JP2003270469A - Dispersion-correction fiber with high figure of merit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dispersion-compensation optical fiber which supports only a basic mode of radiation of 1,550 nm. <P>SOLUTION: The DC fiber is made of quartz glass and has a refractive index profile including a core region 51 surrounded with a clad region 52 with a nominal refractive index n<SB>4</SB>. The core region includes a center core 511 having a nominal refractive index n<SB>1</SB>, a 'trench' 512 which has a nominal refractive index n<SB>2</SB>and surround the center core, and a 'ridge' 513 which has a nominal refractive index n<SB>3</SB>and surrounds the trench. Consequently, a ≥300 ps/(nm dB) figure of merit and a ≥0.01 nm<SP>-1</SP>relative dispersion gradient are provided when refractive index differences and radial sizes of the respective parts meet specified conditions, the center core having a 1.5±0.5 μm and satisfying 0.015<n<SB>1</SB>-n<SB>4</SB><0.035, the trench having a 3.5±1.0 μm width and satisfying -0.012<n<SB>2</SB>-n<SB>4</SB><-0.006, and the ridge having a 2.0±1.0 μm width and satisfying 0.002<n<SB>3</SB>-n<SB>4</SB><0.015. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates generally to improvements to optical fibers, and more particularly to dispersion-correction fiber design.

[0002]

Various mechanisms limit the bandwidth of optical fibers. In a multimode optical fiber, for example, a pulse of light entering one end of the fiber is dispersed in mode dispersion (m) as it emerges from the other end of the fiber.
odal dispersion) exists. This is because multimode fibers support a large number of different modes (ie, paths in the case where photons are considered particles rather than waves) as light spreads along the fiber. Unfortunately, certain modes of the continuous pulse arrive at the remote ends of the fiber at the same time and interfere with each other. In order to avoid this kind of intersymbol interference, the individual pulses of multimode light are transmitted at lower speeds.

However, modal dispersion can be avoided by fibers designed to support the fundamental mode of a particular wavelength. This type of fiber is called a single fiber and has a much higher bandwidth than a multimode fiber. But even here, the pulse of light introduced into one end of the single-mode fiber is somewhat dispersed as it emerges from the distant ends. Applying (ie, modulating) information to a single wavelength lightwave,
This is because it forms a spectrum of wavelengths that propagate at different velocities along the fiber. Therefore,
The various wavelength components (colors), including the modulated light waves, arrive at the distant ends of the fiber at different times, and the resulting pulse of light is "smeared" in time.
Not surprisingly, this is called chromatic dispersion.

A class of optical fibers has been developed and is known as dispersion-correction (DC) fiber, which is
It has a dispersion characteristic opposite to that of the transmission fiber. Figure 9
Referring briefly to, curve 91 is known as 1550
It represents the chromatic dispersion of a transmission fiber in the nanometer (nm) wavelength range. At this wavelength, curve 91 shows that each kilometer (km) of the fiber is +17 psec (p is pico, 10 for each nanometer of source spectral width).
^-12 seconds) is added. The positive (+) polarity merely indicates that wavelengths longer than 1550 nm move slower than shorter wavelengths. For practical purposes, polarity has no meaning. But,
The DC fiber is spliced to the transmission fiber to add an equal but opposite amount of dispersion for the purpose of compensating for this dispersion. Curve 92 represents the chromatic dispersion of a known DC fiber. At 1550 nm, this DC fiber
It gives a dispersion of -17 ps / nm · km. In this way, the total dispersion at 1550 nm is zero when equal lengths of transmission fiber and DC fiber are connected. Unfortunately, at wavelengths above and below 1550 nm, there is still a net chromatic dispersion:
A more desirable dispersion characteristic is required for a DC fiber, such as that shown by curve 93, which is
Not only do they have opposite dispersion polarities with respect to the transmission fiber, but they also have opposite dispersion slopes.

