JP2002525256A - Waveguide with axially varying structure - Google Patents

Abstract

(57) Abstract: The density of the cladding layer (42), and thus the effective index of refraction, varies in a preselected manner along the axial direction of the optical waveguide fiber preform and the optical waveguide fiber drawn from the preform. An optical waveguide fiber preform and an optical waveguide fiber associated therewith. The axial change in the density of the cladding layer (42) depends on air or a volume fraction in the cladding of a glass having a composition different from that of the base clad glass. Axial changes in the cladding index change the modal power distribution of the signal, and thus alter key parameters of the waveguide fiber such as the magnitude and sign of the dispersion, the cutoff frequency and the zero dispersion wavelength. The invention includes a method of making a structure having an axially varying cladding layer. The invention also contemplates a preform in which the waveguide fiber drawn from the preform guides the light with a photonic crystal structure over the entire length of the cladding layer or over the segment length of the segmented cladding layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] Background This application of the invention, the present applicant has been filed on September 15, 1998, which claimed as the priority date of the present application, based on US Provisional Patent Application No. 60 / 100,349.

The present invention is directed to an optical waveguide preform or fiber having an axially varying structure. In particular, the refractive index of the cladding layer of the novel preform or waveguide 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 a method for making the novel waveguide preforms and fibers of the present invention.

[0003] 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” magazine,
Vol. 21, No. 19 (October 1, 1996), Knight et al., "All-silica Single-Mode Optical Fiber with Photonic Crystal Cladding Layer," and Optics Letters Magazine, Vol. Photonic crystals, such as those described in "Infinite Single-Mode Photonic Crystal Fiber" by Birks et al., Vol. 22, No. 13, July 1, 1997. In the above two papers, a single mode fiber having a silica core and a porous silica cladding is described. The pores or pores of the silica cladding layer are elongated and extend from the end of the cladding layer to the end. The holes are arranged in a hexagonal pattern having periodicity, and the cladding layer is made into a photonic crystal. A waveguide fiber so configured can be a single mode fiber at any wavelength.

[0004] Another study of waveguide fibers with a porous, ie porous, cladding layer is described in EP 0810453 A1. In this publication, the cladding layer has elongated holes that serve to lower the average refractive index of the cladding layer. The elongate holes are not arranged in a periodic pattern, so the optical waveguide mechanism of this waveguide is reflection at the core-cladding interface.

[0005] The intrinsic limitlessness of the cutoff wavelength range obtained by the photonic crystal cladding layer,
That is, or alternatively, the absence of any cutoff wavelength is useful for single mode waveguide structures. The relative refractive index difference Δ due to the cladding layer having a specific volume of non-periodic voids is also useful in providing additional structural variables. This volume is controlled by controlling the air filling of the fiber as described below.

However, no axial change in relative refractive index is given to any of the above structures.
Such an axial change is useful for single mode fiber structures that seek to control the dispersion. Furthermore, since the axial change of the relative refractive index depends on the cladding layer, the pore volume,
New sets of parameters, such as hole cross section and hole pattern, can be used to change the mode power distribution of the waveguide and thus the key waveguide fiber properties.
It is conceivable to combine the axial change of the cladding structure with a wide variety of core refractive index profile structures that provide unique waveguide fiber properties. A cladding layer incorporating both optical waveguides by photonic crystals and optical waveguides by refraction is considered to be useful for controlling dispersion in a waveguide structure. Further, the present invention incorporates a cladding layer structure having an arrangement characterized by a periodic or randomly distributed material instead of holes, thereby providing additional flexibility to the waveguide fiber structure. .

[0007] Methods of making novel waveguide fiber preform and fiber, as well as such waveguide preform and fiber SUMMARY OF THE INVENTION The present invention provides additional waveguide structure variable dispersion compensator or distributed control guide Useful for making waveguides.

A first aspect of the present 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,
It is assumed that the cladding glass layer is divided into segments located along the axis of the preform. The density of the cladding glass varies in a direction parallel to the core region, called the preform axis, such that the density of the cladding glass varies from high to low or low to high from segment to segment. That is,
The density of each of the adjacent segments is not a monotonic function of the axial position.

