Polymer optical fiber and manufacturing equipment thereof

Abstract

The embodiment of the utility model relates to the technical field of polymer optical fibers, in particular to a polymer optical fiber and manufacturing equipment thereof. In the embodiment of the invention, the fiber core comprises N fiber core layers which are sequentially arranged from inside to outside, N is an integer, and Ngt; 2; the Mth fiber core layer in the N fiber core layers sleeves the (M-1) th fiber core layer, and M is an integer and belongs to [2, N]; the refractive indexes of the N fiber core layers and the refractive indexes of the reflecting layers are decreased in a stepped mode in any radius direction of the polymer optical fiber from the central axis of the polymer optical fiber. The second fiber core layer to the Nth fiber core layer are polymer blends, the refractive index of the polymer blends is easy to regulate and control, and the control precision is high; therefore, the refractive index of each fiber core layer can easily reach the required theoretical refractive index, so that the control precision of the refractive index of each fiber core layer is improved.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of polymer optical fibers, and in particular to a polymer optical fiber and a manufacturing device thereof. Background Art

[0002] Polymer Optical Fiber (POF), also known as plastic optical fiber or polymer optical fiber, is mainly composed of a transparent plastic core layer with a high refractive index and a transparent plastic reflective layer with a low refractive index.

[0003] Based on the distribution of their refractive index, polymer optical fibers can be divided into step-index polymer optical fiber (SI-POF) and graded-index polymer optical fiber (GI-POF). SI-POF inherently exhibits high modal dispersion, which limits the bandwidth of optical fiber communications. Although GI-POF communication bandwidth can meet requirements, precise control of its radial refractive index is difficult. Summary of the Invention

[0004] In order to improve the adjustment accuracy of the radial refractive index of the polymer optical fiber core, the embodiments of the present application provide a polymer optical fiber and a manufacturing device thereof, which can dope a modified polymer in a polymer matrix to adjust the refractive index of the polymer matrix.

[0005] In a first aspect of the present application, a polymer optical fiber is provided, comprising a core and a reflective layer, wherein the core comprises N core layers arranged sequentially from the inside to the outside, where N is an integer and N>2; the Mth core layer among the N core layers is sleeved on the M-1th core layer, where M is an integer and M∈[2, N]; in any radial direction from the central axis of the polymer optical fiber along the polymer optical fiber, the refractive index of the N core layers and the refractive index of the reflective layer decrease in a step-like manner; among the N core layers, the second to Nth core layers are polymer blends.

[0006] In an embodiment of the present application, the fiber core includes N core layers arranged in sequence from the inside to the outside, N is an integer, and N>2; the Mth core layer among the N core layers is arranged on the M-1th core layer, M is an integer, and M∈[2,N]; in any radial direction along the polymer optical fiber from the central axis of the polymer optical fiber, the refractive index of the N core layers and the refractive index of the reflective layer decrease in a step-by-step manner; the 2nd to Nth core layers are polymer blends, and the method for controlling the refractive index of the polymer blend is simple and has high control accuracy; therefore, the refractive index of each core layer can easily reach the required theoretical refractive index, thereby improving the control accuracy of the refractive index of each core layer.

[0007] In some embodiments, N≥6.

[0008] In some embodiments, along any diameter direction of the polymer optical fiber, the refractive index of the N core layers and the refractive index of the reflective layer tend to be square-index distributed.

[0009] In some embodiments, the theoretical thickness d1 of each core layer satisfies the following formula:

[0010] d1=floor{[(D÷2-10)÷N]}

[0011] The theoretical thickness d2 of the reflective layer satisfies the following formula:

[0012] d2=D÷2-N×d1

[0013] Wherein, D is used to represent the outer diameter of the polymer optical fiber, N is the number of core layers, and floor{} is used to represent a floor rounding function.

[0014] In some embodiments, the refractive index of the M-th core layer satisfies the following formula:

[0015]

[0016] Among them, n′ M It is used to represent the refractive index of the Mth core layer, n′1 is used to represent the refractive index of the first core layer, and D is used to represent the outer diameter of the polymer optical fiber.

[0017] In the second aspect of the present application, a manufacturing device for a polymer optical fiber is also provided, which is used to manufacture the polymer optical fiber as described in the first aspect, and the device includes: N+1 melt feeding barrels, each of the melt feeding barrels is used to output a polymer melt corresponding to the material of each layer of the core layer or the material of the reflective layer; Q layered co-extrusion molds, each of the layered co-extrusion molds includes N+1 layers of flow channels, each of the N+1 layers of flow channels is connected to a melt feeding barrel, and each flow channel is used to extrude one of the core layers or the cladding; wherein Q is an integer, and Q is not less than N.

