Small-size bending insensitive low-group delay multimode optical fiber and preparation method thereof

Abstract

The invention discloses a small-size bending insensitive low-group delay multimode optical fiber and a preparation method, the multimode optical fiber comprises a core layer, a transition layer, a platform layer, an isolation layer, a third sunken cladding layer, a second sunken cladding layer, a first sunken cladding layer and an outer cladding layer which are sequentially arranged from inside to outside, and the relative refractive index difference of the transition layer is-0.04% to-0.03%. The relative refractive index difference of the platform layer ranges from-0.04% to-0.03%, the relative refractive index difference of the isolation layer ranges from-0.035% to-0.03%, the relative refractive index difference of the third sunken wrapping layer ranges from-0.3% to-0.2%, the relative refractive index difference of the second sunken wrapping layer ranges from-0.8% to-0.4%, and the relative refractive index difference of the first sunken wrapping layer ranges from-0.3% to-0.2%. By reasonably designing an optical fiber structure and a doping system, transmission in ten modes is realized, optical fiber attenuation and group delay are reduced, and the bending loss resistance of the optical fiber to long and short wavelengths is enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical communications, and in particular relates to a small-size bend-insensitive low-group-delay multimode optical fiber and a preparation method thereof. Background Art

[0002] With the rapid development of various communication services, traditional single-mode optical fiber is limited by the nonlinear Shannon limit and can no longer meet the needs of more communication services. Therefore, it is urgent to develop new information transmission dimensions to meet the growing demand for communication capacity. Space division multiplexing has attracted widespread attention as a promising method to increase the capacity of optical fiber communication systems. Space division multiplexing includes mode division multiplexing (MDM) and core division multiplexing. Among them, mode division multiplexing technology is a commonly used means to expand the channel capacity in a single optical fiber. This technology usually couples multiple transmission modes in a single optical fiber to increase the number of channels and complete the expansion of communication capacity. The medium of this signal transmission method is multi-mode optical fiber that allows multiple optical fiber modes to be transmitted simultaneously, and this information transmission method generally requires large-scale multiple-input multiple-output digital signal processing MIMO DSP (Multiple in Multiple out Digital Signal Processing) to complete the entire process. In order to meet the need of the receiver to simultaneously receive these signals, optical signals of different modes transmitted through the Multiple in Multiple out method should have minimized DMD (Differential Mode Delay). Larger group delay will increase the complexity of the system receiving link. Therefore, reducing group delay must be paid attention to when designing multimode optical fiber. For mode division multiplexing, while ensuring the minimum DMD, a large number of modes will increase the mutual crosstalk capability of high-order modes, thereby increasing the group delay of the optical fiber. Therefore, when designing mode division multiplexing optical fiber, a smaller number of optical fiber modes is usually used to ensure the low crosstalk capability of the optical fiber.

[0003] In order to meet the requirement of minimizing group delay and low crosstalk between optical signals of different modes, the refractive index structure of the optical fiber core is designed to conform to the Gaussian curve distribution, further constraining the dispersion of high-order modes transmitted in the core. Through such a refractive index structure design, the efficiency of information transmission in the mode division multiplexing system is improved. At the same time, due to the large number of modes of multimode optical fiber, only a small number of modes are used to transmit optical signals, and the utilization rate of the mode and the interference between modes are serious. Therefore, when designing the refractive index profile of multimode optical fiber, a core rod with a small core diameter is generally used to reduce the number of modes of the optical fiber, so that the optical fiber has low crosstalk performance, which can improve the group delay and transmission length of the optical fiber. At present, when conventional multimode optical fiber has a small angle bend, the high-order mode transmitted near the edge of the core is easy to leak out, resulting in signal packet loss. Generally, a method of designing a low refractive index area in the optical fiber cladding is used to limit the leakage of high-order modes and reduce signal loss. In the profile design and process design of small-size bend-insensitive multimode optical fiber, the main difficulty is how to ensure the low loss, low crosstalk, DMD performance and C-band transmission capability of the optical fiber through relevant design.

