Single-channel Systems Research Articles

Analysis of systems for detection and measurement of multifrequency signals

The paper gives comparative analysis of detection characteristics of single-channel systems of processing of multifrequency signals against the white noise background, for different categories of interperiod processing (coherent or noncoherent) in the frequency channels. Also, analysis of accuracy of target’s radial speed measurements is performed depending on the multifrequency signal parameters.

Effect of sliding filters on the soliton optical phase jitter in constant-dispersion systems

The influence of sliding filters on the phase jitter of soliton pulses propagating in single-channel constant-dispersion systems is studied using the perturbation theory. Although sliding filters allow the reduction of the amplified radiative background, they introduce coupling between the soliton amplitude and frequency, and between its timing and phase, which result in a growth of the phase jitter as the cube of the propagation distance. Comparisons of the analytical results with Monte Carlo simulations validate the perturbation theory.

Advanced modulation formats in 40 Gbit/s optical communication systems with 80 km fibre spans

NRZ, duobinary, RZ, CS-RZ and SSB-RZ modulation formats are evaluated numerically at a bit rate of 40 Gbit/s for single-channel and WDM systems using long fibre spans of 80 km SMF + DCF or SMF + IDF × 2. For the single-channel system, conventional RZ with narrow pulses is found to be optimum, whereas CS-RZ performs the best for the WDM system. Using SMF + IDF×2 fibre span results in significant longer transmission distance due to reduced span loss.

Numerical study of random variations of span lengths and span path-average dispersions on dispersion-managed soliton system performance

We have studied the performance of dispersion-managed (DM) soliton systems with random variations of span lengths and span path-average dispersions by numerical simulation. We show that while DM solitons still exist in systems with nonperiodic dispersion maps, those nonperiodic maps tend to degrade system performance. We investigate the performance degradation of both on-off keyed and differential phase-shift keyed DM-soliton systems with random span lengths and random span path-average dispersions. We find that the impairment caused by the span path-average dispersion variation is larger than that caused by the span length variation, and that the reduction in quality factor due to the span length and the span path-average dispersion variations is less in dense wavelength-division multiplexing (WDM) than in single-channel transmission systems. In addition, we also show that keeping the overall path-average dispersion constant within a few spans can reduce the random dispersion map-induced performance degradation.

Nonlinear impairments at various bit rates in single-channel dispersion-managed systems

Simulations of single-channel dispersion-managed transmission systems show that the chromatic dispersion yielding the highest nonlinear impairments depends on the bit rate and the fibre loss according to a practical, dimensionless criterion.

Pulse stabilization by high-order dispersion management

The stabilizing effects of dispersion management (DM) at second and third order are studied for both single-channel and wavelength-division multiplexed (WDM) systems. We first derive a model for the slow evolution of a pulse in an optical fiber with high-order dispersion management (HODM). For single-channel systems, in contrast with conventional DM with constant third-order dispersion, this equation possesses a stable solution, the ground state for its associated Hamiltonian, which propagates nearly periodically under direct numerical simulation. Improved performance for WDM systems is also observed, as complicated pulse interactions, which can lead to undesirable effects such as frequency shift, are prevented by HODM.

A review of portable FES-based neural orthoses for the correction of drop foot

This paper reviews the technological developments in neural orthoses for the correction of upper motor neurone drop foot since 1961, when the technique was first proposed by Liberson and his co-workers. Drop foot stimulator (DFS) developments are reviewed starting with hard-wired single-channel and multichannel surface functional electrical stimulation (FES) systems, followed by implanted drop foot stimulators, and then continuing with microprocessor-based surface and implanted drop foot stimulators. The review examines the role of artificial and "natural" sensors as replacements for the foot-switch as the primary control sensor in drop foot stimulators. DFS systems incorporating real-time control of FES and completely implanted DFS systems finish the review.

Performance optimization of Gaussian apodized fiber Bragg grating filters in WDM systems

Fiber Bragg gratings (FBGs) with Gaussian apodization profiles and zero de index change are studied extensively and optimized for optical filtering in 40-Gb/s single-channel and WDM systems with channel spacing of 100 and 200 GHz, for a single filter and for a cascade of optical filters. In the single-filter case, the optimized FBG leads practically to the same performance for single-channel and WDM systems, due to its low crosstalk introduction. The optimized filter is nonflat-top, with delay distortion below 7 ps, -3 dB bandwidth between 60 and 90 GHz, and is very robust to a variation of the grating length and the dc effective index change. For a cascade of optical filters and a WDM system with channel spacing of 100 GHz, the FBG must be designed carefully due to a tradeoff between crosstalk and accumulated distortion. This tradeoff leads to 1.2 dB of sensitivity degradation relative to the single-filter case, and the optimized filter approaches the flat-top response with -3 dB bandwidth between 110 and 130 GHz and delay distortion of about 3 ps. For a 200-GHz channel spacing, that tradeoff is lessened and the FBG optimization is mainly ruled by the distortion accumulation.

