Advanced optical waveguide shift dispersion

 

(57) Abstract:

Optical waveguide fiber has a low slope of the full dispersion, relatively large diameter of the field of fashion, a large effective area and a relatively simple structure profile of the refractive index of the core. The profile of the refractive index of the core contains three areas. The ability to adjust the height, width and position of the three regions of the profile of the refractive index of the core provides the flexibility required to meet the technical requirements of the light guide fiber with dispersion shifted able to limit the four-wave mixing or phase automodulation. The diameter of the field of fashion is not less than 7.5 μm and the slope of the full dispersion of not more than 0,070 PS/nm2km 7 C.p. f-crystals, 3 ill., 3 table.

The invention relates to a single-mode optical waveguide fiber, which has a wavelength zero dispersion shifted in the range of about 1550 nm, a large effective area and low slope full dispersion. New fiber fiber is the representative of a family of profiles described in application for U.S. patent N 08/378780.

New design one of the effects, due to the high power density of the signal. In addition, the new light guide fiber has low attenuation and resistant to bending in the simple structure of the profile of the refractive index, resulting in low production costs. For some profiles, which are included in the scope of the present invention, curve normalized waveguide dispersion on wavelength is bimodal, thus providing an additional opportunity, which can be used in communication systems with high performance.

For communication systems that use lasers with high power transmitters and receivers with high data rate and spectral multiplexing technique requires the light guide fibers having extremely low, but not zero total dispersion and very low polarization mode dispersion. In addition, the light guide fiber should have characteristics essentially eliminates such nonlinear phenomena as phase automodulation and four-wave mixing. Phase automodulation can be limited by reducing the power density. Four-wave mixing is eliminated by work in the range of institutions waveguide systems, composed of optical amplifiers.

To obtain the optical waveguide with the characteristics required for such complex systems, it has been modeled and tested a large number of profiles of the refractive index. Design with composite core, discussed in U.S. patent N 4715679, provides the flexibility to satisfy the requirements of new systems, and at the same time provides the following basic requirements, such as low attenuation, tight dimensional tolerances, acceptable resistance to bending and high tensile strength. In addition, some designs with composite core is relatively simple to manufacture, allowing improved performance of optical waveguides without excessive increase their value.

Were found certain sections of the core, described in application for U.S. patent N 08/378780 with unusual properties.

In communication systems using spectral multiplexing, preferred are optical waveguides having a relatively flat characteristic of the complete dispersion in the wavelength multiplexed signals. For those systems that use the to four-wave mixing and phase automodulation, be the factors limiting the use of the system.

Thus, there is a need in the optical fiber which has a low slope full dispersion to facilitate spectral multiplexing, allows you to adjust the full dispersion to limit the four-wave mixing, and provides a relatively large area of the field of fashion, so that the power per unit cross-section of the waveguide fiber, was not too great and thus was limited to phase automodulation.

In addition, it is desirable to keep the simplicity and low cost of production inherent in the waveguides with a simple profile of the refractive index, such as speed.

Identify:

The radii of the regions of the core are determined by the refractive index. A separate area begins at the point where the refractive index takes the value corresponding to this area, and ends at the last point where the refractive index typical of this region. The radius will have this definition, unless otherwise specified in the text.

Parameter % is a measure of the relative difference of the refractive indices, optimalny the refractive index in this region of the core,

ncis the refractive index in the region of the shell.

- The term profile refers to the profile of refractive index expressed via (r)%, according to the equation

(r) = (ro)%(1-[(r-ro)/(r1-ro)])

where r is in the interval r0r r1,

is defined above,

the exponent, which determines the shape of the profile.

- The effective area equal to

Aeff= 2(E2rdr)2/(E4rdr),

where the limits of integration correspond to the interval from 0 to ,

E - electric field of the propagating light.

- Normalized waveguide dispersion is determined in accordance with U.S. patent N 4715679 as V d2(bV)/dV2.

Described here is a new light guide fiber meets the requirements for fiber with high performance, low slope dispersion and a large effective area, that is, Aeffmore than 60 μm2. Moreover, the new design of the profile of the refractive index can be adjusted to obtain a bimodal dependence of the normalized dispersion of the waveguide from /c. The term "bimodal" is used to describe the curve, sadest curve normalized waveguide dispersion is flat and thus determines the wavelength interval, whereoand full dispersion insensitive to production tolerances. The other part of the curve has a steeper slope, usually with a slope greater than 2, and thus provides an interval in which small changes in the geometry of the light guide fiber or in the profile of the refractive index create large changes oand thereby complete dispersion. The last characteristic of the geometry of the waveguide or of the profile of the refractive index is ideal for switching full variance between positive and negative values, and thus for control of the complete dispersion of the fiber length. Manage the full dispersion may mean that full dispersion of the entire fiber length is small, although the variance on any significant segment of the fiber is not zero. Thus, in essence, eliminates the non-linear effect of four wave mixing.

