A bend-insensitive step-index orbital angular momentum optical fiber

Abstract

The present invention belongs to the technical field of optical fiber communication, and discloses a bend-insensitive step-type orbital angular momentum optical fiber, which sequentially includes a central core layer, a ring core layer, a ring inner cladding layer, a ring depressed layer, and an outer cladding layer from the inside to the outside; the radius of the central core layer is 2.5 to 5.0 μm, and the relative refractive index difference is -0.1% to 0.1%; the radius of the ring core layer is 8 to 10 μm, and the relative refractive index difference is 0.40% to 0.75%; the radius of the ring inner cladding layer is 11.0 to 12.5 μm, and the relative refractive index difference is -0.1% to 0.1%; the radius of the ring depressed layer is 13.5 to 17.0 μm, and the relative refractive index difference is -0.45% to -0.35%. The OAM optical fiber provided by the present invention has good bending performance for each order mode and can support long-distance signal transmission.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber communication, and more specifically, relates to a bend-insensitive step-type orbital angular momentum optical fiber. Background Art

[0002] In recent years, with the rise of cloud computing, big data, and mobile Internet, data centers with efficient inter-server collaboration and data processing capabilities have become obvious hotspots for the growth of the total amount and density of information, thus posing an urgent requirement for improving the interconnection communication rate of data centers. Due to the characteristics of a large number of devices, complex cabling, and high interface density in data center interconnection communication, simply relying on increasing the modulation bandwidth of devices, adding optical fiber links, or the number of light sources with different stable wavelength outputs will inevitably increase the costs, power consumption, complexity, etc. of system operation or maintenance. Therefore, adopting a new modulation / multiplexing method to increase the transmission rate of a single optical fiber / wavelength under limited bandwidth is regarded as an effective solution to improve the interconnection rate of data centers.

[0003] In an actual optical fiber system, limited by factors such as system signal-to-noise ratio and optical fiber nonlinearity, the capacity expansion capabilities of high-order modulation and polarization multiplexing technologies are still limited, and there are still great challenges in meeting the interconnection communication requirements of the next-generation data centers, such as 800GE, 1TE, or even 1.6TE. The space-division multiplexing (SDM) technology based on multi-core optical fibers or multi-mode optical fibers has great expansion potential in the mode and spatial dimensions of optical fibers and can be compatible with high-order modulation formats and polarization multiplexing technologies. Therefore, it can greatly improve the communication capacity of a single optical fiber / wavelength. In addition, according to an idea proposed by Miller and Kahn of Stanford University based on the Shannon theorem, for a communication system with high power consumption requirements, more spatial channels should be used as much as possible, while relatively reducing the communication capacity of each spatial channel. Therefore, the SDM technology using multiple spatial channels can theoretically achieve a higher transmission capacity per unit power consumption without increasing the number of optical fiber links.

[0004] Space-division multiplexing and mode-division multiplexing technologies can break through the traditional Shannon limit and achieve higher-bandwidth transmission. The space-division multiplexing technology based on few-mode optical fibers has shown great potential in improving the transmission capacity of single-fiber communication systems, and it has become possible to increase the capacity by dozens of times, providing an effective way to solve the capacity bottleneck problem of future optical communication systems. Photonic orbital angular momentum (hereinafter referred to as "OAM") optical fiber is a type of few-mode optical fiber. Implementing single-fiber mode-division multiplexing multi-channel transmission based on the OAM mode is a new method proposed in recent years to greatly expand the information capacity of optical fiber communication. However, compared with traditional single-mode optical fibers, due to the larger number of layers and larger core diameter in the cross-section of OAM optical fibers, the macro-bending and micro-bending performance of the optical fibers is poor, which limits the use of the optical fibers in the field of long-distance communication. How to improve the bending performance of OAM optical fibers is a technical problem that needs to be solved in this field. Summary of the Invention

[0005] The present invention provides a bend-insensitive step-type orbital angular momentum optical fiber, which solves the problem of poor bending performance of photon orbital angular momentum optical fibers in the prior art.

