High bit rate digital subscriber line: a copper bridge to thenetwork of the future

It is argued that the high bit rate digital subscriber line (HDSL), permitting low-cost 1.5 Mb/s copper access, will ease the transition to fiber access by accelerating the use of higher speed services. Copper will dominate over fiber customer access for at least the next ten years. During this period, the success of high-speed switched services will depend on the connectivity provided by both fiber and copper access. HDSL will initially be used to serve private-line DS 1, ISDN primary rate access, and digital loop carrier feeders. Later, the HDSL will be applied to switched services such as metropolitan area networks (MANs) and circuit switched DS1s     

Asymmetric digital subscriber line: interim technology for the nextforty years

The Internet has surfaced as the dominant early market for residential broadband. ADSL, a transmission system capable of realizing rates from 1 to Mb/s over existing telephone lines, fits Internet access requirements perfectly, and offers telephone companies a tool for connecting virtually all Internet users at megabit rates before the next century. ADSL is asymmetric-high-speed downstream, lower-speed upstream-to counteract speed limitations imposed by line length and crosstalk. The transmission technology itself has two essential forms, single-carrier and multicarrier, which must press Shannon's limit to squeeze so many bits through so little bandwidth. With complicated line coding and other features such as integral forward error correction and ATM/Ethernet mode interfaces, ADSL will be the most complex modem ever attached to a telephone line. This will not prevent ADSL from reaching consumer-level pricing within the next two years. We can expect some commercial deployment in 1997 and virtually ubiquitous availability by the end of 1999     

A monolithic subscriber line interface circuit [in bipolar technology]

A monolithic SLIC fabricated with high-voltage dielectric isolation (DI) technology has been proven to have excellent performance and requires a minimum of external circuitry. The SLIC provides battery feed, overvoltage protection (with some external devices), ringing control, supervision, and hybrid functions.     

Design and performance of a novel automatic fiber line testingsystem with OTDR for optical subscriber loops

This paper proposes architecture for a novel automatic fiber line testing system with an optical time-domain reflectometer (OTDR) and describes the system requirements, the design method, and the system evaluation. The results of a trial on a manufactured system and an evaluation of its characteristics are presented with evidence that an in-service optical fiber can be tested with no degradation in communication quality and the desired measurement accuracy and system component characteristics can be realized. In addition, it is confirmed that a failure between an optical fiber cable and a digital service unit (DSU) can be identified with 100% accuracy     

Digital subscriber line (HDSL and ADSL) capacity of the outsideloop plant

The fundamental limits of the outside loop plant to carry high-speed digital (bi-directional HDSL and ADSL) data are reported. The paper focuses on the copper wire pairs, drop lengths, and interconnects that convey data over the “last mile” to almost all businesses and residences in the US. The two major customers, businesses and households, are classified, characterized, and categorized by the distance to the central office or the remote terminal. Their spectral capabilities are computed and their ultimate digital capabilities are reported. The crosstalk limitations inherent in the plant are also computed and verified against the loss of signal due the distance and spectral constraints. The signal to noise ratio can thus be estimated to ascertain the transmission quality through the plant. Accordingly, the paper reports on losses, bandwidths, and bit rates in the first half, and discusses the major bottlenecks in the second half     

OEIC technology and its application to subscriber loops

Recent progress in GaAs- and InP-based optoelectronic integrated circuits (OEICs) for use in optical fiber transmission systems is reviewed. OEIC technology and system demonstrations for short-haul and high-speed transmission are described, and the problems arising in practical applications are discussed. Approaches to resolution of these problems are presented, and future OEIC applications, especially with regard to subscriber loops, are predicted     

A floating, low-power subscriber line interface circuit [bipolar IC technology]

