KR100488267B1 - Wavelength Division Multiplexing Waveguide System - Google Patents

Abstract

The present invention relates to a high capacity optical fiber network operating by wavelength division multiplexing. The systems considered can use span distances in excess of 100 km and provide multiple multiplexed channels operating at gigabits per second.

Description

Wavelength Division Multiplexed Optical Waveguide System

Background of the Invention

Technical field

FIELD OF THE INVENTION The field of the present invention relates to high capacity optical fiber networks operating with wavelength division multiplexing. Considered systems are based on span distances greater than 100 kilometers; It relies on signal amplification rather than repeaters in spans and uses three or more multiple channels, each operating at least 5.0 gbit / sec.

Description of the prior art

The technical level of the field in which the present invention is considered is summarized in the excellent paper entitled "Lightwave", published in November 1992, "Dispersion-shifted Fiber" on pages 25-29. As mentioned in the paper, the most advanced optical fiber systems currently being installed or in the planning stage rely on dispersion-shifted fiber (DS fiber). Many developments have favored a carrier wavelength of 1.55 μm. There is a minimal loss at this wavelength for fibers based on commonly used single mode silica, and the erbium amplifier, the only practical fiber amplifier at present, works best at this wavelength. It has long been known that the linear dispersion null point, ie the radiation wavelength where the chromatic dispersion changes sign and passes through zero, naturally falls to about 1.31 μm for silica based fibers. . The DS fiber, ie, the fiber whose dispersion zero transitions to 1.55 μm, depends on the balance of the two main components of color dispersion, namely material dispersion and waveguide dispersion. Waveguide dispersion is controlled by matching the refractive profile of the fiber.

The use of DS fiber is expected to contribute to multichannel operation, namely wavelength division multiplex (WDM). Here, a plurality of closely spaced carrier wavelengths define separate channels, each of which operates at high capacity, i.e., 5.0 gbit / sec or more. The facilities for the initial WDM or for the upgrades under consideration use three or more channel operations, each operating close enough to zero distribution points, each operating at the same capacity. Systems contemplated are generally based on four or eight WDM channels, each of which can operate at or upgrade to that capacity.

WDM systems use optical amplification rather than signal regeneration if possible. WDM has become practical by replacing conventional repeaters with optical amplifiers that rely on electronic detection and optical regeneration. The use of Er amplifiers enables hundreds of kilometers of fiber spans between repeaters or terminals. Some systems in the planning phase use optical amplifiers spaced 120 km apart over a span length of 360 km.

The reference paper describes the use of narrow spectral linewidths that can be used from distributed feedback (DFB) lasers for high-capacity remote systems. Relatively inexpensive and readily available "Fabry Perot lasers" are sufficient for normal initial operation. As reported in the paper, the systems installed by "Telefonos de Mexico; MCI; and AT & T" are based on DS fiber.

Many studies have considered nonlinear effects (J. Lightwave Technology, Vol. 9 No. 3, published in March 1991, by D. Marcuse, “Single-Channel Operation in Very Long Nonlinear Fibers With Optical”. Amplifiers at Zero Dispersion, and "Effect of Fiber Nonlinearity on Long" by D. Marcuse, AR Chraplyvy and RWTkach, published in January 1991, J. Lightwave Technology, Vol. 9, No. 1, pages 121-128. -Distance Transmission ". Nonlinear effects studied include "Stimulated Brillouin Scattering; Self-Phase and Cross-Phase Modulation; Four-Photon Mixing (4PM) and Stimulated Raman Scattering". It has been previously known that correction of the linear dispersion problem is not the final solution. At least in principle, much higher systems that operate over longer lengths and at higher capacities will eventually need to account for nonlinear effects.

Term description

WDM-Wavelength Division Multiplex, which provides for multi-channel operation within a single fiber. The channels are close enough to be amplified simultaneously by a single optical amplifier. At this time, a commonly used optical amplifier (the erbium-doped silica fiber amplifier) has a usable bandwidth of Δλ ~ 10-20nm.

