An optical fiber preform and a method for preparing the same

Abstract

The present application relates to an optical fiber preform and a method for preparing the same, comprising: determining the mass of silicon powder required for the core layer, the mass of refractive index powder contributing to the refractive index, and the mass of silicon powder required for the cladding based on the core radius, relative refractive index, cladding radius, and mass of the optical fiber preform; uniformly mixing the silicon powder required for the core layer and the refractive index powder contributing to the refractive index to obtain a core preform corresponding to the core layer; feeding the core preform corresponding to the core layer into a core die-casting mold for die-casting to obtain a core preform; feeding the core preform and the mass of silicon powder required for the cladding into a cladding die-casting mold for die-casting to obtain a semi-finished optical fiber preform; and sintering the semi-finished optical fiber preform to obtain an optical fiber preform. The present application can address the problems of poor production stability, low raw material utilization, and difficulty in forming waveguide structures in the prior art of rod making processes.

Description

Technical Field

[0001] The present application relates to the field of optical fiber technology, and in particular to an optical fiber preform and a preparation method thereof. Background Art

[0002] The current mainstream preparation methods for optical fiber preforms are VAD and OVD. They rely on a blowtorch to spray D4 or silicon tetrachloride, which is hydrolyzed under the action of an oxyhydrogen flame to obtain silica powder, which is then collected through a target rod.

[0003] During deposition, the yield of silicon dioxide powder by this method is relatively low, generally only about 40%.

[0004] When doping is carried out, germanium tetrachloride is mainly added to the raw material and germanium dioxide is obtained by hydrolysis.

[0005] In order to obtain different waveguide structures such as core layer and cladding, different blowtorches are needed to spray raw materials with different contents.

[0006] The efficiency of raw material collection is greatly affected by factors such as equipment pressure, air supply stability, air supply temperature, burner structure stability, feed pressure stability, and oxyhydrogen flame stability. If any of these factors fluctuate, the structure and quality of the product will be affected.

[0007] Therefore, the current rod making process still has problems such as poor production stability, low raw material utilization, and difficulty in forming waveguide structures. Summary of the Invention

[0008] The embodiments of the present application provide an optical fiber preform and a method for preparing the same, in order to solve the problems in the related art of the preform making process, such as poor production stability, low raw material utilization, and difficulty in forming a waveguide structure.

[0009] In a first aspect, a method for preparing an optical fiber preform is provided, comprising:

[0010] Based on the core radius, core relative refractive index, cladding radius and the mass of the optical fiber preform, the mass of silica powder required for the core layer and the mass of the refractive index powder that contributes to the refractive index, as well as the mass of silica powder required for the cladding are obtained;

[0011] The silicon powder required for the core layer and the refractive index powder that contributes to the refractive index are mixed to obtain the core layer preform powder corresponding to the core layer;

[0012] Feeding the core layer preform powder corresponding to the core layer into a core layer die-casting mold for die-casting to obtain a core layer preform; feeding the core layer preform and the silicon powder mass required for the cladding into a cladding die-casting mold for die-casting to obtain a semi-finished optical fiber preform rod;

[0013] The optical fiber preform semi-finished product is sintered to obtain an optical fiber preform.

[0014] In some embodiments, based on the core radius, the core relative refractive index, the cladding radius, and the mass of the optical fiber preform, obtaining the mass of silica powder required for the core layer, the mass of the refractive index powder contributing to the refractive index, and the mass of silica powder required for the cladding layer includes the following steps:

[0015] Obtain relative refractive index conversion coefficient;

[0016] Combining the first mapping relationship, the relative refractive index conversion coefficient, the core radius of the optical fiber, the core relative refractive index, the cladding radius and the mass of the optical fiber preform, the mass of the silicon powder required for the core layer and the mass of the refractive index powder that contributes to the refractive index, as well as the mass of the silicon powder required for the cladding are calculated.

[0017] In some embodiments, obtaining the relative refractive index conversion coefficient includes the following steps:

[0018] Weigh a certain mass of silicon powder and refractive index powder that contributes to the refractive index, mix them evenly, and then die-cast them to obtain a core layer prefabricated powder rod;

[0019] The relative refractive index of the core layer prefabricated powder rod is measured, and the relative refractive index conversion coefficient is calculated inversely based on the first mapping relationship, the mass of the weighed silicon powder, and the mass of the refractive index powder.

