Optical fiber with low dispersion and optical transmission system using an optical fiber with low dispersion

 

The invention is used in fiber-optic communication lines. The optical fiber has a Central core with refractive index n1 and the diameter A1 of the first and second peripheral core respectively with n2 and A2 and A3 and n3, and a shell with nwith. The following conditions are true: n1>n3>nwith>n2, A1/A2 is at least 0.4 and not exceed 0.7, A3/A2 does not exceed 1.6. The optical transmission system includes an optical fiber with low dispersion and device for compensation of dispersion, which has a negative chromatic dispersion gradient. Ensured the reduction of the chromatic dispersion and the increase in the effective area of the core. 2 C. and 8 C.p. f-crystals, 11 tab., 5 table.

The invention relates to optical fiber with low dispersion used, for example, when performing optical transmission using wavelength division multiplexing in the range of 1.5 μm and an optical transmission system using such an optical fiber with low dispersion.

BACKGROUND of the INVENTION WITH the development of information society dramatically increased the amount of transmitted information and are experiencing inevitable and urgent solution to the problem, zaklyuchalas ilokano-optical communication. One approach to solving this problem is the implementation of a higher data transfer speed and bandwidth has been the development of optical fiber amplifiers, which can carry out the amplification of the optical signal in the form of light radiation through the use of optical fiber doped with a rare earth element, for example, an optical fiber doped with erbium Er3+(VLA) (EDF). The creation of optical amplifiers using such optical fibers has led to rapid progress in the creation of the signal light high power.

Meanwhile, to increase throughput in optical communication systems have been developed by means of optical transmission using wavelength division multiplexing (division multiplexing wavelength), in which one optical fiber transfer of optical signals with different wavelengths. It is expected that the use of an optical amplifier that uses the above optical fiber in optical communication tools using such spectral multiplexing for transmission of optical signals in an optical transmission system using wavelength division multiplexing) prey relationships.

One of the typical examples of the optical amplifier fiber optic type is WVLA (EDFA) (amplifier-based optical fiber doped with erbium), which contains VLA the aforementioned type. Now continue the ongoing study of the potential use of UVLE for implementation through the above transmission optical signals with wavelength division multiplexing in the wavelength range of 1.5 μm (with a wavelength of 1520 to 1620 nm), which is a band amplification of UVLE, serving as bandwidth.

In Fig. 6A and 6B show examples of the distribution profiles of the refractive index of optical fibers that have been proposed in the related fields of technology as an optical fiber for optical transmission using wavelength division multiplexing in the above wavelength range of 1.5 μm, in particular in the wavelength range near 1550 nm (the wavelength of 1.55 μm), serving as the bandwidth (as the used wavelength range). In Fig.6A shows the distribution profile of the refractive index, consisting of two regions having a different form of distribution, and Fig.6B shows the distribution profile of the refractive index, it is the refractive index, consists of the shell 5, the Central core 1, having a larger refractive index than the refractive index of the shell 5, and the first peripheral core 2 having a refractive index less than the refractive index of the Central core 1, but greater than the refractive index of the shell 5. An optical fiber having a W-shaped distribution profile of the refractive index, consists of the shell 5, the Central core 1, having a larger refractive index than the refractive index of the shell 5, and the first peripheral core 2 having a smaller refractive index than the refractive index of the shell 5.

Among the above-described optical fiber, which has two parts with different shape of the distribution profile of the refractive index of the fiber, for which the wavelength at which the dispersion is equal to zero, is near a wavelength of 1.55 μm, referred to as optical fibers with the dispersion offset. As for the optical fiber with the dispersion shift the wavelength at which the dispersion is equal to zero, is near a wavelength of 1.55 μm, which represents the Central wavelength of the wavelength range of 1.55 μm, the wavelength of 1.55 μm has is but the appearance of the nonlinear effect of four wave mixing. Therefore, in this optical fiber with dispersion offset occurring four-wave mixing light radiation causes the appearance of distortions in the form of a light signal, which makes it impossible to deliver high quality transmission of the optical signal with wavelength division multiplexing.

To overcome this problem have been developed optical fiber with two areas with different shape of the distribution profile of the refractive index with an offset wavelength at which the variance is equal to zero outside of the range of wavelengths of 1.55 μm. However, it is known that the wavelength of 1.55 μm optical fiber of this type has a large gradient of the dispersion. Consequently, in this type of optical fiber is difficult to provide a small value of the difference between the chromatic dispersion in the wavelength range for transmission of optical signals with wavelength division multiplexing (difference between the maximum value and the minimum value of the chromatic dispersion in the wavelength range). Therefore, when using the optical fiber of this type it is impossible to provide a wide bandwidth in the used wavelength range, which icesnow the shape of the distribution profile of the refractive index, functioning as an optical fiber with flattened dispersion, since the above-mentioned difference of the chromatic dispersion is small. However, despite the fact that the effective area of the core (area Andeffthrough which there is an effective distribution of light emission) of the optical fiber, which has two parts with different shape of the distribution profile of the refractive index equal to approximately 45 μm2, the effective area of the core of an optical fiber having a W-shaped distribution profile of the refractive index equal to, for example, about 30 μm2that is approximately 2/3 of the effective area of the core of the optical fiber, which has two parts with different shape of the distribution profile of the refractive index. And in that case, when the effective area of the core is small, which is the case in this situation, when the transmission of optical signals with wavelength division multiplexing has a problem of deteriorating the quality of the transmitted signal in the nonlinear phenomena occurring in the optical fiber.

