CN110297288B - Low-attenuation step type track angular momentum optical fiber - Google Patents

Low-attenuation step type track angular momentum optical fiber Download PDF

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CN110297288B
CN110297288B CN201910300226.6A CN201910300226A CN110297288B CN 110297288 B CN110297288 B CN 110297288B CN 201910300226 A CN201910300226 A CN 201910300226A CN 110297288 B CN110297288 B CN 110297288B
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core layer
optical fiber
refractive index
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oam
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沈磊
张磊
张睿
吴俊�
刘亚萍
周红燕
曹蓓蓓
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Yangtze Optical Fibre and Cable Co Ltd
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    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
    • G02B6/03605—Highest refractive index not on central axis
    • G02B6/03611—Highest index adjacent to central axis region, e.g. annular core, coaxial ring, centreline depression affecting waveguiding
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
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Abstract

The invention relates to a step type low-attenuation orbital angular momentum optical fiber, which comprises a core layer and a cladding, wherein the core layer R1 is 3-5 microns, the delta 1 is-0.08%, the outside of the core layer is sequentially coated with an annular core layer, a sunken cladding and an outer cladding from inside to outside, the annular core layer sequentially comprises an inner annular core layer, a sunken annular core layer and an outer annular core layer from inside to outside, the R2 of the inner annular core layer is 4-6 microns, the delta 2 is 0.7-1%, the R3 of the sunken annular core layer is 5-7 microns, the delta 3 is 0.6-0.9%, the R4 of the outer annular core layer is 7-9 microns, and the delta 4 is 0.7-1%, and Δ 4 is equal or substantially equal to Δ 2, the depressed cladding R5 is 11-16 μm, Δ 5 is-0.6% to-0.3%, the relative refractive index difference is the relative refractive index difference between each layer of the optical fiber and the outer cladding layer, and the outer cladding layer is the one with negative refractive index relative to the pure silicon dioxide layer. The invention can support the long-distance signal transmission of four mode groups, has low attenuation, and has good comprehensive performances of crosstalk of optical fibers, macrobend and microbend loss of each mode and the like.

Description

Low-attenuation step type track angular momentum optical fiber
Technical Field
The invention relates to a space division multiplexing transmission optical fiber for an optical fiber communication system, in particular to a low attenuation step type Orbital Angular Momentum (OAM) optical fiber.
Background
In recent years, with the rise of cloud computing, big data and mobile internet, a data center with efficient collaboration among servers and data processing capability becomes an obvious hotspot for increasing the total information amount and information density, so that an urgent requirement is put on the improvement of the interconnection communication rate of the data center. Because the data center interconnection communication has the characteristics of numerous equipment, complex wiring, high interface density and the like, the cost, the power consumption, the complexity and the like of system operation or maintenance are increased by only increasing the modulation bandwidth of a device and increasing the number of optical fiber links or light sources with different stable wavelengths, and therefore, the transmission rate of a single optical fiber/wavelength under the condition of limited bandwidth is increased by adopting a new modulation/multiplexing mode, and the method is regarded as an effective solution for improving the interconnection rate of the data center.
TABLE 1 relevant standards or requirements for next generation data center interconnect communications
Figure BDA0002028000010000011
Table 1 presents ethernet-related standards for next generation data center interconnect communication. It can be seen that the next generation of communication standards place increasingly stringent requirements on single fiber single wavelength rates. In an actual optical fiber system, the capacity expansion capability of the high-order modulation and polarization multiplexing technology is still limited due to factors such as the signal-to-noise ratio of the system and the nonlinearity of the optical fiber, and a great challenge is still provided for meeting the next generation of data center interconnection communication, such as 800GE, 1TE, and even 1.6 TE. The Space Division Multiplexing (SDM) technology based on the multi-core fiber or the multi-mode fiber has a large expansion potential in the mode and space dimensions of the fiber, and can be compatible with a high-order modulation format and a polarization multiplexing technology, so that the communication capacity of a single fiber/wavelength can be greatly improved. Furthermore, according to a new concept proposed by Miller and Kahn based on shannon's theorem in stanford university, for a communication system with higher power consumption requirement, more spatial channels should be adopted as much as possible while relatively reducing the communication capacity of each spatial channel. Therefore, by adopting the SDM technology of the multi-space channel, on the basis of not increasing the number of optical fiber links, higher transmission capacity can be realized theoretically by unit power consumption, the SDM technology is more suitable for data center interconnection communication with higher requirement on power consumption, and the application potential of the SDM technology is further promoted.
