JP2010140045A - Waveguide having axially varying structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a waveguide fiber preform, which gives an additional waveguide structure variable and is useful for production of a dispersion compensating/controlling waveguide, and a fiber, and to provide a method for producing the waveguide preform and the fiber. <P>SOLUTION: In the optical waveguide fiber preform containing a clad glass layer disposed in a core glass area and on the core glass, the clad glass layer is divided into segments positioned along the axis of the preform, and the density of clad glass is varied in the direction, which is called as a preform axis, parallel to the core area so that the clad glass density is varied from a higher value to a lower value or from a lower value to a higher value from one segment to another segment. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  This application is based on US Provisional Patent Application No. 60 / 100,349, filed on September 15, 1998, which the applicant claims as the priority date of this application.

  The present invention is directed to an optical waveguide preform or fiber having an axially varying structure. In particular, the refractive index of the novel preform or waveguide cladding layer of the present invention varies along the waveguide length. This change is due to a change in the porosity or composition of the cladding layer. The present invention includes the novel waveguide preforms and methods for making the fibers of the present invention.

  Optical waveguides having a cladding layer with a periodic structure have been discussed. As an example, the periodic structure of the cladding layer is described in “Optics Letters”, Vol. 21, No. 19 (October 1, 1996), “Photonic Crystal Cladding” by Knight et al. All-silica single-mode optical fiber with layers "and" Infinite single-mode photo "by Birks et al. In" Optics Letters ", Vol. 22, No. 13 (July 1, 1997) It can be a photonic crystal as described in “Nick Crystal Fiber”. The above two articles describe single mode fibers having a silica core and a porous silica cladding. The voids or pores of the silica cladding layer are elongated and extend from the end to the end of the cladding layer. The holes are arranged in a hexagonal pattern having periodicity to make the cladding layer a photonic crystal. A waveguide fiber so configured can be a single mode fiber at any wavelength.

  Another study result on a waveguide fiber having a porous, ie, clad layer having a large number of pores is described in US Pat. In this publication, the cladding layer has elongated vacancies that serve to lower the average refractive index of the cladding layer. The elongated vacancies are not arranged in a periodic pattern, so the optical waveguide mechanism of this waveguide is reflection at the core-cladding boundary.

  It is useful for single-mode waveguide structures that the intrinsic limit of the cutoff wavelength range obtained with photonic crystal cladding layers, ie, perhaps no cutoff wavelength, is present. The relative refractive index difference Δ due to a specific volume of the cladding layer with non-periodic vacancies is also useful in providing additional structural variables. This volume is controlled by controlling the air fill factor of the fiber as described below.

European Patent Publication No. 0810453

Knight et al., “All Silica Single Mode Optical Fiber with Photonic Crystal Cladding”, Optics Letters, V.21, No.19, 1 October 96 Birks, et al., “Endlessly Single Mode Photonic Crystal Fiber”, Optics Letters, V.22, No.13, 1 July 97

  However, no axial change of the relative refractive index is given to any of the above structures. Such axial variation is useful for single mode fiber structures that seek to control dispersion. In addition, since axial changes in the relative refractive index depend on the cladding layer, new parameters such as hole volume, hole cross-sectional area and hole pattern change the mode power distribution of the waveguide and thus the main waveguide fiber. Available to change properties. Combinations of axial changes in the cladding structure with a variety of core index profile structures that provide unique waveguide fiber properties are possible. A cladding layer that incorporates both optical waveguides by photonic crystals and optical waveguides by refraction is considered useful for controlling dispersion in waveguide structures. Furthermore, the present invention incorporates a cladding layer structure having an arrangement characterized in that it is made of a periodically or randomly distributed material instead of vacancies, thereby providing further flexibility to the waveguide fiber structure. .

  The novel waveguide fiber preforms and fibers of the present invention and methods for making such waveguide preforms and fibers provide additional waveguide structure variables and are useful for making dispersion compensated or dispersion controlled waveguides. is there.