To solve this problem was proposed increasing the effective area of the core through the use of optical fibers, Kayseri 1 is the Central core; figure 2 - first peripheral core; figure 3 - second peripheral core; and figure 5 is a wrapper. However, since the optical fiber of this type has a large gradient of chromatic dispersion in the wavelength range of 1.5 μm and a greater difference between the chromatic dispersion in this wavelength range, applying this proposed optical fiber for transmission using wavelength division multiplexing a problem arises, namely, that becomes noticeable deterioration in the form of a light signal caused by chromatic dispersion.

Moreover, when using optical fiber transmission system using wavelength division multiplexing optical fiber must be made in the form of cable. And because the required property of the cable must be a small increase in loss caused by the bending of the optical fiber and the lateral pressure on the optical fiber, the optical fiber used for transmission using wavelength division multiplexing, should also provide good preservation of their Flexural properties.

However, as explained above, still has not been implemented optical fiber, through which you can receive the necessary effective area of the core, and reduced razy transmission quality, and, in addition, it was difficult to create the optical fiber with the same good characteristics in respect of losses on the bends.

Moreover, in recent years have come close to the practical implementation of such optical amplifiers, as Raman (Raman) amplifier. Raman amplifier has a wider range of amplified wavelengths than the existing UWLA, and can carry out the amplification of the light signal in any given range of wavelengths within, for example, the range of wavelengths from 1450 to 1650 nm. However, the research progress of optical fibers in the wavelength range does not yet exist.

DESCRIPTION of the INVENTION Therefore, the aim of the present invention is to provide an optical fiber with low dispersion, through which you can get as increased effective area of the core, and reduced the difference between the chromatic dispersion in the wavelength range, and, moreover, to reduce the growth losses caused by bending and lateral pressure in the case, when the optical fiber is made cable, and the creation of an optical transmission system using this optical fiber with low dispersion.

In the proposed souwester via an optical fiber with dispersion offset performed by covering the Central core of the first peripheral core by coating the first periphery of the second core peripheral core and by covering the second peripheral core shell, wherein if the maximum value of the refractive index of the Central core is designated as n1, the minimum value of the refractive index of the first peripheral core is designated as n2, the maximum value of the refractive index of the second peripheral core is designated as n3, and the refractive index of the shell is designated as PS, n1>n3>nc>n2; the relative difference1 of the refractive index for the maximum value of the refractive index of the Central core relative to the shell is 0.4%10,7%; the relative difference2 refractive index for the minimum value of the refractive index of the first peripheral core relative to the shell is -0,30%2-0,05%; the relative difference3 indicators pellacci is 0.2%3; the ratio (A1/A2) diameter A1 of the Central core to the diameter A2 of the first peripheral core is at least 0.4 and not exceed 0.7; and the ratio (A3/A2) of the diameter A3 of the second peripheral core to the diameter A2 of the first peripheral core does not exceed 1.6.

In the proposed invention the second example implementation of an optical fiber with low dispersion, characterized in that in addition to the above-described first embodiment structure at the second peripheral core introduced alloying additive that increases the refractive index of SiO2; the distribution of the concentration of the alloying additives in the radial direction of the optical fiber in the second peripheral core has a maximum; and the maximum is closer to the first peripheral core in the radial direction relative to the center of the second peripheral core.

In the invention proposed a third example implementation of an optical fiber with low dispersion, characterized in that in addition to the above-described second example of realization of an additive used GeO2.

In the invention proposed a fourth example implementation of an optical fiber with low dispersion, from what olocco and second peripheral core create part of the membrane with low refractive index, which has a refractive index smaller than that of the shell.

In the invention proposed a fifth example implementation of an optical fiber with low dispersion, characterized in that in addition to the above-described first, second or third options for implementation in the used wavelength range within the range of wavelengths from 1450 to 1650 nm, for him there is no wavelength at which the dispersion is zero.

In the proposed invention the sixth example implementation of an optical fiber with low dispersion, characterized in that in addition to the above-described fourth implementation variant used in the range of wavelengths within the wavelength range from 1450 to 1650 nm, for him there is no wavelength at which the dispersion is zero.

In the proposed invention the seventh example implementation of an optical fiber with low dispersion, characterized in that in addition to the above-described first or second, or third, or sixth variants of realization of the difference between the maximum value and the minimum value of the dispersion in the wavelength range, which has a bandwidth of 30 nm and arbitrarily located within the range of wavelengths from 1450 to 1650 nm is the AI of the optical fiber with low dispersion, characterized in that in addition to the above described fourth variant of realization of the difference between the maximum value and the minimum value of the dispersion in the wavelength range, which has a bandwidth of 30 nm and arbitrarily located within the range of wavelengths from 1450 to 1650 nm, less than 2 PS/nm/km

In the proposed invention the ninth example implementation of an optical fiber with low dispersion, characterized in that in addition to the above-described fifth variant of realization of the difference between the maximum value and the minimum value of the dispersion in the wavelength range, which has a bandwidth of 30 nm and is within the range of wavelengths from 1450 to 1650 nm, less than 2 PS/(nm/km).