Dispersion—When used alone, the term refers to a linear effect due to color dispersion, ie wavelength dependent velocity in the carrier spectrum.

Span-refers to the fiber length without a repeater. This length, which may include optical amplifiers, is the distance between stations (generally between the nearest signal regenerators) where the signal is converted from or in electronic form. This span may define the entire system or be combined with one or more additional spans.

Summary of the Invention

In the most relevant sense, new facilities for initial or contemplated WDM fiber optic communication systems require fibers with substantially minimal dispersion throughout the communication span and prohibit the use of DS fibers of any length. The spans may preferably consist of even fibers with constant dispersion at values of at least 1.5 ps / nm-km. Alternatively, spans may use a series of fibers with different dispersion by "concatenation" or "compensation". Both include fibers with dispersion greater than 1.5 ps / nm-km. Chain connections generally use continuous fiber lengths with positive and negative variances of equal magnitude. Compensation compensates for major fiber lengths with variances of opposite sizes using relatively short length “dispersion matching” fibers with very large variances. The use of WDM systems in the near future allows for a defined small average amount of color dispersion, and the systems considered allow λ ₀ = 1550 nm on average. It is desirable to maintain the dispersion below a certain maximum for any given fiber length in the present system. In particular, in systems where the overall capacity is greater than 40 gbit / sec 4-channel or 80 gbit / sec 8-channel, spontaneous generation that increases the spectral content beyond that introduced by a carrier-generating laser may result in capacity-limited dispersion. I can bring it. Since the resulting color dispersion is virtually nonlinear, the initial pulse content can no longer be recovered. For this purpose, a maximum variance of 8 ps / nm-km can be defined for future more sophisticated systems.

The improved signal capacity is due to the fiber path design which avoids four-photon mixing as a capacity constraint. This consideration includes four or more channel systems having spacings of 2.5 nm or less; Span lengths of at least 300 km; Determine for the allowance of amplifier spacings of at least 100 km. The invention is defined accordingly.

Co- filed US patent application Ser. No. 08/069962 claims a fiber having a shape that ensures a small but critical color dispersion suitable for use with a WDM system. The use of the fiber is regarded as a kind of present invention.

In its broadest sense, the present invention reflects the observation that the relevant mechanisms to be considered in the design of WDM systems where four-photon mixing is considered. Many factors convince the assumption that the teachings of the present invention will appear in the form described above. In one example, it is appropriate in principle to change the carrier wavelength to, for example, λ = 1550 ± 20 nm in order to introduce the necessary dispersion in the DS fiber, but it cannot be easily achieved. In advanced development, erbium amplifiers have an operating peak near 1550 nm. Operating 20 nm outside this peak reduces the carrier power level to an unnecessarily low magnitude for one or more channels. It is conceivable that an alternative to the erbium amplifier or any other change in the design of the amplifier allows this operation. It is even clearer that future systems will continue to be designed taking advantage of the current or more advanced stages of conventional erbium amplifiers.

Four-photon mixing depends on the exact wavelengths of the carriers generated. Evenly spaced four-channel systems inevitably meet this requirement. The importance of 4PM is somewhat reduced for three-channel systems, and in the case of strictly non-uniform intervals in four-channel systems, in principle, 4PM can be avoided. Problems in adopting this approach are that operating parameters beyond the current technical level are required and even if this is realized additional costs are required. Reliable stabilization to maintain this precision is problematic due to, for example, thermal drift.

