CN116256837A - High-bandwidth bending insensitive multimode optical fiber - Google Patents
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- 239000013307 optical fiber Substances 0.000 title claims description 49
- 238000005452 bending Methods 0.000 title description 11
- 238000005253 cladding Methods 0.000 claims abstract description 161
- 239000010410 layer Substances 0.000 claims abstract description 69
- 239000012792 core layer Substances 0.000 claims abstract description 61
- 239000000835 fiber Substances 0.000 claims abstract description 35
- 238000009826 distribution Methods 0.000 claims abstract description 14
- 108700041286 delta Proteins 0.000 claims abstract description 4
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 claims description 51
- 229910052731 fluorine Inorganic materials 0.000 claims description 51
- 239000011737 fluorine Substances 0.000 claims description 51
- 229910052732 germanium Inorganic materials 0.000 claims description 43
- GNPVGFCGXDBREM-UHFFFAOYSA-N germanium atom Chemical compound [Ge] GNPVGFCGXDBREM-UHFFFAOYSA-N 0.000 claims description 43
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims description 25
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 25
- 229910052698 phosphorus Inorganic materials 0.000 claims description 25
- 239000011574 phosphorus Substances 0.000 claims description 25
- 235000012239 silicon dioxide Nutrition 0.000 claims description 15
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- G02B6/03661—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 4 layers only
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Abstract
The invention relates to a high bandwidth bend insensitive multimode fiber for data communication and automobile communication, comprising a core layer and a cladding layer, wherein the refractive index profile of the core layer is parabolic, the cladding layer is sequentially provided with a first inner cladding layer, a second inner cladding layer, a sinking cladding layer and an outer cladding layer from inside to outside, and the high bandwidth bend insensitive multimode fiber is characterized in that the core layer distribution index alpha 1 1.9-2.1, the radius R1 of the core layer is 12-28 mu m, the maximum relative refractive index difference delta 0 of the center of the core layer is 0.8-1.2%, the relative refractive index difference delta 1 at the edge R1 of the core layer is-0.03%, the width (R2-R1) of the first inner cladding layer is 0.4-3 mu m, the relative refractive index difference delta 2 at the outer edge of the first inner cladding layer is-0.3% -0.04%, the refractive index cross section of the first inner cladding layer is distributed in a power index function, and the width (R3-R2) of the second inner cladding layer is 0.5-4 mu m. The invention realizes the optical transmission bandOptimization of wide performance.
Description
Technical Field
The invention relates to a high-bandwidth bending insensitive multimode optical fiber, belongs to the technical field of optical communication, and can be used for transmission of data communication and automobile communication.
Background
Multimode fibers, which are superior solutions for short-distance high-rate transmission networks with low system cost advantages, have been widely used in the fields of data centers, office centers, high-performance computing centers, storage area networks, etc., where the transmission distance that can be supported by the intermodal dispersion in the multimode fibers is greatly limited, and in order to reduce the intermodal dispersion of the fibers, the refractive index profile of the core layer of the multimode fiber needs to be designed into a refractive index profile that gradually decreases continuously from the center to the edge, which is generally referred to as an "α profile". I.e. the refractive index profile satisfying the following power exponent function:
wherein n is 0 Refractive index of the optical fiber axis; r is the distance from the axis of the optical fiber; a is the radius of the optical fiber core; alpha is a distribution index; delta 0 The refractive index difference of the core center relative to the cladding is simply referred to as the relative refractive index difference.
The relative refractive index difference, delta i ：
Wherein n is i For refraction at a distance i from the center of the coreA rate; n is n c The refractive index of the cladding of the fiber is indicated, typically that of pure silica.
By at SiO 2 Doped with a dopant (such as GeO) with refractive index adjusting function at a certain concentration 2 、F、B 2 O 3 、P 2 O 5 、TiO 2 、Al 2 O 3 、ZrO 2 、SnO 2 Etc.) to achieve a core refractive index profile of the multimode optical fiber. Multimode fibers can achieve high bandwidth performance by precisely controlling the core refractive index profile, and thus the designed multimode fibers can support high-rate transmission of hundreds of meters.
