MXPA01002690A - Waveguides having axially varying structure - Google Patents

Abstract

An optical waveguide fiber preform and an optical waveguide fiber drawn therefrom, in which the density and thus the effective refractive indices of the clad layer (42) is caused to change in a pre-selected way axially along the waveguide preform and the associated waveguide fiber. The axial change in density of the clad layer (42) is due to the fraction of the clad volume that is air or a glass of a composition different from that of the base clad glass. The axially variation in clad indices changes the signal mode power distribution, thereby changing key waveguide fiber parameters such as magnitude and sign of dispersion, cut off wavelength and zero dispersion wavelength. The invention includes methods of making the structures having an axially varying clad layer. The invention also contemplates preforms, in which the waveguide fibers drawn therefrom, guide light due to the photonic crystal structure of all of the clad layer length or segments of the clad layer length.

Description

WAVE GUIDES THAT HAVE A STRUCTURE THAT WILL VARIABLE BACKGROUND OF THE INVENTION This request is based on the provisional application S.N. 60 / 100,349, filed on 9/15/98, which we claim as the priority date of this request. The invention is directed to an optical waveguide preform or fiber having a structure that varies in the axial direction. In particular, the new waveguide preform or waveguide exhibits a refractive index of the coating layer that varies along the length of the waveguide, the variation due to change in porosity or composition of the coating layer. The invention includes methods for making the new preform and wave guide fiber. Optical waveguide fibers having a periodically structured coating have been described. As an example, the periodic structure of the coating layer can be a photonic crystal as described by Knight et al., "All silica Single Mode Optical Fiber with Photonic Crystal Cladding", Optics Letters, V. 21, No. 19, October 1, 1996, and by Birks, et al., "Endlessly Single Mode Photonic Crystal Fiber", Optics Letters, V. 22, No. 13, July 1, 1997. In those two articles, a fiber is described. Unique mode that has a silica core and a porous silica coating. The pores or holes in the layer Bato- »m £ * Z. ' The silicone coating is elongated and extends from end to end of the coating layer.The pores are arranged in a periodic hexagonal pattern to form the coating layer in a photonic crystal The waveguide fiber configured in this way can be a single mode fiber at any wavelength Additional work with waveguide fibers having a porous or full coating layer pores are described in European Patent Publication EP 0 810 453 A1 In this publication, the coating layer contains elongated pores that serve to lower the average refractive index of the coating layer.The elongated pores are not arranged in a pattern periodic so that the light guide mechanism at this wavelength is refraction at the core-shell boundary.The essentially unlimited scale of wavelength cut, or, alternatively, The potential absence of any wavelength cut, available in a photonic crystal coating layer, is an advantage in the single-mode waveguide design. It is also useful, in terms of offering an additional design variable, the difference in relative refractive index,?, Due to a coating layer containing a particular volume of non-periodic pores. This volume is controlled by controlling the fraction of air filling in the fiber as described below.

However, none of these designs provides axial changes in relative refractive index. Such axial changes are advantageous in single-mode fiber design designed to provide dispersion handling.

In addition, because the axial changes in the refractive index are 7"due to changes in the coating layer, a new group of parameters is available, such as pore volume, pore cross section, and pore pattern, for altering the energy distribution mode in the waveguide and therefore altering key waveguide fiber properties The combinations of axial changes in coating structure with the numerous core index profile designs are contemplated which will provide unique properties of waveguide fiber Coating layers incorporating photonic crystal light guide and refractive light guide are contemplated as advantageous in waveguide designs for dispersion handling.In addition, the present invention incorporates layer structures of coating that contain a disposition of characteristics, distributed in a periodic or random manner, comprising a matepal instead of pores, which adds additional flexibility in waveguide fiber design.