[0004] In order to obtain a multimode optical fiber with low group delay and good stability, a certain concentration of one or more of germanium, fluorine, chlorine, phosphorus, etc. is usually doped into the core layer of the optical fiber preform to achieve the desired refractive index distribution of the optical fiber core layer. The type and content of the doping elements in the optical fiber core layer will affect the material dispersion of the optical fiber, thereby affecting the sensitivity of the optical fiber group delay to the wavelength. SiO2 doped with germanium has a high material dispersion. Therefore, the wavelength range corresponding to the low group delay performance of the existing multimode optical fiber with a high germanium doping content is very narrow. A small change in the wavelength of the light source will lead to a sharp drop in the group delay performance.

[0005] In the application of wavelength, the current mainstream optical fiber communication bands are divided into five parts according to the transmission loss of quartz, namely O, E, S, C, and L bands, with a wavelength range of 1260 to 1625nm, and the main research on it is currently concentrated on the C band.

[0006] Related research shows that for multimode optical fiber, the core diameter and the core maximum refractive index will affect the number of modes transmitted by the optical fiber, and the amount of doping, viscosity after doping, and core profile refractive index design will affect the optical fiber DMD and C-band group delay. Therefore, in order to make multimode optical fiber have good bending insensitivity and low group delay performance, it is necessary to optimize the doping system, viscosity ratio, and optical fiber profile structure of multimode optical fiber. Summary of the invention

[0007] In order to solve the technical problems existing in the prior art, the object of the present invention is to provide a small-size bend-insensitive low group delay multimode optical fiber and a preparation method thereof.

[0008] In order to achieve the above purpose and the above technical effect, the technical solution adopted by the present invention is:

[0009] A small-size bending-insensitive low-group-delay multimode optical fiber comprises a core layer, a transition layer, a platform layer, an isolation layer, a third depressed cladding, a second depressed cladding, a first depressed cladding and an outer cladding, which are arranged in sequence from the inside to the outside. The refractive index profile of the core layer is parabolic, and the distribution index α is 1.8-2.1. The maximum relative refractive index difference Δ1max at the center of the core layer is 0.35-0.45%, the relative refractive index difference Δ2 of the transition layer is -0.04%-0.03%, the relative refractive index difference of the platform layer is -0.04%-0.03%, the relative refractive index difference of the isolation layer is -0.035%-0.03%, the relative refractive index difference Δ4 of the third depressed cladding is -0.3%-0.2%, the relative refractive index difference Δ5 of the second depressed cladding is -0.8%-0.4%, and the relative refractive index difference of the first depressed cladding is -0.3%-0.2%.

[0010] Furthermore, the radius R2 of the transition layer differs from the radius R1 of the core layer by 0.2-0.5 μm.

[0011] Furthermore, the radius R3 of the platform layer differs from the radius R2 of the transition layer by 1 to 2 μm.

[0012] Furthermore, the radius R4 of the isolation layer differs from the radius R3 of the platform layer by 1 to 2 μm.

[0013] Furthermore, the radius R5 of the third depressed cladding layer differs from the radius R4 of the isolation layer by 1 to 2 μm.

[0014] Furthermore, a radius R6 of the second depressed cladding differs from a radius R5 of the third depressed cladding by 3 to 6 μm.

[0015] Furthermore, a radial width R7 of a single side of the first depressed cladding differs from a radius R6 of the second depressed cladding by 1 to 3 μm.

[0016] Furthermore, the radius R1 of the core layer is 14-16 μm, the highest relative refractive index of the core layer is 0.35%-0.45%, the lowest relative refractive index is 0%, and the relative refractive index of the core layer gradually decreases from 0.35%-0.45% to 0%.

[0017] Furthermore, the small-size bend-insensitive low group delay multimode optical fiber can transmit in ten modes, and the ten transmission modes are: LP01, LP11a, LP12a, LP11b, LP12b, LP02, LP31a, LP21a, LP31b and LP21b.

