KR20010088804A - Multicore and multimode dispersion managed fibers - Google Patents

Abstract

The optical path along an optical fiber including multiple cores or multiple modes is arranged with positive and negative dispersion characteristics. The coupling or coupling mechanism adjusts the relative travel between paths with different dispersion characteristics such that the total dispersion of the combined paths approaches zero dispersion over the range of signal wavelengths intended for transmission.

Description

Multicore and multimode dispersion managed fibers

Color dispersion varies along the waveguide as a function of the waveguide material and structure as well as the signal wavelength. While zero dispersion is possible at certain wavelengths, this zero dispersion is also associated with a phenomenon known as "four wave mixing," which causes crosstalk in adjacent wavelength channels. The four-wave mixing is most pronounced in zero dispersion as well as increasing optical power and reduced channel spacing.

Both color dispersion and quadruple mixing are prevented by dispersing fibers that combine the lengths of the fibers with positive and negative dispersion (assessed at wavelengths for transmission purposes). Four-wave mixing is prevented because only non-zero dispersed fibers are used. Color dispersion is prevented because the length-weight average of positive and negative dispersion is close to zero.

This approach uses positive dispersion fibers to transmit optical signals over distance, and uses a roll of negative dispersion to periodically interfere with the positive dispersion fibers to reduce the average dispersion of the combined optical paths. The dispersion of the compensating module containing is used. However, the compensation module reduces the power of the signal without advancing the signal in the intended direction.

The lengths of the fibers with positive and negative dispersion joined the ends together with the ends to more effectively transmit optical signals with reduced color dispersion. However, the mapping must maintain traces of the dispersing properties of the bonded fibers and two different fibers must be kept in the list.

Dispersion retaining fibers were also made in continuous lengths, replacing sections with dispersion of opposite signs at wavelengths for transmission purposes. Only one fiber should be listed, but the dispersion cycle (i.e. the length of the two sections being repeated) should be selected at the time of manufacture and does not cause the following change. Contaminants can also be inserted into the fibers at the interface between the sections so that the sections must be individually ground and assembled before being drawn to the final form.

The dispersion maintaining cable contains one or more fiber pairs with dispersion of opposite signs. The sections of the cable are joined together such that the positive dispersion fibers of one section are joined with the negative dispersion fibers of an adjacent section. Again, the dispersion event must keep track of the section length and the individual fiber design is limited because the dispersion of the opposite sign must have the same size at the transmitted wavelength.

Summary of the Invention

The present invention includes various embodiments of a fiber optics system that minimizes the fiber inventory and provides more flexibility in the design and performance of the fibers, while compensating for color dispersion and preventing quaternary mixing. In addition, shorter dispersion cycles (i.e., the length over which the variation of variation is repeated) are possible without complicated manufacturing processes and additional dispersion options after manufacture.

One embodiment is an optical system of distributed compensation fibers comprising a single optical fiber having a plurality of consecutive optical paths with different dispersion properties for the transmission of optical signals. One of the optical paths represents a positive dispersion at the central wavelength of the optical signal, and another one of the optical paths represents a negative dispersion at the central wavelength of the optical signal. The coupling mechanism moves the optical signal between the traveling portions of the two paths creating a length-weighted average variance approaching zero at the central wavelength of the optical signal. Preferably, both the dispersion and the dispersion slopes are matched (ie, identical but different in sign) at the center wavelength such that the average dispersion over the wavelength range also remains near zero dispersion.

The continuous light paths may extend parallel or concentric with each other; And, regardless of the intrusion of other coupling structures, the movement of the optical signal between the paths is not hindered by both paths. For example, a single fiber can be constructed with the complexity of the core surrounded by the cladding. Each of the cores forms one of the optical paths with different dispersion properties.

The signals may be moved in a positive direction between the cores by the coupling mechanism type as one or more long period gratings. The coupling mechanism can also be formed as a result of core spacing by placing the core close enough to facilitate signal transmission. The latter coupling mode requires symmetrical dispersion between cores and has a dispersion period equal to the coupling length between the cores. The former coupling mode provides more flexibility in the dispersion characteristics of the core by moving signals between cores at different intervals. Regardless of the coupling mode, the dispersion slopes of the positive and negative dispersion cores are preferably matched such that the resulting average dispersion remains near zero over the intended range of signal wavelengths (ie, small magnitude or opposite sign). .

Yet another embodiment includes a fiber segment having one or more core pairs having opposite sign dispersion characteristics. The segments have one segment of positive dispersing cores aligned with the other dispersing core of the other segment and are joined together from end to end. The length of the segment is chosen to achieve a length-weight average close to zero dispersion. Each pair of cores can be used to transmit signals in parallel by aligning the absolute magnitude of the positive and negative variances, and aligning both the positive and negative distributed cores of one segment to the opposite counterparts of adjacent segments. Multiple pairs of positive and negative distributed cores may be individually arranged to assist transmission with one or more bit rates or applications. More flexibility is also possible in the dispersion event by adjusting the angular indexing between adjacent sections to align various bonds of cores with different dispersion properties.