BRIEF DESCRIPTION OF THE INVENTION The new preform and waveguide fiber and the method to manufacture the preform and wave guide fiber present provide vapables tfega¿ »A-. . ? & & amp; & & & & & amp; waveguide design extras and are advantageous in the manufacture of dispersion compensation or dispersion controlled waveguides. A first aspect of the invention is an optical waveguide fiber preform comprising a glass core region and a coating glass layer disposed on the core glass. For ease of description, the coating glass layer is said to be divided into segments that lie along the axis of the preform. The density of the coating glass changes in one direction, which is called the preform axis, parallel to the core region so that the core glass density changes from segment to segment from a higher value to a lower value or from one lower to one higher. That is, the respective adjacent segment densities are not a monotone function of axial position. The density of the coating layer of the preform can be made to alternate from high to low and from low to high in adjacent segments by changing the porosity of the coating layer. In particular, respective adjacent segments along the axis of the preform could alternate between a condition in which the coating layer contains pores and a condition in which the coating layer is essentially free of pores. In one embodiment of the new preform, the pores are elongated and arranged in a periodic arrangement that may have a passage, that is, a space between corresponding points in the pores. The step can be selected to lie on a number of different scales. For use in optical telecommunication wavelengths the preform step is advantageously selected such that in the fiber drawn from the preform the pitch is in the range of 0.4 μm to 20 μm. A typical outside diameter of the glass fiber is approximately 125 μm. The lower end of this scale provides a step in the stretched fiber 5 effective to form a photonic crystal in the scale of wavelengths of telecommunications signal. However, the applicants have verified that the formation of space or step in the scale of tens of microns can be advantageously used in the elaboration of a waveguide having an axially varying coating. Although it is established in the With an upper limit of 20 μm present, applicants contemplate the utility of even larger coating layer passage characteristics. The upper limit of the spacing characteristic or step is in fact a practical limit determined from the thickness of the coating layer. The applicant has discovered that the diameter of the pores elongated, as well as its passage is important to determine the properties of the waveguide fiber stretched from the preform. In a particular embodiment, the ratio of the pore diameter to pitch of the elongated pore arrangement is in the range of about 0.1 to 0.9. The core glass of the preform can have a wide scale of refractive index profiles. A refractive index profile of a region is the value of the refractive index, or relative refractive index,?, As a function of radial position across the region. The definitions of the refractive index profile, segmented profile,?, And alpha profile are known & M & amp; lSa in the art and can be found in the patent of E.U.A. 5,553,185, Antos et al. or the patent of E.U.A. 5,748,824, Smith, which are incorporated herein by reference. In this way the core region of the preform may have a stepped shape, a trapezoid shape, any of which may be rounded in acute curve changes, or an alpha profile shape. In addition, the core region can be segmented into two or more portions and each of the portions can take alternate profiles that are discussed above. The design of this core region in conjunction with the modulation of the coating layer determines the dispersion properties and other performance characteristics of the wave guide fiber. The refractive index of a base glass material, such as silica, can be changed by incorporating dopants such as germanium, alumina, phosphorus, titanium, boron, fluoro and the like. Rare earth dopants such as erbium, ytterbium, neodymium, thulium, or praseodymium can also be added to provide a preform, which can be stretched in an optical amplifier waveguide fiber. In another embodiment of the new preform, the coating density oscillates between two values from segment to segment along the axis of the preform. This balancing, together with the preselected core structure, determines the dispersion handling characteristics of the fiber, as discussed above. Here again, the density can be controlled by controlling the volume of porosity in the coating layer segments.

As an alternative, the density can be controlled by controlling the volume of an additive glass added to the glass of the base coat layer. The doping glass may appear as elongated filaments in the base glass of the coating. These filaments 5 can be arranged in a periodic pattern in analogy to the arrangement of the elongated pores discussed above. One can speak of filaments as elongated pores that are full, although it should be understood that the filaments can be formed using various methods known in the art. If it is desired that the filament-containing coating layer interact with the light in the manner of a photonic crystal having a full band gap, the size and spacing of the filament must be such as to accommodate a step in the scale of 0.4. μm at 5 μm, and, the respective dielectric constants of the matrix glass and the glass comprising the glass columns contained therein should differ by about a factor of three. Either a porous coating layer or a coating layer filled with filaments can guide light by refraction in the core coating interface, the refractive index of the core being higher than you might think as an average refractive index of 20 the structured coating layer. The preforms described above are manufactured for the purpose of stretching optical waveguide fibers therefrom. From • ^^^^ 3 ^^^^^^^^^^^^^^^^^^^^^^^^ Z ^^^^ ^ ^^^^^^ - = ¿ta tewg4 ^ h In this manner, the invention includes the optical waveguides that are stretched from the new preforms. A further aspect of the invention is a method for manufacturing the new preform from which a new waveguide is stretched. In a first method, a core preform is manufactured by any of several methods known in the art, including external and axial vapor deposition, and MCVD or plasma deposition techniques. The core portion of the preform is solid non-porous. Alternatively, the core preform can be a tube that has open ends and which is not altered in any way before the formation of the preform. This tube will collapse during the stretch step to form a homogenous or doped solid glass core region (if the tube is contaminated). A plurality of glass tubes are fabricated having an opening extending through the tube. The tubes are reduced in dimension by a number pre-selected from locations along the tubes and arranged around the centrally located core preform. Each of the tubes of reduced dimension is essentially identical to the other tubes of reduced dimension. The tubes can collapse totally or partially in the reduced dimensions locations. The arrangement of the tubes The reduced dimension around the centrally located core preform is a preform having axial variation in the density of the coating layer.

