MXPA00008215A - Low slope dispersion managed waveguide - Google Patents

Abstract

Disclosed is a single mode optical waveguide fiber having alternating segments of positive and negative dispersion and dispersion slope. The relative indexes, the refractive index profiles and the radii of the segments are chosen to provide low total dispersion and dispersion slope. One embodiment consists of a first central major index profile (10) of outer radius r1, surrounded by a first annular segment (12) of outer radius r2, surrounded by second annular segment (14) of outer radius r3. Preferred waveguides in accordance with the invention exhibit a dispersion over the range of 1520 to 1625 nm which at all times have a magnitude which is less than 2, and more preferably less than 1 ps/nm2-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. The waveguide also features a low polarization mode dispersion.

Description

WAVE GUIDE CONTROLLED BY REDUCED PENDING DISPERSION FIELD OF THE INVENTION The present invention relates to a single-mode optical waveguide fiber designed for extensive separations between repeaters, high-speed data telecommunication systems. In particular, the single-mode waveguide combines excellent bending strength, reduced attenuation, reduced dispersion and reduced dispersion slope, characteristics that are desirable for long-distance transmission applications.

BACKGROUND OF THE INVENTION In the telecommunications industry, the need for greater information capacity over long distances, without regeneration of electronic signals, has led to a re-evaluation of the profile design of the single-mode fiber index. Recent developments in erbium-doped fiber amplifiers (EDFA) and wavelength division multiplexing have enabled high-capacity light-wave systems. To achieve a high capacity, the channel bit rate and the signal wavelength scales can be increased. When the bit rate is increased above 2.5 Gb / s, the dispersion of the fiber results in a greater degradation over a large distance. On the other hand, if the dispersion is very low, the interactions of multiple channels can cause a mixture of four waves and a degradation in the performance of the system. To reduce dispersion and degradation of FWM, dispersion control has been proposed and demonstrated. Dispersion control can be achieved by controlling the cable, where fibers + D and -D are alternately spliced and fiber control where the reeds of the core with the properties of + D and -D combine to become a fiber . So far, dispersion-controlled fibers employing fibers + D and -D with positive dispersion slope have been proposed, where the final fiber dispersion has a dispersion and a slope similar to the dispersion-modified fiber, in other words, the net dispersion at zero is in the 1550 nm window and the total dispersion slope is positive. However, there is still a need for alternative designs of waveguides controlled by dispersion.

Definitions The following definitions are in accordance with the common usage in the art. The index or refraction profile is defined according to the radii of segments of similar refractive indexes. A particular segment has a first and a last point of refractive index. The radius from the center line of the waveguide to the location of this first point of refractive index is the inner radius of the segment or region of the core. Similarly, the radius from the center line of the waveguide to the location of the last refractive index point is the outer radius of the core segment. The radius of the segment can be defined for convenience in several ways, as will be seen in the description of Figure 1 below. In Figures 1-3, from which the tables 1 and 2 are derived, the radii of the segments of the index profile are defined as follows, where the reference is to a graph of ?% against waveguide radius: * the outer radius of the central major index profile, ri, is measured from the axial center line of the waveguide to the intersection of the central index profile extrapolated with the x axis, ie to the point?% = 0; * the outer radius, r2, of the first annular segment is measured from the axial center line of the waveguide to the intersection of the extrapolated or actual central index profile with the x axis, ie, the point?% = 0; * the outer radius, r3, of the second annular segment is measured from the axial center line of the waveguide to the intersection of the central index profile »extrapolated with the x-axis, that is, the point?% = 0; * the outer radius of any of the additional annular segments is measured analogously to the outer radii of the first and second annular segments; and * the radius of the final annular segment is measured from the center waveguide line to the midpoint of the segment.

The width, w, of a segment is taken to be the distance between the inner and outer radius of the segment. It is understood that the outer radius of a segment corresponds to the inner radius of the next segment. - The relative index,?, Is defined by the equation:?% = 100 x (n-i2 - n22) / 2n-? 2, where ni is the maximum refractive index of the index profile segment 1, and n? is a reference refractive index that is taken to be, in this application, the refractive index of the coating layer. - The term refractive index profile or simply index profile is the ratio between?% Or refractive index and radius in a selected portion of the core. - The term profile a refers to a refractive index profile expressed as a function of? (b)%, where b is the radius, which follows the equation:? (b)% =? (b0) (1 - [| b-b0 | / (brb0)] a), where b0 is the radial point in that the index is a maximum and b1 is the point at which? (b)% is zero and b is on the scale b¡ < b < bf, where delta is already defined, b, is the starting point of profile a, bf is the end point of the profile, and a is an exponent that is a real number. Other index profiles include a step index, triangular, trapezoid and rounded index, whose rounding is almost always due to diffusion of doping in regions of rapid refractive index change.