The space division multiplexing and the module division multiplexing technology can break the traditional Shannon limit, realize the transmission with higher bandwidth, and is the best method for solving the problem of transmission capacity. The optical fibers supporting the multiplexing technology are multi-core optical fibers and few-mode optical fibers. Experiments show that signals can be transmitted in more than one spatial propagation mode by using few-mode optical fibers in combination with the MIMO technology. And the MIMO technology can compensate for mutual coupling between modes, separating each spatial mode at the receiving end. US8948559, US8848285, US8837892, US8705922 and chinese patents CN104067152, CN103946729, etc. propose few-mode fibers with parabolic or step-shaped profiles, but they have respective advantages and disadvantages. Few-mode fibers with stepped profiles are simple to manufacture and easy to mass produce, but typically have a large DGD, even up to several thousand ps/km. Few-mode optical fibers with parabolic profiles have more adjustable parameters, so that the intermodal crosstalk and the DGD reach low levels, but the preparation process is complex, the alpha parameter is difficult to control accurately and uniformly, and the repeatability is not high. And the small fluctuation of the refractive index profile along the axial direction of the prefabricated rod can cause the obvious change of the DGD at different sections of the optical fiber.
In recent years, MDM systems based on ring core fiber (RCF, hereinafter ring core fiber) have been developed. The RCF limited in the first radial order can eliminate the crosstalk influence of the high-order radial modes on some high-order angular modes (such as the crosstalk influence of LP12 on LP31 modes and the like) and different from the common MMF, the high-order modes of the RCF tend to have lower intermodal crosstalk; the radial limitation of the RCF is more beneficial to the stable transmission of the OAM mode; in addition, the RCF fiber does not break the circular symmetry characteristic of the fiber waveguide, and compared with the polarization-maintaining MMF such as an elliptical fiber, the RCF fiber has lower requirements on the drawing process, thereby having higher practical application value.
Despite the above advantages, RCFs still have relatively large fiber attenuation and inter-mode crosstalk relative to conventional MMF/FMF. This is mainly due to the ring-shaped core profile of the RCF, which increases the core-to-cladding interface from one to two of the conventional fibers. Thus, the core cladding interface defects during actual drawing and laying have a more significant effect on the coupling between the modes, resulting in increased crosstalk and fiber attenuation. The Chinese patent CN108680990A reports an orbital angular momentum optical fiber with a ring-shaped core, but the attenuation is more than 1dB/km, and the optical fiber can only be used for short-distance transmission. Chinese patent CN106338793A reports that an RCF fiber can suppress some high-order modes that are easy to couple, but its attenuation is 0.31dB/km, still having a certain gap from low-loss FMF.
The attenuation of the quartz fiber at 600nm-1600nm is mainly from Rayleigh scattering, and the attenuation alpha caused by Rayleigh scatteringRCan be composed ofThe following formula is calculated:
Figure BDA0002028000010000021
wherein λ is the wavelength (μm), and R is the Rayleigh scattering coefficient (dB/km/μm)4) And P is light intensity. When the rayleigh scattering coefficient is confirmed, B is a corresponding constant. Therefore, attenuation alpha caused by Rayleigh scattering can be obtained by determining Rayleigh scattering coefficient RR(dB/km). Rayleigh scattering is caused by density fluctuations on the one hand and concentration fluctuations on the other hand. The Rayleigh scattering coefficient R can thus be expressed as
R＝Rd+Rc
In the above formula, RdAnd RcRespectively, the rayleigh scattering coefficient changes due to density fluctuations and concentration fluctuations. Wherein R iscIn order to have a concentration fluctuation factor which is mainly influenced by the doping concentration of the glass part of the fiber, theoretically less Ge and F or other doping is used, RcThe smaller this is also the reason why some foreign enterprises have adopted pure silica core design in single mode fiber to achieve low attenuation performance.