The tubes may have a circular shape or may be in the form of a polygon of 3 or more sides. The arrangement of tubes around the central core preform may be random or periodic, with the particular geometry selected depending on the type of signal and waveguide interaction 5, either refractive or photonic crystalline, which is desired at the core interface -coating. In the case of a coating layer having photonic crystal properties and a full band gap, the passage of the periodic arrangement of the tubes must be of the order of the wavelength of light signal carried in the waveguide . Instead of pores that are distributed intermittently along the length of the tube, the tubes can be made using an outer matrix glass and a glass column included therein. The individual segments of the tubes could be filled with a glass forming powder or a section of glass filament during manufacturing of the reduced dimension portions or a filament could be placed in the tube before carrying out the dimension reduction. Any of these techniques, filament or powder filling, can be used in a process that provides full tubes in which the filling material has a significantly lower softening temperature than the tube, for example of more than 20 ° C. The alternative case, where the columns have a softening point higher than that of the tubes, is possible by enclosing the assembly of columns and tubes in a larger tube that has a softening temperature close to that of the columns. If the Fiber wave guide stretched from the preform constructed in this way is to act as a photonic crystal, the difference in dielectric constant between the matrix glass and the column glass should be no less than a factor of three. In order to stretch the preform made according to the method, some means must be provided to hold the parts of the preform together. In one embodiment of the new preform, the tubes and the core preform are placed in a larger tube and the larger tube collapses in the tube and core preform assembly. In another embodiment of the preform, the tubes and the core preform can be inserted into mandrels and a layer of soot deposited on the tubes and vitrified. The insertion in mandrels can be facilitated by tying the tubes and the core preform before the chuck or deposition formation step. Tying can be accomplished by heat-bonding the parts of the preforms one to another. Alternatively, a frit can be used to weld the parts of the preform together with glass. Another binding alternative is to use belts to hold together the preform parts until the mandrel formation is completed. The straps can be removed before the start of the deposition or they can be made from a material that will burn easily during the deposition of a ppmera layer of glass soot. A further aspect of the invention is a method for manufacturing a wave guide fiber from the new preform whose general configuration and particular embodiments are described above. A method of stretching a waveguide from the new preform includes the steps of sealing one end of each of the altered tubes surrounding the core preform and stretching a waveguide fiber from the opposite end. The pores inside the altered tubes will persist through the stretch passage because they are sealed in the tubes. Undesired pores or voids between the tubes can be collapsed during the stretch step by applying a vacuum to the end of the preform opposite the end from which a waveguide is drawn. Another embodiment of the method omits the step of sealing one end of the tubes surrounding the preform before the stretching step. The step of altering the cross section of the tubes along their length can also be omitted. In this embodiment, a gas pressure is applied to the unsealed tubes during the stretch step. An increase in the internal gas pressure of the tubes causes the openings in the tubes to remain unchanged or to become longer. A decrease in internal tube pressure causes the tube openings to become smaller or close completely during stretching. In this way the density of the coating layer of the waveguide fiber can be made to change in the axial direction by changing the gas pressure. An advantage of this embodiment is that the coating density can be varied essentially continuously from a solid glass to a glass having a maximum porosity limited only by the number of open tubes in the coating layer and the minimum wall thickness of the glass. the tubes together with the geometry ,, ... ^^ ^. .. ^^ ... ^, .. ^^, ^^^^^^^. 7fe .I -. ^ »^ I ^. ^ > . ^^ fe-. The desired fiber prefers an inert pressurizing gas such as nitrogen or hl 1. Pores or unwanted interstitial voids between the tubes are also subjected to the applied pressure. Depending on the pore size through the tube in relation to the interstitial pore size, the procedure alternatives are: - all pores collapse or close; - all pores are left open; - the interstitial pores are left open while the tube pores are closed; or, - the tube pores are left open while the interstitial pores close. It is understood that the pressure control essentially allows a continuity of values of the ratio of the final interstitial pore size to the final tube pore size. In another embodiment of the method, the preform parts are a core preform as described above having a coating layer comprising an arrangement of glass rods disposed around the core preform. The rod arrangement is formed so that a periodic or random arrangement of pores is present between or through the rods. By intermittently applying a vacuum to this preform during the stretching step, those pores between the rods can be intermittently changed from a value equal to or less than the original pore cross section to a minimum cross section of zero, thereby producing a waveguide that has a density that t »w-Aa varies axially. This same intermittent change in cross section can be achieved by applying a gas pressure to the pores as described above for the open tubes. Here again the possible density of the coating layer can be made to vary essentially continuously from that of solid glass material to a porous glass material having a porosity limited only by the dimensions of the components of the preform and the waveguide stretched from it. The configuration of the preform in this mode is selected so that the viscous forces act to close the pores to neutral pressure. Then, the pore size can be modulated by modulating the positive pressure applied to the preform during stretching. This is the opposite of the mode in which the configuration of the preform is selected so that the pore size can be modulated by modulating the negative pressure. 15 A particularly useful embodiment of the new waveguide is one in which the total dispersion is controlled from segment to segment of the waveguide. The combination of a preselected core refractive index profile with a particular pattern of change in the coating layer segment density causes the total dispersion to alternate between positive and negative values. In a waveguide fiber that has positive total dispersion, shorter wavelengths of light travel faster than light of longer wavelengths. The result is that the algebraic sum of the products of segment length and total dispersion of segment over a total waveguide fiber length, that is, the net total dispersion, can be made equal to a preselected target value. For example, the net total dispersion of a waveguide fiber can be made equal to zero even if no segment of the waveguide has a total dispersion of zero. These and other features of the new preform and the optical waveguide stretched therefrom are further described using the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1a is an illustration of a tube having a circular cross section. Figure 1b is an illustration of a tube having a hexagonal cross section. Figure 2 is a sketch of a tube having segments of reduced dimension. Figure 3 is an illustration of hexagonal tubes arranged around a core preform and inserted into a larger containment tube. Figure 4 is an illustration of a cross section of a preform or waveguide having a core region and a layer of porous or mixed body coating.

