Single-mode optical waveguide with a large effective area
(57) Abstract:Single-mode optical fiber has the profile of the refractive index of the core, consisting of at least four parts. Main features of the design of the core is the presence of at least two non-contiguous parts of the profile core with a positive relative refractive index percent and at least two non-contiguous parts with a negative %. New design of the core of the waveguide enables the creation of single-mode optical fiber for communication systems, long-haul, high data rate and large distance between regenerators, which include optical amplifiers. The structure of the core of the optical fiber enables to produce optical fibers with controlled dispersion with an effective area of more than 60 μm2. 2 S. and 9 C.p. f-crystals, 9 Il., table 1. The invention relates to a single-mode optical waveguide fiber designed for use in communication systems long-haul high-speed transmission, operating in the wavelength range from approximately 1500 to 1600 nm. In particular, a new optical fiber has a large effective area in rabotanadomy9 optical waveguide with a large effective area is characterized by lower non-linear optical effects, including phase automodulation, four-wave mixing, cross-phase modulation and nonlinear scattering. Each of these effects causes the degradation of signals in systems with high power.The scattering processes that lead to degradation of the signal, in the General case described by equation containing member exp(cP/Aeff), where c is a constant, P is the signal power and Aeff- effective area. Other nonlinear effects are described by equations that include the ratio P/Aeffas a multiplier. Thus, the increase in P/Aeffleads to reduction of the nonlinear contribution to the degradation of the light signal.Need to be in communication systems large information capacity in the transmission of signals over large distances without devices regeneration has led to a reappraisal of approaches to the design of the profile of the refractive index single-mode optical fibers.The essence of this reassessment is to create optical waveguides, which are:
- reduce nonlinear effects, such as noted above,
- optimized for the working wavelength range around 1550 nm with a lower attenuation,
- compatible with spectral character low attenuation, high strength, fatigue strength and resistance to bending.Additional requirement aimed at reducing four-wave mixing, can be finding the wavelength corresponding to the zero dispersion optical fiber outside of the working window.Previous studies, such as disclosed in application for U.S. patent N 08/378780 had a starting point the basic concept of the split design of the core, first presented in U.S. patent N 4715679. In the above application N 08/378780 describes a class of structures core waveguides with a large effective area. In this application has been disclosed a specific design that includes at least one region of the core, in which the minimum refractive index was lower than the refractive index of the shell.Using these key characteristics model, which predicts the properties of structures with split core was used to create the family structures of the core, having Aeffand distribution (or the distribution of electric field intensity) fashion, which characterize an optical fiber suitable for use in Napoleone family waveguides with a large effective area.This application is a development of the work disclosed in the application N 08/378780 and the application sent on 9 November 1995.Specific feature of the new family structures profile fiber according to this application is the fact that a large effective area linked with close to zero slope full dispersion in the selected wavelength range. This combination provides less nonlinear degradation of the signal due to the greater effective area, and a smaller linear dispersion at the selected wavelength range.Definition
- The effective area equal to
Aeff= 2(E2rdr)2/(E4rdr), where the integration is performed from 0 to , and E is the electric field corresponding to the propagating light.The effective diameter of Deffcan be defined as a
- Area mode fields of Amfequal (Dmf/2)2Dmfis the diameter of the mode field, measured using the second method Petermann, 2w=Dmfand w2= (2(E2rdr)/[dE/dr]2rdr), where the integration is performed from 0 to infinity.- Alpha profile is defined as:
n(r) = no(1-[r/a] is, measured from the first to the last point of the alpha profile of the refractive index. The value of r can be put equal to zero at the point of n0the alpha profile of the refractive index or the first point of the alpha profile may be offset from the axis of the optical fiber at a specified distance. If equal to 1, then the alpha profile is triangular. If equal to 2, then the alpha profile is parabolic. If more than 2 and is approximately equal to 6, the profile approaches the speed. Really stepped profile of the refractive index corresponds to alpha equal to infinity, but for practical purposes, the speed profile is approximately from 4 to 6.- Width part of the profile of the refractive index is the distance between the two vertical lines going from the respective start and end points of the profile of the refractive index to the horizontal axis of the graph of the dependence of the refractive index of the radius.The relative refractive index ( %) is defined as:
