JPH09304640A - Single-mode optical waveguide with large effective area - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a single-mode optical waveguide fiber which has an extremely large effective area by using a model for predicting characteristics for segmented core design to obtain a family of core design. SOLUTION: The single-mode optical waveguide fiber has a 1550nm operation window composed of a core having a core refractive index distribution divided into three small core segments 8, 2, and 4 and a clad layer having a clad refractive index distribution where at least a part of the core refractive index distribution is larger than at least a part of the refractive index distribution and at least one core segment of the core refractive index distribution is much smaller than its minimum refractive index. Thus, the low-dispersion is obtained which has effective area of approximately >=90 square microns with the 1550nm operation window, approximately a >=1.3 ratio of the effective area to a mode power area, and low dispersion for operation over a wavelength range of 1530 to 1565nm.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a single mode optical waveguide fiber having a large effective area, A _eff , for telecommunications.

[0002]

Single mode waveguides with large effective areas will have reduced nonlinear optical effects including self-phase modulation, four-wave mixing, cross-phase modulation and nonlinear dispersion processing. Each of these effects causes signal degradation in high power systems. In general, distributed processing that degrades a signal is performed by a term where c is a constant and P is a signal power, exp
It is described by an equation involving (cP / A _eff ).
Other non-linear effects are described by equations involving the multiplier ratio P / A _eff . Thus, increasing A _eff results in a decrease in the non-linear contribution to optical signal degradation.

The requirement has led to a reassessment of single mode fiber refractive index profile designs in the telecommunications industry, which seeks large information capacity over long distances without regenerators. Until now, the focus of this reevaluation has been to provide the next optical waveguide. A waveguide that reduces the non-linear effects as described above. -A waveguide optimized for the low attenuation operating wavelength range of about 1550 nm. A waveguide compatible with optical amplifiers. Waveguides that maintain desirable properties of optical waveguides such as low attenuation, high strength, fatigue resistance and bending resistance.

US Patent Application No. 08/378,
Previous work, such as that described in US Pat. No. 780, has been described in U.S. Pat. No. 4,715,679 Bhabagatoura.
gavatula) first started with the basic concept of segmented core design. Larger effective area waveguides were developed for the core design hierarchy described in 08 / 378,780 above. A particular design containing at least one core with a minimum index below the index of the cladding was revealed in such application.

[0005]

Further studies of core index profile designs with regions of index lower than the minimum cladding index reveal two important features of waveguide fibers with very large effective areas. I chose The first feature is the modal power distribution weighted by radius,
That is, when E ² × r, where E is an electric field and r is a radius, is illustrated with respect to the radius, it has a unique characteristic that at least two modes are obtained. The bimodal modal power distribution can occur as a double peak or as one peak with adjacent flat shoulders. It will be appreciated that the modal power distribution is determined by the waveguiding structure contained in the refractive index profile of the waveguide. The refractive index distribution is known,
It has a more complex mode power distribution characteristic curve than the power distribution of two modes. The new and very large effective area waveguide
Also characterized by an A _eff to A _mf ratio (see definition below) of greater than 1.3.

Using these important features, a model for predicting properties for a segmented core design is used to obtain a family of core designs, the core design being
_eff , modal power distribution (ie electric field strength power distribution), effective area to mode field area ratio that characterizes a waveguide fiber suitable for use in very high performance telecommunications systems.

[0007]

[Means for Solving the Problems]

 (Definition) Effective area is shown by the following formula.

[0008]

## EQU1 ## A _eff = 2π (∫E ² rdr) ² / (∫E ⁴ rdr) In this equation, the integration limit is from 0 to infinity, and E is the electric field that cooperates with the propagating light. The effective diameter D _eff is defined by the following equation.

[0009]

[Equation 2]

The mode field area A _mf is π (D _mf /
2) ² where D _mf is Peterman II
The mode field diameter measured using the method, 2w
= D _mf and w ² = (2∫E ² rdr / ∫ [dE / dr] ² rd
r), and the integration limit is from 0 to infinity. The ratio is R = A
_eff / A _mf .

The alpha contour is defined by the following equation.

[0012]

(Equation 3)

Where n ₀ is the maximum index of the alpha index profile, delta Δ is as defined above, r is the radius, and a is the first point to the end of the alpha index profile. Is the radius measured up to the point. R, which should be zero at the n ₀ point of the alpha index profile, can be chosen, ie the first point of the index profile is interpreted as the selected distance from the waveguide centerline. An alpha contour with an alpha α equal to 1 is a triangle. When alpha is 2, the index profile is parabolic. As the value of alpha becomes greater than 2 and approaches 6, the index profile becomes more nearly a step index profile. The true step index profile is described by an infinite alpha, but about 4 to 6
Up to alpha is for practical step index distributions.

