Multi-core optical fiber
By designing a tangent prefabricated optical fiber and a sub-clad structure with refractive index gradient in multi-core optical fiber, the interference and continuity loss problems caused by the reflection of optical signals to the core layer are solved, and the effective constraints of optical signals and the improvement of transmission distances are achieved. .
Patent Information
- Application Number
- CN202421174838.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-05-27
- Publication Date
- 2025-02-18
- Estimated Expiration
- 2034-05-27
AI Technical Summary
In the multi-core optical fiber, the optical signal is reflected to the core layer, causing interference and errors in the core layer's optical signal, and the large core spacing leads to continuous loss.
A multi-core optical fiber structure is designed in which the outer peripheral surfaces of two adjacent prefabricated optical fibers are tangent to form a core spacing of 0, and a refractive index gradient is set in the outer cladding and multiple sub-clad layers to achieve total reflection and binding of the optical signal.
It effectively reduces the crosstalk of optical signals to other cores, reduces signal loss, and increases the transmission distance of optical signals in the core layer.
Smart Images
Figure CN222506600U_ABST
Abstract
Description
Technical Field
[0001] The utility model relates to the technical field of optical fibers, in particular to a multi-core optical fiber. Background Art
[0002] The optical fiber structure consists of a core, cladding, and coating. The refractive index of the core is greater than that of the cladding. The optical signal is transmitted by total reflection in the core. However, due to factors such as the purity and microbending of the core, part of the optical signal will be refracted and penetrate into the cladding, causing optical signal attenuation. Multi-core optical fiber is a space-division multiplexing optical fiber with multiple independent single-mode cores in a common cladding area. It is divided into strongly coupled multi-core optical fiber and weakly coupled multi-core optical fiber according to the core spacing.
[0003] Due to the refraction and penetration of optical signals, the signal entering the cladding will enter other fiber cores, causing interference with the optical signals in other fiber cores, causing bit errors and poor communication network quality. However, if low signal crosstalk is achieved by setting a sunken cladding structure, the signal will be reflected back into the fiber core, affecting the signal in the fiber core, causing the fiber core signal to be strengthened or offset, and due to the large core spacing of multi-core optical fibers, splicing losses will occur. Utility Model Content
[0004] The purpose of the utility model is to provide a multi-core optical fiber to achieve the confinement of the optical signal in the core layer, to solve the problem of the optical signal being reflected into the core layer and interfering with the optical signal in the core layer, and to achieve a core spacing of 0 for the multi-core optical fiber, thereby reducing the splicing loss of the optical signal.
[0005] In order to achieve the above object, the utility model provides a multi-core optical fiber, comprising:
[0006] A plurality of prefabricated optical fibers and an outer cladding, wherein the outer circumferential surfaces of two adjacent prefabricated optical fibers are tangent to each other, and the outer cladding is coated on the surfaces of the plurality of prefabricated optical fibers;
[0007] The prefabricated optical fiber comprises a core layer and a cladding layer coated on the surface of the core layer, and the refractive index of the core layer is higher than the refractive index of the cladding layer;
[0008] The cladding includes a plurality of sub-claddings arranged in sequence from the inside to the outside, the refractive index of the sub-cladding located on the inside and the refractive index of the sub-cladding located on the outside are both smaller than the refractive index of the sub-cladding located in the middle, the sub-cladding located on the inside is in contact with the core layer, and the number of the sub-claddings is at least three.
[0009] Compared with the prior art, the multi-core optical fiber provided by the utility model includes multiple prefabricated optical fibers and an outer cladding, wherein the outer circumferences of two adjacent prefabricated optical fibers are tangent to each other, which makes the core spacing between the two adjacent prefabricated optical fibers 0, which is beneficial to reducing the splicing loss of optical signals. The outer cladding provided by the utility model is coated on the surface of multiple prefabricated optical fibers, and the outer cladding can protect the multiple prefabricated optical fibers it coats, thereby extending the service life of the prefabricated optical fibers.