% = [(n21-n2c)/2n21]100, where n1the core refractive index, and n2cis the refractive index of the shell. Unless otherwise noted, n1- poppy is any of refraction selected minimum refractive index in the glass layer of the shell. The area in the core with a refractive index lower than this minimum value, shall be considered as having a negative refractive index.- Resistant fibers to bending is given by the standard procedure, which is measured insertion losses caused by bending of the fiber in the 1 turn around a mandrel with a diameter of 32 mm and 100 turns around a mandrel with a diameter of 75 mm, the Maximum allowed attenuation caused by bending, usually defined for the working window of about 1300 nm and about 1550 nm.An alternative test of the bending conducted to compare the relative stability of the optical fiber to bending, is a test bending conducted using the combs and pins. In this test, the measured insertion losses in an optical fiber, whose initial state is essentially no loss due to bending. Then the optical fiber braid comb pins and re-measure the attenuation. The loss due to bending, defined as the difference between the measured attenuation. Comb pin is a set of ten cylindrical pins, placed in a row and secured in an upright position on the flat top of Thibaut so, to ensure contact of the waveguide with a part of the surface of the pins.- The relative change of the profile indexi% refraction means that any i% can be changed individually or together with others on that percentage.- The relative change of the combined radius means that the change of total radius r of the core is distributed in proportion to the radii of the individual parts of the core.The invention
The present invention provides the need for single-mode optical waveguide fiber, which provides the advantage of a relatively large effective surface area, in combination essentially flat dispersion, i.e. the steepness of the dispersion in the extended operating range of wavelengths equal to about 0.03 PS/nm2-km or less.In the first aspect of the invention relates to a single-mode waveguide having a glass core that includes at least four parts. Each part is characterized by the profile of the refractive index, an outer radius riandi%. The lower the index the refractive index and r refers to the particular part. Parts are numbered from the, having a refractive index of ncthat surrounds the core. The core has two non-contiguous parts with positive % and two additional non-contiguous parts with a negative %. When using this basic configuration of the core were found many setsi% rithat provide essentially flat curve full dispersion, that is, a curve having a slope of about 0.03 PS/nm2km or less in a predetermined wavelength range and an effective area of at least 60 μm2. The effective area of several core constructions with this configuration exceeds 70 μm2.The preferred embodiment of this aspect of the invention provides essentially zero dispersion slope in the wavelength range from approximately 1450 to 1580 nm. This range includes the region of small attenuation in the region of 1550 nm and the wavelength range with high-gain optical amplifier doped with erbium.Preferred valuesifor two non-contiguous parts with positive % lie in the range from approximately 0.1 to 0.8%. For the two parts with a negative % preferred ranges of values are from-0.80 who uppy, including the alpha profile in the range from approximately 1 to 6, a stepped refractive index, rounded step profile of the refractive index and trapezoidal profile. The preferred profile of the refractive index for parts with negative % selected from the group comprising an inverted trapezoidal, inverted staggered and inverted rounded step profile of the refractive index. It is clear that in the specific profile of the one part, negative % can be in the form of an inverted trapezoid, while the other part with a negative% is the refractive index in the form of an inverted rounded steps. The number of combinations and permutations in the profiles of the refractive index, separated by at least 4 parts, very great. Thus, the search of the structures of the profile of the refractive index of the core, which provide the desired properties of the optical fiber for practical purposes, is carried out using computer simulation.Diffusion of dopant in the Central area of the line can cause the decrease of the refractive index in the center in the form of an inverted cone. In addition, diffusion in areas of sharp changes concentating model, considering essentially any change in the profile of the refractive index due to reverse diffusion of dopant. A typical form of the reduction of the refractive index caused by diffusion, near the center is an inverted cone having a base radius of not more than approximately 2 microns.In the most preferred embodiment of the invention, parts 1 and 3 have positive %, and parts 2 and 4 have a negative %. As noted above, parts are numbered sequentially, starting with 1 for the part that includes the longitudinal axis of symmetry of the waveguide. In this embodiment, the radii have the following limits: r1in the range from approximately 3 to 5 μm, r2- no more than approximately 10 μm, r3- no more than about 17 microns, and r4- no more than approximately 25 microns. The corresponding % of the parts in this embodiment of the invention has the following limits:1- in the range of about 0.20 to 0.70%,2% and4% in the range of about from - 0.80 to - 0,15% and3% in the range of about from 0.05 to 0.20%.The model of the core can be used in two ways:
- you can enter the structural parameters, i.e. aliceaacostai% rieach part, and to calculate the parameters of the waveguide, which correspond to this structure, or