[0018] In some embodiments, the melt feed barrel includes: a feed port, which is used to input solid polymer particles corresponding to the material of each layer of the core layer or the material of the reflective layer; a screw extruder, which is connected to the feed port, and the screw extruder is used to convert the polymer particles input from the feed port into a polymer melt; a precision metering pump, which is respectively connected to the screw extruder and a flow channel of each of the layered co-extrusion molds, and the precision metering pump is used to input the polymer melt generated from the screw extruder into a flow channel of each of the layered co-extrusion molds according to a preset output volume.

[0019] In some embodiments, the melt feeding barrel further includes: an exhaust device, the exhaust device is connected to the screw extruder, and the exhaust device is used to discharge the gas generated when the screw extruder is working.

[0020] In some embodiments, the melt feeding barrel further includes an air pressure sensor, which is used to monitor the air pressure in the exhaust device.

[0021] In some embodiments, the layered co-extrusion mold includes: an air chamber with controllable air pressure, the air chamber is arranged on the side of the layered co-extrusion mold away from the fiber outlet of the layered co-extrusion mold, the air chamber is connected to each of the flow channels of the layered co-extrusion mold, and gas is stored in the air chamber. The gas is used to apply pressure to the polymer material in the flow channel to push the polymer material in the flow channel to move toward the fiber outlet direction.

[0022] It should be understood that the contents described in the Summary of the Invention are not intended to define the key or important features of the present disclosure, nor are they intended to limit the scope of the present disclosure. Other features of the present disclosure will become readily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments of the present invention. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0024] Figure 1 It is the refractive index distribution diagram of the existing GI-POF;

[0025] Figure 2 This is a schematic diagram of the light propagation path in the existing GI-POF;

[0026] Figure 3 It is the refractive index distribution diagram of the existing SI-POF;

[0027] Figure 4 This is a schematic diagram of the light propagation path in the existing SI-POF;

[0028] Figure 5 is a schematic diagram of the structure of a polymer optical fiber and a refractive index distribution diagram of the polymer optical fiber provided in some embodiments of the present application;

[0029] Figure 6 is a refractive index profile of a polymer optical fiber provided in some embodiments of the present application;

[0030] Figure 7 is a refractive index fitting curve of the polymer optical fiber provided in some embodiments of the present application;

[0031] Figure 8 is a schematic diagram of the path of light in a polymer optical fiber provided by some embodiments of the present application;

[0032] Figure 9 is a schematic structural diagram of a polymer optical fiber provided by some embodiments of the present application from one perspective;

[0033] Figure 10 is a refractive index profile of a polymer optical fiber provided by other embodiments of the present application;

[0034] Figure 11 is a refractive index fitting curve of a polymer optical fiber provided in other embodiments of the present application;

[0035] Figure 12 is a schematic diagram of a production device for polymer optical fibers provided in some embodiments of the present application;

[0036] Figure 13 is a schematic structural diagram of a layered co-extrusion die provided in some embodiments of the present application;

[0037] Figure 14 It is a schematic structural diagram of a polymer feeding barrel provided in some embodiments of the present application. DETAILED DESCRIPTION

[0038] The principles and spirit of the present disclosure will be described below with reference to several exemplary embodiments shown in the accompanying drawings. It should be understood that the description of these specific embodiments is only intended to enable those skilled in the art to better understand and implement the present disclosure, and is not intended to limit the scope of the present disclosure in any way. In the following description and claims, unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those of ordinary skill in the art.

[0039] As used herein, the term "including" and similar terms should be understood as open inclusion, i.e., "including but not limited to." The term "based on" should be understood as "based at least in part on." The term "one embodiment" or "the embodiment" should be understood as "at least one embodiment." The terms "first," "second," etc. may refer to different or the same objects and are only used to distinguish the objects referred to, and do not imply a specific spatial order, temporal order, order of importance, etc. of the objects referred to.

[0040] Figure 1 is the refractive index distribution curve of the existing graded-index polymer optical fiber (GI-POF) provided in some embodiments of the present application. Figure 1 The GI-POF 10 includes a core 11 and a reflective layer 12, wherein the refractive index at the axis O of the core 11 is n'1, and the refractive index of the reflective layer 12 is n". The refractive index of the core 11 is gradually distributed along any radial direction of the GI-POF from the axis O, and the refractive index of the GI-POF gradually decreases from the axis O along the radial direction of the GI-POF. Specifically, the refractive index of the core 11 can be parabolically distributed along the radial direction of the GI-POF from the axis O. For example, Figure 2 A schematic diagram of the propagation path of high-order mode light waves in the GI-POF 10 is shown, as shown in FIG. Figure 2 As shown, the propagation path of the high-order mode light wave in the GI-POF 10 is approximately a sine wave.