Indeed, for wavelength division multiplexing (WDM) systems operating in the 40 Gb / sec and above, compensation of dispersion slope as well as dispersion polarity is required. This type of compensation is achieved when the relative dispersion slope (RDS) of the DC fiber is equal to the RDS of the transmission fiber. RDS is defined as the dispersion slope divided by the variance (ie (RDS = S /
D)). A recently developed reduced gradient transmission fiber is disclosed in US Pat. No. 5,878,182,
It has a slope of 45 ps / (nm ² · km) and a variance of +4.5 ps / (nm · km), resulting in 1550
It has an RDS of 0.01 nm ⁻¹ in nm. This type of fiber is a TrueWave (R) RS
Commercially available as optical fiber from Lucent Technology. However, even with this fiber requiring compensation, no commercial DC fiber is recognized as having an RDS greater than 0.0035 nm ⁻¹ .

In an optical transmission system, dispersion compensation, as roughly shown in FIG.
Achieved by connecting C fiber, D for convenience
C-fibers are stored in modular form. It is important to have the insertion loss of the dispersion-compensation module as low as possible, for the following reasons: the amplifier design is simpler; the transmission system has a lower signal to noise ratio; the input to the dispersion-compensation module. Non-linear effects can be reduced because the power can be reduced. The insertion loss of the dispersion-compensation module arises from two main contributors: (i) the splice loss at the junction between the transmission fiber and the DC fiber; (ii) the loss due to the DC fiber itself. Module insertion loss is defined as the ratio of the dispersion class to the DC fiber attenuation,
This can be reduced by using a DC fiber with a high figure of merit. Unfortunately, even with the highest level of DC fiber, the figure of merit is 200 ps / (nm ・ dB)
Is less than.

US Pat. No. 5,361,319 (Ant
os) discloses a DC fiber and system in which modules are inserted at appropriate intervals to compensate for dispersion. Each module contains a DC fiber of suitable length to produce a dispersion of approximately equal magnitude (but opposite polarity) to the dispersion of the transmission fiber in the path. Unfortunately, the DC fiber disclosed by Antos only has a relatively small negative chromatic dispersion (absolute value <= 100 ps / nm.km, eg -65 ps / nm.km), so Long D
C fiber must be used (eg 150k
39 km DC to compensate for dispersion in m transmission fiber
Fiber is required). Moreover, Antos's technique is obviously only practical for dispersion compensation applications, and for dispersion slope, the authors also considered that compensation was "not really easy to achieve". There is.

US Pat. No. 5,448,674 (Ven
gskar) discloses a DC fiber with a relatively high dispersion (typically> 150 ps / nm · km absolute) and a negative dispersion slope, both of which are essential improvements over Antos technology. Indicates. To obtain this kind of result, DC of Vengsarkar
The fiber supports at least an order of magnitude higher mode in addition to the fundamental LP mode (LP ₀₁ ). The disadvantage is the added complexity of adding a mode converter, which potentially increases losses. Another problem is that the fiber is multimode, which means that the modal noise due to intermode interference is S
This means lowering the N ratio grade.

Therefore, what is needed is a DC fiber with high dispersion, a negative dispersion slope, and a high figure of merit. Meeting these compounding goals of single mode optical fibers is a long-sought goal of DC fiber designers.

[0010]

SUMMARY OF THE INVENTION In broad terms, the present invention is implemented in a single mode optical fiber that compensates for chromatic dispersion in an optical fiber communication system at an operating wavelength of about 1550 nm. This dispersion-compensating (DC) optical fiber
It has a refractive index profile including a core region, which is made of fused silica and is surrounded by a cladding region having a nominal refractive index n ₄ . The core region includes a central core having a nominal index of refraction n ₁ , a “trench” surrounding the central core having a nominal index of refraction n ₂ , and a “ridge” surrounding a trench having a nominal index of refraction n _3. I'm out. A range of refractive index profiles has been identified that yields the desired DC fiber. This range is
When expressed in the form of refractive index difference, it is as follows. 0.015 <n _{1 to} n ₄ <0.035; −0.012 <n _{2 to} n ₄ <−0.006; 0.002 <n _{3 to} n ₄ <0.015.