[0009] The cladding layer density of the preform can be changed by changing the porosity of the cladding layer.
It can be made to change from high to low and from low to high between adjacent segments. In particular, each of the adjacent segments along the preform axis alternates between a state in which the cladding layer contains voids and a state in which the cladding layer is substantially free of voids. In one embodiment of the novel preform of the present invention, the cavities are elongated and are arranged in a periodic array structure that may have a pitch, i.e., a spacing between isotopic points of the cavities. Many different ranges of pitch 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 a glass fiber is about 125 μm. The shortest value in the range gives the pitch of the drawn fiber that is effective for forming a photonic crystal in the telecommunications signal wavelength range. However, Applicants have demonstrated that spacings or pitches in the range of tens of μm can also be used effectively to fabricate waveguides with cladding that varies axially. Although the upper limit is 20 μm herein, Applicants anticipate the usefulness of longer cladding layer pitches. The upper limit of the structure spacing or pitch is effectively a practical limit determined by the cladding layer thickness.

Applicants have found that not only the pitch of the elongated holes, but also the diameter, is important in characterizing 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 between about 0.1 and 0.1.
9 range.

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 the radial position within that region. The definitions of the refractive index profile, segmentation profile, Δ, and α profile are known in the art and are incorporated herein by reference to US Pat. No. 5,553,185 to Antos or Smith or Smith. U.S. Pat. No. 5,748,824. In other words, the core region of the preform may be of a staircase type or a trapezoidal type, or an α profile type, in which a portion where the inclination changes abruptly may be rounded. Further, the core region is segmented into two or more portions, each of which can take any one of the profiles described above. This core region structure, together with the cladding layer modulation, determines the dispersion characteristics and other performance characteristics of the waveguide fiber.

[0012] The refractive index of a base glass such as silica is determined by using germanium oxide, alumina, phosphorus,
It can be changed by adding a dopant such as titanium oxide, boron, fluorine and 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 along the preform axis from segment to segment. This switching, in combination with the pre-selected core structure, defines the dispersion control characteristics of the fiber as described above. Again, the density can be controlled by controlling the pore 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 cladding 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 holes discussed above. The filament can, of course, be formed using several processes known in the art, but can also be an elongated void filled with the filament. If the cladding layer with the filaments is to interact with light in the form of a photonic crystal with a complete bandgap, the size and spacing of the filaments 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, which is considered to be the average refractive index of the structured cladding layer. it can.

The above-described preform is manufactured for the purpose of drawing an optical waveguide fiber from the preform. Thus, the present invention includes optical waveguides drawn from the novel preforms 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 core preform is prepared by any of several methods known in the art, including external and axial vapor deposition, and internal (MCVD) or plasma deposition. It is produced by The core of the preform is solid with no voids. Alternatively, the core preform may 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 collapses during the drawing process to form a homogeneous or (if the hollow tube is doped) doped solid glass core region. A plurality of glass tubes having a cavity extending through the hollow tube are produced. The hollow tube is reduced in diameter at a preselected number of locations along the hollow tube and placed around a centrally located core preform. Each of the reduced diameter hollow tubes is essentially the same as any other reduced diameter hollow tube. The hollow tube may be partially or completely crushed at the reduced diameter position. A preform having a reduced diameter hollow tube around a core preform placed at the center is a preform having an axial change in cladding layer density.

The cross section of the hollow tube can be circular or polygonal with three or more sides. The hollow tube around the central core preform is of a specific size and shape chosen at the core-cladding interface, depending on the type of signal-waveguide interaction, refraction or photonic crystal. Can be arranged randomly or periodically. In the case of a cladding layer having the characteristics of a photonic crystal 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 light transmitted through the waveguide.

Instead of the holes intermittently distributed along the length of the hollow tube, the hollow tube can be manufactured using the surrounding base glass and the columnar glass contained in the surrounding base glass. The individual segments of the hollow tube can be filled with glass forming powder or fragments of glass filaments during the formation of the reduced diameter portion, or the hollow tube can be filled with filaments before the reduction is performed. Either of these filament or powder filling methods can be used in a process to provide a filled hollow tube whose filler is much lower than the hollow tube, eg, having a softening temperature above 20 ° C. On the other hand, by storing the aggregate of the columnar glass and the hollow tube in a thicker hollow tube having a softening temperature close to the softening temperature of the columnar glass, it becomes possible to make the softening point of the columnar glass higher than that of the hollow tube. In the case where a waveguide drawn from a preform configured as such functions 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 to combine the components of the preform together. In one embodiment of the novel preform of the present invention, the hollow tube and core preform are contained within a thicker hollow tube, and the thicker hollow tube is collapsed onto the hollow tube and core preform assembly. .

