MXPA01002754A - Multicore and multimode dispersion managed fibers - Google Patents

Abstract

Optical pathways along optical fibers, including multiple cores or multiple modes, are arranged with positive and negative dispersion characteristics. Coupling or connecting mechanisms regulate relative lengths of travel between the pathways having different dispersion characteristics so the total dispersion of the combined pathways approaches zero dispersionover a range of signal wavelengths intended for transmission.

Description

CONTROLLED FIBERS IN THE DISPERSION OF MULTIPLE NUCLEI AND MULTIPLE MODES TECHNICAL FIELD 5 This application is based on the provisional application number of sene 60 / 100,495, filed on September 16, 1998, which is claimed as the priority date of this application. Optical signals traveling in typical fiber-optic media experience small changes, which over a distance may result in a significant loss of signal quality. One such change involves chromatic dispersion. The fiber controlled in the dispersion possesses positive and negative dispersion characteristics, which are mixed to produce an offset average in its length close to zero dispersion.

BACKGROUND OF THE INVENTION The chromatic dispersion varies along the waveguides in function of the material and structure of the waveguides, as well as the wavelength of the signal. Zero dispersion is possible at particular wavelengths, but zero dispersion is also associated with phenomena known as "four-wave mixture" that produces diaphhoty in ^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^ Adjacent wavelength channels. A mixture of four waves is very pronounced in the zero dispersion, but it also increases with the optical energy and the spacing of small channels. Both the chromatic dispersion and the mixture of four waves in the fiber controlled in the dispersion that combines lengths of positive and negative dispersion fibers (calculated at wavelengths intended for transmission) are avoided. The mixing of four waves is avoided because only the non-zero dispersion fiber is used. Chromatic dispersion is avoided because a compensated average in the lengths of the positive and negative dispersions is close to zero. One such approach employs positive dispersion fiber to transmit optical signals over distances and dispersion compensating modules containing rolls of negatively dispersed fibers to periodically interrupt the positive dispersion fiber, to reduce the average dispersion of the path. combined optics However, the compensation modules reduce the signal strength without advancing the signals to their desired destination. End-to-end positive and negative dispersion fiber lengths have been spliced to more efficiently transmit 20 optical lengths with reduced chromatic dispersion. However, graphic representation is required to follow the course of the dispersion characteristics of the combined fiber and two different fibers must be kept in inventory. g ___? _ ^ __? __________ l_ ^ r "-? -" * '-! * es ^ - ^ ~ - "• - - - ^ • * £ * fe * - * ~ - * *. * ...» ~ & Controlled fibers in the dispersion have also been made in continuous lengths with alternating sections having scattering signs opposite wavelengths intended for transmission. Only one fiber should be inventoried, but the dispersion period 5 (ie the length over which the two sections are repeated) must be chosen at the time of manufacture and is not subject to subsequent change. Pollution can also enter the fiber in interfaces between the sections, which must be polished separately and assembled before being stretched to their final shape. The cables controlled in the dispersion contain one or more pairs of fibers that have opposite scatter signs. Sections of the cables are spliced together so that the positive dispersion fibers of a section are attached to the negative dispersion fibers of the adjacent section. Again, the graphic representation of the dispersion is needed to follow the course of the section lengths and the design of the individual fibers is limited because the scatters of opposite signs must be of equal magnitude to the transmitted wavelengths.

BRIEF DESCRIPTION OF THE INVENTION The invention includes various modalities of fiber-optic systems that compensate for chromatic dispersion and prevent the mixing of four waves, while minimizing fiber inventories and providing more flexibility in the design and performance of the fibers. They are also possible shorter dispersion periods (ie durations in which dispersion changes are repeated) without complicating manufacturing and additional dispersion options after fabrication. One embodiment is a fiber optic compensated dispersion system that includes a single optical fiber having a plurality of continuous optical paths with different scattering characteristics for conducting optical signals. One of the optical paths exhibits a positive dispersion at a central wavelength of the optical signals and other of the optical paths exhibits negative dispersion at the longitude of the optical wavelengths. a central optical signals. A coupling mechanism changes the optical signals between portions that travel forward of the two paths producing an average dispersion compensated in their length that approaches zero at the central wavelength of the optical signals. Preferably, both the dispersion and the slope are equated of dispersion (eg equal but with opposite signs) at the central wavelength, so that the average dispersion through a whole range of wavelengths also remains close to the zero dispersion. The continuous optical paths can be extended parallel or concentrically one or the other; and beyond the presence of any intrusive coupling structures, the change of the optical signals between the trajectories does not require the interruption of any of the two trajectories. For example, a single fiber can be constructed with a plurality of cores . jpJwgnfeB-bfa- -rá .. '? íí | ^^ * j3i ^ &«i tfí i * ^^^^ _ ^ surrounded by coating. Each of these nuclei forms one of the optical paths with different dispersion characteristics. The signals between the cores can be positively changed, designing a coupling mechanism as one or more long period graticules. The coupling mechanism can also be designed as a consequence of the spacing of the cores, placing the cores sufficiently close together to support the signal transfers. This last coupling mode requires symmetric dispersion characteristics between the cores and has a dispersion period equal to the