The single fiber may also be configured as a multimode fiber having a primary mode path and a higher-order mode path with different dispersion values to form concentric optical paths with different dispersion properties. In another embodiment, the coupling mechanism comprises one or more mode couplers, the mode coupler also having a tapered coupling or long period for moving the optical signal between the basic and higher order mode paths. Can be formed as a lattice.

The basic mode may be arranged to indicate positive variance, and the higher order mode may be arranged to indicate higher negative variance magnitude. Thus, the mode coupler in this arrangement is arranged to move the optical signal to the basic mode at intervals longer than the higher order mode. However, with suitable core profile design and selection of standard frequencies, the dispersion and dispersion slopes of the primary and secondary modes can be made to represent the same but different signs. It is also possible to further limit the signal at a standard frequency value far from the mode cutoff value.

Various connectors are used to pass signals transmitted on multicore or multimode fibers to singlemode singlecore fibers. For example, an optical grating may be used to move an optical signal from one core aligned with a single mode single core fiber to another, or from a higher mode to a basic mode to transmit more over a single mode single core fiber. Can be used to move it. Tapered coupling can also be used to transmit a signal in single core or basic mode. In addition, separate single-mode single core fibers may be attached to other cores of the multicore fiber, and switches may be used to further transmit signals from one attached fiber to conventional single mode single core fibers.

The multicore fibers can be produced by conventional processes having a relationship to the dispersion properties of the modes. The multicore fibers may be prepared by assembling two or more core canes in a preform prior to the process of drawing conventional fibers. Various arrangements of tubes or rods can be used to align the core cans at intervals, and soot overcladding can be consolidated around the core structure to seal the structure in the mold. .

The present invention is based on US Provisional Application No. 60 / 100,495, filed Sep. 16, 1998.

Optical signals traveling in the optical media of standard fibers produce small changes over distance that can cause significant loss of signal quality. Such changes include color dispersion. Dispersion-retaining fibers have positive and negative dispersion properties, which are mixed to produce a length-weight average close to zero dispersion.

1A is an enlarged cross-sectional view of a multicore optical fiber having two offset cores of different dispersion characteristics.

1B is a simplified enlarged cross-sectional view of another multicore optical fiber having one central core and one offset core with different dispersion characteristics.

1C is an enlarged cross-sectional view of another multicore optical fiber having two concentric cores of different dispersion characteristics.

FIG. 2 is a side view showing two segmented lengths of a multicore fiber that are relatively spun together and joined together.

3A and 3B are graphs showing the refractive index profiles of two cores of a multicore fiber having a refractive index shown as a function of the core radius "r".

3C-3F are graphs showing selective refractive index profiles that are particularly suitable for achieving negative dispersion.

4 is another side view of a multicore fiber schematically modified to include a long period grating for optically coupling two cores.

5 is an enlarged cross-sectional view of a multicore fiber with four cores-two cores having positive dispersion characteristics and two cores having negative dispersion characteristics.

6 is a side view of a tapered coupling for connecting two cores of the multicore fiber of FIG. 1A to a conventional single core fiber.

7 is a side view of a coupling that transfers a signal between two cores of a multicore fiber and a connector connecting one of the two cores of the multicore fiber and the core of a conventional single core fiber.

8 is a side view of a multimode fiber with a continuous long period grating to shift signals between modes with different dispersion characteristics.

FIG. 9 is a graph showing the standard propagation constant “b _n ” versus the standard frequency “V” of a multimode fiber illustrated in a stepped profile core design.

10 is a graph showing the standard waveguide dispersion "d _n " versus the standard frequency "V" of the waveguide in the same stepped profile core design.

11 is an enlarged cross-sectional view of a preform supporting two core kane in a bored-out rod.

12 is a similarly sized cross sectional view of a preform supporting two core kane in a tube.

FIG. 13 is a similarly sized cross sectional view of two core kane secured together by a specially shaped rod.

14 is another cross-sectional view of a similar size showing two core kane locked together prior to melting the preform around the two cores.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

The multicore optical fiber 10 shown in FIG. 1A has a positive dispersion core 12 and a negative dispersion core 14 surrounded by a conventional cladding 16. Dispersion of opposite signs of the two cores 12 and 14 is referenced in relation to the center wavelength of the wavelength range (typically corresponding to the erbium amplifier window) for transmission by the fiber 10. In order to maintain dispersion over the wavelength range from 1530 nm to 1560 nm, the positive core can be designed similar to SMF 1528 fibers, and the negative core can be designed similar to 1585 LS or leaf products. Can be. Both fibers are available from New York, Corning and Corning Incorporated. In other wavelength ranges, other forms of known core designs may be used and will also be described briefly.

