire dispersion micrographs from the sample of interest during a given heating profile. The results were supported by the rheological and contact angle measurements. It was found out that the increased mobility of CNTs in conjunction with the ineffective interfacial interaction between the nanotubes and resin was the main reason for the degradation of dispersion during the curing process.

Chromatic dispersion monitoring using semiconductor optical amplifier

An all-optical real-time chromatic dispersion (CD) monitoring technique is proposed and demonstrated for 40 Gbit/s differential phase-shifts keying (DPSK) signal, utilizing the cross modulation effects of semiconductor optical amplifier (SOA). The optical power of the output spectral components, which is from the probe’s frequency up to the signal bandwidth, is used for CD monitoring. This technique provides a wide monitoring range with large variation scale. The impacts of the polarization mode dispersion (PMD) and the optical signal-to-noise ratio (OSNR) on the CD monitoring results are theoretically analyzed and then experimentally investigated, showing that they have slight influence on the monitoring results within a certain range. Furthermore, simulated results for quadrature phase shift keying (QPSK) signal at 80 Gbit/s are also demonstrated, indicating that this technique is suitable for advanced modulated format as well.

Signed chromatic dispersion monitoring of OOK signal by evaluating the distance ratio of delay tap sampling

We analyze the residual chromatic dispersion (CD) monitoring of non-return-to-zero on–off keying (NRZ-OOK) signals using delay-tap asynchronous sampling. By evaluating the distance ratio of delay-tap plots and using a 0.5-bit optical delay interferometer (ODI), signed residual CD can be monitored accurately via numerical simulations. This CD monitoring method is independent of optical signal-to-noise ratio (OSNR) and polarization-mode dispersion (PMD). The measuring range was around ±900ps/nm for 10-Gbit/s NRZ-OOK link and ±60ps/nm for 40G link, the monitoring error is smaller than 2ps/nm.

Coded-subcarrier-aided chromatic dispersion monitoring scheme for flexible optical OFDM networks.

A simple coded-subcarrier aided scheme is proposed to perform chromatic dispersion monitoring in flexible optical OFDM networks. A pair of coded label subcarriers is added to both edges of the optical OFDM signal spectrum at the edge transmitter node. Upon reception at any intermediate or the receiver node, chromatic dispersion estimation is performed, via simple direct detection, followed by electronic correlation procedures with the designated code sequences. The feasibility and the performance of the proposed scheme have been experimentally characterized. It provides a cost-effective monitoring solution for the optical OFDM signals across intermediate nodes in flexible OFDM networks.

Group velocity dispersion monitoring for QPSK signals using direct detection

ABSTRACTIn this letter, we propose a technique to monitor the group velocity dispersion analyzing a quadrature phase‐shift keying modulated optical signal. The method is based on the analysis of the direct detection electrical signal power, measured at the clock frequency, being able to return the dispersion magnitude value and sign. The proposed method was tested for 20 Gb/s signal in a dispersion range of [−600,600] ps/nm. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2078–2080, 2014

Chromatic dispersion monitoring and adaptive compensation using pilot symbols in an 8 x 125 Gbit/s all-optical OFDM system

We propose and experimentally demonstrate a novel technique for chromatic dispersion (CD) monitoring and adaptive compensation in an 8 x 12.5 Gbit/s all-optical orthogonal frequency-division multiplexing (AO-OFDM) system by using two pilot symbols and a virtually imaged phased array (VIPA) for a tunable CD compensator. The two pilot symbols are added to the first and the last sub-channels of the OFDM signal, and their relative time delay is detected and used for CD estimation at the CD monitoring circuit. The monitored CD value is fed to VIPA for CD compensation. In the experiments, the relative time delay between the two pilot symbols was successfully observed, and the adaptive CD compensation drastically improved the bit-error-rate (BER) from over 10(-5) to under 10(-9). The estimated CD values showed less than 10 ps/nm difference from the values measured by a photonic dispersion analyzer, which is accurate enough since the AO-OFDM system can keep BER<10(-9) upto 20 ps/nm residual CD.

ACUTE MYOCARDIAL INFARCTION SPECIFICS IN PATIENTS WITH CHRONIC TONSILLITIS

Aim. To investigate the clinical specifics of acute myocardial infarction(AMI) in patients with chronic tonsillitis.Material and methods. The study included 70 patients at early AMI stages (Days 1–2). The following parameters were analysed: anthropometry, blood biochemistry, myocardial necrosis markers, QT interval dispersion, echocardiography and Holter ECG monitoring parameters, and a confirmed medical diagnosis of chronic tonsillitis in medical history.Results. In 31 patients with confirmed chronic tonsillitis, higher body mass index values, a significantly higher incidence of acute heart failure (19,4%; p&lt;0,05) and anterior AMI (70%), higher glucose levels at admission (7,58±0,62 mmol/l), and a higher end-diastolic size of right ventriculum (3,04±0,19 cm vs. 2,66±0,05 cm) were observed. Mean daytime and peak nighttime heart rate values were higher than in other patients.Conclusion. Patients with confirmed chronic tonsillitis were characterised by a more severe clinical course of AMI. There is some evidence that chronic tonsillitis is also associated with metabolic syndrome.