In the proposed invention the tenth example implementation of an optical transmission system, characterized in that it has an optical transmission line, which contains an optical fiber with low dispersion according to any of the above examples of implementation from the first to the ninth and a compensation of the dispersion having a negative gradient of the chromatic dispersion in the wavelength range from 1450 to 1650 nm, and the positive gradient of the chromatic dispersion of the optical lines is offering the above-mentioned specific refractive indices1,2 and3 set by the following equations (1)-(3):1 = {(n12nc2)/2nc2}100 ...(1)2 = {(n22nc2)/2nc2}100 ...(2)3 = {(n32nc2)/2nc2}100 ...(3) the Primary objective of the proposed invention is an optical fiber with low dispersion is the provision in a given wavelength range, for example, within the range of wavelengths from 1450 to 1650 nm as increased effective area of the core, and reduced the difference between the chromatic dispersion in the used wavelength range. The distribution of the refractive index and the relationship of the diameters of cores in the proposed invention the optical fiber with low dispersion optimized so that it was possible to achieve this first goal, and also to reduce the growth losses caused by bending and lateral pressure in the case, when the optical fiber is made cable. Thus, via an optical fiber with low dispersion according to the invention can be obtained as increased effective area of the core, the growth of losses, caused by bending and lateral pressure in the case, when the optical fiber is made cable. Description of specific examples of the optical fiber with low dispersion, the proposed invention will be described below in the section devoted to the ways of practical use of the invention.

In one example implementation of an optical fiber with low dispersion according to the invention the second peripheral core doped with additive, which increases the refractive index of SiO2; the distribution of the concentration of the alloying additives in the radial direction of the optical fiber in the second peripheral core has a maximum; and the maximum is closer to the first peripheral core in the radial direction relative to the center of the second peripheral core. And in another example implementation between the shell and the second peripheral core create part of the membrane with low refractive index, which has a refractive index smaller than that of the shell.

In these examples, the implementation can actually be implemented in the short-wave wavelength cutoff. Therefore, through these designs can be achieved even greater efface wavelengths and can be obtained optical fiber, with extra-low dispersion capable of operating in single mode.

Moreover, in the example implementation, in which, as described above, in the radial direction of the optical fiber, the maximum distribution concentration of the alloying additives which increase the refractive index of SiO2the second peripheral core is located closer to the first peripheral core in the radial direction relative to the center of the second peripheral core, and if the additive is used GeO2then, the optical fiber can be easily manufactured using existing technology for the industrial production of optical fibers.

If the optical fiber with low dispersion according to the invention has such an example implementation that is used in the range of wavelengths within the wavelength range from 1450 to 1650 nm, for example, in the wavelength range from 1530 to 1560 nm, for him there is no wavelength at which the variance is equal to zero if, for example, in this wavelength range are sending optical signals with wavelength division multiplexing, it can be done suppression of occurrence of four-wave mixing, and therefore, can bylismy the wavelength range can be set arbitrarily within the range of wavelengths from 1450 to 1650 nm.

And if in an optical fiber with low dispersion according to the invention the difference between the maximum value and the minimum value of the estimated variance in the above wavelength range has a value of 2 PS/(nm/km) or less, for example, when performing transmission of optical signals with wavelength division multiplexing in the wavelength range certainly can be done suppression of distortion of the signal due to chromatic dispersion.

In the optical transmission system according to the invention using the optical transmission line, which contains the above-described optical fiber with low dispersion, and, in addition, in the wavelength range from 1450 to 1650 nm positive gradient of the chromatic dispersion of this optical transmission line, which contains an optical fiber with low dispersion, reduced by the negative gradient of the chromatic dispersion compensation devices dispersion. Since the gradient of the chromatic dispersion in the above wavelength range can be made close to zero and can be made even greater suppression of the influence of chromatic dispersion, by means of the proposed invention is an optical transmission system mo what Platinium.

A BRIEF description of the DRAWINGS Fig.1 illustrates a detailed view of patterns of distribution of refractive index in the radial direction (the distribution of refractive index along the cross-section) for the first variant implementation of the optical fiber with low dispersion according to the invention; Fig. 2A is a detailed view of patterns of distribution of refractive index in the radial direction for the second variant implementation of the optical fiber with low dispersion according to the invention.

Fig. 2B illustrates an explanatory image of the distribution of refractive index in the radial direction of the optical fiber shown for comparison; Fig.3 depicts a detailed view of patterns of distribution of refractive index in the radial direction for the third variant of implementation of the optical fiber with low dispersion according to the invention;
Fig. 4 represents a graph of the dispersion characteristics for the variant of implementation of the optical transmission system using an optical fiber with low dispersion according to the invention together with the dispersion characteristic of the optical fiber with low dispersion used in this optical system is worn graph of the dispersion characteristics of the dispersion compensation, used in the above embodiment, the optical transmission system; and
Fig.6A-6B depict explanatory views of distribution (refractive index distribution of the refractive index along the cross-section in the radial direction of the optical fibers proposed for use in optical transmission systems using wavelength division multiplexing of the related technical field.