The application of multimode optical fibers is often a narrow cabinet, distribution box, vehicle communication, etc. integrated system, and the optical fibers can experience a small bending radius. When conventional multimode fibers are bent at small angles, high order modes propagating near the edges of the core can easily leak out, thereby causing signal loss. In designing the refractive index profile of a bending-resistant multimode fiber, a method of adding a low refractive index region to the cladding of the fiber can be used to limit leakage of high order modes, so as to minimize signal loss. However, the introduction of a depressed cladding causes a change in the propagation constant of the higher order modes near the core edge, resulting in an increase in modal dispersion of the fiber.
Research shows that multimode fibers tend to exhibit higher bandwidth performance for a particular wavelength window only at a given time of refractive index profile, and that significant degradation in bandwidth performance occurs when the fiber application window is shifted to a larger or smaller wavelength. Therefore, from the application point of view, the design of the multimode optical fiber needs to be improved, so that the multimode optical fiber is compatible with the existing OM3/OM4 multimode optical fiber, has lower bandwidth-wavelength sensitivity, meets the application requirements of the WDM technology in a certain band range, and has excellent bending resistance so as to adapt to the new requirements of the transmission technology progress on the multimode optical fiber. By optimizing the type, concentration and mode of the doping component, the multi-component doped optical fiber can have smaller chromatic dispersion than the single germanium-doped core layer of the traditional multimode optical fiber, thereby having higher bandwidth in a wider range so as to meet the bandwidth requirements of 850-953 nm wavelength division multiplexing and 980nm transmission.
In the actual manufacturing process, the fluctuation of equipment and process can cause the actual profile to deviate from the ideal profile, influence the optical performance of the optical fiber, and cause the increase of the waste fiber rate. Particularly, under a multi-element doping system, the component difference among doped layers is large, and element diffusion, thermal expansion coefficient, stress change caused by viscosity difference and the like in the processes of deposition, shrinkage, wire drawing and the like can lead to refractive index profile distortion, and particularly the edge of a core layer is extremely easy to be influenced by a cladding structure and the component. In order to be able to produce high bandwidth bend insensitive multimode fibers, it is desirable to reduce the effects of depressed cladding and profile distortions on the propagation modes within the multimode fiber core.
Disclosure of Invention
For convenience of description of the present invention, some terms are defined:
core rod: a preform comprising a core layer and a portion of a cladding layer;
radius: the distance between the outer boundary and the center point;
refractive index profile: the relationship between the refractive index of the glass of an optical fiber or optical fiber preform (including a core rod) and its radius;
DMD: differential mode delay, when a laser light source is used, the optical pulse delay difference between the fastest mode and the slowest mode excited in the multimode optical fiber is used for evaluating the bandwidth performance of the multimode optical fiber when the laser light source is used;
DMD test: adopting a single-mode probe with a mode field diameter of 5 mu m to continuously emit light pulses to the tested optical fiber, simultaneously scanning the probe, moving the probe from the axis of the optical fiber to the edge, each time moving by 1 mu m, and recording and superposing the light pulses at each position on the same time domain graph at a receiving end to form a DMD index;
contribution of fluorine (F): the relative refractive index difference (Δf) of the fluorine-doped (F) silica glass relative to the pure silica glass, thereby representing the fluorine-doped (F) amount;
contribution of germanium (Ge): the relative refractive index difference (Δge) of germanium (Ge) doped silica glass relative to pure silica glass, thereby representing the amount of germanium (Ge) doped;
contribution amount of phosphorus (P): the relative refractive index difference phosphorus (Δp) of the phosphorus (P) -doped silica glass relative to the pure silica glass represents the amount of phosphorus (P).
The technical problem to be solved by the invention is to provide the high-bandwidth bending insensitive multimode optical fiber with reasonable core layer and cladding structure design aiming at the defects in the prior art.
