Broadband bend-resistant multimode optical fiber

Abstract

The present invention provides a broadband bend-resistant multimode optical fiber, comprising a core layer, a base tube, a depressed cladding layer and an outer cladding layer, wherein the base tube, the depressed cladding layer and the outer cladding layer have radial cross sections that are all circular rings, and are characterized in that: the core layer is doped with GeO2, P2O5 and F, the core layer is a refractive index gradient zone, the core layer radius is R1, the base tube is sleeved on the outside of the core layer, the width of the base tube is R2-R1, the depressed cladding layer is arranged on the outside of the base tube, the width of the depressed cladding layer is R3-R2, the outer cladding layer is sleeved on the outside of the depressed cladding layer, the width of the outer cladding layer is Rmax-R3, and the molar concentrations of P2O5 and F in the core layer vary with the radius of the core layer. The broadband bend-resistant multimode optical fiber provided by the present invention reduces the cost of the manufactured bend-resistant multimode optical fiber and has good bend-resistant performance.

Description

Technical Field

[0001] The present invention relates to the field of optical communications, and in particular to a broadband bend-resistant multimode optical fiber. Background Art

[0002] Traditional bend-resistant multimode optical fiber is manufactured by the in-tube method, in which GeO2-doped quartz is deposited on the core layer, F-doped quartz deep-sunk cladding is deposited on the outside, and the outer layer is covered with a pure quartz tube. However, since the deposited core layer of the multimode optical fiber itself is very large and the deposition rate of the multimode preform is much lower than that of the single-mode preform, the price of multimode optical fiber in the market is much higher than that of single-mode optical fiber. At present, there are not many methods to reduce the manufacturing cost of multimode optical fiber, mainly by increasing the deposition rate, increasing the core rod size and cheap raw materials, but these methods are limited by the process and also come at the cost of slightly increasing the attenuation of the multimode optical fiber. Summary of the invention

[0003] In view of this, it is necessary to provide a broadband bend-resistant multimode optical fiber, which reduces production costs and has good bend-resistant performance.

[0004] The present invention provides a broadband bend-resistant multimode optical fiber, comprising a core layer, a base tube, a depressed cladding layer and an outer cladding layer, wherein the cross sections of the base tube, the depressed cladding layer and the outer cladding layer along the radial direction are all circular rings, the core layer is doped with GeO2, P2O5 and F, the core layer is a refractive index gradient zone, the radius of the core layer is R1, the base tube is sleeved on the outside of the core layer, the distance from the center of the core layer to the boundary of the base tube is R2, the width of the base tube is R2-R1, the depressed cladding layer is arranged on the outside of the base tube, the distance from the center of the core layer to the boundary of the depressed cladding layer is R3, the width of the depressed cladding layer is R3-R2, the outer cladding layer is sleeved on the outside of the depressed cladding layer, the distance from the center of the core layer to the boundary of the outer cladding layer is Rmax, the width of the outer cladding layer is Rmax-R3, the molar concentration of F in the core layer changes with the radius of the core layer, and satisfies the following formula:

[0005]

[0006] Among them, M F0 is the molar concentration of F at the center of the core layer, β F The value range of M is 6-10. F (r) represents the molar concentration of F at a radial distance r from the central axis of the core layer.

[0007] Furthermore, the β F The value range of is preferably 7-9.

[0008] Furthermore, the molar concentration of P2O5 in the core layer varies with the radius of the core layer, satisfying the following formula:

[0009]

[0010] Among them, M P0 is the molar concentration of P2O5 in the core layer, β p The value range is 2.0-4.5, the M P (r) represents the molar concentration of P2O5 at a radial distance r from the central axis of the core layer.

[0011] Furthermore, the β p的 The preferred value range is 2.5-3.5.

[0012] Furthermore, the refractive index difference Δn0 at the center of the core layer is 0.0127-0.0167, the core layer radius R1 is 22-26 μm, the width R2-R1 of the base tube is 5.5-10.5 μm, and the distance Rmax from the center of the core layer to the edge of the outer cladding is 62.5±2.5 μm.