In an exemplary embodiment of the invention, a radial dimension having a width has very good results, eg a figure of merit greater than 300 ps / (nm · dB),
And / or was found to give a relative dispersion slope greater than 0.01 nm ⁻¹ : central core: radius = 1.5 ± 0.5 μm; trench: width = 3.5 ± 1.0 μm; ridge: width = 2 ± 1.0 μm of 0.0.

In one embodiment, the DC fiber of the present invention is used to compensate for a standard single mode transmission fiber of an optical transmission system; in another embodiment, the DC fiber of the present invention is: Used to compensate non-zero dispersion shifted transmission fiber.

[0013]

SUMMARY OF THE INVENTION The present invention is an improvement in a DC fiber having a ridge-free W-shaped profile design. It appears that there is a cooperation between this central core, trench and ridge in the desired DC quality, beyond the scope of profile design.

The invention and its mode of operation will be more clearly understood from the following detailed description, as read through the accompanying drawings.

Terminology The following definitions are in line with common usage in the art: Chromatic dispersion-difference in the group velocity values of electromagnetic waves of different wavelengths-channel of a single mode fiber when uncompensated A first order effect (having an amplitude that is linearly power dependent) that constitutes a major limit to the amount of information (related to the allowed bit rate, limited by pulse spreading due to different speeds of the wavelength containing the pulse) Be done). Figure of Merit (FOM) -The ratio obtained by dividing the numerical value of the dispersion of an optical fiber by the attenuation of that fiber at a particular wavelength. Non-zero dispersion shifted fiber (Non-Zero Disp
ERSION SHIFTED FIBER) (NZD
F)-in the fiber, at a certain operating wavelength (λ _op ), a certain magnitude (typically 0.8 p)
An optical fiber with a dispersion rating of s / nm · km). This type of fiber is described in US Pat. No. 5,878,1.
No. 82, which is particularly advantageous in WDM systems. Refractive Index Profile--The change in refractive index measured at different radial distances from the fiber's central axis. Relative Dispersion
n Slope) (RDS) -the ratio obtained by dividing the numerical value of the dispersion slope of an optical fiber by the dispersion of that fiber at a particular wavelength. Ridge--An annular region where the index of refraction increases relative to adjacent bounding regions in an optical fiber. Trench--An annular region where the index of refraction is reduced relative to adjacent bounding regions in an optical fiber. Unshifted Fiber (USF) --- A fiber whose chromatic dispersion null point λ ₀ is at a nominal wavelength value of 1310 nm and whose dispersion at 1550 nm is +17 ps / (nm
・ Km). USF is also referred to as standard single mode fiber. W-shaped profile--Refractive index profile with a central core surrounded by a trench and an outer cladding. The index of refraction of the trench is below that of the central core or cladding.

[0016]

In the manufacture of optical fibers, glass preform rods are suspended vertically and moved in a furnace at a controlled speed. The preform softens in the furnace and the glass fiber is freely drawn from the molten end of the preform rod by a capstan located at the base of the drawing tower. (The drawn fibers are thousands of diameters smaller than the preform rod, but still have the same index of refraction profile.) The surface of glass fibers is susceptible to damage caused by attrition, so It is necessary to coat the fiber later, but before contacting any other surface objects. Do not damage the glass surface by applying the coating material,
The coating material is applied in a fluid state. Once applied, the coating material must solidify before the glass fiber reaches the capstan. This solidification is generally achieved in a short time by photocuring. Photocuring is the process by which a liquid coating material is converted to a solid by exposure to electromagnetic radiation. FIG. 1 has a structure suitable for the present invention,
A double coated optical fiber 10 is disclosed. As shown, two layers of coating material have been applied to drawn glass fiber 50, which comprises a light-transmission core region 51 surrounded by a cladding region 52. The glass fiber 50 is about 125
It has a diameter of micrometer. An inner layer 11, called the primary coating material, is applied to the glass fiber 50, and an outer layer 12, called the secondary coating material, is applied to the primary coating material 11. Secondary coating materials generally have relatively high modulus (eg, 10
⁹ Pa), which has the effect of handling, and the primary coating material has a relatively low modulus (for example 10 ⁶ Pa), which results in a cushion that reduces microvent losses. Before the primary coating cures
A secondary material can be applied, in which case both coatings will be cured simultaneously by radiation in the ultraviolet region of the electromagnetic spectrum.