The width of the index profile segment or core segment is the distance between two vertical lines drawn to the horizontal axis from each start and end point of the index profile of the index versus radius graph. The% refractive index delta or% Δ is expressed by the following equation.

[0015]

## EQU4 ##% Δ = [(n ₁ ² −n _c ² ) / 2n ₁ ² ] × 100 In this formula, n ₁ is the refractive index of the core and n _c is the refractive index of the cladding. Unless otherwise stated, n ₁ is the maximum index in the region of the core characterized by% Δ.

The zero reference for the index of refraction is chosen as the minimum index of refraction in the cladding glass layer. Regions of the refractive index in the core below this minimum value are assigned negative values. Generally, the refractive index distribution has associated effective refractive index distributions of different shapes. The effective index profile can be used instead of its associated index profile without changing the waveguide performance. `` Single mode optical fiber (Singl
e Mode Fiber Optics) ", Marcel Decker (Marce
l Dekker Inc.), Luke B. Yun Home (Luc B. Je
unhomme), 1990, p. 32, section 1.3.2.
See

Bend performance is determined by a reference test method in which the attenuation induced by winding a waveguide fiber around a mandrel is determined. Standard test is 32mm
The performance is investigated for a waveguide fiber with one turn around the mandrel and 100 turns around the 75 mm mandrel. The maximum allowable attenuation induced by bending is typically about 1300 nm and about 1550 in the operating window.
Specified in nm.

Another bend test is a pin array bend test used to compare the relative resistance of a waveguide fiber to bending. To perform this test, attenuation loss is measured on a waveguide fiber that is essentially free of induced losses. The waveguide fiber is then woven around the pin array and the attenuation is measured again. The bend-induced loss is the difference between the two measured dampings. A pin array is a set of 10 cylindrical pins arranged in a single row and held in a fixed vertical position on a flat surface. The pin spacing is 5 mm from center to center. The pin diameter is 0.67 mm. During testing, sufficient stress is applied to cause the waveguide fiber to conform to a portion of the pin curve. SUMMARY OF THE INVENTION The present invention provides a very high performance optical fiber by efficiently solving the problems introduced by their non-linear waveguide effects and by introducing optical amplifiers in telecommunications system designs. Meet the demand for waveguide fiber.

This need is met by providing a single mode optical waveguide fiber having a very high effective area while still maintaining at least comparable bending performance to that of standard single mode step index waveguide fibers. Be done. Similarly, the damping must be low enough to allow long regenerator spacing, require fiber strength, and fatigue resistance must be sustained.

In particular, in the one-winding bending test on the standard 32 mm mandrel, the following examples show 1550 nm.
It has an induced loss due to bending of 0.05 dB or less at the measurement wavelength. Similarly, in a 100-turn 75 mm mandrel test, the bend-induced attenuation is less than 0.05 dB at 1310 nm and 0.10 at 1550 nm.
It is below dB. These results are equivalent to those of the reference step index fiber.

Therefore, the first aspect of the present invention is at least 3
A single mode optical waveguide fiber having a core with two distinct segments. The segments are distinguished from each other by a refractive index profile defined on a particular radial spacing. Features that provide a large effective area without sacrificing bending performance are: One is the presence in the core of at least one segment having a refractive index portion that is even less than the minimum refractive index of the cladding.

The other is at least two segments having a refractive index portion greater than the maximum refractive index of the cladding.
Although the electric field power is distributed over a larger core area, the presence of the coupling of the positive and negative refractive index cores helps guide the propagating light to well meet the bending loss requirements. In general, a fiber of the present invention having at least 3 distinct cores and having at least one core having a negative index of refraction has the following properties.

The attenuation corresponds to that of a reference step index single mode waveguide fiber. The bending loss is less than that of the reference step index single mode waveguide fiber. The weighted electric field distribution is a power distribution of at least two modes, as shown by curve 24 in FIG. 4, for example.
The effective area is greater than 90 square microns in the 1550 nm operating window and may exceed 350 square microns in that window.

The ratio R = A _eff / A _mf is greater than about 1.3,
And it may exceed 3.7. Generally, the 1550 nm operating window includes the wavelength range of about 1530 nm to 1565 nm. There are four families of preferred embodiments of this first aspect.
Or having a core containing five separate index segments. In each of these examples, the two non-adjacent segments have a negative index of refraction. Each segment is characterized by a refractive index Δ% and a width measured along the waveguide fiber radius.

The segment is the shape of the refractive index distribution, the refractive index Δ
% And the segment radius measured from the zero radius point of the waveguide center at each core segment to the final point. The width of each segment is found from the difference in radius. For example, if a ₀ is the radius drawn at the last point of the first core segment and a ₁ is the radius drawn at the last point of the second core segment, then a
_1- a ₀ is the width of the second segment.