- you can enter the functional parameters, i.e. the wavelength of the cutoff wavelength corresponding to the zero dispersion, the slope of the full dispersion, effective area, the diameter of the mode field, the operating range of wavelengths and attenuation of the waveguide, due to bending, and to calculate a family of structures that provide such functionality.Thus, the second aspect of the invention relates to the creation of optical fibers having at least four parts. Two non-contiguous parts have positive % and two non-contiguous parts have a negative %. Values of riandi% the relevant parts selected to create the waveguide, characterized by:
- full tilt variance about 0.03 PS/nm2or less in the wavelength range from approximately 1400 to 1575 nm,
the wavelength corresponding to the zero dispersion, which lies outside of the working window, i.e. in the range from approximately 1,200 to 1,500 nm or more approximately 1575 nm (the upper limit is determined by the required dispersion in the working window. For most applications, the upper limit is poslovnim bend at the comb pins, no more than 20 dB.Remarkable feature of the collection waveguides in this second aspect of the invention is the ease of their production. In particular, these waveguides are relatively insensitive to changes ini% +/-3% and changes the combined radii of +/-1%, which illustrates the calculated data are given in table. 1.These and other aspects and advantages of a new family of core constructions will be described with the following drawings.Brief description of drawings
In Fig. 1a and 1b illustrate the General form of a variant of implementation of the new profile of the refractive index of the core with four parts,
in Fig. 2a and 2b presents concrete examples of new options for performing profile of the refractive index of the core with four parts,
in Fig. 3 shows a typical characteristic of the complete dispersion of the new optical fiber,
in Fig. 4 compares the Deffand the diameter of the mode field in a wavelength range for a subset of structures new profiles core,
in Fig. 5a, 5b and 5c shows the sensitivity of the full dispersion to changes in radius or refractive index of parts in the new profile of the refractive index of Serdtsev is passing data to 1 Gbps and above, when the distances between regenerators more than 100 km, typically use optical amplifiers or multiplexing using wavelength division multiplexing. Thus, manufacturers of fiber optic forced to develop the waveguides, which are less susceptible to non-linear effects due to more powerful signals or four-wave mixing, which may occur in multiplex systems. It is clear that a suitable optical fiber must also have a low linear dispersion and low attenuation. In addition, to provide a multiplexing using wavelength division multiplexing, optical fiber should have these properties in particular the extended wavelength range.A special advantage because of its lower cost and more flexibility are the design of the waveguide, which is relatively easy to manufacture and which can control the variance. Described here designs are well suited to control the dispersion, wherein the dispersion of the waveguide change in length of the optical fiber to change the full variance between positive and negative values.New design split core according to the present application provides the above required properties.e shows the dependence % of the radius of the waveguide. Although in Fig. 1a and 1b shows only four discrete parts, it should be understood that the fulfillment of the functional requirements can be provided by forming the core with more than four parts. However, embodiments of the that has fewer parts, it is usually easier to manufacture and therefore preferred.Characteristic elements of the structure profile of the refractive index for the new optical fiber shown with parts 4 and 8 of the core, which are non-contiguous parts having a positive %, and parts 2 and 6 of the core, which are non-contiguous parts having a negative %. Parts with positive and negative can be categorized in more than one part. The profile of the refractive index corresponding to each part can be adjusted to achieve this configuration, the core that provides the desired properties of the optical fiber.The dashed lines 10, 12 and 14 show an alternative form of the profile of the refractive index for the three parts, including a new core of the waveguide. The outer radii of 5, 7, 9 and 11 parts can also be modified to achieve the configuration of the core, which provides the required NWO is clear, the problem of development is most easily solved using computer simulation. The main elements of this model are discussed in the application N 08/323795.In Fig. 1b illustrates a variant of the new configuration of the fiber core. In this case part 16 and 20, with a positive% are the first and third parts. The second and fourth parts 18 and 22 have a negative %. Lines 3 and 21 on the respective Fig. 1a and 1b represent the refractive index of the shell, which is used to calculate the parameters % parts.Example 1. An embodiment of the invention with four parts
In Fig. 2a depicts an embodiment of a new core waveguide having four parts 26, 28, 30 and 32. Form each part is a rounded step. The rounding of the corners of the stepped profile, as well as reduction 24 of the refractive index near the center line, may be due to diffusion of dopant in the manufacture of optical fibers. You can compensate for this diffusion, for example, by alloying operation, but often this is not required.In Fig. 2a1% part 26 is close to 0,39%,2% part 28 is close to -0,25%,3% part 30 is close to 0,12% and4% part 32 plavlenii, approximately 4 and 6.5, 15, and 22 microns.This structure core provides such characteristics of optical fiber:
- diameter mode field 9 µm,
- Deffof 9.3 μm,
- Aeff68 μm2,
