Microstructured optical fiber preform and method for manufacturing the same

Abstract

The present disclosure provides a kind of microstructure optical fiber preform and its manufacturing method, method includes the following steps: S101: with chemical vapor deposition torch to the target stick direction emit silica, to deposit preform loose body on target stick;S102: if the thickness of the preform loose body reaches the first specified value, while emitting high-purity quartz powder to the target stick direction with low-temperature plasma torch, continue to emit silica to the target stick direction with the chemical vapor deposition torch, to continue to deposit preform loose body on target stick;S103: if the thickness of the preform loose body reaches the second specified value, stop emitting high-purity quartz powder with the low-temperature plasma torch, but continue to emit silica to the target stick direction with the chemical vapor deposition torch, to continue to deposit preform loose body on target stick;S104: if the weight of the preform loose body reaches the third specified value, the preform loose body is treated at high temperature to form the microstructure optical fiber preform.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of optical fiber transmission, and more particularly to a microstructured optical fiber preform and a method of manufacturing the same. BACKGROUND

[0002] In most microstructured optical fibers, a plurality of voids are axially extended around a core region along the entire length of the optical fiber. Among them, at least one microstructure is introduced in the optical fiber structure, such as a void structure in the cladding, or a defect structure in the core, etc., so as to obtain different performance from the conventional optical fiber. Unlike ordinary single-mode optical fibers, most microstructured optical fibers are composed of a single quartz material with a uniform void distribution therein, thereby having flexible dispersion characteristics, low loss characteristics, high nonlinearity characteristics, and high birefringence characteristics. In the prior art, in the microstructured optical fiber structure, the voids in the cladding are arranged around the core of the optical fiber in a regular periodic distribution. If a cross section of the optical fiber is taken along the length of the optical fiber, the same independent voids can be found in the uniform periodic void distribution.

[0003] In the prior art, the manufacturing method of the microstructured optical fiber adopts a "stacking-drawing" method, which stacks silica rods or thin tubes according to the required shape and aggregates them together to form a preform in a high-temperature processing mode. Then the preform is drawn into an optical fiber. However, the "stacking-drawing" method has some defects. For example, it is difficult to stably aggregate hundreds of extremely thin rods or tubes together, and external tools are needed, which can easily contaminate the product. Moreover, gaps can be generated during the stacking and aggregation into a preform, which can introduce foreign impurities, thereby significantly increasing the attenuation of the optical fiber. In addition, the preform is composed of multiple rods or tubes, which can easily cause internal defects due to interface misalignment, and uncontrollable deformation of the voids. In addition, the low production efficiency and high production cost also make this method not very suitable for industrial production. The mechanical stacking method currently used to manufacture optical fibers is difficult to aggregate before forming a preform glass rod, and it is also difficult to form a relatively uniform void in the drawn optical fiber.

[0004] Therefore, it is desirable to develop a structural design of an optical fiber preform with a void distribution different from a periodic distribution, and to develop a manufacturing method of such an optical fiber preform. SUMMARY

[0005] In order to develop a structural design of an optical fiber preform with a void distribution different from a periodic distribution, and to develop a manufacturing method of such an optical fiber preform, the present disclosure proposes a microstructured optical fiber preform and a method of manufacturing the same.

[0006] One aspect of the present disclosure relates to a microstructured optical fiber preform, comprising:

[0007] A core region having a first refractive index and a cladding region having a second refractive index, the refractive index of the cladding region being less than the refractive index of the core region such that light transmitted through the optical fiber is substantially maintained within the core region, the cladding region including a plurality of non-periodically distributed voids therein.

[0008] The microstructured optical fiber preform, the distance between the voids and the core region is not less than 4% of the diameter of the optical fiber preform.

[0009] In the cladding region, the distance from the core region is not more than 12% of the diameter of the optical fiber preform, the percentage of void area is not more than 15% and not less than 3%.

[0010] Another aspect of the present disclosure relates to a method for manufacturing a microstructured optical fiber preform, comprising the following steps:

[0011] S101: spraying silica towards the target rod with a chemical vapor deposition torch to deposit a preform loose body on the target rod;

[0012] S102: if the thickness of the preform loose body reaches a first specific value, continue spraying silica towards the target rod with the chemical vapor deposition torch while spraying high-purity quartz powder towards the target rod with a low-temperature plasma torch to continue depositing the preform loose body on the target rod;

[0013] S103: if the thickness of the preform loose body reaches a second specific value, stop spraying high-purity quartz powder with the low-temperature plasma torch, but continue spraying silica towards the target rod with the chemical vapor deposition torch to continue depositing the preform loose body on the target rod;

[0014] S104: if the weight of the preform loose body reaches a third specific value, perform high-temperature treatment on the preform loose body to form the microstructured optical fiber preform.