Figure 5 is an illustration of a cross section of a waveguide having a core region and a porous coating layer in which the pores are due to interstitial pores between the coating layer tubes. 5 Figures 6a & b show cross sections of per-forms or waveguides having respective solid and porous or mixed-body coating layers. Figures 6c, e, & g show the core index profiles of preforms or waveguides having a solid coating layer. 10 Figures 6d, f, & h show the core index profiles of preforms or waveguides having a porous or mixed body coating layer.

DETAILED DESCRIPTION OF THE INVENTION 15 The new waveguide waveguide or waveguide preform utilizes the guide properties of coating layers having an axially varying refractive index that is lower than that of the waveguide core. A waveguide fiber is contemplated in which the guide is made by structuring the coating layer to act as a photonic core having a band gap, at least over certain portions of the length of the waveguide. In each type of coating, the properties ^; & amp; amp; amp; amp; amp; J.4 ¿É¿S »i É & The desired coating compositions are achieved by altering the composition of coating material or its distribution. U * One mode alters the coating layer including pores of particular size and shape. In an analogous way, is Z included instead? 5 of the pores is a material that has a different dielectric constant from the base coat glass. In each case, the energy distribution mode of the light signal in the waveguide is affected, thereby affecting the properties of the waveguide. Because the core and cladding can be changed in the new preform or waveguide fiber, it is done available a large amount of flexibility for a fiber optic guide fiber designer. An interesting embodiment that is discussed and described in this document is one in which the elongated pores or glass filaments are included in the coating layer. Two possible substructures of said The coating layer is illustrated in FIGS. 1 a and 1 b, which are cross sections of tubes having respective central line pores 4 and 6. The material surrounding the pore has a circular shape 2 in FIG. hexagonal 8 in figure 1 b. The shape of the outer side is selected to accommodate a preferred pattern of pores that will be formed by the structures in the coating layer. The pores 4 and 6 could be filled with a material comprising a glass having a dielectric constant different from the surrounding glass or matrix material.