In another embodiment of the present preform, the hollow tube and the core preform can be inserted into a chuck, and a soot layer is deposited on the hollow tube and vitrified. By bundling the hollow tube and the core preform before the insertion or deposition process into the chuck, the insertion into the chuck can be easily performed. Bundles are achieved by thermally connecting the components of the preform together. Alternatively, a frit can be used to glass fuse the components of the preform together. Another tying method is to use ties to keep the preform members together until insertion into the chuck is complete. The ligature can be removed prior to the start of the deposition, or can be made of a material that will not burn easily during the deposition of the first glass soot layer.

Another aspect of the invention is a method of making a waveguide fiber from the novel preform of the invention, the general configuration and specific embodiments of which are described above. One embodiment of a method of drawing a waveguide from a novel preform of the present invention includes the steps of sealing one end of each of the deformed hollow tubes surrounding the core preform and providing a waveguide fiber from one end opposite the sealed end. Is drawn. The pores in the deformed hollow tube are enclosed in the hollow tube, so that they remain through the drawing process. Unwanted voids or pores between the hollow tubes can be crushed 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 core preform 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. Due to the increased internal gas pressure of the hollow tube, the cavity of the hollow tube remains unchanged or increases. As the internal gas pressure decreases, the cavity in the hollow tube becomes smaller or completely closed during drawing. That is,
By changing the gas pressure, an axial change in the density of the waveguide fiber cladding layer can be created. The advantage of this embodiment is that the cladding density from solid glass, together with the desired geometry of the finished waveguide fiber, the maximum porosity limited only by the number of open hollow tubes in the cladding layer and the minimum wall thickness of the hollow tubes Can be changed essentially continuously up to a glass having An inert pressurized gas such as nitrogen or helium is preferred. Undesired interstitial voids or pores between the hollow tubes are similarly exposed to the applied pressure. Depending on the size of the pores in the hollow tube relative to the size of the pores, the process is:-all pores collapse or close;-all pores are left open;-pores Is left open, while the hollow tube cavity is closed; or-the hollow tube cavity is left open, while the interstitial cavity is closed. Naturally, the pressure control allows the value of the ratio of the final gap pore size to the final hollow tube pore size to be varied essentially continuously.

In yet another embodiment of the method, the preform member is a core preform as described above, having a cladding layer comprising an array of glass rods disposed around the core preform. The rod array is shaped such that a periodic or random row of holes exists between or through the rods. By intermittently applying vacuum to this preform during the drawing process, the pores between the rods are intermittently reduced from a value less than or equal to the original pore cross-section to a minimum cross-section of zero. Thus, a waveguide having a change in axial density 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, the possible cladding layer densities are essentially from the density of the solid glass material to the density of the porous glass material having porosity limited only by the dimensions of the preform member and the waveguide drawn from the preform. Can be continuously changed. The preform configuration in this embodiment is selected such that at neutral pressure, viscous forces act to close the holes. The pore size can then be modulated by applying 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 the modulated pressure reduction.

A particularly useful embodiment of the novel waveguide of the present invention is a waveguide where the total dispersion is controlled for each segment of the waveguide. By combining a preselected core index profile with a particular pattern of change in cladding layer segment density, the total dispersion alternates between positive and negative values. In a waveguide fiber having a positive total dispersion, light travels faster than longer wavelength light as wavelength decreases. The result is that the algebraic sum of the product of the segment length and the total dispersion of the segment over the entire length of the waveguide fiber, ie, the net total dispersion, can be equal to a preselected target value. For example, the net total dispersion of a waveguide fiber can be equal to zero, even though the total dispersion of any segment of the waveguide is not zero.