FIG. 2 illustrates the chromatic dispersion of an optical fiber and more particularly shows how the overall property 23 is formed by an additional combination of materials and waveguide dispersion components. The material dispersion 21 is essentially related to the particular material (eg, fused silica) used in making the optical fiber. On the other hand, the waveguide dispersion 22 is controlled by the refractive index profile of the optical fiber, and unlike the material dispersion, which is, for example, the variation of the refractive index of silica glass measured at different radius distances from the central axis of the fiber, The dispersion can be tailored appropriately by the designer to obtain the desired overall properties 23. Unlike the material dispersion, the waveguide dispersion can be shaped to some extent by the design engineer to produce the desired overall properties 23. Unfortunately, there are "side effects" associated with any particular overall property, which in other words is waveguide dispersion 2.
Changing 2 also changes other properties such as cutoff wavelength, bending loss, mode field diameter, and so on. While it is possible to design an optical fiber with any given dispersion characteristic, that fiber may not help at all when viewed on the basis of more practical considerations.
For example, the bending loss limit value is such that the bending loss at 1550 nm is 0.01 for a bending radius of 75 mm.
It was set as a point exceeding dB / km. Although a particular index profile may, on the one hand, provide the desired dispersion properties, it may also produce excessive bending loss, in which case it becomes unacceptable.

FIG. 3 shows the ITU Commendat.
Ion G. Distributed covered by 652-non
1 shows a dispersion characteristic (300) of a shift fiber (USF). U
SF is the most widely used fiber type
Sometimes referred to as "standard" single-mode fiber.
It It was commercialized in 1983. Optical fiber
The glass composition that is commonly used in making is approximately 1
Wavelength λ at 310 nm _oHas zero variance at. Only
And the theoretical minimum loss of fiberglass is the most
The typical fiber amplifier operates at about 1550 nm
It (Erbium-doped fiber is Er
³⁺1530 to 1565 with transition of dopant ion
Used to amplify optical signals with wavelengths in the nm range
It ) It is preferable to operate in the 1550 nm region
In addition to the standard single-mode fiber
Since a number of systems are already installed, technicians
For the purpose of canceling dispersion at 1550 nm, dispersion-
Compensating (DC) fiber connected in series with this type of fiber
Designed to be. In practice, it is a suitable length DC
The fiber is wound on a spool to form a DC module
And then connected to the transmission fiber at regular intervals.
Depending on the length of these intervals, the optical amplifier is
Or not.
Nevertheless, DC fiber is a standard single-mode fiber.
Not only used for fiber, but also operating wavelength λ
_opWith any fiber where dispersion exists in
Used for.

FIG. 4 is a DC fiber overall dispersion characteristic 400 according to the present invention. In particular, the significant amount of negative dispersion obtained in the C and L bands of optical transmission (1530-1610 nm) is particularly desirable. Moreover, its negative dispersion slope in this wavelength range is well suited to compensate the positive dispersion slope of many transmission fibers (see FIG. 3 for an example). As discussed in connection with FIG. 2, the overall dispersion characteristic of the fiber, including the DC fiber of the present invention, is a combination of material dispersion and waveguide dispersion, where waveguide dispersion is determined by the refractive index profile. Therefore, in the following,
In order to produce the DC fiber according to the present invention, the refractive index profile is discussed in combination with the material dispersion properties of fused silica.