[0020] In some embodiments, the first mapping relationship includes:

[0021]

[0022] Wherein, Δ% is the relative refractive index of the core layer, m1 is the mass of silicon powder, m2 is the mass of the refractive index powder that contributes to the refractive index, and K1 is the relative refractive index conversion coefficient.

[0023] In some embodiments, the mass of silica powder required for the core layer, the mass of refractive index powder contributing to the refractive index, and the mass of silica powder required for the cladding are calculated inversely based on the first mapping relationship, the relative refractive index conversion coefficient, the core radius of the optical fiber, the relative refractive index of the core layer, the cladding radius, and the mass of the optical fiber preform, including the following steps:

[0024] According to the core radius and cladding radius of the optical fiber and the mass of the optical fiber preform, the total mass of the powder required for the core layer is obtained;

[0025] According to the total mass of the powder required for the core layer, the relative refractive index of the core layer, the first mapping relationship, and the relative refractive index conversion coefficient, the mass of the silicon powder required for the core layer and the mass of the refractive index powder contributing to the refractive index are obtained;

[0026] The mass of silicon powder required for the cladding is obtained based on the mass of the optical fiber preform and the total mass of powder required for the core layer.

[0027] In some embodiments, when the core layer of the optical fiber has N layers, and N ≥ 2,

[0028] The core radius of the optical fiber includes the radius of each core layer, and the core relative refractive index includes the relative refractive index of each core layer;

[0029] The silicon powder required for the core layer and the refractive index powder material that contributes to the refractive index are mixed to obtain a core layer prefabricated powder corresponding to the core layer, including: the silicon powder required for each core layer and the refractive index powder material that contributes to the refractive index are mixed to obtain a core layer prefabricated powder corresponding to each core layer;

[0030] The core layer preform powder corresponding to the core layer is fed into the core layer die-casting mold for die-casting to obtain a core layer preform, including the following steps:

[0031] Along the radial direction of the optical fiber, from inside to outside, firstly, the core layer preform powder corresponding to the first core layer is fed into the core layer die-casting mold corresponding to the first core layer for die-casting to obtain the first core layer preform;

[0032] Then, the core layer prefabricated powder corresponding to the second core layer and the first core layer prefabricated part are fed into the core layer die-casting mold corresponding to the second core layer for die-casting to obtain the second core layer prefabricated part;

[0033] Similarly, finally, the core layer preform powder corresponding to the Nth core layer and the N-1th core layer preform are fed into the core layer die-casting mold corresponding to the Nth core layer for die-casting to obtain the core layer preform.

[0034] In some embodiments, the preparation method further comprises the following step of obtaining the size of the core layer die-casting mold:

[0035] Get the radius conversion coefficient affected by pressure;

[0036] The radius of the core layer die-casting mold is obtained by combining the second mapping relationship, the radius conversion coefficient, and the core layer radius of the optical fiber;

[0037] The length of the core layer die-casting mold is obtained according to the mass of silicon powder required for the core layer, the mass of the refractive index powder contributing to the refractive index, the radius of the core layer die-casting mold, and the density of the core layer preform powder in a naturally accumulated state when filled.

[0038] In some embodiments, obtaining a radius conversion coefficient affected by pressure includes the following steps:

[0039] Weigh a certain mass of core layer preform powder, put it into a test mold for die casting, and obtain a core layer preform powder rod;

[0040] The core layer preform powder rod is sintered and drawn, and the core layer radius of the optical fiber is obtained by measurement. The radius conversion coefficient affected by pressure is calculated by combining the second mapping relationship and the radius of the test mold.

[0041] In some embodiments, the second mapping relationship includes: r=D*K2

[0042] Where D is the radius of the test mold, r is the core radius of the optical fiber, and K2 is the radius conversion coefficient affected by pressure.

[0043] In a second aspect, an optical fiber preform is provided, characterized in that it is prepared by any of the above methods for preparing an optical fiber preform.