These alternative approaches may not be taken seriously into newly installed systems, but would be worth upgrading to already installed systems, especially those with DS fibers.

details

Normal

It is now known that the ultimate goal to be achieved by the DSF is to be hampered by the very perfection in which color dispersion is removed. In the DSF specification table, the allowed dispersion tolerance of <3.5 ps / nm-km over the wavelength range λ = 1525-1575 nm, which itself is sufficient for nonlinear dispersion to cause difficulty in WDM operation in future systems. Confirmation. It has now been found that planned systems are inoperable because of their nonlinear form. Constrained nonlinearity, ie four-photon mixing (4PM), was recently known and referred to above as "Effect of Fiber Nonlinearity on Long-Distance Transmission" cited above. It is described with reference to. For most purposes, 4PM has been considered only for academic interest. The cited paper considers well test systems with span lengths of 7500 km. In particular, not only continued sales and installation of DSFs for WDM operation, but also inplace systems (based on much shorter common span lengths) agree with this view.

With advanced circuit design, it is possible to reduce the constraints imposed by 4PM. Note that channel spacings and modulation formats may lead to continued use of DSF for heavily reduced capacity, i.e., limited number of channels and limited distances of WDM systems. Currently considered WDM systems are not allowed, which is made possible by the practice of the present invention. Replacement of DSFs may be accomplished with capacities sought, such as four-channel operation, at least 5 Gb / sec capacity per channel; Repeater span lengths greater than 360 kilometers and channel spacings of 1.0 nm to 2.0 nm are allowed. System designers will easily understand and implement this teaching.

As elsewhere in this specification, specific sizes are exemplary but may be designed to satisfy a practical purpose in the near future. As an example, channel spacings of 1.0 nm or greater allow for easily attainable frequency stabilization of transmitters and receivers. Narrower intervals with larger allowable system capacity may be justified using the reduction effect of 4PM of the present invention. Design considerations lead to an assumed spacing of 0.8 nm.

The teachings rely on the background knowledge of those skilled in the art. Strictly speaking, 4PM appears as a fluctuating gain or loss as a power penalty due to constructive and destructive interference that inevitably involves signals of different channels. 4PM is not a noise source. Since the effect is signal distortion in which the amplitude of the portion is increased and the amplitude of the portion is reduced, the effect may not be corrected later. Since the size of 4PM is power dependent, the effect can be reduced by reducing the launch power. For a given fiber span length, insertion loss can be reduced by an approach that increases the number of amplifiers to allow for a reduction in firing power. As defined in the terminology, WDMF allows the use of amplifiers operating at power levels hindered by the DSF for WDM, each of which is considered. For these purposes, the inventive progress is defined in that the amplifier spacing is at least 120 km with one or more amplifiers operating at a firing power level of 2.5mw / Gb-sec.

These considerations relate to loss budgets, including splice losses of 33 dB and aging effects over the spacing between amplifiers. Other considerations may suggest other methods. As an obvious example, subsea systems may use substantially longer span lengths than are considered for ground use due to the larger installation and maintenance costs of regenerator equipment. This in turn requires narrower amplifier spacings, i.e. spacings of 100 km or less.

While the systems of the present invention meet the high level of expectations of the system designer, these expectations appear to be impossible with current DSFs.

1 shows a characteristic WDM system that is considered as a near future installation. This consists of four transmitters 10, 11, 12 and 13 coupled to a passive 4: 1 combiner 14. The combined signal is introduced into a fiber transmission line 15 provided with two optical amplifiers 16 and 17. At the end of the receiver, the four-channel signals are split by the demultiplexer 18, and the separated signals are then routed to four players 19, 20, 21 and 22.

Although Figure 1 represents the systems of the present invention that may include a greater number of channels, eight-channel systems are currently contemplated. Longer systems may include longer spans or multiple spans so four transmitters can act as a player. In one system in the planning phase, the span length is 360 km and the amplifier spacing is 120 km. The channel spacing, or difference in carrier wavelength, is 200 GHz (or about 1.5 nm). As discussed, the fiber path may consist primarily of invariant, fixed, distributed fibers from end to end, and may consist of stranded or compensated fibers.