In the 5-segment embodiment, each of the segments has an index distribution that is essentially stepped, that is, each segment is characterized by a constant index of refraction. Due to the diffusion of dopants during the manufacture of the waveguide core, the corners of the steps are rounded, ie curved. Generally, rounding
Small amount of does not affect the waveguide fiber performance. If rounding is important, a mathematical description of the rounded index profile is included in the design used to calculate the properties of the particular segmented core waveguide.

An important finding made in analyzing the novel refractive index profile embodiment is that the centerline refractive index profile, that is, the line of FIG. 1, while the first core region segment retains the desired waveguide performance. It can have various shapes as shown in 8 and 6. In general, a particular waveguide index profile has an associated equivalent index profile. See definition above. Disclosing and claiming particular refractive index profile shapes will be understood to include the equivalents in the disclosure and claims.

Refractive index Δ for 4 and 5 segment cores
Specific settings for% and width ranges are given here. However, it will be understood that there are an infinite number of distributions that provide the essentially required A _eff , R value and electric field distribution. One is with a functional core design, and without moving important waveguide properties outside a particular target range, width or segment substitution or segment index profile or index Δ%.
You can make adjustments in. Thus, given the family of acceptable core designs given herein, including related designs to provide a particular waveguide fiber functionality,
Will be appreciated.

In each of the following examples, the cladding layer has a substantially constant refractive index n _c whenever Δ% is assigned. A family of optical waveguides with four core segments has been found to have exceptionally high A _eff and good bending resistance, and has the following characteristics. The first core segment begins at the waveguide fiber centerline and has an alpha contour and about 0.7% to 1.2%.
% Of Δ ₀ % and a ₀ in the range of about 1.5 to 3.5 microns, the second adjacent core segment has a Δ _{1 of} less than about −0.10%. % And having a ₁ in the range of about 6.5 to 11 microns, third
Core segment of Δ ranges from approximately 0.3% to 0.8%
₂ % and a _{2 in} the range of about 7.5 to 14 microns
Having a fourth core segment of about −0.10.
And having a delta _3% less than%, to have a ₃ in the range of about 10 to 32 microns, and the radius a is not more than about 35 microns.

The preferred parameters of this 4-segment core family have the parameters in the table below.

[0031]

[Table 1] ━━━━━━━━━━━━━━━━━━━━━━━━ ∆ ₀ % in the range of 0.65% to 1.0% About 2.8 microns to 3 A _{0 in the} micron range Δ ₀ % less than about −0.10% Δ ₁ % in the range of about 6 to 8 μm a ₁ about 0.50% to 0.8% Δ ₂ % in the range of about 8 to 10 μm A _{2 of} about −0.10% Δ ₃ % radius of about 13 to 16 microns, approximately equal to a ₃ a ₃ radius a ━━━━━━━━━━━━━━━━━━━ ━━━━━ The lower bound on the negative Δ% segment is set rather by the throughput, rather than the waveguide fiber performance requirements. Currently, a level of about -0.8% is reached.

The alpha contour describes a succession of curves that begin to approach steps when alpha is in the range of 4 or more, with a triangular shape or alpha = 1, a parabolic shape or alpha = 2. The alpha contour may have an inverted conical index dip above its centerline.
The model has sufficient flex resistance to accommodate such depressions.

A preferred embodiment of a core region having a refractive index profile of four core segments is shown in FIG. 11 and has the features in the table below.

[0034]

[Table 2] ━━━━━━━━━━━━━━━━━━━━━━━━ Approximately 0.65% to 1.00% Δ ₁ % 3.35 +/- R ₁ equal to 0.30 microns Δ ₂ % less than about −0.10% r ₂ equal to 7.2 +/− 0.60 microns Δ ₃ % in the range from about 0.50% to 0.85% R ₃ equal to .1 +/- 0.70 microns r ₄ less than about -0.10% r ₄ equal to 14.5 +/- 1.0 microns r ₄ ━━━━━━━━━━━━━ ━━━━━━━━━━━━ The definitions of these distribution parameters are given below.

In the case of a core index profile of 5 core segments, the family of the profile is defined as follows. The refractive index profile begins at the center of the waveguide and travels outward, the first core segment measuring Δ ₀ % in the range of about 0 to 0.20% and the centerline of the optical waveguide fiber. The second core segment has a radius in the range of about 0.50 to 1.50 microns and the second core segment has a radius of about 0.5.
Having a Δ ₁ % in the range of 5% to 1.2% and a radius a in the range of about 0.5 to 4.5 microns, the third core segment having a Δ of less than about −0.1%. Having a ₂ % and a ₂ in the range of about 6 to 12 microns, the fourth core segment having a Δ ₃ % in the range of about 0.2% to 0.8% and about 7%.
Having a ₃ in the range from 1 to 16 microns, fifth
Core segment of less than about -0.1% Δ ₄ % and about 13
To have a ₄ in the range of 26 to 26 microns, and the core radius a is in the range of about 25 to 35 microns.