PREFERRED embodiments of the INVENTION
For a more detailed explanation of the invention will now be described several embodiments of the invention based on the accompanying drawings. In the following explanation of embodiments, the elements having the same name as the elements in the examples of the related art are assigned the same number of positions, and their repeated descriptions are omitted. In Fig.1 shows the distribution profile of the refractive index (distribution of refractive index) for the first variant implementation of the optical fiber with low dispersion according to the invention.

As shown in the drawing, an optical fiber with low dispersion has a Central core 1, which covered the first accessories is Riverina core 3 is covered with the shell 5. In addition, if an optical fiber with low dispersion, the maximum value of the refractive index of the Central core 1 is designated as n1, the minimum value of the refractive index of the first peripheral core 2 is designated as n2, the maximum value of the refractive index of the second peripheral core 3 is designated as n3, and the refractive index of the shell 5 is designated as PS, n1>n3>TS>n2.

The most distinctive feature of this first variant embodiment of the invention is that the relative difference3 refractive index for the maximum value of the refractive index of the second peripheral core 3 relative to the shell 5 perform equal to at least 0.2%, and the maximum value n3 the refractive index of the second peripheral core 3 perform much higher than the refractive index of the PS shell 5. And in this first embodiment, the relative difference1 of the refractive index for the maximum value of the refractive index of the Central core 1 relative to the shell 5 perform equal to at least 0.4%, but not exceeding 0,7% (0,4%2-0,05%).

In the preferred embodiment of this first variant implementation of the relative difference1 of the refractive index for the maximum value of the refractive index of the Central core 1 relative to the shell 5 perform at least equal, at 0.42%, but not exceeding 0,62% (0,42%10,62%), and the relative difference2 refractive index for the minimum value of the refractive index of the first peripheral core 2 relative to the shell 5 perform equal to at least -0,25% but not exceeding -0,05% (-0,252-0,05%).

Moreover, in the preferred embodiment of the first variant of implementation, the ratio (A1/A2) diameter A1 of the Central core 1 to the diameter A2 of the first peripheral core 2 perform at least equal, 0,4, but not in excess of 0.7, and the ratio (A3/A2) of the diameter A3 of the second peripheral core 3 to the diameter A2 of the first peripheral core 2 do not previewdata A2 first peripheral core 2 is less than 1.5.

In an optical fiber with low dispersion of this first variant of implementation there are no particular restrictions on the structure of the optical fiber. The optical fiber having the above-described distribution profile of the refractive index, can be manufactured, for example, by doping the Central core 1 and the second peripheral core 3 Germany dioxide (GeO2and alloying of the first peripheral core 2 fluorine (F). The alloying additive to the second peripheral core 3 is not limited GeO2and as it can be used any other additive that increases the refractive index of SiO2for example, Al2About3or like her.

In the example shown in Fig.1, the distribution of the concentration of the alloying additives GeO2in the radial direction of the optical fiber in the Central core 1 has a maximum at the center of the Central core 1. While the distribution concentration of the alloying additives GeO2in the radial direction of the optical fiber in the second peripheral core 3 also has a maximum at the center of the second peripheral core 3 in the radial direction. Alternatively, the optical valuescope fiber, than the center of the Central core 1.

In this first embodiment, by setting the distribution profile of the refractive index and the relationship of the diameters of the core: the Central core 1, the first peripheral core 2 and the second peripheral core 3 such as described above, can be obtained as increased effective area of the core, and reduced the difference between the chromatic dispersion in the used wavelength range. Moreover, the optical fiber with low dispersion according to this first variant implementation is used in the wavelength range low loss caused by bending, and can be obtained good performance when combining the optical fibers in the cable.

In particular, in an optical fiber with low dispersion according to this first embodiment, the effective size of the core perform equal to at least 45 μm2and the absolute value of the dispersion (in units of PS/(nm/km)) in the whole range of wavelength 1530 nm to a wavelength of 1560 nm perform equal to at least 2 but not greater than 12, so that in the used wavelength range for optical fiber lacked the wavelength at which the dispersion R of the t of the variance in the entire used wavelength range set such he is not greater than 0.05 PS/(nm2/km), and the difference between the maximum value and the minimum value of dispersion in the used wavelength range (the difference of the variance) is set such that it does not exceed 2 PS/(nm/km).

When determining the above distribution profile of the refractive index and the relationship of the diameters of the core authors of the present invention through experimental studies and modeling were obtained characteristics of different optical fibers. In the result, it was found that in the case when the above-mentioned relative difference1 refractive index is less than 0.4%, despite the fact that it is possible to realize an increased effective area of the core and the reduced gradient of the chromatic dispersion, losses at bends in the optical fiber have a tendency to increase, and it is difficult to provide good characteristics of the optical fiber in the case when in the cable.

On the other hand, it was found that in the case when the relative difference1 refractive index exceeds 0.7%, the gradient of the chromatic dispersion becomes large; the difference chromatic disperse distribution of refractive index; and the effective area of the core becomes approximately equal to the effective area of the core of the optical fiber, which has two parts with different shape of the distribution profile of the refractive index. For these above reasons, in this first embodiment of the invention the relative difference1 refractive index set in the range from 0.4 to 0.7%.