[0013] Furthermore, the core layer radius R1 is preferably 23-24 μm, and the width of the base tube is preferably 6.5-9.5 μm.

[0014] Furthermore, the depressed cladding is deposited on the outer wall of the substrate tube or formed by coating a fluorine-doped quartz on the outer side of the substrate tube.

[0015] Furthermore, the width R3-R2 of the depressed cladding is 3.5-5.5 μm, the refractive index difference Δn2 of the depressed cladding is -0.007 to -0.004, K=Δn2*(R3-R2), and -0.025 <K<-0.022。

[0016] Furthermore, the refractive index profile of the core layer is distributed in an α power exponential function, where α is the refractive index profile distribution parameter of the gradient zone, wherein the central refractive index of the core layer is n0, the boundary refractive index of the core layer is n1, and the refractive index of the substrate is n sio2 The refractive index of the depressed cladding is n2, and the refractive index of the outer cladding is n C , the refractive index calculation formula of the optical fiber is:

[0017]

[0018] Among them, α is in the range of 1.90-2.10, r is the radial distance from any point on the core layer to the center of the core layer, n1=n SiO2 , nc=n SiO2 , Δ is the relative refractive index difference between the core center and the core boundary Δ=(n0 2 -n1 2 ) / (2n02 ).

[0019] The broadband bend-resistant multimode optical fiber provided by the present invention does not need to deposit a depressed portion, and the high-cost depressed cladding deposition layer is removed. A depressed layer is prepared on the outer wall of the base tube by a cheap method / or a cheap F-doped quartz is coated on the outer wall. The optical fiber produced by the preform rod increases by 20% or more than other bend-resistant multimode optical fiber preform rods with the same deposition amount, thereby reducing the cost of the manufactured bend-resistant multimode optical fiber and having good bend-resistant performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the refractive index profile of an optical fiber in one embodiment of the present invention.

[0021] Figure 2 Schematic diagram of the variation of F doping amount with core layer radius in one embodiment of the present invention.

[0022] Figure 3 Schematic diagram of the variation of F doping amount with core layer radius in another embodiment of the present invention.

[0023] Figure 4 for Figure 3 Schematic diagram of the variation of the doping amount of P2O5 with the radius of the core layer in an embodiment.

[0024] The following specific implementation manner will further illustrate the present invention in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "or / and" used herein includes any and all combinations of one or more of the related listed items.

[0027] See also Figure 1 , Figure 1 The diagram is a schematic diagram of the refractive index profile of a broadband bend-resistant multimode optical fiber in one embodiment of the present invention. The optical fiber is used for data transmission and includes, from the inside to the outside, a core layer, a base tube, a depressed cladding layer and an outer cladding layer.

[0028] The core layer is based on silicon dioxide, doped with GeO2, P2O5 and F. The core layer is a refractive index gradient region, and the cross-section of the core layer is circular with a radius of R1, that is, the radius of the gradient region is R1. In this embodiment, the radius R1 of the gradient region is 22-26 μm, preferably 23-24 μm. The refractive index profile of the core layer is distributed in an α-power exponential function, where α is the refractive index profile distribution parameter of the gradient region, and its α value is 1.90-2.10. The central refractive index of the core layer is n0, and the refractive index difference Δn0 between it and the refractive index of the outer cladding ranges from 0.0127 to 0.0167. The refractive index at the boundary of the core layer is n1.

[0029] The base tube is sleeved outside the core layer. The cross-section of the base tube along the radial direction is annular, with an inner diameter of R1 and an outer diameter of R2. The width of the base tube is R2 - R1. Through software simulation, it is found that when the width of the base tube is greater than 5.5 μm, all modes of this bending-resistant multimode optical fiber can be confined to the core layer gradient region for transmission, and most of the energy is distributed in the core layer region, and no transmission modes are found in the base tube region and the depressed region; when the width of the base tube is less than 5.5 μm, transmission modes begin to exist in the base tube, which will cause the measured core diameter of the optical fiber to be greater than 52.5 μm, that is, the upper limit of the standard core diameter; when the platform region is greater than 10.5 μm, the bending performance of the multimode optical fiber designed in this patent deteriorates or does not meet the bending performance standard of similar bending-resistant multimode optical fibers. Therefore, in this embodiment, the width R2 - R1 of the base tube is 5.5-10.5 μm, preferably 6.5-9.5 μm. The refractive index of the base tube is n sio2 , the refractive index n1 at the boundary of the core layer and the refractive index n of the base tube sio2 are the same. In this embodiment, the base tube is a pure silicon dioxide sleeve, and the refractive index difference between it and the core layer boundary and the outer cladding is 0.