The two cores 12 and 14 extend in parallel with the optical axis 18 of the fiber 10 and the distance "S" which can be adjusted to block or promote automatic coupling between the cores 12 and 14. Separated by. As indicated above, the distance " S " is large enough to block approximately automatic coupling. In manufacture, core kines having a core-clad ratio of at least 0.4 are generally spaced apart sufficiently to provide the required separation. An optional notch 20 on the outer surface of the fiber 10 provides the reference point with an angular refractive index of the segmented length of the fiber 10.

In FIG. 2, the two segmented lengths 10A and 10B of the original continuous fiber 10 are aligned in the axial direction before being joined together, such as a splicer designed for polarizing fibers, It is rotated relatively around two segmented length aligned axes 18A and 18B. The degree of rotation is selected to align the positive dispersion core 12A of the fiber segment 10A together with the negative dispersion core 14B of the fiber segment 10B. In addition, design symmetry may allow the negative dispersing core 14A of the fiber segment 10A to be aligned simultaneously with the positive dispersing core 12B of the fiber segment 10B. The segments 10A and 10B can be adjusted such that the average variance along the combined length of the two segments 10A and 10B as well as all consecutive pairs of segments approaches zero variance.

If the two cores 12A, 14A and 12B, 14B of each segment 10A and 10B are used to transmit different signals, the positive and negative variances of the two cores must be the same magnitude and the two segments The lengths of 10A and 10B must be the same. However, if only one of each segment core transmits a signal (e.g., core 12A of segment 10A and core 14B of segment 10B), the distribution of the two cores may be at different sizes. It will be optimized, and segments of different lengths can be combined to obtain an average variance close to zero. The dispersion slopes of the two cores are also preferably matched to maintain an average dispersion close to zero over a wavelength range for transport purposes.

Instead of bonding the segmented lengths of the fibers 10 to replace the optical paths between the positive and negative dispersing cores 12 and 14, passive or active coupling may be provided between the advancing lengths of the cores 12 and 14. Can be. Passive coupling can be achieved by reducing the separation " S " between cores such that power transfer occurs between cores in the desired dispersion period with the same coupling length. The positive and negative variance of the cores 12 and 14 should be symmetric about the center wavelength (ie, equal in magnitude) because the signal consumes half of their time in each of the cores 12 and 14. In addition, the propagation constants of the two separate cores 12 and 14 should be approached as far as possible to assist in more complete conversion of power. The coupling length is determined by the difference between the two lowest order super-mode propagation constants of the constituent waveguide and can be designed colorimetrically or chromatically.

3A and 3B show the refractive index profiles of the positive and negative dispersion cores 12 and 14 modified such that the effective refractive index "n (eff)" between the two cores 12 and 14 is the same. Dispersing the core 12 of the both has a simple step-like profile (GeO ₂ -SiO the SiO _{2 cladding. 2)} and the core size and the effective index of refraction "n (eff)" between the cladding value. The negative dispersion core 14 is a "w-shaped" or segmented core that up-doing the cladding to match the effective refractive index "n (eff)" of the positive dispersion core 12. (SEGCOR) has a profile design. For example, the doped cladding may be comprised of GeO ₂ -SiO ₂ or TiO ₂ -SiO ₂ . (Note: the dotted lines in FIG. 3B represent the refractive index levels around the silica cladding 16.)

In general, more complex profile shapes are required to produce negative dispersion and dispersion slopes as opposed to cores with positive dispersion. Four embodiments are shown in FIGS. 3C-3F that each can assist negative dispersion without excessively including other optical properties such as effective area, mode field diameter, warpage and micro warpage. Arrows across the profile lines indicate the flexibility of the design to change individual line segments of the profile.

The profile of FIG. 3C can be used to obtain either positive or negative variance with a positive or negative variance slope. The design of FIG. 3D is particularly useful for obtaining positive or negative variances with relatively large effective areas. The two designs of Figures 3E and 3F can also be considered for variance control with a low loss configuration.

Active coupling between the cores 12 and 14 may be achieved by forming one or more long period gratings between the cores shown in FIG. The coupling function is local such that the two cores 12 and 14 can be designed independently. For example, the core dispersion size and propagation constant between the cores 12 and 14 may vary. The spacing between the gratings 24 can be adjusted to compensate for other magnitudes of the core variance so that the length-weight average still approaches zero variance. Taping may be used to join the long period grating 24 to increase the coupling function.

The long period grating 24 may be formed from a photosensitive core material exposed to a pattern of actinic radiation to create index perturbation in the fiber 10. The cladding region between the cores 12 and 14 can also be made of photo-refractive, which enhances the coupling function. The long period grating 24 may be recorded with a high power excimer laser during fiber drawing operations. Since the coupling mechanism does not add contaminants to the fiber 10, the dispersion cycle can be quite small and numerous.

