WO2020108141A1 - Bending-resistant wide band multimode optical fiber - Google Patents

Abstract

Disclosed is a bending-resistant wide band multimode optical fiber, comprising a core layer, a base tube, a recessed cladding and an outer cladding. The radial cross sections of the base tube, the recessed cladding and the outer cladding are all circular rings. The core layer is doped with GeO2, P2O5 and F, the core layer is a refractive index gradually variable region, and the radius of the core layer is R1. The base tube is sheathed outside the core layer, and the width of the base tube is R2 - R1. The recessed cladding is provided on an outer side of the base tube, and the width of the recessed cladding is R3 - R2. The outer cladding is sheathed outside the recessed cladding, and the width of the outer cladding is Rmax - R3. The molar concentrations of P2O5 and F in the core layer vary with the radius of the core layer. The cost of the manufactured bending-resistant multimode optical fiber is reduced, and the bending-resistant multimode optical fiber has good bending resistance.

Description

Broadband bending-resistant multimode fiber Technical field

The invention relates to the field of optical communication, in particular to a broadband bending-resistant multimode optical fiber.

Background technique

The traditional bending-resistant multimode optical fiber is manufactured by the in-tube method, in which the core layer is deposited with quartz doped with GeO ₂ , the outer surface is deposited with a deep-dipped cladding of quartz doped with F, and the outer layer is covered with a pure quartz sleeve. However, because the deposition core layer of the multimode optical fiber itself is large, and the deposition rate of the multimode preform is much lower than that of the single mode preform, the price of the multimode optical fiber in the market is much higher than that of the single mode optical fiber. At present, there are not many methods to reduce the manufacturing cost of multimode fiber, mainly to increase the deposition rate, increase the size of the core rod and cheap raw materials, but these methods are limited by the process, but also bring a slight increase in the loss of multimode fiber Big price.

Summary of the invention

In view of this, it is necessary to provide a broadband bending-resistant multimode optical fiber, which reduces the production cost and has good bending resistance.

The invention provides a broadband anti-bending multimode optical fiber, which includes a core layer, a base tube, a depressed cladding and an outer cladding. The radial cross-sections of the base tube, the depressed cladding and the outer cladding are all rings. The core layer is doped with GeO ₂ , P ₂ O ₅ and F, the core layer is a gradient refractive index region, the core layer radius is R1, the base tube is sleeved outside the core layer, the core The distance from the center of the layer to the boundary of the base tube is R2, the width of the base tube is R2-R1, the depressed cladding is disposed outside the base tube, and the center of the core layer to the boundary of the depressed cladding The distance is R3, the width of the depressed cladding is R3-R2, the outer cladding is sleeved on the outside of the depressed cladding, the distance from the center of the core layer to the boundary of the outer cladding is Rmax, the The width of the outer cladding layer is Rmax-R3, and the molar concentration of F in the core layer varies with the radius of the core layer, satisfying the following formula:

Where, M _F0 is the molar concentration of F in the center of the core layer, and the value range of β _F is 6-10, and the M _F (r) represents the radial distance r of the F at the center axis of the core layer The molar concentration at.

Further, the value range of β _F is preferably 7-9.

Further, the molar concentration of P ₂ O ₅ in the core layer varies with the radius of the core layer, satisfying the following formula:

Where, M _P0 is the molar concentration of P ₂ O ₅ in the center of the core layer, β _{p has a} value range of 2.0-4.5, and M _P (r) represents the diameter of the P ₂ O ₅ at the central axis of the core layer To the molar concentration at distance r.

Further, the value range of β _p is preferably 2.5-3.5.

Further, the refractive index difference Δn ₀ at the center of the core layer is 0.0127-0.0167, the radius R1 of the core layer is 22-26 μm, the width R2-R1 of the base tube is 5.5-10.5 μm, and the center of the core layer The distance Rmax to the outer cladding edge is 62.5±2.5 μm.

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

Further, the depressed cladding layer is deposited on the outer wall of the base pipe or formed on the outer side of the base pipe by a fluorine-doped quartz.

Further, the width R3-R2 of the depressed cladding layer is 3.5-5.5 μm, the refractive index difference Δn ₂ of the depressed cladding layer is -0.007～-0.004, K=Δn ₂ *(R3-R2), and satisfy -0.025<K<-0.022.