[0018] The present invention also discloses a method for preparing a small-size bend-insensitive low-group-delay multimode optical fiber, comprising the following steps:

[0019] S1, preparing the core layer by reduced pressure plasma chemical vapor deposition method:

[0020] S2, using a plasma chemical vapor deposition method to prepare a transition layer, a platform layer, an isolation layer, a third depressed blanket, a second depressed blanket, and a first depressed blanket respectively;

[0021] S3, preparing the outer cladding;

[0022] S4, combining the core layer, transition layer, platform layer, isolation layer, third depressed cladding, second depressed cladding, first depressed cladding and outer cladding to form an optical fiber preform;

[0023] S5, drawing the optical fiber preform to obtain the small-size bend-insensitive low group delay multimode optical fiber.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention discloses a small-size bending-insensitive low-group-delay multimode optical fiber and a preparation method thereof. By rationally designing the optical fiber structure and doping system, the number of available modes is optimized, transmission in ten modes is achieved, mode dispersion is reduced, and thus the group delay of the optical fiber is reduced. At the same time, the optical fiber viscosity is optimized. By designing the platform layer and the isolation layer, the stress and viscosity between the sunken cladding layer and the core layer can form continuity, and the mutation area is eliminated, thereby reducing the optical fiber attenuation and the group delay of the optical fiber, and reducing the sensitivity of the optical fiber group delay to the wavelength, so that the optical fiber has good anti-bending performance and low delay performance. By designing three layers of depressed cladding, namely the third depressed cladding, the second depressed cladding and the first depressed cladding, the optical fiber is able to enhance its resistance to bending loss at long and short wavelengths. The additional bending loss caused by winding the multimode optical fiber twice with a bending radius of 7.5 mm at a wavelength of 850 nm is less than 0.2 dB, and the additional bending loss caused by winding the multimode optical fiber twice with a bending radius of 7.5 mm at a wavelength of 1550 nm is less than 0.5 dB. The maximum differential mode delay is less than 37.76 ps / km, and at a wavelength of 1550 nm, based on MFMP (mirror flip mode arrangement), the transmission distance can reach 3000 km. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of a refractive index profile of the present invention;

[0027] Figure 2 It is a schematic diagram of the fluorine doping amount of the present invention. DETAILED DESCRIPTION

[0028] The present invention is described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0029] A brief summary of one or more aspects is given below to provide a basic understanding of these aspects. This summary is not an exhaustive overview of all conceived aspects, and is neither intended to identify the key or critical elements of all aspects nor to define the scope of any or all aspects. Its only purpose is to give some concepts of one or more aspects in a simplified form as a prelude to a more detailed description that will be given later.

[0030] like Figure 1-2 As shown, a small-size bend-insensitive low-group-delay multimode optical fiber comprises a core layer, a transition layer, a platform layer, an isolation layer, a third depressed cladding, a second depressed cladding, a first depressed cladding and an outer cladding arranged in sequence from the inside to the outside. The refractive index profile of the core layer is parabolic, the distribution index α is 1.8 to 2.1, the maximum relative refractive index difference Δ1max at the center of the core layer is 0.35 to 0.45%, and the radius R1 of the core layer is 14 to 16 μm; the relative refractive index difference Δ2 of the transition layer is -0.04% to -0.03%, and the radius R2 of the transition layer differs from the radius R1 of the core layer by 0.2 to 0.5 μm; the relative refractive index difference of the platform layer is -0.04% to -0.03%, and the radius R3 of the platform layer differs from the radius R2 of the transition layer by 1 to 2 μm; the relative refractive index difference Δ3 of the isolation layer is -0.035% to -0.03%, and the radius R2 of the isolation layer is 0.2 to 0.5 μm. The radius R4 differs from the radius R3 of the platform layer by 1 to 2 μm; the relative refractive index difference Δ4 of the third depressed cladding is -0.3% to -0.2%, and the radius R5 of the third depressed cladding differs from the radius R4 of the isolation layer by 1 to 2 μm; the relative refractive index difference Δ5 of the second depressed cladding is -0.8% to -0.4%, and the radius R6 of the second depressed cladding differs from the radius R5 of the third depressed cladding by 3 to 6 μm; the single-side radial width R7 of the first depressed cladding differs from the radius R6 of the second depressed cladding by 1 to 3 μm, the relative refractive index difference of the first depressed cladding is -0.3% to -0.2%, and the radius R8 of the outer cladding is 62 μm to 63 μm.