Referring to FIG. 5, there is shown a cross-section of an uncoated glass fiber 50 schematically showing a plurality of layers 511, 512, 513, 521, 522, each layer being a conductor of the fiber. It has a different index of refraction to modify the waveguide dispersion properties. FIG. 5 shows that the refractive index remains perfectly constant during rapid level changes in the radial direction, but this is not the case for a fiber that can be manufactured. In reality, FIG.
3 shows an actual refractive index profile of a DC fiber according to the present invention. Note first that the index of refraction drops at the geometric center of the central core 511 (ie, at the fiber radius r = 0). The drop 501 in the refractive index is an optical aberration caused by a specific manufacturing process that is normally used. For example, the descent shown in FIG. 6 is due to a modified chemical vapor deposition (MCVD) process, which was illustratively used to make the DC fiber of the present invention. However, the descent 501 does not adversely affect the transmission quality of the resulting DC fiber because it is relatively narrow and can be modified in the desired direction to modify the optical transport properties of the fiber.

The desired DC fiber quality is low loss,
It includes a negative dispersion slope, a large negative dispersion, and a large figure of merit index. These fiber qualities are achieved by choosing the appropriate index profile at a given wavelength. In the present invention, the fiber is made of fused silica and has a refractive index profile that includes a core region surrounded by an outer cladding region having a nominal refractive index n ₄ . The core region comprises a central core 511 having a nominal index of refraction n ₁ , a “trench” 512 having a nominal index of refraction n ₂ and surrounding the central core, and a “ridge” 513 having a nominal index of refraction n ₃ and surrounding the trench. ing. An inner layer having a deposited cladding material 521 of nominal refractive index n ₄ surrounds the ridge 513. The inner layer of the deposited cladding is effective in protecting the core regions 511-513 from impurities in the outer cladding 522 that migrate to the core region and adversely affect its light-transport properties. As an example, the outer cladding 522 may be a relatively less pure glass tube that is deposited as a coating layer over the relatively pure core region using the well known rod-in-tube technique. The core regions 511-513 have a diameter of less than 15 microns,
Note that the drawing of FIG. 5 does not represent the actual size ratio because the outer cladding layer 522 has a diameter of approximately 125 microns.

Shown below are three example profiles that provide DC fibers with desirable properties. Each profile contains 5 layers: Usually an appropriate amount of Ge is used to obtain the desired index of refraction.
A central core which is a high refractive index region made of SiO ₂ doped with O ₂ . 2. In order to obtain a desired refractive index, surrounding the appropriate amount of core is a low refractive index region which is composed in doped SiO ₂ GeO ₂ and F trench. 3. Desired in order to obtain the refractive index, the ridge surrounding the appropriate amount of GeO ₂ and the trench is doped high refractive index region that consists of SiO ₂ was in F. 4. Inner layer of the deposited cladding surrounding the ridge. This is a region that has no effect on transmission quality, but has the same index of refraction as the outer cladding, which reduces splice losses in the fiber. The deposited clad is usually P ₂ 0 ₅
And F of SiO ₂ doped with its appropriate amount. 5. Outer cladding made of SiO ₂ .

[Table 1]

[Table 2]

[Table 3] Highly negative (ultranegative) index drop

[0023] In all of the above embodiments, the refractive index of the trench is more negative than the DC fiber known (i.e. Δ ^-> 0.5%). This type of level reduces or eliminates the GeO ₂ content of the core,
Greater design flexibility is needed in C-fibers to be realized. Modified chemical vapor deposition (MCVD)
Is used as an example of the present invention. Also previously, the standard MC
With the VD method, a Δ ^- grade of greater than 0.5% was achieved at a lower deposition rate than fluorine-doping. The preform is
A two-step process in which a soot layer is produced with SiCl ₄ , O ₂ , optionally He at 1700 ° C. or 1800 ° C.
ess) and then 15 to 140 m
m / mm torch speed, 2200 ° C or 2350 ° C
, Sintered in a stream of SiF ₄ . For more information on this process, see Fiber Optic Communications Council (Optical Fi).
ber Communications Conf
ence) digest, A. E. Miller
OFC 96, document TuL1, pp. 56-
57, "Highly Negative Delta Cladding for Modified Chemical Vapor Deposition," (Ultranegate delta clad).
a cladding for modified c
chemical vapor position)
Are disclosed in. By optimizing the process conditions at a high _S i _{O 2} processing speed, low 0.71% delta ^- was achieved.

