JP2002504702A - Low gradient dispersion management waveguide - Google Patents

Abstract

SUMMARY A single mode optical waveguide fiber having alternating segments of positive and negative dispersion and dispersion gradient is disclosed. The relative refractive index, relative refractive index distribution and radius of the segments are selected to have low total dispersion and low dispersion gradient. As one example, the first central refractive index distribution of the outer diameter r ₁ (10) is surrounded by a first annular segment of the outer diameter r ₂ (12), further this second annular segment having an outer diameter r ₃ Surrounded by (14). Preferred waveguides according to the invention always have a dispersion of less than 2, preferably 1 ps / nm ² -km, over the range 1520 to 1625 nm. The total dispersion of the waveguide is in the range of about -2.0 to +2.0 ps / nm-km at 1550 nm. Further, the present waveguide is characterized by low polarization mode dispersion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a single-mode optical waveguide fiber designed for long-haul communication systems with long repeater spacing and high data signal rates. In particular, such single-mode waveguides have excellent bending resistance, low attenuation, low dispersion, and low dispersion gradient as characteristics desired for long-distance transmission applications.

[0002]

[Prior art]

The need in the long-distance communications industry to achieve greater information capacity over long distances without the use of electronic signal regenerators has led to a re-evaluation of single-mode fiber refractive index profile designs. In recent years, the development of erbium-doped fiber amplifiers (EDFAs) and wavelength division multiplexers has enabled high capacity waveguide systems. Achieving high capacity can increase the channel bit rate and signal wavelength range. Here, as the bit rate increases beyond 2.5 Gb / s, fiber dispersion becomes a major deteriorating factor over long distances. On the other hand, if the dispersion is too low, four-wave mixing (FWM) due to multi-channel interactions can occur, degrading system performance. In order to reduce such dispersion and FWM degradation, dispersion management has been proposed and demonstrated. Distributed management is achieved by either cable management in which + D and -D fibers are alternately connected (spliced) or fiber management in which a core cane having the characteristics of + D and -D is integrated into one fiber and drawn. You can do it.

[0003]

[Problems to be solved by the invention]

Conventionally, dispersion management fibers using + D and -D fibers having a positive dispersion slope have been proposed, in which the final fiber dispersion has a dispersion and a slope similar to that of a dispersion-shifted fiber. That is, it has a net zero dispersion in the 1550 nm window and the total dispersion gradient is positive. However, there is still a need for other designs of dispersion management waveguides.

Definitions The following definitions are consistent with common usage in the prior art. An index profile is defined in terms of the radius of a series of index segments. A particular segment has a first and last index point (position). The radius from the waveguide centerline to the first index point is the inner radius of the core region or segment. Similarly, the radius from the waveguide centerline to the last index point is the outer radius of the core segment.

[0005] The segment radius can be expediently defined in a number of ways, which is illustrated in FIG.
Will be described later. In FIGS. 1 to 3 and Tables 1 and 2 obtained from the figures, the radius of the refractive index distribution segment is defined as follows with reference to a chart of Δ% vs. waveguide radius. * The outer radius r ₁ of the central main refractive index distribution is measured from the center line of the waveguide to the X-axis of the central refractive index distribution, that is, the intersection point extrapolated to the Δ% = 0 position. * The outer radius r ₂ of the first annular segment, the center line of the waveguide, the central refractive index distribution to the X-axis, i.e. delta% = 0 position extrapolated intersection to and Wakashi Ku measured to the point that down as Things. * The outer radius r ₃ of the second annular segment is measured from the center line of the waveguide to the intersection where the central refractive index distribution is extrapolated to the X-axis, that is, to the Δ% = 0 position. * The outer radii of all additional annular segments are measured as well as the outer radii of the first and second annular segments. * The radius of the last annular segment is measured from the waveguide centerline to the segment center point.