Despite the fact that the relative difference of the refractive index of1 can be set arbitrarily within the above range, if the distribution profile of the refractive index of the Central core 1 is a distribution profile in the form of functions with exponentin the preferred embodiment, the relative difference of the refractive index of1 set slightly lower when largeand a few more at small. The term distribution profile of the refractive index in a function with exponent" means that the refractive index has the form of the curve y = -xaccepts values from 4 to 6, and the relative difference of the refractive index of1 in the preferred embodiment, takes the values from 0.53 to 0.60%.

In that case, if the relative difference2 refractive index is made smaller than -0,30%, although the gradient of the chromatic dispersion becomes small, also becomes small and the effective area of the core. And in that case, when the relative difference2 refractive index set greater than -0,05%, while the effective area of the core becomes large, the gradient magnitude of the chromatic dispersion becomes approximately the same as in the optical fiber, which has two parts with different shape of the distribution profile of the refractive index of the related prior art. For these above reasons, in this first embodiment of the invention the relative difference2 refractive index set in the range -0,30%2-0,05%.

Moreover, in the optical fiber described above, the distribution profile of the refractive index, as the ratio (A1/A2) diameter endencia to in the wavelength range from 1450 to 1650 nm becomes more difficult to achieve low losses at bends. And there is a tendency of shifting the effective wavelength cutoff in the long wavelength region and the functioning of the optical fiber as a single-mode becomes difficult. And in that case, if the above ratio (A1/A2) is less than 0.4, the range of wavelengths from 1450 to 1650 nm becomes noticeable increase in losses at bends, and the optical fiber becomes unsuitable for use in the cable. On the other hand, if the above ratio (A1/A2) exceeds 0.7, it becomes difficult obtaining low values of the chromatic dispersion and the optical fiber becomes unsuitable for optical transmission using wavelength division multiplexing in the wavelength range from 1450 to 1650 nm. For these reasons, in the above-described first embodiment of the invention the above-mentioned ratio (A1/A2) is set equal to, at least, 0,4, but not exceeding 0,7.

And when the second peripheral core 3 has a large diameter and the ratio (A3/A2) of the diameter A3 of the second peripheral core 3 to the diameter A2 of the first peripheral core 2 exceeds 1.6, the effective wavelength cutoff is shifted in sensible. For this reason, in this first embodiment of the invention is the ratio (A3/A2) is set such that it does not exceed 1.6.

In this first embodiment, the distribution profile of the refractive index and the relationship of the diameters of the cores were determined on the basis of the above studies. This has resulted in both increased the effective area of the core, and reduced the difference between the chromatic dispersion in the wavelength range; implemented the suppression of occurrence of four-wave mixing; in the used wavelength range received low losses at bends; and may be provided for obtaining high performance in the case when the optical fiber is made cable.

Table 1 shows the relative difference1,2 and3 refractive indices, the relationship of the diameters of cores A1/A2 and A2/A3 and the core diameter A3 for each of the examples 1 through 9 that serve as specific examples of this first variant of the invention, as well as the specifications for each of their examples. While Table 2 shows the parameters for the examples used for comparison.

In ˆ) and loss curves are shown for a wavelength of 1550 nm. And all losses on the curves represent values for the case where the diameter of the bending of the optical fiber is equal to 20 mm And in spite of the fact that Table 1 is not specified, the optical fiber of all of examples 1 to 9 are effective wavelength cutoff, located in the shorter wavelength region of the used wavelength range, located in the wavelength range from 1450 to 1650 nm, it is possible the functioning of the single-mode fiber.

In particular, in examples 8 and 9 losses at bends is less than 1 dB/m and can be reduced not only the growth losses caused by bending and lateral pressure in the case, when the optical fiber is made cable, but also the increase in loss caused by minor bends.

In Table 2 in example 1, are shown for comparison, the optical fiber has a W-shaped distribution profile of the refractive index is shown in Fig.6B, and example 2 are given for comparison, the optical fiber has two areas with different shape of the distribution profile of the refractive index type, which is depicted in Fig.6A. In Table 2 the relative difference1 refractive index was obtained in exactly the same way, ka is the difference2 refractive index was obtained in exactly the same way as described in the first embodiment. For example 2 are given for comparison, the relative difference2 refractive index is the relative difference of the refractive index for the maximum value of the refractive index of the first peripheral core 2 relative to the shell 5, which is obtained using the above expression (2) when the maximum value of the refractive index of the first peripheral core 2, is equal to n2, and the refractive index of the shell 5, is equal to PS. From a comparison of the characteristics listed in Tables 1 and 2, it is clear that all of examples 1 through 9 have a large effective area of the core, than examples 1 and 2, shown for comparison, and have a smaller gradient dispersion than examples 1 and 2 are given for comparison. Thus, by comparing the examples 1 through 9 with examples 1 and 2, shown for comparison, it was confirmed that this first variant embodiment of the invention has good characteristics. That is, in this first embodiment of the invention obtained as increased effective area of the core,the second range of wavelengths provided with low loss, due to bending, when the diameter of the bending of the optical fiber 20 mm, which is less than 20 dB/m, thus, we have obtained good specifications for a cable made of optical fiber.