coupling duration between the cores. The first coupling mode allows more flexibility in the dispersion characteristics of the cores, changing the signals between the cores at unequal intervals. Regardless of the coupling mode, the dispersion variants of the positive and negative dispersion cores (eg low magnitudes and opposite signs) are preferably equated, so that the resulting average dispersion remains close to 0 behind any desired range of wavelengths of the signals. Another embodiment includes fiber segments having one or more pairs of cores that have opposite sign scattering characteristics. The end-to-end segments are spliced together with a positive dispersion core of one segment aligned with the negative dispersion core of the other segment. Segment lengths are chosen to achieve a compensated average in the length close to dispersion 0. Both cores of each pair can be used to transmit signals in parallel, equaling the lute magnitudes of the positive and negative dispersions and aligning the nuclei to dispersion both positive and negative in a segment within the opposite counterparts in adjacent segments. Multiple walls of positive and negative dispersion cores can be arranged separately to support the transmission of more than one speed or application bit. Further flexibility in the graphical representation of the dispersion is also possible, by controlling the angular separation between adjacent sections to align various combinations of cores having characteristics of dispersion that differ. The single fiber can also be constructed as a multi-mode fiber having a fundamental mode trajectory and a higher order mode trajectory with different dispersion values to form concentric optical paths with dispersion characteristics different. The coupling mechanism of this additional embodiment includes one or more mode couplers, which can also be designed as tapered couplings or long-period gratings, to change the optical signals between fundamentally higher order paths. The fundamental mode can be arranged to exhibit positive dispersion and the higher order mode can be arranged to exhibit a higher magnitude of negative dispersion. In accordance with the above, the mode couplers of this arrangement are placed to change the optical signals to the fundamental mode during longer intervals than the higher order modes. However, with the appropriate design of the core profiles and the selection of the normalized frequency, the dispersion and the dispersion slopes of the fundamental and second order modes, equal but with opposite signs, can be made. Also, a better restriction of signals to normalized frequency values far from the mode cutoff values is possible. Multiple connectors can be used to pass signals transmitted in multi-core or multi-mode fiber to a fiber of unique and single-core mode. For example, optical grids can be used to change an optical signal from one core to another that is aligned with the single-mode and single-core fiber or higher to the fundamental mode for additional transmission of the single-mode fiber. and single core. Taper couplings can also be used to drive the signals to a single core or to a fundamental mode. In addition, single-core and single-core separated fibers can be joined to different cores of a multi-core fiber and a switch can be used to further transmit signals from one of the fibers joined to a common single-core and single-core fiber. . The fiber can be used in multiple ways with conventional methods taking into consideration the dispersion characteristics of the modes. Fiber can be made from multiple cores by assembling two or more core rods into a preform before stretching conventionally the fiber. Several depositions of tubes or rods can be used to align and space the core rods and an overcoat of carbon black can be consolidated around the core structures to seal the structures within the preform.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1A is a substantially enlarged end view of a multi-core optical fiber having two decentralized cores 10 with different scattering characteristics. Figure 1B is a similarly enlarged end view of another optical fiber optical core having a centered core and an offset core with different dispersion characteristics. Figure 1C is a similarly enlarged end view of another multi-core optical fiber having two concentric cores with different scattering characteristics. Figure 2 is a less enlarged side view, showing two segments segmented fiber multicore relatively rotated and spliced together. Figures 3A and 3B contain profiles of refractive indexes of the two cores of the multi-core fiber with a refractive index plotted as a function of the core radius "r".

Figures 3E-3F contain alternative profiles of refractive indices that are particularly suitable for achieving relative dispersion. Figure 4 is another side view of the multi-core fiber 5 schematically modified to include a grid of long periods to optically couple the two cores. Figure 5 is a substantially enlarged end view of a multi-core fiber having four cores - two with positive scattering characteristics and two with negative scattering characteristics. Figure 6 is a side view of a tapered coupling for connecting two cores of the multi-core fiber of Figure 1A to a conventional single core fiber. Figure 7 is a side view of a coupling that exchanges 15 signals between the two core cores of the multi-core fiber cores and one connector that links one of the two cores of the multi-core fiber to the core of the fiber conventional single core. Figure 8 is a side view of a multi-mode fiber having a succession of long-period gratings for changing signals 20 between modes having different scattering characteristics. Figure 9 is a graph of the standardized propagation constant "bn" graph with respect to the normalized frequency "V" of the multi-mode fiber exemplified by a step profile core design. Figure 10 is a graph of the normalized waveguide dispersion "dn" plotted with respect to the normalized frequency "V" of the waveguide for the same pitch profile core design. Figure 11 is a substantially enlarged end view of a preform that supports two core rods inside a barreled rod. Figure 12 is a similarly sized end view of a preform that supports two core rods within a tube. Figure 13 is a similarly sized end view of two core rods fixed together by a specially shaped rod. Figure 14 is another similarly sized end view showing two core rods fixed together before melting the preform around the two cores.