  A first aspect of the invention is an optical waveguide fiber preform that includes a core glass region and a cladding glass layer disposed on the core glass. For simplicity of explanation, it is assumed that the clad glass layer is divided into segments located along the preform axis. The density of the clad glass changes in a direction parallel to the core region, called the preform axis, so that the clad glass density changes from high to low or from low to high from segment to segment. That is, the density of each adjacent segment is not a monotonic function of axial position.

  The preform cladding layer density can be made to vary from high to low and from low to high between adjacent segments by changing the porosity of the cladding layer. In particular, each of the adjacent segments along the preform axis alternates between a state in which the cladding layer contains vacancies and a state in which the cladding layer does not substantially contain vacancies. In one embodiment of the novel preform of the present invention, the vacancies are elongated and arranged in a periodic array structure that can have a pitch or spacing between vacancies. Pitches in many different ranges can be selected. For use at optical telecommunications wavelengths, it is beneficial to select the preform pitch such that the fiber pitch drawn from the preform is in the range of about 0.4 μm to 20 μm. A typical outer diameter of the glass fiber is about 125 μm. The shortest value in the range provides the pitch of the drawn fiber that is effective in forming a photonic crystal in the telecommunications signal wavelength range. However, the applicant of the present application has demonstrated that it can be effectively used to fabricate a waveguide having a cladding whose interval, that is, the pitch in the range of several tens of μm also changes in the axial direction. In the present specification, the upper limit is set to 20 μm, but the applicants expect the usefulness of the pitch of the longer cladding layer structure. The upper limit of the structure interval, that is, the pitch is practically determined by the thickness of the cladding layer.

  Applicants have found that not only the pitch of the elongated holes, but also the diameter, is important for the characterization of the waveguide fiber drawn from the preform. In certain embodiments, the ratio of the pore diameter to the array pitch of the elongated pores is in the range of about 0.1 to 0.9.

  The preform core glass can have a wide range of refractive index profiles. The refractive index profile of a region is the value of the refractive index or relative refractive index difference Δ as a function of radial position within that region. The definitions of refractive index profile, segmented profile, Δ, and α profile are known in the art and are included herein by reference, such as Antos et al., US Pat. No. 5,553,185 or Smith. U.S. Pat. No. 5,748,824. In other words, the core region of the preform can be a staircase type or a trapezoidal type, or an α profile type in which the portion where the slope changes abruptly may be rounded. Furthermore, the core region is segmented into two or more parts, each part taking any one of the profiles described above. This core region structure, coupled with the cladding layer modulation, determines the dispersion characteristics and other operational performance of the waveguide fiber.

  The refractive index of a base glass such as silica can be changed by adding a dopant such as germanium oxide, alumina, phosphorus, titanium oxide, boron, fluorine, or the like. Rare earth dopants such as erbium, ytterbium, neodymium, thulium, or praseodymium can also be added to provide a preform that can be drawn into an optical amplifier waveguide fiber.

  In another embodiment of the novel preform of the present invention, the cladding density switches between two values each time it moves from segment to segment along the preform axis. This switching, in combination with a preselected core structure, defines the fiber dispersion control characteristics as described above. Again, the density can be controlled by controlling the void volume of each segment of the cladding layer. Alternatively, the density can be controlled by controlling the amount of dopant glass added to the base clad layer glass. The dopant glass appears as elongated filaments in the cladding matrix glass. These filaments can be arranged in a periodic array similar to the arrangement of elongated vacancies discussed above. Of course, the filament can be formed using a number of processes known in the art, but it can also be an elongated void filled with a filament. If the cladding layer with filaments is to interact with light in the form of a photonic crystal with a complete forbidden band, the filament size and spacing must be compatible with a pitch in the range of about 0.4 μm to 5 μm. The dielectric constant of the base glass must be about three times the dielectric constant of the glass forming the columnar glass contained in the base glass.

  Both the porous cladding layer and the filament-filled cladding layer can guide light by reflection at the core-cladding interface if the refractive index of the core is higher than the refractive index regarded as the average refractive index of the structured cladding layer.

  The preform described above is manufactured for the purpose of drawing an optical waveguide fiber from the preform. Thus, the present invention includes an optical waveguide drawn from the novel preform of the present invention.