The invention adopts the technical proposal for solving the problems that: comprises a core layer and a cladding layer, wherein the refractive index profile of the core layer is parabolic (alpha power exponent function distribution), the cladding layer sequentially comprises a first inner cladding layer, a second inner cladding layer, a depressed cladding layer and an outer cladding layer from inside to outside, and is characterized in that the refractive index of the core layer is alpha 1 1.9-2.1, the radius R1 of the core layer is 12-28 mu m, the maximum relative refractive index difference delta 0 of the center of the core layer is 0.8-1.2%, the relative refractive index difference delta 1 at the edge R1 of the core layer is-0.03%, the width (R2-R1) of the first inner cladding layer is 0.4-3 mu m, the relative refractive index difference delta 2 at the outer edge of the first inner cladding layer is-0.3% -0.04%, the refractive index cross section of the first inner cladding layer is distributed as a power index function, and the relative refractive index difference delta (R) is:
the width (R3-R2) of the second inner cladding is 0.5-4 mu m, the relative refractive index difference delta 3 of the outer side edge of the second inner cladding is-0.45% -0.03%, the width (R4-R3) of the depressed cladding is 3.0-9.0 mu m, the relative refractive index difference delta 4 is-0.9% -0.45%, and the outer cladding is a pure silica glass layer.
According to the scheme, the first inner cladding layer
When alpha is 2 1-2, said first inner cladding +.>
When alpha is 2 Not less than 0.5<1。
According to the scheme, the relative refractive index difference delta 2-delta 1 of the outer edge of the first inner cladding is less than or equal to-0.04%.
According to the scheme, the refractive index profile of the second inner cladding is distributed in a power index function, and the relative refractive index difference delta (r) is:
According to the scheme, the relative refractive index difference delta 3-delta 2 of the outer edge of the second inner cladding is less than 0.1%.
According to the scheme, the core layer is a silicon dioxide glass layer co-doped with germanium, fluorine or germanium, phosphorus and fluorine, the fluorine of the core layer is used as a negative doping agent, the fluorine doping amount is increased in the direction from the center of the core layer to the edge of the core layer, the fluorine doping contribution amount delta F0 at the center of the core layer is-0.01% -0.1%, and the fluorine doping contribution amount delta F1 at the edge of the core layer is-0.4% -0.1%.
According to the scheme, the first inner cladding is a silicon dioxide glass layer doped with germanium, fluorine or germanium, phosphorus and fluorine, the fluorine doping amount of the first inner cladding is increased from the inner layer to the outer side edge, wherein the fluorine doping contribution amount delta F1 at the edge of the core layer is equal to the fluorine doping contribution amount delta F1 'at the inner layer of the first inner cladding, and the germanium doping contribution amount delta Ge1 at the edge of the core layer is equal to the germanium doping contribution amount delta Ge1' at the inner layer of the first inner cladding.
According to the scheme, the germanium doping contribution delta Ge2 at the outer side edge of the first inner cladding is 0.02% -0.30%, and the fluorine doping contribution delta F2 at the outer side edge of the first inner cladding is-0.4% -0.05%.
According to the scheme, when the first inner cladding adopts germanium, phosphorus and fluorine co-doping, the width of the first inner cladding is 1-3 mu m.
According to the scheme, the second inner cladding is a silicon dioxide glass layer co-doped with fluorine or germanium, phosphorus and fluorine.
According to the scheme, when the second inner cladding is doped with germanium, phosphorus and fluorine, the thickness (R3-R2) of the second inner cladding is more than or equal to 1.5 mu m, and the phosphorus doping contribution quantity delta P of the second inner cladding is less than 0.1 percent.
According to the scheme, the optical fiber has a bandwidth of 6000MHz-km or more at a wavelength of 850nm, 2600MHz-km or more at a wavelength of 953nm, and 2000MHz-km or more at a wavelength of 980 nm.
According to the scheme, the bending additional loss of the optical fiber at the wavelength of 850nm, which is caused by 2 circles around the optical fiber with the bending radius of 7.5 mm, is less than or equal to 0.1dB; at 1300nm, the bend parasitic loss caused by 2 turns with a 7.5 millimeter bend radius is less than or equal to 0.3dB.
