Haul Communication Research Articles

Tail Extrapolation in MLSE Receivers Using Nonparametric Channel Model Estimation

This paper presents a method for determining the probability of rare events, in particular for probability density function (pdf) and bit error rate (BER) estimation. The derivation of the method is based on the presumption that the pdf is a member of a family of distributions very often named as the generalized exponential (GE) class of distributions. Based on high reliability estimations obtained in short simulation/measurement times, the low probably events are estimated accurately by extrapolation. The suggested method can be applied to some distributions that are different from GE distributions, such as noncentral chi-square distributions, to extrapolate to low probability events, with some extrapolation error. It can also be applied to BER estimation. The method is in particular helpful for estimating channels suffering from both severe signal distortion causing undesired intersymbol interference (ISI) of several symbols, and from severe noise. Such conditions prevail, for example, in metro and long haul high-speed optical fiber communication systems. So the method may be implemented in particular in maximum-likelihood sequence estimation (MLSE) optical receivers using nonparametric channel model estimation. A special use of the extrapolation method is explained for practical systems using trellis branch metrics derived from the estimated pdf to decode the transmitted sequence of symbols.

Proposal for optical fiber designs with ultrahigh effective area and small bending loss applicable to long haul communications

A proposal for the multiclad MII optical fiber structure with ultralarge effective area and small bending loss is presented. For the proposed structure small dispersion and dispersion slope are obtained thanks to what we believe to be a novel design method. The suggested design method is based on a weighted fitness function, which is applied to the genetic algorithm optimization technique. In the meantime, the foregoing structure introduces a special fiber whose mode field diameter is small and approximately insensitive to the variation of the effective area. Compared to the work reported previously, our method can precisely set the zero dispersion wavelength. The designed dispersion-shifted single-mode fibers have effective area, mode field diameter, and quality factor respectively within [150-194.79] microm(2), [6.82-7.95] microm, and [3.04-3.85] at lambda(0)=1.55 microm. An analytical method is used for the calculation of the dispersion and its slope. These calculations give dispersion and dispersion slope of [(-2.57 x 10(-4))-(-0.085)] ps/km/nm and approximately 0.064 ps/km x nm(2), respectively.

Linear and nonlinear distortion effects in direct detection 40 Gb/s MSK modulation formats multi-span optically amplified transmission

The generation of minimum shift keying (MSK) requires a linear variation of the phase, hence a constant frequency of the optical carrier. However, the generation of the optical phase may be preferred by driving an optical modulator using sinusoidal signal for practical implementation. Thus a nonlinear variation of the carrier phase, hence some distortion effects are produced. In this paper, we investigate the use of linear and nonlinear phase shaping filtering and their impacts on MSK modulated optical signals transmission over optically amplified long haul communications system. The evolution of the phasor of the in-phase and quadrature components is illustrated for lightwave-modulated signal transmission. The distinct features of three different MSK modulation formats: linear MSK, weakly nonlinear MSK and strongly nonlinear MSK and their transmission are simulated. Transmission performance obtained indicates the resilience of the MSK signals in transmission over multi-optically amplified multi-spans.

Wavelength shift keying modulation up to 35 Gb/s with wavelength tone reuse to multiplex two 40 Gb/s DPSK signals

Fast optical frequency shift keying or wavelength shift keying (WSK) modulation offers advantageous features for applications in long haul communications and in optical labeling for packet routing. This includes simple demodulation by optical filtering and constant amplitude envelope providing tolerance to fiber nonlinear effects during transmission. In this paper we report on the generation of WSK signals up to 35 Gb/s with reuse of the wavelength tones for polarization multiplexing two independent 40 Gb/s DPSK signals. Transmission over a 50 km fiber link of the resultant three channel signal is also reported.