DETAILED DESCRIPTION OF THE INVENTION A multi-core optical fiber 10 shown in FIG. 1A has a positive dispersion core 12 and a negative dispersion core 14 surrounded by a coating 16. Reference dispersions of opposite signs of the two cores 12 and 14 are referred to at the central wavelength of a range of wavelengths (typically corresponding to the erbium amplification window) intended for fiber transmission 10. For the control of the dispersion over a wavelength range of 1530 nm to 1560 nm, the positive core similar to a SMF 1528 fiber can be designed and can be Design the negative core similar to a product of 5 1585 LS or sheet. Both fibers are obtainable from Corning Incorporated, Corning, New York. For other wavelength ranges, different types of known core designs can be used, as will be described shortly. The two cores 12 and 14 extend parallel to an optical axis 10 of the fiber 10 and are separated by a distance "S" which can be adjusted either to avoid or promote automatic coupling between cores 12 and 14. As shown in FIG. sample, the distance "S" is, presumably, large enough to avoid automatic coupling. During fabrication, the core rods with core coating ratios of 0.4 or more are spaced apart generally sufficiently apart to provide the required insulation. An optional notch 20 in a periphery of the fiber 10 provides a reference point for angularly indexing portions fed from the fiber 10. In FIG. 2, two segmented sections 10A and 10B of the originally continuous fiber 20 are aligned axially and rotated relatively around their aligned axes 18A and 18B before being spliced together, for example with splicers designed for fibers that maintain polarization. The amount of rotation is selected to align the core of ^^^^^^^^^^^^^^? ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^ Positive dispersion 12A of the fiber segment 10A with the negative dispersion core 14B of the segment delibra 10B. In addition, the design symmetry can also allow the simultaneous alignment of the negative scattering core 14A of the figure segment 10A with the positive scattering core 12B of the segment of FIG. 10B. The segments 10A and 10B can be adjusted in length, such that the average dispersion along the combined length of the two segments 10A and 10B as well as along any pairs of successive segments, approaches the zero dispersion. . If the two cores 12A, 14A and 12B, 14B of each segment 10A and 10B are used to conduct different signals, then the positive and negative dispersions of the two cores must be equal in magnitude and the two segments 10A and 10B must be equal in size. length. However, if only one of the cores in each segment carries signals (eg core 12A of segment 10A and core 14B of segment 10B), the dispersions of the two cores can then be optimized at different magnitudes and different length segments can be combined to achieve an average dispersion approaching zero. The dispersion slopes of the two cores are also preferably equated, in order to maintain an average dispersion approaching zero over the entire range of wavelengths intended for transmission. Instead of splicing segmented sections of the fiber 10 to alternate the optical path between the positive and negative dispersion cores 12 and 14, passive or active coupling between stretches can be provided. -_-_- á__iii ____ i _____ ¿__ ^^ progressive nuclei 12 and 14. It can be done in passive coupling by reducing the separation "S" between the nuclei, so that energy transfers occur between the nuclei in a period of desired dispersion, which is equal to the coupling duration. The positive and negative dispersions of nuclei 12 and 14 must be symmetric around the central wavelength (ie equal in magnitude), because the signals consume half of their time in each of nuclei 12 and 14. Also, the propagation constants between two cores 12 and 14 considered in isolation should be as close as possible to support more complete energy transfers. The coupling length is determined by the difference of the propagation constants of the two supermodes of the smallest order of the mixed waveguides and can be designed to be achromatic or chromatic. Figures 3A and 3B illustrate index profiles of positive and negative dispersion cores 12 and 14 modified to equal an effective index "n (ef)" between the two cores 12 and 14. The positive dispersion core 12 has a profile of simple step (Ge? 2-Si? 2 core with SiO2 coating) and an effective index "n (ef)" sized between core and coating values. The negative dispersion core 14 has a "w-type" or segmented core (SEGCOR) profile design with some slight upward doping of the coating to match the "n (ef)" effective index of the positive dispersion core 12. For example, the doped coating may be composed of Ge? 2-SiO2 or TiO2-SiO2. (Note: the line of stroke of Figure 3B represents the index level of the surrounding silica cladding 16). Generally, more complex profile shapes are required to produce the negative dispersion and an opposite dispersion to that of a core with positive dispersion. Four more examples are shown in Figures 3C-3F, each capable of withstanding the negative dispersion without unduly compromising other optical properties, such as the effective area, the mode field diameter, the flexion and the microflexion. The arrows that cross the profile lines indicate design flexibilities to alter individual line segments of the profiles. The profile of Figure 3C can be used to achieve either positive or negative dispersions with positive or negative dispersion slopes. The 3D figure design is particularly useful for achieving positive or negative dispersions with relatively large effective areas. The last two designs, figures 3E and 3F, can also be considered for the control of dispersion with low loss manufacturing. The active coupling between the nuclei 12 and 14 can be effected, forming one or more long period gratings 24 between the nuclei, as shown in figure 4. The coupling function is localized, so that the two can be independently designed nuclei 12 and 1. For example, the scattering magnitudes of the core and the propagation constants between cores 12 and 14 may vary. The spacing between the gratings 24 can be adjusted to compensate for the different magnitudes of the dispersions of the core, so that the average compensated in the longitude still approaches the zero dispersion. The long period tapers 24 can be used to increase the coupling function. The long-period gratings 24 can be formed with photosensitive core materials that are exposed to an actinic retention pattern to produce index disturbances in the fiber 10. The coating area between the cores 12 and 14 can also be photorefrigerant to enhance the coupling function. You can enter information in the long period grid 24 with a high power excimer laser during a fiber stretching operation. The dispersion periods can be considerably small and numerous, because the coupling mechanisms do not add contamination to the fiber 10. The accuracy of the grid is not very critical, because the band of The required spectral response is considerably wide and the long-period gratings typically have periods in the order of a few microns. Also, the magnitudes of the index disturbances can be considerably low (avoiding the need for hydrogen loading) because the long-period grid 24 can occupy a distance relatively large (for example one or two meters) along the fiber 10 without detrimental effects. You can write information on index disturbances or one point at a time or several points at a time, especially at higher traction speeds. You could write information also in perturbations of indexes or bends with a high-power CO2 laser