And the parameter RdDepending on the virtual temperature of the glass, in the case of a pure silicon core design, to ensure total reflection of the fiber, a relatively low index of refraction of the F-doped inner cladding must be used for matching. Therefore, the viscosity of the core layer part of the pure silicon core is relatively high, and meanwhile, the viscosity of the inner cladding layer doped with a large amount of F is low, so that the viscosity matching imbalance of the optical fiber structure is caused, the virtual temperature of the optical fiber is rapidly increased, and the R of the optical fiber is causeddAnd (4) increasing. This not only counteracts the benefits of reduced doping, but is more likely to cause fiber attenuation reversal anomalies.
Disclosure of Invention
For convenience in describing the present disclosure, the following terms are defined:
relative refractive index difference Δ niThe relative refractive index difference between each layer of the optical fiber (except the outer cladding layer) and the outer cladding layer.
The layer closest to the central axis is defined as a core layer and the outermost layer is an outer cladding layer according to the change of the refractive index from the central axis of the fiber core.
Relative refractive index difference Deltan of each layer of optical fiberiDefined by the following equation:
Figure BDA0002028000010000031
wherein n isiIs the refractive index of the layers (except the cladding) of the optical fiber, ncIs the outer cladding refractive index.
The relative refractive index difference contribution Δ Ge of the Ge doping of the core layer of the optical fiber is defined by the following equation:
Figure BDA0002028000010000032
wherein n isGeGe dopant for the core, in pure silica doped without other dopants, causes a change in the refractive index of the silica glass, where ncIs the refractive index of pure silica.
The relative refractive index difference contribution Δ F of the optical fiber core layer F doping is defined by the following equation:
Figure BDA0002028000010000033
wherein n isFF dopant as core, in pure silica doped without other dopants, causes a change in the refractive index of the silica glass, where ncIs the refractive index of pure silica.
Effective area of each mode of the fiber:
Figure BDA0002028000010000041
where E is the electric field associated with propagation and r is the distance from the axis to the point of electric field distribution.
The technical problem to be solved by the present invention is to provide a low attenuation step type optical fiber with orbital angular momentum, which can support long-distance signal transmission of four mode groups and has low attenuation, and has good comprehensive performance such as crosstalk, macrobending loss and microbending loss of each mode.
The technical scheme adopted by the invention for solving the problems is as follows: the composite material comprises a core layer and a cladding, and is characterized in that the radius R1 of the core layer is 3-5 mu m, the relative refractive index difference Delta 1 of the core layer is-0.08%, the outside of the core layer sequentially wraps an annular core layer, a sunken cladding and an outer cladding from inside to outside, the annular core layer sequentially comprises an inner annular core layer, a sunken annular core layer and an outer annular core layer from inside to outside, the radius R2 of the inner annular core layer is 4-6 mu m, the relative refractive index difference Delta 2 is 0.7% -1%, the radius R3 of the sunken annular core layer is 5-7 mu m, the relative refractive index difference Delta 3 is 0.6% -0.9%, the radius R4 of the outer annular core layer is 7-9 mu m, the relative refractive index difference Delta 4 is 0.7% -1%, the Delta 4 is equal to Delta 2 or basically equal to the same, the radius R5 of the sunken cladding is 11-16 mu m, and the relative refractive index difference Delta 5 is-0.6% -0.3%, the relative refractive index difference is the relative refractive index difference between each layer (core layer, annular core layer and depressed cladding layer) of the optical fiber and the outer cladding layer, the outer cladding layer is an outer cladding layer with a negative refractive index relative to the pure silica layer, and the radius R6 is 62.5 mu m.
According to the scheme, the relative refractive index difference of the outer cladding layer (relative to a pure silicon dioxide layer) is-0.3% -0.5%.
According to the scheme, the optical fiber supports the propagation of 4 OAM mode groups on the C wave band: OAM-0 order, OAM- +/-1 order, OAM- +/-2 order and OAM- +/-3 order.
According to the scheme, the core layer is a germanium-fluorine co-doped silica glass layer or a fluorine-doped silica glass layer, wherein the fluorine-doped relative refractive index difference contribution amount is-0.02% -0.3%.