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

[0026] DETAILED DESCRIPTION The novel waveguide preform or waveguide fiber of the present invention the invention is lower than the refractive index of the waveguide core, utilizing waveguide properties of the cladding layer having a refractive index that varies in the axial direction I do. A waveguide fiber is conceivable in which a waveguide is formed by forming a clad layer in a structure that functions as a photonic crystal having a forbidden band over at least a portion of the waveguide length. By changing the composition or distribution of the cladding material in each type of cladding, desired cladding characteristics can be obtained.

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

A notable embodiment disclosed and described herein is one in which elongated holes 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 a hollow tube having central axis holes 4 and 6, respectively. The material surrounding the holes is circular 2 in FIG. 1A and hexagon 8 in FIG. 1B. The profile 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 surrounding glass material, that is, a material made of glass having a dielectric constant different from that of the base glass.

The steps of a method for changing one of the substructures are shown in FIG. Hollow 12
Are formed in the exemplary hollow tube 10. The depression is formed in the central cavity or filament by a narrow region 1 separated by a region 16 in which the central cavity of the hollow tube is not deformed.
Make 4. By assembling such a lower structure around the core region, a clad layer whose refractive index changes in the axial direction is obtained. Further, the substructure may be arranged such that the central holes or filaments 18 form a periodic array. The periodic array can have a pitch of photonic crystals designed for use in the preferred wavelength range. At present, the important wavelength range for telecommunications applications is around 600
nm to 2000 nm.

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

Embodiment Referring to FIG. 3, a waveguide preform and a fiber can be manufactured as follows. Hexagonal substructures 20 and 22 having a cavity along the central axis are assembled in a cladding layer surrounding core preform 30. The entire assembly of hexagonal hollow tubes surrounding core preform 30 is encased in hollow tube 28. In the details of the figure, the cavity of the undercarriage is indicated by point 26.

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

[0034] The hollow tube 28 can be used before or during drawing of the preform into the waveguide fiber.
Inside can be crushed on the assemblage. To ensure proper cladding porosity control, a pressure in the range above atmospheric pressure is applied to the hollow tube 28 during the drawing process. Over a first pressure range beginning at atmospheric pressure and ending above a predetermined atmospheric pressure, the cavity of the substructure will be closed by the action of viscous forces present during the drawing process. Over a second pressure range, which starts at a pressure slightly higher than the highest pressure in the first pressure range and continues to rise, cavities will still be present in the cladding layer after drawing is completed. The size of the cavity is controlled by the magnitude of the applied pressure. The pressure applied to the underlying structure cavity is varied from a value in a first pressure range during the drawing process to a value in a second pressure range. That is, the cavity diameter varies from zero to a preselected diameter corresponding to a pressure selected from the second range. Modulation of the applied pressure produces a corresponding axial modulation of the cladding layer density or refractive index. That is, the density and the average refractive index of the cladding layer change along the axial direction of the waveguide fiber.

COMPARATIVE EXAMPLE 1 An optical waveguide preform is manufactured as described in the above example, except that the end of the lower structure is sealed in this comparative example. Further, the hollow tube is provided with a recess as shown in FIG. Each of the hollows of the substructure hollow tube is matched to each of the hollows of the other hollow tubes in the hollow tube 28. This indentation is maintained by bundling or other means as described above.

An optical waveguide fiber is drawn from the preform end facing the sealed 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 lower structure hollow tube is sealed. Thus, the deformed, or hollowed, sealed hollow tube forms an elongated cavity arranged in essentially the same pattern as the preform substructure. The hollow portion of the hollow tube collapses to form a substantially uniform cladding cross section. The elongated cavities are axially separated one by one with the crushed cladding sections having a substantially uniform cross section. The elongated holes are separated one by one in the cross-section by the tube wall of the substructure. The vacuum, together with the viscous forces that act on the preform during drawing, serve 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, together with the applied vacuum, acts to close the cavity of the unsealed core hollow tube and create a solid glass core.

FIG. 4 is a view taken from a cross-sectional photograph of a waveguide fiber drawn according to the present embodiment. The core region 32 is solid glass and the cross-section of the cladding region includes exemplary holes 34 that serve to lower the average refractive index of the cladding layer.

It is understood that holes 34 can be created with dimensions or arrangements such that the signal wavelength is in the forbidden band of the photonic crystal so that the signal forms a photonic crystal that is confined to the core region.