during the traction operation to effect a similar coupling function. Other perforations can be used to form similar gratings including stress-induced variations, periodically compressing the fiber or by length variations in periodic trajectory by periodic microflexion. Additional information on long period gratings and mode couplers can be found in a document entitled "Long-Period Fiber Gratings as Band-Rejection Filters" by Vengsarkar et al., Published in the Journal of Lightwave Technology, Vol. 14, No. 1, January 1996, pages 58-65, and in another document entitled "Helical-Grating Two-Mode fiber Spatial-Mode Coupler" by Poole et al., Also published in the Journal of Lightwave Technology, vol. 9, No. 5, May 1991, pages 598-604. Both documents are hereby incorporated by reference. More than two cores can be formed into a single fiber, as shown in Figure 5. Two positive dispersion cores 32 and 34 and two negative dispersion cores 36 and 38 of a fiber 30 are surrounded by a common coating 40. they can pair the nuclei 32-38 into groups of positive and negative scattering cores (for example 32, 36 and 34, 38) and the paired cores can be optimized in terms of speeds or application of individual bits. Alternatively, the pareos can be varied to provide more flexibility for the graphic representation of the dispersion by varying the angular indexing between adjacent sections of the fiber 30. In ^^^^^^^^^^^^^^^^^^^^ Other words, the same fiber 30 can be used to support a plurality of different graphic dispersion displays. A simulated core 44 provides a reference point for angularly indexing the fiber 30 about an optical axis 46. 5 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 can cause dispersion problems of polarization mode. 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 or the cores 32, 34, 10 36 and 38 of the fiber 30 can be surrounded by individual coating zones to optimize the performance of the separated optical paths through a fiber 30. When connecting conventional single or similar fiber waveguide structures such as in-line amplifying stations or at link ends, the two cores of each pareo are related to a single core of the conventional waveguide. Figure 6 depicts a tapered coupling 60 connecting the controlled fiber 10 in the dispersion to a conventional single-mode fiber 70. Two waveguides 62 and 64 are aligned with the positive dispersion 20 and negative 12 and 14 fiber cores. 10, but only the waveguide 64 is aligned with a single core 66 of the conventional fiber 70. Within the coupling, the two waveguides 62 and 64 are tapered together to transfer energy to the waveguide 64. __________ a_É ____ g -.A ^ - AB --_. ..-. ^. ¿_. ¿. ^ _ ^ T __ ^ _. ^ _ A___ ^^ ^ ^ ^^ The long-period grid 24 can also be used in place of the tapered coupling 60 as shown in Fig. 7 to direct optical signals to the appropriate core (for example to the core 12) before interconnecting with the conventional fiber 70. The core 66 of the conventional fiber 5 is aligned with the core 14 of the fiber controlled in the dispersion 10 to receive optical signals propagating along the controlled fiber in the dispersion 10. A groove substrate V 72 supports the desired alignment between the fibers 10 and 70. The conventional fiber 70 may be aligned with either of the two cores 12 or 14 of the fiber controlled in the dispersion 10 or each of the cores 12 and 14 may be aligned with a separate conventional fiber. In the last case, an optical switch (not shown) can be used to alternately connect the separated conventional fibers to a single conventional fiber. The switch can be controlled with a sensor 15 that detects the presence or absence of a signal in either of the two separate conventional fibers. Figure 1B depicts an alternative fiber 10 'having two similar cores 12' and 14 'embedded with a common coating 16'. In contrast to the core 12 of the fiber 10 (shown in Figure 1A), the core 20 12 'is centered along the optical axis 18' of the alternative fiber 10 '. The other core 14 'is offset from the axis 18'. The 12 'centered core is easier to align with the typical fiber cores. However, the end-to-end splicing of the ^^^^^^^ r ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ A ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ sections of the alternating fiber 10 'to change the signals between the centered core 12' and the core 14 'centering is more difficult. According to the above, the signal transfers between the cores 12 'and 14' preferably take place by lateral coupling. Before any end-to-end connections 5, the signals are preferably changed to the central core 12 ', for example by tapering the fiber 10', or by using a tapered coupling as shown in FIG. 6. Instead of centering only one of the nuclei 12 'around the optical axis 18', figure 1C shows another alternative fiber 10"that has god 12"and 14" cores centered around an optical axis 18"in a concentric pattern Side couplers can be used to change signals between the concentric 12" and 14"cores Fiber 10" with concentric cores 12"and 14" They exhibit less birefringence and are easier to manufacture using conventional manufacturing techniques. Concentric cores can also be used additional or concentric nuclei in combination with decentered nuclei. Another approach to dispersion control in optical fibers is shown in Figure 8. An optical fiber of multiple modes is shown 80 having a central core 82 and a surrounding cladding 84 to support more than one mode of optical transmission. A mode, such as a mode fundamental, exhibits positive dispersion; and another mode, such as a second order mode, exhibits negative dispersion. Information is inputted into the long-period gratings 86 in the fiber 80 along the optical axis 88 in a repeating pattern that regulates the relative duration of the optical signals in each ^^^^^^ _ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^ a ^^^^ _ ^^^ one of the modes, so that the average dispersion compensated in the length approaches 0. Consistent with the representation in figure 8, a negative dispersion of the second order mode has a magnitude greater than a positive dispersion in a fundamental way. Accordingly, the spacing LF which measures the path length between the gratings 86 in the fundamental mode is greater than a spacing LH which measures the path length between the lattices 86 in the second order mode. Other combinations are possible, including dispersions of opposite signs of equal magnitude between two operating poles. Equally spaced grids can be used to uniformly distribute the optical path lengths between the two different modes. Also, modes of higher order than the second can be used for procedures such as dispersion of reduction polarization mode. The reticles can change the signals to the third order and higher modes, and from them, but the unwanted losses to the intervening modes can limit the utility of the higher order modes. Figures 8 and 9 plot the exemplary performance of the multimode fiber 80 considered with a pitch index profile core. In Figure 8, a normalized propagation constant "bn" is plotted against the normalized frequency "V", which can be defined mathematically as follows: ^^^ * ^ ^ Hg "^^^^^^^^^^^^^^^^^^^^^^^ / K - n2 2pa rl _ ~ n, -«, where "ß" is the propagation constant, "nT is the core index, W is the coating index,"? "is the central wavelength of a range, and" k "is the constant p /? "a" is the core ray of the waveguide.The normalized propagation constant, which is related to "n (ef)", varies between "0" and "1", with "0" representing the propagation entirely in the coating and representing "1" propagation entirely in the nucleus.