[0010] In addition, the prefabricated optical fiber provided by the utility model includes a core layer and a cladding layer coated on the surface of the core layer, and the refractive index of the core layer is higher than the refractive index of the cladding layer, so that the optical signal continuously generates total reflection at the interface between the core layer and the cladding layer, which is beneficial to confine the optical signal in the core layer, can reduce signal loss, and increase the transmission distance of the optical signal in the core layer. Because the refractive index of the sub-cladding layer located on the inner side and the refractive index of the sub-cladding layer located on the outer side are both smaller than the refractive index of the sub-cladding layer located in the middle part, and the sub-cladding layer located on the inner side is in contact with the core layer. Based on this, in the process of the optical signal refracting from the core layer into the cladding layer, the optical signal will first refract from the core layer to the sub-cladding layer located on the inner side. At this time, due to factors such as the purity and micro-bending of the core layer, a part of the optical signal can pass through the sub-cladding layer located on the inner side, and be reflected into the core layer at the interface between the sub-cladding layer located on the inner side and the sub-cladding layer located in the middle part, while another part of the optical signal will then be refracted into the sub-cladding layer located in the middle part. Since the refractive index of the inner subcladding is lower than that of the middle subcladding, part of the optical signal refracted to the middle subcladding can pass through the middle subcladding and be reflected back to the core layer at the interface between the middle subcladding and the outer subcladding, thereby reducing the attenuation of the optical signal to a certain extent, while the other part of the optical signal will then be refracted to the outer subcladding. Since the refractive index of the middle subcladding is higher than that of the outer subcladding, the optical signal refracted to the outer subcladding can be totally reflected and re-enter the core layer, thereby achieving the confinement of the optical signal in the core layer, reducing the crosstalk of the optical signal to other prefabricated optical fibers, reducing signal loss, and increasing the transmission distance of the optical signal in the core layer. It is worth noting that the number of sub-claddings in the present invention is at least three. As the number of sub-claddings increases, the probability that the light signal refracted from the core layer to the cladding is re-reflected to the core layer becomes higher. That is to say, when the number of sub-claddings is at least three, the probability of total reflection of the light signal at the interface between the core layer and the cladding can be significantly increased.
[0011] At the same time, in the process of the optical signal being refracted from the inner sub-cladding to the middle sub-cladding, the optical signal reflected from the middle sub-cladding back to the core layer can be superimposed on or offset with the optical signal reflected from the inner sub-cladding back to the core layer, and in the process of the optical signal being refracted from the middle sub-cladding to the outer sub-cladding, the optical signal reflected from the outer sub-cladding back to the core layer can be superimposed on or offset with the optical signal reflected from the inner sub-cladding back to the core layer, thereby increasing the transmission distance of the optical signal and solving the problem of the optical signal being reflected into the core layer and interfering with the optical signal of the core layer. BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings:
[0013] Figure 1 A schematic structural diagram of a multi-core optical fiber provided in this embodiment is shown.
[0014] Description of reference numerals:
[0015] 100-prefabricated optical fiber; 101-core layer; 102-cladding; 1021-inner sub-cladding; 1022-middle sub-cladding; 1023-outer sub-cladding; 200-outer cladding; 300-coating; a Tangent point between two adjacent prefabricated optical fibers. DETAILED DESCRIPTION
[0016] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.
[0017] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present utility model, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. The meaning of "several" is one or more, unless otherwise clearly and specifically defined.
[0018] It should be noted that the modifications of "one" and "plurality" mentioned in the present disclosure are illustrative rather than restrictive, and those skilled in the art should understand that unless otherwise clearly indicated in the context, it should be understood as "one or more".
[0019] In view of the problem that when low signal crosstalk is achieved by setting a depressed cladding structure in the prior art, the optical signal is reflected into the core layer and interferes with the core layer signal. The embodiment of the utility model provides a multi-core optical fiber to achieve the confinement of the optical signal in the core layer, which can solve the problem that the optical signal is reflected into the core layer and interferes with the optical signal in the core layer, and can also achieve a core spacing of 0 for the multi-core optical fiber, thereby reducing the connection loss of the optical signal. Figure 1 FIG. 2 shows a schematic diagram of the structure of the multi-core optical fiber provided in this embodiment. Figure 1 As shown, the multi-core optical fiber includes a plurality of prefabricated optical fibers 100 and an outer cladding 200 . The outer circumferences of two adjacent prefabricated optical fibers 100 are tangent to each other, and the outer cladding 200 is coated on the surfaces of the plurality of prefabricated optical fibers 100 .