COMPARATIVE EXAMPLE 2 Another process is a process in which the lower structure is solid and arranged in a thick hollow tube similarly to Comparative Example 1 described above. However, in this case, the substructure is not deformed. Vacuum is applied intermittently to the hollow tube 28 during drawing, so that interstitial cavities, ie, vacancies between substructures, alternately collapse (vacuum is applied) or remain in the cladding layer as elongated voids. (Vacuum is turned off). 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 cavities 36 present in the cladding layer are interspersed between solid parent cladding glass 38. In the axial direction, the porous portions of the cladding are separated one by one by non-porous portions made of substantially homogeneous void-free cladding glass.

The effect of introducing holes into the cladding layer is shown in four pairs of figures constituting FIG. FIG.
A shows a cross section of the non-porous portion of the waveguide fiber. The core or core preform 40 is surrounded by a solid cladding glass layer 42. In FIG. 6B, the core or core preform 44 is surrounded by a porous cladding layer 42. 6A and 6B
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. The first component of each pair, FIGS. 6A, 6C, 6E and 6G, has a solid cladding layer, while the second component of each pair, FIGS. 6B, 6D, 6F and 6H, It has a porous cladding layer.

The effect of the elongated voids 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 portion of the waveguide featuring the refractive index profile of FIG. 6C will be broader than the mode power distribution of the signal propagating in the waveguide region having the refractive index profile of FIG. 6D. Of course, other properties such as total dispersion, total dispersion slope, cut-off wavelength, and zero dispersion wavelength will also be different at different axial portions along the novel waveguide of the present invention. From one suitably configured and drawn preform, a waveguide fiber having the above-described axial change in waveguide fiber properties is made.

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

In FIGS. 6G and 6H, an axial change in the cladding refractive index results in a first core profile 56 having three distinct annular regions 60, 62 and 64 for the cladding layer 57. In contrast, there are only two distinct annular regions 66 and 68 in the core profile 58 for the index of refraction of the cladding layer 59, which is porous, ie, has a large number of holes.

The dispersion compensating ability of the novel waveguide preform of the present invention and the waveguide fiber drawn from this preform can be easily seen from FIG. 6 (C to H). In addition, modal 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, thus increasing the efficiency in using the novel waveguides of the present invention. Provides flexibility.

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

[Brief description of the drawings]

FIG. 1A is a view of a hollow tube having a circular cross section.

FIG. 1B is a diagram of a hollow tube having a hexagonal cross section.

FIG. 2 is a perspective view of a hollow tube having a reduced diameter segment.

FIG. 3 is an illustration of a hexagonal hollow tube placed around a core preform and inserted into a thicker supporting hollow tube.

FIG. 4 is a cross-sectional view of a preform or waveguide having a core region and a porous or composite cladding layer.

FIG. 5 is a cross-sectional view of a waveguide having a porous cladding layer having holes formed by voids between a core region and a cladding layer hollow tube.

FIG. 6A shows a cross section of a preform or waveguide having a solid cladding layer.

FIG. 6B shows a cross section of a preform or waveguide having a porous or composite cladding layer.

FIG. 6C shows an example of a core refractive index profile of a preform or waveguide having a solid cladding layer.

FIG. 6D shows a core refractive index profile corresponding to FIG. 6C for a preform or waveguide having a porous or composite cladding layer.

FIG. 6E shows another example of a core refractive index profile of a preform or waveguide having a solid cladding layer.

FIG. 6F shows a core refractive index profile corresponding to FIG. 6E for a preform or waveguide having a porous or composite cladding layer.

FIG. 6G shows yet another example of a core refractive index profile of a preform or waveguide having a solid cladding layer.

FIG. 6H shows a core refractive index profile corresponding to FIG. 6G for a preform or waveguide having a porous or composite cladding layer.