Below is the description of the second variant of realization of the optical fiber with low dispersion according to the invention. Described here is the second version of the implementation is the distribution profile of the refractive index shown in Fig.2A. In this optical fiber with low dispersion of the refractive index has a maximum at the place where the refractive index of the second peripheral core 3 reaches its maximum value, which is located closer to the first peripheral core 2 in the radial direction relative to the center of the second peripheral core 3. In other words, the distribution profile of the refractive index shown in Fig. 2A represents, essentially, the same distribution profile of the refractive index, which is shown in Fig.1. In a preferred embodiment, the maximum refractive index of the second peripheral core 3 are placed as close as possible to the edge of the first peripheral core 2.

The profile is distributed is placed dioxide concentrations Germany (GeO2in the radial direction of the optical fiber serving as an alloying agent that increases the refractive index of SiO2you enter the second peripheral core 3 is closer to the first peripheral core 2 in the radial direction relative to the center of the second peripheral core 3.

Because this second variant embodiment of the invention has such a distribution profile of the refractive index, there is an effect, which consists in shortening the effective wavelength cutoff, which certainly allows the operation of the optical fiber as a single in the entire used wavelength range.

Table 3 shows the design parameters and characteristics for example 10, which serves as a concrete example of this second variant implementation and shown in Fig.2B, which shows essentially the same structure as in example 10. Table 3 also shows the design parameters and characteristics of the prototype 1, in which the distribution concentration of the alloying additives GeO2the second peripheral core 3 is made essentially constant along the radial direction of the optical fiber is s different from the parameters of example 10, and in which the maximum distribution concentration of the alloying additives GeO2entered into the second peripheral core 3, in the radial direction of the optical fiber was placed near the edge of the first peripheral core 2. Design parameters and characteristics to those of examples 11 and 12 are shown in Table 4. In Table 4 the location of the maximum concentration GeO2the second peripheral core 3 along the radial direction of the optical fiber is expressed in such a way that the location of the edge of the first peripheral core 2 is taken as 0, and the edge of the shell 5 is taken as 1.

Table 4 shows the design parameters and characteristics of test samples 2 and 3 have essentially the same options as examples 11 and 12, but is designed so that the maximum distribution concentration of the alloying additives GeO2entered into the second peripheral core 3 along the radial direction of the optical fiber is located closer to the shell 5.

From these tables it is clear that the effective wavelength cutoff strongly varies with the concentration of the alloying additives GeO2entered into the second peripheral core 3.

In the Pref is on the bends are made equal, approximately 1 dB/m, and there is a tendency that, for example, chromatic dispersion and the gradient of the dispersion is slightly increased when the displacement of the maximum refractive index of the second peripheral core 3 in the direction of the first peripheral core 2 in the radial direction relative to the center of the second peripheral core 3. However, it is possible to adjust the chromatic dispersion and the magnitude of the gradient of the dispersion in any other way than moving the maximum refractive index of the second peripheral core 3. For example, there may be change in the refractive index of the Central core 1 or the first peripheral core 2.

In a preferred embodiment, the effect of the adjustment of the estimated variance and gradient dispersion receive by moving the location of the maximum refractive index of the second peripheral core 3 in the direction of the first peripheral core 2 at 1/3 the width of the second peripheral core 3. It is also preferred from the viewpoint of processability and dispersion parameters during production.

The authors of the present invention, it was found that in the case when you have to create significantly more effen relative difference1,2 and3 indices of refraction, the ratio (A1/A2) diameter A1 of the Central core 1 to the diameter A2 of the first peripheral core 2 and the ratio (A3/A2) of the diameter A3 of the second peripheral core 3 to the diameter A2 of the first peripheral core 2 ask within a specified interval specified in the description of Fig.1, then sometimes, depending on the values of the parameters (for example, those who have experienced sample 1), a situation arises in which the effective wavelength cutoff is shifted to the long wavelength region.

That is, in the General case, when the optical fiber for increasing the effective area of Aeff core creates a second peripheral core 3, is offset from the wavelength cutoff in the long wavelength region. And, for example, in the case of test sample 1 according to Table 3, the situation may arise in which in the used wavelength range within the range of wavelengths from 1450 to 1650 nm, the optical fiber may not function as a single mode.

In this regard, to ensure the ability to operate in single-mode regime, the authors of the present invention have made various issledovaniia, in the case when the distribution of refractive index of the second peripheral core 3 made in the form of the distribution, shown for example in Fig.2A, which is the case in examples 10, 11 and 12, it is possible to a much greater extent to reduce the effective wavelength cutoff and implement the increase in the effective area of the core and reducing the difference between the chromatic dispersion in the used wavelength range.

That is, the maximum refractive index of the second peripheral core 3 is moved in the direction of the first peripheral core 2 in the radial direction relative to the center of the second peripheral core 3, which is the case in examples 10, 11 and 12, which are shown in Fig.2A, in Tables 3 and 4. This leads to a shift in the wavelength cutoff in the short wavelength region and allows to obtain an optical fiber, which can function as a single mode in the wavelength range within the range of wavelengths from 1450 to 1650 nm.