- Total dispersion is defined as the algebraic sum of waveguide dispersion and material dispersion. Sometimes, the total dispersion is called chromatic dispersion in the art. The total dispersion units are ps / nm-km. - The bending strength of a wave guide fiber is expressed as induced attenuation under prescribed test conditions. Normal test conditions include 100 turns of waveguide fiber around a 75mm diameter mandrel and 1 turn of waveguide fiber around a 32mm diameter mandrel. In each test condition, fold induced attenuation is measured, usually in units of dB / (unit length). In the present application, the bend test employed is 5 turns of the wave guide fiber around a 20 mm diameter mandrel, a more demanding test than is required for the more severe operating environment of this guide fiber cool.

BRIEF DESCRIPTION OF THE INVENTION One aspect of the present invention relates to a single-mode optical waveguide comprising a first segment of fiber component having a positive dispersion and a positive dispersion slope, and a second fiber component having a negative dispersion. and a negative dispersion slope, wherein the waveguide is alternated by its length between segments of the first fiber component and the second fiber component, and wherein the first fiber component segment has a length that is at least twice the length of the second fiber component segment. The waveguide is optimized for the wavelength window that operates at reduced attenuation at around 1550 nm, that is, in the window between approximately 1520 to 1625 nm. The waveguide according to the invention may consist of a unitary fiber having the various first and second segments therein, e.g., alternating sections of positive and negative dispersion and slope of dispersion. Alternatively, the waveguide may consist of a cable in which the various sections of fiber component are connected along the length of the cable. Another aspect of the present invention relates to a single mode optical waveguide that controls chromatic fiber dispersion providing a smaller total dispersion and a reduced dispersion slope. Preferred waveguides according to the invention have a dispersion on the scale of 1520 to 1625 nm, which at all times has a magnitude that is less than 2, and more preferably less than 1 ps / nm2-km. The total dispersion of the waveguide fiber is on the scale of approximately -2.0 to +2.0, more preferably around -1.0 to +1.0, and even more preferably around -0.5 to +0.5 ps / nm-km at 1550 nm. The rl,?% And the refractive index profiles of the various positive and negative dispersion segments are also selected to provide a total attenuation at 1550 nm not greater than 0.25 dB / km. All these properties are achieved while maintaining high strength, optimum fatigue resistance and optimum bending strength, i.e., an induced bend loss not greater than about 0.5 dB, for a turn around a 32 mm mandrel, and no greater than 0.5 dB for 100 turns around a 75 mm mandrel. The waveguides according to the invention are also compatible with optical amplifiers. Also, the cut-off wavelength of the cable-shaped fiber is less than 1520 nm. A further benefit is a polarization mode dispersion of less than about .5 ps / (km) 1/2, more preferably less than .3 ps / (km) 1/2 and almost always almost 0.1 ps / (km) 1/2 Other features and advantages of the invention will be explained in the detailed description below, and in part it will be simple to those skilled in the art from that description or it will be recognized by practicing the invention, as described herein, that includes the detailed description below, the claims, as well as the accompanying drawings. It will be understood that the above general description and the following detailed description are only exemplary of the invention and are intended to provide a general overview or framework for understanding the nature and character of the invention as claimed. The attached drawings are included to provide a better understanding of the invention and are incorporated and constitute a part of this specification. The drawings illustrate various embodiments of the invention and together with the description serve to explain the principles and operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a negative dispersion fiber segment profile for use in accordance with the invention. Figure 2 illustrates an alternative negative dispersion fiber segment index profile according to the invention. Figure 3 illustrates an alternative and preferred negative dispersion fiber segment profile. Figure 4 illustrates the dispersion characteristics of an alternate segment + D and -D fiber. Figure 5 illustrates the dispersion versus distance of a fiber controlled by dispersion and flattened by dispersion. Figure 6 illustrates the dispersion against the wavelength curve for a controlled and flattened dispersion fiber according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITY Reference will now be made in detail to the preferred embodiments of the invention, the examples of which are described with the aid of the accompanying drawings. Wherever possible, the same reference numerals will be used in the drawings to designate the same or similar parts.

