Single-mode optical fiber

 

(57) Abstract:

Single-mode optical fiber includes a first core having a constant refractive index within a given radius from the center of the optical fiber, the second core, which covers the first core and has a refractive index which decreases from the refractive index of the first core with the increase of its radius, and a sheath that covers the second core and has a refractive index less than the minimum refractive index of the second core. The optical fiber has low dispersion and low loss. 5 C.p. f-crystals, 10 ill.

The technical field

The invention relates to a single-mode optical fiber, and more particularly to a single-mode optical fiber, the refractive index of which is changed according to the radius of the core.

Art

In General, an optical fiber for long ultrafast and broadband communications when you use must be low loss, low dispersion and low dispersion slope at the wavelength. The optical fiber having such characteristics is usually a fiber with dispersion shifted or fiber with the governmental structures to satisfy the above requirements, applicable to optical characteristics.

The change in refractive index can be obtained by creating an annular zone for the core, the refractive index of which varies according to the shape of a triangle, or by creating a core, which has a structure with dual core, corresponding to the refractive index of the convex type.

In Fig. 1 shows the relative difference of the refractive indices depending on the normal radius of the core, which is described in U.S. patent 5553185. Here, when nC0- this is the maximum core refractive index, and nC1is the refractive index of the shell, the relative difference between the refractive indices is expressed as (nC02-nC12)/2nC02. In this way the difference in refractive index between the cladding and core is larger by lowering the refractive index annular region adjacent to the core, allowing it turns out low dispersion slope.

In order to expand the difference in refractive indices between the core and the shell to increase the refractive index of the core or lower the refractive index of is used to increase the refractive index, making it impossible to obtain the refractive index over a predetermined level. In the second method, the losses increase dramatically in the field of long waves due to the reduced area. In order to solve the problem, the ratio of the shell radius to the radius of the core must be large. In Fig. 2 shows the losses that depend on each wavelength of the optical fiber, when the ratio of the shell radius to the radius of the core is equal to 6 and 7, as described in U.S. patent 4447127. The solid line represents the case when the ratio of the diameter of the shell to the core diameter is 6, and the dotted line represents the case when the ratio of the diameter of the shell to the core diameter is 7. Here a and a', each has a relative difference between the refractive indices of 0, indicating that the refractive index of the shell is the same as in the core. b and b', each has a relative difference between the refractive indices of 0.2, and c', each has a relative difference between the refractive indices of 0.23, d and d', each has a relative difference between the refractive indices of 0.25, and e and e', each has a relative difference between the refractive indices of 0.27.

However, when the method of manufacturing an optical fiber, which Oy method still has problems namely, that it is difficult to manufacture an optical fiber preform having a large aperture, and a lot of time for making optical fibres.

Disclosure of the invention

To solve the above problems, the present invention features a single-mode optical fiber, the refractive index of which is changed to obtain low dispersion and low dispersion slope.

Thus, to achieve this goal features a single-mode optical fiber containing the first core, having a constant refractive index within a given radius from the center of the optical fiber, the second core, which covers the first core and has a refractive index which decreases from the refractive index of the first core with the increase of its radius, and a sheath that covers the second core and has a refractive index less than the minimum refractive index of the second core.

Brief description of drawings

Fig. 1 is a graph showing the change in the refractive index, low dispersion slope, in accordance with the prior art;

Fig. 2 is a graph that shows the radius of the core is equal to 6 and 7;

Fig. 3 is a cross-section of single-mode optical fiber, the corresponding variant of the present invention;

Fig. 4 shows the distribution of the refractive index of the optical fiber shown in Fig.3;

Fig. 5A and 5B show the distribution of the refractive index of the optical fiber in accordance with another variant of realization of the present invention;

Fig. 6 shows the distribution of the refractive index of the optical fiber in accordance with another alternative implementation of the present invention;

Fig.7 is a graph showing the change of the slope of the dispersion with respect to change and1/a2Fig.4;

Fig. 8 shows the slope of the dispersion obtained by modifying and1at fixed n1n2and a2Fig.4;

Fig. 9 shows the slope of the dispersion obtained by changing a2when a1/a2according Fig.4, continuously; and

Fig.10 shows the loss at the wavelength of 1.55 μm depending on a1/a2according Fig.4.

The preferred embodiment of the invention

As shown in Fig.3, the optical fiber includes first and second core 300 and 302 and the shell 304. Distribution showing the elmline first core 300, with the radius and1from the centre, the constant value of n1. The refractive index of the second core 302 having a radius a2and covering the first core 300, linearly decreases from the refractive index of n1the first core to n2. The refractive index of the sheath 304 is equal to n0that is less than n2. Such a distribution of refractive index is a combination of speed distribution of the refractive index, low dispersion, and a triangular distribution of the refractive index with low loss.