Relative Dispersion Slope (RDS) Wide wavelength range dispersion compensation is required for multi-channel high speed WDM systems. This means that in addition to dispersion polarity, it is also necessary to compensate for dispersion slope. The condition for compensating for dispersion and slope at the same time is that the relative dispersion slope (RDS) of the dispersion-compensating fiber is equal to the RDS of the compensated fiber. RDS is defined as the dispersion slope divided by the dispersion. NZDF fiber has lower dispersion and therefore higher RDS than unshifted single mode fiber.
Have. As stated in the discussion above,
Lucent's TrueWave RS fiber
Gradient of 0.045 ps / (nm ² · km) and +4.
It has a dispersion of 5 ps / (nm · km) and achieves an RDS of 0.01 nm ⁻¹ at 1550 nm, which is the lowest RDS in the commercial NZDF.

The following table summarizes the measured transmission qualities for three exemplary fibers in which the above performances have been achieved:

[Table 4]

Fiber A has the highest FOM, but
RDS is low. This type of fiber helps to reduce the amount of DC fiber needed to compensate for a particular length of transmission fiber. Having a high FOM means that the insertion loss associated with that DC module is low.

Fiber B has an RDS that provides slope compensation for a good standard single mode transmission fiber.
Compared to the DC fiber that has been realized so far for the slope compensation of this kind of transmission fiber, the fiber B has 60%
Has a high FOM.

Fiber C has an RDS that provides 94% slope compensation over the Lucent TrueWave RS optical fiber described above, which is a popular non-zero dispersion fiber (NZDF). Compared to the DC fiber for the complete slope compensation of NZDF at 1550 nm achieved so far, Fiber C has improved bend loss performance, which is particularly suitable for use in erbium-doped fiber amplifiers. DC fiber. Fiber C has 100% higher FOM than previously realized fibers.

By appropriately selecting the radius and the refractive index, the chromatic dispersion characteristics of the DC fiber can be adjusted to 15 wavelength range.
It can be designed to obtain high grade negative dispersion, negative dispersion slope, and high figure of merit at 30-1610 nm. These dimensions and refractive indices are summarized below. For convenience, the delta (Δ) and normalized Δ values are presented as they are familiar to those skilled in the art of designing:

[Table 5]

A detailed description of the procedure for making an optical preform is readily available. The preform may be monolithic or composite. The core rod and inner cladding layer comprising the core region (central core, trench, ridge) are preferably modified chemical vapor deposition (M
CVD) or by one of the processes using soot chemistry--eg, vapor phase external deposition (Outside Vapor Deposition).
n) or vapor phase axial method (Vapor Axial D)
Preferably, it is formed by means of the E. position). The outer cladding preferably comprises an undoped silica tube coated onto the core rod. Preform MCVD fabrication and coating procedures are well known in the art and will be omitted and will not be repeated here.

FIG. 7 discloses an optical fiber system 700 in which a span of optical transmission fiber 730,
An optical transmitter 710 and a receiver 720 are included. This span is the first predetermined length L _x of the transmission fiber 730.
Is connected to a DC fiber 10 having a second predetermined length L _y . For the transmission fiber 730 having a positive dispersion, the transmitter 710 has an operating wavelength (λ _op ).
Fires light. However, after traveling the distance L _x ,
Once the amount of positive dispersion has accumulated, then a fiber optic DC module 740 having a negative dispersion at λ _op is introduced. This module is typically of length L _y shorter than L _x.
The DC fiber 10 of FIG. By adding a length of DC fiber, additional loss is introduced, along with the loss introduced by the transmission fiber 730, which needs to be handled by the receiver 720 or amplifier (not shown) associated with the module 740. is there. The need for this type of system has been strongly acknowledged mainly by the desire to upgrade existing optical networks currently operating at 1310 nm and operate at 1550 nm to increase their capacity. (1310n
The transmission fiber that normally operates at m is +
Note that we have a dispersion of 17 ps / nm · km, so we need to introduce an equal and opposite amount of dispersion at 1550 nm in order to achieve compensation. ) In a first exemplary embodiment, the transmission fiber 730 comprises a 100 km standard single mode fiber having the dispersion characteristics shown in FIG.