S-band gain flattened distributed fiber Raman amplifier with chirped fiber bragg grating filter

S-band gain flattened distributed fiber Raman amplifier with a bandwidth from 1 488 nm to 1 541 nm (53 nm in width), an averaged gain of 10 dB and a gain ripple of ±0.6 dB is obtained successfully, in which a single-wavelength high power fiber Raman laser with wavelength of 1 427.2 nm is used as the pump and the chirped fiber Bragg grating is used as the gain flattening filter. Besides, filter wavelength division multiplexer (FWDM) is used as the multi-signal multiplexer and 1 427 nm/1 505 nm coarse wavelength division multiplexer (CWDM) is used as the pump-signal coupler. The gain media are G652 fiber of 50 km in length and dispersion compensation fiber (DCF) of 5 km in length. Moreover, the location arrangements of different type of fibers and the effect caused by gain flattening filter as well as their solutions are discussed in detail. It is very significant to extend the range of optical fiber communication band and increase the capacity of fiber communication especially for ultra-long haul and ultra-high capacity communication system.

The characterization of step index single mode silica fiber for long haul signal communication

The optical properties of single mode fibers, which are drawn from the silica preform made by MCVD technique, have been studied. The properties such as cutoff wavelength, chromatic dispersion, and polarization mode dispersion (PMD) were studied for 2.3 km length of single mode fiber (SMF). The cutoff wavelength was measured by fiber optic test procedure (FOTP)-80 which was found to be 1179 nm. The chromatic dispersion was measured by FOTP-169 at various wavelengths, the zero dispersion being observed at 1503 nm. The PMD was measured by interferometric method, and exhibited the magnitude of 0.07 ps at 1550 nm. The results are discussed to assess the suitability of these fibers for long haul communication systems.

Optical fibre design using evolutionary strategies

The design of optical fibres for applications where many performance targets have to be met simultaneously is a non‐trivial process. An evolutionary strategy (ES) combined with an algorithm to model the appropriate fibre parameters was used to design an optical fibre suitable for long haul high bandwidth communications. The ES code was developed using an object oriented approach and a parallel version was also incorporated. This allowed for the rapid implementation and subsequent design of fibres with properties of interest. Design constraints arising from the fibre manufacturing process were incorporated.

Epitaxial Si1-xGex Films and Superlattice Structures Grown by CVD for Infrared Photodetectors

AbstractIntegration of photodetectors with high responsitivity in the near infrared (1.3-1.55 μm) on standard Si electronic circuits is important for a variety of applications in the field of on-chip, local area and long haul optical communications. In this work we report on a detailed structural and optical characterization of epitaxial Si1-xGex films and Si1-xGex /Si multilayers grown by chemical vapor deposition on (100) Si wafers. Cross-sectional transmission electron microscopy analyses show that metastable strained Si1-xGex films of few nanometer with x>40% can be deposited at low growth temperature and pressure. Absorption measurements on these films demonstrate the extension of the photo-response to 1.55 μm. Using these films as active layers Schottky integrated photodetectors have been fabricated.

Resonant-cavity-enhanced heterostructure metal–semiconductor–metal photodetector

We report a GaAs-based high-speed, resonant-cavity-enhanced, heterostructure metal–semiconductor–metal photodetector with Al0.24Ga0.76As/Al0.9Ga0.1As distributed Bragg reflector operating around 850 nm. The photocurrent spectrum shows a clear peak at this wavelength with full width at half maximum (FWHM) of around 30 nm. At resonance wavelength, a seven-fold increase can be achieved in quantum efficiency compared to a detector of the same absorption depth. The top reflector is a delta modulation doped Al0.24Ga0.76As that also acts as the barrier enhancement layer thus providing very low dark current values. The breakdown voltage is above 20 V. Time response measurements show rise time, fall time, and FWHM of 8.8 ps, 9 ps, and 8.1 ps, respectively, giving a 3-dB bandwidth of about 33 GHz. Combination of low dark current, fast response, wavelength selectivity, and compatibility with high electron mobility transistors makes this device especially suitable for short haul communications purposes.

A Novel PSK Homodyne Optical Receiver for Long Haul Communications

In this paper a novel balanced optical phase locked loop has been proposed for the reception of PSK signals in long-haul optical communication systems. The effect of loop propagation delay, which cause serious restriction on the requirement of laser linewidth, have been considerably reduced in this new loop. Moreover, the data-to-phase-lock cross-talk effect has been eliminated. The performance of the new loop has been studied when the loop is preceded by optical amplifiers.