A step in the method of altering one of the substructures is illustrated in Figure 2. Indents have been formed 12 in the illustrative tube 10. The indentations produce restricted regions 14 in the central pore or filament separated by regions 1 on which the central portion 5 of the tube is unaltered. An assembly of said substructures around a core region provides a coating layer that has axial variations in its refractive index. In addition, the substructures may be arranged so that the central pores or filaments 18 form a periodic arrangement. The periodic arrangement may have the passage of a photonic crystal designed to be used on a preferred wavelength scale. Currently, the wavelength scale of interest for telecommunications applications is from 600 nm to 2000 nm. A waveguide preform according to the present invention is shown in Figure 3. In this example, the substructures are tubes 20 and 22 having essentially identical hexagonal cross sections. The difference in hue between the tubes 20 and 22 indicates that the plurality of substructures can be formed in a secondary structure which is then assembled into a coating layer. As an alternative the nuance may indicate that the structures are compositional and can be assembled to form a composition pattern having area components larger than those of the individual substructures. Said assembly could be made for example in a procedure in which the secondary structures are extruded, assemble and then stretch to a desired cross-sectional area. The process of extrusion and stretching is described and discussed in the provisional application S: N. 60 / 094,069 filed on July 30, 1998.

EXAMPLE With reference to Figure 3, a preform and waveguide fiber can be manufactured as follows. The hexagonal substructures 20 and 22, which have an opening along the center line, are assembled in a coating layer surrounding the core preform 30. The entire assembly of hexagonal tubes surrounding the core preform 30 is made stable by placing on the tube 28. The details of the illustration show the substructure openings as points 26. In FIG. this example, tubes 20 and 22 have a free surface of indentations. The ends of the tubes in the plane of figurs 3 are shown as unsealed, by means of illustrative points 26 which indicate an opening. The tube 28 can collapse with the assembly before or during the stretching of the preform into a waveguide fiber. To ensure the Adequate control of the coating porosity, a pressure that is on the scale from atmospheric pressure or upwards is applied to the tube 28 during the stretching step. On a first pressure scale that starts at atmospheric pressure and ends at a predetermined pressure above the ^^^^^^^^^^^ fe ^^^^^^^^^^% ^^^^^^^^ & ^^^^^^^^^ atmosphere, the substructure openings will close due to the action of viscous forces that exist during the stretch step. On a second pressure scale, which starts slightly above the highest pressure in the first pressure scale and continues upward, there will be 5 openings in the coating layer after the stretch is complete. The size of the openings is controlled by the magnitude of the applied pressure. The pressure applied to the openings in the substructure varies between a value in the first pressure scale and a value in the second pressure scale during the stretching step. In this way, the diameter of the openings varies from zero to the preselected diameter corresponding to the selected pressure of the second scale. The modulation of the applied pressure produces a corresponding axial modulation of the density of the coating layer or refractive index. That is, the density and the average refractive index of the coating layer vary throughout the axial dimension of the wave guide fiber.