In many of the preferred embodiments, the core radius coincides with the outer radius of the final core segment. An optical waveguide having a core index profile described by this family of distributions has an effective area of greater than 350 square microns and further without attenuation or other significant degradation of performance properties such as strength or fatigue resistance, It may have better bending resistance than that of the reference step index waveguide.

In the five core segment embodiment described above, the first segment can have a variety of alpha contour shapes without significantly affecting the waveguide properties. Similarly, the alpha contour may be inverted conical and include a central dip in the index of refraction. This central depression can result from doping control during preform manufacture, or as a result of controlling preform dopants and diffusion during manufacture.

A third embodiment of the core index profile of the present invention is a waveguide having a core characterized by three negative index segments. The first core segment is about −
It has a Δ ₀ % of less than 0.10% and an a ₀ in the range of about 0.1 to 2.5 microns. The second core segment is about 0.5%
From having a ₁ of delta _1% and ranges from about 0.5 to 4.5 micron 1.2% range.

The third core segment has a Δ ₂ % of less than about -0.1% and an a ₂ in the range of about 6 to 12 microns. The fourth core segment has Δ ₃ % in the range of about 0.2% to 0.8% and a ₃ in the range of about 7 to 14 microns. The fifth core segment has a Δ ₄ % of less than about −0.1% and an a ₄ in the range of about 13 to 30 microns.

The core radius a is in the range of about 20 to 35 microns. The choice of these preferred embodiments is due to ease of manufacture, associated manufacturing costs and consistently consistent target _Aeff.
And the design ability to provide bending resistance. It is most cost-effective to use an alpha contour on the center and a step index profile on the remaining core segments for the purpose of obtaining two index dips in most four segment designs. A 5-segment design using a step index profile for all segments may be preferable in some cases.

It is clear that many permutations and combinations of these segmented core designs are possible. Thus, it is understood that these particular examples represent members of the gradient index family. The scope of the present invention includes this family of index profiles. A property sought in modeling that generally guarantees a suitable waveguide core design is that the radius-weighted modal power distribution is at least two modes. The modal power is proportional to the square of the propagating electric field. In the preferred embodiment, the model is used to find those core designs where the bimodal power distribution is a curve with two peaks.

An embodiment that occurs at radii where the first mode power maximum is between 0 and 5 microns and the second mode power maximum is greater than 8 microns is at least for reference step index waveguide fibers. It provides a waveguide fiber with as good a bending resistance and a large A _eff as those specified in.

[0043]

DETAILED DESCRIPTION OF THE INVENTION The investigation of the properties of particular segmented core designs continues to hold pace with the ever-increasing demand for high capacity long haul waveguide fibers. Data rates in the terabit range are being investigated, and systems with regenerator spacing greater than 100 km are being considered.

The above application, for example, the patent application 08/37
In No. 8,780, it was suggested that designs containing core segments with a lower index of refraction than the cladding should be further investigated, as the core can result in optical waveguide fibers with large effective areas. The finding revealed in this application is that, in fact, the effective area can be much larger than previously reported and is possible for designs containing one core segment with a refractive index at least lower than that of the cladding. Is. further,
The core design of the present invention provides a large A _eff waveguide that is well confined in the emitted light and has no degradation in bending resistance compared to the reference step index single mode fiber. In many of the designs, large A _eff waveguides show superior bending performance compared to the standard step index single mode.

A general example of the core refractive index profile of the present invention is shown in FIG. The core consists of four refractive index segments, consisting of a first segment 8, a third segment 4 having a round step index profile and two regions 2 having a refractive index lower than that of the cladding. There is. The wavy curve 6 in the first segment shows another possible shape for the first segment index profile. The segment 4 can also have various shapes without any significant influence on the characteristics of the waveguide fiber. The low gradient index segments 2 may differ from each other in terms of width and minimum refractive index. Similarly, segment 2 can have a slight positive or negative slope and can be somewhat round in shape. The lower bound on Δ% for segment 2 depends on throughput. A Δ-percentage value of about −0.80% provides a waveguide with specific properties.

The effect of this index profile on the propagating light is to confine a portion of the propagating power in the first segment defined by 8 and the adjacent low index region 2.
The second part of the optical power is guided by the structure 4 together with the low refractive index outer region 2. The large A _eff is a result of structure 4 guiding the power away from the waveguide center.
Bending resistance is not sacrificed because light confinement is provided by the outer low index region 2.