In this first embodiment, a standard single mode fiber is used as the transmission fiber and the dispersion compensation is a DC containing 10 nm DC fiber 10.
This is accomplished via module 740. Its typical dispersion characteristics are shown in FIG. The attenuation at 100 km of transmission fiber 730 is about 20 decibels, and the total splice loss associated with the attenuation at 9 km of DC fiber 10 is less than 7 decibels. In a preferred embodiment of the invention,
Further, the DC module 740 may include, for example, an erbium-doped fiber amplifier (E
DFA) or reverse excitation of the DC fiber itself by light energy at different wavelengths (reverse)
apparatus for performing a pumping action, thereby filed Aug. 9, 2000, Lucent T
Raman amplification is achieved with the method disclosed in US patent application Ser. No. 09 / 634,966 (A.F. Judy 6) assigned to technologies.

In the second exemplary embodiment, the transmission fiber 730 comprises Lucent Technology's TrueWave RS fiber with a nominal length of 100 km. This fiber has a nominal dispersion of +4.5 ps / (nm · km) at 1550 nm, and +
It has a nominal slope of 0.045 ps / (nm ² · km). DC fiber 10 of length corresponding to Example 3 above
Is wound on a spool to form a DC module 740 with a total dispersion of -452 ps / nm. 1550
RDS of DC module in nm is 0.0095 nm
It was ^-1 . A short intermediate fiber (not shown) is inserted between the DC fiber 10 and the transmission fiber 730 to reduce splice losses. Transmission fiber and DC
Loss reduction connection technology between fibers is described in application number _______
______________ (Riis 1-1-2), Application No. ________________
-1-3). Of the transmission fiber 730,
Actual measurements of dispersion grade and slope at 1550 nm are +4.5 ps / (nm · km) and 0.
044ps / (nm ² · km) and 0.0092n
It becomes an RDS value of m ⁻¹ . The actual length of the transmission fiber is 96 km and the total dispersion is 458 ps / nm. The residual dispersion measured in this second exemplary embodiment is shown in FIG. The residual dispersion is ± 0.04 for the C-band.
Note that it only gives a change of ps / (nm · km).

While various particular embodiments of the present invention have been described in conjunction with the figures, modifications are possible within the scope of the invention. For example, it is understood that the DC fibers of the present invention can be used to compensate transmission fibers other than standard single mode fibers.

[Brief description of drawings]

FIG. 1 is a perspective view of an optical fiber having two protective coating layers.

FIG. 2 is a graph of the dispersion characteristic of an optical fiber as a function of wavelength, showing its material dispersion and waveguide dispersion components.

FIG. 3 is a graph of dispersion characteristics of a standard (unshifted) single mode optical fiber.

FIG. 4 is a graph of an exemplary dispersion characteristic of a DC fiber according to the present invention.

FIG. 5 is a cross-sectional view of an uncoated optical fiber showing several layers of various index materials.

FIG. 6 is a diagram showing a refractive index profile of a DC fiber according to the present invention.

FIG. 7 discloses an optical transmission system including a transmission fiber spliced to a length of DC fiber according to the present invention.

8 is a graph showing the residual dispersion measured in the present optical transmission system of FIG. 7 when the NZDF transmission fiber is compensated by the DC fiber according to the present invention.

FIG. 9 is a graph showing the chromatic dispersion of a transmission fiber and two different DC fibers known as a function of wavelength.