COMPARATIVE EXAMPLE 1 An optical waveguide preform is manufactured as described in the previous example except that in this comparative example the ends of the substructure tubes are sealed. In addition, the tubes are indented as shown in Figure 2. The respective indentations of the substructure tubes are kept in register each with the others in the tube 28. The record is kept tying or by other means as described above. An optical waveguide fiber is stretched from the ends of the preform opposite the sealed ends of the substructure tubes. During the stretching a vacuum can be applied to the preform tube 28 at the preform end which has the sealed substructure tubes. In this way, the indented, ie altered, tubes that are sealed form elongated pores, arranged in essentially the same pattern as that of the substructures in the preform. The indented portions of the tubes collapse to form a substantially homogenous cross section of coating. The elongated pores are separated axially from one another by those collapsed sections of coating having a substantially homogeneous cross-section. The elongated pores are separated one from the other in cross section by the walls of the substructures. The vacuum, together with the viscous forces exerted on the preform during stretching, serves to close unwanted interstitial pores between the substructure tubes. In one embodiment of the wave guide and preform of this comparative example, the core portion of the preform can be an assembly of tubes having the desired composition and unsealed ends. During stretching, the viscous forces, together with the vacuum applied, act to ^ ¡A a? G = Mft > l ~? ¡»< »TtteftsMJ a.i gs¿ * ^ ^^ Ú ^ s s ^ s ^ SU - * - close the openings in the unsealed core tubes to produce a solid glass core. Figure 4 is a drawing taken from a photograph of a cross section of a waveguide fiber drawn according to the example. The core region 32 is solid glass and the cross section of the coating region contains illustrative pores 34 which serve to reduce the average refractive index of the coating layer. It is understood that the pores 34 could be sized or configured to form a photonic crystal that confines the signal to the core region because the signal wavelength lies in the band gap of the crystal.

EXAMPLE OF COMPARISON 2 An alternate procedure is one in which the substructures are solid and are arranged within a large tube as in Comparative Example 1 above. However, in this case, the substructures are unaltered. During the stretching, a vacuum is applied intermittently to the tube 28 so that the interstitial pores, ie those between the substructures, collapse alternately (the vacuum is applied) or remain as elongated pores (the vacuum goes out) in the coating layer. The result of said procedure is shown in figure 5, which is a drawing taken from a photograph of the cross section of the layer of .r * 1 * & ss m * m Lower coating of wave guide fiber; The elongated pores 36 that are present in the coating layer are interspaced between the glass matrix 38 of solid coating. In the axial direction, the porous portions of the coating are separated from one another by the non-porous portions 5 of glass of pore-free coating, substantially homogeneous. The effect of the introduction of pores into the coating layer is shown by the pairs of figures making FIG. 6. A cross section of a non-porous portion of the waveguide fiber is shown in FIG. 6a. The nucleus or core preform 40 is surrounded by the layer of solid coating glass 42. In Figure 6b, the core or core preform 44 is surrounded by the porous coating layer 46. The cores of Figures 6a and 6b, 6c and 6d, 6e and 6f, and 6g and 6h correspond to each other in that the pairs can be stretched from the same preform. The first member of the pairs, ie, Figure 6a, c, e, and g has a layer of solid coating while each of the second members of the pairs, fig. 6b, d, f, and h have a porous coating layer. The effect of the elongated pores in the porous coating layer is illustrated in the pairs of figures showing the refractive index profile. For example, a stepped index core 48 in Figure 6c has an index difference with reference to the index of the coating layer 49. Figure 6c corresponds to the solid core and the coating structure shown in Figure 6a. In comparison, the index difference between the core index 50 and the average index 51 of the layer of Porous coating as shown in Figure 6d is larger. The U, energy mode distribution ISe, a signal in a portion of the guide wave characterized by the refractive index profile of figure 6c will be wider compared to the energy distribution modi? cation of a propagated signal in the waveguide region that has the index profile of refraction of figure 6d. It will also be understood that other properties, such as total dispersion, total dispersion curve, wavelength cutoff, zero dispersion wavelength are also different for different axial portions along the new waveguide. A properly constructed and stretched preform produces a waveguide fiber having these axial variations in waveguide fiber properties. In analogy with figures 6c and 6d, Figures 6e and 6f show the relative profiles for the case in which the core has three segments. The core 52 has a given index profile in relation to the coating layer 53. By introducing pores into the coating layer, the difference in the largest refractive index between the core index 54 and the layer index is achieved. Coating 56. Here again, the relative index difference alters the energy distribution mode of a signal propagated in the waveguide. In figures 6g and 6h the axial change in the index of coating results in a first profile 56, relative to the index of the coating layer 57, having three distinct annular regions 60, 62 and 64. In contrast, the core profile 58, relative to the index of the layer The porous or full-pore lining 59 has only two distinct annular regions 66 and 68. The potential of the new wave guide preform and associated waveguide fiber to compensate for the dispersion is easily observed in FIGS. 6 (FIG. ch). In addition, the control of the energy distribution mode provides control of said key waveguide fiber parameters such as wavelength cutoff, zero dispersion wavelength, and the magnitude and waveguide dispersion signal, providing for thus great flexibility in the uses of the new waveguide. Although they have been described and illustrated in the present particular embodiments of the invention, the invention is nevertheless limited only by the following claims.