[0006] The present invention provides a bend-insensitive step-type orbital angular momentum optical fiber, which sequentially includes a central core layer, an annular core layer, an annular inner cladding layer, an annular depressed layer, and an outer cladding layer from the inside to the outside; the radius r1 of the central core layer is 2.5-5.0 μm, and the relative refractive index difference Δ1 between the central core layer and the outer cladding layer is -0.1% to 0.1%; the radius r2 of the annular core layer is 8-10 μm, and the relative refractive index difference Δ2 between the annular core layer and the outer cladding layer is 0.40% to 0.75%; the radius r3 of the annular inner cladding layer is 11.0-12.5 μm, and the relative refractive index difference Δ3 between the annular inner cladding layer and the outer cladding layer is -0.1% to 0.1%; the radius r4 of the annular depressed layer is 13.5-17.0 μm, and the relative refractive index difference Δ4 between the annular depressed layer and the outer cladding layer is -0.45% to -0.35%.

[0007] Preferably, the radius r5 of the outer cladding layer is 62.0-62.5 μm, and the outer cladding layer is a pure silica layer.

[0008] Preferably, the bend-insensitive step-type orbital angular momentum optical fiber further includes an inner coating layer and an outer coating layer sequentially coated on the outer cladding layer; the diameter of the inner coating layer is 170-200 μm, and the diameter of the outer coating layer is 235-255 μm.

[0009] Preferably, the diameter of the inner coating layer is 180-190 μm, and the diameter of the outer coating layer is 240-250 μm.

[0010] Preferably, the Young's modulus of the inner coating layer is less than 1 MPa, and the curing degree is 90%-95%; the Young's modulus of the outer coating layer is greater than 1000 MPa, and the curing degree is 95%-99%.

[0011] Preferably, the Young's modulus of the inner coating layer is 0.5 Mpa, and the Young's modulus of the outer coating layer is 1200 Mpa.

[0012] Preferably, the bend-insensitive step-type orbital angular momentum optical fiber supports the propagation of 4 OAM mode groups in the C band: OAM-0 order, OAM-±1 order, OAM-±2 order, and OAM-±3 order.

[0013] Preferably, at a wavelength of 1550 nm, the attenuation of each order mode is less than or equal to 0.23 dB / km.

[0014] Preferably, for the bend-insensitive step-type orbital angular momentum optical fiber, at a wavelength of 1550 nm, the microbend loss of each order mode is less than or equal to 1 dB / km.

[0015] Preferably, for the bend-insensitive step-type orbital angular momentum optical fiber, at a wavelength of 1550 nm, when bent 10 turns with a bending radius of R = 15 mm, the macro-bend loss of each order mode is equal to or less than 0.03 dB.

[0016] One or more technical solutions provided in the present invention have at least the following technical effects or advantages:

[0017] The bend-insensitive step-type orbital angular momentum optical fiber provided by the present invention sequentially includes a central core layer, an annular core layer, an annular inner cladding layer, an annular depressed layer, and an outer cladding layer from the inside to the outside. Through reasonable design of the profile radius and relative refractive index difference of each layer of the optical fiber, especially by setting the annular depressed layer with an intermediate depression, the macro-bend of each mode of the optical fiber can be made smaller. In addition, on the basis of optimizing the macro-bend performance of the optical fiber, the present invention also optimizes the coating process of the OAM optical fiber. By optimizing the thickness (i.e., diameter), modulus, and curing degree of the coating layer, the micro-bend performance of each mode of the OAM optical fiber can be improved. With the above comprehensive improvements, the optical fiber provided by the present invention can not only support long-distance signal transmission of four mode groups with low attenuation, but also has good comprehensive performance such as macro-bend and micro-bend loss of each mode of the optical fiber. Description of the Drawings

[0018] Figure 1 It is a schematic diagram of the radial cross-sectional structure of a bend-insensitive step-type orbital angular momentum optical fiber provided by an embodiment of the present invention;

[0019] Figure 2 It is a refractive index profile diagram of a bend-insensitive step-type orbital angular momentum optical fiber provided by an embodiment of the present invention. Detailed Embodiments

[0020] To facilitate the introduction of the content of the present invention, some terms are first defined:

[0021] Radius r: The distance between the outer boundary of this layer and the center point of the optical fiber.

[0022] Refractive index profile: The relationship between the glass refractive index of an optical fiber or an optical fiber preform (including a core rod) and its radius.

[0023] Relative refractive index difference: Δ% = [(n i 2 - n0 2 ) / 2n i 2 × 100% ≈ (n i - n0) / n0 × 100%, ni n0 and n are the refractive indices of the respective parts of each corresponding optical fiber and the refractive index of the pure silica glass of the outer cladding, respectively.

[0024] The glass part of the optical fiber refers to the glass fiber in the optical fiber without the coating layer.