[0044] The beneficial effects of the technical solution provided by this application include:

[0045] An embodiment of the present application provides an optical fiber preform and a method for preparing the same. The overall concept of the preparation method provided in the embodiment of the present application is as follows: based on various parameters of the optical fiber to be drawn, such as the core radius, the relative refractive index of the core, and the cladding radius of the optical fiber, and combined with the mass of the optical fiber preform to be prepared, the mass of various raw material powders of the core layer and the mass of the silica of the cladding are calculated, and then die-casting is performed and finally sintering is performed to obtain the optical fiber preform.

[0046] Since the required mass of various raw material powders is calculated based on the various parameters of the optical fiber to be drawn and the mass of the required optical fiber preform rod, only the required amount can be used, which can reduce raw material waste and improve raw material utilization. In addition, through die-casting, production stability can be improved and the difficulty of waveguide structure molding can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0048] Figure 1 Flowchart of the method for preparing an optical fiber preform provided in an embodiment of the present application. DETAILED DESCRIPTION

[0049] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0050] See also Figure 1 As shown, an embodiment of the present application provides a method for preparing an optical fiber preform, the preparation method comprising the following steps:

[0051] 101: Based on the core radius, core relative refractive index, cladding radius and mass of the optical fiber preform, the mass of silica powder required for the core layer and the mass of the refractive index powder that contributes to the refractive index, as well as the mass of silica powder required for the cladding are obtained.

[0052] 102: The silicon powder required for the core layer and the refractive index powder that contributes to the refractive index are mixed to obtain a core layer preform powder corresponding to the core layer.

[0053] In step 102 , silicon powder and refractive index powder that contributes to the refractive index need to be prepared first.

[0054] Specifically, a hydrolysis-based oxyhydrogen combustion process is performed within a reaction chamber to produce high-purity silica powder. The resulting high-purity silica powder is then collected in a dust collector. The collected high-purity silica powder then enters a purification device and undergoes a purification process to produce high-purity, dry silica powder. The purification process conditions can be customized based on actual needs. For example, a temperature of 850°C, a dehydrating agent flow rate of 20 slm, and a treatment time of 8 hours are employed.

[0055] Using a hydrolysis-based oxyhydrogen combustion process, hydrogen and oxygen are burned within a reaction chamber to produce a high-purity refractive index powder. The resulting high-purity refractive index powder is then collected in a dust collector. The collected high-purity refractive index powder then enters a purification device, where it undergoes a purification process to produce a high-purity, dry refractive index powder. Purification process conditions can be customized to meet specific needs. For example, a temperature of 850°C, a dehydrating agent flow rate of 15 slm, and a treatment time of 6 hours are employed.

[0056] 103: feeding the core layer preform powder corresponding to the core layer into a core layer die-casting mold for die-casting to obtain a core layer preform; feeding the core layer preform and the silicon powder mass required for the cladding into a cladding die-casting mold for die-casting to obtain a semi-finished optical fiber preform rod.

[0057] 104: Sintering the optical fiber preform semi-finished product to obtain an optical fiber preform.

[0058] The overall concept of the preparation method provided in the embodiment of the present application is as follows: based on the various parameters of the optical fiber to be drawn, such as the core radius, the relative refractive index of the core, and the cladding radius of the optical fiber, and combined with the mass of the optical fiber preform to be prepared, the mass of various raw material powders of the core layer and the mass of the silica of the cladding are calculated, and then die-casting is performed and finally sintering is performed to obtain the optical fiber preform.

[0059] Since the required mass of various raw material powders is calculated based on the various parameters of the optical fiber to be drawn and the mass of the required optical fiber preform rod, only the required amount can be used, which can reduce raw material waste and improve raw material utilization. In addition, through die-casting, production stability can be improved and the difficulty of waveguide structure molding can be reduced.

[0060] Since the back calculation is performed based on various parameters of the optical fiber to be drawn and the mass of the optical fiber preform to be prepared, the various parameters of the optical fiber and the mass of the optical fiber preform are known quantities.

[0061] Since this application utilizes the concept of die casting, the raw materials can be in powder form, especially the elements that contribute to the refractive index, which can form a powdery substance. For example, as an example, the refractive index powder uses germanium dioxide, and the element that contributes to the refractive index is germanium.