[0041] For light waves of the same frequency, their propagation speed in a propagation medium is inversely proportional to the medium's refractive index; that is, the higher the refractive index, the slower the propagation speed. When high-order mode signals propagate through an optical fiber, they move from the higher-index region near the inner core to the lower-index region near the outer core. Therefore, in the lower-index region of the core, although the high-order mode signals have a longer path, they propagate at a higher speed. This higher propagation speed compensates for the longer path. Compared to high-order mode signals, low-order mode signals propagate closer to the fiber's central axis. Low-order mode signals have a shorter path within the core but a lower propagation speed. Therefore, high-order and low-order mode signals entering the GI-POF 10 simultaneously can arrive at the receiver at the same or similar times, reducing modal dispersion and signal broadening within the GI-POF 10, resulting in a higher communication bandwidth. The high-order mode signal is used to represent the optical signal propagating near the interface between the core and the reflective layer in the optical fiber; the low-order mode signal is used to represent the optical signal propagating near the central axis of the optical fiber.

[0042] Figure 3 is the refractive index distribution curve of the existing step-index polymer optical fiber (SI-POF) provided in some embodiments of the present application. Figure 3 The SI-POF 20 includes a core 21 and a reflective layer 22, wherein the refractive index of the core 21 is n'1 and the refractive index of the reflective layer 22 is n". The refractive index of the core 21 remains unchanged along the radial direction from the axis of the SI-POF 20. Since the numerical aperture of the SI-POF 20 is large and it is a multimode optical fiber, it has a high modal dispersion. The light waves of the high-order modes (such as Figure 4 The path of L1 in the SI-POF 20 is longer, and the time required to reach the end face of the SI-POF 20 is longer, which is different from the low-order mode light waves (such as Figure 4 The time difference between L2 in FIG1 and L2 reaching the end face of SI-POF 20 is large, causing signal broadening and limiting the communication bandwidth of SI-POF 20. The data transmission rate of conventional SI-POF can reach 100Mbps×100m.

[0043] Existing SI-POFs typically consist of only one core layer and one reflective layer. While it's possible to adjust the refractive indices of the core and reflective layers to bring the core's refractive index closer to that of the reflective layer, thereby lowering the SI-POF's numerical aperture (NA) and increasing its data transmission rate, even if the SI-POF's NA is reduced to 0.3, its data transmission rate still doesn't exceed 1 Gbps per 50m, far from meeting the needs of future communication applications.

[0044] Specifically, the numerical aperture (NA) of a polymer optical fiber is used to reflect the coupling efficiency between the optical fiber and the light source. The NA can be calculated using the following formula:

[0045]

[0046] Wherein, N1 is the refractive index of the core material, and N2 is the refractive index of the reflective layer material.

[0047] Future communication system applications will demand increasingly higher data rates. This is particularly true for military equipment communication systems, next-generation car internet, smart home networks, LiDAR, video surveillance, and industrial automation control networks. These networks require communication media to be resistant to vibration and electromagnetic interference, offer high communication bandwidth, high optical coupling efficiency, and bend resistance. Specifically, bandwidth performance is required to reach at least 3 GHz x 50 m per channel. Among common wired communication media, polymer optical fiber (SI-POF) is widely used due to its vibration and electromagnetic interference resistance, high coupling efficiency, and bend resistance. However, the communication bandwidth of SI-POF is only 100 MHz x 100 m. While GI-POF meets these bandwidth requirements, its raw materials, made from perfluorinated or semi-fluorinated polymers, are expensive. Furthermore, the complex production process, involving preform drawing, prevents continuous production like extrusion. Furthermore, the radial refractive index of the optical fiber preform is difficult to adjust, making precise adjustment difficult and potentially resulting in an unstable refractive index profile.

[0048] Specifically, methods for producing preforms include gel polymerization and centrifugal polymerization. The gel polymerization method utilizes the gel effect, which causes the peripheral methyl methacrylate monomer to be trapped in a gel layer, resulting in a faster polymerization rate. This in turn drives the dopant to aggregate radially inward, ultimately resulting in a radial refractive index gradient of the optical fiber preform, with a high center and low ends. The centrifugal polymerization method utilizes materials with different refractive indices and densities, subjecting them to different centrifugal forces in the same device, thereby forming material layers at different locations and different refractive index gradients. However, neither of these two production methods makes it easy to adjust the radial refractive index distribution of the optical fiber preform.

[0049] Based on this, an embodiment of the present application provides a polymer optical fiber and a preparation method thereof, wherein the core of the polymer optical fiber includes N (N>2) core layers arranged sequentially from the inside to the outside, and the refractive index of the N core layers and the refractive index of the reflective layer decrease in a step-like manner along any radial direction of the polymer optical fiber from the central axis of the polymer optical fiber; among the N core layers, the second to Nth core layers are polymer blends; the raw material composition of the polymer blend includes a polymer matrix and a modified polymer. The modified polymer is used to reduce the refractive index of the polymer matrix. By regulating the mass ratio of the polymer matrix and the modified polymer, a polymer blend with a target refractive index corresponding to each core layer can be obtained; therefore, the refractive index of each core layer is easy to regulate, and there is no need to dope inert high-refractive-index materials to avoid increased optical attenuation of the optical fiber. In order to facilitate readers' understanding of this application, it is explained below in conjunction with specific embodiments.