Fig.5A and 5B show the distribution of the refractive indices of the optical fiber according to another implementation variant of the present invention. The optical fiber according to Fig.5A further comprises a third core in addition to the first and second cores, and the optical fiber according to Fig.5B further comprises a fourth core on the outside of the third core according to Fig.5A. Here, the refractive index of n3the third core is less than the minimum refractive index of n2the second core, and a refractive index of n4the fourth core is smaller than the refractive index of n3the refractive index of the optical fiber according to another implementation variant of the present invention. The optical fiber according to Fig.6 further comprises third and fourth core in addition to the first and second core according to Fig.4. Here, the refractive index of the third core - n2that is equal to the minimum refractive index of the second core, and the refractive index of the fourth core-a3that is smaller than a refractive index of n2the third core and greater than the refractive index of n0shell.

Fig. 7-10 show the correlation between the distribution of the refractive index and structure in order to meet the requirements of such optical characteristics, such as low dispersion, low dispersion slope and low loss optical fibers having the above-described complex distribution of refractive indices.

Fig. 7 is a graph showing the change of the slope of the dispersion with respect to change and1/a2according Fig. 4. Here N is the (relative difference between the refractive indices of the first core relative difference between the refractive indices of the second core)/(the relative difference between the refractive indices of the first core). The profile of the refractive index of Serdtsev is isenia N. In accordance with the schedules shown in Fig.7, when the refractive index of n2small, i.e., when N is large, if a1/a2small, i.e., the profile of the refractive index of the triangle, the slope of the dispersion has a greater value. On the other hand, when a1/a2increases and reaches a specified value, the slope of the dispersion has the lowest value. In addition, when the refractive index of n2increasing speed, i.e., when N becomes smaller, the slope of the dispersion varies in a narrow range, even when changed and1/a2and the steepness of the dispersion becomes almost constant irrespective of a1/a2. Thus, a small dispersion slope can be obtained in the range of N from 0.2 to 0.85 and in the range and1/a2equal to 0.7 or less. In addition, the optimal small dispersion slope can be obtained by combining appropriately n1n2and a1/a2each other.

Fig. 8-10 show the graphs for the steepness of the dispersion obtained for variants of optical fiber made on the basis of the values shown in Fig.7.

Fig. 8 shows the slope of the dispersion, Tisno dispersion, obtained by changing a2when a1/a2(Fig.4) is a constant value.

Fig. 10 shows the loss at the wavelength of 1.55 μm depending on a1/a2according Fig. 4. As shown in Fig.10, as1/a2becomes smaller, i.e. the profile of the refractive index becomes triangular in shape, the losses are small. As a1/a2becomes larger, i.e. the profile of the refractive index becomes stepwise, losses become large. That is, to obtain the optical characteristics of low loss, it is preferable triangular shape of the distribution of refractive index. When a1/a2is in the range between 0 and 0.7, you can get a loss of approximately 0,22 dB/km

Therefore, to obtain low dispersion and low loss it is preferable that the optical fiber had a distribution of refractive index, representing the unity of form type stairs and triangular type.

Industrial applicability

According to the present invention is governed by the structure of the core of the optical fiber, and optical fiber has a distribution index p of the aqueous type, having low loss, thus manufacturing an optical fiber having low dispersion and low loss. In addition, the refractive index of the triangular core of large radius, sensitive to increased losses due to micro and macro bending because of the failure of the centre, combined with graded refractive index smaller radius having low losses at bends. Therefore, can be reduced losses at bends.

1. Single-mode optical fiber containing the first core, having a constant refractive index within a given radius from the center of the optical fiber, the second core, which covers the first core and has a refractive index which decreases from a value of the refractive index of the first core with the increase of its radius, and a sheath that covers the second core and has a refractive index smaller than the minimum value of the refractive index of the second core.

2. Single-mode optical fiber under item 1, characterized in that the ratio of the radius of the first core to the radius of the second core is in the range between 0 and 0.7.

3. Singlemode omline first core - the relative difference of the refractive index of the second core) / (the relative difference between the refractive indices of the first core is in the range between 0.2 and 0,85.

4. Single-mode optical fiber under item 1, characterized in that it further contains a lot of fibre, which cover the second core.

5. Single-mode optical fiber under item 4, characterized in that the set of cores that cover the second core, have a refractive index which decreases in steps with increasing radius and has a value smaller than the minimum refractive index of the second core, and greater than the refractive index of the shell.

6. Single-mode optical fiber under item 4, characterized in that the core, directly covering the second core of the many core has the same refractive index as the minimum refractive index of the second core.

 

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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

FIELD: fiber-optics.

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

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