In the present invention, an optical waveguide controlled by dispersion and reduced slope fiber is obtained by incorporating alternating segments of a first fiber component having positive dispersion and positive dispersion slope, and a second fiber component having negative dispersion and negative dispersion slope, wherein the first fiber component has a length that is at least twice, more preferably at least three times and more preferably at least five times the length of the second fiber component. The waveguides of the present invention may be in the form of a unitary fiber having alternate sections of positive and negative dispersion and slope of dispersion. Said fiber could be made, for example, with the assembly of alternating core tablets having desired index profiles within a tube or other support device. Alternating core tablets will create the desired alternating positive and negative dispersion characteristics. The tube containing these alternating component tablets can be coated with a silica coating layer, and the resulting preform can be consolidated and made into a continuous fiber having alternate sections of positive and negative dispersion and dispersion slope along its length . Said processing techniques are described in more detail, for example, in the patent application of E.U.A. Serial No. 08 / 844,997, filed April 23, 1997, the specification and drawings of which are hereby incorporated by reference in their entirety.

In an alternative mode, the waveguide consists of a wired waveguide. For example, the waveguide may consist of a first fiber component having positive dispersion and positive dispersion slope, having a length of at least 50 km, and more preferably at least 75 km in length, and the second fiber component (negative dispersion and negative dispersion slope) having a length less than 20 km, but more preferably less than 15 km in length. Said wired waveguide may be disposed between the amplifiers in a fiber optic communication system. The second fiber component can be placed alternatively on the amplifier side within the amplifier or amplifier module itself. The first fiber component, i.e., having positive dispersion and positive dispersion slope, can be provided by the use of conventional single-mode fiber, such as SMF 28 sold by Corning Incorporated. The SMF-28 has a total dispersion of 17 ps / nm.km, and a dispersion slope of 0.06 ps / nm2.km at 1550 nm. A variety of fiber profiles can be employed to provide the second fiber component having negative dispersion and negative dispersion slope. In a preferred embodiment of the invention, the negative component fiber segment has three or four segments to the profile. Figure 1 illustrates one embodiment of said preferred profile of three segments for the negative dispersion and negative dispersion slope segment component. The profile in figure 1 consists of a first central index index 10 of outer radius r-i, surrounded by a first annular segment 12 of outer radius? Z, surrounded by a second annular segment 14 of outer radius r3. A variety of shapes of profiles can be used, as illustrated, for example, by dotted lines related to the possible shapes of profiles for the first central major index profile 10 in Figure 1. The novel one-wave optical waveguide Mode is characterized by its segmented core design that provides the unusual combination of properties discussed here. These properties are achieved through the selection of an appropriate form of refractive index profile of each of the segments, and of the selection of the appropriate delta refractive index,?%, And the radial extension, r-i, of the segments. It is known that profile parameters interact. For example, a central region profile a having one of about 1 will have a different radius from a central region having a trapezoid index to provide fibers having essentially identical properties. The index profiles of the respective segments can be of virtually any particular shape, including a profile a, a step index profile or a trapezoid profile. Unless special steps are inserted into the procedure, the refractive index profiles will be rounded off at the points where the refractive index changes sharply. The rounding is due to the diffusion of the impurifying materials used to change the base vitreous refractive index. Therefore, any of these index profiles can be rounded off at particular points; For example, a step index profile that has a positive?% will almost always have the upper and lower corners rounded off. The preferred parameters for the radius against delta for a three-segment profile that can be used to form a negative dispersion-negative dispersion fiber segment that is employed in the present invention are explained in Table I below. As can be seen in the table, the fiber may or may not include a central recessed index area, as usually originated by the migration of the germanium dopant.

TABLE I A core segment tablet of the negative dispersion fiber illustrated in Figure 1 was combined with conventional single mode fiber (SMF28) having positive dispersion and positive scattering slope and becoming a fiber. The fiber illustrated by the solid line in Figure 1 presents a negative dispersion, ie, approximately -35 ps / nm.km and a dispersion slope of approximately .15 ps / nm2.km at 1550 nm. In this way, in this case (DSMF / SSMF) = 17 / 0.06 = 280, while (Dn / Sn) = -35 / .15 = -233. Consequently, (Dp / Sp) / (Dn / Sn) = .83, which is very close to 1, as desired.

Figure 2 illustrates said four-segment fiber core profile which is useful as a dispersion fiber segment of negative dispersion slope according to the invention. The profile illustrated in figure 2 incorporates two regions of lowered index 12 and 16. The preferred parameters for radio-delta for the various profiles of four segments that can be used to form the fiber segment are explained in Table II below. of negative dispersion, negative dispersion slope, which may be used in the present invention.