A subscriber line interface circuit is described which is smaller than and dissipates substantially less heat than conventional circuits which perform similar functions. Worst case heat dissipation in the circuit is only 0.65 W as compared to conventional arrangements which dissipate up to 4 W. The battery feed function is accomplished by a small 1.5 W DC-to-DC converter which also includes circuitry for detecting loop supervisory functions. The floating nature of the output circuitry renders it immune to power line induction and common mode power crosses. Primary protection from lightning and other induced surges utilizes conventional carbon block type protectors. Secondary circuit protection is accomplished with a high voltage diode and simple carbon composition resistor. Circuit disconnect is accomplished with a medium voltage SCR for ringing and loop testing the subscriber line. The battery feed control and loop supervisory functions have been realized in a low voltage, linear integrated circuitry using CBIC technology.     

A CMOS line equalizer for a digital subscriber loop

An adaptive line equalizer for a 200-kb/s digital subscriber loop is developed in the form of a monolithic LSI and implemented using 2.5-/spl mu/m CMOS technology. Most analog portions consist of switched-capacitor circuits successfully designed to minimize power consumption, the amount of hardware, and off-chip components. The main features of the LSI equalizer are an /spl radic/f step equalizer, a five-tap decision-feedback equalizer using /spl Delta/M D/A conversion, a newly developed wave difference method (WDM), tankless timing extraction PLL, and a line driver. Consequently, the LSI can equalize a 52-dB line loss with four bridge taps; it dissipates only 67 mW, and the chip area is 5.7/spl times/5.9 mm/SUP 2/.     

A high-voltage IC for a transformerless trunk and subscriber line interface

A new high-voltage, junction-isolated, complementary bipolar technology has been used to fabricate an IC for a transformerless trunk and subscriber line interface. The new technology provides both vertical p-n-p and n-p-n transistors with BV/SUB CE0/ greater than 60 V, betas of 100, and f/SUB T/'s of 200 MHz. It permits the straightforward op amp realization of a new op amp circuit configuration in transformerless line circuits. The new configuration uses the high-voltage IC plus some low voltage control circuitry to provide limited current battery-feed, loop-closure detection, reverse-battery signaling, two-wire to four-wire conversion, lightning protection, power-down capability, and longitudinal performance which is independent of the battery-feed current magnitude.     

A switching regulator and lightning protector for a subscriber line interface circuit

Two monolithic ICs, a switching regulator and a crowbar protector circuit fabricated in a 90-V complementary bipolar technology are described. These devices enhance the performance of a basic subscriber-line interface circuit (SLIC) by extending the range to the customer so that 20-mA DC feed current can be supplied to a 2800-/spl Omega/ loop without the need for a -72-V office battery. The power dissipation of the entire SLIC subsystem is at most 1.5 W for any length of subscriber loop. All circuitry is robustly protected from foreign 60-Hz and lightning voltages.     

Transmission characteristics of a coaxial optical fiber line

A coaxial optical fiber line is proposed and studied as a long-distance transmission medium. The radial structure consists of a core surrounded by two clads. The inner clad has higher refractive index than the core and the outer clad. Guided modes are thus characterized by a concentrated field in the inner clad and evanescent fields in both the core and the outer clad. Using a rigorous modal analysis, characteristic curves for a monomode coaxial fiber line are presented. It is shown that the zero-dispersion wavelength can be placed at any desired value by proper choice of the refractive index contrast and the fiber dimensions. The proposed coaxial line compares well with the known W-profiled line with respect to ease of manufacture and dispersion characteristics     

Novel optical line codes tolerant to fiber chromatic dispersion

A novel family of optical line codes to counteract the effects of a dispersive fiber is presented. The performance of the first code in the family, referred to as order-1 code, is analytically evaluated and compared to that of the duobinary and phased amplitude-shift signaling (PASS) codes, which are a modified form of duobinary proposed by Stark et al. (1999). The order-1 line code turns out to be very robust to chromatic dispersion and, for a given penalty, allows the bridging of a distance 1.5 times (or more) greater than duobinary. The novel family of codes was conceived by exploiting the finding that, approximately, a very dispersive fiber turns an input pulse into the form of its Fourier transform seen in the time domain. Higher-order codes allow the bridging of larger distances if combined with appropriate chirping     