Claims (2)

1. NOVELTY OF THE INVENTION CLAIMS 1. An optical waveguide preform comprising: a central core glass surrounded by and in contact with a coating glass layer to form a preform, the preform has a first and a second end and an axis between the same, and the coating layer comprises a plurality of annular segments that extend 10 sequentially along the axis, in which the segments are characterized by a preselected density different from the preselected density of the segments immediately adjacent to each segment, and, the density of each segment is higher or lower than that of both immediately adjacent segments.
2. 2. The optical waveguide preform according to claim 1, further characterized in that the segments, which have a preselected density lower than that of the adjacent segments, contain pores. 3.- The optical waveguide preform in accordance with the Claim 2, further characterized in that the segments having a preselected density higher than that of the adjacent segments also contain pores. 4. - The gu waveform g according to claim 2, further characterized in that the pores are elongated and have their claim 3, further characterized in that the pores are elongated and have their long dimension oriented along the axis of the preform 6. The optical waveguide preform according to claim 4, further characterized in that the elongated pores form a periodic arrangement 7. The optical waveguide preform according to claim 5, characterized also because the elongated pores form a periodic arrangement 8. The optical waveguide preform according to any of claims 6 or 7, further characterized in that the step of the periodic arrangement is such that the waveguide fiber stretched from the preform to a pre-selected diameter contains a periodic arrangement of elongated pores that have a step in the scale of 0.4 μm to 20 μm 9. The optical waveguide preform according to any of claims 6 or 7, further characterized in that the elongated pores have a diameter and the ratio of the diameter to the passage of the periodic arrangement is in the scale from 0.1 to 0.9. 10. - The optical waveguide preform according to claim 1, further characterized in that the core glass has a refractive index profile that is selected from a group consisting of a step, a rounded step, a trapezoid, a trapezoid rounded, an alpha profile, and a segmented profile in which segments of the segmented profile are selected from the group consisting of a porous layer, a step, a rounded step, a trapezoid, a rounded trapezoid, and an alpha profile. 11. The optical waveguide preform according to claim 10, further characterized in that the core glass comprises silica glass having a dopant selected from the group consisting of germanium, alumina, phosphorus, titanium, boron and fluoro. 12. The optical waveguide preform according to claim 11, further characterized in that the core glass comprises silica impurified with a substance selected from the group consisting of erbium, ytterbium, neodymium, thulium and praseodymium. 13. The optical waveguide preform according to claim 1, further characterized in that the density of a coating layer segment has one of two pre-selected values. 14. The optical waveguide preform according to claim 13, further characterized in that the segment of coating glass layer having the first of the two preselected densities is a first homogeneous composition, and the segment of glass layer from ^^^^^^^^^^^^^^^^^^^ & ^^^ m * coating that has the second of the two pre-selected densities comprises a first porous composition. 15. The optical waveguide preform according to claim 14, further characterized *?., Because the pores of the optical waveguide layer 5 coating that has the second density pre-selected are * elongated and have their long dimension oriented along the axis of the »Preform 16. The optical waveguide preform according to claim 15, further characterized in that the elongated pores form a periodic arrangement. 17. The optical waveguide preform according to claim 16, further characterized in that the step of the periodic arrangement is such that a waveguide fiber stretched from the preform to a pre-selected diameter contains a periodic arrangement of pores 15 elongated ones that have a step in the scale from 0.4 μm to 20 μm. 18. The optical waveguide according to claim 13, further characterized in that the segment of glass coating layer having the first of two preselected densities is a first homogeneous composition having a dielectric constant, and the segment of The coating glass layer having the second of the two pre-selected densities comprises a first porous composition, in which the pores are elongated and the length dimension of the pores is oriented along the axis of the preform, and in which, the elongated pores are filled with a material having a second dielectric constant, in which, the first and second dielectric catatants differ by a factor of at least three. 19. The optical wave guide according to claim 18, characterized adepfts because the elongated filled pores form a periodic arrangement. 20. The optical waveguide preform according to claim 19, further characterized in that the step of the periodic arrangement is such that a waveguide fiber stretched from the preform to a pre-selected diameter contains a periodic arrangement of elongated pores that have a step on the scale from 0.4 μm to 20 μm. 21. An optical waveguide fiber stretched from the preform according to any of claims 1-7 or claims 10-20. 