According to the first aspect of the invention, a new fiber optic fiber, to which the above definition has been given and which has the above useful properties, is a singlemode fiber optic fiber having a wavelength of zero dispersion in the range of from about 1500 to 1600 nm, that is, the fiber BR>
- Central area of radius A1where the radius is measured from the axis of the waveguide having the profile of the refractive index with = 1, the maximum refractive index of n1and the relative difference of the refractive indices1%;

- the second area having a first point immediately after A1and the last point on the radius A2the maximum refractive index of n2and the relative difference of the refractive indices2%,

a third region having the first point immediately after A2and the last point at radius A, the maximum refractive index of n3and the relative difference of the refractive indices3%.

These parameters are related by the following relations:

n1> n2> n nc;

A1/A in the range from 0.4 to 0.6;

A2/A in the range of from about 0.78-0.88 and

3%/1% in the range of about 0.16 to 0.39.

These ratios result in such characteristics of the waveguide fiber as the wavelength of zero dispersion in the range from 1520 to 1600 nm and the slope of the full dispersion is not more of 0.085 PS/nm2km.

The fiber in accordance with the first embodiment of izopet is from 5,55 to 6.05 microns and

A range from 6.5 to 7.0 μm.

The relation 3%/1% is about 0,165 and1% from 0.9 to 1.0%. This variant embodiment of the invention has characteristics such as wavelength zero dispersion in the range from 1530 to 1550 nm, the slope of the full dispersion is not more than 0.07 PS/nm2km and the diameter of the field of fashion no less of 8.4 μm.

In accordance with a modification of this variant embodiment of the invention, the second region of the core has a flat profile of the refractive index and n2approximately equal to nc. The third area of the core has a trapezoidal shape profile of the refractive index essentially flat top.

The fiber in accordance with another embodiment of the invention according to the first aspect has:

A1in the range from 3.25 to 3.75 microns,

A2in the range from 5.1 to 6 μm and

A range from 6.5 to 7.5 μm.

The relation3%/1% is about 0.18 and1% from 0.9 to 1.0%, which provides a waveguide properties, the wavelength of zero dispersion in the range from 1535 to 1585 nm, the slope of the full dispersion is not more 0,065 PS/nm2km, the diameter of the field of fashion is not less than 7.5 μm and bimodal Crestline of the invention the first region of the core has a Central portion with a profile in the form of an inverted cone, the base radius of which is not more than about 1.5. In addition, near the end of the first region of the profile of the refractive index of the slope of the triangular profile is reduced. These two characteristics of the Central region of the core are typical for diffusion or leaching of alloying of the workpiece during manufacture. In most applications, this phenomenon of diffusion does not have a significant impact on the performance characteristics of the waveguide. However, in cases where diffusion is significantly modifies the properties of the waveguide can be performed compensation diffusion at the stage of harvesting. Thus, their presence provides the best match between the simulated and the real profile of the refractive index. The second core has a flat profile of the refractive index and n2essentially equal to nc.

Bimodal normalized waveguide dispersion of this sub-option can be described by the critical wavelength of the light guide fibercand the working wavelength, or wavelength of the signal . In particular, the curve is normalized waveguide dispersion is essentially flat when 0,68 c/ 0.8 and has a slope of more than Palin as the light guide fiber, with the core of the three areas, with the Central region has a stepped profile of the refractive index. Keeping similar definitions of terms, n1> n3> n2nc, A1/A, about 0.3, A2/A about of 0.85 and3%/1% about 0,39. This new fiber optic fiber has a wavelength of zero dispersion in the range from 1520 to 1600 nm and a slope full of dispersion is not more 0,070 PS/nm2km.

The fiber in accordance with a variant of the second aspect of the invention has:

A1in the range from 2.25 to 2.55 microns;

A2in the range of from 6.35 to 7.4 μm and

A in the range of about 7.5 to 8.5 microns.

The relation3%/1% is about 0,39 and1% to about 0.6%. The light guide fiber according to this variant embodiment of the invention has a wavelength of zero dispersion in the range from 1525 to 1600 nm, the slope of the full dispersion is not more than 0.07 PS/nm2km and the diameter of the field of fashion is not less than 8.0 μm.