[0050] An embodiment of the present application provides a polymer optical fiber comprising a core and a reflective layer, wherein the core is the light-guiding region of the polymer optical fiber; the reflective layer, also known as the cladding, is the material surrounding the core. The core has a greater refractive index than the reflective layer. The core comprises N core layers arranged sequentially from the inside out, where N is an integer and N>2. The Mth core layer of the N core layers is sheathed over the M-1th core layer, where M is an integer and M∈[2,N]. The refractive indices of the N core layers and the reflective layer decrease in a stepwise manner along any radial direction from the central axis of the polymer optical fiber. Among the N core layers, the second to Nth core layers are polymer blends, the raw material composition of the polymer blend including a polymer matrix and a modified polymer, wherein the modified polymer is used to reduce the refractive index of the polymer matrix. The refractive index of each core layer is a constant value; that is, for each core layer, its refractive index does not vary along the radial direction of the polymer optical fiber.

[0051] Specifically, in some embodiments, the first fiber core layer is cylindrical, the second to Nth fiber core layers are annular, and the second to Nth fiber core layers are sequentially sleeved on the first fiber core layer.

[0052] For example, Figure 5 The refractive index distribution diagrams of polymer optical fibers provided in some embodiments of the present application are shown. Figure 5 As shown, N = 6. The six core layers are the first core layer D1, the second core layer D2, the third core layer D3, the fourth core layer D4, the fifth core layer D5, and the sixth core layer D6. D7 is the reflective layer. D1 has the highest refractive index, n'1, while the reflective layer has the lowest refractive index, n". Along any radial direction from the central axis of the polymer fiber, the refractive indices of the N core layers and the reflective layers decrease in a step-like manner.

[0053] In some embodiments, N ≥ 6. When N is less than 6, although the refractive index of the polymer optical fiber decreases in a step-like manner overall, since the number of core layers is generally only 3 to 5 and the thickness of each core layer is too large, the refractive index between two adjacent core layer materials tends to change rapidly, and the refractive index distribution of the core cannot be approximated by a gradual change, which is not conducive to reducing the modal dispersion of the polymer optical fiber.

[0054] In the prior art, in order to increase the refractive index of the polymer matrix material, a high-refractive-index inert dopant is usually used to dope the polymer matrix material with high light transmittance. In order to ensure that the composite material of the core layer (that is, the first core layer) has the largest refractive index, the core layer material must be doped with the most inert dopant. Since the transmittance of the inert dopant is lower than that of the polymer matrix, doping a large amount of inert dopant will increase the absorption loss of the core layer material, increase the loss in the main light transmission area, greatly increase the light attenuation of the polymer optical fiber, and is not conducive to the transmission of optical signals. In the embodiments of the present application, the light attenuation problem of the polymer optical fiber caused by the use of inert dopants can be avoided by doping a modified polymer into the polymer matrix to reduce the refractive index of the polymer matrix.

[0055] Specifically, in some embodiments, the first fiber core layer is cylindrical, the second to Nth fiber core layers are annular, and the second to Nth fiber core layers are sequentially sleeved on the first fiber core layer.

[0056] For example, Figure 5 The structural diagrams of polymer optical fibers provided by some embodiments of the present application are shown. Figure 5 As shown, the core of the polymer optical fiber includes 6 core layers, which are D1, D2, D3, D4, D5 and D6, and the reflection layer of the polymer optical fiber is D7. The refractive index of the 6 core layers decreases in a step-by-step manner from the axis of the polymer optical fiber along the radial direction of the polymer optical fiber.

[0057] In an embodiment of the present application, the refractive index of the core layer decreases in a step-like manner from the axis of the polymer optical fiber along the radial direction of the polymer optical fiber; the polymer optical fiber has at least 6 core layers. By increasing the number of core layers and reducing the thickness of each core layer, the refractive index distribution of the polymer optical fiber can be made to tend to decrease in a gradual manner. Therefore, the high-order mode carrying the optical signal will be continuously refracted in multiple core layers in the polymer optical fiber until the incident angle meets the numerical aperture, undergoing total reflection, returning to the polymer optical fiber, and undergoing multiple refractions and a total reflection again. Since the propagation speed of light in materials with different refractive indices is inversely proportional to the refractive index of the material, although the high-order mode travels a longer path in the optical fiber, it has a greater propagation speed as compensation, so that the time when the high-order mode finally reaches the receiving end is close to or almost equal to that of the low-order mode, thereby reducing optical mode dispersion and thus reducing optical signal broadening.

[0058] The polymer optical fiber provided in the embodiment of the present application can retain the advantage of the large core diameter of the polymer optical fiber; at the same time, when connected to a light source, even if the polymer optical fiber and the light source deviate slightly due to vibration, the optical signal can be normally coupled into the polymer optical fiber.