[0031] The highest relative refractive index of the core layer is 0.35% to 0.45%, the lowest relative refractive index is 0%, and the relative refractive index of the core layer gradually decreases from 0.35% to 0.45% to 0%.

[0032] The highest relative refractive index of the transition layer is 0%, the lowest relative refractive index is -0.04% to -0.03%, and the relative refractive index of the transition layer gradually decreases from 0% to -0.04% to -0.03%.

[0033] The core layer and the transition layer are both silica glass layers doped with fluorine, chlorine and germanium.

[0034] The platform layer, the isolation layer, the third depressed cladding, the second depressed cladding and the first depressed cladding are all silicon dioxide glass layers doped with fluorine and chlorine elements.

[0035] The outer cladding is a pure silica glass layer.

[0036] The multimode optical fiber disclosed in the present invention can transmit in more than ten modes, and the transmission wavelength is 1535nm-1570nm in the C band. The ten transmission modes are: LP01, LP11a, LP12a, LP11b, LP12b, LP02, LP31a, LP21a, LP31b and LP21b.

[0037] The multimode optical fiber disclosed in the present invention has an additional bending loss of less than 0.2 dB caused by winding two turns with a bending radius of 7.5 mm at a wavelength of 850 nm; an additional bending loss of less than 0.5 dB caused by winding two turns with a bending radius of 7.5 mm at a wavelength of 1550 nm, and a maximum differential mode delay of less than 37.76 ps / km. The multimode optical fiber of the present invention has a transmission distance of up to 3000 km at a wavelength of 1550 nm based on MFMP (mirror flip mode arrangement).

[0038] The present invention is directed to wavelength λ∈[λC-Δλ;λC+Δλ], Max|DMD link|<37.76ps / km, wherein λC is the central transmission wavelength of the desired working band of the optical fiber, 2Δλ (the fluctuation range of wavelength λ∈[λC-Δλ;λC+Δλ]) is the width of the working band, and Max|DMD link| is the absolute maximum value of the differential mode group delay between any combination of guided modes. λC=1550nm and Δλ=15nm. The present invention is in the 1530~1565nm band, Max|DMD link|<37.76ps / km.

[0039] In order to obtain a multimode optical fiber with low group delay and good stability, the core refractive index profile of the multimode optical fiber needs to be designed to have a refractive index distribution that continuously and gradually decreases from the center to the edge, that is, the refractive index distribution of the following power exponential function:

[0040]

[0041] Where n(0) is the refractive index of the optical fiber axis, r is the distance from the optical fiber axis, a is the radius of the optical fiber core, r<a, α is the distribution index, and Δ is the refractive index of the core center relative to the cladding.

[0042] In order to balance the stress and viscosity of the core layer and the depressed cladding, a platform layer is designed between the core layer and the depressed cladding. Since the stress between the core layer and the depressed cladding varies with the radius during the drawing process of multimode optical fiber, and considering the different dopants in the optical fiber, the platform layer will deform after drawing. Therefore, the deformation amount of the platform layer is preset when designing the optical fiber. The relative refractive index change of the optical fiber cannot be a constant value. A platform layer with a fixed relative refractive index and an isolation layer with a relative refractive index inclined upward are designed.

[0043] In order to improve the ability of optical fiber to resist macrobending loss, three depressed claddings, namely the third depressed cladding, the second depressed cladding and the first depressed cladding, are designed between the isolation layer and the outer cladding. Among them, the third depressed cladding and the first depressed cladding can improve the ability of optical fiber to resist bending loss for short wavelengths, and the second depressed cladding reduces the refractive index by doping fluorine and other dopants, which can improve the ability of optical fiber to resist bending loss for long wavelengths.