[0030] The depressed cladding is sleeved outside the base tube. The cross-section of the depressed cladding along the radial direction is annular. Specifically, the depressed cladding is deposited on the outer wall of the base tube or a fluorine-doped quartz is sleeved outside the base tube. In this embodiment, the depressed cladding is deposited on the outer wall of the base tube by means of plasma outer cladding. The inner diameter of the depressed cladding is R2, the outer diameter is R3, and the width of the depressed cladding is R3 - R2. In this embodiment, the width R3 - R2 of the depressed cladding is 3.5-5.5 μm, and the refractive index is n2. The refractive index difference Δn2 of the depressed cladding is set between -0.007 and -0.004. Define K = Δn2 * (R3 - R2), and satisfy -0.025 < K < -0.022. The introduction of the K value is used to ensure that the bending loss of the bending-resistant multimode optical fiber meets the standard, and at the same time ensure that there are no transmission modes and energy in the base tube region.

[0031] The outer cladding is sleeved on the outside of the depressed cladding, the radial cross section of the outer cladding is annular, the inner diameter of the outer cladding is R3, the outer diameter is Rmax, and the refractive index of the outer cladding is n C In this embodiment, the Rmax is set between 60-65 μm. In this embodiment, the outer cladding is a pure silica sleeve, and the refractive index of the outer cladding is n C and the boundary refractive index n1 of the core layer and the refractive index n sio2 same.

[0032] The refractive index distribution of the optical fiber meets the requirements of formula (1):

[0033]

[0034] Wherein, α is the refractive index profile distribution parameter of the gradient zone, r is the radial distance from any point A on the core layer to the core axis, Δ is the relative refractive index difference between the core layer center and the core layer boundary, Δ=(n0 2 -n1 2 ) / (2n0 2 ).

[0035] The molar concentration of F in the core layer varies with the radius of the core layer, satisfying formula (2):

[0036]

[0037] Among them, M F0 is the molar concentration of F at the center of the core layer, β F The value range of M is 6-10, preferably 7-9. F (r) represents the molar concentration of F at a radial distance r from the central axis of the core layer.

[0038] like Figure 2 As shown, in one embodiment of the present invention, the core layer center is doped with GeO2 with a molar concentration of 13% to 14% and F with a molar concentration of 0.2% to 0.8%. The boundary of the gradient zone is doped with GeO2 with a molar concentration of 1.4% to 8% and F with a molar concentration of 5% to 7%. The molar concentration of F in the core layer varies with the radius of the core layer, satisfying formula (2), the concentration of F in the substrate and the outer cladding is 0, and the concentration of F in the sunken cladding is M Fd To maximize the bandwidth of multimode optical fiber, the inter-mode dispersion must be minimized, that is, an optimal profile refractive index distribution parameter must be selected, and Δα is obtained according to the calculation formula of the optimal profile refractive index distribution parameter difference. opt(850-950nm) is 0.05, indicating that the optical fiber can achieve a maximum effective mode bandwidth (EMB) in the broadband range of 850nm to 950nm and can meet the requirements of wavelength division multiplexing by arbitrarily selecting four wavelengths in the range of 850nm to 950nm.

[0039] The molar concentration of P2O5 in the core layer varies with the radius of the core layer and satisfies the following formula:

[0040]

[0041] Among them, M P0 is the molar concentration of P2O5 at the core layer, the M P (r) represents the molar concentration of P2O5 at a radial distance r from the central axis of the core layer, β p The value range is 2.0-4.5, preferably 2.5-3.5.