[0062] In the above step 101, based on the core radius, the core relative refractive index, the cladding radius, and the mass of the optical fiber preform, the mass of the silica powder required for the core layer, the mass of the refractive index powder contributing to the refractive index, and the mass of the silica powder required for the cladding are obtained, which includes the following steps:

[0063] 201: Obtain the relative refractive index conversion coefficient.

[0064] Specifically, obtaining the relative refractive index conversion coefficient includes the following steps:

[0065] 301: Weigh a certain mass of silicon powder and refractive index powder that contributes to the refractive index, mix them evenly, and then die-cast to obtain a core layer prefabricated powder rod.

[0066] 302: Measure the relative refractive index of the core layer preform powder rod, and reversely calculate the relative refractive index conversion coefficient based on the first mapping relationship, the mass of the weighed silicon powder, and the mass of the refractive index powder.

[0067] The first mapping relationship includes:

[0068]

[0069] Wherein, Δ% is the relative refractive index of the core layer, m1 is the mass of silicon powder, m2 is the mass of the refractive index powder that contributes to the refractive index, and K1 is the relative refractive index conversion coefficient.

[0070] The relative refractive index conversion coefficient is a conversion coefficient between the proportion of the refractive index powder contributing to the refractive index in the total mass of the powder required for the core layer and the relative refractive index of the core layer. It can be regarded as the inherent characteristic of the refractive index powder and is a constant.

[0071] In order to make the calculation result more accurate, it is also possible to calculate multiple relative refractive index conversion coefficients, take the average value, and use it as K1.

[0072] Alternatively, multiple relative refractive index conversion coefficients may be calculated, and linear fitting may be performed between the multiple relative refractive index conversion coefficients and the relative refractive index of the corresponding core layer to obtain K1.

[0073] Alternatively, multiple relative refractive index conversion coefficients may be calculated, and polynomial fitting may be performed between the multiple relative refractive index conversion coefficients and the relative refractive index of the corresponding core layer to obtain K1.

[0074] Which of the above methods for obtaining the relative refractive index conversion coefficient is used can be determined according to actual circumstances.

[0075] 202: Combining the first mapping relationship, the relative refractive index conversion coefficient, the core radius of the optical fiber, the core relative refractive index, the cladding radius, and the mass of the optical fiber preform, reversely calculate the mass of silica powder required for the core layer, the mass of the refractive index powder that contributes to the refractive index, and the mass of silica powder required for the cladding.

[0076] Specifically, step 202 includes the following steps:

[0077] 401: According to the core radius and cladding radius of the optical fiber and the mass of the optical fiber preform, the total mass of the powder required for the core layer is obtained.

[0078] Since the optical fiber is proportionally smaller than the optical fiber preform, the mass proportion of the core layer in the optical fiber is the same as the mass proportion of the portion corresponding to the core layer in the optical fiber preform.

[0079] Take a core layer and a cladding layer as an example.

[0080] The total mass of powder required for the core layer = the mass of the optical fiber preform × (π*a 2 h) / (π*b 2 h), a and b are the core radius and cladding radius of the optical fiber, respectively, and h is the length of the optical fiber. Before and after sintering, the density of the preform rod and the optical fiber basically changes too little, so the density of the preform rod and the optical fiber can be regarded as equal, so they are offset in the calculation.

[0081] 402: Obtaining the mass of silicon powder required for the core layer and the mass of refractive index powder contributing to the refractive index based on the total mass of powder required for the core layer, the relative refractive index of the core layer, the first mapping relationship, and the relative refractive index conversion coefficient.

[0082] According to the total mass of powder required for the core layer, the relative refractive index of the core layer, and the relative refractive index conversion coefficient, by substituting them into the first mapping relationship, the mass of the refractive index powder that contributes to the refractive index can be calculated. Then, based on the total mass of powder required for the core layer, the mass of silicon powder required for the core layer can be calculated.

[0083] 403: Based on the mass of the optical fiber preform and the total mass of powder required for the core layer, the mass of silica powder required for the cladding layer is obtained. Subtract the total mass of powder required for the core layer from the mass of the optical fiber preform to obtain the mass of silica powder required for the cladding layer.