[0006] The width W of a segment is the distance between the inner and outer radii of the segment. It will be appreciated that the outer radius of a segment coincides with the inner radius of the next segment. - relative refractive index delta% is defined by _{Δ% = 100 × (n 1} 2 -n 2 2) / 2n 1 2. Here, n ₁ is the maximum refractive index of the refractive index distribution segment 1, and n ₂ is the reference refractive index, and in this specification, is the refractive index of the cladding layer. The term index profile is the relationship between Δ% or index and radius over a selected part of the core; -The term of the α distribution is a refractive index distribution expressed by the following formula of Δ (b)%, where b
Is the radius.

Δ (b)% = Δ (b ₀ ) (1− [| b−b ₀ | / (b ₁ −b ₀ )] ^α ) where b ₀ is the radial position of the maximum refractive index, b _1, Δ (b)% of a zero position, also, b is in the range of b _i ≦ b ≦ b _f. Delta follows the definition above. b _i is the start position of the α distribution. b _f is the position of the end of the α distribution. Α is a real number exponent.

[0008] Other refractive index profiles include step index, triangular, trapezoidal, rounded step index. Here, the rounding is generally formed by diffusing a dopant into a steep refractive index change region. -Total dispersion is defined as the algebraic sum of waveguide dispersion and material dispersion. Total dispersion is also called chromatic dispersion in the prior art. The unit of total dispersion is ps / nm-km. -The bending resistance of a waveguide fiber is described by the attenuation induced under the specified test conditions. Standard test conditions are to wind the waveguide fiber 100 times around a 75 mm diameter mandrel, or to wind the waveguide fiber once around a 32 mm diameter mandrel. Under each test condition, bending-induced attenuation is usually measured in dB / (unit length). The bending test used herein was performed by winding the waveguide fiber five times around a 20 mm diameter mandrel. This meets more stringent requirements than the current waveguide fiber operating environment.

[0009]

[Means for Solving the Problems]

One feature of the present invention is a single mode optical waveguide comprising a first fiber component segment having a positive dispersion and a positive dispersion gradient and a second fiber component segment having a negative dispersion and a negative dispersion gradient. In such a waveguide, segments of the first fiber component and the segments of the second fiber component are alternately arranged along a length direction, and the first fiber component segment has at least two lengths of the second fiber component segment. It has twice the length. This waveguide is optimized for low attenuation operation in the wavelength window around 1550 nm, ie between about 1520 nm and 1625 nm.

A waveguide according to the present invention comprises a unit fiber in which various first and second segments, for example, sections having positive and negative dispersion and dispersion gradient are alternately arranged. Alternatively, the waveguide comprises a cable that connects various fiber component sections along the length of the cable. Another aspect of the invention relates to a single mode optical waveguide that manages the chromatic dispersion of the fiber by providing a low total dispersion and a low dispersion slope. Preferred waveguides according to the invention always have a dispersion of magnitude less than ² ps / nm ² -km in the range from 1520 nm to 1625 nm, more preferably less than 1 ps / nm ² -km. The total dispersion of the waveguide fiber is in the range of about -2.0 to +2.0 ps / nm-km at 1550 nm, more preferably about -1.0 to +1.0 ps / nm-km, even more preferably About -0.5 to + 0.5ps / nm-
km. The r _i , Δ _i % and refractive index distribution of the various positive and negative dispersion segments are 1
At 550 nm, it is selected to give a total attenuation of less than 0.25 dB / km.

[0011] All of these properties are achieved while maintaining high strength, good fatigue resistance and good bending resistance. That is, the induced bending loss is about 0.5 dB or less when wound once around a 32 mm mandrel, and is 0.05 dB or less when wound 100 times around a 75 mm mandrel. The waveguide according to the invention is also compatible with optical amplifiers. Further, the cutoff wavelength of the fiber in a state where the cable is formed is less than 1520 nm. A further advantage is that
About 0.5ps / (km) ^1/2, more preferably, 0.3 ps / (miles) below ^1/2, more preferably about 0.
The polarization mode dispersion is less than 1 ps / (km) ^1/2 .