[0020] The prefabricated optical fiber 100 includes a core layer 101 and a cladding layer 102 coated on the surface of the core layer, and the refractive index of the core layer 101 is higher than the refractive index of the cladding layer 102. The cladding layer 102 includes a plurality of sub-cladding layers sequentially coated from the inside to the outside, wherein the refractive index of the sub-cladding layer 1021 located on the inside and the refractive index of the sub-cladding layer 1023 located on the outside are both smaller than the refractive index of the sub-cladding layer 1022 located in the middle, and the sub-cladding layer 1021 located on the inside contacts the core layer 101, and the number of the sub-cladding layers is at least three.
[0021] It is understandable that if Figure 1 As shown, the outer cladding 200 in the embodiment of the utility model can protect the multiple prefabricated optical fibers 100 covered thereon and prolong the service life of the prefabricated optical fibers 100. The outer circumferences of two adjacent prefabricated optical fibers 100 are tangent to each other, and the tangent point of the two adjacent prefabricated optical fibers 100 is a, which makes the core spacing of the two adjacent prefabricated optical fibers 100 0, which is beneficial to reduce the splicing loss of the optical signal.
[0022] In addition, the refractive index of the core layer 101 provided by the utility model is higher than that of the cladding layer 102, so that the optical signal constantly generates total reflection at the interface between the core layer 101 and the cladding layer 102, which is beneficial to confine the optical signal in the core layer 101, reduce the loss of the optical signal, and increase the transmission distance of the optical signal in the core layer 101. Since the inner sub-cladding layer 1021 is in contact with the core layer 101, in the process of the optical signal being refracted from the core layer 101 into the cladding layer 102, the optical signal will first be refracted from the core layer 101 to the inner sub-cladding layer 1021. At this time, due to factors such as the purity and microbend of the core layer 101, a part of the optical signal can pass through the inner sub-cladding layer 1021 and be reflected into the core layer 101 at the interface between the inner sub-cladding layer 1021 and the middle sub-cladding layer 1022, while another part of the optical signal will then be refracted into the middle sub-cladding layer 1022. Since the refractive index of the inner sub-cladding 1021 is lower than that of the middle sub-cladding 1022, a portion of the optical signal refracted to the middle sub-cladding 1022 can pass through the middle sub-cladding 1022 and be reflected back to the core layer 101 at the interface between the middle sub-cladding 1022 and the outer sub-cladding 1023, thereby reducing the attenuation of the optical signal to a certain extent, while another portion of the optical signal will then be refracted to the outer sub-cladding 1023. Since the refractive index of the middle sub-cladding 1022 is higher than that of the outer sub-cladding 1023, the optical signal refracted to the outer sub-cladding 1023 can be totally reflected and re-enter the core layer 101, thereby achieving the confinement of the optical signal in the core layer 101, reducing the crosstalk of the optical signal to other prefabricated optical fibers 100, reducing the signal loss, and increasing the transmission distance of the optical signal in the core layer 101. It is worth noting that the number of sub-claddings in the present invention is at least three. As the number of sub-claddings increases, the probability that the light signal refracted from the core layer to the cladding is re-reflected to the core layer increases. That is to say, when the number of claddings is at least three, the probability of total reflection of the light signal at the interface between the core layer and the cladding can be significantly increased.
[0023] At the same time, in the process of the optical signal being refracted from the inner sub-cladding 1021 to the middle sub-cladding 1022, the optical signal reflected from the middle sub-cladding 1022 back into the core layer 101 can be superimposed on or offset with the optical signal reflected from the inner sub-cladding 1021 back into the core layer 101, and in the process of the optical signal being refracted from the middle sub-cladding 1022 to the outer sub-cladding 1023, the optical signal reflected from the outer sub-cladding 1023 back into the core layer 101 can be superimposed on or offset with the above-mentioned two sections of optical signals reflected into the core layer 101, thereby increasing the transmission distance of the optical signal and solving the problem of the optical signal being reflected into the core layer 101 and interfering with the optical signal of the core layer 101.
[0024] Exemplarily, taking the number of sub-claddings as three as an example: the cladding includes a first cladding, a second cladding, and a third cladding arranged in sequence from the inside to the outside.