[0025] The method for testing the macro-bending additional loss refers to the method specified in IEC60793-1-47.

[0026] The method for testing the micro-bending loss refers to the method specified in IEC TR 62221.

[0027] To better understand the above technical solution, the above technical solution will be described in detail below in combination with the accompanying drawings of the specification and specific embodiments.

[0028] This embodiment provides a bend-insensitive step-type orbital angular momentum optical fiber. Refer to Figure 1 , Figure 2 , which sequentially includes a central core layer, a ring core layer, a ring inner cladding layer, a ring depressed layer, and an outer cladding layer from the inside to the outside; the radius r1 of the central core layer is 2.5 to 5.0 μm, and the relative refractive index difference Δ1 between the central core layer and the outer cladding layer is -0.1% to 0.1%; the radius r2 of the ring core layer is 8 to 10 μm, and the relative refractive index difference Δ2 between the ring core layer and the outer cladding layer is 0.40% to 0.75%; the radius r3 of the ring inner cladding layer is 11.0 to 12.5 μm, and the relative refractive index difference Δ3 between the ring inner cladding layer and the outer cladding layer is -0.1% to 0.1%; the radius r4 of the ring depressed layer is 13.5 to 17.0 μm, and the relative refractive index difference Δ4 between the ring depressed layer and the outer cladding layer is -0.45% to -0.35%; the radius r5 of the outer cladding layer is 62.0 - 62.5 μm, and the outer cladding layer is a pure silica layer.

[0029] The central core layer, the ring core layer, and the ring inner cladding layer are all germanium-doped or germanium-chloride co-doped silica glass layers, and the ring depressed layer is a fluorine-doped silica glass layer.

[0030] In addition, the bend-insensitive step-type orbital angular momentum optical fiber further includes an inner coating layer and an outer coating layer sequentially coated on the outer cladding layer, that is, the inner coating layer and the outer coating layer are successively on the optical fiber glass part. The diameter of the inner coating layer is 170 to 200 μm, the Young's modulus is less than 1 MPa, and the curing degree is 90% to 95%; the diameter of the outer coating layer is 235 to 255 μm, the Young's modulus is greater than 1000 MPa, and the curing degree is 95% to 99%.

[0031] In a preferred embodiment, the inner coating layer has a diameter of 180 - 190 μm and a Young's modulus of 0.5 Mpa; the outer coating layer has a diameter of 240 - 250 μm and a Young's modulus of 1200 Mpa.

[0032] The bend-insensitive step-type orbital angular momentum fiber supports the propagation of 4 OAM mode groups in the C band: OAM-0 order, OAM-±1 order, OAM-±2 order, and OAM-±3 order.

[0033] In the bend-insensitive step-type orbital angular momentum fiber at a wavelength of 1550 nm, the attenuation of each order mode is less than or equal to 0.23 dB / km, and the microbend loss of each order mode is less than or equal to 1 dB / km.

[0034] In the bend-insensitive step-type orbital angular momentum fiber at a wavelength of 1550 nm, when bent 10 turns with a bending radius of R = 15 mm, the macro-bend loss of each order mode is equal to or less than 0.03 dB.

[0035] According to the technical solution of the bend-insensitive step-type orbital angular momentum fiber described above, the parameters of the fiber are designed within its specified range. The main parameters of the refractive index profile structure of the produced fiber are shown in Table 1, and the main performance parameters of the prepared fiber are shown in Table 2.

[0036] Table 1 Main parameters of the refractive index profile structure of the fiber

[0037] Example 1 Example 2 Example 3 r1 (μm) 3 3.5 4.3 r2 (μm) 8.2 8.8 9.5 r3 (μm) 11.3 11.7 12.2 r4 (μm) 13.8 15.1 16.2 r5 (μm) 62.5 62.3 62.5 Δ1 (%) 0 0 0 Δ2 (%) 0.68 0.55 0.43 Δ3 (%) 0 0 0 Δ4 (%) -0.38 -0.41 -0.39

[0038] Table 2 Main performance parameters of the fiber

[0039]

[0040] It can be seen that while the present invention ensures the propagation of 4 OAM mode groups in the C band of the fiber, the attenuation, macro-bend, and micro-bend performances of the four modes are all very good, making it suitable for long-distance trunk communication.

[0041] The bend-insensitive step-type orbital angular momentum fiber provided by the embodiment of the present invention has at least the following technical effects:

[0042] 1. Through the reasonable design of each layer profile of the fiber, especially by setting the annular sunken layer with a middle depression, the macro-bend of each mode of the fiber is reduced.