- wavelength cutoff 1400 nm,
- the loss due to bending on the comb pins, 20 dB and
- full tilt variance of up to 0.03 PS/nm2-km.Comparative example 2. An embodiment of the invention with four parts
In Fig. 2b depicts an embodiment of a new core waveguide having four parts 36, 38, 40 and 42. Form each part is a rounded step. As noted above, the rounding of the corners of the stepped profile, as well as the decrease of the refractive index near the axis, may be due to diffusion of dopant.In Fig. 2b1% part 36 is close to 0.40 per cent,2% part 38 is close to -0,25%,3% part 40 is close to 0,12% and4% part 42 is close to -0,25%. The respective outer radii of the parts, starting from the inner part and following in the outer direction, is equal to approximately 4, 6,5, 15 and 23.5 microns.Note that the structural differences between the profiles of the refractive index shown in Fig. 2a and 2b, is of lichen 1-2 microns.This structure core provides such characteristics of optical fiber:
- the diameter of the mode field of 9.2 μm,
- Aeff72 μm2,
- wavelength cutoff 1404 nm,
- the loss due to bending on the comb pins, 12 dB and
- full tilt variance of up to 0.03 PS/nm2-km.Wavelength cutoff marginally increased, but the resistance to bending has improved tremendously, a aeffin the comparative example has increased by approximately 6%. Structural changes, which together provide an improved waveguide is increased % in parts with a negative refractive index and the increase of the radius. It is a measure of the sustainability of a new configuration profile of the core refractive index to external influences in the sense that an increase in Aeffand resistance to bending can be achieved simultaneously.Graph 46 full dispersion characteristic of the new design of the profile of the refractive index of the core, shown in Fig. 3. The flat region of the curve 44 covers the wavelength range from approximately 1400 to 1570 nm. Thus, the working wavelength range of the nonlinear dis is and by maintaining a low full dispersion at the operating wavelength.The advantage of a subset of the new core constructions illustrated in Fig. 4. The effective diameter of 48 greater than the diameter 50 of the mode fields in the wavelength range of at least 1200 to 1800 nm. A larger value of Deffis used to limit non-linear effects due to the reduction of signal power per unit area. Smaller diameter mode field provides better resistance to bending, since a large proportion of the signal power is directed by the waveguide than emitted. It is this property of the fiber core of the new waveguide limits the nonlinear effects and, at the same time, provides good retention of energy within the waveguide and, thus, good resistance to bending.The relative insensitivity of the spectral dependence of the total variance change full radius shown in Fig. 5a. Curve 54 is a reference curve for the core, combined with the radius r. Curve 58 represents the full dispersion in an optical fiber with a combined radius of the core, defined above, is 1% greater than r. Curve 56 represents the entire dispersion in an optical fiber with a combined radius of the core is 1% less than r. Note that the offset is of full dispersion to changes in the refractive index of any or all of the parts illustrated in Fig. 5b. Curve 60 is the reference curve. Curves 64 and 62 represent the full variance for cases where the refractive index changes by +3% and -3% respectively. Here again the curves 64 and 62 do not differ from the reference curve 60 greater than about 2 PS/nm-kmThe table below gives the average value and standard (RMS) deviation of the selected parameters of the optical fiber, when combined radius varies by +/-1%, and the refractive index simultaneously changed to +/-3%. The reference profile is essentially the same as in comparative example 2.It is seen that the deviation from the target values slightly, this indicates that the design of the core provides a relatively stable properties of the optical fiber for these changes in the structure of the core of the optical fiber.Change the radius, which lead to a change of sign of the full dispersion shown in Fig. 5c. Reference, as before, is the curve 54 full dispersion in Fig. 5a. The change of the combined radius of 1.5% gives a curve 68 full dispersion. The change of the combined radius of 2.5% and 4.5% leads to curves 66 and 70 full dispersion, respectively. Thus, the new konstrukcije changing radius along the fiber will result in periodic changes of sign of the full dispersion, so the total variance for the whole segment of optical fiber can be made essentially equal to zero, while the full dispersion of the points along the waveguide fiber is not zero. This control fully dispersed essentially eliminates four-wave mixing while maintaining a very low complete dispersion throughout the length of the waveguide.Although there have been described particular embodiments of the invention, it is nonetheless limited only by the following formula. 