According to the scheme, the annular core layer is a germanium-fluorine co-doped silica glass layer, wherein the fluorine-doped relative refractive index difference contribution amount is-0.02% -0.2%.
According to the scheme, the crosstalk between the OAM-0 order mode and the OAM- +/-1 order mode of the optical fiber is smaller than-5 dB/50km, the crosstalk between the OAM- +/-1 order mode and the OAM- +/-2 order mode is smaller than-13 dB/50km, the crosstalk between the OAM- +/-2 order mode and the OAM- +/-3 order mode is smaller than-13 dB/50km, and the crosstalk between the OAM- +/-1 order mode and the OAM- +/-3 order mode is smaller than-21 dB/50 km.
According to the scheme, the attenuation of each mode of the optical fiber at the wavelength of 1550nm is less than or equal to 0.23 dB/km. Preferably, the attenuation of each order mode of the optical fiber at the wavelength of 1550nm is less than or equal to 0.21 dB/km.
According to the scheme, the microbending loss of each mode of the optical fiber at the wavelength of 1700nm is less than or equal to 5 dB/km.
According to the scheme, at the wavelength of 1550nm of each mode of the optical fiber, the macrobending loss of 10 turns of R15mm bending radius bending is equal to or less than 0.25dB, and the macrobending loss of 1 turn of R10mm bending radius bending is equal to or less than 0.75 dB.
The invention has the beneficial effects that: 1. by adopting the germanium-fluorine co-doped core layer design, the viscosity matching in the optical fiber is reasonably designed, the defects in the optical fiber preparation process are reduced, and the attenuation coefficient of the optical fiber is reduced. Not only can long-distance signal transmission of four mode groups be supported, but also each mode group has a lower attenuation coefficient. 2. Through the reasonable design of each layer of the section of the optical fiber, especially through arranging the annular core layer with the sunken middle part, the crosstalk among the modes of the optical fiber is lower. 3. The comprehensive performance parameters of macrobending, microbending loss and the like of the four mode groups of the optical fiber are good in application wave band. The long-distance signal transmission of four mode groups can be carried out by using a space division multiplexing technology, each mode has a lower attenuation coefficient, and low-loss few-mode multiplexing transmission can be supported. 4. The outermost cladding of the optical fiber is a fluorine-doped cladding with negative refractive index, so that the doping amount of the annular core layer can be reduced, and the attenuation of the optical fiber is further reduced. 5. The invention adopts a step type core layer structure, adopts PCVD technology to deposit the core rod in the preparation of the optical fiber, and then sleeves the outer sleeve for drawing, thereby not only facilitating the manufacture and production, but also reducing the production cost. 6. The method is based on a first-order perturbation theory model of the optical fiber, and is used for researching the influence of each design parameter (ring core average radius, thickness, relative refractive index difference and refractive index distribution) of the RCF on the coupling coefficient between adjacent modes, further optimizing the optical fiber design, further reducing the optical fiber attenuation and the crosstalk between the modes, and preparing the low-attenuation optical fiber by using a method for reducing the Rayleigh scattering of each mode of the optical fiber. Finally, the OAM mode division multiplexing communication system with high distance capacity, low implementation cost and low complexity is realized, and a basis is provided for upgrading the next generation data center optical fiber interconnection communication system.
Drawings
Fig. 1 is a schematic view of a radial cross-section structure of an embodiment of the present invention.
FIG. 2 is a schematic representation of a cross-sectional view of the refractive index of an optical fiber according to one embodiment of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and examples.