The claimed WDM systems differ from those currently planned, primarily in the nature of fiber transmission lines. Previous systems were designed on the premise that color dispersion was a factor in capacity control. It was expected that the use of dispersion shifted fiber (DSF) would allow four channels of WDM target, i.e. an initial span length of 360 km, capacity per channel of 5 gbit / sec each. It is the intention of the present invention that four-photon mixing (4PM), which is a form of nonlinear dispersion, hinders the achievement of the 4-channel 20 gbit / sec capacity target. The direct result is the elimination of the use of DS fibers of arbitrary length. Newly installed systems are now expected to use distributed fiber. Constraints by any color dispersion imposed will be offset by chain linkage or compensation.

The two approaches allow the use of fibers with substantial dispersions, ie the use of fibers with a dispersion of 4 ps / nm-km or more when measured at λ = 1550 nm. Both require precisely defined fiber lengths to accurately compensate for dispersion and reduce it to an appropriate level. First, the chain linkage uses "normal" distributed fibers with variances of opposite codes of length. "Normal" means a fiber with a dispersion introduced at or below the material dispersion of the system, which is less than about 18 ps / nm-km in the fiber currently in use. This approach is considered important for subsea installations but has been generally ignored for ground use. This solution requires precise length determination for each fiber type prior to installation. Secondly, compensation compensates for normal fibers using relatively short lengths of highly dispersed fibers. The compensation fiber is expected to rest on reels installed at the amplifier or at the end points.

2 to 5

The “eye” diagram in these figures tracks the channel power as a function of time.

These diagrams are obtained by plotting the received signal as a function of time, and then plotting the time base again by one bit interval. The abscissa interval is about 1 bit long. These overlapping 64 bits define the most likely (reinforcement and cancellation) interference case due to transmission on three channels adjacent to a particular floated channel. This eye diagram shows the worst case of damage measured by the maximum coordinate value of the curves (by the vertical size of the empty space between the peak and zero). An overly intact system shows a clear discrepancy between "ones" and "zeros", with a large "eye opening" in the center of the diagram. An intact system is believed to have a "eye opening" of 1.0. Actual systems operating at an aperture of about 0.9 are believed to be substantially intact. Since actual systems are designed for such openings, substantially greater damage requires expensive design changes, i.e., design changes by reducing amplifier / compensation distance and / or reducing amplifier firing power in the case of WDM.

The diagrams show 64-bit patterns and include both the effects of dispersion due to (linear) dispersion and nonlinear refractive index. For consistency, all curves are for the third channel. The causative factors are mainly color dispersion, 4PM, and SPM. Since the operating power levels are low enough, other nonlinear effects can be ignored (nonlinear effects at very low levels include: Stimulated Brillouin Scattering and Stimulated Raman Scattering). Spurious lines are due to all possible interactions. The importance of this diagram lies in the "opening of the eye", that is, the part of space where there is nothing between the peak and the zero.

2 shows channel spacing of 200 GHz (1.5 nm); Span length of 360 km; Has an amplifier spacing of 120 km; An eye diagram of a DSF 4-channel WDM system operating at 5 Gb / sec per channel capacity. Its ˜0.560 opening is inadequate for operation. Since it is a nonlinear dispersion, dispersion and SPM can be ignored, so the closing of the eye shape is entirely due to 4PM.

3 is an eye diagram for a WDMF system operating under the same conditions. The ocular opening of ˜0.814 in such a system is sufficient contrast for operation. The system of this figure is not compensated for its + 2p / nm-km dispersion. The use of compensation fiber to reduce its dispersion will further improve the operation, which is not necessary under these conditions but will allow for increased capacity.

4 shows the use of fibers with a variance of +16 ps / nm-km for the same WDM system. Since the dispersion value is high enough, 4PM is not significant under those operating conditions. Spurious lines are due to dispersion and SPM. The opening is ˜0.414.

FIG. 5 shows all the factors of FIG. 4 but compensates for the variance by zero at each amplifier position (with an inter-amplifier spacing of 120 km). Compensation based only on (linear) variance increases the eye opening to ˜0.924 when the SPM is completely ignored. Based on this plot, under the operating conditions described above, there is no need to consider the SPM for compensation over at least 120 km line lengths of the system.