The lattice precision is not very important because the response bands of the required spectrum are quite wide, and long period gratings typically have orders of magnitude on the order of millions of microns. In addition, since the long-period lattice 24 occupies a relatively large distance (eg, 1 or 2 meters) along the fiber 10 without causing a toxic effect, the magnitude of the refractive index perturbation may be quite low. (The need for hydrogen loading is avoided). The refractive index perturbation can be recorded as one point at a time or several points at a time, especially at higher draw rates. Refractive index or curvature perturbation can also be recorded with a high power CO ₂ laser in draw operation to achieve similar coupling function. Other perturbations can be used to form similar gratings that include stress-reducing changes due to periodic fiber compression or changes in path length due to periodic micro deflections.

Additional information on long-period gratings and mode couplers can be found in Vengsarkar et al., "Long-Period Fiber Gratings as Band-Rejection Filters"., Published in Journal of Lightwave Technology, Vol. 14, No. 1, January 1996, pages 58-65, and in another paper, "Helical-Grating Two-Mode Fiber Spatial-Mode Coupler" by Pole et al., Published in Journal of Lightwave Technology, Vol. 9, No. 5, May 1991, pages 598-604. Both papers are incorporated herein by reference.

Two or more cores may be formed from the single fiber shown in FIG. 5. Two positive dispersion cores 32 and 34 and two negative dispersion cores 36 and 38 of the fiber 30 are surrounded by a conventional cladding 40. The cores 32-38 may be paired in groups of positive and negative distributed cores (eg 32, 36 and 34, 38), and the paired cores may be optimized for individual bit rates or applications. have. Optionally, the pair can be varied to provide more flexibility for dispersion events by changing the angular index of refraction between adjacent sections. That is, the same fiber 30 can be used to aid in the complexity of different dispersion events. A dummy core 44 provides a reference point for the angular index of refraction of the fiber 30 around the optical axis 46.

Similar to the cores 12 and 14 of the fiber 10, the cores 32, 34, 36, and 38 of the fiber 30 are offset from the optical axis 46, which causes the problem of polarization mode dispersion. Can cause. Periodic twisting or continuous rotation of the fibers 10 or 30 can be used to reduce this problem. The cores 12 and 14 of the fiber 10 and the cores 32, 34, 36 and 38 of the fiber 30 are each individually to optimize the performance of the individual light paths through the fibers 10 and 30. It may be surrounded by a cladding region of.

When connected to conventional singlemode fiber or similar waveguide structures, such as in-line amplifier stations or link terminations, the two cores of each pair are connected to a single core of a conventional waveguide. 6 shows a tapered coupling 60 connecting dispersing fibers 10 to conventional monomodal fibers 70. Two waveguides 62 and 64 align with the positive and negative dispersion cores 12 and 14 of the fiber 10, but only the waveguide 64 aligns with a single core 66 of the conventional fiber 70. do. Within the coupling, the two waveguides 62 and 64 are tapered together to divert power to the waveguide 64.

The long period grating 24 may also be used at the location of the tapered coupling 60 shown in FIG. 7 so that the optical signal is directed to the appropriate core (eg core 12) prior to bonding the conventional fiber 70. . The core 66 of the conventional fiber 70 is aligned with the core 14 of the dispersion holding fiber 10 for receiving the optical signal propagating along the dispersion holding fiber 10. The material 72 of the V-groove supports the desired alignment between the fibers 10 and 70.

The conventional fiber 70 may be aligned with one of the cores 12 or 14 of the dispersion retaining fiber 10, or each core 12 and 14 may be aligned with an individual conventional fiber. In the latter case, optical switches (not shown) are used to alternately connect individual conventional fibers to conventional single fibers. The switch can be controlled by a sensor capable of detecting the presence or absence of a signal in one of the individual conventional fibers.

1B shows a replacement fiber 10 'having two similar cores 12' and 14 'inserted into a conventional cladding 16'. In contrast to the core 12 of the fiber 10 (shown in FIG. 1A), the core 12 ′ is centered along the optical axis 18 ′ of the replacement fiber 10 ′. The other core 14 'is offset from the axis 18'.

The central core 12 'is more easily aligned to the core of standard fibers. However, it is more difficult to join the sections of the optional fiber 10 'from end to end to shift the signal between the centered core 12' and the offset core 14 '. Thus, signal transmission between the cores 12 'and 14' is preferably generated by side coupling. Prior to connection from one end to the end, the signal is preferably moved to the central core 12 'in such a manner as to taper the fiber 10' or to use the tapered coupling shown in FIG.

Instead of centering one of the cores 12 'with respect to the optical axis 18', Figure 1C also has two cores 12 "and 14" centered with respect to the optical axis 18 'in a concentric pattern. Another optional fiber 10 'is shown. Side couplers can be used to move signals between concentric cores 12 "and 14". Fiber 10 "with concentric cores 12" and 14 "exhibits less birefringence and is more easily manufactured using conventional construction techniques. Additional concentric cores or concentrics coupled to offset cores Cores can also be used.