  Another aspect of the invention is a method of making a novel preform from which a novel waveguide is drawn. In the first method, the co-appliform is one of several methods known in the art, including external vapor deposition and axial vapor deposition, and internal (MCVD) or plasma deposition. It is produced by. The core part of the preform is solid without voids. Alternatively, the co-appli foam can be a hollow tube that is open at both ends and has not been deformed in any way prior to forming the preform. The hollow tube is crushed during the drawing process to form a homogeneous or doped solid glass core region (if the hollow tube is doped). A plurality of glass tubes having a cavity extending through the hollow tube is produced. The hollow tube is reduced in diameter at a preselected number of locations along the hollow tube and placed around a centered co-appli foam. Each of the reduced diameter hollow tubes is essentially the same as any other reduced diameter hollow tube. The hollow tube may be crushed to some extent or completely at the reduced diameter position. A preform in which a reduced diameter hollow tube is arranged around a cored foam formed in the center is a preform having an axial change in the cladding layer density.

  The cross section of the hollow tube can be circular or it can be a polygon with more than two sides. The hollow tube around the central co-appliform is of a specific size and shape chosen depending on the type of signal-waveguide interaction, either refractive or photonic crystal, desired at the core-cladding interface Can be arranged randomly or periodically. In the case of a cladding layer having the characteristics of photonic crystals and a completely forbidden band, the pitch of the periodic arrangement of the hollow tubes must be approximately the same as the signal wavelength of the light traveling through the waveguide.

  A hollow tube can be produced using the surrounding base glass and the columnar glass contained in the surrounding base glass instead of the holes distributed intermittently along the length of the hollow tube. Individual segments of the hollow tube can be filled with glass-forming powder or glass filament fragments when forming the reduced diameter portion, or the hollow tube can be filled with filaments before the diameter reduction is performed. Any of these filament or powder filling methods can be used in a process to provide a filled hollow tube having a softening temperature where the filler is much lower than the hollow tube, for example above 20 ° C. On the other hand, when the aggregate of columnar glass and hollow tubes is accommodated in a thicker hollow tube having a softening temperature close to that of columnar glass, the softening point of the columnar glass can be higher than that of the hollow tube. When the waveguide drawn from the preform thus configured serves as a photonic crystal, the dielectric constant of the base glass must be about three times or more that of the columnar glass.

  In order to draw a preform made according to the present method, some means must be provided for bringing together the members of the preform. In one embodiment of the novel preform of the present invention, the hollow tube and the co-appli foam are housed in a thicker hollow tube, and the thicker hollow tube is crushed onto the hollow tube and the co-appli foam assembly. .

  In another embodiment of the preform, the hollow tube and the co-appliform can be inserted into a chuck and a soot layer is deposited on the hollow tube and vitrified. Insertion into the chuck can be easily performed by bundling the hollow tube and the co-appli foam before the insertion into the chuck or the deposition step. Binding is accomplished by connecting the preform members together with heat. Alternatively, a frit can be used to glass fuse the members of the preform together. Another binding method is to use a knot to keep the preform members together until insertion into the chuck is complete. The knot can be removed before deposition begins, or can be made of a material that does not easily burn when the first glass soot layer is deposited.

  Another aspect of the present invention is a method of making a waveguide fiber from the novel preform of the present invention whose general configuration and specific embodiments are described above. One embodiment of a method for drawing a waveguide from a novel preform of the present invention includes a step of sealing each end of a deformed hollow tube surrounding a co-appliform and a waveguide fiber from one end facing the sealed end. A step of drawing. Since the voids in the deformed hollow tube are sealed in the hollow tube, they remain throughout the drawing process. Undesirable voids or pores between the hollow tubes can be collapsed during the drawing process by applying a vacuum to the preform end opposite the end where the waveguide is drawn.