22. An optical waveguide fiber stretched from the preform according to any of claims 1-7 or claims 10-20, further characterized in that the core has a refractive index profile and the segment densities are selected to provide, in conjunction with the core profile, a total dispersion that alternates between positive and negative values as the segment density alternates between different preset densities, to provide a waveguide fiber having a net dispersion equal to a pre-determined value. -selected. 23. - A method for manufacturing an optical waveguide fiber preform comprising the steps of: a) manufacturing a core preform having an axis along; b) manufacturing a plurality of glass tubes having an interior dimension and an extrusion and an axis along; c) forming along the longitudinal axis in each of the plurality of glass tubes a V number, N, of sections of reduced inner and outer dimension, in which, the N sections of reduced dimension are spaced apart, one of another, by a section of the tube; d) arranging the plurality of tubes of step c) in an arrangement surrounding the core preform; wherein the axis along the core preform is substantially parallel to the longitudinal axis of the tubes. 24. The method according to claim 23, further characterized in that the tubes of step b) have a cross-sectional shape selected from the group consisting of a circle, a # 15 triangle, a parallelogram, and a polygon. 25. The method according to claim 23, further characterized in that the arrangement is random. 26. The method according to claim 23, further characterized in that the arrangement is periodic. 27. The method according to claim 23, further characterized in that the reduced interior dimension is zero. 28. The method according to claim 23, further characterized in that the tube has a first composition and a ^^^^^^ ^^^^^^^ ^ ^ ^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^ first dielectric constant, and during or before the training step c) each of the sections that the N sections are filled with a material that has a second composition and a second dielectric constant, in which the first dielectric constant differs from the second dielectric constant by at least a factor of three. • ^ 29.- The method according to claim 23, * further characterized in that the tube has a first composition and a first refractive index, and during or before the forming step c) each of the sections separating the N sections are filled with a material having a second composition and a second index of refraction, in which the first index of refraction is larger than the second index of refraction. The method according to claim 23, further characterized in that it includes the steps of: e) inserting the arrangement f 15 of step d) into an outer tube; and f) collapse e! outside of the tube on the 9 disposition. 31.- The method according to claim 30, further characterized in that it additionally includes the step of depositing glass soot particles in the outer tube. The method according to claim 23, further characterized in that it additionally includes the steps of: e) tying the pipe arrangement of step d) to keep them in register with each other; and f) depositing glass soot on the beam. • ^^^^ ^^^^^, ^^^ & ^ ^^ ^ - ^. ^ -r¿aSJÉiiÉÉ8Ég ^^ 33. - The method according to claim 32, further characterized in that the tying step includes gluing the glass tubes together and the innermost tubes to the core preform by means of heating the tubes. 34.- The method according to claim 32, further characterized in that the tying step includes gluing the glass tubes to one another and the innermost tubes to the core preform using melted glass. A method for manufacturing an optical waveguide fiber comprising the steps of: a) manufacturing a preform according to any of claims 23-34; b) sealing one end of the glass tubes; c) stretching a wave guide fiber from the end of the preform opposite the end of the preform having the sealed tubes; and d) applying a vacuum to the end of the preform opposite the end that is being stretched. 36.- A method for manufacturing an optical waveguide fiber comprising the steps of: a) manufacturing a core preform; b) manufacturing a plurality of glass rods having a cross section in cross; c) arranging the plurality of rods in an arrangement surrounding the core preform so that the arrangement contains a plurality of pores; d) inserting the rod arrangement and the core preform into a tube to form a preform for stretching; e) stretching an optical waveguide fiber from the preform to stretch; and f) during step e) applying a variable pressure to the tube. 37. - The method according to claim 36, further characterized in that the applied pressure varies between atmospheric pressure and a preselected pressure below atmospheric pressure. 38. The method according to claim 37, further characterized in that the pre-selected pressure is sufficient to at least partially collapse the pores. 39.- The method according to claim 37, further characterized in that the applied pressure varies between a first 10 preselected pressure greater than or equal to atmospheric pressure and a second pre-selected pressure greater than the first preselected pressure.