[0012] Additional features and advantages of the invention will be set forth in the description which follows, and in part will be readily apparent to one skilled in the art from the description. It will also be recognized by executing the disclosure of the present specification including the detailed description of the invention, the claims, and the drawings described below. The foregoing description and the following detailed description of the invention are merely exemplary of the present invention, and are intended to provide an overview or framework for understanding the invention recited in the claims. I do. The accompanying drawings are included or incorporated into and constitute a part of this specification to provide a further understanding of the invention. The drawing is
BRIEF DESCRIPTION OF THE DRAWINGS Various embodiments of the present invention are shown and provide a description of the principles and operation of the present invention along with the detailed description of the invention.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

The cited references are for the details of the preferred embodiments of the present invention and the embodiments described in conjunction with the accompanying drawings. In the drawings, wherever possible, the same reference numbers have been used to refer to the same or like parts. In the present invention, a low gradient dispersion managed fiber optic waveguide alternates a first fiber component having a positive dispersion and a positive dispersion gradient and a second fiber component having a negative dispersion and a negative dispersion gradient. Achieved by incorporating segments. The first fiber component has a length at least twice, more preferably at least three times, and most preferably at least five times the length of the second fiber component.

The waveguide of the present invention may be in the form of a unitary fiber having alternating sections of positive and negative dispersion and dispersion gradient. For example, such a fiber may be manufactured by alternately integrating core tablets having a desired refractive index profile in a tube or other support device. Alternating core tablets alternately create the desired positive and negative dispersion characteristics. The tube containing these alternating component tablets becomes an outer cladding with a silica cladding layer, and the resulting preform is consolidated and drawn into a continuous fiber along its length. Forming an alternating part of the positive and negative dispersion and dispersion slope. For example, such a method of manufacture is disclosed in U.S. Patent Application Serial No. 08 / 844,997, filed April 23, 1997, and such specification and drawings are incorporated herein by reference in their entirety. Shall be done.

[0015] In another embodiment, the waveguide comprises a cabled waveguide. For example, the waveguide has a positive dispersion and a positive dispersion gradient of at least 50 km, more preferably,
It comprises a first fiber component having a length of at least 75 km and a second fiber component (of negative dispersion and negative dispersion gradient) having a length of less than 20 km, more preferably less than 15 km. This type of waveguide forming a cable can be placed between amplifiers in a fiber optic communication system. The second fiber component may alternatively be located on the amplifier side within the amplifier or the amplifier module itself.

A first fiber component having a positive dispersion and a positive dispersion gradient may be provided by utilizing a conventional single mode fiber, such as SMF 28 available from Corning. SMF-28 has a total dispersion of 17 ps / nm-km at 1550 nm and a dispersion gradient of 0.06 ps / nm ² -km. Various fiber distributions can be used to provide a second fiber component having a negative dispersion and a negative dispersion gradient. In a preferred embodiment of the invention, the negative component fiber segments have three or four segments in the distribution.

FIG. 1 illustrates one embodiment of a preferred three-segment distribution of negative dispersion and negative dispersion gradient fiber segment components. As shown in FIG. 1, the distribution is outside the first central refractive index distribution 10 of radius r _1, a first annular segment 12 of the outer radius r ₂ which surrounds this second outer radius r ₃ which further surrounds this It consists of an annular segment 14. As shown in FIG. 1, various distribution types shown by dotted lines can be used in connection with the distribution types that can be used in the first central refractive index distribution 10.

Segments that give the combination of extraordinary properties described herein
The core design characterizes the novel single-mode optical waveguide. These properties are achieved by selecting the appropriate refractive index profile for each segment and the appropriate relative index of refraction delta Δ _i % and radial extent r _i of the segments. It is well known that distribution parameters interact. For example, a central region α distribution of about 1 has a different radius than a central region having a trapezoidal refractive index profile that provides fibers with substantially the same properties.