1. Single-mode optical waveguide fiber containing glass core, located symmetrically relative to the longitudinal axis of the optical fiber and including at least four parts, each of which has a profile of refractive index, the relative refractive indexi% and an outer radius of ri, where i is an integer that refers to specific parts, and the parts are numbered sequentially from 1 to n, starting with the first part, located on the specified axis, and a layer of glass shell formed over the specified core and encloses the core, and the specified layer has a refractive index of nc, characterized in that m is ENISA least two non-contiguous parts of the core have a negative relative refractive index percent, and outer radius riand the value ofi% of each of the specified portion is selected to provide a dispersion slope of 0.03 PS/nm2km or less at the predetermined wavelength range and an effective area of more than 60 μm2.2. Single-mode optical waveguide fiber according to p. 1, wherein the predefined wavelength range 1450 - 1580 nm.3. Single-mode optical waveguide fiber under item 1, characterized in that the said at least two parts with positive % have % in the range of 0.1 to 0.8%, and these at least two parts with a negative % have % in the range(-0,80) - (-0,1)%.4. Single-mode optical waveguide fiber under item 1, characterized in that the said at least two parts with positive % have a profile index of refraction selected from the group including alpha-profile, which lies in the range 1 to 6, the stepped profile of the refractive index, the speed profile of the refractive index with rounded corners and a trapezoidal profile, and these at least two parts with a negative % have a profile index of refraction selected from the group comprising an inverted stepped profile indicator rotten the tx2">5. Single-mode optical waveguide fiber according to p. 4, characterized in that the profile of the refractive index of the first part of this glass core's maximum refractive index n1refraction is displaced away from the axis of the waveguide, and the profile of the refractive index decreases monotonically from the value of n1to the value of the refractive index on the axis, forming around the axis of the decrease of the refractive index in the form of an inverted cone that has a base radius of not more than 2 μm.6. Single-mode optical waveguide fiber under item 5, characterized in that the glass core contains four parts, and1% and3% positive, and2% and4% negative.7. Single-mode optical waveguide fiber according to p. 6, wherein r1is in the range of 3 to 5 μm, r2not more than 10 μm, r3not more than 17 μm, and r4not more than 25 μm and r4> r3> r2> r1.8. Single-mode optical waveguide fiber according to p. 7, characterized in that the glass core has a 1% in the range of 0.20 to 0.70%,2% in the range(-0,80) - (-0,15)%, 3% in the range of 0.05 - 0.20%4% in diaphana, located symmetrically relative to the longitudinal axis of the optical fiber and including at least four parts, each of which has a profile of refractive index, the relative refractive indexi% and an outer radius of ri, where i is an integer that refers to specific parts, and the parts are numbered sequentially from 1 to n, starting with the first part, located on the specified axis, and a layer of glass shell formed over the specified core and encloses the core, and the specified layer has a refractive index of nc, characterized in that at least two non-contiguous parts of the core have a positive relative index percent of refraction and at least two non-contiguous parts of the core have a negative relative refractive index percent and an outer radius of riandi% of each of the specified portion is selected so as to provide the following performance characteristics: a dispersion slope of 0.03 PS/nm2km or less in the wavelength range 1400 - 1575 nm, the wavelength corresponding to the zero dispersion outside of the working window, lying in the range 1450 - 1580 nm, the diameter of the mode field is greater than 9 μm and attenuation, abusable.9, characterized in that the performance is insensitive to changes ini% +/-3% and the change of the combined radius of +/-1%.11. Single-mode optical waveguide fiber under item 9, characterized in that the profile of the core varies along the fiber length to provide a pre-determined total dispersion corresponding to this segment of the fiber.
FIELD: optical and electronic industry; production of fiber optic components having electrooptical effect.
SUBSTANCE: the inventions are dealt with optical and electronic industry, and may be used for development engineering of transmitting systems and data processing, in which application of the fiber optic components with electrooptical effect is expedient. The fiber consists of a core, a light conducting shell, a light-absorbing shell containing light-absorbing elements and current-carrying electrodes. The method includes operations of a down-draw of separate glass rods from glasses fillets composing elements of a fiber, piling up a pack of a with the form of cross-section of a hexahedron or a square including piling of electrodes, afterstretching of preform and its pulling into a fiber with application of a polymeric coating. The invention allows to create a single-mode fiber with heightened electrooptical effect from the glasses having a Kerr constant by 1.5 order higher than one of a quartz glass, to produce fibers with the given structure of shells, cores and control electrodes at simplification of process of a drawing down of fibers.
EFFECT: the invention ensures creation of a single-mode fiber with heightened electrooptical effect, to produce fibers with the given structure of shells, cores and control electrodes, to simplify process of fibers drawing down.
13 cl, 9 dwg
SUBSTANCE: fiber has core and cover. Fiber is made in such a way, that in case of change of radiuses of beds with different refraction coefficients, at least one optical property of core, for example, effective section of core Aeff and slant of dispersion curve, reach appropriate limit values in given range of deflections from base radius. Length of cut wave equals 1450 nm or less. Optical fibers have practically constant optical properties and allow to vary chromatic dispersion in certain limits.
EFFECT: higher efficiency.
2 cl, 14 dwg