[0042] See also Figure 3 and Figure 4 In another embodiment of the present invention, the center of the core layer is doped with GeO2 having a molar concentration of 9.6% to 10.8%, F having a molar concentration of 0.4% to 1.5%, and P2O5 having a molar concentration of 3.2% to 3.5%. The boundary of the gradient zone is doped with GeO2 having a molar concentration of 8% to 9%, F having a molar concentration of 4.5% to 5%, and P2O5 having a molar concentration of 0% to 1.2%. The molar concentration of F in the core layer varies with the radius of the core layer and satisfies formula (2), where M F0 is the molar concentration of F at the core layer, β F The value range is 6.5 to 9, preferably 7 to 8.5, the F concentration in the base tube and the outer cladding is 0, and the F concentration in the depressed cladding is M Fd The molar concentration of P2O5 in the core layer varies with the radius of the core layer and satisfies formula (3). To maximize the bandwidth of a multimode optical fiber, its inter-modal dispersion must be minimized, that is, an optimal profile refractive index distribution parameter must be selected. Δα is obtained according to the calculation formula of the optimal profile refractive index distribution parameter difference. opt (850-950nm) is 0.005, indicating that the optical fiber can achieve a maximum effective mode bandwidth (EMB) in the broadband range of 850nm to 950nm and can meet the requirements of wavelength division multiplexing by arbitrarily selecting four wavelengths in the range of 850nm to 950nm.

[0043] The present invention will be further described below in conjunction with specific embodiments.

[0044] Example 1

[0045] This example adopts PCVD process to prepare optical fiber preform, the difference n0-nc between the central refractive index of the core layer and the refractive index of the outer cladding is 0.0145, the difference n1-nc between the boundary refractive index of the core layer and the refractive index of the outer cladding is 0, the difference n2-nc between the refractive index of the depressed cladding and the outer cladding is -0.005, the radius R1 of the gradient zone is 24.3μm, the width R2-R1 of the base tube is 8.1μm, the width R3-R2 of the depressed cladding is 4.9μm, Rmax is 62.5μm, k=-0.0245, the core layer is doped with GeO2 and F, and the doped F satisfies the formula (2) The doping concentration of the depressed cladding F is 1.3%, the dispersion at the center of the optical fiber is -97ps / (nm·km), the core diameter of the tested multimode optical fiber is 49.4um, the numerical aperture NA of the optical fiber is 0.1995, and the bending loss test values ​​of 2 turns around R7.5mm are: the bending loss at a wavelength of 850nm is 0.01dB, and the bending loss at a wavelength of 1300nm is 0.1dB; the bending loss test values ​​of 2 turns around R15mm are: the bending loss at a wavelength of 850nm is 0.04dB, and the bending loss at a wavelength of 1300nm is 0.02dB.

[0046] Example 2

[0047] This example adopts MCVD process to prepare optical fiber preform, the difference n0-nc between the central refractive index of the core layer and the refractive index of the outer cladding is 0.0139, the difference n1-nc between the boundary refractive index of the core layer and the refractive index of the outer cladding is 0, the difference n2-nc between the refractive index of the depressed cladding and the outer cladding is -0.0056, the radius R1 of the gradient zone is 24.85μm, the width R2-R1 of the base tube is 8.5μm, the width R3-R2 of the depressed cladding is 4.15μm, Rmax is 62.5μm, k=-0.02296, the core layer is doped with GeO2, F and P2O5, and the doped F and P2O5 are fully The requirements of formulas (2) and (3) are met, the doping concentration of the depressed cladding F is 15.45%, the dispersion at the center of the optical fiber is -96.2 ps / (nm·km), the core diameter of the tested multimode optical fiber is 50.3 um, the numerical aperture NA of the optical fiber is 0.1953, and the bending loss test values ​​of 2 turns around R7.5 mm are: the bending loss at a wavelength of 850 nm is 0.13 dB, and the bending loss at a wavelength of 1300 nm is 0.29 dB; the bending loss test values ​​of 2 turns around R15 mm are: the bending loss at a wavelength of 850 nm is 0.01 dB, and the bending loss at a wavelength of 1300 nm is 0.05 dB.