The RP method: a new tool for the iterative solution of the nonlinear Schrodinger equation

An original approach to the solution of the nonlinear Schrodinger equation (NLSE) is pursued in this paper, following the regular perturbation (RP) method. Such an iterative method provides a closed-form approximation of the received field and is thus appealing for devising nonlinear equalization/compensation techniques for optical transmission systems operating in the nonlinear regime. It is shown that, when the nonlinearity is due to the Kerr effect alone, the order n RP solution coincides with the order 2n + 1 Volterra series solution proposed by Brandt-Pearce and co-workers. The RP method thus provides a computationally efficient way of evaluating the Volterra kernels, with a complexity comparable to that of the split-step Fourier method (SSFM). Numerical results on 10 Gb/s single-channel terrestrial transmission systems employing common dispersion maps show that the simplest third-order Volterra series solution is applicable only in the weakly nonlinear propagation regime, for peak transmitted power well below 5 dBm. However, the insight in the nonlinear propagation phenomenon provided by the RP method suggests an enhanced regular perturbation (ERP) method, which allows the first order ERP solution to be fairly accurate for terrestrial dispersion mapped systems up to launched peak powers of 10 dBm.

Correction to "phase jitter in single-channel soliton systems with constant dispersion"

Correction to "phase jitter in single-channel soliton systems with constant dispersion"

Phase jitter in single-channel soliton systems with constant dispersion

The phase jitter of optical solitons in single-channel communication systems with constant dispersion and distributed amplification is studied in detail. The variational method is used to derive equations that model phase jitter caused by amplifier noise. These equations are solved analytically. Simple formulas are obtained for the phase variance of an ensemble of solitons, which together cover the entire range of practical transmission distances. These formulas are validated for parameters of current interest by numerical solutions of the nonlinear Schroedinger equation.

Prechirp in NRZ-based 40-Gb/s single-channel and WDM transmission systems

We investigate the impact of the prechirp on nonreturn-to-zero (NRZ)-based single-channel and 40-Gb/s/ch wavelength-division-multiplexing systems over standard single-mode fibers by means of numerical simulations. It was shown that prechirping of NRZ pulses improve the total transmission length and make the NRZ pulses more robust to Kerr-nonlinearities.

Theory and applications of biotelemetry.

In this study, biotelemetry and its evolution is explained in detail. Bioelectric and physiological variables could be measured by biotelemetry systems. The development of a biotelemetry system and its principal operation are presented. The components of a biotelemetry system are explained. Biomedical data has been telemetered through every medium between two sites by using a variety of modulated energy forms. Designing of the link between transmitter and receiver is described. Important factors in designing a backpack or implanted telemeter are explained. The main features of implanted biotelemetry units are determined. Single-channel and multichannel biotelemetry systems are defined. The types of telemetry, and a comparison thereof, are given. The power sources of biotelemetry systems and features of different power sources are explained. A survey of biotelemetry applications on humans and animals is presented and advantages of using biotelemetry systems are determined.

Robustness of reduced temporal phase unwrapping in the measurement of shape

The predictions of success rate and depth uncertainty for the negative exponential sequence used for temporal phase unwrapping of shape data are generalized to include the effect of a reduced sequence and speckle noise in single-channel and multichannel systems, respectively. To cope with the reduction of the sequence, a scaling factor is introduced. A thorough investigation is made of the performance of this algorithm, called the reduced temporal phase-unwrapping algorithm. Two different approaches are considered: a single-channel approach in which all the necessary images are acquired sequentially in time and a multichannel approach in which the three channels of a color CCD camera are used to carry the phase-stepped images for each fringe density in parallel. The performance of these two approaches are investigated by numerical simulations. The simulations are based on a physical model in which the speckle contrast, the fringe modulation, and random noise are considered the sources of phase errors. Expressions are found that relate the physical quantities to phase errors for the single-channel and the multichannel approaches. In these simulations the single-channel approach was found to be the most robust. Expressions that relate the measurement accuracy and the unwrapping reliability, respectively, with the reduction of the fringe sequence were also found. As expected, the measurement accuracy is not affected by a shorter fringe sequence, whereas a significant reduction in the unwrapping reliability is found as compared with the complete negative exponential sequence.

Effects of symmetries on single-channel systems: Perfect transmission and reflection

We study the effects of symmetries on resonant transport in single-channel systems with an emphasis on their implications for atomic wires. Employing an expression of the scattering matrix in terms of its poles, it is shown that the mirror reflection and time-reversal symmetries lead generically to transmission and reflection peaks of magnitude 1, resulting in perfect transmission and perfect reflection, respectively. In particular, it is demonstrated that even when multiple resonances overlap and resonance shapes are distorted considerably, the perfect transmission (perfect reflection) can still occur provided that a system is free from ``pair annihilation'' events of two perfect transmissions (two perfect reflections). It is argued that these results can remain valid even when the employed expression of the scattering matrix becomes inapplicable, because the symmetries create certain topological structures of transmission and reflection amplitudes that stabilize the perfect transmission and reflection. Crossover from resonant transport to ballistic transport is also discussed. Results are discussed in connection with recent works on atomic wires.