The propagations that take place more in the core are more tightly bound than the propagations that take place more in the coating. The "V" value of the normalized frequency has an inverse relationship with the central wavelength "?". The curves LPo., LP-n, and LP02 represent the modes of fundamental order, second and third, respectively. According to the exemplary graph of Figure 9, a normalized frequency greater than 2.4 is required to support more than one mode; but an even greater value is needed in the vicinity of 3.5 to properly restrict the signal for most practical applications. As shown in Figure 10, the normalized frequency of about 3.5 also provides an operating region with waveguide normalized scatter of opposite signs "Dn", which is defined empirically as follows: Vd2Vb. D. = dV2 although the normalized frequencies of less than 3.5 provide the possibility of much higher dispersion, the signal restriction of second order mode is reduced. The operation from the cutting of the second order mode (ie significantly greater than V = 2.4) reduces the losses of flexion and microflexion and the polarization division as well. Periodic or continuous twisting of the fiber 80 can also be used to reduce the polarization mode dispersion.

The waveguide dispersion "D" measured in units ps / km nm can be calculated as follows: c? where "?" It is a relative difference of indexes. The guide dispersion of "D" waves have the opposite sign to the standardized waveguide dispersion "Dn", so that the waveguide dispersion of the fundamental mode "LP01" is positive and the waveguide dispersion of the second order mode "LPn" is negative. At normalized frequencies greater than 2.4, the waveguide dispersion "D" for the fundamental mode LP01 of the pitch index fiber is considerably low, so that any significant chromatic dispersion is mainly attributable to the dispersion of material. In the 1550 nm window, the chromatic dispersion of the fundamental mode for ______ £ M1 £ ?? O3? -------: -: ?? __ [_? _-- r__i __ ^^ - • "•" "* '^^^^^ the index fiber of step is limited to around 17-20 ps / km nm However, complex core profile designs including segmented core and ring profiles can be used to produce higher dispersion values. Core designs are also selected. between the positive and negative dispersion cores, to properly relate the dispersion slope, so that the average dispersion remains close to 0 across a whole range of wavelengths of signals. However, multiple-mode and multi-core designs can be combined within individual fibers to provide even greater control over dispersion, while other design criteria are also optimized. For example, you can forming either or both cores 12 and 14 of the fiber 10 depicted in Figure 1A or the other cores depicted in Figures 1 B and 1C, as multi-mode cores and the dispersion requirements between modes and cores could be divided. Conventional manufacturing techniques can be used to produce the multimode fiber 80 and photorefrigerative techniques similar to those described above for multi-core fibers can be used to input information into the grid. Although long period gratings 86 are preferred for mode coupling, other patterns and forms of disturbances can also be used, "_ *"? T -_ .. '_. ^^ mm ^^^ jlg ^., ^^ ^^^^^^^^^ including variations in diameter, to change signals between different modes. Remaining figures of the drawings, Figures 11-14, illustrate various preforms (also referred to as "blanks") for manufacturing the multi-core optical fibers described above, using various rod-in-tube and OVD techniques (Optical vapor deposition) developed for polarization retention fibers A fiber preform 90 shown in Figure 11 has a rod 92 which is drilled to receive two glass core rods 94 and 96. The rod 92 is made of a Coating material and the two glass core rods 94 and 96 include core and coating materials applied in sequence by optical vapor deposition in distributions of index profiles that produce different dispersion characteristics. 98, q which is also made of the coating material, to the outside of the rod and is consolidated to complete the preform 90. A multi-core fiber stretched to the preform has at least two cores extending parallel to each other and exhibiting characteristics of different dispersion. A fiber preform 100 shown in Figure 12 has two glass core rods 102 and 104 and two filling rods 106 and 108 mounted within a tube 110., and a consolidatable carbon black 112 surrounds the tube 110. The two core rods 102 and 104 have core and sheath distributions that support different dispersion characteristics. The filling rods 106 and 108, the tube 110 and the carbon black 112 are entirely made of coating materials that Sé form together with the core rods 102 and 104 to complete the preform. Figure 13 depicts a preform 120 including a specially formed rod 114 of facing material that supports two core rods 116 and 118 with different dispersion characteristics. A consolidatable carbon black 122, which is also made of a coating material, surrounds the rod 114 and the two core rods 116 and 118. The two core rods 116 and 118 can be attached to the rod 114 to support the two core rods in desired relative positions until the preform 120 is consolidated. The preform 130, as shown in Figure 14, includes two core rods 132 and 134 that are joined together and surrounded by a consolidatable carbon black 136 The core rods 132 and 134 have different dispersion characteristics and index profiles that can either promote or prevent automatic coupling between the stretched eventual cores of the preform 130. The carbon black overcoats 98, 112, 122 and 136 they contract during the consolidation producing axial as well as radial forces that seal the components inside the preforms 90, 100, 120 and 130. During the subsequent traction procedure However, photorefrigeration techniques can be used to produce couplings between the cores and polarization mode reduction techniques can be used to compensate the coating asymmetries that surround the nuclei. Index marks may be formed on the periphery of the preforms or filler rods made of distinguishable coating materials may be mounted at observable positions to provide angular reference points. The twin-core rods 94-96, 102-104, 116-118 and 132- 134 within the four preforms have opposite sign dispersions with equal or unequal absolute magnitudes. Coupling either periodic or continuous can be used to achieve a mean dispersion mediated in length approaching zero for dispersions of equal magnitudes. However, dispersions of unequal magnitudes require periodic couplings that cause the unequal lengths of displacement in the different scattering cores to achieve the same average dispersion compensated by the length approaching zero.