The invention has the beneficial effects that: 1. according to the invention, through the design of the first inner cladding power exponent function distribution structure, the differential mode time delay (DMD) performance of the multimode optical fiber is improved, and the optimization of the optical transmission bandwidth performance is realized; 2. the double inner cladding design avoids the mutual influence between the core layer and the sunken cladding layer and the refractive index distortion of the core layer caused by diffusion, stress and the like; 3. the mode of doping germanium and fluorine in the first inner cladding and doping fluorine in the second inner cladding is adopted, so that diffusion caused by huge doping element concentration difference between layers is avoided, and profile distortion caused by diffusion is reduced; 4. the reasonable germanium and fluorine concentration ratio and gradient change of the inner cladding improve the material viscosity matching of the inner cladding and the depressed cladding, the stress change of the optical fiber is gentle, and the section distortion caused by the stress is reduced; 5. the optical fiber of the invention not only can be compatible with the existing OM3/OM4 multimode optical fiber, but also can support the wavelength division multiplexing technology within the wavelength range of 850 nm-950 nm; 6. the reasonable design of the parameter of the sinking cladding improves the bending insensitive property of the optical fiber, and can be applied to access networks, vehicle-mounted optical communication networks and miniaturized optical devices.
Drawings
FIG. 1 is a schematic view of refractive index profile of a comparative example of the present invention.
FIG. 2 is a schematic representation of a refractive index profile of one embodiment of the present invention.
Fig. 3 is the DMD test result of one comparative example of the present invention.
Fig. 4 is a DMD test result for one embodiment of the invention.
Detailed Description
Specific examples will be given below to further illustrate the present invention.
The embodiment of the invention comprises a core layer and a cladding layer, wherein the refractive index profile of the core layer is parabolic, the cladding layer sequentially comprises a first inner cladding layer, a second inner cladding layer, a depressed cladding layer and an outer cladding layer from inside to outside, and the refractive index distribution of the multimode fiber core cladding layer needs to meet the following relation:
wherein, delta (R) is a function of the relative refractive index difference along the radius, delta 0 is the relative refractive index difference at the center of the core, R1 is the radius of the core, delta 1 is the relative refractive index difference at R1, alpha 1 Is the refractive index distribution index of the core layer; r2 is the outer diameter of the first inner cladding, Δ2 is the relative refractive index difference at the outer diameter (outer edge) of the first inner cladding, α 2 A refractive index distribution index of the first inner cladding; r3 is the outer diameter of the second inner cladding, delta 3 is the relative refractive index difference at the outer diameter of the second inner cladding, alpha 3 A refractive index distribution index of the second inner cladding; r4 is the outer diameter of the depressed cladding, and Δ4 is the relative refractive index difference of the depressed cladding; r5 is the outer diameter of the outer cladding, delta 5 is the relative refractive index difference of the outer cladding, and the outer cladding is pure silica glass.
The relative refractive index difference, Δi:
wherein n is i Refractive index at i from the center of the core; n is n c The refractive index of the cladding of the fiber is indicated, typically that of pure silica.
The core layer of the multimode fiber is a silicon dioxide glass layer co-doped with germanium, fluorine or germanium, phosphorus and fluorine, and the multi-element doping can effectively reduce the sensitivity of bandwidth to wavelength, so that the multimode fiber has higher bandwidth in a wider wavelength range.
Refractive index edge of first inner claddingThe radial direction gradually decreases according to the distribution index so as to change the propagation constant of the high-order mode of the core layer and compensate the bandwidth deterioration caused by the sagging cladding layer and the profile distortion. The refractive index of the first inner cladding is smaller than the refractive index n of the outer cladding c So that the propagation constant of the mode in the first inner cladding layer
Is a leaky mode. Thus, the influence of the cladding and the technological process on the high-order mode transmitted by the core layer is reduced, and the reduction of the bandwidth of the optical fiber caused by introducing more new high-order modes is avoided.