Further, the refractive index profile of the core layer is distributed as a power exponential function, α is the distribution parameter of the refractive index profile of the gradient region, wherein the central refractive index of the core layer is n ₀ , and the boundary refractive index of the core layer The rate is n ₁ , the refractive index of the base tube is n _sio2 , the refractive index of the depressed cladding is n ₂ , the refractive index of the outer cladding is n _C , and the calculation formula of the refractive index of the optical fiber is:

Where α ranges from 1.90 to 2.10, r is the radial distance from any point on the core layer to the center of the core layer, n ₁ = n _SiO2 , nc = n _SiO2 , and Δ is the center of the core layer The relative refractive index difference Δ=(n ₀ ² -n ₁ ² )/(2n ₀ ² ) with the boundary of the core layer.

The broadband anti-bending multimode optical fiber provided by the present invention, because it does not need to deposit the concave part, removes the high-cost depressed cladding deposit layer, and uses a cheap method to prepare a depressed layer/or coat an inexpensive F-doped quartz on the outer wall of the base tube The optical fiber produced by the preform is increased by 20% or more compared with other bending multimode optical fiber preforms with the same deposition amount, which reduces the cost of the manufactured bending multimode optical fiber and has good bending performance.

BRIEF DESCRIPTION

FIG. 1 is a schematic diagram of the refractive index profile of an optical fiber according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of the variation of the doping amount of F with the radius of the core layer according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of the variation of the doping amount of F with the radius of the core layer in another embodiment of the present invention.

FIG. 4 is a schematic diagram of the variation of the doping amount of P ₂ O ₅ with the radius of the core layer in the embodiment of FIG. 3.

The following specific embodiments will further illustrate the present invention with reference to the above drawings.

detailed description

The technical solutions in the embodiments of the present invention will be described clearly and completely in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by a person of ordinary skill in the art without making creative efforts fall within the protection scope of the present invention.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field of the present invention. The terminology used in the description of the present invention herein is for the purpose of describing specific embodiments, and is not intended to limit the present invention. The term "or/and" as used herein includes any and all combinations of one or more related listed items.

Please refer to FIG. 1. FIG. 1 is a schematic diagram of the refractive index profile of a broadband anti-bending multimode optical fiber according to an embodiment of the present invention. The optical fiber is used for data transmission. The optical fiber includes a core layer and a base tube in order from inside to outside. , Sagging cladding and outer cladding.

The core layer uses silicon dioxide as a matrix, and the core layer is doped with GeO ₂ , P ₂ O ₅ and F, the core layer is a graded refractive index region, and the cross section of the core layer is circular. The radius is R1, that is, the radius of the gradient area 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 as a power exponential function, and α is the distribution parameter of the refractive index profile of the gradient region, and its α value is 1.90-2.10. The central refractive index of the core layer is n ₀ , and the refractive index difference Δn _{0 of} the core layer ranges from 0.0127 to 0.0167, and the boundary refractive index of the core layer is n ₁ .

The base pipe is sleeved on the outer side of the core layer. The radial cross section of the base pipe is annular, the inner diameter is R1, the outer diameter is R2, and the width of the base pipe is R2-R1. Through software simulation, it is found that when the width of the base tube is greater than 5.5um, all modes of the bending-resistant multimode fiber can be restricted to be transmitted in the core layer gradient area, and most of the energy is distributed in the core layer area, the base tube area and the sag There is no transmission mode found in the area; when the width of the base tube is less than 5.5um, the base tube begins to have a transmission mode, which will result in the test fiber core diameter greater than 52.5um, which is the upper limit of the standard core diameter; when the platform area is greater than 10.5um, The bending performance of the multimode optical fiber designed by this patent becomes poor, or does not meet the bending resistance performance standards 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 , and the boundary refractive index n _{1 of} the core layer is the same as the refractive index n _{sio2 of} the base tube. In this embodiment, the base tube is a pure silica sleeve , The refractive index difference between the boundary of the core layer and the outer cladding layer is 0.

The sagging cladding is sleeved on the outside of the base pipe, and the radial cross-section of the sagging cladding is ring-shaped. Specifically, the sagging cladding is deposited on the outer wall of the base pipe or outside the base pipe The outer casing is formed of fluorine-doped quartz. In this embodiment, the depressed cladding layer is deposited on the outer wall of the base tube by 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 of the depressed cladding R3-R2 is 3.5-5.5 μm, refractive The rate is n ₂ . The refractive index difference Δn _{2 of} the depressed cladding is set between -0.007～-0.004, and K=Δn ₂ *(R3-R2) is defined, and it satisfies -0.025<K<-0.022, and the K value is introduced to ensure The bending loss of the bending-resistant multimode optical fiber meets the standard, and at the same time, it is ensured that the base tube region has no transmission mode and energy.