[Explanation of symbols]

 20, 22, 28 Hollow tube 34, 36 Void 40, 44 Core region 42, 46 Cladding layer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G02B 6/00356 G02B 6/00 356A 376 376Z 6/10 6/10 C 6/20 6/20 Z ( 81) Designated countries EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE), AL, AM, AT , AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CU, CZ, DE, DK, EE, ES, FI, GB, GE, GH, GM, HR, HU, ID, I L, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, MW, MX, O, NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, UA, UG, US, UZ, VN, YU, ZWF terms (reference 2H050 AB05X AB06X AB07X AB08X AB09X AB10X AB18X AC24 AC28 AC62 AC81 AD00 4G021 BA01 BA02 BA03 BA04 BA11 BA12 BA13 BA15 HA01 4G062 AA06 AA07 BB02 CC07 LA02 LA03 LA04 LA06 LA07 LA08 LA10

Claims (39)

[Claims] 1. An optical waveguide preform comprising: a central core glass surrounded by a cladding glass layer and in contact with said cladding glass layer to form a preform; said preform having first and second ends and said A cladding layer having an axis between the first and second ends, the cladding layer including a plurality of annular segments extending continuously along the axis; wherein a preselected density of each of the segments is equal to the respective segment. An optical waveguide preform, wherein the density of each of the segments is higher or lower than the density of any of the adjacent segments, different from the preselected density of the segments adjacent to. 2. The optical waveguide preform according to claim 1, wherein said segments wherein said preselected density is lower than said density of adjacent segments have holes. 3. The optical waveguide preform according to claim 2, wherein said segments wherein said preselected density is higher than said density of adjacent segments also have voids. 4. The optical waveguide preform according to claim 2, wherein said holes are elongated, and a longitudinal direction of said holes is along said axis of said preform. 5. The optical waveguide preform according to claim 3, wherein said holes are elongated, and a longitudinal direction of said holes is along said axis of said preform. 6. The optical waveguide preform according to claim 4, wherein said elongated holes form a periodic array. 7. The optical waveguide preform according to claim 5, wherein said elongated holes form a periodic array. 8. The pitch of the periodic array is such that the waveguide fiber drawn from the preform to a preselected diameter has a periodic array of elongated holes having a pitch in the range of 0.4 μm to 20 μm. The optical waveguide preform according to claim 6, wherein the optical waveguide preform has a pitch. 9. The method of claim 6, wherein the elongated holes have a diameter and a ratio of the diameter to the pitch of the periodic array ranges from about 0.1 to 0.9.
Or the optical waveguide preform according to any one of the above items 7. 10. The method according to claim 10, wherein the core glass has a step shape, a rounded step shape,
A trapezoidal shape, a rounded trapezoidal shape, an α profile, and a refractive index profile selected from the group consisting of a segmented profile, wherein the segments of the segmented profile are a porous layer, a stepped shape, a rounded stepped shape, a trapezoidal shape. The optical waveguide preform according to claim 1, wherein the preform is selected from the group consisting of a mold, a rounded trapezoidal mold, and an α profile. 11. The optical waveguide preform according to claim 10, wherein said core glass contains silica glass having a dopant selected from the group consisting of germanium oxide, alumina, phosphorus, titanium oxide, boron and fluorine. . 12. The optical waveguide preform according to claim 11, wherein said core glass contains silica doped with a substance selected from the group consisting of erbium, ytterbium, neodymium, thulium and praseodymium. 13. The optical waveguide preform according to claim 1, wherein said density of cladding layer segments has one of two preselected values. 14. The cladding glass layer segment having a first density of the two preselected densities has a homogeneous first composition, and wherein the cladding glass layer segment has a first composition of a homogenous first composition. 14. The optical waveguide preform according to claim 13, wherein the clad glass layer segment having a density of 2 is made of the porous first composition. 15. The method of claim 14, wherein the holes of the cladding layer having the second preselected density are elongated, and the long dimension of the holes is along the axis of the preform. An optical waveguide preform as described. 16. The optical waveguide preform according to claim 15, wherein said elongated holes form a periodic array. 17. The periodic array of pitches wherein the waveguide fiber drawn from the preform to a preselected diameter has a periodic array of elongated holes having a pitch in the range of 0.4 μm to 20 μm. 17. The optical waveguide preform according to claim 16, wherein the pitch is a pitch. 18. The cladding glass layer segment having the first density of the two preselected densities has a homogeneous first composition having a dielectric constant and the two preselected densities. The clad glass layer segment having the second density of the density is made of the porous first composition, the pores are elongated,