Optimal schemes of standard range chart for auto-correlated observations

In order to ensure homogeneous quality of the manufactured products, monitoring the process variance is as important as monitoring the process mean. Monitoring of process dispersion is also as important as monitoring the process mean. In actual practice, some process outputs are correlated, the performance of the (R) chart may have adverse effect on it. The performance of the chart is measured in terms of the average run length (ARL), which is the average number of samples before an out-of-control signal is obtained. In this paper, an attempt is made to counter the autocorrelation by designing the new (R) chart named modified (R) chart, based on sum of chi-squares. The performance of this modified (R) chart is computed for sample size of 4 and compared with conventional (R) chart. It is observed that when the level of correlation (Φ) increases, the performance of the conventional as well as modified (R) chart deteriorates. It is found that modified (R) chart performs much better than a conventional (Shewhart) (R) chart for all the cases.

Monitoring of Metal Dispersion in Kumaon Hills (INDIA) Through Active Monitoring Using Moss

Bryophytes have been used as a terrestrial bio-monitors and bio-indicators of air pollution and are recognized as more sensitive to pollution than other plants. In present study common moss species, i.e. Rhodobryumgiganteum (Schwaegr) Par., Rhynchostegielladivaricatifolia (Renauld&amp;Cardot), PohliaelongataHedw, Racomitriumcrispulum (Hook. f. et Wils.), Pleuroziumshcreberi, Hylocomiumsplendens, Hypnumcupressiforme, Brachytheciumrutabulum, Homalotheciumsericeum, Racomitriumcrispulum were collected from monitoring sites and were validated for their tolerance potential by measuring chlorophyll fluorescence signals. Amongst above species validated for tolerance, moss Racomitriumcrispulum (Hook. f. et Wils.) is inducted for monitoring program. Collected samples were air dried, then cleaned and digested. The levels of Zn, Cu, Cd and Pb have been determined in transplants of the moss Racomitriumcrispulum (Hook. f. et Wils.) from the area of Almora, Nainital and Pithoragarh of Kumaon hills. High metallic load was measured in moss harvested from locations in proximity of higher traffic density areas, which is attributed to the enhanced tourism during summer and monsoon season. In rural areas high value of Zn and, Cu attributes to their use in fertilizers. Positive significant correlations were obtained between Pb-Zn and Zn-Cu that suggest a common origin of these metals. Elemental concentration in moss Racomitriumcrispulum was in order Zn&gt;Pb ~ Cu&gt; Cd in summer while, same was Zn&gt; Cu &gt;Pb&gt; Cd in winter season and in rain Zn&gt; Cu &gt;Pb&gt; Cd that reflects atmospheric trace elemental load. Bioaccumulation ability of this moss was evaluated statistically using DMR test and cartographically presented on contour maps obtained from SURFER program.

強制放電分散型電解放電加工の加工特性（第2報）

強制放電分散型電解放電加工の加工特性（第2報）

Simultaneous monitoring of first-order polarization mode dispersion and chromatic dispersion based on RF power detection technique

We propose a novel technique for independent and simultaneous monitoring of first-order polarization mode dispersion (PMD) and chromatic dispersion (CD). For PMD monitoring, radio frequency (RF) power is detected after asymmetric filtering by a band-stop filter (BSF). The RF tone power ratio (PR) of the double sideband (DSB) to the single sideband (SSB) signal components is utilized for CD monitoring. We discuss the performance for 80Gb/s NRZ-DQPSK signal by simulation. Simultaneous monitoring of 246.7ps/nm CD with a 22.3dB dynamic range (DR) and 50ps differential group delay (DGD) with a 42.7dB DR can be realized at 10GHz detection band. When only CD is monitored, the detection frequency can be further decreased to 5GHz, where the monitoring range (MR) is 356ps/nm and DR is 30.5dB. The influences of other parameters, such as the BSF offset, the bandwidths of BSF and electrical-band-pass-filter (EBPF), the filter shape, and the modulation rate and format, are investigated in the paper.

On Enhanced Interquartile Range Charting for Process Dispersion

A careful monitoring of process dispersion is necessary to get optimum output from any process. Control charts are very important process monitoring tools of Statistical Process Control toolkit. Interquartile range (IQR) is a famous dispersion measure that is used to monitor process dispersion in quality control literature. In this study, a set of auxiliary information-based Shewhart-type IQR charts are proposed for efficient monitoring of process dispersion under bivariate normal, t and gamma distributed processes. The control structures of the proposed charts are developed, and their performances are evaluated in terms of Average Time to Signal (ATS), Average Extra Quadratic Loss and Average Ratio to ATS. Comparisons are made among different charts to establish their superiorities for a quicker detection of process changes. An illustrative example is also provided to elaborate the procedural details of the proposed IQR charts using a real data set. Copyright © 2013 John Wiley & Sons, Ltd.

In line 40 Gb/s group‐velocity dispersion monitoring

ABSTRACTIn this article, we propose a technique to monitor the group‐velocity dispersion (GVD) of an optical signal modulated at 40 Gb/s. The described method is based on the measurement of the electrical signal power at the clock frequency and is able to return the magnitude value and sign of the GVD. We show that this technique is capable to return the GVD in the range [−60, 60] ps/nm, with an error of 3 ps/nm. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:206–208, 2014