[0059] In some embodiments, the material of the first core layer is a polymer matrix, the material of the second to Nth core layers is a polymer blend, and the raw material composition of the polymer blend includes a polymer matrix and a modified polymer, and the material of the reflective layer is a modified polymer; wherein the refractive index of the modified polymer is lower than the refractive index of the polymer matrix; in the second to Nth core layers, the modified polymer is used to reduce the refractive index of the polymer matrix.

[0060] In the embodiments of the present application, the refractive index of the polymer matrix is adjusted by doping a modified polymer into the polymer matrix. The modified polymer needs to have the following characteristics: (1) the polymer matrix and the modified polymer have the same operating wavelength window; (2) the refractive index of the modified polymer is lower than that of the polymer matrix; (3) the modified polymer is physically compatible with the polymer matrix to form a polymer blend; and (4) it does not chemically react with the polymer matrix in the molten state.

[0061] For example, in some embodiments, the polymer matrix is polymethyl methacrylate (PMMA); in this case, the modified polymer needs to meet the following conditions: (1) have the same operating wavelength window as PMMA, that is, have lower absorption loss at the operating wavelengths of 520nm and 650nm; (2) have a refractive index lower than that of PMMA; (3) be physically compatible with PMMA to form a polymer blend; and (4) not chemically react with PMMA in the molten state.

[0062] Specifically, in certain embodiments of the present application, the modified polymer includes at least one of polyperfluoroethylene propylene, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, or polybutyl methacrylate.

[0063] In some embodiments, the outer diameter of the polymer optical fiber is 0.25 mm to 2.0 mm, and the thickness of the reflective layer is 10 μm to 20 μm.

[0064] Figure 6 The refractive index distribution diagram of a polymer optical fiber with 6 core layers provided by some embodiments of the present application is shown. Figure 7 Showed Figure 6 The refractive index fitting curve of the polymer optical fiber in . Figure 6 and Figure 7 It can be seen that the refractive index distribution of the polymer optical fiber with 6 core layers is close to a gradient change, which makes the polymer optical fiber have smaller bending loss.

[0065] In some embodiments, the theoretical thickness d1 of each core layer satisfies the following formula:

[0066] d1=floor{[(D÷2-10)÷N]}

[0067] Where d1 is used to represent the theoretical thickness of the core layer, D is used to represent the outer diameter of the polymer optical fiber, N is the number of core layers, and floor{} is used to represent the floor rounding function.

[0068] Specifically, in the above formula, rounding down means rounding down to an integer less than the calculated result when the calculated result is not an integer. [(D ÷ 2 - 10) ÷ N] is used to represent the calculated theoretical thickness of each core layer.

[0069] At this time, the theoretical thickness d2 of the reflective layer satisfies the following formula:

[0070] d2=D÷2-N×d1

[0071] Wherein, d2 is used to represent the thickness of the reflective layer.

[0072] Specifically, in some implementations, the refractive index of the M-th core layer is calculated by the following formula:

[0073]

[0074] Where n1 is used to represent the refractive index of the first core layer, M is an integer and M∈[1, N], n′ M It is used to indicate the refractive index of the Mth core layer, and D is used to indicate the outer diameter of the polymer optical fiber.

[0075] For example, in some embodiments, the theoretical outer diameter of the polymer optical fiber is 1000 μm, the number of core layers N of the polymer optical fiber is 6, the material of the first core layer (i.e., the polymer matrix) is PMMA, and the materials of the modified polymer and the reflective layer are both PVDF. The refractive index of PMMA is 1.492, and the refractive index of PVDF is 1.42. Therefore:

[0076] The theoretical thickness of the core layer is:

[0077] d1=floor{[(D÷2-10)÷N]}=floor{[(1000÷2-10)÷6=floor81.6667=81μm

[0078] The theoretical thickness of the reflective layer is:

[0079] d2=D÷2-N×d1=1000÷2-6×81=14μm

[0080] The refractive index of the Mth core layer is:

[0081]

[0082] In this embodiment, the refractive index distributions of the core layers and reflective layers of the polymer optical fiber are shown in Table 1, where d represents the distance between the core layer and the reflective layer and the central axis.

[0083] Table 1

[0084]

[0085]

[0086] In this embodiment, the first through sixth core layers constitute the primary space of the optical waveguide, while the reflective layer enhances the physical properties (e.g., flexibility, tensile strength, tensile yield strength, and break strength) and optical coupling capability of the polymer optical fiber. The reflective layer has the largest refractive index difference with the sixth core layer, which helps increase the numerical aperture of the outermost layer, thereby facilitating optical coupling with large-area signal sources.