In another embodiment of the method, the step of sealing one end of the hollow tube surrounding the co-appli foam before the drawing step is omitted. The step of changing the cross-sectional area along the length of the hollow tube can also be omitted. In this embodiment, gas pressure is applied to the unsealed hollow tube during the drawing process. As the internal gas pressure in the hollow tube increases, the hollow tube cavity remains unchanged or becomes larger. As the internal gas pressure decreases, the cavity in the hollow tube becomes smaller or completely closed upon drawing. That is, an axial change in the density of the waveguide fiber cladding layer can be created by changing the gas pressure. The advantage of this embodiment is that the maximum porosity is limited only by the number of open hollow tubes in the cladding layer and the minimum wall thickness of the hollow tubes, as well as the desired geometry of the finished waveguide fiber, from solid glass to the cladding density. It can be changed essentially continuously up to glass with An inert pressurized gas such as nitrogen or helium is preferred. Undesirable interstitial pores or pores between the hollow tubes are also exposed to the applied pressure. Depending on the size of the void in the hollow tube relative to the size of the gap void, the process is:
-All voids are crushed or closed;
-All vacancies are left open;
Either one of the following:-the void in the hollow tube is left open, while the void in the hollow tube is closed; or the void in the hollow tube is left open, while the void in the hollow tube is closed. Of course, by pressure control, the value of the ratio of the final gap pore size to the final hollow tube pore size can be changed essentially continuously.

  In yet another embodiment of the method, the preform member is a co-appli foam as described above having a cladding layer comprising a glass rod array disposed about the co-appli foam. The rod array is shaped so that a periodic or random array of holes exists between or through the rods. By intermittently applying vacuum to this preform during the drawing process, the holes between the rods are lowered from a value equal to or smaller than the original hole cross section to intermittently change to a minimum cross section of zero. Therefore, a waveguide having an axial density change can be manufactured. As described above for open hollow tubes, the same intermittent cross-sectional area change can be achieved by applying gas pressure to the holes. Again, possible cladding layer densities are essentially from the density of the solid glass material to the density of the porous glass material having a porosity limited only by the dimensions of the preform member and the waveguide drawn from the preform. Can be changed continuously. The preform configuration in this embodiment is chosen such that at neutral pressure, the viscous force acts to close the pores. The pore size can then be modulated by applying a modulated pressure to the preform during drawing. This is the opposite of the previous embodiment where the preform configuration is chosen so that the pore size can be modulated by modulation decompression.

  A particularly useful embodiment of the novel waveguide of the present invention is a waveguide in which the total dispersion is controlled for each segment of the waveguide. By combining a preselected core refractive index profile with a specific pattern of change in cladding layer segment density, the total dispersion is alternated between positive and negative values. In a waveguide fiber with positive total dispersion, the shorter the wavelength, the faster the light travels than the longer wavelength light. The result is that the algebraic sum of the product of the segment length and the total dispersion of the segments over the entire length of the waveguide fiber, i.e. 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 though none of the segments of the waveguide have a total dispersion of zero.

  The above and other features of the novel preform of the present invention and the optical waveguide drawn from the preform will be further described with reference to the drawings.

Illustration of a hollow tube with a circular cross section Illustration of a hollow tube with a hexagonal cross section A sketch of a hollow tube with reduced diameter segments Illustration of a hexagonal hollow tube placed around a co-appli foam and inserted into a thicker support hollow tube Cross section of a preform or waveguide with a core region and a porous or composite cladding layer Cross-sectional view of a waveguide with a porous cladding layer, with a core region and voids due to gap voids between the cladding layer hollow tubes Diagram showing a cross section of a preform or waveguide with a solid cladding layer Figure showing a cross section of a preform or waveguide with a porous or composite cladding layer Diagram showing an example core refractive index profile of a preform or waveguide with a solid cladding layer Diagram showing core refractive index profile corresponding to FIG. 6C for a preform or waveguide having a porous or composite cladding layer Diagram showing another example of the core refractive index profile of a preform or waveguide with a solid cladding layer Diagram showing core refractive index profile corresponding to FIG. 6E for a preform or waveguide having a porous or composite cladding layer Diagram showing another example of the core refractive index profile of a preform or waveguide with a solid cladding layer Diagram showing core refractive index profile corresponding to FIG. 6G for a preform or waveguide with a porous or composite cladding layer

  The novel waveguide preform or waveguide fiber of the present invention utilizes the waveguide properties of a cladding layer having a refractive index that varies in the axial direction that is lower than the refractive index of the waveguide core. A waveguide fiber that can be guided by forming a cladding layer in a structure that works as a photonic crystal having a forbidden band over at least a portion of the waveguide length is conceivable. In each type of clad, desired clad characteristics can be obtained by changing the composition or distribution of the clad material.