The bimodal power distribution for the four segment embodiment of the novel segmented core design is shown in FIG. 2, which is a graph of weighted field strength as a function of radius. The inner peak 10 corresponds to the first segmented waveguide structure of the segmented core. Peak 12 corresponds to the waveguide structure located near the core periphery. The amplitude of peak 12 decreases sharply with increasing radius, ensuring that light is well confined and bending resistance is improved.

The definition of the refractive index distribution Δ and the radius is shown in FIG. As shown in FIG. 11, in the 4-segment embodiment, each position of Δ ₁ %, Δ ₂ %, Δ ₃ % and Δ ₄ % is 6
8, 70, 72 and 74. The radii of each of the four segments used in the model calculation were all measured from the waveguide fiber centerline and are shown as 76, 78, 80 and 82 in FIG.
Is shown in These or similar definitions of Δ% and radius are used in all model calculations.

The particular designed feature included in FIG. 2 is A
_eff = 210 square microns and the cutoff wavelength measured on the fiber is 1562 nm. In cable construction, the cutoff wavelength is typically 200 nm to 40 nm.
It is reduced by 0 nm. Thus, for cutoff wavelengths, the designed fiber is suitable for high performance systems with 1310 nm or 1550 nm windows.

The model was tested for actual accuracy by comparing it with expected waveguide fiber characteristics. The index profile as shown in FIG. 3 is an actual waveguide fiber profile with a central alpha contour 14, a reduced index region 16 and a round step index ring 18.
Note the diffusion region on the waveguide centerline. The model is
This inverted conical shape, centerline index depression is taken into account. Table 1 shows good agreement between the model and actual waveguide fiber properties, with the exception of the 200 nm offset between the actual and model cutoff wavelengths. This difference is considered acceptable, subject to the dependence of the cutoff wavelength on the physical properties of the waveguide being measured. Although the example refractive index profile does not include segments with negative Δ% as shown in FIG. 3, this example illustrates the general accuracy of the model for the family of refractive index profiles disclosed herein.

[0051]

[Table 3] The characteristic weighted field strength pattern of the new core design is shown as curve 24 in FIG. The double peak pattern is clearly different from the pattern of the reference dispersion shifted fiber shown as curve 20 in FIG. The reference dispersion-shifted waveguide fiber index design includes a first segment with an alpha contour, a flat index profile ring with an index close to that of the cladding layer, and a second ring with a round step index profile. including.

United States Patent Application No. 08/378,
The large effective area design category disclosed in No. 780 is curve 2
It has the property of weighted field strength indicated by 2. As expected, these designs show a weighted field strength pattern with the regions migrating out towards larger radii. For completeness, the field strengths of these three separate core distribution designs are shown in FIG. Curve 64 is the electric field strength of the reference dispersion shifted waveguide fiber, and curve 66 is the above-mentioned patent application 08/37.
The field strength of the design of No. 8,780 and the curve 62
Is a characteristic of the electric field strength of the large effective area design of the present invention. The double peak curve 62 is quite different from the curves characteristic of the other two designs.

5 (a), 5 (b) and 5 (c)
Shows a modification of the refractive index profile design having two regions with a refractive index profile lower than the cladding index. Each figure shows two low index regions 26 and two step or round step index regions 28. The design of FIG. 5 (a) includes a core region 30 that matches the cladding index. A preferred embodiment from these three index profiles is shown in FIG. 5 (c). The two low index regions are located away from the first segment of the core region. Thus, the electric field distribution is moved away from the waveguide center where the effective area is increasing. A low index ring around the core region serves to confine the propagating light and hold it in the waveguide to provide acceptable bending resistance.

Another first segment profile is shown in FIG. 5 (c) as a dashed curve near the step index profile 28. These options, including them, include a diffusion dip above the centerline, resulting in an effective area and R-ratio all acceptable. Example 1-2 Two Low Refractive Index Distributions In FIG. 6, the designed core region distribution has a central diffusing depression 30,
It is similar to an inverted cone, with a minimum Δ% of about 0.18 and a maximum radius of about 1 micron. First
Ring 32 has a round step index with a maximum Δ% 0.80 and a radius a ₀ of about 3 microns. The low index profile segment 34 has a refractive index Δ% of −0.18 and a radius a ₁ of about 7.5 microns. The second ring 32 is about 0.5
Round step index with Δ% of 0 and a _{2 of} about 11 microns. Low refractive index distribution segment 34
Has a refractive index Δ% of −0.18 and a radius a ₃ of about 23 microns. The core region ends at the point where its index of refraction reaches that of the cladding layer, which in this case is approximately 24
The radius is in microns.