The thickness, refractive index profile parameters of the first inner cladding layer are related to the refractive index profile of the core layer. By adjusting the relative refractive index difference Delta2, the width R2-R1 and the distribution index alpha at the outer diameter of the first inner cladding 2 The influence of the depressed cladding and the profile distortion on the high-order mode of the core layer can be effectively reduced, and the mode bandwidth of the multimode fiber is improved. When (when)
When alpha 2 is more than or equal to 1 and less than or equal to 2; more preferably, alpha 2 is more than or equal to 1 and less than or equal to 1.5. When->
When the alpha 2 is more than or equal to 0.5,<1。/>
in FIG. 3 of the DMD of a comparative example, the higher order modes at the edge of the core layer are biased to the left, and the propagation constants of the higher order modes are smaller, where Δ2 can be set to be smaller
And greatly, the propagation constant of a high-order mode of the core layer is increased, the modal dispersion of the high-order mode is reduced, and simultaneously alpha 2 is adjusted to ensure that the change trend of the first inner cladding close to the core layer is similar to that of the first inner cladding, so that the abrupt change of the refractive index profile is avoided. The DMD graph of an embodiment after adjustment is shown in fig. 4, in which the intermodal dispersion between the higher-order mode and the lower-order mode is significantly reduced, and the fiber bandwidth is increased.
The relative refractive index difference delta 2-delta 1 between the edges of the first inner cladding and the core layer is less than or equal to-0.04 percent so as to ensure that the first inner cladding has enough influence on the higher-order mode of the core layerIs large enough. However, when the first inner cladding refractive index Δ2 is too low or the width R2-R1 is too large, the number of leaky modes is too large, which in turn reduces the bandwidth of the optical fiber. To limit the number of leaky modes, R2 inside and outside the first inner cladding 2 (Δ0-Δ2)-R1 2 (Delta0-Delta1) is between 0.2 and 2.5 mu m 2 The value of the relation between the parameters inside and outside the first inner cladding layer is 0.2-2.5 μm 2 Between them.
And at the high temperature in the wire drawing process, elements such as germanium, phosphorus, fluorine and the like doped in the core layer are diffused, so that the refractive indexes of the core layer edge and the inner cladding layer of the optical fiber section are changed compared with the refractive indexes of corresponding positions of the prefabricated rod. Meanwhile, the viscosity difference between the core layer and the cladding layer forms residual stress under the action of wiredrawing tension, and the refractive index profile is distorted under the action of photoelastic. The first inner cladding is a silicon dioxide glass layer doped with germanium, fluorine or germanium, phosphorus and fluorine, the fluorine doping amount of the first inner cladding is increased from the inner side to the outer side, wherein the fluorine doping contribution amount delta F1 at the edge of the core layer is equal to the fluorine doping contribution amount delta F1 'at the inner diameter of the first inner cladding, and the germanium doping contribution amount delta Ge1 at the edge of the core layer is equal to the germanium doping contribution amount delta Ge1' at the inner diameter of the first inner cladding. By reasonable doping component proportion, profile distortion caused by diffusion and stress can be reduced.
In the preparation process of the multimode optical fiber, a flowmeter is adopted to control the entering of reactants. The flowmeter is unstable when suddenly opened from a closed state, and the fluctuation in a small range is extremely large. When the multimode optical fiber is prepared by an in-tube method, the deposition is started from the cladding layer to the core layer, the refractive index of the first inner cladding layer is gradually increased from outside to inside, and the flowmeter of the germanium precursor is also gradually increased. Therefore, before the core layer with the highest refractive index control precision requirement is prepared, the flowmeter of the germanium precursor is gradually increased to the target opening degree from the small opening degree, and compared with the process of suddenly opening, the process of slowly changing is more controllable and stable.
When germanium and fluorine are co-doped in the first inner cladding, the width of the first inner cladding is 0.4-2.5 mu m, the germanium doping contribution delta Ge2 at the outer diameter of the first inner cladding is 0.02% -0.30%, and the fluorine doping contribution delta F2 at the outer diameter of the first inner cladding is-0.4% -0.05%. When the first inner cladding adopts germanium, phosphorus and fluorine co-doping, the width of the first inner cladding is 1-3 mu m.
The second inner cladding is used for compensating the large difference of the components of the core layer and the depressed cladding, balancing the difference of the internal concentration and the external concentration, increasing the diffusion distance to reduce the influence of diffusion on the refractive index profile, and reasonable material composition, viscosity matching and smooth gradual change of the refractive index to reduce the refractive index change of the optical fiber caused by the technological process. The refractive index of the second inner cladding is graded, and the distribution index alpha 3 is more than or equal to 0.5 and less than or equal to 5.