TABLE II Any of the profiles described herein may also include a centerline dives section, which is a lowered relative refractive index area that is less than the delta peak of the first larger core segment. These dips of central line usually originate what is called burning or migration of impurifying ions, which sometimes occurs during the development of fiber optic waveguides. The waveguides according to the invention preferably have a dispersion on the scale of 1520 to 1625 nm which at all times has a magnitude that is less than 2, and more preferably less than 1 ps / nm2-km. The total dispersion of the waveguide fiber is on the scale of about -2.0 to +2.0, more preferably about -1.0 to +1.0, and more preferably still about -0.5 to +0.5 ps / nm-km at 1550 nm. The rl,?% And the refractive index profiles of the various positive and negative dispersion segments are also selected to provide a total attenuation at 1550 nm not greater than 0.25 dB / km. All these properties are achieved while maintaining high strength, optical fatigue resistance and optimum bending strength, that is, an induced bending loss of no greater than about 0.5 dB for 100 turns around a 75 mm mandrel. The waveguides according to the invention are also compatible with optical amplifiers. Also, the cut-off wavelength of the cable-shaped fiber is less than 1520 nm. A further benefit is a polarization mode dispersion of less than about .5 ps / (km) 1/2, more preferably less than .3 ps / (km) 1/2. A dispersion controlled waveguide that is particularly preferred in the present invention controls chromatic fiber dispersion by providing a negative total dispersion, as well as a reduced dispersion slope. In systems where the suppression of potential soliton formation is important, it is desirable that the total dispersion of the waveguide fiber be negative, so that the linear dispersion can not counteract the non-linear autophase modulation that occurs for signals of high power. To equalize the chromatic dispersion of fiber, preferably the following relationship should be satisfied as accurately as possible.

DpLp + DnLn = O where D and L represent dispersion and fiber length, the subscripts "p" and "n" represent positive and negative dispersion fiber components. In addition, to equalize the dispersion slope, the following relationship should preferably be satisfied as accurately as possible: (Dp / Sp) / (Dn / Sn) = 1, where S is the dispersion slope. The waveguides described herein are suitable for use in long-range, high power transmission applications, including conventional RZ (return to zero) or NRZ (no return to zero), as well as soliton transmission applications. The definition of high power and large distance has significance only in the context of a particular telecommunication system, wherein a bit rate, a bit error rate, a multiplexing scheme, and perhaps optical amplifiers are specified. There are other factors known to those skilled in the art, which have an impact on the meaning of high power and great distance.

However, for most purposes, high power is an optical power greater than about 10 mW per channel. In some applications, signal power levels of 1 mW or less are still sensitive to non-linear effects, so that Aeff is still an important consideration in such lower power systems. A great distance is one in which the distance between the electronic regenerators can exceed 100 to 120 km. Regenerators will be distinguished from repeaters, which use optical amplifiers. The separation of repeaters, especially in systems of high data density, can be less than half the spacing of the regenerator. The invention will be clearer thanks to the following example which has the purpose of exemplifying the invention.

EXAMPLE A refractive index profile of three segments which is particularly preferred for being used as the negatively sloped negative dispersion fiber segment is illustrated in Figure 3. This particular profile has a dispersion of -35.47 ps / nm.km and a slope of -0.1018 ps / nm2.km at 1550 nm. The cut-off wavelength is 1.18 microns and the loss by bending of set of pins of 1.3 dB, MFD of 4.8 microns and Deff of 4.68 microns at 1550 nm. Figure 4 illustrates the dispersion characteristics achieved when a positive dispersion fiber component, in this case SMF-28, is combined with the negative dispersion fiber component of the variety described in the variety of Figure 3 having the following parameters: Table III lists the resulting properties of dispersion and dispersion slope, as well as the dispersion to dispersion ratio ratio achieved with this combination of alternating fiber segments.

TABLE III Figure 5 illustrates the axial design of the resulting waveguide fiber, as a function of the dispersion over the waveguide length (nm.km) for the resultant fiber controlled by dispersion and flattened by dispersion. Figure 6 illustrates the resulting characteristics of total dispersion of the controlled fiber and flattened by dispersion. Lp / Ln is around 2: 1 in this example. The period Ln + Lp is around 3 km. As can be seen in Figure 6, for this design example, the total dispersion is much less than 1 ps / nm.km, and in fact it is less than about 0.5 ps / nm.km, from 1520 to 1620 nm. This coincides with the window of reduced loss of single-mode fibers. According to the loss spectrum of a conventional single mode fiber, the attenuation is less than .22 dB / km from 1520 to 1620 nm. It will be apparent to those skilled in the art that various modifications and variations may be made to the present invention without departing from the spirit and scope of the invention. Therefore, it is intended that this invention encompass the modifications and variations of the present invention, as long as it is within the scope of the appended claims and their equivalents.