The designed properties of this example are shown in the following table.

[0056]

[Table 4] ━━━━━━━━━━━━━━━━━━━━━━━━ Mode field diameter 9.8 microns D _eff 18.1 microns A _eff 257 square microns R 3.41 Cutoff wavelength 1809 nm Zero dispersion 1561 nm Dispersion slope 0.151 ps / nm ² -km ━━━━━━━━━━━━━━━━━━━━━━━━━ Bending performance is a standard step single mode It is equal to that of the waveguide.

The designed waveguide is from 1535 nm to 15
It is ideal in every respect for high performance waveguide telecommunications systems operating over the 75 nm range. However, the dispersion slope should be lower for systems operating in both 1310 nm and 1550 nm windows. Effective area is in a trade-off for improved dispersion slope. Or, as another option, a segmented core distribution can be designed that provides low total dispersion in the 1310 nm window. (Comparative example 2) The core refractive index distribution shown in FIG.
6 differs from that of FIG. 6 only in that the segment index of is triangular, and it has a maximum Δ% of about 0.7, has no diffuse cone on the centerline, and is about 4 microns. a ₀ .

The designed parameters are shown in the following table.

[0059]

[Table 5] ━━━━━━━━━━━━━━━━━━━━━━━━ Mode field diameter 10.0 micron D _eff 16.4 micron A _eff 210 square micron R 2.69 Cut-off wavelength 1834 nm Zero dispersion 1562 nm Dispersion slope 0.16 ps / nm ² -km ━━━━━━━━━━━━━━━━━━━━━━━━━ It should be noted that a large modification of has a small effect on the waveguide parameters.

A distribution with three low index regions 36 is shown in FIG. Ring 38 is shown to be a step index, but may be a round step index. Further, the first ring may be an alpha contour. (Example 3-3 segment low refractive index distribution) The distribution of FIG. 9A shows three low refractive index regions, that is, a region whose refractive index is lower than that of the cladding layer 52 and two round step refractive index rings. 54 and. The first low refractive index region is −
An inverted cone with a minimum Δ% of 0.18 and a maximum radius of about 1 micron. Continuing from the center, the radii and Δ% for the remaining core regions are 3 microns and 0.85%, 7 microns and −0.18, 10 microns and 0.7%, and 20 microns and −0.1%, respectively. 18%.

This core index profile results in the following designed waveguide parameters.

[0062]

[Table 6] ━━━━━━━━━━━━━━━━━━━━━━━━ Mode field diameter 9.65 microns D _eff 15.96 microns A _eff 200 square microns R 2.74 Cutoff wavelength 1740 nm Zero dispersion 1562 nm Dispersion gradient 0.137 ps / nm ² -km ━━━━━━━━━━━━━━━━━━━━━━━━ (Comparative Example 4-3 Low refraction) The refractive index distribution of FIG. 9 (b) is narrowed so that the width of the central diffusion reversal cone has a refractive index lower than that of the cladding only in the portion where the central line distribution is small. Except for this, it is essentially the same as that of Example 3.

The designed waveguide characteristics are shown in the following table.

[0064]

[Table 7] ━━━━━━━━━━━━━━━━━━━━━━━━ Mode field diameter 9.79 microns D _eff 18.42 microns A _eff 267 square microns R 3.54 Cut-off wavelength 1738 nm Zero dispersion 1544 nm Dispersion slope 0.124 ps / nm ² -km ━━━━━━━━━━━━━━━━━━━━━━━━━ Fig. 9 (a) and Fig. 9 Comparing the distribution results of (b), FIG.
It is derived that the distribution of (b) is desirable. Because the R ratio is higher and the cutoff wavelength is not substantially affected,
And the zero dispersion is from the wavelength window 1535 nm to 1575 n.
It is better matched to WDM at m, which is essentially consistent with erbium optical amplifier operation.

Example 3 and Comparative Example 4 clearly demonstrate the need to model a segmented core distribution. The number of possible distributions in a segmented core concept is essentially infinite. Thus, the most efficient and time / cost efficient way to find a family of distributions with a given set of properties is to perform extensive design studies before the actual fabrication of the novel segmented core waveguide. .

For the embodiment shown in FIG. 11, distribution parameter limits are given in the summary of the invention. A refractive index profile of about 2500 in the core design family shown in FIG. 11 was designed. The calculated waveguide characteristics are shown in the following table.

