A method for preparing a photonic crystal fiber preform

Abstract

The present invention belongs to the technical field of photonic crystal fibers, and particularly relates to a method for preparing a preform of a photonic crystal fiber. The preform prepared by the preparation method of the present invention has good quality, a smooth surface, few gaps, no bubbles inside, and a transparent and bright appearance. The aperture size and quantity thereof can be controlled by the diameter and quantity of the low-melting-point alloy rods in the mold, and preforms of different sizes and structures can be prepared as required. Demolding is simple, and there is no need to extract or extrude redundant parts, making the inside of the obtained photonic crystal fiber preform smoother. Moreover, the preparation method is simple, the conditions are mild, and it can be prepared without applying pressure.

Description

Technical Field

[0001] The present invention belongs to the technical field of photonic crystal fibers. More specifically, it relates to a method for preparing a preform of a photonic crystal fiber. Background Art

[0002] Photonic Crystal Fibers (PCF) are a type of fiber developed in recent years, and have a periodic microstructure on their cross-section. Compared with traditional single-mode and multi-mode fibers, photonic crystal fibers have many advantages such as low transmission energy consumption and no cut-off modes. The key to preparing photonic crystal fibers lies in the preparation and drawing of photonic crystal fiber preforms. The main methods for preparing photonic crystal fiber preforms include the stacking method, the drilling method, and the injection molding method. Currently, the commonly used method is the stacking method. The finished product rate of the photonic crystal fiber preform prepared by the stacking method is high, but the gaps between the obtained rods cannot be completely filled, and there will always be a certain gap left, and the inner surface of the holes in the obtained preform is rough. For example, a Chinese patent application discloses a method for preparing a photonic crystal fiber preform and its pipe arrangement equipment. It uses the stacking method to prepare a porous photonic crystal fiber preform. Although its fiber finished product rate is high, there will be gaps during the stacking process. During the drawing process of the polymer photonic crystal fiber preform, the air in the gaps expands when heated, thereby destroying the original structure of the polymer photonic crystal fiber preform and making the inner surface of the holes in the preform rough. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the defects and deficiencies that the photonic crystal fiber preform obtained by the existing preparation method has gaps between the rods, a rough inner surface of the holes, and many bubbles, and to provide a method for preparing a photonic crystal fiber preform. The photonic crystal fiber preform obtained by this method has a smooth inner surface of the holes, few gaps, no bubbles inside, a transparent and bright appearance, and simple and rapid demolding.

[0004] The above object of the present invention is achieved by the following technical solutions:

[0005] A method for preparing a photonic crystal fiber preform, comprising the following steps:

[0006] React methyl methacrylate with an initiator at 70 - 80 °C for 1 - 1.5 h, then pour it into a mold, first dry it once at 40 - 65 °C for 20 - 40 h, and then dry it twice at 65 - 90 °C for 40 - 70 min to obtain polymethyl methacrylate, and heat it to 100 - 110 °C until the low-melting-point alloy tube and low-melting-point alloy rod in the mold melt, thus obtaining.

[0007] The mold is composed of several low-melting-point alloy rods, low-melting-point alloy tubes, and fixing devices at both ends; several low-melting-point alloy rods are arranged in the low-melting-point alloy tubes, and the fixing devices at both ends of the low-melting-point alloy tubes fix the several low-melting-point alloy rods through several holes and prevent the pouring raw materials from flowing out; between the fixing devices, a pouring port is arranged at the port tube body near the low-melting-point alloy tube for pouring raw materials.

[0008] The present invention uses a two-stage drying method to dry the raw materials poured into the mold. By controlling the temperature and time of the two-stage drying, with the temperature of the first-stage drying lower than that of the second-stage drying, the obtained preform of the photonic crystal fiber can have good quality, a smooth surface, few gaps, no bubbles inside, and a transparent and bright appearance. If the temperature of the first-stage drying is higher than that of the second-stage drying, a violent polymerization phenomenon will occur. In addition, too high or too low temperatures in the first-stage drying and the second-stage drying will also affect the surface smoothness of the obtained preform and its quality effect.