[0044] The present invention also discloses a method for preparing a small-size bend-insensitive low-group-delay multimode optical fiber, comprising the following steps:

[0045] S1, using reduced pressure plasma chemical vapor deposition method to prepare the core layer doped with fluorine, chlorine and germanium:

[0046] S2, using a plasma chemical vapor deposition method to prepare a transition layer, a platform layer, an isolation layer, a third depressed blanket, a second depressed blanket, and a first depressed blanket respectively;

[0047] S3, preparing the outer cladding;

[0048] S4, combining the core layer, transition layer, platform layer, isolation layer, third depressed cladding, second depressed cladding, first depressed cladding and outer cladding to form an optical fiber preform;

[0049] S5, drawing the optical fiber preform to obtain the small-size bend-insensitive low group delay multimode optical fiber.

[0050] Example 1

[0051] like Figure 1-2As shown, a small-size bend-insensitive low group delay multimode optical fiber includes a core layer, a transition layer, a platform layer, an isolation layer, a third depressed cladding, a second depressed cladding, a first depressed cladding and an outer cladding arranged in sequence from the inside to the outside. The refractive index profile of the core layer is parabolic, the distribution index α is 2, the maximum relative refractive index difference Δ1max at the center of the core layer is 0.4%, the radius R1 of the core layer is 14μm, fluorine and germanium are co-doped in the transition layer, the radius R2 of the transition layer differs from the radius R1 of the core layer by 0.4μm, that is, R2-R1=0.4μm, the minimum relative refractive index difference Δ2 of the transition layer is -0.035%, and the maximum relative refractive index difference is 0%, the radius R3 of the platform layer differs from the radius R2 of the transition layer by 1.5μm, that is, R3-R2=1.5μm, the relative refractive index difference of the platform layer is -0.035%, fluorine is doped in the isolation layer, and its minimum relative refractive index difference is -0.035%, and the maximum relative refractive index difference is -0.03 2%, the radius R4 of the isolation layer differs from the radius R3 of the platform layer by 1.2μm, that is, R4-R3=1.2μm, the relative refractive index difference Δ4 of the third depressed cladding is -0.25%, the radius R5 of the third depressed cladding differs from the radius R4 of the isolation layer by 1.2μm, that is, R5-R4=1.2μm, the relative refractive index difference Δ5 of the second depressed cladding is -0.6%, the radius R6 of the second depressed cladding differs from the radius R5 of the third depressed cladding by 6μm, that is, R6-R5=6μm, the single-sided radial width R7 of the first depressed cladding differs from the radius R6 of the second depressed cladding by 1.2μm, that is, R7-R6=1.2μm, the relative refractive index difference of the first depressed cladding is -0.25%, and the radius R8 of the outer cladding is 62μm.

[0052] The performance test of Example 1 was carried out, and the results are shown in Table 1.

[0053] Table 1

[0054]

[0055]

[0056] It can be seen from Table 1 that the multimode optical fiber disclosed in Example 1 can transmit in more than ten modes, the transmission wavelength is C band 1535nm-1570nm, and the ten transmission modes are: LP01, LP11a, LP12a, LP11b, LP12b, LP02, LP31a, LP21a, LP31b and LP21b.

[0057] The multimode optical fiber disclosed in Example 1 has an additional bending loss of less than 0.2 dB at 850 nm wavelength with a bending radius of 7.5 mm for two turns; and an additional bending loss of less than 0.5 dB at 1550 nm wavelength with a bending radius of 7.5 mm for two turns, and a maximum differential mode delay of less than 37.76 ps / km. The transmission distance of the multimode optical fiber at 1550 nm wavelength can reach 3000 km based on MFMP (mirror flip mode arrangement).

[0058] A method for preparing a small-size bend-insensitive low-group-delay multimode optical fiber comprises the following steps:

[0059] S1, using reduced pressure plasma chemical vapor deposition method to prepare the core layer doped with fluorine, chlorine and germanium:

[0060] Specifically, SiCl4, GeCl4, CF4, and O2 are used as raw materials, and a core rod (i.e., a core layer) having a maximum relative refractive index difference Δ1max of 0.4% and a distribution index α of 2 is prepared by deposition and melting;

[0061] S2, using a plasma chemical vapor deposition method to prepare a transition layer, a platform layer, an isolation layer, a third depressed blanket, a second depressed blanket, and a first depressed blanket respectively;

[0062] S3, using commercially purchased liner and casing to prepare the outer cladding;

[0063] S4, combining the core layer, transition layer, platform layer, isolation layer, third depressed cladding, second depressed cladding, first depressed cladding and outer cladding to form an optical fiber preform;

[0064] S5, drawing the optical fiber preform to obtain the small-size bend-insensitive low group delay multimode optical fiber.