Claims (80)

1. NOVELTY - IT INVENTION CLAIMS 1. - A multi-core fiber for controlling chromatic dispersion, comprising: a plurality of cores surrounded by a coating; said cores having a refractive index different from said coating for conducting optical signals; and exhibiting sayings 10 nuclei a difference of the dispersion values between said nuclei.
2. 2. The fiber according to claim 1, further characterized in that one of said cores exhibits a positive dispersion value and another of said cores exhibits a negative dispersion value.
3. 3. The fiber according to claim 2, further characterized in that said cores also exhibit positive and negative dispersion slopes.
4. 4. The fiber according to claim 2, further characterized in that the positive and negative dispersion values are symmetrical around a central wavelength of the optical signals.
5. 5. The fiber according to claim 4, further characterized in that said cores are located sufficiently close together to support the coupling between the cores. 6. - The confosppraad fiber with claim 5, further characterized in that the propagation constants between said cores are approximately equal. 7. The fiber conformed with claim 1, further characterized in that one of said cores is a multi-mode core. 8. The fiber according to claim 7, further characterized in that said multi-mode core includes a first mode exhibiting a positive dispersion and a second mode exhibiting a negative dispersion. 9. The fiber according to claim 1, further characterized in that said cores are spaced sufficiently apart from one another to avoid coupling between said cores. 10. The fiber according to claim 9, further characterized in that the fiber also includes portions that are tapered to promote the transfer of the optical signals between said cores. 11. The fiber according to claim 9, further characterized in that disturbances are formed in said cores to promote the transfer of the optical signals between said cores. 12. The fiber according to claim 11, further characterized in that said disturbances are also formed in a coating region between said cores to facilitate coupling between said cores. 13. - The fiber according to claim 11, further characterized in that said disturbances are arranged to form a plurality of optical gratings for transferring optical energy between said cores. 14. The fiber according to claim 11, further characterized in that said disturbances are arranged to change the optical signals between said cores in a pattern that produces an average dispersion compensated in the length approaching zero at a central wavelength of optical signals. 15. The fiber according to claim 11, further characterized in that fiber taper is used together with said disturbances to promote the transfer of the optical signals between said cores. 16. The fiber according to claim 1, further characterized in that said fiber is divided into two sections that are rotated relative to each other and are joined together in relatively rotated positions to align a first pair of said cores that They exhibit different dispersion values. 17. The fiber according to claim 16, further characterized in that said two fiber sections are relatively rotatable to another angular position to align a second pair of said cores that exhibit different dispersion values. 18. - The fiber according to claim 17, further characterized in that said first pair of cores is optimized for a first bit rate and said second pair of cores is optimized for a second bit rate. 19. The fiber according to claim 1, further comprises a fiber interface for connecting one of said plurality of cores that is not centered within said sheath with a core of an attached fiber that is centered within a sheath. 20. The fiber according to claim 1, further characterized in that said fiber is twisted at least periodically to avoid polarization mode dispersion. 21. The fiber according to claim 1, further comprising a coupling mechanism that transfers the optical signals between progressive portions of said cores, providing an average dispersion compensated in the length approaching zero at a central wavelength. of optical signals. 22. The fiber according to claim 21, further characterized in that said cores exhibit dispersion slopes that are relatively equal, so that the average dispersion compensated in the length approaches zero for a range of wavelengths of the signals optical 23.- A multi-mode fiber to control chromatic dispersion, comprising: a core surrounded by a coating that supports multimodal transmissions of light along an optical axis; a first path along said optical axis having a first dispersion value; a second path along said optical axis having a second dispersion value; said first and second dispersion values differing from one another; and a plurality of mode couplers along the optical axis for coupling light in either direction between said first and second mode trajectories. 24. The fiber according to claim 23, further characterized in that said first mode trajectory is a path of fundamental mode having a positive dispersion value. 25. The fiber according to claim 24, further characterized in that said second mode path is a higher order mode having a negative dispersion value. 26. The fiber according to claim 23, further characterized in that said dispersion values between the first and the second mode trajectories have opposite signs and unequal absolute magnitudes. 27. The fiber according to claim 26, further characterized in that the light coupling between said first and second mode trajectories takes place at unequal trajectory lengths to compensate for the unequal absolute magnitudes of the scattering values. »^ ^^ tó ^^^^ g & ^^^^^^^^^^^^^^^^^^^^ 28. - The fiber according to claim 23, further characterized in that said dispersion values between the first and the second mode trajectories have opposite signs and approximately equal magnitudes. 29. The fiber according to claim 23, further characterized in that said mode couplers are formed with index perturbations. 30. The fiber according to claim 29, further characterized in that said index perturbations form a grid of long periods. 31. The fiber according to claim 23, further characterized in that said couplers are formed at least in part with tapered portions of the fiber. 32. The fiber according to claim 23, further characterized in that said couplers are spaced so as to produce an average dispersion compensated in the length approaching zero at a central wavelength of the light transmissions. 33.