[0009] The mold of the present invention uses low-melting-point alloy tubes and low-melting-point alloy rods. The raw materials are poured into the mold, and the heating temperature is controlled so that the raw materials do not melt while the low-melting-point alloy rods and low-melting-point alloy tubes made of low-melting-point alloy melt, thereby obtaining a preform of the photonic crystal fiber with a corresponding structure. The pore size and quantity of the obtained preform can be controlled by the diameter and quantity of the low-melting-point alloy rods, and preforms of different sizes and structures can be prepared as needed. At the same time, the demolding is simple, there is no need to extract or extrude redundant parts, the inside of the obtained preform of the photonic crystal fiber is smoother, and the mold can also be reused.

[0010] Preferably, the initiator is benzoyl peroxide or azobisisobutyronitrile (AIBN).

[0011] Preferably, the alloy in the low-melting-point alloy tube and the low-melting-point alloy rod is composed of two or more of bismuth, cadmium, tin, lead, dysprosium, or indium.

[0012] Preferably, the ratio of the addition amount of methyl methacrylate to the initiator is 80 - 120 ml: 0.1 g.

[0013] Preferably, the temperature of the first-stage drying is 40 - 60 °C.

[0014] Preferably, the time of the first-stage drying is 22 - 30 h.

[0015] Preferably, the temperature of the second-stage drying is 70 - 80 °C.

[0016] Preferably, the time of the second-stage drying is 45 - 60 min.

[0017] Preferably, the methyl methacrylate also undergoes impurity removal treatment.

[0018] More preferably, the steps of the impurity removal treatment are as follows:

[0019] Wash methyl methacrylate with 5-6% sodium hydroxide solution until colorless, then wash with water until neutral. After separating the water layer, dry the organic layer with anhydrous sodium sulfate.

[0020] The present invention has the following beneficial effects:

[0021] The preform of the photonic crystal fiber prepared by the preparation method of the present invention has good quality, a smooth surface, few gaps, no bubbles inside, and a transparent and bright appearance. The pore size and number can be controlled by the diameter and number of the low melting point alloy rods in the mold, and preforms with different sizes and structures can be prepared as needed. The demolding is simple, and there is no need to extract or extrude redundant parts, making the inside of the pores of the obtained photonic crystal fiber preform smoother. Moreover, the preparation method is simple, the conditions are mild, and it can be prepared without applying pressure. Description of the Drawings

[0022] Figure 1 It is a schematic structural diagram of the mold, where 1 is the low melting point alloy rod, 2 is the low melting point alloy tube, 3 is the fixing device, and 4 is the pouring port; a is the front view of the mold, and b is the enlarged front view of the fixing device 3.

[0023] Figure 2 It is a photo of the preform prepared in Example 1.

[0024] Figure 3 It is a photo of the preform prepared in Example 2.

[0025] Figure 4 It is a photo of the preform prepared in Example 3.

[0026] Figure 5 It is a photo of the preform prepared in Example 4.

[0027] Figure 6 It is a photo of the preform prepared in Comparative Example 1.

[0028] Figure 7 It is a photo of the preform prepared in Comparative Example 2.

[0029] Figure 8 It is a photo of the preform prepared in Comparative Example 3.

[0030] Figure 9 It is a photo of the preform prepared in Comparative Example 4.

[0031] Figure 10 It is a photo of the preform prepared in Comparative Example 5.

[0032] Figure 11Photograph of the preform obtained in Comparative Example 6.

[0033] Figure 12 Photograph of the preform obtained in Comparative Example 7.

[0034] Figure 13 Photograph of the preform obtained in Comparative Example 8.

[0035] Figure 14 Photograph of the preform obtained in Comparative Example 9.

[0036] Figure 15 Photograph of the preform obtained in Comparative Example 10. Detailed Description of the Invention

[0037] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field.

[0038] Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0039] The mold used in the experiment is composed of 4 low-melting alloy (52% bismuth, 40% lead, and 8% cadmium) rods 1, a low-melting alloy tube 2, and fixing devices 3 at both ends; 4 low-melting alloy rods 1 are arranged in the low-melting alloy tube 2, and the fixing devices 3 at both ends of the low-melting alloy tube 2 fix the 4 low-melting alloy rods 1 through 4 holes and prevent the pouring raw materials from flowing out; between the fixing devices 3, a pouring port 4 is arranged at the port tube body near the low-melting alloy tube 2 for pouring raw materials (the structural schematic diagram is as Figure 1 )

[0040] Preparation of Photonic Crystal Fiber Preform in Example 1

[0041] S1. Add 250 ml of methyl methacrylate to a separatory funnel, wash it several times with 50 ml of 5% sodium hydroxide solution until colorless, wash it with distilled water until neutral, separate the aqueous layer, and then add anhydrous sodium sulfate to the organic layer for drying to obtain purified methyl methacrylate.