A modification of this variant embodiment of the invention has a virtually flat profile of the refractive index of the second region, and this factor essentially equal to nc. The profile of the refractive index of the third Oblates as defined below, restrictions on the ratio of the critical wavelength to the wavelength of the signal. The curve is normalized dispersion of the waveguide is essentially flat for 0,72c/ 0,80 and has a slope of more than about 2, for a c/ > 0,80.

It should be clear that small deviations from the above-described profile of the refractive index does not significantly affect the properties or performance of the light guide fiber. In addition, in the art it is known the concept of an equivalent profile of the refractive index. Equivalent to the profile of the refractive index are such profiles, which are essentially interchangeable in the light guide fiber.

A new family of profiles of the refractive index described here, includes the equivalent profile options and profile, which only slightly deviate from the described profile. For example, a stepped region may have rounded corners or sloping sides, either concave or convex upper portion. The phenomenon of diffusion of the dopant, which is found in some methods of manufacturing billets waveguide, also usually does not significantly affect the characteristics or performance of the light guide fiber. However, in cases where diffusion can significantly change harak refractive index or geometric relationships can be adjusted, that is adjusted to achieve the required characteristics and performance of the light guide fiber.

In Fig. 1 shows a core, consisting of the three areas and have a triangular, that is, s = 1, the profile of the refractive index of the Central region.

In Fig. 2a shows the profile of the refractive index of the three areas in which the Central region of the profile is in the middle part of the recess in the form of a cone, and the end part has a value of slope less than 1.

In Fig. 2b shows a plot of the normalized dispersion of the waveguide fromc/, which refers to the profile of the refractive index shown in Fig. 2a.

In Fig. 3a shows a profile with three areas in the Central region of the stepped profile of the refractive index.

In Fig. 3b shows a plot of the normalized dispersion of the waveguide fromc/, which refers to the profile of the refractive index shown in Fig. 3a.

Single-mode optical waveguide with graded refractive index has become an industry standard due to its high bandwidth, low attenuation and ease of design of the profile of the refractive index. This is the service provider of refraction leads to lower costs for organizations supplying and laying of fiber-optic cable.

However, when there is a need in the waveguide with a higher performance, it was necessary to structure the profile of the refractive index with greater flexibility. Described here is a new core from several areas is representative of this type of profile of the refractive index, which is discussed in U.S. patent N 4715679 and described in more detail in the patent applications U.S. N 08/378780 and 08/323795. The design of the core of the three areas has sufficient flexibility in order to meet the requirements of communication systems with high performance.

Since the number of possible profiles of the refractive index for the core with several areas, as described in U.S. patent N 4715679 is essentially infinite, it is convenient to study a sample profile of the refractive index using the model to calculate the performance of the light guide fiber, based on the parameters of the refractive index of the core and its geometry.

For this invention the functional requirements of the light guide fiber include low slope dispersion, work μm2. The diameter of the field of fashion in the preferred case is the same or increased compared to the standard light guide fiber dispersion-shifted.

In the study of the profiles of the refractive index, which meet these requirements, it was discovered additional advantage. For some of the new profiles with the three regions of the graph of a normalized dispersion of the waveguide defined in U.S. patent N 4715679 as Vd2(Vb)/dV2built depending on the relationshipc/, whereccritical wavelength and the wavelength of the signal, has a bimodal slope. The first part of the curve is essentially flat. Therefore, the wavelength of zero dispersion and critical wavelength is relatively insensitive to changes in the geometry of the light guide fiber, for example the radius of the core. Therefore, attenuated manufacturing tolerances and increases the percentage yield.

The second part of the curve normalized waveguide dispersion has a slope, most about 2. For this part of the curve wavelength zero dispersion and critical wavelength can have values varying within wide limits depending on the geometry of the turmoil between positive and negative values. In this way the full waveguide dispersion can be made small over the entire length of the fiber, although any part of the length of the light guide fiber full dispersion is non-zero. Therefore, four-wave mixing may be limited without much deterioration in complete dispersion.

An optical waveguide having three areas, shown in Fig. 1. Note that in Fig. 1 shows the definitions of radii A1, A2and A. Central region 2 has a profile that is equal to 1, that is, the triangular profile of the refractive index. The second region 4 is shown with several options, including a flat profile with a refractive index equal to nc, speed profile 10 and more General curve 8 of the refractive index. The profile of the refractive index is chosen so that n1> n3> n2ncwhere subscript of the refractive index corresponds to the number field. The third area is shown as line 6. It is clear that small changes of the profile 6 of the refractive index can be made without significant impact on the function of the waveguide. For example, the upper part of the line may have the inclination or bending.