[0025] When the optical signal of the core layer is refracted into the first cladding, a part of the optical signal can be reflected from the interface between the first cladding and the second cladding to the core layer, while the other part of the optical signal will then be refracted into the second cladding. Since the refractive index of the first cladding is less than that of the second cladding, a part of the optical signal refracted into the second cladding can be reflected back into the core layer from the interface between the second cladding and the third cladding. This part of the optical signal can be superimposed or offset with the optical signal reflected from the first cladding back into the core layer, thereby reducing the interference of the reflected optical signal on the optical signal of the core layer to a certain extent, while the other part of the optical signal will then be refracted into the third cladding. Since the refractive index of the second cladding is greater than that of the third cladding, the optical signal refracted into the third cladding can be totally reflected, thereby realizing the binding of the optical signal in the core layer, reducing the crosstalk of the optical signal to other prefabricated optical fibers, reducing signal loss, and increasing the transmission distance of the optical signal in the core layer. The totally reflected optical signal can be superimposed or offset with the optical signal reflected from the two claddings (i.e., the first cladding and the second cladding) back to the core layer, thereby solving the problem of the optical signal reflected into the core layer interfering with the core layer signal.
[0026] Assuming that the number of claddings is 4 and the optical signal entering the cladding is a quarter wavelength, the cladding includes the first cladding, the second cladding, the third cladding and the fourth cladding, which are sequentially arranged from the inside to the outside. When the optical signal of a quarter wavelength is refracted from the core layer into the first cladding, a part of the optical signal can be reflected from the interface between the first cladding and the second cladding to the core layer, and the reflected light of this part is the first reflected light, while the other part of the optical signal of a quarter wavelength will be refracted into the second cladding c. Since the refractive index of the first cladding is less than the refractive index of the second cladding, a part of the optical signal refracted into the second cladding can be reflected from the interface between the second cladding and the third cladding and return to the core layer, and the reflected light of this part is the second reflected light. The second reflected light can be superimposed or offset with the first reflected light, thereby reducing the interference of the reflected optical signal on the optical signal of the core layer to a certain extent, and the other part of the optical signal of a quarter wavelength will then be refracted into the third cladding. Since the refractive index of the second cladding is greater than that of the third cladding, the optical signal refracted to the third cladding can be totally reflected at the interface between the third cladding and the fourth cladding, and the reflected light of this part is the third reflected light. The third reflected light, the second reflected light and the first reflected light can be superimposed or offset. If part of the optical signal fails to be totally reflected due to factors such as the purity and microbending of the third cladding, at this time, this part of the quarter-wavelength optical signal will be refracted into the fourth cladding. Since the refractive index of the third cladding is less than that of the fourth cladding, this part of the optical signal is reflected back to the core layer, thereby achieving the binding of the optical signal in the core layer, reducing the crosstalk of the optical signal to other prefabricated optical fibers, reducing signal loss, and increasing the transmission distance of the optical signal in the core layer. In this process, the optical signal reflected from the first cladding to the fourth cladding to the core layer can be superimposed or offset, thereby solving the problem of the optical signal reflecting into the core layer interfering with the core layer signal.
[0027] Specifically, when the first reflected light corresponds to the peak of the optical signal, if the second reflected light corresponds to the peak of the optical signal, the peaks of the two optical signals can be superimposed; if the second reflected light corresponds to the trough of the optical signal, the two optical signals will cancel each other out.
[0028] When the first reflected light corresponds to the peak of the optical signal, and the second reflected light corresponds to the peak of the optical signal, if the third reflected light corresponds to the peak of the optical signal, the three optical signals can be superimposed; if the third reflected light corresponds to the trough of the optical signal, a part of the optical signal can be offset, that is, the optical signal is the first reflected light + the second reflected light - the third reflected light. It should be understood that there are many other superposition and offset situations for the first reflected light, the second reflected light and the third reflected light, which can be adjusted according to actual conditions and are not limited here.