The inventors believe that the reason for this is the following. From the totality of modes of propagation of radiation in optical fiber fashion LP0m(m= 2,3. ..) and LP11have a wider distribution A refractive index of the second peripheral core 3 in the direction of the first peripheral core 2 in the radial direction relative to the center of the second peripheral core 3 can prevent the spread of light emission fashion LP0mand fashion LP11when that will be provided to only a small impact on the fashion LP01light radiation propagating through the optical fiber, and thus provide the possibility of its functioning as a single mode.

On the basis of these studies was defined above variant of the first variant of the invention, which has the above useful properties, which are presented in Tables 3 and 4.

Now will be described the third option is the implementation of optical fiber with low dispersion according to the invention. This third version of the implementation is the distribution profile of the refractive index shown in Fig.3. This distribution profile of the refractive index is essentially the same as shown in Fig.1, except that between the shell 5 and the second peripheral core 3 create part 4 of the shell with a low refractive index, which has a lower refractive index than the shell 5.

For this variant of the design of the optical fiber with low dispersion inventors have carried out exactly the same studies as those that were held plant design, it is shown in Fig.3, in which through the creation of part 4 of the shell with a low refractive index can be obtained the same effect as moving the location of the maximum in which the refractive index of the second peripheral core 3 reaches the maximum value, in the direction of the first peripheral core 2 in the radial direction relative to the center of the second peripheral core 3.

Table 5 shows the design parameters and characteristics for example 13, which serves as a concrete example of this variant implementation, with part 4 of the shell with a low refractive index, as well as design parameters and characteristics of the test sample 4, having essentially the same construction as example 13, but in which there is a portion 4 of the shell with a low refractive index. From Table 5 it is clear that by creating between the shell 5 and the second peripheral core 3 of part 4 of the shell with a low refractive index can reduce the effective wavelength cutoff.

Below is a description of a variant of implementation of the optical transmission system according to the invention. This optical system has an optical transmission line re is written options exercise and a compensation of the dispersion, which has a negative gradient of the chromatic dispersion in the wavelength range from 1450 to 1650 nm. The hallmark of this optical transmission system is that the positive gradient of the chromatic dispersion of the optical transmission line, which contains an optical fiber with low dispersion, reduce through the device of dispersion compensation.

As an example, was created optical transmission system by connecting an optical fiber with low dispersion, having the same structure and parameters as the example 7 of Table 1, with a compensation of the dispersion, which has a negative dispersion and a negative chromatic dispersion gradient.

The device dispersion compensation for this application was completed using optical fiber compensating the dispersion, the distribution profile of the refractive index of which has the form shown in Fig. 5A. That is, the device of the dispersion compensation is performed using an optical fiber, dispersion compensating, which has a first peripheral core 2, which covered the Central core 1, the second peripheral core 3, which covered the first periferia, providing compensation for dispersion, the maximum value of the refractive index of the Central core 1 is designated as n1, the minimum value of the refractive index of the first peripheral core 2 is designated as n2, the maximum value of the refractive index of the second peripheral core 3 is designated as n3, and the refractive index of the shell 5 is designated as PS, n1>n3>TS>n2. And the value of the relative difference1,2 and3 refractive index in the optical fiber, providing compensation of dispersion, different from those that were used in the above embodiments, the implementation of optical fiber with low dispersion according to the invention, the value of1 is approximately 2.85 percent,2 is approximately -1% and3 is equal, approximately, to 1.28%. And the relationship of the diameters of cores (A1/A2/A3) is equal to approximately 1/3/3,7.

From the viewpoint of the dispersion characteristics of the device compensation of dispersion is in the range of wavelengths from 1450 to 1650 nm negative dispersion (for example, about -150 PS/nm/km or less at a wavelength of 1550 nm) and negative is key. Therefore, in the optical transmission system, the ratio of the length of an optical fiber with low dispersion of example 7 to the length compensation devices dispersion was made equal to 98 to 2.

In the wavelength range from 1530 to 1600 nm optical transmission system has a dispersion characteristic shown by the curve "a" in Fig.4. By curve "b" in Fig.4 shows the dispersion characteristic of the optical fiber with low dispersion from example 7 in the wavelength range from 1530 to 1600 nm.

It Is Evident From Fig. 4 it is clear that in the case when the optical transmission system is formed by connecting the device to compensate for dispersion having a negative chromatic dispersion gradient, which is depicted in Fig.5B, the optical fiber 7 with a low dispersion in the optical transmission system as a whole can be carried out significant additional decrease in the difference of the variance in the used wavelength range (in this case, this range of wavelengths is within a range of wavelengths from 1450 to 1650 nm). As an example of the structure of the compensation of the dispersion used in this embodiment, the optical transmission system according to the invention is a device having, aswas described above, when using a dispersion compensation this type of device can be made having a small length. Consequently, the use of devices compensating dispersion of this type leads to decrease the impact on the nonlinear properties and other parameters, other than the dispersion characteristics, and allows you to create an optical transmission system, with good characteristics of the optical fiber with low dispersion according to the above-mentioned variants of implementation, and is able to perform high-quality transmission with wavelength division multiplexing.