Some Markovian Queuing Retrial Systems under Light-Traffic Conditions

The asymptotic behavior of the time of the first loss of a demand in Markovian single-channel and multichannel queuing retrial systems with a finite buffer and an external Markovian environment is analyzed. Two cases are studied: (a) the ratio of the input rate to the service rate tends to zero and (b) the ratio of the input rate to the service rate and the ratio of the input rate to the retrial rate tend to zero simultaneously. The method of so-called i>S-sets and the concept of a monotone structure introduced by Anisimov are used to prove the exponential approximation of the time of the first call loss and Poisson approximation of a flow of lost demands for both cases.

Black-box identification of digital waveform recorders

The paper presents an overview on the problem of waveform recorder characterization, stressing the opportunity of working out a standard for the model identification of a recorder. As a concrete contribution to this project, the authors propose a unified complete behavioral model for single-channel data acquisition systems, discuss the suitability of known test methods for its identification, and draw some guidelines for the construction of a complete identification procedure.

Optimization of pre- and post-dispersion compensation schemes for 10-Gbits/s NRZ links using standard and dispersion compensating fibers

We perform a systematic numerical optimization of pre- and post-compensation normalized sections using standard and dispersion compensating fibers for non-return to zero 10-Gbits/s single channel systems. By independently varying the power at the different types of fibers inputs and the compensation ratio, we find that the post-compensation performs better than precompensation at the expense of stricter parameter tolerance. Moreover, we show that both pre- and post-compensated systems can be significantly improved by using passive predistortion at the transmitter.

Dispersion-management in fiber communication lines using Raman amplification

We propose a dispersion management scheme combined with Raman amplification that supports strongly confined optical pulses with potential applications in ultra-high speed single-channel optical communication systems.

Rare-Earth-Doped Fibers for Telecommunications Applications

Primarily to meet the dramatic increase in Internet traffic, a substantial expansion in new fiber-optic networks has been seen in the last few years, increasing the total amount of transmission fiber deployed in the field. However, increased capacity has also been achieved by utilizing more of the available bandwidth present in the currently installed fiber. A key component in facilitating this increase in bandwidth is the erbium-doped fiber amplifier (EDFA), which provides efficient broad-band gain in the 1530–1560-nm telecommunications window. Erbium-doped glasses can be drawn into low-loss fiber, and the width of the gain band can be controlled with glass composition. With appropriate composition and design, EDFAs can simultaneously amplify 32 or more wavelengths, providing a 32-fold increase in data capacity over single-channel systems. These devices can boost signal strength by a factor of 1000, with high reliability and low noise at data rates exceeding 1 Tbit/s. In this article, we review some of the properties that are key to the success of EDFAs and discuss the potential for other rare-earth-doped glass-fiber combinations that may find possible applications in future telecommunications networks.Fiber optics have revolutionized the telecommunications industry, providing more information capacity and greater distances between signal boosters than copper wire and coaxial cable. The attenuation in coaxial systems increases exponentially with signal frequency, making high-speed transmission over long distances impractical. The best copper systems have a bandwidth of about 10 Mbit/s and are limited to lengths of less than 200 m at high data rates. In contrast, the attenuation of SiO2 optical fibers is low and independent of signal frequency, thus optical fiber can easily support 100 Gbit/s (10,000 times the capacity of copper) over 80 km and is currently only limited by the speed of the transmission and receiving electronics, with capacities in excess of 50 Tbit/s theoretically possible.1 For links in excess of 80 km, signal amplification is necessary to prevent total loss of the signal. In the 1980s, amplification was done with electronic devices called repeaters that detected the light, converted it to an electronic signal, amplified, retimed, and then retransmitted it as an optical pulse.The field of optical telecommunications has itself undergone a revolution. In the late 1980s, the invention of the all-optical amplifier allowed for simultaneous amplification of multiple channels in a single optical fiber each at a different wavelength or color of light. SiO2 fibers have a minimum in attenuation in the infrared (IR) portion of the optical spectrum near 1550 nm, as shown in Figure 1. The EDFA fortuitously provides high gain and low noise in the 1530-1560-nm spectral window. This technology now enables simultaneous amplification of 32 channels in a single fiber without the need for optical-to-electronic conversion. Thus single-fiber capacities of 320 Gbit/s are currently being deployed today. To perform this electronically, each channel would have to be separated (demultiplexed), amplified by its own costly repeater, and then recombined (multiplexed) in the fiber. Researchers are now perfecting 100-channel EDFAs in the lab.