The core layer has the radius of R1, is of a step-type structure, and has the relative refractive index difference delta 1; the core layer is sequentially coated with an inner annular core layer, a sunken annular core layer, an outer annular core layer, a sunken cladding layer and an outer cladding layer from inside to outside, the radius of the inner annular core layer is R2, and the relative refractive index difference is delta 2; the radius of the sunken annular core layer is R3, and the relative refractive index difference is delta 3; the radius of the outer annular core layer is R4, and the relative refractive index difference is delta 4; the radius of the sunken cladding is R5, and the relative refractive index difference is delta 5; the relative refractive index difference is the relative refractive index difference between each layer (the core layer, the annular core layer and the sunken cladding layer) of the optical fiber and the outer cladding layer, the outer cladding layer is the outer cladding layer with negative refractive index relative to the pure silica layer, the relative refractive index difference (relative to the pure silica layer) of the outer cladding layer is-0.3% -0.5%, and the radius R6 of the outer cladding layer is 62.5 mu m. The structure and the main performance parameters of the 5 embodiments of the optical fiber of the present invention are shown in tables 1 and 2.
Table 1: example Structure of optical fiber
Figure BDA0002028000010000051
Figure BDA0002028000010000061
Table 2: example Main Performance parameters of optical fibers
Figure BDA0002028000010000062

Claims (7)

1. A low-attenuation step type track angular momentum optical fiber comprises a core layer and a cladding, and is characterized in that the radius R1 of the core layer is 3-5 microns, the relative refractive index difference delta 1 of the core layer is-0.08%, the outside of the core layer sequentially wraps an annular core layer, a sunken cladding and an outer cladding layer from inside to outside, the annular core layer sequentially comprises an inner annular core layer, a sunken annular core layer and an outer annular core layer from inside to outside, the radius R2 of the inner annular core layer is 4-6 microns, the relative refractive index difference delta 2 is 0.7% -1%, the radius R3 of the sunken annular core layer is 5-7 microns, the relative refractive index difference delta 3 is 0.6% -0.9%, the radius R4 of the outer annular core layer is 7-9 microns, the relative refractive index difference delta 4 is 0.7% -1%, the delta 4 is equal to delta 2 or basically equal to the same, the radius R5 of the sunken cladding layer is 11-16 microns, the relative refractive index difference delta 5 is-0.6% -0.3%, the relative refractive index difference is the relative refractive index difference between each layer of the optical fiber and the outer cladding layer, the outer cladding layer is the one with negative refractive index relative to the pure silicon dioxide layer, and the radius R6 is 62.5 mu m; the optical fiber supports the propagation of 4 OAM mode groups on a C wave band: OAM-0 order, OAM- +/-1 order, OAM- +/-2 order and OAM- +/-3 order; the crosstalk between the OAM-0 order mode and the OAM- +/-1 order mode of the optical fiber is smaller than-5 dB/50km, the crosstalk between the OAM- +/-1 order mode and the OAM- +/-2 order mode is smaller than-13 dB/50km, the crosstalk between the OAM- +/-2 order mode and the OAM- +/-3 order mode is smaller than-13 dB/50km, and the crosstalk between the OAM- +/-1 order mode and the OAM- +/-3 order mode is smaller than-21 dB/50 km.
2. The low attenuation step-index angular momentum optical fiber of claim 1, wherein said outer cladding has a relative refractive index difference of-0.3% to-0.5%.
3. The low attenuation step index angular momentum optical fiber according to claim 1 or 2, wherein said core layer is a germanium-fluorine co-doped silica glass layer or a fluorine-doped silica glass layer, wherein the fluorine-doped relative refractive index difference contribution amount is-0.02% to-0.3%.
4. The low attenuation step index angular momentum optical fiber according to claim 1 or 2, wherein said annular core layer is a germano-fluorine co-doped silica glass layer, wherein the fluorine-doped relative refractive index difference contribution is in the range of-0.02% to-0.2%.
5. The low attenuation step-type orbital angular momentum optical fiber according to claim 1 or 2, wherein said optical fiber has attenuation of each order mode at a wavelength of 1550nm which is less than or equal to 0.23 dB/km.
6. A low attenuation step-type angular momentum optical fiber according to claim 1 or 2, wherein each mode of said optical fiber has a microbend loss at a wavelength of 1700nm of less than or equal to 5 dB/km.
7. The low attenuation step-type angular momentum optical fiber according to claim 1 or 2, wherein each mode of said optical fiber has a macrobending loss of 0.25dB or less for 10 bends with a bending radius of R15mm and a macrobending loss of 0.75dB or less for 1 bend with a bending radius of R10mm at a wavelength of 1550 nm.
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