The refractive index distribution of each segment can be of virtually any particular shape, including an α distribution, a step refractive index distribution, or a trapezoidal distribution. A special step (process) is inserted in the forming process to round the refractive index distribution at the position where the refractive index changes sharply. Such "rounding" is due to diffusion of the dopant material used to change the refractive index of the base glass. As described above, any of these refractive index distributions can be rounded at a specific position. For example, a step refractive index profile having a positive Δ% will typically have rounded upper and lower corners.

Table 1 shows preferred parameters for radius and delta for a three segment distribution. Such a distribution may be used to form negative dispersion, a negative dispersion gradient fiber segment used in the present invention. As can be seen from the table, the fiber can optionally include a refractive index region having a central depression, for example, which is typically formed by diffusion of a germania dopant.

[0021]

[Table 1]

The negative dispersion fiber core segment tablet shown in FIG. 1 is drawn into fiber in combination with a conventional single mode fiber (SMF28) having a positive dispersion and a positive dispersion gradient. The fiber shown by the solid line in FIG. 1 shows a negative dispersion, ie, a dispersion slope of about -35 ps / nm-km and about 0.15 ps / nm ² -km at 1550 nm. In this case, (D _SMF / S _SMF ) = 17 / 0.06 = 280, while (D _n / S _n ) =-35 / 0.15 = -23
3 Therefore, (D _p / S _p ) / (D _n / S _n ) = 0.83, which is preferably very close to unity.

FIG. 2 shows a four segment fiber core distribution that can be used for negative dispersion gradient fiber segments according to the present invention. The distribution shown in FIG. 2 includes two reduced index regions 12 and 16. Table 2 shows preferred parameters of radius versus delta for the various four-segment distributions used to form negative dispersion and negative dispersion gradient fiber segments that can be used in the present invention.

[0024]

[Table 2]

[0025] Any of the distributions disclosed herein can also include a dip in the refractive index at the center line in the cross section (center line dip). And this is a depressed relative refractive index region below the delta value of the peak of the first central core segment.
Such centerline dips are typically caused by so-called burn-out or migration of dopant ions. And, in some cases, it occurs in the manufacturing process of the optical fiber waveguide.

The waveguide according to the invention preferably exhibits a dispersion of magnitude always less than ² ps / nm ² -km, more preferably less than 1 ps / nm ² -km, over the range 1520 nm to 1625 nm. The total dispersion of the waveguide fiber is about -2.0 to +2.0 at 1550 nm, more preferably -1.0
To +1.0, most preferably -0.5 to +0.5 ps / nm-km. The r _i , Δ _i % and the refractive index distribution of the various positive and negative dispersion segments are also selected to provide a total attenuation of less than 0.25 dB / km at 1550 nm.

All of these properties are achieved while maintaining high strength, good fatigue resistance and good bending resistance. That is, the induced bending loss is about 0.5 dB or less for a single turn on a mandrel of about 32 mm and 0.05 or less for 100 turns on a 75 mm mandrel. The waveguide according to the invention is also compatible with optical amplifiers. Also, the cut-off wavelength of the cabled fiber is less than 1520 nm. A further advantage is about 0.5ps /
(km) ^1/2 , more preferably less than 0.3 ps / (km) ^1/2 .

One particularly preferred dispersion managed waveguide according to the present invention controls fiber chromatic dispersion by providing a negative total dispersion as well as a low dispersion slope. It is desirable that the total dispersion of the waveguide fiber be negative, since suppression of potential soliton formation is important in the system and linear dispersion cannot counteract nonlinear self-phase modulation caused by high power signals .

In order to equalize the chromatic dispersion of the fiber, the following relational expressions should preferably be satisfied as close as possible. D _p L _p + D _n L _n = 0, where D and L are each, dispersion and fiber length, subscript "p" and "n" represents the positive and negative dispersion fiber component. Further, in order to equalize the dispersion gradient, it is preferable that the following relational expressions should be satisfied as closely as possible.