Example 1. The profile of the refractive index with three of the area is aerovane when searching for fibers with low slope full dispersion wavelength zero dispersiono/in the second window. It has been found that by suitable settings of the profile of the refractive index are: (A1/A0,5; A3/A0,86;3%/1% 0,165. In table. 1 shows the characteristics of the two waveguides, obtained by simulation.

In table. 1 shows the parameters of the light guide fibers, dispersion-shifted, with a very low slope full dispersion and the large diameter of the field of fashion. For these waveguides, Aeffis more than 70 μm2.

Another of the light guide fiber included in this example has A1/A = 0,46, A2/A = 0,84 - 0,85,3%/1% = 0,39, A = 7,1 - 7,2 and1% 0,9. In this case, the slope of the full dispersion is slightly higher and amounts to about of 0.085 PS/nm2km, but Aeffincreases to values of about 75 to 80 μm2.

A variant embodiment of the invention similar to those shown in Fig. 1, shown in Fig. 2a. In this case, the simulated profile of the refractive index was changed to better reflect the real conditions of production. Some ways of casting the light guide fibers require high temperature processing of the workpiece at the time when it is in the form of powder (soot) in the best of the dopant ions leach from the glass soot or diffuse through it.

The result of this leaching or diffusion can be represented by a profile of the refractive index shown in Fig. 2a. Region 20 of failure in the form of a cone on the axis may be due to leaching of dopant from the soot. The radius 12 of the base of the cone is usually not more than about 1.5 μm. Parts 14 and 18 of the profile of the refractive index are alloying impurity, which was diffusional in the area 22 of the adjacent regions of the profile of the refractive index, with a higher concentration of dopant. As a consequence, the part 24 of the profile of the refractive index with = 1 has a wedge-shaped part 14, and trapezoidal profile 16 of the refractive index has a broader base and less steep slopes of the parties.

Example 2. The profile of the refractive index with three fields = 1, diffusion of dopant

Simulated optical waveguide fiber with three regions having the shape of the profile of the refractive index shown in Fig. 2a. The radial position of A1, A2and A shown on the horizontal axis. Parameters of the profile of the refractive index used in the calculation were:1/A0,50; A2/A0,79;3%/1% 0,18. The results are shown in table. 2.

< the change of wavelengthobetween values above and below the 1550 nm. This last property makes the design suitable for use in waveguides with controlled dispersion, as described above. The diameter of the field of fashion is acceptable for moderate densities of signal power.

Normalized waveguide dispersion depending on thec/, which corresponds to the profile of the refractive index of the example 2 shown in Fig. 2b. The flat portion of the curve 26 is the area whereoinsensitive to manufacturing deviations in the geometry of the light guide fiber. Steeper part of the curve 28 represents the area, useful in the production of the light guide fiber with controlled dispersion.

A variant embodiment of the invention shown in Fig. 3a is especially simple in construction and relatively simple to manufacture, which makes possible the fabrication process with low cost. Central stepped profile 30 of the refractive index is separated from the trapezoidal region 34 region 32 with a lower refractive index. Stepped and curved areas 36 and 38 are shown as alternatives for the region 32, the refractive index of which is essentially equal to the refractive index Alenia in Fig. 3a with the second region, which was adopted by the profile 32 of the refractive index, was simulated using the parameters:1/A 0,3; A2/A of 0.85 and3%/1% 0,39. The simulation results are shown in table. 3.

Note that the slope of the full dispersion for the last two examples, the light guide fibers is very low and the diameter of the field of fashion is more than 8.0 µm. In the first example was obtained in an extremely large diameter of the field of fashion of the light guide fiber, while the slope of the full dispersion is only 0,070 PS/nm2km.

Example also shows that it is possible to increase Aeffin exchange for a higher slope full dispersion. The specific application determines the appropriate compromise when choosing the characteristics of the fiber.

For this profile, the refractive index has a corresponding curve normalized dispersion of the waveguide depending on the relationshipc/. As shown in Fig. 3b, the curve is relatively flat for ac/ in the range of about 0.72 to 0.8. Steeper part of the curve mainly has a slope greater than about 2, for ac/ more than 0.8.