Claims (19)

9 NOVELTY OF THE INVENTION CLAIMS

1. - A single mode optical waveguide comprising: a first fiber component having positive dispersion and positive dispersion slope, and a second fiber component having negative dispersion and negative dispersion slope.

2. The waveguide according to claim 1, further characterized in that said first fiber component has a length that is at least twice the length of the second fiber component.

3. The waveguide according to claim 1, further characterized in that said first fiber component has a length that is at least five times the length of the second fiber component.

4. The waveguide according to claim 1, further characterized in that the first and second fiber components are selected such that said waveguide shows a dispersion above the scale of 1520 to 1625 nm, which in all moment has a magnitude less than 2 ps / nm2-km.

5. The waveguide according to claim 1, further characterized in that the first and second fiber components are selected such that said waveguide shows a dispersion above the scale of 1520 to 1625 nm, which in all moment has a magnitude less than 1 ps / nm2-km.

6. The waveguide according to claim 1, further characterized in that the first and second fiber components are selected such that said waveguide shows a total dispersion in the scale of about -2.0 to +2.0 ps / nm -km at 1550 nm.

7. The waveguide according to claim 1, further characterized in that the first and second fiber components are selected such that said waveguide shows a total dispersion in the scale of about -2.0 to +0.0 ps / nm -km at 1550 nm.

8. The waveguide according to claim 7, further characterized in that said waveguide has an induced bend loss not greater than about 0.5 dB, for a turn around a mandrel of 32 mm, a wavelength fiber-cut fiber in the form of a cable less than 1520 nm, and a polarization mode dispersion less than .5 ps / (km) 1/2 approximately.

9. The waveguide according to claim 1, further characterized in that said waveguide comprises a wired waveguide, and this is placed between the amplifiers, and the first component is at least 50km in length, and The second fiber component is less than 20 km in length.

10. The waveguide according to claim 1, further characterized in that said waveguide comprises a wired waveguide, and this is placed between the amplifiers, and the first component is at least 75km in length, and The second fiber component is less than 15 km in length.

11. The waveguide according to claim 1, further characterized in that said first fiber component includes single mode fiber having a pass index profile.

12. The single-mode optical fiber according to claim 11, further characterized in that the second fiber component includes a core having at least three segments, wherein the first segment has an outer radius? on the scale of approximately 1.25 to 5.0 μm, a ??% on the scale of approximately 0.5 to 2.0%, the second segment has an outer radius r2 on the scale of around 1.25 to 10.0 μm and a? 2% on the scale from about -0.5 to about -0.1%, and the third second segment has an outside radius r3 on the scale of about 2.5 to 15.0 μm and a? 3% on the scale of about 0.1 to about 1.0%.

13. The single-mode optical fiber according to claim 12, further characterized in that said second fiber component comprises a fourth segment having an outer radius r2 on the scale of about 5.0 to 25.0 μm at? 2% in the scale of approximately -0.5 to -0.05%.

14. A single-mode optical waveguide comprising: a first fiber component having positive dispersion and positive dispersion slope and a second fiber component having negative dispersion and negative dispersion slope, further characterized in that said first fiber component has a length that is at least twice the length of the second fiber component, and the profiles of the first and second fiber components are selected such that the waveguide has a dispersion above of the scale from 1520 to 1625 nm which at all times has a magnitude that is less than 2 ps / nm2-km.

15. The waveguide according to claim 14, further characterized in that the first fiber component has a length of at least five times the length of the second fiber component.

16. The waveguide according to claim 15, further characterized in that the first and second components are selected such that said waveguide shows a dispersion above the scale of 1520 to 1625 nm, which at all times has a magnitude less than 1 ps / nm2-km.

17. The waveguide according to claim 14, further characterized in that the first and second fiber components are selected such that said waveguide shows a total dispersion on the scale of about -2.0 to +2.0 ps / nm -km at 1550 nm.

18. The waveguide according to claim 17, further characterized in that the first fiber component includes a single mode fiber having a pass index profile, and the second fiber component includes a core having the minus three segments, where the first segment has an outside radius ri on the scale of approximately 1.25 to 5.0 μm, a ??% on the scale of approximately 0.5 to 2.0%, the second segment has an outer radius r2 on the scale of about 1.25 to 10.0 μm and a? 2% on the scale of about -0.5 to about -0.1%, and the third second segment has an outside radius r3 on the scale of about 2.5 to 15.0 μm and a? 3% on the scale from about 0.1 to about 1.0%.

19. The single-mode optical fiber according to claim 1, further characterized in that the second fiber component is contained within an optical amplifier.