  In one embodiment, the cladding layer is altered by including holes of a specific size and shape. In a similar embodiment, a material having a different dielectric constant than the base clad glass is included instead of the vacancies. In either case, the mode power distribution of the signal light in the waveguide is affected, and thus the waveguide characteristics are affected. In the novel waveguide preform or fiber of the present invention, both the core and the cladding can be varied, thereby providing very high flexibility to the optical waveguide fiber designer.

  Notable embodiments disclosed and described herein are those in which elongated vacancies or glass filaments are included in the cladding layer. Two possible substructures for such a cladding layer are shown in FIGS. 1A and 1B, which are cross-sectional views of hollow tubes each having central axial holes 4 and 6. The material surrounding the pores is a circle 2 in FIG. 1A and a hexagon 8 in FIG. 1B. The outline is chosen to match the preferred hole pattern formed by the substructure of the cladding layer.

  The holes 4 and 6 can be filled with a material made of glass having a dielectric constant different from that of the surrounding glass material, that is, the base glass.

  The process steps for changing one of the substructures are shown in FIG. A recess 12 is formed in the exemplary hollow tube 10. The indentation creates a narrow region 14 in the central hole or filament that is separated by a region 16 in which the central hole of the hollow tube is not deformed. By assembling such substructures around the core region, a cladding layer whose refractive index varies in the axial direction can be obtained. Furthermore, the substructure can be arranged such that the central holes or filaments 18 form a periodic array. The periodic array can have a photonic crystal pitch designed for use in the preferred wavelength range. Currently, an important wavelength range for telecommunications applications is about 600 nm to 2000 nm.

  A waveguide preform according to the present invention is shown in FIG. In this example, the substructure is hexagonal hollow tubes 20 and 22 having essentially the same cross-section. The difference in shading between the hollow tubes 22 and 22 indicates that the secondary structure can then be formed by the multiple substructures and then assembled in the cladding layer. Alternatively, it can be shown in shading that the composition of the substructure is different and can be assembled to form a synthetic pattern having a larger synthetic area than the individual substructure. Such an assembly can be made, for example, by a process in which secondary structures are extruded and assembled and then drawn to the desired cross-sectional area. The extrusion and drawing process is disclosed and described in US Provisional Patent Application No. 60 / 094,609, filed July 30, 1998.

  Referring to FIG. 3, a waveguide preform and fiber can be fabricated as follows. Hexagonal substructures 20 and 22 having cavities along the central axis are assembled in a cladding layer surrounding the co-appli foam 30. The entire assembly of hexagonal hollow tubes that surround the co-appli foam 30 is placed into the hollow tube 28 for rest. In the details of the figure, the substructure cavity is shown at point 26.

  In this example, there are no depressions on the surfaces of the hollow tubes 20 and 22. The end of the hollow tube in the plane of FIG. 3 is shown as unsealed by an exemplary point 26 indicating a cavity.

  The hollow tube 28 can be collapsed onto the assembly before or during drawing of the preform to the waveguide fiber. In order to ensure proper cladding porosity control, a pressure in the range exceeding atmospheric pressure is applied to the hollow tube 28 during the drawing process. Over the first pressure range starting at atmospheric pressure and ending above the predetermined atmospheric pressure, the substructure cavity will close due to the action of the viscous forces present during the drawing process. Over the second pressure range starting at a pressure slightly higher than the highest pressure in the first pressure range and continuing to rise, the cavity will be present in the cladding layer even after drawing is complete. The size of the cavity is controlled by the magnitude of the applied pressure. The pressure applied to the cavity of the substructure is varied from a value in the first pressure range during the drawing process to a value in the second pressure range. That is, the cavity diameter varies from zero to a preselected diameter corresponding to a pressure selected from the second range. The modulation of the applied pressure creates an axial modulation of the corresponding cladding layer density or refractive index. That is, the density and average refractive index of the cladding layer change along the axial direction of the waveguide fiber.