Remote area monitoring for noise mitigation

The USAF has been required to conduct noise measurements to assess the impact of its flying mission. In 1984 as part of a Record of Decision to fly super-sonic flights over Valentine, Texas and Reserve, New Mexico, the USAF had to conduct sonic boom monitoring that cost over $1.5M. Validation studies have been conducted to increase the public’s confidence in the noise models used for the Air Force Air Installation Compatible Use Zone program. In 1992 the USAF developed a noise monitor that could be put around the neck of an animal for studies to determine the effects of military overflights on wildlife. The USAF has started a new development program to consolidate all of its noise measurement requirements into a remote monitoring package. This package will use different sensors and data compression for various measurements but the same radio transmitter hooked to a long haul communications system to transmit the data back to a remotely located computer system for analysis. This capability will allow the USAF to do real-time monitoring of noise impacts for determining its mitigation effectiveness.

Optical Fibre Communication Systems for Voice and Video Signals—State-of-the Art

The optical fibre communication systems have a tremendous potential of carrying a large number of voice and video signals. Many fibre systems have already been installed and many more are planned and are under development. They are useful for all kinds of applications, such as submarine communications, intercity long haul communications, metropolitan trunking systems, subscriber loops and military communications in a telecommunication network. These applications and some of the new customer services which can be provided by fibre optic systems are reviewed. Current trends in the development of the components such as the optical sources, detectors and fibres are presented. Sources and detectors at long wavelengths, 1300 and 1600 nm range, where the fibre attenuation and dispersion are minimum, and the single-mode fibres are in advanced stages of development. Far greater repeater spacings than possible with metallic cables, would be achieved by using them in optical fibre systems. The ever-growing demand on telecommunication services can be met by a two-prong approach: (i) exploiting new wideband media like optical fibres and (ii) compression of bandwidths of the voice and the video signals at the source. Techniques of bandwidth reduction and progress made in generation of digital speech and picture signals at low bit rates are reviewed. Multiplexing methods and various line codes used in baseband transmission systems arc summarized.

A Review of Fiber Optical Transmission Systems

A review is given of some of the fundamentals of fiber optical transmission systems including fiber optical waveguides, optical sources, and photodetectors. Fiber optical systems can, in principle, compete with twisted pair, coaxial cable and waveguide facilities in virtually all sectors of the communication network. These systems are attractive because fiber optical waveguides are potentially inexpensive, have miniature cross section, are strong and flexible, have light weight, and can transmit broad band signals over long distances with low distortion. Recent advances in glass materials technology and fiber fabrication procedures have resulted in fiber waveguides with losses as low as 4dB/km in the important wavelength region around 8200A corresponding_ to the output of the GaA1As laser. The range of applications of fiber optical systems extend from short and long haul communications to wiring within buildings and between computer terminals, as well as to a variety of military applications which capitalize on the unique properties of glass fibers.

Minimum cost routing for static network models

AbstractThis paper develops techniques which can be applied to long range planning studies for the domestic long haul communications network. The problem studied is how to select a path through the network for each point‐to‐point demand for communications channels, so that the total network cost is minimized. The problem is to minimize total network cost, subject to multicommodity flow requirements and concave link cost functions. Finding an exact solution is difficult because of the concavity of the cost functions and the complexity (100 to 200 nodes and 200 to 300 links) of the network structure. A specialized technique is developed to provide locally optimal solutions to the problem, one of minimizing a concave function over a convex constraint set. When the link cost displays a fixed charge, a modification of the iterative algorithm provides acceptable a modification of the iterative algorithm provides acceptable solutions. Even though the global optimum cannot be found amidst the immense number of local optima, several sample problems demonstrate the value of the techniques developed.A companion paper will extend this work to the dynamic routing problem, of deciding how to route future demands and install transmission facilities so as to minimize the present worth of expenditures during the study interval. The methods and goals of these modeling efforts will be discussed in the companion paper.