Optical fiber recirculating delay line incorporating a fibergrating array

For a practical optical fiber recirculating delay line the maximum notch depth and tunable free spectral range are difficult to achieve because of fixed coupling coefficient and loop length. We present here an optical fiber recirculating delay line incorporating a fiber grating array. In this work, the effect of insertion loss in the delay loop is investigated and used to maximize the notch depth of the frequency response. The tunable free spectral range is obtained from the wavelength dependent loop length introduced by the fiber grating array     

Texture investigation of copper interconnects with a different line width

To understand the effect of line width on textural and microstructural evolution of Cu damascene interconnect, three Cu interconnects samples with different line widths are investigated. According to x-ray diffraction (XRD) results, the (111) texture is developed in all investigated lines. Scattered {111}〈112〉 and {111}〈110〉 texture components are present in 0.18-μm-width interconnect lines, and the {111}〈110〉 texture was developed in 2-μm-width interconnect lines. The directional changes of the (111) plane orientation with increased line width were investigated by XRD. In addition, microstructure and grain-boundary character distribution (GBCD) of Cu interconnect were measured using electron backscattered diffraction (EBSD) techniques. This measurement demonstrated that a bamboo-like microstructure is developed in the narrow line, and a polygranular structure is developed in the wider line. The fraction of ∑3 boundaries is increased as the line width increases but is decreased in the blanket film. A new interpretation of textural evolution in damascene interconnect lines after annealing is suggested, based on the state of stress and growth mechanisms of Cu deposits.     

Sliding-block line codes to increase dispersion-limited distance ofoptical fiber channels

We investigate the use of a run-length-limited (RLL) sliding-block line code to reduce the effects of intersymbol interference in high-speed (multi-Gb/s) data transmission over the direct-detection single-mode optical fiber channel. In addition to their well-known use for synchronization purposes, line codes can be designed to eliminate certain worst-case patterns that would otherwise preclude reliable data transmission at high rates and very long fiber lengths. The code considered here prohibits isolated “one's” (the 010 pattern) from appearing in the transmitted sequence. Simulation results indicate that this code, coupled with a simple compensation scheme at the receiver, can significantly increase dispersion-limited data rates and/or fiber lengths for both externally modulated and directly modulated systems. While our emphasis is on one particular line code, we discuss sliding block coding for the optical fiber channel in a general context     

Adaptive polling algorithm to provide subscriber and service differentiation in a Long-Reach EPON

A novel interleaved polling algorithm for Long-Reach EPONs is proposed in order to simultaneously provide subscriber and class of service differentiation. It is demonstrated that the new polling algorithm applied to a typical 100 km Long-Reach EPON performs better than centralized methods, where bandwidth prediction is needed to overcome the higher round trip time in which ONUs cannot transmit. As polling methods in Long-Reach EPONs do not require prediction, they are much simpler and show less computational complexity than centralized schemes, avoiding the inaccuracy of bandwidth prediction. Simulation results show that the new algorithm increases the achieved throughput when compared to centralized algorithms with traffic prediction, obtaining a significant reduction of both mean packet delay and packet loss ratio for the highest priority service level profiles.     

Theory and implementation of a Raman active fiber delay line

In an optical delay line made of a single-mode reentrant fiber loop, Raman amplification is used to compensate for recirculating signal losses. Concurrent Stokes noise amplification limits the system performances. A theoretical model shows that the signal-to-noise ratio decays as the reciprocal of the number of signal recirculations. Experimental results obtained with a 760-m-long fiber loop operated atlambda = 1.12 mum are presented. A new pump modulation technique resulting in improved output signal stability is reported whereupon optical delays up to 3 ms were achieved.