Example 1
The optical waveguide preform is manufactured as described in the above example, except that the end of the lower structure is sealed in this example. Further, the hollow tube is recessed as shown in FIG. Each of the substructure hollow tube recesses is aligned with each of the other hollow tube recesses in the hollow tube 28. This indentation is maintained by a bundle or other means as described above.

  The optical waveguide fiber is drawn from the preform end facing the sealing end of the lower structure hollow tube. During drawing, a vacuum can be applied to the preform hollow tube 28 at the end of the preform where the substructure hollow tube is sealed. Thus, the deformed, or indented, sealed hollow tube forms elongated vacancies that are arranged in essentially the same pattern as the preform substructure. The hollow portion of the hollow tube is crushed to form a substantially homogeneous cladding cross section. The elongated vacancies are axially separated one by one in the above-described collapsed clad section having a substantially homogeneous cross section. The elongated holes are separated one by one in the cross section by the tube wall of the substructure. Along with the viscous forces acting on the preform during drawing, the vacuum serves to close unnecessary gaps between the substructure hollow tubes.

  In one embodiment of the preform and waveguide of this comparative example, the core portion of the preform can be a hollow tube assembly having the desired composition and unsealed ends. During drawing, the viscous force acts to close the cavity of the core hollow tube that is not sealed with the applied vacuum to create a solid glass core.

  FIG. 4 is a view taken from a cross-sectional photograph of a waveguide fiber drawn in accordance with this example. The core region 32 is solid glass and the cross section of the cladding region includes exemplary vacancies 34 that serve to lower the average refractive index of the cladding layer.

  Naturally, since the signal wavelength is in the forbidden band of the photonic crystal, the holes 34 can be sized or arranged to form a photonic crystal in which the signal is confined in the core region.

Example 2
Another process is a process in which the lower structure is solid and is disposed in a thick hollow tube as in the first embodiment. However, in this case, the substructure is not deformed. During drawing, a vacuum is intermittently applied to the hollow tube 28, so that the gap vacancies, ie the vacancies between the substructures, are alternately crushed (vacuum is applied) or the cladding layer remains elongated. Remains in (vacuum is cut). The result of such a process is shown in FIG. 5, which is a diagram taken from a cross-sectional photograph of the cladding layer of the waveguide fiber. Elongated voids 36 present in the cladding layer are scattered between solid base metal cladding glass 38. In the axial direction, the porous portions of the clad are separated one by one by non-porous portions made of clad glass having substantially uniform voids.

  The effect of introducing holes into the cladding layer is shown in the four pairs of diagrams constituting FIG. FIG. 6A shows a cross section of the non-porous portion of the waveguide fiber. The core or co-appli foam 40 is surrounded by a solid cladding glass layer 42. In FIG. 6B, the core or co-appli foam 44 is surrounded by a porous cladding layer 42. The cores of FIGS. 6A and 6B, FIGS. 6C and 6D, FIGS. 6E and 6F, and FIGS. 6G and 6H coincide with each other, and each pair can be drawn from the same preform. Each pair of first components, ie FIGS. 6A, 6C, 6E and 6G, has a solid cladding layer, while each of the pair of second components, ie FIGS. 6B, 6D, 6F and 6H, It has a porous cladding layer.

  The effect of elongated vacancies in the porous cladding layer is shown in three pairs of figures showing the refractive index profile. For example, the core 48 of the stepped refractive index profile of FIG. 6C has a different refractive index than the cladding layer refractive index 49. FIG. 6C corresponds to the solid core and cladding structure of FIG. 6A. In comparison, as shown in FIG. 6D, the refractive index difference between the core refractive index 50 and the average refractive index 51 of the porous cladding layer is larger. The mode power distribution of the signal in the waveguide portion characterized by the refractive index profile of FIG. 6C will be broader than the mode power distribution of the signal propagating through the waveguide region having the refractive index profile of FIG. 6D. Of course, other characteristics such as total dispersion, total dispersion slope, cutoff wavelength, and zero dispersion wavelength are also different at different axial portions along the novel waveguide of the present invention. From one appropriately configured and drawn preform, a waveguide fiber having the above axial variations in waveguide fiber properties is produced.