[0067]

[Table 8] ━━━━━━━━━━━━━━━━━━━━━━━━ λ ₀ = 1580 +/- 30nm Total dispersion slope = 0.085 +/- 0.02ps / nm ² -km Mode field diameter = 8.0 +/- 0.5 micron A _eff = 265 +/- 35 micron λ _c = 1850 +/- 100nm Pin array bending loss average = 9.6dB Pin array end loss intermediate number 7. The 0 dB pin array range was 3 to 25 dB. ━━━━━━━━━━━━━━━━━━━━━━━━

[Brief description of drawings]

FIG. 1 is a graph of a core refractive index profile with two segments having a refractive index less than that of a cladding layer in an optical waveguide fiber having four segments.

FIG. 2 is a weighted field strength vs. radius graph for an exemplary embodiment of a novel core index profile.

FIG. 3 is a graph of a segmented core index profile showing that the designed parameters were compared to the parameters measured on a waveguide fiber having this index profile.

FIG. 4 is a graph of weighted field strength for a 3-segmented core waveguide type.

FIG. 5 is a graph of a core refractive index profile having two segments having a refractive index smaller than that of a cladding layer in an optical waveguide fiber having five segments.

6 is a graph of a modification of the embodiment shown in FIG.

FIG. 7 is a graph of core refractive index profile designed with four segments and a first triangular segment.

FIG. 8 is a graph of a core refractive index profile having three segments having a refractive index smaller than that of a cladding layer in an optical waveguide fiber having five segments.

FIG. 9 is a graph of a core refractive index profile having three segments having a refractive index smaller than that of a cladding layer in an optical waveguide fiber having five segments.

FIG. 10 is a graph of electric field strength versus radius for an exemplary embodiment of a core refractive index profile of the present invention.

FIG. 11 is a graph of a core refractive index profile with 4 segments, showing the definition of the refractive index profile Δ and the radius used in the model.

[Explanation of symbols for main parts]

 2 Low refractive index profile segment 4 3rd segment 6, 8 1st core region segment

Claims (16)