[0042] S2. Pour the methyl methacrylate after impurity removal into a triangular flask, measure 0.25 g of benzoyl peroxide, cover the stopper, react for 1 h under a constant temperature water bath at 75 °C with continuous stirring, cool to room temperature, pour it into a mold, do not fill it up completely, leave a certain space to prevent spraying, seal the pouring opening of the mold with plastic wrap, dry it at 50 °C for 24 h first, and then dry it at 75 °C for 60 min to obtain polymethyl methacrylate. The melting point of polymethyl methacrylate is between 150 and 220 °C. Raise the temperature of the drying oven to 100 °C. Wait for the low melting point alloy tube and low melting point alloy rod to melt, and then wash it to obtain polymethyl methacrylate.

[0043] Preparation of Photonic Crystal Fiber Preform in Example 2

[0044] S1. Add 250 ml of methyl methacrylate to a separatory funnel, wash it several times with 50 ml of 5% sodium hydroxide solution until it is colorless, wash it with distilled water until it is neutral. After separating the water layer, add anhydrous sodium sulfate to the organic layer for drying to obtain methyl methacrylate after impurity removal.

[0045] S2. Pour the methyl methacrylate after impurity removal into a triangular flask, measure 0.25 g of benzoyl peroxide, cover the stopper, react for 1 h under a constant temperature water bath at 80 °C with continuous stirring, cool to room temperature, pour it into a mold, do not fill it up completely, leave a certain space to prevent spraying, seal the pouring opening of the mold with plastic wrap, dry it at 50 °C for 24 h first, and then dry it at 75 °C for 60 min to obtain polymethyl methacrylate. The melting point of polymethyl methacrylate is between 150 and 220 °C. Raise the temperature of the drying oven to 100 °C. Wait for the low melting point alloy tube and low melting point alloy rod to melt, and then wash it to obtain polymethyl methacrylate.

[0046] The difference from Example 1 is that the reaction temperature under the constant temperature water bath in step S2 is changed to 80 °C, and the reagents and conditions of the other steps are the same as those in Example 1.

[0047] Preparation of Photonic Crystal Fiber Preform in Example 3

[0048] S1. Add 250 ml of methyl methacrylate to a separatory funnel, wash it several times with 50 ml of 5% sodium hydroxide solution until it is colorless, wash it with distilled water until it is neutral. After separating the water layer, add anhydrous sodium sulfate to the organic layer for drying to obtain methyl methacrylate after impurity removal.

[0049] S2. Pour the methyl methacrylate after impurity removal into a triangular flask, measure 0.25 g of benzoyl peroxide, cover with a stopper, react for 1 h under a constant temperature water bath at 75 °C with continuous stirring, cool to room temperature, pour into a mold, do not fill it up completely, leave a certain space to prevent spraying, seal the pouring opening of the mold with plastic wrap, dry at 40 °C for 24 h first, and then dry at 80 °C for 60 min to obtain polymethyl methacrylate. The melting point of polymethyl methacrylate is between 150 and 220 °C. Raise the temperature of the drying oven to 100 °C, wait for the low melting point alloy tube and low melting point alloy rod to melt, and wash to obtain polymethyl methacrylate.

[0050] The difference from Example 1 is that the temperature of the first drying in step S2 is changed to 40 °C, and the temperature of the second drying is changed to 80 °C. The reagents and conditions of the remaining steps are the same as those in Example 1.

[0051] Preparation of the photonic crystal fiber preform in Example 4

[0052] S1. Add 250 ml of methyl methacrylate to a separatory funnel, wash it several times with 50 ml of 5% sodium hydroxide solution until colorless, wash it with distilled water until neutral, separate the water layer, and add anhydrous sodium sulfate to the organic layer for drying to obtain the methyl methacrylate after impurity removal.