  Similar to FIGS. 6C and 6D, FIGS. 6E and 6F show the relative refractive index for the case where the core has three segments. The core 52 has a given index profile for the cladding layer 53. By introducing holes into the cladding layer, a larger refractive index difference is obtained between the core refractive index 54 and the cladding layer refractive index 55. Again, the relative refractive index difference changes the mode power distribution of the signal propagating through the waveguide.

  In FIGS. 6G and 6H, the axial change in cladding refractive index results in a first core profile 56 having three distinct annular regions 60, 62 and 64 relative to the cladding layer 57. In contrast, there are only two distinct annular regions 66 and 68 in the core profile 58 for the refractive index of the porous, i.e., multi-hole, cladding layer 59.

  The dispersion compensation capability of the novel waveguide preform of the present invention and the waveguide fiber drawn from the preform can be easily understood from FIGS. In addition, mode power distribution control allows control of key waveguide fiber parameters such as cutoff wavelength, zero dispersion wavelength, and the magnitude and sign of waveguide dispersion, and thus high in the use of the novel waveguide of the present invention. Flexibility is given.

  While particular embodiments of the present invention have been disclosed and described herein, the present invention is nevertheless limited only by the scope of the claims.

20, 22, 28 Hollow tube 34, 36 Hole 40, 44 Core region 42, 46 Clad layer

Claims (17)

  An optical fiber including a solid core region without voids surrounded by a porous cladding layer including randomly arranged voids, wherein the clad layer with voids extends from the solid core region. An optical fiber characterized by being spaced.   2. The optical fiber according to claim 1, wherein the vacant clad layer is elongated and includes vacancies dispersed along a solid clad glass matrix in the vacant clad layer.   The optical fiber according to claim 1, wherein the core glass region has a refractive index profile selected from the group consisting of a step type, a rounded step type, a trapezoidal type, and an α profile.   The optical fiber according to claim 1, wherein the core glass comprises silica glass doped with a dopant selected from the group consisting of germanium oxide, alumina, phosphorus, titanium oxide, boron, and fluorine.   2. The optical fiber according to claim 1, wherein the core glass includes silica glass doped with a dopant selected from the group consisting of alumina, phosphorus, titanium oxide, and fluorine.   The optical fiber according to claim 1, wherein the core glass includes silica glass doped with germanium oxide.   The optical fiber according to claim 6, wherein the refractive index profile of the core glass includes a step index refractive index profile.   2. The optical fiber according to claim 1, wherein the holes of the cladding layer are elongated and have a length along the axis of the preform.   The optical fiber of claim 1, wherein the core glass region comprises silica doped with a material selected from the group consisting of erbium, ytterbium, neodymium, thulium and praseodymium.   An optical fiber comprising a void-free solid core glass region surrounded by a porous glass cladding layer, wherein the solid core glass region is doped with erbium, ytterbium, neodymium, thulium or praseodymium An optical fiber comprising:   The optical fiber according to claim 10, wherein the porous clad layer includes randomly arranged holes.   The optical fiber according to claim 10, wherein the porous cladding layer is spaced from the solid core glass region.   An optical waveguide preform for producing an optical fiber including a solid core region without voids surrounded by a porous cladding layer, wherein the porous cladding layer is spaced from the solid core region. An optical waveguide preform comprising randomly arranged holes.   14. The optical waveguide preform according to claim 13, wherein the porous clad layer is elongated and includes pores dispersed along a solid clad glass matrix in the porous clad layer.   14. The optical waveguide preform according to claim 13, wherein the core glass includes silica glass doped with a dopant selected from the group consisting of alumina, phosphorus, titanium oxide, and fluorine.   The optical waveguide preform according to claim 13, wherein the core glass includes silica glass doped with germanium oxide.   The optical waveguide preform according to claim 13, wherein the refractive index profile of the core glass includes a step index refractive index profile.

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