(D _p / S _p ) / (D _n / S _n ) = 1 Here, S is a dispersion gradient. The waveguides described herein are suitable for use in high power and long distance transmission, and include conventional RZ (zero feedback) or NRZ (non-zero feedback), as well as the use of soliton transmission. . The definition of high power and long distance is only meaningful in the context of a particular long distance communication system, where the bit rate, bit error rate, multiplexing scheme and optical amplifier are specified. It will be apparent to those skilled in the art that additional factors may occur while implying high power and long distance. However, for most purposes, high power is optical power in excess of about 10 mW per channel. In certain applications, the following signal power level 1mW is sensitive to nonlinear effects, thus, A _{e ff} is important in low power systems.

A long distance is one in which the distance between electrical regenerators can be 100 to 120 km or more.
Regenerators are distinguished from repeaters that utilize optical amplifiers. Particularly in high data density systems, the repeater spacing may be less than half the conventional regenerator spacing. The present invention will be further clarified by the following examples, which are intended to show typical examples of the present invention.

[0032]

【Example】

A particularly suitable three segment refractive index profile for use as negative dispersion and negative gradient fiber segments is shown in FIG. This particular distribution, at 1550 nm, is -35.47
It exhibits a dispersion of ps / nm-km and a gradient of -0.1018 ps / nm ² -km. The cutoff wavelength is 1.18 microns, the pin array bending loss is 1.3 dB, the MFD is 4.8 microns, and the D _eff is 4.68 microns at 1550 nm.

When the positive dispersion fiber component in this case of SMF-28 is combined with the negative dispersion fiber component disclosed in FIG. 3, the dispersion characteristics shown in FIG. 4 are achieved. These have the following parameters:

[0034]

[Table 3]

Table 3 below shows the resulting dispersion and dispersion slope characteristics and the ratio of dispersion to dispersion slope achieved by the combination of the alternating fiber segments.

[0036]

[Table 4]

FIG. 5 shows the axial design of the resulting dispersion-controlled waveguide fiber, which flattens the resulting dispersion for dispersion over the waveguide length (nm-km). FIG. 6 shows the overall dispersion characteristics resulting from flattening the dispersion and fiber control. L _p / L _n, in this example about 2: 1. Period L _n + L _p is approximately 3 km.
As can be seen from FIG. 6, for the example of this design, the total dispersion is less than 1 ps / nm-km and
It is less than about 0.5 ps / nm-km in the range from 20 nm to 1620 nm. This is consistent with the low loss window of a single mode fiber. According to the loss spectrum of a conventional single mode fiber, the attenuation is less than 0.22 dB / km in the range from 1520 nm to 1620 nm.

It will be apparent to those skilled in the art that various modifications and variations can be made by the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

[Brief description of the drawings]

FIG. 1 is a diagram showing a refractive index distribution of a negative dispersion fiber segment according to the present invention.

FIG. 2 is a diagram showing a refractive index distribution of another negative dispersion fiber segment according to the present invention.

FIG. 3 illustrates a refractive index profile of another preferred negative dispersion fiber segment according to the present invention.

FIG. 4 is a diagram illustrating dispersion characteristics of a fiber according to the present invention in which + D and −D segments are alternated.

FIG. 5 is a diagram showing dispersion with respect to the distance of a dispersion flattening and dispersion management fiber according to the present invention.

FIG. 6 is a diagram illustrating dispersion with respect to wavelength of a dispersion flattening and dispersion management fiber according to the present invention.

[Explanation of symbols]

 10 First central refractive index distribution 12, 16 Refractive index reduction area 14 Second annular segment

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Claims (19)