[0065] Parts or structures not specifically described in the present invention may adopt existing technologies or existing products and will not be described in detail here.

[0066] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A small-size bend-insensitive low group delay multimode optical fiber, characterized in that: The invention comprises a core layer, a transition layer, a platform layer, an isolation layer, a third depressed cladding, a second depressed cladding, a first depressed cladding and an outer cladding, which are arranged in sequence from the inside to the outside. The refractive index profile of the core layer is parabolic, and the distribution index α is 1.8-2.

1. The maximum relative refractive index difference Δ1max at the center of the core layer is 0.35-0.45%, the relative refractive index difference Δ2 of the transition layer is -0.04%-0.03%, the relative refractive index difference of the platform layer is -0.04%-0.03%, the relative refractive index difference Δ3 of the isolation layer is -0.035%-0.03%, the relative refractive index difference Δ4 of the third depressed cladding is -0.3%-0.2%, the relative refractive index difference Δ5 of the second depressed cladding is -0.8%-0.4%, and the relative refractive index difference of the first depressed cladding is -0.3%-0.2%.

2. A small-size bend-insensitive low group delay multimode optical fiber according to claim 1, characterized in that: The radius R2 of the transition layer differs from the radius R1 of the core layer by 0.2 to 0.5 μm.

3. The small-size bend-insensitive low group delay multimode optical fiber according to claim 1, characterized in that: The radius R3 of the platform layer differs from the radius R2 of the transition layer by 1 to 2 μm.

4. The small-size bend-insensitive low group delay multimode optical fiber according to claim 1, characterized in that: The radius R4 of the isolation layer differs from the radius R3 of the platform layer by 1 to 2 μm.

5. The small-size bend-insensitive low group delay multimode optical fiber according to claim 1, characterized in that: The radius R5 of the third depressed cladding layer differs from the radius R4 of the isolation layer by 1 to 2 μm.

6. The small-size bend-insensitive low group delay multimode optical fiber according to claim 1, characterized in that: The radius R6 of the second depressed cladding differs from the radius R5 of the third depressed cladding by 3-6 μm.

7. The small-size bend-insensitive low group delay multimode optical fiber according to claim 1, characterized in that: The radial width R7 of the first depressed cladding and the radius R6 of the second depressed cladding differ by 1 to 3 μm.

8. The small-size bend-insensitive low group delay multimode optical fiber according to claim 1, characterized in that: The radius R1 of the core layer is 14-16 μm, the highest relative refractive index of the core layer is 0.35%-0.45%, the lowest relative refractive index is 0%, and the relative refractive index of the core layer gradually decreases from 0.35%-0.45% to 0%.

9. The small-size bend-insensitive low group delay multimode optical fiber according to claim 1, characterized in that: The small-size bend-insensitive low group delay multimode optical fiber can transmit in ten modes, and the ten mode transmission modes are: LP01, LP11a, LP12a, LP11b, LP12b, LP02, LP31a, LP21a, LP31b and LP21b.

10. A method for preparing a small-size bend-insensitive low-group-delay multimode optical fiber, characterized in that: The following steps are involved: S1, preparing the core layer by reduced pressure plasma chemical vapor deposition method: S2, using a plasma chemical vapor deposition method to prepare a transition layer, a platform layer, an isolation layer, a third depressed blanket, a second depressed blanket, and a first depressed blanket respectively; S3, preparing the outer cladding; S4, combining the core layer, transition layer, platform layer, isolation layer, third depressed cladding, second depressed cladding, first depressed cladding and outer cladding to form an optical fiber preform; S5, drawing the optical fiber preform to obtain the small-size bend-insensitive low group delay multimode optical fiber.

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