Another approach to maintaining dispersion in optical fibers is shown in FIG. 8. Represents a multimode optical fiber 80 having a central core 82 and surrounded by a cladding 84 designed to support one or more modes of optical transmission. One mode, like the default mode, represents a positive dispersion; And another mode, such as the secondary mode, exhibits negative dispersion. A long period grating 86 is recorded in the fiber along the optical axis 88 in an iterative pattern that controls the relative duration of the optical signal in each mode such that the length-weight average variance approaches zero.

As shown in Fig. 8, the negative dispersion of the secondary mode has a magnitude larger than the positive dispersion of the basic mode. Therefore, the interval L _F for measuring the length of travel between the gratings 86 in the basic mode is larger than the interval L _H for measuring the length of travel between the gratings 86 in the secondary mode. Other combinations are possible, including variance with the same sign of opposite magnitude between the two modes of operation. Equally spaced gratings can be used to evenly distribute the light travel length between two different modes. Also, secondary or higher modes can be used for the same purpose as reducing polarization mode dispersion. The interval may shift the signal from or to the third and higher order modes, but unintended loss of the intervening mode may limit the usefulness of the higher order mode.

8 and 9 graphically illustrate exemplary performance of multimodal fibers 80 with stepped refractive index profile cores in mind. In Fig. 8, the mathematically defined standard propagation constant "b _n " is shown for the frequency "V":

Where "β" is the propagation constant, "n ₁ " is the core refractive index, "n ₂ " is the cladding refractive index, "λ" is the central wavelength range and k is the constant 2π / λ, and "a" is the radius of the waveguide core . The standard propagation constant associated with "n (eff)" varies between "0" and "1", where "0" represents propagation throughout the cladding and "1" represents propagation throughout the core. More propagation in the core is more tightly coupled than more propagation in the core. The standard frequency value "V" has an inverse relationship with the center wavelength "λ". Curves LP ₀₁ , LP ₁₁ and LP ₀₂ represent the primary, secondary and tertiary modes, respectively. According to the example graph of FIG. 9, a standard frequency greater than 2.4 is required to support one or more modes; However, larger values around 3.5 are needed to properly limit the signal to be most practically applied.

As shown in FIG. 10, there is also provided an operating region with a standard waveguide dispersion "D _n " of opposite sign, which is defined as follows experimentally with a standard frequency of approximately 3.5:

Although the standard frequency of less than 3.5 offers the possibility for higher dispersion, the limitation of the second mode signal is reduced. Operation away from the blocking of the secondary mode (i.e. significantly higher than V = 2.4) reduces the disruption of polarization as well as the loss of warpage and micro warping. Periodic or continuous twisting of the fiber 80 may also be used to reduce polarization mode dispersion.

The waveguide dispersion "D" measured in ps / km nm can be calculated as follows.

Here, "Δ" is the difference in relative refractive index. The waveguide dispersion "D" has a sign opposite to the standard dispersion "D _n " so that the waveguide dispersion of the basic mode "LP ₀₁ " is positive and the waveguide dispersion of the second mode "LP ₁₁ " has a negative value. .

At standard frequencies greater than 2.4, the waveguide dispersion "D" for the base mode LP ₀₁ of stepped refractive fibers is significantly lower so that all major color dispersions are due to material dispersion. At a window of 1550 nm, the chromatic dispersion of the fundamental mode for stepped refractive fibers is limited to around 17-20 ps / km nm. However, more complex core profile designs, including segmented core and ring profiles, can be used to produce higher dispersion values. The core design between the positive and negative dispersion cores is chosen to properly connect the dispersion slopes so that the average dispersion remains near zero over the range of signal wavelengths. For example, the dispersion slopes may be the same in magnitude but opposite in sign or lower in absolute magnitude.

In addition, multimodal and multicore designs can be combined within individual fibers to provide more control over dispersion while also optimizing other design features. For example, one or both of the cores 12 and 14 of the fiber 10 shown in FIG. 1A, or the other cores shown in FIGS. 1B and 1C, may be formed as a multimode core, and the requirements for dispersion This can be separated between the mode and the core.

Conventional construction techniques can be used to produce the multimode fibers 80, and optical refractive index techniques similar to those described above for multicore fibers can be used to record the grating. While long period gratings 86 are preferred for mode coupling, other patterns and perturbation patterns, including diameter changes, may also be used to move signals between different modes.

The remaining FIGS. 11-14 illustrate various prototypes (also referred to as "blanks") for making the aforementioned multicore optical fibers using various rod-in-tube and OVD (optical vapor deposition) techniques that improve polarization fibers. Expressed).