Closure induced by SPM is a nonlinear effect. Compensation over a longer length increases the closure more than three times due to this effect, for example by installing the compensation fiber only at the end of the span. This diagram suggests that even this is not so important. Preferred for fibers with less dispersion, eg, less than 8 ps / nm-km, is expected to be important only for systems with substantially larger compensation to compensation or significantly larger capacities. .

I. Transmission Line

A) WDM Fiber

DS fiber does not require any offset connections or compensation, which is primarily the reason that DS fiber is preferred over other approaches. The WDM fiber of co-pending US patent application Ser. No. 08/069962 is expected to replace DS fiber in near future systems that do not allow dispersion nulling. These fibers with color dispersion in the tolerance range of 1.5-4 ps / nm-km are used for four-channel, 360 km span length, 20 gbit / sec systems. Future systems with much larger capacity / span lengths may further reduce linear dispersion using compensated WDM fiber lines. For the reasons described in the co- filed application, it is preferred that the sign of variance required in the WDM fiber is positive (+ 1.5-4 ps / nm-km). Thus, the compensation fiber will be negative variance. As described in co-pending applications, the implications of the teachings of the present invention are beyond the described dispersion ranges. This range of specifications is eventually appropriate for the systems under consideration. The use of smaller variances, i.e., less than 1.0 ps / nm-km, is somewhat reduced compared to the specified range, but the use of DSF continues to ensure improved capacity.

As mentioned above, WDMF can be used while satisfying multiple system requirements without equalization, but equalization can further increase capacity. In addition to the equalization possible by the use of compensating fibers, certain types of chain connections are attractive. Here, the chain linkage requires WDMF lengths with opposite sign variances, with both lengths preferably being within a dispersion range of 1.5-4 ps / nm-km.

An experimental specification table for WDM fibers suitable for near future systems is given below:

WDM Specification Table

Design considerations relate to small but critical dispersion, which is a major difference from DSF. In particular, other design standards regarding macrobending loss, mode field diameter, etc., are generally consistent with prior art fiber (eg, DSF) designs and may change as advances are made. have. Pages 105-121 of the "AT & T Technical Journal", vol. 65, fifth edition, published in 1986, are representative. The fiber comprises a germanium doped core, based on silica, with one or more cladding layers that can be made of silica or can be doped down with fluorine. The overall structure of 125 μm has a core diameter of about 6 μm. The index peak has Δn of 0.013 to 0.015 for undoped silica. Typical shapes are triangular or trapezoidal, Δn It can be placed on a 20 μm platform of 0.002. The designated WDM fiber can be compensated by a spool of compensation fiber. Compensation fibers of pending US patent application Ser. No. 07 / 978,002, filed concurrently on November 18, 93, are suitable for this purpose. Illustrative structures have a dispersion of 2 ps / nm-km.

B) compensation

The principle is explained. It can take the form of a major length of fiber with a positive sign variance carried by the compensation fiber of negative variance. Like the WDM fiber, the compensation fiber may be of the type described in co-pending US patent application.

It has been found that the self-phase modulation, i.e., the nonlinear effect that results in random generation of different wavelengths is small. From Figures 4 and 5, it is concluded that the compensation for the (linear) variance of the appropriate distance (in this case 120 km apart amplifier position) effectively removes the SPM as a consideration. Under this situation, a fiber with λ ₀ = 1310 nm is acceptable (if the inconvenience and cost of compensation are ignored). Future WDM systems (360 km span length, 4-channel, 5 gbit / channel), where the specification is close to the base, allow ˜17 ps / nm-km dispersion of uncorrected material of fibers with λ ₀ = 1310 nm. Future systems with longer spans or larger capacities may use fiber with a dispersion of ˜8 ps / nm-km.