[0053] S2. Pour the methyl methacrylate after impurity removal into a triangular flask, measure 0.25 g of benzoyl peroxide, cover with a stopper, react for 1 h under a constant temperature water bath at 75 °C with continuous stirring, cool to room temperature, pour into a mold, do not fill it up completely, leave a certain space to prevent spraying, seal the pouring opening of the mold with plastic wrap, dry at 65 °C for 24 h first, and then dry at 90 °C for 45 min to obtain polymethyl methacrylate. The melting point of polymethyl methacrylate is between 150 and 220 °C. Raise the temperature of the drying oven to 100 °C, wait for the low melting point alloy tube and low melting point alloy rod to melt, and wash to obtain polymethyl methacrylate.

[0054] The difference from Example 1 is that the temperature of the first drying in step S2 is changed to 65 °C, the temperature of the second drying is changed to 90 °C, and the time of the second drying is 45 min. The reagents and conditions of the remaining steps are the same as those in Example 1.

[0055] Preparation of the photonic crystal fiber preform in Comparative Example 1

[0056] S1. Add 250 ml of methyl methacrylate to a separatory funnel, wash it several times with 50 ml of 5% sodium hydroxide solution until colorless, wash it with distilled water until neutral, separate the water layer, and add anhydrous sodium sulfate to the organic layer for drying to obtain the methyl methacrylate after impurity removal.

[0057] S2. Pour the purified methyl methacrylate into a triangular flask, measure 0.25 g of benzoyl peroxide, cover the flask with a stopper, react for 1 h in a constant temperature water bath at 75 °C with continuous stirring, cool to room temperature, pour it into a mold (using a glass rod for the mold), do not fill it up completely, leave some space to prevent spraying, seal the pouring opening of the mold with plastic wrap, dry it at 50 °C for 24 h first, and then dry it at 75 °C for 60 min to obtain polymethyl methacrylate. The melting point of polymethyl methacrylate is between 150 and 220 °C. After cooling, directly pull it out to obtain polymethyl methacrylate.

[0058] The difference from Example 1 is that the low melting point alloy rod in the mold in step S2 is replaced with a glass rod, and the reagents and conditions in the remaining steps are the same as those in Example 1.

[0059] Preparation of the preform of the photonic crystal fiber for Comparative Example 2

[0060] S1. Add 250 ml of methyl methacrylate to a separatory funnel, wash it several times with 50 ml of 5% sodium hydroxide solution until it is colorless, wash it with distilled water until it is neutral. After separating the aqueous layer, add anhydrous sodium sulfate to the organic layer for drying to obtain the purified methyl methacrylate.

[0061] S2. Pour the purified methyl methacrylate into a triangular flask, measure 0.25 g of benzoyl peroxide, cover the flask with a stopper, react for 1 h in a constant temperature water bath at 75 °C with continuous stirring, cool to room temperature, pour it into a mold (the alloy rod of the mold is an aluminum rod), do not fill it up completely, leave some space to prevent spraying, seal the pouring opening of the mold with plastic wrap, dry it at 50 °C for 24 h first, and then dry it at 75 °C for 60 min to obtain polymethyl methacrylate. The melting point of polymethyl methacrylate is between 150 and 220 °C. Raise the temperature of the drying oven to 100 °C. After cooling, directly pull it out to obtain polymethyl methacrylate.

[0062] The difference from Example 1 is that the low melting point alloy rod in the mold in step S2 is replaced with an aluminum rod, and the reagents and conditions in the remaining steps are the same as those in Example 1.

[0063] Preparation of the preform of the photonic crystal fiber for Comparative Example 3

[0064] S1. Add 250 ml of methyl methacrylate to a separatory funnel, wash it several times with 50 ml of 5% sodium hydroxide solution until it is colorless, wash it with distilled water until it is neutral. After separating the aqueous layer, add anhydrous sodium sulfate to the organic layer for drying to obtain the purified methyl methacrylate.

[0065] S2. Pour the methyl methacrylate after impurity removal into a triangular beaker, measure 0.25 g of benzoyl peroxide, cover with a stopper, react in a constant temperature water bath at 75 °C for 1 h with continuous stirring, cool to room temperature, pour into a mold, do not fill it up completely, leave some space to prevent spraying, seal the pouring opening of the mold with plastic wrap, dry at 75 °C for 60 min first, and then dry at 50 °C for 24 h to obtain polymethyl methacrylate. The melting point of polymethyl methacrylate is between 150 and 220 °C. Raise the temperature of the drying oven to 100 °C, wait for the low melting point alloy tube and low melting point alloy rod to melt, and wash to obtain polymethyl methacrylate.