[0048] Example 3

[0049] This example adopts MCVD process to prepare optical fiber preform, the difference n0-nc between the central refractive index of the core layer and the refractive index of the outer cladding is 0.0141, the difference n1-nc between the boundary refractive index of the core layer and the refractive index of the outer cladding is 0, the difference n2-nc between the refractive index of the depressed cladding and the outer cladding is -0.0052, the radius R1 of the gradient zone is 25.05μm, the width R2-R1 of the base tube is 6.4μm, the width R3-R2 of the depressed cladding is 4.5μm, Rmax is 62.5μm, k=-0.0234, the core layer is doped with GeO2, F and P2O5, and the doped F and P2O5 meet According to the requirements of formulas (2) and (3), the doping concentration of the depressed cladding F is 15.45%, the dispersion at the center of the optical fiber is -96.2 ps / (nm·km), the core diameter of the tested multimode optical fiber is 50.9 um, the numerical aperture NA of the optical fiber is 0.1967, and the bending loss test values ​​of 2 turns around R7.5 mm are: 0.06 dB at a wavelength of 850 nm, and 0.2 dB at a wavelength of 1300 nm; the bending loss test values ​​of 2 turns around R15 mm are: 0.006 dB at a wavelength of 850 nm, and 0.07 dB at a wavelength of 1300 nm.

[0050] Example 4

[0051] This example adopts MCVD process to prepare optical fiber preform, the difference n0-nc between the central refractive index of the core layer and the refractive index of the outer cladding is 0.0143, the difference n1-nc between the boundary refractive index of the core layer and the refractive index of the outer cladding is 0, the difference n2-nc between the refractive index of the depressed cladding and the outer cladding is -0.0062, the radius R1 of the gradient zone is 24.9μm, the width R2-R1 of the base tube is 8.9μm, the width R3-R2 of the depressed cladding is 3.7μm, Rmax is 62.5μm, k=-0.02232, the core layer is doped with GeO2, F and P2O5, and the doped F and P2O5 are fully The requirements of formulas (2) and (3) are met, the doping concentration of the depressed cladding F is 15.45%, the dispersion at the center of the optical fiber is -96.2 ps / (nm·km), the core diameter of the tested multimode optical fiber is 50.6 um, the numerical aperture NA of the optical fiber is 0.1981, and the bending loss test values ​​of 2 turns around R7.5 mm are: the bending loss at a wavelength of 850 nm is 0.18 dB, and the bending loss at a wavelength of 1300 nm is 0.37 dB; the bending loss test values ​​of 2 turns around R15 mm are: the bending loss at a wavelength of 850 nm is 0.03 dB, and the bending loss at a wavelength of 1300 nm is 0.1 dB.

[0052] From the above examples, it can be seen that at a wavelength of 850nm, the additional loss of the optical fiber after bending for two turns with a radius of 7.5mm does not exceed 0.18dB, and the additional loss after bending for two turns with a radius of 15mm does not exceed 0.01dB; at a wavelength of 1300nm, the additional loss after bending for two turns with a radius of 7.5mm does not exceed 0.37dB, and the additional loss after bending for two turns with a radius of 15mm does not exceed 0.1dB. The optical fiber has an effective mode bandwidth of 5700MHz-km to 2500MHz-km in the broadband range of 850nm to 950nm, and has good bending resistance.

[0053] The broadband bend-resistant multimode optical fiber provided by the present invention does not need to deposit a depressed portion, and the high-cost depressed cladding deposition layer is removed. A depressed layer is prepared on the outer wall of the base tube by a cheap method / or a cheap F-doped quartz is coated on the outer wall. The optical fiber produced by the preform rod increases by 20% or more than other bend-resistant multimode optical fiber preform rods with the same deposition amount, thereby reducing the cost of the manufactured bend-resistant multimode optical fiber and having good bend-resistant performance.

[0054] Those skilled in the art should recognize that the above embodiments are only used to illustrate the present invention, and are not intended to limit the present invention. As long as they are within the spirit of the present invention, appropriate changes and modifications to the above embodiments are within the scope of protection claimed by the present invention.