[0029] It can be understood that the refractive index of the inner subcladding is equal to the refractive index of the outer subcladding, and when the number of subcladdings is greater than three, the refractive index of each subcladding in the middle is equal. In other words, the refraction degree and transmission speed of each optical signal in the inner subcladding are the same as those in the outer subcladding, and the refraction degree and transmission speed of each optical signal in the middle subcladding are the same. It is not only easy to select the corresponding dielectric film as the material source of the inner subcladding and the outer subcladding, but also easy to control the optical signal refracted into the inner subcladding, the outer subcladding or the middle subcladding. It should be understood that the specific control method can be adjusted according to actual conditions and is not limited here.
[0030] In an optional manner, the radius of the core layer in the embodiment of the utility model is 4-5μm, and the thickness of each sub-cladding is 1.26-1.625μm. When the radius of the core layer is 4-5μm, the transmission rate of the optical signal is high, and the propagation distance in the core layer is relatively long. The thickness of each sub-cladding in the embodiment of the utility model is 1.26-1.625μm: when the thickness of the inner sub-cladding is 1.26-1.625μm, it can meet the requirement that when the optical signal in the core layer is refracted to the sub-cladding, part of the optical signal can be re-reflected into the core layer, reducing the attenuation of the optical signal. When the thickness of the outer sub-cladding is 1.26-1.625μm, it can increase the probability of the optical signal refracted to the outer sub-cladding being totally reflected into the core layer, reducing the attenuation of the optical signal. If the thickness of the inner sub-cladding is less than 1.26μm, the propagation distance of the optical signal is too small, and it is not easy to be reflected into the core layer at the interface between the inner sub-cladding and the middle sub-cladding. If the thickness of the inner sub-cladding is greater than 1.625 μm, the propagation distance of the optical signal is too large, and it is also difficult to be reflected into the core layer at the interface between the inner sub-cladding and the middle sub-cladding. Since the refractive index of the inner sub-cladding and the outer sub-cladding are both smaller than the refractive index of the middle sub-cladding, the transmission speed of the optical signal refracted to the middle sub-cladding is slower. When the thickness of the middle sub-cladding is 1.26-1.625 μm, it is easier to control the transmission speed of the optical signal in the middle sub-cladding.
[0031] In addition, the material source of the core layer can be selected from glass, glass-resin composite materials, glass-metal composite materials or dopant-modified glass. Among them, the glass-resin composite material can be selected from glass-olefin resin composite materials, glass-epoxy resin composite materials or glass-phenolic resin composite materials; the glass-metal composite material can be selected from glass-alkali metal (e.g., sodium and potassium) composite materials or glass-alkaline earth metal (e.g., magnesium and calcium) composite materials. The dopant can include at least one of cerium dioxide, phosphorus pentoxide and germanium dioxide. The material source of the inner sub-cladding and the material source of the outer sub-cladding can both be selected from at least one of polytetrafluoroethylene, graphene, glass fiber reinforced plastic and polyester fiber film, and the material source of the middle sub-cladding can be selected from at least one of doped silicon dioxide, carbon-doped silicon dioxide, polyimide and polyparaxylene. And during use, the relative refractive index of the inner sub-cladding and the middle sub-cladding should be kept consistent. Similarly, the relative refractive index of the outer sub-cladding and the middle sub-cladding should also be kept consistent.
[0032] In an optional manner, the refractive index of the outer cladding in the embodiment of the utility model is equal to the refractive index of the sub-cladding located in the middle. Based on this, when the number of sub-claddings is three, and the optical signal refracted from the sub-cladding located in the middle to the sub-cladding located on the outside cannot be totally reflected, at this time, the optical signal that has not been totally reflected will be refracted into the outer cladding coated on the surface of the prefabricated optical fiber. Since the refractive index of the outer cladding is equal to the refractive index of the sub-cladding located in the middle, and the refractive index of the outer cladding is greater than the refractive index of the sub-cladding located on the outside, this part of the optical signal is reflected back to the core layer, thereby achieving the binding of the optical signal in the core layer, reducing the crosstalk of the optical signal to other prefabricated optical fibers, reducing signal loss, and increasing the transmission distance of the optical signal in the core layer. In this process, the optical signals from the outer cladding and the sub-cladding to the core layer can be superimposed or offset, thereby solving the problem of the optical signal reflecting into the core layer interfering with the core layer signal. It can be seen that the outer cladding in the embodiment of the utility model can not only prevent external electromagnetic interference and is not easily destroyed by external forces, but also ensure that the optical signal is fully reflected into the core layer, reduce the crosstalk of the optical signal to other prefabricated optical fibers, reduce signal loss, and increase the transmission distance of the optical signal in the core layer.