Considering the SPM, multiple compensations are made along each span length. The requirements for a near future WDM system are met by compensation of about 17 ps / nm-km fiber in each amplifier (eg 120 km spacing). The achievement of the present invention is useful for shorter span length systems, as discussed. Equalization (by compensation or chain linking) must not be done at such short lengths to operate as a full DS fiber. Equalization at a distance of 1 km is excluded for this reason. Lengths less than 20 km should be most avoided. For economic reasons, practical system designs that provide tens of kilometers (eg, 50 kilometers or more) of boiled fiber are suitable.

C) chain connection

Considerations for system performance are very similar to those for compensation. The chain connection over fiber lengths much shorter than about 20 km results in line behavior approaching the DS fiber. Also, a convenient design using boiled lengths of tens of kilometers is appropriate. An additional possible limiting nonlinear effect, SPM is allowed in the 20 gbit four channel systems considered. Planned upgrades and higher capacity new installations may set a good maximum dispersion of about 8 ps / nm-km.

Like compensation, the chain link completely eliminates the mean variance. Currently planned WDM systems may not require such accuracy. It is sufficient to reduce the variance to the variance (≧ 2.0 ps / nm-km) of the presented WDM fiber specification table.

The chain linkage is not expected to play a major role in the near future terrestrial systems. There is even more potential for subsea systems.

D) Other Considerations

Span lengths have been discussed in relation to the system under consideration. 360 km spans are provided. Such a system may also include shorter span lengths. These considerations may be described in broader terms. The basic approach is useful in all WDM systems as long as the freedom of design is allowed and the tolerance of the design is relaxed. The 5 gbit / sec, four-channel system benefits significantly from span lengths of approximately 200 km from this teaching. The relationship between capacity and span length is defined as follows:

B ² L ≤ 10400 / D (Eq.1)

From here:

B = bit rate [gbit / sec]

L = length [km]

D = mean dispersion [ps / nm-km]

Since the length varies with the square of the bit rate, the corresponding span length is 50 km for a line capacity of 10 gbit / sec. In general, systems based on the teachings of the present invention comprise at least one fiber span according to Eq.1.

II. transmitter

These components, as well as receivers and optical amplifiers, are described in detail in 1992 published in "Fiber Laser Sources and Amplifiers IV", SPIE, vol. 1789, pages 260-266. The transmitter consists of a laser for each channel. The laser outputs are individually modulated and the modulated signals are multiplexed and fed to the transmission line.

III. receiving set

At the end of the span length, such a component may be at the end of the present system, or may be part of a signal regenerator. The receiver comprises means for demultiplexing channels. This requires a device that passes the channel wavelength of interest, while blocking other wavelengths. This can be a simple splitter combined with optical fibers at the output ports tuned to each channel (see Nagel's paper) or a device that combines the splitting and filtering functions within a single unit.

IV. Optical amplifier

Today, this component is an erbium amplifier. A useful gain region of a single erbium amplifier is λ = 40-50 nm. When the amplifiers are connected in series, the net gain is small (since the amplitude in the "gain area" is reduced on one side of the peak). The 10-20 nm bandwidth referenced is an appropriate value for a three-amplifier span.

V. Other Considerations

Most other considerations are standard. Almost without exception, WDM systems designed for use with DS fibers can be used directly in the present invention. System design follows the considerations common to the prior art and the present invention. The channel spacing should allow the channels to fit within the peak of the optical amplifier. The maximum span length is set by insertion loss, firing power and allowable pulse spread. Considerations may of course be tailored to the imposed restrictions. For example, the use of WDM fiber without compensation sets a limit on the product of bit rate and span length. The span length may be set as needed, for example, where compensation is provided or where the stranded fiber length begins.

Planned WDM systems use external modulation to reduce dispersion penalty and improve the spectral stability of the channels.

1 is a schematic diagram of a WDM system for explaining various types of the present invention.

2 through 5 show the coordinates of power and time, contrast between 1 and 0 in the bitstream, due to various forms of dispersion including 4PM and linear dispersion for 4-channel systems. "eye" diagram showing contrast.