[Claims] 1. A core having a core refractive index distribution in which the refractive index distribution is subdivided into at least three core segments,
At least a portion of the core index profile is greater than at least a portion of the index profile and at least one core segment of the core index profile has a minimum index of refraction less than its minimum index of refraction A clad layer having a clad refractive index distribution
A single mode optical waveguide fiber having an m operating window having an effective area of greater than about 90 square microns at a 1550 nm operating window and a ratio of effective area to mode power region of greater than about 1.3, from 1530 nm to 1565 n.
A single mode optical waveguide fiber comprising a low dispersion waveguide fiber for operation over the m wavelength range. 2. The core refractive index distribution has five core segment
Two core segments that are not adjacent to each other
The minimum refractive index of the clad layer is smaller than that of the cladding layer.
Small and the waveguide waveguides in each core segment
The last point from the zero reference point on the center line of the fiber is a
A is the radius of a₀, A₁, A _Two, A_ThreeAnd a
The unit of claim 1 defined as a radius.
One-mode optical waveguide fiber. 3. The first core segment is from a zero reference point.
Radius a₀Up to the point and n₀Constant refractive index of
And the second core segment has a width (a₁-A ₀) And pole
Large refractive index n₁Has a round step index distribution of
The core segment has a width (a_Two-A₁) And a constant refractive index n_Two
And the fourth core segment has a round step index component
Cloth and maximum refractive index n_ThreeAnd width (a_Three-A_Two) Has a fifth
Core segment of width (a-a_Three) And a constant refractive index n_Four
3. The single mode of claim 2 having
Optical waveguide fiber. 4. The cladding layer has a constant index of refraction n _c , n ₀ and n ₂ are less than n _c , or n ₀ and n ₄ are less than n _c , and n ₂ and n _4. The single mode optical waveguide fiber according to claim 3, wherein ₄ is smaller than n _c . 5. The core segments are Δ ₀ %, Δ ₁ %, Δ
The first core segment is defined by refractive indices Δ% of ₂ %, Δ ₃ % and Δ ₄ %, respectively, and the first core segment has a Δ ₀ % in the range of about 0 to 0.2%.
And having an a ₀ in the range of about 0.50 to 1.5 microns, the second core segment has Δ ₁ % in the range of about 0.5% to 1.2% and about 0.50 to 4.5. The third core segment has a Δ ₂ % less than about −0.1 and about 6 with an a _{1 in the} micron range.
From has a ₂ in the range of 12 microns, a fourth core segment of has a ₃ in the range of delta _3% and about 7 in the range of about 0.2% 0.8% 16 microns, The fifth core segment has a Δ ₄ % of less than about −0.1 and about 1
A single mode optical waveguide fiber according to claim 4 having an a ₄ in the range of 3 to 26 microns and a core radius a in the range of about 25 to 35 microns. 6. The core refractive index distribution has four core segmentation.
Two core segments that are not adjacent to each other
The minimum refractive index of the clad layer is smaller than that of the cladding layer.
Small and the waveguide waveguides in each core segment
The last point from the zero reference point on the center line of the fiber is a
A is the radius of a₀, A₁, A _TwoAnd the radius of a
6. Any of claims 1 to 5 characterized in that
A single mode optical waveguide fiber according to item 1. 7. Each of the core segments has a Δ%, the first core segment has an alpha contour and a Δ ₀ % in the range of about 0.7% to 1.2% and about 1.5 to 3. The second core segment has a Δ ₁ % less than about −0.10 and a ₁ in the range of about 6.5 to 11 microns, and the third core segment has a ₀ in the range of 5 microns. The fourth core segment has Δ ₂ % in the range of about 0.3% to 0.8% and a ₂ in the range of about 7.5 to 14 microns, and the fourth core segment has Δ ₃ % of less than about −0.10 and It has a ₃ in the range of about 10 to 32 microns, and a single mode optical waveguide of claim 6 wherein lies in the range of about 25 to 35 microns. 8. The first core segment of the alpha contour has a trapezoidal quasi-effective index profile, starting at the waveguide fiber centerline and progressing outwardly, the trapezoidal shape being approximately 1.
With a horizontal portion with a radial magnitude in the range from 1 to 3 microns and an adjacent linear sloped portion, Δ ₁ % is essentially unchanged and a ₀
The single mode waveguide fiber of claim 7, wherein is in the range of about 1.5 to 4.5 microns. 9. The alpha contour has an inverted conical shape with a central refractive index depression, the circular base of the cone being .0.
The single mode waveguide fiber of claim 7 having a radius in the range of 10 to 1.0 microns. 10. Δ ₀ % is in the range of about 0.65% to 1.0% and a ₀ is in the range of about 2.8 to 3.5 microns, and the second core segment is about −0. Δ ₁ % less than .1 and about 6
The _first core segment has an a ₁ in the range of about 0.5 to 8 microns and the third core segment has Δ ₂ % in the range of about 0.50% to 0.85% and a ₂ in the range of about 8 to 10 microns; 4 core segments have Δ ₃ % less than about −0.1 and about 1
Have a ₃ in the range of 3 to 16 microns, and a is a ₃
8. The single mode waveguide fiber according to claim 7, wherein 11. The single mode waveguide fiber of claim 7, 8, 9 or 10 wherein alpha is in the range 1 to 6. 12. The core refractive index distribution is subdivided into five core segments, and the minimum refractive index of three core segments that are not adjacent to each other is smaller than the minimum refractive index of the cladding layer, The last point from the zero reference point on the waveguide fiber centerline in the segment is a ₀ , a ₁ , a ₂ , a ₃ and a, respectively, where a is the radius of the core.
The single mode optical waveguide fiber of claim 1 defined as the radius of 13. The core segments are each Δ
First core segment-Δ ₀ % less than 0.1 and about 0.1, defined by refractive indices Δ% of ₀ %, Δ ₁ %, Δ ₂ %, Δ ₃ % and Δ ₄ %, respectively.
Has a ₀ in the range of about 0.5 to 2.5 microns and the second core segment has Δ ₁ % in the range of about 0.50% to 1.2% and in the range of about 0.5 to 4.5 microns. a ₁ and the third core segment has a Δ ₂ % of less than about −0.1 and about 6
From has a ₂ in the range of 12 microns, a fourth core segment of has a ₃ in the range of delta _3% and about 7 in the range of about 0.2% 0.8% 14 microns, the 5 core segment has Δ ₄ % less than about -0.1% and a ₄ in the range of about 13 to 30 microns, and the radius of the a core is in the range of about 20 to 35 microns. The single mode optical waveguide fiber according to claim 11. 14. A core having a core refractive index distribution in which the refractive index distribution is subdivided into at least three core segments; at least a portion of the core refractive index distribution being greater than at least a portion of the refractive index distribution and A single-mode optical waveguide fiber comprising: a cladding layer having a cladding refractive index distribution in which at least one core segment of the core refractive index distribution has a minimum refractive index smaller than its minimum refractive index. A single-mode optical waveguide fiber having a radius-weighted electric field strength, the weighted electric field strength being bimodal. 15. The single mode optical waveguide fiber of claim 14, wherein the bimodal weighted field strengths have at least two distinct maxima. 16. The bending loss induced by a single winding of the optical waveguide around a 32 mm diameter mandrel is 155.
Less than 0.05 dB at 0 nm and diameter of 75
The bending loss induced by winding the optical waveguide 100 times around the mm mandrel is 0.0 at 1310 nm.
5. It is 5 dB or less and 0.10 dB or less at 1550 nm, respectively.
3. The single mode optical waveguide fiber described in 3.