[0066] The difference from Example 1 is that the order of the first drying and the second drying in step S2 is reversed, and the reagents and conditions of the remaining steps are the same as those in Example 1.

[0067] Preparation of the photonic crystal fiber preform of Comparative Example 4

[0068] S1. Add 250 ml of methyl methacrylate to a separatory funnel, wash it several times with 50 ml of 5% sodium hydroxide solution until colorless, wash it with distilled water until neutral, separate the water layer, and add anhydrous sodium sulfate to the organic layer for drying to obtain the methyl methacrylate after impurity removal.

[0069] S2. Pour the methyl methacrylate after impurity removal into a triangular beaker, measure 0.25 g of benzoyl peroxide, cover with a stopper, react in a constant temperature water bath at 75 °C for 1 h with continuous stirring, cool to room temperature, pour into a mold, do not fill it up completely, leave some space to prevent spraying, seal the pouring opening of the mold with plastic wrap, dry at 65 °C for 24 h first, and then dry at 75 °C for 60 min to obtain polymethyl methacrylate. The melting point of polymethyl methacrylate is between 150 and 220 °C. Raise the temperature of the drying oven to 100 °C, wait for the low melting point alloy tube and low melting point alloy rod to melt, and wash to obtain polymethyl methacrylate.

[0070] The difference from Example 1 is that the temperature of the first drying in step S2 is changed to 65 °C, and the reagents and conditions of the remaining steps are the same as those in Example 1.

[0071] Preparation of the photonic crystal fiber preform of Comparative Example 5

[0072] S1. Add 250 ml of methyl methacrylate to a separatory funnel, wash it several times with 50 ml of 5% sodium hydroxide solution until colorless, wash it with distilled water until neutral, separate the water layer, and add anhydrous sodium sulfate to the organic layer for drying to obtain the methyl methacrylate after impurity removal.

[0073] S2. Pour the methyl methacrylate after impurity removal into a triangular flask, measure 0.25 g of benzoyl peroxide, cover with a stopper, react in a constant temperature water bath at 75 °C for 1 h with continuous stirring, cool to room temperature, pour into a mold, do not fill it up completely, leave a certain space to prevent spraying, seal the pouring opening of the mold with plastic wrap, dry at 50 °C for 24 h first, and then dry at 90 °C for 60 min to obtain polymethyl methacrylate. The melting point of polymethyl methacrylate is between 150 and 220 °C. Raise the temperature of the drying oven to 100 °C, wait for the low melting point alloy tube and low melting point alloy rod to melt, and wash to obtain polymethyl methacrylate.

[0074] The difference from Example 1 is that the temperature of the secondary drying in Step S2 is changed to 90 °C, and the reagents and conditions of the other steps are the same as those in Example 1.

[0075] Preparation of Photonic Crystal Fiber Preform of Comparative Example 6

[0076] S1. Add 250 ml of methyl methacrylate to a separatory funnel, wash it several times with 50 ml of 5% sodium hydroxide solution until it is colorless, wash it with distilled water until it is neutral. After separating the water layer, add anhydrous sodium sulfate to the organic layer for drying to obtain the methyl methacrylate after impurity removal.

[0077] S2. Pour the methyl methacrylate after impurity removal into a triangular flask, measure 0.25 g of benzoyl peroxide, cover with a stopper, react in a constant temperature water bath at 75 °C for 1 h with continuous stirring, cool to room temperature, pour into a mold, do not fill it up completely, leave a certain space to prevent spraying, seal the pouring opening of the mold with plastic wrap, dry at 60 °C for 30 h to obtain polymethyl methacrylate. The melting point of polymethyl methacrylate is between 150 and 220 °C. Raise the temperature of the drying oven to 100 °C, wait for the low melting point alloy tube and low melting point alloy rod to melt, and wash to obtain polymethyl methacrylate.

[0078] The difference from Example 1 is that the drying method in Step S2 is changed to only dry once, and the reagents and conditions of the other steps are the same as those in Example 1.