The outer cladding is sleeved on the outer side 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, the outer cladding refractive index n _C and the core layer The boundary refractive index n ₁ and the refractive index n _{sio2 of} the substrate tube are the same.

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

Where α is the distribution parameter of the refractive index profile of the gradient region, r is the radial distance from any point A on the core layer to the core axis, and Δ is the relative refractive index difference between the center of the core layer and the boundary of the core layer , Δ=(n ₀ ² -n ₁ ² )/(2n ₀ ² ).

The molar concentration of F in the core layer changes with the radius of the core layer, satisfying formula (2):

Where, M _F0 is the molar concentration of F in the center of the core layer, and the value range of β _F is 6-10, preferably 7-9, and the M _F (r) indicates that F is in the center of the core layer The molar concentration at the radial distance r of the axis.

As shown in FIG. 2, in an embodiment of the present invention, the center of the core layer is doped with GeO ₂ 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 region is doped with GeO ₂ with a molar concentration of 1.4% to 8% and F with a molar concentration of 5% to 7%. Wherein, the molar concentration of F in the core layer changes with the radius of the core layer, satisfying formula (2), the concentration of F in the base tube and the outer cladding is 0, and the concentration of F in the depressed cladding M _Fd is a constant. To maximize the bandwidth of the multimode fiber, the inter-mode dispersion must be minimized, that is, an optimal profile refractive index distribution parameter must be selected, and Δα _opt (850- 950nm) is 0.05, indicating that the optical fiber can achieve the maximum effective mode bandwidth (EMB) in the wideband range of 850nm to 950nm, and it can satisfy the choice of four wavelengths for wavelength division multiplexing at 850nm to 950nm.

The molar concentration of P ₂ O ₅ in the core layer varies with the radius of the core layer, satisfying the following formula:

Wherein, M _P0 as the center core layer P ₂ O ₅ molar concentration of the M _P (r) represents the P ₂ O ₅ molar concentration of the radial distance r from the central axis of the core, β _p The value range is 2.0-4.5, preferably 2.5-3.5.

3 and 4, in another embodiment of the present invention, the center of the core layer is doped with GeO ₂ with a molar concentration of 9.6% to 10.8% and F and 3.2% with a molar concentration of 0.4% to 1.5% 3.5% of P ₂ O ₅ . The boundary of the gradient region is doped with GeO ₂ with a molar concentration of 8% to 9%, F with a molar concentration of 4.5% to 5%, and P ₂ O ₅ with 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 in the center of the core layer, and β _{F has a} value range of 6.5 to 9, preferably From 7 to 8.5, the concentration of F in the base tube and the outer cladding is 0, and the concentration M _Fd in the depressed cladding is constant. The molar concentration of P ₂ O ₅ in the core layer varies with the radius of the core layer and satisfies formula (3). To maximize the bandwidth of the multimode fiber, it is necessary to minimize the dispersion between the modes, that is, to select one The best profile refractive index distribution parameter, according to the calculation formula of the difference of the best profile refractive index distribution parameter, the Δα _opt (850-950nm) is 0.005, indicating that the optical fiber can achieve an effective mode bandwidth in the wideband range of 850nm to 950nm (EMB) can reach the maximum, and meet the arbitrary selection of four wavelengths for wavelength division multiplexing from 850nm to 950nm.

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

Example 1

In this example, a PCVD process is used to prepare an optical fiber preform. The difference between the central refractive index of the core layer and the outer cladding layer n ₀ -nc is 0.0145, and the difference between the boundary refractive index of the core layer and the outer cladding layer n ₁ -nc is 0, the refractive index difference n ₂ -nc of the depressed cladding and the outer cladding is -0.005, the radius R1 of the gradient region is 24.3 μm, the width of the base tube R2-R1 is 8.1 μm, the depressed cladding The width of R3-R2 is 4.9μm, Rmax is 62.5μm, k=-0.0245, the core layer is doped with GeO ₂ and F, the doped F meets the requirements of formula (2), the doping of the depressed cladding layer F The impurity concentration is 1.3%, the dispersion in the center of the fiber is -97ps/(nm·km), the core diameter of the test multimode fiber is 49.4um, the numerical aperture of the fiber is 0.1995, and the bending loss test with R7.5mm for 2 turns Value: bending loss at 850nm wavelength is 0.01dB, bending loss at 1300nm wavelength is 0.1dB; bending loss at 2 turns with R15mm test value: bending loss at 850nm wavelength is 0.04dB, bending loss at 1300nm wavelength is 0.02dB.