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[Procedure amendment]

[Submission date] September 10, 2002 (2002.9.1)
0)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kuang Nguyen Tronri             Denmark DK-2630 Tastra             Up, 3 Tevi, Tarstrap Guard             Svey 89 F-term (reference) 2H050 AB04Y AB05X AB08Y AB10X                       AB10Y AB20X AB20Y AC09                       AC15 AC28 AC73 AC76 AD00

Claims (10)

[Claims] 1. An article comprising a length of dispersion-compensating (DC) optical fiber [10] designed to support only the fundamental mode of radiation at 1550 nm, the DC fiber being made from fused silica. And has a refractive index profile that includes a core region [51] surrounded by a cladding region [52] having a nominal refractive index n ₄ , the core region having a nominal refractive index n ₁ [511] ], And a "trench" surrounding the central core and having a nominal index of refraction n _2.
[512] and a "ridge" surrounding the trench and having a nominal index of refraction n _3.
[513] and 0.015 <n ₁ −n ₄ <0.035, −0.012 <n ₂ −n ₄ <−0.006, and 0.002 <n ₃ −n ₄ <0. An article characterized by being 0.15. 2. Article according to claim 1, wherein the core region [51] has the following dimensions: central core radius = 1.5 ± 0.5 μm trench width = 3.5 ± 1.0 μm, and An article having a ridge width = 2.0 ± 1.0 μm. 3. The article according to claim 2, wherein: Furthermore, between the ridge [513] and the outer cladding [522]
An annular ring of deposited cladding material [521] located at
Including The deposited cladding is at least 1.0 micron
Width, and substantially n _FourTo have a refractive index equal to
Characterized articles. 4. The article of claim 1, wherein the refractive index profile forms a relative dispersion slope (RDS) such that the ratio of dispersion slope to dispersion at 1550 nm is approximately equal to 0.01 nm ^−1. An article characterized by being selected for. 5. The article according to claim 1, wherein the DC fiber [10] has an insertion loss and a negative slope and an overall negative of more than −100 ps / (nm · km) at 1550 nm. And a refractive index profile that gives a dispersion characteristic [400] having a dispersion and a ratio of the dispersion to the insertion loss at 1550 nm has a figure of merit (FOM) of which absolute magnitude exceeds 300 ps / (nm. Articles characterized by eggplant. 6. Article according to claim 1, wherein the DC fiber [10] is negative than insertion loss and negative slope and ps / (nm · km) of −200 at 1550 nm. A refractive index profile giving dispersion characteristics having dispersion, wherein the ratio of dispersion to insertion loss at 1550 nm has a figure of merit (FOM) of which absolute magnitude exceeds 200 ps / (nm · dB). Articles to be. 7. Article according to claim 1, wherein the DC fiber [10] is negative than insertion loss and negative slope and ps / (nm · km) of −120 at 1550 nm. Have a refractive index profile that gives a dispersion characteristic [400] with dispersion, and the ratio of dispersion to insertion loss at 1550 nm has a figure of merit (FOM) with an absolute magnitude of greater than 240 ps / (nm · dB). An article characterized by. 8. The article according to claim 1, wherein the central core [511] achieves a nominal refractive index n ₁ .
A trench [512] containing SiO ₂ doped with an appropriate amount of GeO ₂ and surrounding the central core is doped SiO ₂ with an appropriate amount of GeO ₂ and F to achieve a nominal index of refraction n ₂ . A ridge [513] that includes and surrounds the trench is G to achieve a nominal index of refraction n _3.
SiO ₂ doped with appropriate amounts of eO ₂ and F
An article comprising: 9. The article according to claim 8, wherein the cladding region [52] comprises inner and outer layers of silica glass [521,522], the inner layer [521] being a ridge [513]. An article adjacent to and comprising SiO ₂ doped with P ₂ O ₅ and F. 10. The article of claim 1, wherein the length of DC fiber [10] is a module [74].
0] and is located in an optical transmission system [700] operating at a wavelength λ _op in the range 1530 to 1610 nm, the transmission system comprising a transmitter [710], a receiver [72].
0], a length of single mode transmission fiber [730]) having a positive dispersion and a positive dispersion slope at λ _op , the transmission fiber and the DC fiber being in series between a transmitter and a receiver. An article characterized by being connected to.