[0079] Preparation of Photonic Crystal Fiber Preform of Comparative Example 7

[0080] S1. Add 250 ml of methyl methacrylate to a separatory funnel, wash it several times with 50 ml of 5% sodium hydroxide solution until it is colorless, wash it with distilled water until it is neutral. After separating the water layer, add anhydrous sodium sulfate to the organic layer for drying to obtain the methyl methacrylate after impurity removal.

[0081] S2. Pour the methyl methacrylate after impurity removal into a triangular flask, measure 0.25 g of benzoyl peroxide, cover with a stopper, react for 1 h under a constant temperature water bath at 75 °C with continuous stirring, cool to room temperature, pour into a mold, do not fill it up completely, leave some space to prevent spraying, seal the pouring opening of the mold with plastic wrap, dry at 40 °C for 12 h first, then dry at 60 °C for 10 h, and finally dry at 75 °C for 60 min to obtain polymethyl methacrylate. The melting point of polymethyl methacrylate is between 150 and 220 °C. Raise the temperature of the drying oven to 100 °C. Wait for the low melting point alloy tube and low melting point alloy bar to melt, and then wash to obtain polymethyl methacrylate.

[0082] The difference from Example 1 is that the drying method in Step S2 is changed to drying in three times, and the reagents and conditions of the remaining steps are the same as those in Example 1.

[0083] Preparation of Photonic Crystal Fiber Preform for Comparative Example 8

[0084] S1. Add 250 ml of methyl methacrylate to a separatory funnel, wash it several times with 50 ml of 5% sodium hydroxide solution until colorless, wash it with distilled water until neutral. After separating the water layer, add anhydrous sodium sulfate to the organic layer for drying to obtain the methyl methacrylate after impurity removal.

[0085] S2. Pour the methyl methacrylate after impurity removal into a triangular flask, measure 0.25 g of benzoyl peroxide, cover with a stopper, react for 1 h under a constant temperature water bath at 60 °C with continuous stirring, cool to room temperature, pour into a mold, do not fill it up completely, leave some space to prevent spraying, seal the pouring opening of the mold with plastic wrap, dry at 50 °C for 24 h first, then dry at 75 °C for 60 min to obtain polymethyl methacrylate. The melting point of polymethyl methacrylate is between 150 and 220 °C. Raise the temperature of the drying oven to 100 °C. Wait for the low melting point alloy tube and low melting point alloy bar to melt, and then wash to obtain polymethyl methacrylate.

[0086] The difference from Example 1 is that the reaction temperature under the constant temperature water bath in Step S2 is changed to 60 °C, and the reagents and conditions of the remaining steps are the same as those in Example 1.

[0087] Preparation of Photonic Crystal Fiber Preform for Comparative Example 9

[0088] S1. Add 250 ml of methyl methacrylate to a separatory funnel, wash it several times with 50 ml of 5% sodium hydroxide solution until colorless, wash it with distilled water until neutral. After separating the water layer, add anhydrous sodium sulfate to the organic layer for drying to obtain the methyl methacrylate after impurity removal.

[0089] S2. Pour the methyl methacrylate after impurity removal into a triangular flask, measure 0.25 g of benzoyl peroxide, cover the stopper, react under a constant temperature water bath at 75 °C for 2 h with continuous stirring, cool to room temperature, pour it into a mold, do not fill it up completely, leave a certain space to prevent spraying, seal the pouring opening of the mold with plastic wrap, dry it at 50 °C for 24 h first, and then dry it at 75 °C for 60 min to obtain polymethyl methacrylate. The melting point of polymethyl methacrylate is between 150 and 220 °C. Raise the temperature of the drying oven to 100 °C. Wait for the low melting point alloy tube and low melting point alloy rod to melt, and then wash it to obtain polymethyl methacrylate.

[0090] The difference from Example 1 is that the reaction time under the constant temperature water bath in Step S2 is changed to 2 h, and the reagents and conditions of the remaining steps are the same as those in Example 1.

[0091] Preparation of Photonic Crystal Fiber Preform for Comparative Example 10

[0092] S1. Add 250 ml of methyl methacrylate to a separatory funnel, wash it several times with 50 ml of 5% sodium hydroxide solution until it is colorless, wash it with distilled water until it is neutral. After separating the water layer, add anhydrous sodium sulfate to the organic layer for drying to obtain the methyl methacrylate after impurity removal.