[0043] 2. On the basis of optimizing the macro-bend performance of the fiber, the thickness, modulus, and curing degree of the coating layer are optimized, and the micro-bend performance of each mode of the fiber is optimized.

[0044] 3. The comprehensive performance parameters such as the attenuation of the four mode groups of the fiber of the present invention are good in the application band, and the space division multiplexing technology can be used for long-distance signal transmission of the four mode groups.

[0045] 4. Compared with the existing OAM optical fibers with a large number of circular air holes in the fiber structure, the existing OAM optical fibers have complex preparation methods, difficult wire drawing, unstable fiber geometry, and it is difficult to produce long-drawn optical fibers with stable quality, which is not conducive to mass production for long-distance trunk communication. Since the present invention adopts a step-type core layer structure, the PCVD technology can be used to deposit the core rod in the preparation of the optical fiber, and then an outer sleeve is sleeved for wire drawing. The present invention is not only easy to manufacture and produce, but also reduces the production cost. It is beneficial to realize an OAM mode division multiplexing communication system with a high distance-capacity product, low implementation cost, and low complexity, and helps to upgrade the optical fiber interconnection communication system of the next-generation data center.

[0046] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the examples, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A bend-insensitive step-index orbital angular momentum optical fiber, characterized in that, It sequentially includes a central core layer, an annular core layer, an annular inner cladding layer, an annular depressed layer, an outer cladding layer, and an inner coating layer and an outer coating layer sequentially coated on the outer cladding layer; the radius r1 of the central core layer is 2.5 - 5.0 μm, and the relative refractive index difference Δ1 between the central core layer and the outer cladding layer is -0.1% - 0.1%; the radius r2 of the annular core layer is 8 - 10 μm, and the relative refractive index difference Δ2 between the annular core layer and the outer cladding layer is 0.40% - 0.75%; the radius r3 of the annular inner cladding layer is 11.0 - 12.5 μm, and the relative refractive index difference Δ3 between the annular inner cladding layer and the outer cladding layer is -0.1% - 0.1%; the radius r4 of the annular depressed layer is 13.5 - 17.0 μm, and the relative refractive index difference Δ4 between the annular depressed layer and the outer cladding layer is -0.45% - -0.35%; the diameter of the inner coating layer is 170 - 200 μm, and the diameter of the outer coating layer is 235 - 255 μm; the Young's modulus of the inner coating layer is less than 1 MPa, and the curing degree is 90% - 95%; the Young's modulus of the outer coating layer is greater than 1000 MPa, and the curing degree is 95% - 99%.

2. The bend-insensitive step-index orbital angular momentum optical fiber according to claim 1, wherein The radius r5 of the outer cladding layer is 62.0 - 62.5 μm, and the outer cladding layer is a pure silica layer.

3. The bending-insensitive step-type orbital angular momentum optical fiber according to claim 1, wherein The diameter of the inner coating layer is 180 - 190 μm, and the diameter of the outer coating layer is 240 - 250 μm.

4. The bending-insensitive step-type orbital angular momentum optical fiber according to claim 1, wherein The Young's modulus of the inner coating layer is 0.5 Mpa, and the Young's modulus of the outer coating layer is 1200 Mpa.

5. The bending-insensitive step-type orbital angular momentum optical fiber according to claim 1, wherein The bend-insensitive step-type orbital angular momentum fiber supports the propagation of 4 OAM mode groups in the C band: OAM-0 order, OAM-±1 order, OAM-±2 order, and OAM-±3 order.

6. The bending-insensitive step-type orbital angular momentum optical fiber according to claim 1, wherein At a wavelength of 1550 nm, the attenuation of each order mode of the bend-insensitive step-type orbital angular momentum fiber is less than or equal to 0.23 dB / km.

7. The bend-insensitive step-type orbital angular momentum optical fiber according to claim 1, characterized in that At a wavelength of 1550 nm, the micro-bend loss of each order mode of the bend-insensitive step-type orbital angular momentum fiber is less than or equal to 1 dB / km.

8. The bend-insensitive step-type orbital angular momentum optical fiber according to claim 1, characterized in that, At a wavelength of 1550 nm, when the bend-insensitive step-type orbital angular momentum fiber is bent 10 turns with a bending radius of R15 mm, the macro-bend loss of each order mode is equal to or less than 0.03 dB.

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