The fiber preform 90 shown in FIG. 11 has a perforated rod 92 to receive two glass kines 94 and 96. The rod 92 is made of cladding material, and the two glass core kines 94 and 96 are applied to the core and cladding material applied to the sequence by optical vapor deposition in the refractive index profile distribution producing different dispersion properties. Include. A glass suit 98, also made of the cladding material, is applied to the outside of the rod and consolidated to complete the preform 90. Multicore fibers drawn from the preform have at least two cores that extend parallel to one another and exhibit different dispersion properties.

The fiber preform shown in FIG. 11 has two glass core kines 102 and 104 and two filling rods 106 and 108 installed in the tube 110, and a soot 112 that can be consolidated is the tube 110. Wraps. The two core kines 102 and 104 have a core and cladding distribution to aid in different dispersion properties. The filling rods 106 and 108, the tube 110 and the soot 112 are all made of molten cladding material with the core kines 102 and 104 to complete the preform.

FIG. 12 shows a preform 120 comprising a specially shaped rod 114 of cladding material supporting two core kines 116 and 118 with different dispersing properties. A compactable suit 122 also made of cladding material wraps the rod 114 and two kines 116 and 118. The two core kines 116 and 118 may be secured to the rod 114 to support the two core kane at a desired relative position until the preform 120 is consolidated.

The preform 130 shown in FIG. 13 includes two core kines 132 and 134 surrounded by a suit 136 that can be fixed and consolidated together. The core kines 132 and 134 have different dispersion properties and refractive index profiles that can promote or prevent automatic coupling between final cores drawn from the preform 130.

The overcladding 98, 112, 122, and 136 of the soot is retracted during consolidation where both axial and radial forces are produced that seal the parts in the preforms 90, 100, 120, and 130. In the continuous drawing process, a photorefractive index technique can be used to produce coupling between the cores, and a polarization mode reduction technique can be used to compensate for the asymmetry of the cladding surrounding the core. A refractive index mark may be formed outside of the preform, or a fill rod made of a material distinct from the cladding may be installed at the observable point to provide a reference angular point.

Paired core kines 94-96, 102-104, 116-118, and 132-134 within the four preforms have variances of opposite signs of equal or different absolute magnitudes. Either periodic or continuous coupling can be used to achieve a length-weighted average variance approaching zero for a variance of equal size. However, periodic coupling is required so that different size dispersions have the same length-weight average dispersion, with different travel lengths approaching zero at different distribution cores.

Claims (84)