- The fiber according to claim 32, further characterized in that said first and second mode trajectories exhibit dispersion slopes that are relatively equal, so that the average dispersion compensated in the length approaches zero for a range of lengths wave of light transmissions. ^ bHM ÜÜi 34. - A fiber-optic compensated system in the dispersion, comprising: a first multi-core fiber section having a first core exhibiting a positive dispersion value and a second core exhibiting a negative dispersion value; a second section of 5-core fiber having a core exhibiting a positive dispersion value and a second core exhibiting a negative dispersion value; and an optical interface between said first and second multi-core fiber sections aligning said first core of the first fiber section with said second core of the second fiber section, to control an average dispersion along the combined length of the second fiber section. said fiber sections. 35.- An optical system according to claim 34, further characterized in that said first and second cores of each of the first and second fiber sections are sufficiently 15 spaced apart to avoid undesirable coupling between said first and second cores. 36.- An optical system according to claim 34, further characterized in that said second core of the first fiber section is aligned with said first core of the second fiber section, 20 to control the average dispersion. 37.- An optical system according to claim 36, further characterized in that said second core of the first fiber section and said first core of the second fiber section exhibit slopes ^ jIj j ^ ¡¡: Lj ^. ..., ___ ^ - ,. ^ -. . . | 3_ .. | ...? j? j & amp; & amp; & 8 dispersion which are equated so that the average dispersion along a combined length of said fiber sections approaches zero for a range of wavelengths transmitted through the combined fiber sections. 38.- An optical system according to claim 34, further characterized in that said first and second fiber sections of multiple cores also have third cores that exhibit positive dispersion values and a fourth core that exhibits negative dispersion values. 39.- An optical system according to claim 38, further characterized in that said first core of the first fiber section is aligned with said second core of the second fiber section, to complete the first optical path between said optimized fiber sections. for transmissions at a first bit rate and said third core of the first fiber section is alignable with said fourth core of the second fiber section for transmitting optical signals at a second bit rate. 40.- An optical system according to claim 38, further characterized in that said first and third cores of said first fiber section are separately aligned with said second core of the second fiber section, to provide different dispersion compensations. 41. - An optical system according to claim 40, and further characterized in that said first and third cores of said first fiber section are also separately aligned with said fourth core of the second fiber section to provide more dispersion compensation choices. 42. An optical system according to claim 34, further characterized in that index marks are applied to the fiber sections to aid the desired angular indexing between the fiber sections at the optical interface. 43. An optical system according to claim 34, further characterized in that splicers designed for fibers that maintain polarization provide said optical interface. 44. An optical system according to claim 34, further characterized in that said first and second fiber sections are substantially identical sections that originate from the same fiber. 45.- A fiber-optic system compensated in the dispersion, comprising: a fiber of multiple modes having a trajectory of fundamental mode and a trajectory of higher order mode with different dispersion values; a plurality of mode couplers along the optical axis of the fiber that changes optical signals in one direction and another between said paths in fundamental ways and of higher order; an optical system component aligned with the optical axis of the fiber to further conduct the optical signals; and one of said A * - mode couplers to direct the optical signals to one of the mode paths in an interface with the system component. 46. The system according to claim 45, further characterized in that said fundamentally mode trajectory has a positive dispersion value and said higher order mode trajectory has a negative dispersion value. 47.- The system according to claim 46, further characterized in that said negative dispersion value has a magnitude higher than said positive dispersion value. 48. The system according to claim 47, further characterized in that said mode couplers change the optical signals between said fundamental mode path and said higher order mode path at unequal intervals between the mode trajectories. 49. The system according to claim 45, further characterized in that said coupler directs the optical signals to said path in a fundamental manner in anticipation of said optical system component. 50.- The system according to claim 45, further characterized in that said optical system component is an optical amplifier and said coupler in a way directs the optical signals to said higher order mode path following said optical amplifier. 51. The system according to claim 45, further characterized in that said mode couplers include disturbances of indices along the optical axis to transfer optical signals between said mode trajectories. 52. A fiberoptic system compensated in the dispersion, comprising: a single optical fiber having a plurality of continuous optical paths with different scattering characteristics for conducting optical signals; a first of said optical paths displaying a positive dispersion at a central wavelength of the optical signals; a second of said optical paths exhibiting negative dispersion at the central wavelength of the optical signals; and a coupling mechanism that changes the optical signals between progressive portions of said first and second trajectories that produce a conventional average dispersion in the length approaching zero at the central wavelength of the optical signals. 53. The system according to claim 52, further characterized in that said first and second optical paths extend parallel to one another and said coupling mechanism changes the optical signals between parallel portions of said first and second trajectories. 54.- The system according to claim 53, further characterized in that said first and second optical trajectories . _ ^ A * a »_t * a ____ you are formed by a first and a second nucleus surrounded by a coating. The system according to claim 54, further characterized in that said single optical fiber has a central axis and said first core is aligned with said central axis and said second core is offset from said central axis. 56.