[0084] Furthermore, when the optical fiber core has N layers and N ≥ 2:

[0085] The core radius of the optical fiber includes the radius of each core layer, and the core relative refractive index includes the relative refractive index of each core layer;

[0086] The silicon powder required for the core layer and the refractive index powder material that contributes to the refractive index are mixed to obtain a core layer prefabricated powder corresponding to the core layer, including: the silicon powder required for each core layer and the refractive index powder material that contributes to the refractive index are mixed to obtain a core layer prefabricated powder corresponding to each core layer;

[0087] The relative refractive index and radius of each core layer are known quantities. The mass of the silicon powder required for each core layer and the refractive index powder contributing to the refractive index can be calculated using the calculation principle of step 401 above, which will not be repeated here.

[0088] The core layer preform powder corresponding to the core layer is fed into the core layer die-casting mold for die-casting to obtain a core layer preform, including the following steps:

[0089] 501: along the radial direction of the optical fiber, from inside to outside, first feed the core layer preform powder corresponding to the first core layer into the core layer die-casting mold corresponding to the first core layer for die-casting to obtain a first core layer preform.

[0090] 502: The core layer preform powder corresponding to the second core layer and the first core layer preform are then fed into a core layer die-casting mold corresponding to the second core layer for die-casting to obtain a second core layer preform.

[0091] 503: Similarly, finally, the core layer preform powder corresponding to the Nth core layer and the N-1th core layer preform are fed into the core layer die-casting mold corresponding to the Nth core layer for die-casting to obtain the core layer preform.

[0092] Furthermore, the preparation method further comprises the following step of obtaining the size of the core layer die-casting mold:

[0093] 601: Obtaining a radius conversion coefficient affected by pressure. The radius conversion coefficient affected by pressure can be used as a characteristic of the die-casting powder and is a constant.

[0094] Specifically, obtaining the radius conversion coefficient affected by pressure includes the following steps:

[0095] 701: Weigh a certain mass of core layer preform powder, place it into a test mold for die casting, and obtain a core layer preform powder rod;

[0096] 702: Sintering and drawing the core layer preform powder rod, measuring to obtain the core layer radius of the optical fiber, and combining the second mapping relationship and the radius of the test mold to reversely calculate the radius conversion coefficient affected by pressure.

[0097] The second mapping relationship includes:

[0098] r=D*K2

[0099] Where D is the radius of the test mold, r is the core radius of the optical fiber, and K2 is the radius conversion coefficient affected by pressure.

[0100] 602: Obtaining the radius of the core layer die-casting mold by combining the second mapping relationship, the radius conversion coefficient, and the core layer radius of the optical fiber;

[0101] 603: Determine the length of the core die-casting mold based on the mass of silicon powder required for the core layer, the mass of the refractive index powder that contributes to the refractive index, the radius of the core die-casting mold, and the density of the core preform powder in its naturally accumulated state when filled. The core preform powder includes the silicon powder required for the core layer and the refractive index powder that contributes to the refractive index.

[0102] When the core layer has multiple layers, the size of the core layer die-casting mold corresponding to each core layer can be calculated according to the above principle, so that the core layer die-casting mold corresponding to each core layer can be manufactured.

[0103] An embodiment of the present application further provides an optical fiber preform, which is prepared using the method for preparing an optical fiber preform of any of the above embodiments.

[0104] In the description of this application, it should be noted that the terms "upper" and "lower" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application. Unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be internal communication between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0105] It should be noted that, in this application, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0106] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A method for preparing an optical fiber preform, characterized in that: It includes: Obtain relative refractive index conversion coefficient; Combining the first mapping relationship, the relative refractive index conversion coefficient, the core radius of the optical fiber, the core relative refractive index, the cladding radius, and the mass of the optical fiber preform, the mass of the silica powder required for the core layer, the mass of the refractive index powder that contributes to the refractive index, and the mass of the silica powder required for the cladding are calculated. The first mapping relationship includes: Where ∆% is the relative refractive index of the core layer, m1 is the mass of silicon powder, m2 is the mass of refractive index powder that contributes to the refractive index, and K1 is the relative refractive index conversion coefficient; The silicon powder required for the core layer and the refractive index powder that contributes to the refractive index are mixed to obtain the core layer preform powder corresponding to the core layer; Feeding the core layer preform powder corresponding to the core layer into a core layer die-casting mold for die-casting to obtain a core layer preform; feeding the core layer preform and the silicon powder mass required for the cladding into a cladding die-casting mold for die-casting to obtain a semi-finished optical fiber preform rod; The optical fiber preform semi-finished product is sintered to obtain an optical fiber preform.