[0087] In other embodiments, the theoretical outer diameter of the polymer optical fiber is 1000 μm, the number of core layers N of the polymer optical fiber is 9, the material of the first core layer (i.e., the polymer matrix) is PMMA, and the materials of the modified polymer and the reflective layer are both PVDF. Then:

[0088] The theoretical thickness of the core layer is:

[0089] d1=floor{[(D÷2-10)÷N]}=floor{[(1000÷2-10)÷9=floor54.4444=54μm

[0090] The theoretical thickness of the reflective layer is:

[0091] d2=D÷2-N×d1=1000÷2-9×54=14μm

[0092] The refractive index of the Mth core layer is:

[0093]

[0094] The refractive index distribution of the core and reflective layer of the polymer optical fiber is shown in Table 2, where d is used to represent the distance between the core layer and the reflective layer material and the central axis.

[0095] Table 1

[0096]

[0097]

[0098] For example, Figure 5-7 The refractive index distribution and refractive index fitting curve of a polymer optical fiber with 6 core layers are shown. Figure 8A schematic diagram of the propagation path of light waves in a polymer optical fiber with 6 core layers provided by some embodiments of the present application is shown. Figure 8 It can be seen that the propagation path of the light wave in the polymer optical fiber with 6 core layers is close to a sine curve. Figure 9-11 The structural diagram, refractive index distribution and refractive index fitting curve of polymer optical fiber with 9 core layers are presented. Figure 5-7 and Figure 9-11 It can be seen from the refractive index distributions of the two polymer optical fibers with different numbers of core layers that when the outer diameter of the polymer optical fiber remains unchanged, the more core layers there are and the smaller the thickness of each core layer, the closer the refractive index fitting curve of the polymer optical fiber is to a gradient distribution, which is more conducive to improving the modal dispersion of the polymer optical fiber.

[0099] In some embodiments, along any diametrical direction of the polymer optical fiber, the refractive indices of the N core layers and the reflective layer tend to have a square-ratio distribution. In this embodiment, when the refractive index of the polymer optical fiber has a square-ratio distribution along its diameter, high-order mode optical signals have a higher velocity compensation and a longer travel path in the low-refractive-index effective core layer, allowing low-order mode signals and high-order mode signals to arrive at the end face of the polymer optical fiber at the same or similar times, thereby reducing the modal dispersion of the polymer optical fiber and increasing the communication bandwidth.

[0100] The present application also provides a polymer optical fiber manufacturing apparatus for manufacturing the polymer optical fiber provided in the above embodiments. The apparatus comprises: N+1 melt feed barrels, each of which is used to output a polymer melt corresponding to the material of each core layer or a polymer melt corresponding to the material of the reflective layer. The apparatus also comprises: Q layered co-extrusion dies, each of which comprises N+1 layers of flow channels, each of the N+1 layers of flow channels being connected to a melt feed barrel, and each flow channel being used to extrude one of the core layers or the cladding layers; wherein Q is an integer and is not less than N.

[0101] In some embodiments, the manufacturing equipment also includes: a feed port, a screw extruder and a precision metering pump, wherein the feed port is used to input solid polymer particles corresponding to the material of each fiber core layer or the material of the reflective layer; the screw extruder is connected to the feed port, and the screw extruder is used to convert the polymer particles input from the feed port into a polymer melt; the precision metering pump is respectively connected to the screw extruder and a flow channel of each layered co-extrusion mold, and the precision metering pump is used to input the polymer melt generated from the screw extruder into a flow channel of each layered co-extrusion mold according to a preset output volume.

[0102] In the embodiments of the present application, if the optical fiber extrusion equipment only produces a single optical fiber mode according to conventional production methods, the flow rate of a single layer of polymer optical fiber material (each core layer or reflective layer material) extruded by a single extruder is too large, resulting in a large thickness of each layer of polymer optical fiber material. If the number of core layers N is also large, the diameter of the polymer optical fiber preform extruded from the layered co-extrusion die mouth will be too large, which is not conducive to thinning the polymer optical fiber preform to make the optical fiber preform into a polymer optical fiber. At the same time, the interface between each two layers of polymer optical fiber material needs to be flat and smooth to reduce the linear scattering effect of the optical fiber and thus reduce the attenuation of the optical fiber. The method of extruding a single layer of polymer optical fiber material by a single extruder will result in the prepared multi-step refractive index polymer optical fiber not having too many step-like changes, resulting in excessive changes in the refractive index between each core layer, and an inability to achieve an approximately gradual change, resulting in the polymer optical fiber modal dispersion not being well improved.