The same is she, which is:

- can be made as a waveguide with controlled dispersion;

- has a simple structure and, therefore, low costs;

- provides a very low slope full of dispersion required for systems with high data transmission rate, which may use a spectral multiplexing or have large regeneration sites, and

- provides a sufficiently large diameter of the field of fashion, in order to limit non-linear optical effects such as four-wave mixing and phase automodulation or cross-phase modulation.

1. Single-mode optical waveguide fiber containing a core profile of the refractive index that contains three areas: the first area is the last point at radius A1the maximum refractive index of n1and the relative difference of the refractive indices1%, the second region has the first point directly behind the radius A1the last point on the radius A2the maximum refractive index of n2and the relative difference of the refractive indices2%, the third area is the first point directly behind the radius A3% layer membrane surrounding said core and having a maximum refractive index of nwithand n1> n3> n2> nwith, wherein if said first region has a profile, A1/A is in the range from 0.40 to 0.60, A2/A in the range of 0.78 to 0.88 and3%/1% in the range from 0.16 to 0.39, and if she has a stepped profile of the refractive index, then A1/A is about 0.30, A2/A is about to 0.85 and3%/1% to about 0.39 and mentioned single-mode optical waveguide fiber has a wavelength of zero dispersion in the range from 1520 to 1600 nm and the slope of the full dispersion in the case of profile no more than 0,095 PS/nm2km, and in the case of the stepped profile of the refractive index is not more than 0.70 PS/nm2km.

2. Single-mode optical waveguide fiber under item 1, characterized in that if it has a profile, A1is in the range from 3.25 to 3.50 μm, A2- in the range of 5.55 to 6.05 μm, A range from 6.5 to 7.0 µm,3%/1% is about 0,165 and1% from 0.9 to 1.0%, thereby providing a wavelength zero dispersion in the range from 1530 to 1550 nm, the effective area AeffBolsa less of 8.4 μm, and if it has a step profile of the refractive index, then A1is in the range from 2.25 to 2.55 microns, A2- in the range of from 6.35 to 7.4 μm, A range from 7.5 to 8.5 μm,3%/1% is about 0,39 and1% to about 0.6%, thereby providing a wavelength zero dispersion in the range from 1525 to 1600 nm, Aeffmore than 60 μm2the slope of the full dispersion is not more than 0.07 PS/nm2km and the diameter of the field of fashion is not less than 8.0 μm.

3. Single-mode optical waveguide fiber under item 1 or 2, characterized in that the said second area has a flat profile of the refractive index and the refractive index n2approximately equal to the refractive index of the shell, and the third region has a trapezoidal profile of the refractive index.

4. Single-mode optical waveguide fiber under item 1, characterized in that A1is in the range of 2.55 to 3.0 μm, A2- in the range from 4.2 to 5.8 μm, A range from 5.0 to 6.9 μm,3%/1% in the range from 0.25 to 0.39 and1% is from 0.9 to 1.0%, thereby providing a wavelength zero dispersion in the range from 1530 to 1550 nm, the slope of the full dispersion is not more 0,095 PS/nm2km, Aefffiber under item 1, characterized in that A1is in the range from 3.25 to 3.75 microns, A2range from 5,10 to 6 μm, A range from 6.5 to 7.5 μm,3%/1% is about 0.18 and1% is from 0.9 to 1.0%, thereby providing a wavelength zero dispersion in the range from 1535 to 1585 nm, the slope of the full dispersion is not more 0,065 PS/nm2km, the diameter of the field of fashion is not less than 7.5 μm and a bimodal curve normalized waveguide dispersion.

6. Single-mode optical waveguide fiber under item 5, characterized in that the said first region has a Central section with a depression in the form of an inverted cone that has a base radius of not more than 1.5 μm, the portion of the profile about A1has a smaller slope than the slope of the profile, with a value of 1, the above-mentioned second region has a flat profile and a refractive index approximately equal to the refractive index of the shell, and the third region has a trapezoidal profile of the refractive index.

7. Single-mode optical waveguide fiber according to p. 6, characterized in that it is characterized by a curve normalized waveguide dispersion fromc/ and has a critical wavelengthcand the length of the function, actually zero for ac/ in the range from 0.68 to 0.8, and a slope greater than 2, for ac/ of greater than 0.8.

8. Single-mode optical waveguide fiber according to p. 3, characterized in that it is characterized by a curve normalized waveguide dispersion fromc/ and has a critical wavelengthcand the wavelength of the signal are equal and characterization of a normalized waveguide dispersion of the above-mentioned waveguide has a slope, in fact, equal to zero for ac/ in the range from 0.72 to 0.8, and a slope greater than 2, for ac/ of greater than 0.8.5

 

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