[0033] Exemplarily, the material source of the outer cladding in the embodiment of the utility model includes at least one of polyethylene, polyurethane and carbon fiber composite material, and the thickness thereof is 54 to 71 μm. Within this range, not only the anti-electromagnetic clutter interference and wear resistance of the outer cladding can be ensured, but also the refractive index of the outer cladding can be ensured to be equal to the refractive index of the sub-cladding located in the middle.
[0034] In an alternative approach, Figure 1 As shown, the multi-core optical fiber in the embodiment of the utility model further includes a coating 300, which is formed on the surface of the outer cladding 200 away from the prefabricated optical fiber 100. The coating material is polyimide, ultraviolet light coating resin or modified polyimide, which can protect the surface of the prefabricated optical fiber 100 from damage, improve its mechanical strength, and reduce attenuation. At the same time, it can also form a total internal reflection structure together with the cladding 102 in the prefabricated optical fiber 100, so that the optical signal can be transmitted along the extension direction of the core layer 101. It should be understood that the modified material of the modified polyimide in the embodiment of the utility model can be adjusted according to actual conditions, and is not limited here.
[0035] Exemplarily, the thickness of the coating in the embodiment of the utility model is 4 μm to 6 μm. Within this range, the strength of the multimode optical fiber can be improved. If the thickness of the coating is less than 4 μm, the coating strength of the multimode optical fiber cannot reach the preset strength. If the thickness of the coating is greater than 6 μm, the thicker coating will produce greater internal stress on the prefabricated optical fiber, deteriorating the attenuation and warping characteristics of the multimode optical fiber, and making the multimode optical fiber more susceptible to brittle fracture during subsequent use.
[0036] The above is only a specific implementation of the utility model. Obviously, various modifications and combinations can be made to it without departing from the spirit and scope of the utility model. Accordingly, this specification and the drawings are only exemplary illustrations of the utility model defined by the attached claims, and are deemed to have covered any and all modifications, changes, combinations or equivalents within the scope of the utility model. Obviously, those skilled in the art can make various changes and modifications to the utility model without departing from the spirit and scope of the utility model. In this way, if these modifications and variations of the utility model fall within the scope of the claims of the utility model and their equivalents, the utility model is intended to include these changes and variations. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the utility model, which should be covered within the scope of protection of the utility model. Therefore, the scope of protection of the utility model shall be based on the scope of protection of the claims.
Claims
1. A multi-core optical fiber, characterized in that: include: A plurality of prefabricated optical fibers and an outer cladding, wherein the outer circumferential surfaces of two adjacent prefabricated optical fibers are tangent to each other, and the outer cladding is coated on the surfaces of the plurality of prefabricated optical fibers; The prefabricated optical fiber comprises a core layer and a cladding layer coated on the surface of the core layer, and the refractive index of the core layer is higher than the refractive index of the cladding layer; The cladding includes a plurality of sub-claddings arranged in sequence from the inside to the outside, the refractive index of the sub-cladding located on the inside and the refractive index of the sub-cladding located on the outside are both smaller than the refractive index of the sub-cladding located in the middle, the sub-cladding located on the inside is in contact with the core layer, and the number of the sub-claddings is at least three.
2. The multi-core optical fiber according to claim 1, characterized in that: The refractive index of the sub-cladding located on the inner side is equal to the refractive index of the sub-cladding located on the outer side. When the number of the sub-claddings is greater than three, the refractive index of each of the sub-claddings located in the middle is equal.
3. The multi-core optical fiber according to claim 1, characterized in that: The radius of the core layer is 4-5 μm, and the thickness of each sub-cladding layer is 1.26-1.625 μm.
4. The multi-core optical fiber according to claim 1, characterized in that: The refractive index of the outer cladding is equal to the refractive index of the sub-cladding located in the middle portion.
5. The multi-core optical fiber according to claim 1, characterized in that: The thickness of the outer cladding layer is 54-71 μm.
6. The multi-core optical fiber according to claim 1, characterized in that: The multi-core optical fiber further includes a coating layer formed on a surface of the outer cladding layer facing away from the prefabricated optical fiber.