Example 2

In this example, the optical fiber preform is prepared by the MCVD process. The difference between the central refractive index of the core layer and the outer cladding layer n ₀ -nc is 0.0139, and the difference between the boundary refractive index of the core layer and the outer cladding layer n ₁ -nc is 0, the refractive index difference n ₂ -nc of the depressed cladding and the outer cladding is -0.0056, the radius R1 of the gradient region is 24.85 μm, the width of the base tube R2-R1 is 8.5 μm, the depressed cladding The width R3-R2 is 4.15μm, Rmax is 62.5μm, k=-0.02296, the core layer is doped with GeO2, F and P2O5, the doped F and P2O5 meet the requirements of formula (2)(3), the The doping concentration of the depressed cladding F is 15.45%, the dispersion of the fiber center is -96.2ps/(nm·km), the core diameter of the test multimode fiber is 50.3um, the numerical aperture NA of the fiber is 0.1953, and R7.5mm Test value of bending loss around 2 turns: bending loss at 850nm wavelength is 0.13dB, bending loss at 1300nm wavelength is 0.29dB; testing value of bending loss at 2 turns with R15mm: bending loss at 850nm wavelength is 0.01dB, The bending loss at 1300nm wavelength is 0.05dB.

Example 3

In this example, an optical fiber preform is prepared by the MCVD process. The difference between the central refractive index of the core layer and the outer cladding layer n ₀ -nc is 0.0141, and the difference between the boundary refractive index of the core layer and the outer cladding layer n ₁ -nc is 0, the refractive index difference n ₂ -nc of the depressed cladding and the outer cladding is -0.0052, the radius R1 of the gradient region is 25.05 μm, the width of the base tube R2-R1 is 6.4 μm, the depressed cladding The width R3-R2 is 4.5μm, Rmax is 62.5μm, k=-0.0234, the core layer is doped with GeO2, F and P2O5, the doped F and P2O5 meet the requirements of formula (2)(3), the The doping concentration of the depressed cladding F is 15.45%, the dispersion in the center of the fiber is -96.2ps/(nm·km), the core diameter of the test multimode fiber is 50.9um, the numerical aperture of the fiber is 0.1967, with R7.5mm Test value of bending loss around 2 turns: bending loss at 850nm wavelength is 0.06dB, bending loss at 1300nm wavelength is 0.2dB; testing value of bending loss at 2 turns with R15mm: bending loss at 850nm wavelength is 0.006dB, The bending loss at 1300nm wavelength is 0.07dB.

Example 4

In this example, the optical fiber preform is prepared by the MCVD process. The difference between the central refractive index of the core layer and the outer cladding layer n ₀ -nc is 0.0143, and the difference between the boundary refractive index of the core layer and the outer cladding layer n ₁ -nc is 0, the refractive index difference n ₂ -nc of the depressed cladding and the outer cladding is -0.0062, the radius R1 of the gradient region is 24.9 μm, the width of the substrate tube R2-R1 is 8.9 μm, the depressed cladding The width R3-R2 is 3.7μm, Rmax is 62.5μm, k=-0.02232, the core layer is doped with GeO2, F and P2O5, the doped F and P2O5 meet the requirements of formula (2)(3), the The doping concentration of the depressed cladding F is 15.45%, the dispersion in the center of the fiber is -96.2ps/(nm·km), the core diameter of the test multimode fiber is 50.6um, the numerical aperture of the fiber is 0.1981, with R7.5mm Test value of bending loss around 2 turns: bending loss at 850nm wavelength is 0.18dB, bending loss at 1300nm wavelength is 0.37dB; testing value of bending loss at 2 turns with R15mm: bending loss at 850nm wavelength is 0.03dB, The bending loss at 1300nm wavelength is 0.1dB.

It can be seen from the above example that the additional loss of the optical fiber at a wavelength of 850 nm and two turns around a radius of 7.5 mm does not exceed 0.18 dB, and the additional loss of a two-turn curve at a radius of 15 mm does not exceed 0.01 dB; The additional loss of 2 turns around the radius bend does not exceed 0.37dB, and the additional loss of 2 turns around the radius of 15mm does not exceed 0.1dB. In the wideband range of 850nm to 950nm, the optical fibers have Effective mode bandwidth and good bending resistance.