The elongated direction of the holes is along the axis of the preform, and the elongated holes are filled with a material having a second dielectric constant, wherein the first dielectric constant is at least three times the second dielectric constant. The optical waveguide preform according to claim 13, wherein the optical waveguide preform is provided. 19. The optical waveguide preform according to claim 18, wherein said elongated filled holes form a periodic array. 20. The pitch of the periodic array is such that the waveguide fiber drawn from the preform to a preselected diameter has a periodic array of elongated holes having a pitch in the range of 0.4 μm to 20 μm. The optical waveguide preform according to claim 19, wherein the optical waveguide preform has a pitch. 21. An optical waveguide fiber drawn from the preform according to any one of claims 1 to 7 or 10 to 20. 22. The segment density alternates between different preselected densities to obtain a waveguide fiber wherein the core has a refractive index profile and a net dispersion equal to a preselected value. 21. The method according to claim 1, wherein the total variance alternating between positive and negative values is selected to give the segment density in combination with the core profile.
An optical waveguide fiber drawn from the preform according to any one of the preceding claims. 23. A method of making an optical waveguide fiber preform, comprising: a) making a core preform having a major axis; b) forming a plurality of glass hollow tubes having inner and outer dimensions and a major axis. Forming; c) forming N sections of reduced inner and outer dimensions along each of the long axes of the plurality of glass hollow tubes; The dimension sections are each separated by a section of the hollow tube; and d) arranging the plurality of hollow tubes of step c) in an array surrounding the core preform; The long axis of the foam being substantially parallel to the long axis of the hollow tube. 24. The hollow tube of step b) having a cross-sectional shape selected from the group consisting of a circle, a triangle, a parallelogram, and a polygon.
3. The method according to 3. 25. The method of claim 23, wherein said sequence is random. 26. The method according to claim 23, wherein said arrangement is periodic. 27. The method of claim 23, wherein said reduced interior dimension is zero. 28. The compartment wherein the hollow tube has a first composition and a first dielectric constant and separates the N compartments during or before the forming step c). Are filled with a material having a second composition and a second dielectric constant, and
3. The dielectric constant of said second dielectric constant is at least three times said second dielectric constant.
3. The method according to 3. 29. The compartment wherein the hollow tube has a first composition and a first refractive index and separates the N compartments during or before the forming step c). Are filled with a material having a second composition and a second refractive index, and
24. The method of claim 23, wherein the index of refraction is greater than the second index of refraction. 30. The method further comprises: e) inserting the array of step d) into a surrounding hollow tube; and f) collapsing the surrounding hollow tube onto the array. The method of claim 23, wherein: 31. The method of claim 30, further comprising depositing glass soot particles on the surrounding hollow tube. 32. The method according to claim 32, further comprising the steps of: e) bundling the array of hollow tubes of step d) to hold the hollow tubes in place with each other; 24. The method of claim 23, further comprising: depositing glass soot on the hollow tube array. 33. The bundling step includes a step of connecting the glass hollow tubes to each other and the innermost hollow tube to the core preform by heating the hollow tubes. 33. The method according to claim 32. 34. The method of claim 32, wherein the bundling step includes connecting the glass hollow tubes to one another and the innermost hollow tube to the core preform using a glass frit. The described method. 35. A method for producing an optical waveguide fiber, comprising: a) producing a preform according to the method of any one of claims 23 to 34; b) sealing one end of the glass hollow tube. C) drawing a waveguide fiber from the end of the preform opposite the end of the preform having a sealed hollow tube; and d) the waveguide facing the end of the preform to be drawn. Applying a vacuum to the end of the reform. 36. A method for producing an optical waveguide fiber, comprising: a) producing a core preform; b) producing a plurality of glass rods having a cross-sectional shape; Placing in an array surrounding the core preform and including a plurality of holes; d) inserting the rod array and the core preform into a hollow tube to form a drawn preform; e) Drawing an optical waveguide fiber from a drawing preform; and f) applying a varying pressure to the hollow tube during step e). 37. The method of claim 36, wherein said applied pressure varies between atmospheric pressure and a preselected pressure below atmospheric pressure. 38. The method of claim 37, wherein said preselected pressure is sufficient to at least partially collapse said voids. 39. The method of claim 39, wherein the applied pressure varies between a first preselected pressure greater than or equal to atmospheric pressure and a second preselected pressure higher than the first preselected pressure. 38. The method of claim 37, wherein