The present invention is not limited to the above variants of the implementation and can be used different ways of practical implementation of the invention. For example, in the optical transmission system according to the invention to reduce the difference between the dispersion in the wavelength range of exercise combining optical transmission line, which contains an optical fiber with low dispersion according to one of the above embodiments, and devices compensating dispersion having a negative chromatic dispersion gradient in the used wavelength range. transmission can be performed by connecting an optical fiber with low dispersion in one of the above embodiments with another optical fiber, for example, with an optical fiber, which can operate in single mode.

And the design of compensation of dispersion used in the embodiment, the optical transmission line has no particular restriction and can be selected such that it is convenient. However, in the case when the device dispersion compensation is performed using the above-described optical fiber compensating the dispersion can be easily manufacturing the device and its connection to the optical transmission line, which contains an optical fiber with low dispersion.

In the above embodiments, the implementation of optical fiber with low dispersion of the Central core 1 and the second peripheral core 3 doped dioxide Germany (GeO2), and the first peripheral core 2 doped with fluorine (F). However, in alternative option for the implementation of optical fiber with low dispersion according to the invention may be included in the distribution profile of the refractive index shown in Fig. 1, 2 or 3 by doping the first peripheral core 2 Germany dioxide (Deo2) and fluorine (F) and adjust the number of these went the obreteniyu.

In addition, although each of the above embodiments, the optical fiber with low dispersion was created so that in the wavelength range from 1530 to 1560 nm for him was no such wavelength at which the dispersion is zero, the optical fiber with low dispersion according to the invention can be designed so that it no wavelength zero dispersion used in any range of wavelengths within the wavelength range from 1450 to 1650 nm. In that case, if the optical fiber with low dispersion according to the invention is created in a similar way, because there can be suppressed the occurrence of four-wave mixing in the implementation of transmission with wavelength division multiplexing in the wavelength range, it is possible to obtain an optical fiber with low dispersion, suitable for transmission using wavelength division multiplexing in a wider band of frequencies.

INDUSTRIAL APPLICABILITY
As described above, the optical fiber with low dispersion according to this invention and an optical transmission system using such an optical fiber with low dispersion can provide as Uwe is apatone wavelengths and, therefore, they are highly suitable for transmission using wavelength division multiplexing.


Claims

1. Optical fiber with low dispersion, which represents an optical fiber with dispersion offset is made by covering the Central core of the first peripheral core, coating the first periphery of the second core peripheral core and covering the second peripheral core shell, in which, if the maximum value of the refractive index of the Central core is designated as n1, the minimum value of the refractive index of the first peripheral core is designated as n2, the maximum value of the refractive index of the second peripheral core is designated as n3, and the refractive index of the shell is designated as PS, n1>n3>nc>n2; the relative difference1 of the refractive index for the maximum value of the refractive index of the Central core relative to the shell is 0.4%10,7%; the relative difference2 refractive index for the minimum value until the2-0,05%; the relative difference3 refractive index for the maximum value of the refractive index of the second peripheral core relative to the shell is 0.2%3; the ratio (A1/A2) diameter A1 of the Central core to the diameter A2 of the first peripheral core is at least 0.4 and not exceed 0.7; and the ratio (A3/A2) of the diameter A3 of the second peripheral core to the diameter A2 of the first peripheral core does not exceed 1.6.

2. Optical fiber with low dispersion under item 1, characterized in that the second peripheral core introduced alloying additive that increases the refractive index of SiO2the distribution of the concentration of the alloying additives in the radial direction of the optical fiber in the second peripheral core has a maximum, while the maximum is located on the periphery of the core in the radial direction relative to the center of the second peripheral core.

3. Optical fiber with low dispersion under item 2, characterized in that the additive is GeO2.

4. Optical fiber with low dispersion according to any of the izkuyu refractive index, which has a refractive index smaller than that of the shell.

5. Optical fiber with low dispersion according to any one of paragraphs. 1-3, characterized in that in the used wavelength range within the range of wavelengths from 1450 to 1650 nm, there is no wavelength at which the dispersion is zero.

6. Optical fiber with low dispersion under item 4, characterized in that in the used wavelength range within the range of wavelengths from 1450 to 1650 nm, there is no wavelength at which the dispersion is zero.

7. Optical fiber with low dispersion according to any one of paragraphs. 1-3 and 6, characterized in that the difference between the maximum value and the minimum value of the dispersion in the wavelength range with a bandwidth of 30 nm, which is randomly located within the range of wavelengths from 1450 to 1650 nm, less than 2 PS/(nm/km).

8. Optical fiber with low dispersion under item 4, characterized in that the difference between the maximum value and the minimum value of the dispersion in the wavelength range with a bandwidth of 30 nm, which is randomly located within the range of wavelengths from 1450 to 1650 nm, less than 2 PS/(nm/km).

9. Optical fiber with low who icine dispersion in the wavelength range with a bandwidth of 30 nm, which is randomly located within the range of wavelengths from 1450 to 1650 nm, less than 2 PS/(nm/km).

10. Optical transmission system, which contains an optical transmission line, which contains an optical fiber with low dispersion according to any one of paragraphs. 1-9 and a compensation of the dispersion, which has a negative gradient of the chromatic dispersion in the wavelength range from 1450 to 1650 nm, in which the positive gradient of the chromatic dispersion of the optical transmission lines in this wavelength range is reduced by the compensation device variance.

 

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