2. The method for preparing an optical fiber preform according to claim 1, wherein: Obtaining the relative refractive index conversion coefficient includes the following steps: Weigh a certain mass of silicon powder and refractive index powder that contributes to the refractive index, mix them evenly, and then die-cast them to obtain a core layer prefabricated powder rod; The relative refractive index of the core layer prefabricated powder rod is measured, and the relative refractive index conversion coefficient is calculated inversely based on the first mapping relationship, the mass of the weighed silicon powder, and the mass of the refractive index powder.

3. The method for preparing an optical fiber preform according to claim 1, wherein: Combining the first mapping relationship, the relative refractive index conversion coefficient, the core radius of the optical fiber, the core relative refractive index, the cladding radius, and the mass of the optical fiber preform, the mass of the silica powder required for the core layer, the mass of the refractive index powder contributing to the refractive index, and the mass of the silica powder required for the cladding are calculated, including the following steps: According to the core radius and cladding radius of the optical fiber and the mass of the optical fiber preform, the total mass of the powder required for the core layer is obtained; According to the total mass of the powder required for the core layer, the relative refractive index of the core layer, the first mapping relationship, and the relative refractive index conversion coefficient, the mass of the silicon powder required for the core layer and the mass of the refractive index powder contributing to the refractive index are obtained; The mass of silicon powder required for the cladding is obtained based on the mass of the optical fiber preform and the total mass of powder required for the core layer.

4. The method for preparing an optical fiber preform according to claim 1, wherein: When the core layer of the optical fiber has N layers and N ≥ 2, The core radius of the optical fiber includes the radius of each core layer, and the core relative refractive index includes the relative refractive index of each core layer; The silicon powder required for the core layer and the refractive index powder material that contributes to the refractive index are mixed to obtain a core layer prefabricated powder corresponding to the core layer, including: the silicon powder required for each core layer and the refractive index powder material that contributes to the refractive index are mixed to obtain a core layer prefabricated powder corresponding to each core layer; The core layer preform powder corresponding to the core layer is fed into the core layer die-casting mold for die-casting to obtain a core layer preform, including the following steps: Along the radial direction of the optical fiber, from inside to outside, firstly, the core layer preform powder corresponding to the first core layer is fed into the core layer die-casting mold corresponding to the first core layer for die-casting to obtain the first core layer preform; Then, the core layer prefabricated powder corresponding to the second core layer and the first core layer prefabricated part are fed into the core layer die-casting mold corresponding to the second core layer for die-casting to obtain the second core layer prefabricated part; Similarly, finally, the core layer preform powder corresponding to the Nth core layer and the N-1th core layer preform are fed into the core layer die-casting mold corresponding to the Nth core layer for die-casting to obtain the core layer preform.

5. The method for preparing an optical fiber preform according to claim 1, wherein: The preparation method further comprises the following steps of obtaining the size of the core layer die-casting mold: Get the radius conversion coefficient affected by pressure; The radius of the core die-casting mold is obtained by combining the second mapping relationship, the radius conversion coefficient, and the core radius of the optical fiber; the second mapping relationship includes: r=D*K2, where D is the radius of the test mold, r is the core radius of the optical fiber, and K2 is the radius conversion coefficient affected by pressure; The length of the core layer die-casting mold is obtained according to the mass of silicon powder required for the core layer, the mass of the refractive index powder contributing to the refractive index, the radius of the core layer die-casting mold, and the density of the core layer preform powder in a naturally accumulated state when filled.

6. The method for preparing an optical fiber preform according to claim 5, wherein: Obtaining the radius conversion coefficient affected by pressure includes the following steps: Weigh a certain mass of core layer preform powder, put it into a test mold for die casting, and obtain a core layer preform powder rod; The core layer preform powder rod is sintered and drawn, and the core layer radius of the optical fiber is obtained by measurement. The radius conversion coefficient affected by pressure is calculated by combining the second mapping relationship and the radius of the test mold.

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