The second inner cladding is a silicon dioxide glass layer co-doped with fluorine or germanium, phosphorus and fluorine, wherein the fluorine doping contribution quantity delta F3 at the outer diameter of the second inner cladding is-0.5% to-0.1%. When the refractive index difference between the depressed cladding and the first inner cladding is large, such as delta 4-delta 2< -0.4%, the second inner cladding can be doped with germanium and fluorine, and the germanium doping contribution delta Ge3 at the outer diameter of the second inner cladding is less than 0.15%. The germanium doping contribution of the second inner cladding is gradually reduced along the radial direction, so that the viscosity and concentration between the first inner cladding and the depressed cladding are gradually changed, and the diffusion of germanium of the core layer into the cladding is reduced.
Δ3 may be greater than Δ2, but Δ3- Δ2 needs to be < 0.1%. When Δ3 is much larger than Δ2, the second inner cladding higher order modes are excessive, resulting in bandwidth degradation.
Compared with germanium, the improvement of the phosphorus on the glass viscosity is more obvious, and the phosphorus is doped in the second inner cladding, so that the viscosity of the second inner cladding can be greatly reduced, and the viscosity matching condition of the second inner cladding and the dip cladding is improved. When the second inner cladding is doped with phosphorus, the thickness of the second inner cladding is not less than 1.5 mu m. The phosphorus doping contribution Δp of the second inner cladding is < 0.1%.
The first and second inner cladding layers with negative refractive indexes can improve the mode dispersion of the higher-order modes of the core layer and can also effectively improve the bending resistance of the optical fiber.
The outer cladding is a pure silica glass layer, and the outer diameter of the conventional multimode fiber is generally 62.5+/-2.5 mu m. Multimode fibers of larger or smaller outer diameters, such as 40.+ -.2. Mu.m, 50.+ -.2. Mu.m, 70.+ -.4. Mu.m, etc., can also be prepared.
The refractive index profile of an actual optical fiber is graded between layers, and is not stepped, and the boundary between layers is determined as follows. The core layer edge R1 is the position where the relative refractive index difference is reduced to-0.03% within the radius requirement range of the R1. The outer diameter R4 of the depressed cladding is a position where the relative refractive index difference increases to-0.03 to 0.03% within the required range of the width R4-R3. Within the above-described range of R2-R1 width requirements, the outer diameter R2 of the first inner cladding is the apex position determined based on the first derivative of the relative refractive index difference with respect to the radius or the inflection point position determined based on the first derivative of the relative refractive index difference with respect to the radius. Within the above-described range of R3-R2 width requirements, the outer diameter R3 of the second inner cladding is the apex position determined based on the first derivative of the relative refractive index difference with respect to the radius or the inflection point position determined based on the first derivative of the relative refractive index difference with respect to the radius. When delta 2 is larger than delta 3, adopting inflection point judgment; when Δ2 is smaller than Δ3, then vertex determination is required.
A set of preforms was prepared and drawn as described in this example, using a two-layer coating of multimode optical fibers, such as a two-layer UV cured acrylic resin, with the optical fibers having the structure and major performance parameters set forth in Table 1.
Table 1: major structural and performance parameters of optical fibers
Claims (14)
1. A high-bandwidth bend insensitive multimode optical fiber comprises a core layer and a cladding layer, wherein the refractive index profile of the core layer is parabolic (alpha power exponential function distribution), the cladding layer sequentially comprises a first inner cladding layer, a second inner cladding layer, a dip cladding layer and an outer cladding layer from inside to outside, and is characterized in that the refractive index of the core layer is alpha 1 1.9-2.1, the radius R1 of the core layer is 12-28 mu m, the maximum relative refractive index difference delta 0 of the center of the core layer is 0.8-1.2%, and the relative refractive index at the edge R1 of the core layerThe difference delta 1 is-0.03%, the width (R2-R1) of the first inner cladding is 0.4-3 mu m, the relative refractive index difference delta 2 of the outer edge of the first inner cladding is-0.3% -0.04%, the refractive index cross section of the first inner cladding is distributed in a power index function, and the relative refractive index difference delta (R) is:
the width (R3-R2) of the second inner cladding is 0.5-4 mu m, the relative refractive index difference delta 3 of the outer side edge of the second inner cladding is-0.45% -0.03%, the width (R4-R3) of the depressed cladding is 3.0-9.0 mu m, the relative refractive index difference delta 4 is-0.9% -0.45%, and the outer cladding is a pure silica glass layer.