A plurality of cores surrounded by cladding; A core having a refractive index different from that of the cladding for transmitting an optical signal; And And a core exhibiting a different dispersion value among the cores. The fiber of claim 1, wherein one of the cores exhibits a positive dispersion value and another one of the cores exhibits a negative dispersion value. The fiber of claim 2 wherein the core exhibits positive and negative dispersion slopes. The fiber of claim 2, wherein the positive and negative dispersion values are symmetrical with respect to the central wavelength of the optical signal. 5. The fiber of claim 4 wherein the core is positioned close enough to support the coupling between the cores. 6. The fiber of claim 5 wherein the propagation constant between the cores is about the same value. The fiber of claim 1 wherein one of the cores is a multimodal core. 8. The fiber of claim 7, wherein the multimode core comprises a first mode representing positive dispersion and a second mode representing negative dispersion. The fiber of claim 1 wherein the cores are positioned sufficiently apart to prevent coupling between the cores. 10. The fiber of claim 9, wherein the fiber also includes a tapered portion to enhance transmission of optical signals between cores. 10. The fiber of claim 9, wherein the perturbation formed in the core enhances the transmission of the optical signal between the cores. 12. The fiber of claim 11 wherein the perturbation is also formed in the cladding region between the cores to facilitate coupling between the cores. 12. The fiber of claim 11 wherein the perturbation is arranged to form a plurality of gratings for transmitting optical power between cores. 12. The fiber of claim 11 wherein the perturbation is arranged to shift the optical signal between the cores in a pattern that produces a length-weighted average dispersion approaching zero at the central wavelength of the optical signal. 12. The fiber of claim 11, wherein the fiber tapering used with the perturbation enhances the transmission of optical signals between cores. The method of claim 1 wherein the fibers are divided into two lengths that are rotated relative to each other and joined together in a relatively rotated position to align the first pair of cores exhibiting different dispersion values. Fiber. The fiber of claim 16 wherein the two lengths of the fiber are rotated relatively to another angular position to align the second pair of cores exhibiting different dispersion values. 18. The fiber of claim 17 wherein the first pair of cores is optimized for a first bit rate and the second pair of cores is optimized for a second bit rate. The fiber of claim 1, wherein the fiber further comprises a fiber interface that connects one of a plurality of cores not centered within the cladding with a core of adherent fiber centered within the cladding. The fiber of claim 1, wherein the fiber is warped at least periodically to prevent polarization mode dispersion. The fiber of claim 1, wherein the fiber further comprises a coupling mechanism for transmitting the optical signal between the forward portions of the core to provide a length-weighted average dispersion approaching zero at the central wavelength of the optical signal. 22. The fiber of claim 21 wherein the core exhibits a relatively consistent dispersion slope such that the length-weight average dispersion approaches zero over the wavelength range of the optical signal. A core surrounded by a cladding that supports multimodal transmission of light along the optical axis; A path in a first mode along the optical axis having a first dispersion value; A path in a second mode along the optical axis having a second dispersion value; Different first and second variance values; And And a plurality of mode couplers along an optical axis for coupling light back and forth between the first and second mode paths. 24. The fiber of claim 23 wherein the first mode pathway is a basic mode pathway with a positive dispersion value. 25. The fiber of claim 24 wherein the path of the second mode is a higher order mode with a negative dispersion value. 24. The fiber of claim 23 wherein the variance values between the first and second mode paths have opposite signs and different absolute sizes. 27. The fiber of claim 26, wherein coupling of light between the first and second mode paths occurs at different path lengths to compensate for different absolute magnitudes of the dispersion values. 24. The fiber of claim 23 wherein the variance between the first and second mode paths has opposite signs and approximately the same size. The fiber of claim 23 wherein the mode coupler is formed by refractive index perturbation. 30. The fiber of claim 29 wherein the refractive index perturbation forms a long period grating. The fiber of claim 23, wherein the mode coupler is formed at least in part by a tapered portion of the fiber. 24. The fiber of claim 23 wherein the mode coupler is spaced apart to produce a length-weight average dispersion approaching zero at the center wavelength at which light is transmitted. 33. The fiber of claim 32, wherein the first and second mode pathways exhibit relatively consistent dispersion slopes such that the length-weight average dispersion approaches zero over a range of wavelengths at which light is transmitted. A section of the first multimodal fiber having a first core representing a positive dispersion value and a second core representing a negative dispersion value; A section of second multimode fiber having a first core representing a positive dispersion value and a second core representing a negative dispersion value; And To establish an optical interface between the first and second multicore fiber sections that align the first core of the first fiber section to the second core of the second fiber section to adjust the average dispersion along the combined length of the fiber section. Optical system of the dispersion compensation fiber comprising a. 35. The optical system of claim 34, wherein the first and second cores of the sections of each of the first and second fibers are sufficiently spaced apart to prevent unwanted coupling between the first and second cores. 35. The optical system of claim 34, wherein the second core of the first fiber section is aligned with the first core of the second fiber section to adjust the average dispersion. 37. The range of wavelengths transmitted through a section of fiber wherein the second core of the first fiber section and the first core of the second fiber section have an average dispersion along the combined length of the fiber section. Optical system having a dispersing slope matched to approach zero in 35. The optical system of claim 34, wherein the first and second multicore fiber sections also have a third core representing a positive dispersion value and a fourth core representing a negative dispersion value. 39. The method of claim 38, wherein the first core of the first fiber section is aligned with the second core of the second fiber section to complete a first optical path between the fiber sections optimized for transmission at a first bit rate, And the third core of the first fiber section is aligned with the fourth core of the second fiber section for transmission of the optical signal at a second bit rate. 39. The optical system of claim 38, wherein the first and third cores of the first fiber section are individually aligned with the second core of the second fiber section to provide different dispersion compensation. 41. The optical of claim 40, wherein the first and third cores of the first fiber section are also individually aligned to the fourth core of the second fiber section to provide more selectivity for dispersion compensation. system. 35. The optical system of claim 34, wherein a refractive index mark applied to the fiber section assists desired angular indexing between fiber sections of the optical interface. 35. The optical system of claim 34, wherein a splicer designed for polarization-bearing fibers provides the optical interface. 