The broadband anti-bending multimode optical fiber provided by the present invention, because it does not need to deposit the concave part, removes the high-cost depressed cladding deposit layer, and uses a cheap method to prepare a depressed layer/or coat an inexpensive F-doped quartz on the outer wall of the base tube The optical fiber produced by the preform is increased by 20% or more compared with other bending multimode optical fiber preforms with the same deposition amount, which reduces the cost of the manufactured bending multimode optical fiber and has good bending performance.

Persons of ordinary skill in the art should realize 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 make appropriate changes to the above embodiments within the spirit and scope of the present invention And changes fall within the scope of the claimed invention.

Claims (9)

A broadband anti-bending multimode optical fiber includes a core layer, a base tube, a depressed cladding and an outer cladding. The radial cross-sections of the base tube, the depressed cladding and the outer cladding are all rings, and the characteristics are as follows: The core layer is doped with GeO ₂ , P ₂ O ₅ and F, the core layer is a gradient refractive index region, the core layer radius is R1, the base tube is sleeved outside the core layer, the 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 disposed outside the base tube, and the center of the core layer to the depressed cladding layer The distance of the boundary is R3, the width of the depressed cladding is R3-R2, the outer cladding is sleeved on the outside of the depressed cladding, and the distance from the center of the core layer to the boundary of the outer cladding is Rmax. The width of the outer cladding layer is Rmax-R3, and the molar concentration of F in the core layer changes with the radius of the core layer, satisfying the following formula:

Where, M _F0 is the molar concentration of F in the center of the core layer, and the value range of β _F is 6-10, and the M _F (r) represents the radial distance r of the F at the center axis of the core layer The molar concentration at. The broadband bending-resistant multimode optical fiber according to claim 1, wherein the value range of the β _F is 7-9. The broadband anti-bending multimode optical fiber according to claim 1, wherein the molar concentration of P ₂ O ₅ in the core layer changes with the radius of the core layer, satisfying the following formula:

Where, M _P0 is the molar concentration of P ₂ O ₅ in the center of the core layer, β _{p has a} value range of 2.0-4.5, and M _P (r) represents the diameter of the P ₂ O ₅ at the central axis of the core layer To the molar concentration at distance r. The broadband anti-bending multimode optical fiber according to claim 3, wherein _the value range of β _p is 2.5-3.5. The broadband anti-bending multimode optical fiber according to claim 1, wherein the refractive index difference Δn _{0 in the} center of the core layer is 0.0127-0.0167, the radius R1 of the core layer is 22-26 μm, and the The width R2-R1 is 5.5-10.5 μm, and the distance Rmax from the center of the core layer to the edge of the outer cladding layer is 62.5±2.5 μm. The broadband bending-resistant multimode optical fiber according to claim 5, wherein the core layer radius R1 is 23-24 μm, and the width of the base tube is 6.5-9.5 μm. The broadband anti-bending multimode optical fiber according to claim 1, wherein the depressed cladding layer is deposited on the outer wall of the base pipe or is formed by coating a fluorine-doped quartz on the outer side of the base pipe. The broadband bending-resistant multimode optical fiber according to claim 1, wherein the width R3-R2 of the depressed cladding is 3.5-5.5 μm, and the refractive index difference Δn ₂ of the depressed cladding is -0.007～- 0.004, K=Δn ₂ *(R3-R2), and satisfy -0.025<K<-0.022. The broadband anti-bending multimode optical fiber according to claim 1, characterized in that the refractive index profile of the core layer is distributed by an exponential function of α, and α is the distribution parameter of the refractive index profile of the gradient region, wherein the core layer The central refractive index is n ₀ , the boundary refractive index of the core layer is n ₁ , the refractive index of the base tube is n _sio2 , the refractive index of the depressed cladding is n ₂ , and the refractive index of the outer cladding is n _C , the refractive index calculation formula of the optical fiber is:

Where α ranges from 1.90 to 2.10, r is the radial distance from any point on the core layer to the center of the core layer, n ₁ = n _SiO2 , nc = n _SiO2 , and Δ is the center of the core layer The relative refractive index difference Δ=(n ₀ ² -n ₁ ² )/(2n ₀ ² ) with the boundary of the core layer.

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