[Claims] 1. A single mode optical waveguide comprising: a first fiber component having a positive dispersion and a positive dispersion gradient; and a second fiber component having a negative dispersion and a negative dispersion gradient. 2. The waveguide of claim 1, wherein said first fiber component has a length at least twice as long as said second fiber component. 3. The waveguide of claim 1, wherein said first fiber component has a length at least five times a length of said second fiber component. 4. The method of claim 1, wherein the first and second fiber components are selected such that the waveguide has a dispersion of less than ² ps / nm ² -km over a range from 1520 nm to 1625 nm. 2. The waveguide according to claim 1, wherein: 5. The method according to claim 1, wherein the first and second fiber components are selected such that the waveguide has a dispersion of less than 1 ps / nm ² -km over a range from 1520 nm to 1625 nm. 2. The waveguide according to claim 1, wherein: 6. The method of claim 1, wherein the first and second fiber components are selected such that the waveguide has a total dispersion at 1550 nm in the range of about -2.0 to +2.0 ps / nm-km. 2. The waveguide according to 1. 7. The method of claim 1, wherein the first and second fiber components are selected such that the waveguide has a total dispersion at 1550 nm in the range of about -2.0 to 0 ps / nm-km. The described waveguide. 8. The waveguide has an induced bending loss of about 0.5 dB or less when wound once around a 32 mm mandrel, and the cut-off wavelength of the fiber with the cable formed is less than 1520 nm; The waveguide according to claim 7, wherein the polarization mode dispersion is less than 0.5ps / (km) ^1/2 . 9. The waveguide comprises a waveguide forming a cable, wherein the waveguide is disposed between amplifiers, the first component is at least 50km long, and the second fiber component is 20km long. 2. The waveguide of claim 1, wherein the length is less than. 10. The waveguide comprising a waveguide forming a cable, wherein the waveguide is disposed between amplifiers, the first component is at least 75km long, and the second fiber component is 15km long. 2. The waveguide of claim 1, wherein the length is less than. 11. The waveguide according to claim 1, wherein the first fiber component comprises a single mode fiber having a step refractive index distribution. 12. The second fiber component comprises a core having at least first to third three segments, wherein the first segment has an outer radius r ₁ in the range of about 1.25 to 5.0 μm and about 0.5. From
And a delta _1% in 2.0% range, the second segment, and a delta _2% in the range from the outer radius r ₂ to about -0.5 in the range of about 1.25 to 10.0μm -0.1% The third segment has an outer radius r ₃ in the range of about 2.5 to 15.0 μm and about 0.1 to about 0.1 μm.
Single-mode optical fiber according to claim 11, comprising a delta _3% in the range of 1.0%. Wherein said second fiber component, further comprising a fourth segment and a delta _2% in the range from the outer radius r ₂ to about -0.5 in the range of about 5.0 to 25.0μm -0.05% 13. The single mode optical fiber according to claim 12, wherein: 14. A single mode optical waveguide fiber comprising: a first fiber component having a positive dispersion and a positive dispersion gradient; and a second fiber component having a negative dispersion and a negative dispersion gradient. The fiber component has a length at least twice as long as the length of the second fiber component, and the waveguide always has a dispersion of less than ² ps / nm ² -km over the range 1520 nm to 1625 nm. A single mode optical waveguide, wherein the refractive index profiles of the first and second fiber components are selected to have. 15. The waveguide of claim 14, wherein the first fiber component has a length that is at least five times a length of the second fiber component. 16. is the first and the second fiber component is selected, the waveguide over a range of 1625nm from 1520 nm, always and characterized by having a dispersion size of less than 1 ps / nm ² -km 16. The waveguide according to claim 15, wherein: 17. The method of claim 17, wherein the first and second fiber components are selected such that the waveguide has a total dispersion at 1550 nm in a range of about -2.0 to +2.0 ps / nm-km. 14. The waveguide according to 14. 18. The first fiber component comprises a single mode fiber having a step refractive index distribution, the second fiber component comprises a core having at least first to third three segments, and the first fiber component comprises: The segment has an outer radius r ₁ in the range of about 1.25 to 5.0 μm and a Δ ₁ % in the range of about 0.5 to 2.0%, and the second segment has an outer radius r in the range of about 1.25 to 10.0 μm. Radius r ₂ and about -0.5
From and a delta _2% in the range of -0.1%, the third segment, and a delta _3% within the outer radius r ₃ in the range of from about 2.5 to 15.0μm from about 0.1 to 1.0% 18. The waveguide according to claim 17, comprising: 19. The single mode optical fiber according to claim 1, wherein the second fiber component is in an optical amplifier.