[0103] In an embodiment of the present application, in a layered extrusion process, multiple screw-type melt feed barrels are used to extrude materials for different core layers. The extrusion screws need to adapt their power to the material. Structurally, the more core layers, the better. The greater the number of core layers, the thinner the thickness of each core layer, and the less material required for each core layer. Therefore, the material flow rate per unit time of the extrusion screw of a single melt feed barrel is far greater than the material required for each layer of the polymer optical fiber. As a result, during the extrusion of the polymer optical fiber, the material will be squeezed and deformed by the extrusion die. If the volume of the extrusion die is increased, the cross-sectional area of the initially drawn optical fiber will be too large, which is not conducive to the subsequent drawing and cooling of the optical fiber. Therefore, in order to fully utilize the extrusion power of current screw extruders, the embodiments of the present application adopt a multi-fiber co-extrusion process. The production device is configured to produce multiple optical fibers simultaneously, that is, the number of optical fibers produced simultaneously must be greater than or equal to the set number of effective core layers. Each extrusion screw simultaneously extrudes material for the same core layer of multiple optical fibers, which not only solves the problem of excess extrusion but also increases optical fiber production. Taking the production of distributed structure polymer optical fiber with 6 effective core layers as an example, the production line is equipped with at least 7 melt feeding barrels. Figure 12 The provided polymer optical fiber production equipment is equipped with 7 melt feed barrels and 7 layered co-extrusion dies; among them, the 7 melt feed barrels are the first to sixth polymer melt feed barrels and the reflective layer polymer melt feed barrel (i.e., the coating layer polymer melt feed barrel); the 7 layered co-extrusion dies are optical fiber dies No. 1 to No. 7.

[0104] like Figure 13As shown, each melt feed barrel includes an inlet 131, a screw extruder 132, a precision metering pump 133, an exhaust device 134, an air pressure sensor 135, an exhaust port 136, a discharge port 137, a first temperature sensor 138, and a second temperature sensor 139. The inlet 131 is connected to the screw extruder 132 and is used to input solid polymer raw materials, such as polymer-based plastic particles or modified polymer plastic particles, into the screw extruder 132. The screw extruder 132 is connected to the precision metering pump 133, which converts the input raw materials into polymer melt and inputs the polymer melt into the precision metering pump 133. The precision metering pump 133 controls the flow rate of the polymer melt discharged from the discharge port 137. The discharge port 137 is used to input the polymer melt into the layered co-extrusion die. A first temperature sensor 138 is mounted on the screw extruder 132 and is used to detect the temperature of the polymer melt in the screw extruder 131. A second temperature sensor 139 is mounted on the precision metering pump 133 and is used to detect the temperature of the polymer melt in the precision metering pump 133. An exhaust device 134 is connected to the screw extruder 132 and is used to discharge gas generated in the screw extruder 132 through an exhaust port 136. An air pressure sensor 135 is used to detect the air pressure in the exhaust device 134.

[0105] In this embodiment, each melt feed barrel is provided with an independent screw extruder, which squeezes the polymer melt into the channel corresponding to the same core layer or unified reflective layer in each layered co-extrusion mold through a precision metering pump, thereby transporting the polymer melt to the same core layer or reflective layer of the corresponding polymer optical fiber of the 7 optical fiber molds.

[0106] Figure 14 The structure of the layered co-extrusion die from one perspective and the schematic diagram of the layered co-extrusion principle are shown as an example. Figure 14 As shown, the feed inlets of the layered co-extrusion die include a first feed inlet 611, a second feed inlet 612, a third feed inlet 613, a fourth feed inlet 614, a fifth feed inlet 615, a sixth feed inlet 616, and a seventh feed inlet 617, which are arranged sequentially along the fiber output direction. The first to sixth feed inlets are feed inlets for the polymer melt corresponding to the first to sixth core layer materials, respectively, and the seventh feed inlet is feed inlet for the polymer melt corresponding to the reflective layer material. The first to sixth feed inlets 611 to 616 are connected to the first layer flow channel 601, the second layer flow channel 602, the third layer flow channel 603, the fourth layer flow channel 604, the fifth layer flow channel 605, and the sixth layer flow channel 606, respectively. The polymer melt of each layer is fed into each layer flow channel from the first to sixth feed inlets 611 to 616. The feed flow rate of each layer flow channel is strictly controllable.

[0107] In some embodiments, the first feed port is used to input a molten polymer matrix, the second through sixth feed ports are used to input a molten blend of the polymer matrix and a modified polymer, and the seventh feed port is used to input a molten modified polymer material. Furthermore, the mass ratios of the polymer matrix and the modified polymer in the molten blends input through the second through sixth feed ports vary; the mass ratio of the modified polymer in the molten blend increases from the second to the sixth feed ports.

[0108] The end of the mold body away from the fiber outlet is a pressure-controllable air chamber 610. The fiber outlet direction refers to the direction in which the polymer optical fiber is drawn after being extruded from the fiber outlet of the layered co-extrusion mold.

[0109] After each layer of raw material enters the extrusion die, it will continue to move forward in the mold and fit together with the next layer of material, forming a structure in which the polymer ring of this layer fits together with the polymer ring of the next layer, until all the fiber core layers and reflective layers are fitted together in the mold and extruded from the mold.