Claims

1. A broadband bend-resistant multimode optical fiber, comprising a core layer, a base tube, a depressed cladding layer and an outer cladding layer, wherein the cross-sections of the base tube, the depressed cladding layer and the outer cladding layer along the radial direction are all circular rings, characterized in that: The core layer is doped with GeO2, P2O5 and F, the core layer is a refractive index gradient zone, the core layer radius is R1, the substrate tube is sleeved outside the core layer, the distance from the center of the core layer to the boundary of the substrate tube is R2, and the width of the substrate tube is R2-R1, the depressed cladding is arranged on the outside of the substrate tube, the distance from the center of the core layer to the boundary of the depressed cladding is R3, and the width of the depressed cladding is R3-R2, the outer cladding is sleeved outside the depressed cladding, the distance from the center of the core layer to the boundary of the outer cladding is Rmax, and the width of the outer cladding is Rmax-R3, the molar concentration of F in the core layer changes with the radius of the core layer, and satisfies the following formula: Among them, M F0 is the molar concentration of F at the center of the core layer, β F The value range of M is 6-10. F (r) represents the molar concentration of F at a radial distance r from the central axis of the core layer; The molar concentration of P2O5 in the core layer varies with the radius of the core layer and satisfies the following formula: Among them, M P0 is the molar concentration of P2O5 in the core layer, β p The value range is 2.0-4.5, the M P (r) represents the molar concentration of P2O5 at a radial distance r from the central axis of the core layer; The center of the core layer is doped with GeO2 at a molar concentration of 9.6% to 10.8%, F at a molar concentration of 0.4% to 1.5%, and P2O5 at a molar concentration of 3.2% to 3.5%, and the boundary of the gradient zone is doped with GeO2 at a molar concentration of 8% to 9%, F at a molar concentration of 4.5% to 5%, and P2O5 at a molar concentration of 1.2%.

2. The broadband bend-resistant multimode optical fiber according to claim 1, characterized in that: The β F The value range is 7-9.

3. The broadband bend-resistant multimode optical fiber according to claim 1, characterized in that: The β p The value range is 2.5-3.

5.

4. The broadband bend-resistant multimode optical fiber according to claim 1, characterized in that: The refractive index difference Δn0 at the center of the core layer is 0.0127-0.0167, the core layer radius R1 is 22-26 μm, the width R2-R1 of the base tube is 5.5-10.5 μm, and the distance Rmax from the center of the core layer to the edge of the outer cladding is 62.5±2.5 μm.

5. The broadband bend-resistant multimode optical fiber according to claim 4, characterized in that: The core layer radius R1 is 23-24 μm, and the base tube width is 6.5-9.5 μm.

6. The broadband bend-resistant multimode optical fiber according to claim 1, characterized in that: The depressed cladding is deposited on the outer wall of the substrate tube or is formed by coating a fluorine-doped quartz on the outer side of the substrate tube.

7. The broadband bend-resistant multimode optical fiber according to claim 1, characterized in that: The width R3-R2 of the depressed cladding is 3.5-5.5 μm, the refractive index difference Δn2 of the depressed cladding is -0.007~-0.004, K=Δn2*(R3-R2), and satisfies -0.025 <K<-0.022。 8. The broadband bend-resistant multimode optical fiber according to claim 1, characterized in that: The refractive index profile of the core layer is distributed in an α power exponential function, where α is the refractive index profile distribution parameter of the gradient zone, wherein the central refractive index of the core layer is n0, the boundary refractive index of the core layer is n1, and the refractive index of the substrate tube is n sio2 The refractive index of the depressed cladding is n2, and the refractive index of the outer cladding is n C , the refractive index calculation formula of the optical fiber is: Among them, α is in the range of 1.90-2.10, r is the radial distance from any point on the core layer to the center of the core layer, n1=n SiO2 ,nc=n SiO2 , Δ is the relative refractive index difference between the core center and the core boundary Δ=(n0 2 -n1 2 ) / (2n0 2 ).

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