2. The high bandwidth bend insensitive multimode fiber of claim 1 wherein said first inner cladding
When alpha is 2 1-2, said first inner cladding +.>
When alpha is 2 Not less than 0.5<1。
3. The high bandwidth bend insensitive multimode optical fiber of claim 1 or 2 wherein the relative refractive index difference Δ2- Δ1% or less at the outer edge of said first inner cladding layer is less than or equal to-0.04%.
4. The high bandwidth bend insensitive multimode fiber according to claim 1 or 2 wherein the second inner cladding refractive index profile is a power exponential function distribution having a relative refractive index difference Δ (r) of:
5. The high bandwidth bend insensitive multimode fiber of claim 4 wherein the second inner cladding outer edge has a relative refractive index difference Δ3- Δ2< 0.1%.
6. The high bandwidth bend insensitive multimode optical fiber according to claim 1 or 2, wherein the core layer is a silica glass layer co-doped with germanium, fluorine or germanium, phosphorus and fluorine, fluorine of the core layer is used as a negative dopant, the fluorine doping amount is increased from the center of the core layer to the edge direction of the core layer, the fluorine doping contribution amount delta F0 of the center of the core layer is-0.01% - -0.1%, and the fluorine doping contribution amount delta F1 of the edge of the core layer is-0.4% -0.1%.
7. The high bandwidth bend insensitive multimode optical fiber of claim 6 wherein the first inner cladding is a silica glass layer co-doped with germanium, fluorine or germanium, phosphorus, fluorine, the first inner cladding exhibiting an increasing fluorine doping level from the inner layer to the outer side edge, wherein the fluorine doping contribution Δf1 at the core edge is equal to the fluorine doping contribution Δf1 'at the inner layer of the first inner cladding, and the germanium doping contribution Δge1 at the core edge is equal to the germanium doping contribution Δge1' at the inner layer of the first inner cladding.
8. The high bandwidth bend insensitive multimode fiber of claim 7 wherein the germanium doping contribution Δg2 at the outer edge of the first inner cladding is between 0.02% and 0.30%, and the fluorine doping contribution Δf2 at the outer edge of the first inner cladding is between-0.4% and-0.05%.
9. The high bandwidth bend insensitive multimode fiber of claim 7 wherein the first inner cladding has a width of 1 to 3 μm when the first inner cladding is co-doped with germanium, phosphorus, fluorine.
10. The high bandwidth bend insensitive multimode fiber of claim 7 wherein said second inner cladding is fluorine or germanium, phosphorus, fluorine co-doped silica glass layer.
11. The high bandwidth bend insensitive multimode fiber of claim 10 wherein the second inner cladding has a thickness (R3-R2) of greater than or equal to 1.5 μm and a phosphorus doping contribution Δp of less than 0.1% when the second inner cladding is co-doped with germanium, phosphorus, and fluorine.
12. The bend insensitive multimode optical fiber according to claim 1 or 2, wherein said fiber has a bandwidth above 6000MHz-km at 850nm wavelength, above 2600MHz-km at 953nm wavelength, and above 2000MHz-km at 980nm wavelength.
13. The bend insensitive multimode optical fiber according to claim 1 or 2, wherein said fiber has a bend add-on loss of less than or equal to 0.1dB at a bend radius of 7.5 millimeters for 2 turns at a wavelength of 850 nm; at 1300nm, the bend parasitic loss caused by 2 turns with a 7.5 millimeter bend radius is less than or equal to 0.3dB.
14. A bend insensitive multimode optical fiber as claimed in claim 1 or 2, wherein R2 inside and outside the first inner cladding 2 (Δ0-Δ2)-R1 2 (Delta0-Delta1) is between 0.2 and 2.5 mu m 2 Between them.
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