35. The optical system of claim 34, wherein the first and second fiber sections are substantially identical sections oriented from the same fiber. Multimode fibers having basic mode pathways and higher order mode pathways having different dispersion values; A plurality of mode couplers along the optical axis of the fiber for moving the optical signal back and forth between the basic and higher order mode pathways; An optical system component aligned with the optical axis of the fiber to transmit more of the optical signal; And And one of the mode couplers arranged such that the optical signal is directed at one of the mode paths at an interface with a system component. 46. The system of claim 45, wherein the basic mode path has a positive variance value and the higher order mode path has a negative variance value. 47. The system of claim 46, wherein the negative variance has a magnitude greater than the positive variance. 48. The system of claim 47, wherein the mode coupler moves the optical signal between the primary mode path and the higher order mode path at different intervals between the mode paths. 46. The system of claim 45, wherein said one mode coupler directs an optical signal to a basic mode path prior to said optical system component. 46. The system of claim 45, wherein the optical system component is an optical amplifier and the one mode coupler directs an optical signal to the optical amplifier after a higher order mode path. 46. The system of claim 45, wherein the mode coupler includes refractive index perturbation along an optical axis to transmit optical signals between the mode paths. A single optical fiber having a plurality of continuous optical paths having different dispersion characteristics for transmitting the optical signal; A first optical path representing positive dispersion at the central wavelength of the optical signal; A second optical path representing negative dispersion at a central wavelength of the optical signal; And And a coupling mechanism to move the optical signal between the forward and forward portions of the first and second paths to produce a length-weighted average dispersion approaching zero at the center wavelength of the optical signal. . 53. The system of claim 52, wherein the first and second optical paths extend parallel to each other and the coupling mechanism moves the optical signal between parallel portions of the first and second paths. 54. The system of claim 53, wherein the first and second light paths are formed of first and second cores surrounded by cladding. 55. The system of claim 54, wherein the single optical fiber has a central axis, the first core is aligned with the central axis, and the second core is offset from the central axis. 55. The system of claim 54, wherein the single optical fiber has a central axis and both the first and second cores are offset from the central axis. 55. The system of claim 54, wherein the first core is a multimode core having a first mode representing positive dispersion and a second mode representing negative dispersion. 55. The system of claim 54, wherein the coupling mechanism includes a plurality of couplers for moving the optical signal in a positive direction before and after between the first and second cores. 59. The apparatus of claim 58, wherein the first and second cores exhibit opposite sign variances of different magnitude at the central wavelength of the optical signal, and the coupler is arranged to move the signal between the first and second cores at different intervals. System characterized in that the. 55. The system of claim 54, wherein the coupling mechanism is formed as a result of the first and second cores being positioned close enough to support the transmission of the optical signal between the cores. 61. The system of claim 60, wherein the first and second cores exhibit opposite signs of approximately the same magnitude at the center wavelength of the optical signal. 53. The system of claim 52, wherein the first and second optical paths extend concentrically with each other, and the coupling mechanism moves the optical signal between concentric portions of the first and second paths. 63. The system of claim 62, wherein the single fiber is a multimode fiber and the first and second optical paths are a basic mode path and a higher order mode path with different dispersion values. 64. The system of claim 63, wherein the coupling mechanism includes a plurality of mode couplers for moving the optical signal in a positive direction before and after the primary and higher mode paths. 66. The system of claim 63, wherein the first and second cores exhibit variance of opposite signs of approximately the same magnitude at the center wavelength of the optical signal. 53. The system of claim 52, wherein the coupling mechanism is formed by perturbation in the light path. 67. The system of claim 66, wherein said coupling mechanism comprises a plurality of optical gratings. 53. The system of claim 52, wherein the system comprises third and fourth optical paths having different dispersion characteristics for transmitting the optical signal. 69. The apparatus of claim 68, wherein the coupling mechanism is adapted to move an optical signal between the first and second paths in a first dispersion period and an optical signal between the third and fourth paths in a second dispersion period. And a coupler. 53. The system of claim 52, wherein said first optical path represents a positive dispersion slope and said second optical path represents a negative dispersion slope. 53. The system of claim 52, wherein the first and second optical paths represent a dispersion slope approaching zero. Aligning at least two glass core canes with different refractive index profiles; Wrapping the glass core can with a glass cladding material; Melting the cladding material surrounding the core cane to produce a glass preform; And A method of making a multicore fiber for transmitting an optical signal with reduced color dispersion, comprising drawing a multicore fiber from a preform having at least two cores extending in parallel with each other and exhibiting different dispersion properties. . 73. The method of claim 72, wherein at the central wavelength of the optical signal the first core represents positive dispersion and the second core represents negative dispersion. 73. The method of claim 72, wherein the wrapping comprises applying the cladding material as an optical soot. 73. The method of claim 72, wherein the step of aligning includes aligning the two core kane with a glass rod having a refractive index similar to the wrapped cladding material. 76. The method of claim 75, wherein the glass rod supports the two core canes. 73. The method of claim 72, further comprising attaching the two core kane prior to wrapping the two core kane with the glass cladding material. 73. The method of claim 72, further comprising forming a coupling between the two cores. 73. The method of claim 72, further comprising applying a refractive index mark to provide a reference angle to the fiber. As the signal travels along the fiber, the fiber arranged to have two parallel light paths having dispersion characteristics of opposite signs at the center wavelength of the signal; And Coupling the signal back and forth between successive portions of two parallel paths of the fiber such that the signal is exposed to an average dispersion approaching zero dispersion. How to compensate for variance. 81. The method of claim 80, wherein the coupling step includes moving signals between different cores of the multicore fiber. 81. The method of claim 80, wherein the coupling step includes moving signals between different modes of the multimode fiber. 81. The method of claim 80, wherein the coupling step includes moving signals between two parallel paths in a positive direction at different intervals between the paths. 81. The method of claim 80, wherein the coupling step includes arranging parallel paths for transmitting signals for the same duration.