* Explanation of symbols for main parts of the drawings

10, 11, 12, 13: transmitter 14: 4: 1 combiner

15: transmission line 16, 17: optical amplifier

18: Demultiplexer 19, 20, 21, 22: player

Claims (16)

A wavelength division multiplexed optical waveguide system, A transmitter for generating, modulating, and multiplexing modulated channel carriers and introducing them into a transmission line, said transmitter characterized by a "system wavelength" having a magnitude within a wavelength range of grouped channel carriers; A receiver for performing functions including demultiplexing modulated channel carriers; Optical amplifiers; And a transmission line of an optical fiber comprising at least one fiber span, one end of which is defined by the transmitter and the other end of which is defined by the receiver, the span comprising at least one optical amplifier. In the wavelength division multiplexing optical waveguide system, A major portion of the fiber defining the span is characterized by having an absolute color dispersion in the range of 1.5-8 ps / nm-km at the system wavelength. The method of claim 1, And the system wavelength is approximately 1550 nm. The method of claim 2, Substantially all of the fibers defining the span have a substantially uniform color dispersion. The method of claim 3, wherein Wherein the color dispersion is at least 2 ps / nm-km. The method of claim 2, And the average linear dispersion of the fibers defining the span is equalized to approximately zero magnitude by including at least two fiber lengths having dispersions of different codes. The method of claim 5, Substantially all of the fibers defining the span have a uniform color dispersion of at least 2 ps / nm-km, and equalization is due to the inclusion of a compensation fiber. The method of claim 2, And the optical amplifiers are made of erbium-doped silica. The method of claim 7, wherein The wavelength division multiplexed optical waveguide system in which the extreme wavelengths of the channels define a spectrum of 20 nm or less. The method of claim 8, A wavelength division multiplexing optical waveguide system using at least four channels spaced apart by 0.8 to 4 nm. The method of claim 1, The substantial length of the fibers in the spans (substantial length) are wavelength division multiplexed optical waveguide system has a λ ₀ ~ 1550nm,. A wavelength division multiplexed optical waveguide system, A transmitter for generating, modulating, and multiplexing modulated channel carriers and introducing them into a transmission line, said transmitter characterized by a "system wavelength" having a magnitude within a wavelength range of grouped channel carriers; A receiver for performing functions including demultiplexing modulated channel carriers; Optical amplifiers; And a transmission line of an optical fiber comprising at least one fiber span, one end of which is defined by the transmitter and the other end of which is defined by the receiver, the span comprising at least one optical amplifier. In the wavelength division multiplexing optical waveguide system, The at least one fiber span was installed after May 28, 1993, and the optical fiber of the span consists of at least two fibers having essentially opposite sign variances such that the absolute value of the mean variance in the span A wavelength division multiplexing optical waveguide system, characterized in that less than 4 ps / nm-km. The method of claim 11, The fiber of one of the fibers has a dispersion substantially the same as the fiber material dispersion, and the equalization is due to the inclusion of a compensation fiber. The method of claim 11, Wherein one fiber of the fibers has a dispersion of at least 8 ps / nm-km and the equalization is due to the inclusion of a compensation fiber. The method of claim 11, The major portion of the fiber defining the span consists essentially of first fibers having a variance of a first sign and second fibers having a variance of an opposite sign of the first sign, the first fiber And the second fiber has dispersion values of the same order of magnitude. The method of claim 1, Wherein the range is 1.5-4 ps / nm-km. An article comprising at least one optical fiber suitable for use in wavelength division multiplexing systems, the fiber comprising a core and a clad, having an attenuation of 0.25 dB / km or less at 1550 nm. , Wherein the article has a dispersion slope of less than 0.095 ps / (nm ² -km), An article characterized in that the absolute magnitude of the average color dispersion at 1550 nm for a fiber length of at least 2.2 km is 1.5-8 ps / nm-km.