- The system according to claim 54, further characterized in that said single optical fiber has a central axis and both the first and second cores are offset from said central axis. 57. The system according to claim 54, further characterized in that said first core is a multi-mode core having a first mode exhibiting positive dispersion and a second mode exhibiting negative dispersion. The system according to claim 54, further characterized in that said coupling mechanism includes a plurality of couplers that positively change the optical signals in one direction and another between said first and second cores. 59.- The system according to claim 58, further characterized in that said first and second cores exhibit dispersions of opposite signs and of different magnitudes to the central wavelength of the optical signals and said couplers are arranged ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^ * aJü -__ fca to change the signals between said first and second cores at unequal intervals. 60.- The system according to claim 54, further characterized in that said coupling mechanism is formed as a result of the placement of said first and second cores sufficiently close together to support the transfers of the optical signals between said core. 61.- The system according to claim 60, further characterized in that said first and second cores exhibit dispersions of opposite signs and of magnitudes approximately equal to the central wavelength of the optical signals. 62.- The system according to claim 52, further characterized in that said first and second optical paths extend concentrically to each other and said coupling mechanism changes the optical signals between concentric portions of said first and second trajectories. 63.- The system according to claim 62, further characterized in that said single fiber is a multi-mode fiber and said first and second optical paths are a fundamental mode trajectory and a higher order mode trajectory with dispersion values. different 64.- The system according to claim 63, further characterized in that said coupling mechanism includes a plurality of couplers so as to positively change the optical signals in one direction or another between said paths of fundamental and higher order. The system according to claim 63, further characterized in that said first and second cores exhibit dispersions of opposite signs and of magnitudes approximately equal to the central wavelength of the optical signals. 66.- The system according to claim 52, further characterized in that said coupling mechanism is formed by disturbances in said optical paths. 67.- The system according to claim 66, further characterized in that said coupling mechanism includes a plurality of optical reticles. 68.- The system according to claim 52, which further includes a third and a fourth optical paths with different dispersion characteristics to conduct optical signals. 69.- The system according to claim 68, further characterized in that said coupling mechanism includes couplers to change the optical signals between said first and second trajectories in a first dispersion period and couplers to change the optical signals between said third and fourth trajectories in a second dispersion period. ^ g ^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ S ^ ^ ^^^^^^^^^^^^^^ ^^^^^^^^^^ 70. - The system according to claim 52, further characterized in that said "first optical path exhibits a positive scattering slope and said second optical path exhibits a negative scattering slope. 71.- The system according to claim 52, further characterized in that said first and second optical paths exhibit scattering slopes approaching zero. 72.- A method of making a multi-core fiber to transmit optical signals with reduced chromatic dispersion, comprising the steps of: aligning at least two glass core rods having refractive index profiles that differ from one another; surround the glass core rods with a glass coating material; melting the surrounding coating material to the core rods to form a glass preform; and stretching a multi-core fiber of the preform having at least two cores extending parallel to each other and actuating different dispersion characteristics. 73. The method according to claim 72, further characterized in that the first of the nuclei exhibits positive dispersion and the second of the nuclei exhibits negative dispersion at a central wavelength of the optical signals. The method according to claim 72, further characterized in that said step of encircling includes applying the coating material as an optical black. ..a «afa ~ > - »> *. * A? 'Áü¡? BB ^ BB¡K & »K * ^ ^ te ^ M j-« Mf- ^ a-S 75. The method according to claim 72, further characterized in that said step of aligning includes aligning two core rods with a glass rod having a refractive index similar to that of the surrounding coating material. 76. The method according to claim 75, further characterized in that the glass rod supports the two core rods. The method according to claim 72, which includes the additional step of joining the two core rods together before surrounding them when the glass coating material. 78. The method according to claim 72, which includes the additional step of forming a coupling between the two cores. 79. The method according to claim 72, which includes the additional step of applying an index mark to provide an angular reference point on the fiber. 80.- A method of compensating the chromatic dispersion introduced to an optical signal that propagates along the optical row, comprising the steps of: directing the signal along the fiber, which is arranged to have two optical paths Parallel with characteristics to scatter of signs opposite a central length of the signal; and coupling the signal one way or the other between continuous portions of the two parallel paths of the fiber, so that the signal is arranged at a mean dispersion approaching zero dispersion. 81,. The method according to claim 80, further characterized in that said pad or coupling includes changing the signal between different cores of a multi-core fiber. 82. The method according to claim 80, further characterized in that said step of coupling includes changing the signal between different modes of a fiber of multiple modes. 83. The method according to claim 80, further characterized in that the step of coupling includes positively changing the signals between the two parallel paths at unequal intervals between the paths. 84. The method according to claim 80, further characterized in that said step of coupling includes arranging the parallel paths to conduct the signal of equal duration.