[0093] S2. Pour the methyl methacrylate after impurity removal into a triangular flask, measure 0.25 g of benzoyl peroxide, cover the stopper, react under a constant temperature water bath at 75 °C for 0.5 h with continuous stirring, cool to room temperature, pour it into a mold, do not fill it up completely, leave a certain space to prevent spraying, seal the pouring opening of the mold with plastic wrap, dry it at 50 °C for 24 h first, and then dry it at 75 °C for 60 min to obtain polymethyl methacrylate. The melting point of polymethyl methacrylate is between 150 and 220 °C. Raise the temperature of the drying oven to 100 °C. Wait for the low melting point alloy tube and low melting point alloy rod to melt, and then wash it to obtain polymethyl methacrylate.

[0094] The difference from Example 1 is that the reaction time under the constant temperature water bath in Step S2 is changed to 0.5 h, and the reagents and conditions of the remaining steps are the same as those in Example 1.

[0095] Take pictures of the photonic crystal fiber preforms obtained in Examples 1 - 4 and Comparative Examples 1 - 10 and observe their morphologies. The photos of the photonic crystal fiber preforms obtained in Examples 1 - 4 and Comparative Examples 1 - 10 are as Figures 2 to 15 shown.

[0096] From Figures 2 to 15It can be seen that: the preforms prepared in Examples 1 to 3 have smooth surfaces, no gaps and bubbles, and are transparent and bright in appearance; the preform prepared in Example 4 has only a small number of bubbles; while the preforms prepared in Comparative Examples 1 to 10 have poor quality, with rough surfaces, many gaps and bubbles, and low transparency.

[0097] The morphologies of the photonic crystal fiber preforms obtained in Examples 1 to 4 are shown in Table 1:

[0098] Table 1 Morphologies of the Photonic Crystal Fiber Preforms Obtained in Examples 1 to 4

[0099]

[0100] The morphologies of the photonic crystal fiber preforms obtained in Comparative Examples 1 to 10 are shown in Table 2:

[0101] Table 2 Morphologies of the Photonic Crystal Fiber Preforms Obtained in Examples 1 to 4

[0102]

[0103] It can be seen from Table 1 and Table 2 that the photonic crystal fiber preforms prepared in Examples 1 to 3 of the present invention have smooth surfaces, few gaps, no bubbles inside, and are transparent and bright in appearance, and all have better quality than those of the comparative examples.

[0104] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for preparing a preform of a photonic crystal fiber, characterized in that, The steps are as follows: Methyl methacrylate and an initiator are reacted at 70 - 80 °C for 1 - 1.5 h and then poured into a mold. First, it is dried once at 40 - 60 °C for 22 - 30 h, and then dried twice at 70 - 80 °C for 45 - 60 min to obtain polymethyl methacrylate. Then it is heated to 100 - 110 °C until the low - melting - point alloy tubes and low - melting - point alloy rods in the mold melt, thus obtaining the product; The mold is composed of several low - melting - point alloy rods (1), low - melting - point alloy tubes (2) and fixing devices (3) at both ends; several low - melting - point alloy rods (1) are arranged in the low - melting - point alloy tubes (2). The fixing devices (3) at both ends of the low - melting - point alloy tubes (2) fix several low - melting - point alloy rods (1) through several holes and prevent the casting raw materials from flowing out; between the fixing devices (3), a casting port (4) is arranged at the port tube body near one side of the low - melting - point alloy tube (2) for casting raw materials.

2. The preparation method according to claim 1, wherein The initiator is benzoyl peroxide or azobisisobutyronitrile.

3. The preparation method according to claim 1, characterized in that, The alloy in the low - melting - point alloy tube and the low - melting - point alloy rod is composed of two or more of bismuth, cadmium, tin, lead, dysprosium or indium.

4. The preparation method according to claim 1, characterized in that, The ratio of the addition amounts of methyl methacrylate and the initiator is 80 - 120 ml:0.1 g.

5. The preparation method according to claim 1, characterized in that, The methyl methacrylate also undergoes impurity removal treatment.

6. The preparation method according to claim 5, wherein The steps of the impurity removal treatment are as follows: Wash methyl methacrylate with a sodium hydroxide solution with a concentration of 5 - 6% until it is colorless, then wash it with water until it is neutral. After separating the water layer, dry the organic layer with anhydrous sodium sulfate.

Images