[0110] In an embodiment of the present application, after the Pth layer of material advances a certain distance in the die channel, it converges with the P+1th layer of material, and the P+1th layer of material covers the Pth layer of material. By controlling the flow rate, temperature, etc. of the materials, as well as the structural design of the die opening, when the P+1th layer of material covers the Pth layer of material, the interface between the two layers of material is flat and smooth, thereby reducing the linear loss caused by the instability of the optical fiber structure. At the same time, the parameters such as flow rate, temperature, and pressure of the two adjacent layers of material can be adjusted according to the conditions of the interface, so that the extrusion process can be achieved in real time and controllable. Wherein, P∈[1,N].

[0111] A pressure-controlled chamber at the front of the die provides pressure for the material flow path. Dry air or an inert gas is typically used. Because each screw delivers a small amount of polymer melt to its corresponding layer, insufficient material force can cause the melt to remain in the die for an extended period. This can lead to the following problems: 1. Blockage of the extrusion die, resulting in mold damage; 2. Excessive mold temperature increases, causing burns and increased fiber attenuation; 3. When adjacent polymer melt layers are bonded in the co-extrusion die, the interface becomes uneven, increasing fiber loss. The pressure chamber provides dry air or inert gas to each layer, pressurizing it and propelling it through the die. The pressure in each layer is independently controlled and equipped with a pressure sensor for continuous monitoring and adjustment, ensuring that the gas is used to propel the polymer melt through the die without creating bubbles in the melt.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above. For the sake of simplicity, they are not provided in detail. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in this field should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polymer optical fiber comprising a core and a reflective layer, characterized in that: The fiber core comprises N fiber core layers arranged sequentially from the inside to the outside, where N is an integer and N>2; The Mth fiber core layer among the N fiber core layers is sleeved on the M-1th fiber core layer, where M is an integer and M∈[2, N]; In any radial direction of the polymer optical fiber from the central axis thereof, the refractive index of the N core layers and the refractive index of the reflective layer decrease in a step-like manner; Among the N core layers, the material of the second to Nth core layers is a polymer blend.

2. The optical fiber according to claim 1, wherein N≥6。 3. The optical fiber according to claim 2, wherein In any diameter direction of the polymer optical fiber, the refractive index of the N core layers and the refractive index of the reflective layer tend to be square-rate distributed.

4. The optical fiber according to claim 1, wherein The thickness d1 of each core layer satisfies the following formula: d1=floor{[(D÷2-10)÷N]} The thickness d2 of the reflective layer satisfies the following formula: d2=D÷2-N×d1 Wherein, D is used to represent the outer diameter of the polymer optical fiber, N is the number of core layers, and floor{} is used to represent a floor rounding function.

5. The optical fiber according to any one of claims 1 to 4, characterized in that The refractive index of the M-th core layer satisfies the following formula: Among them, n′ M It is used to represent the refractive index of the Mth core layer, n′1 is used to represent the refractive index of the first core layer, d1 is used to represent the thickness of each core layer, and D is used to represent the outer diameter of the polymer optical fiber.

6. A polymer optical fiber manufacturing device, characterized in that: The manufacturing device is used to manufacture the polymer optical fiber according to any one of claims 1 to 5, and the device comprises: N+1 melt feeding barrels, each of which is used to output a polymer melt corresponding to the material of each core layer or the material of the reflective layer; Q layered co-extrusion dies, each of the layered co-extrusion dies comprising N+1 layers of flow channels, each of the N+1 layers of flow channels being connected to one of the melt feed barrels, and each of the flow channels being used to extrude one of the core layers or the reflective layer; Wherein, Q is an integer and Q is not less than N.

7. The device according to claim 6, characterized in that The melt feeding barrel comprises: A material inlet, the material inlet being used to input solid polymer particles corresponding to the material of each core layer or the material of the reflective layer; a screw extruder connected to the feed port, and configured to convert the polymer particles inputted from the feed port into a polymer melt; A precision metering pump is respectively connected to the screw extruder and a flow channel of each of the layered co-extrusion dies, and the precision metering pump is used to input the polymer melt generated by the screw extruder into a flow channel of each of the layered co-extrusion dies according to a preset discharge volume.

8. The device according to claim 7, characterized in that The melt feeding barrel also includes: An exhaust device is connected to the screw extruder and is used to discharge the gas generated when the screw extruder is working.

9. The device according to claim 8, characterized in that The melt feeding barrel further includes an air pressure sensor, which is used to monitor the air pressure in the exhaust device.

10. The device according to any one of claims 6 to 9, characterized in that The layered co-extrusion die comprises: An air chamber with controllable air pressure is arranged on a side of the layered co-extrusion die away from the fiber outlet of the layered co-extrusion die, and the air chamber is connected to each of the flow channels of the layered co-extrusion die. Gas is stored in the air chamber, and the gas is used to apply pressure to the polymer material in the flow channel to push the polymer material in the flow channel to move in the fiber outlet direction.

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