[0015] The low-temperature plasma torch comprises a Venturi tube connected to a cavity for storing high-purity quartz powder.

[0016] The low-temperature plasma torch sprays high-purity quartz powder towards the target rod when the high-purity inert gas passes through the Venturi tube.

[0017] The distance between the low-temperature plasma torch and the chemical vapor deposition torch is not more than 200 mm.

[0018] The number of the chemical vapor deposition torches is at least 2, and the gas outlet angles of the chemical vapor deposition torches are the same or deviate from each other by a first angle.

[0019] The number of the low-temperature plasma torches is at least one, and the low-temperature plasma torches have the same gas outlet angle as at least one of the chemical vapor deposition torches or have a second angle deviated from each other.

[0020] The first specific value is 3-10 layers, and the difference between the second specific value and the first specific value is 50-150 layers.

[0021] In the high-temperature treatment of the preformed loose body, the water and metal impurities are removed through the treatment of a drying agent and a strong oxidant, at least one inert gas is introduced to replace the air in the preformed loose body, and calcination is performed at a temperature of 1500-1550 ℃ to form a microstructure optical fiber preform rod containing voids only in the cladding region. The microstructure optical fiber preform rod is in a glass body form.

[0022] In the prior art, the silica powder layer (prepared by chemical vapor deposition) is shrunk by heating the powder layer with relatively uniform particle size at a temperature lower than the melting point of the powder layer, so that the substance spontaneously fills the gap between the particles to densify and form a glass body with low free energy and stable performance.

[0023] In the present disclosure, a small amount of high-purity quartz powder (physically sprayed from a low-temperature plasma torch) is doped in the silica powder layer (prepared by chemical vapor deposition) with relatively uniform particle size. During high-temperature densification, the particle size difference between the high-purity quartz powder and the powder layer causes distortion dislocation of the grain boundary, forming a glass body containing a certain amount of micro voids. The existence of the voids reduces the refractive index of the cladding, and further makes the refractive index difference between the core region and the cladding meet the design requirements.

[0024] The present disclosure can control the proportion of the high-purity quartz powder sprayed by the low-temperature plasma torch and the silica sprayed by the chemical vapor deposition torch on the surface of the deposited layer by adjusting the size of the inert gas flow of the low-temperature plasma torch, and further control the size and number of the voids. In the cladding manufacturing, the distribution of the voids is increased by increasing the sprayed high-purity quartz powder, to further adjust the refractive index difference between the core and the cladding. BRIEF DESCRIPTION OF DRAWINGS

[0025] More details, features and advantages of the present disclosure are disclosed in the following description of exemplary embodiments in conjunction with the accompanying drawings, in which:

[0026] Figure 1 A flowchart of a manufacturing method of a microstructure optical fiber preform rod according to an exemplary embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0027] The present disclosure can be implemented in various forms and should not be interpreted as being limited to the embodiments set forth herein, which are provided for a more thorough and complete understanding of the present disclosure.

[0028] The various steps recited in the method embodiments of the present disclosure can be performed in different orders and / or in parallel. In addition, the method embodiments can include additional steps and / or omit performing the steps shown. The scope of the present disclosure is not limited in this regard.

[0029] The term "comprising" and variations thereof as used herein are open-ended, that is, "including but not limited to". The term "based on" is "based, at least in part, on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments". Related terms shall be construed accordingly. It is to be noted that the recitation of "first", "second", etc. concepts in the present disclosure merely serve to differentiate different apparatuses, modules or units, and does not imply a sequence or interdependence of the functions performed by these apparatuses, modules or units.

[0030] It should be noted that the modification of "one", "multiple" mentioned in the present disclosure is illustrative and not restrictive, and those skilled in the art should understand that unless the context clearly indicates otherwise, it should be understood as "one or more".

[0031] Microstructured optical fiber is a new type of optical fiber, which is uniformly arranged with voids along the axial direction in quartz optical fiber, and there is a periodic two-dimensional structure from the end face of the optical fiber. If one of the holes is damaged and missing, a defect will occur, and light can propagate in the defect. Unlike ordinary single-mode optical fibers, microstructured optical fibers are composed of a single quartz material with periodic void distribution. Since the arrangement and size of the voids in the microstructured optical fiber have a lot of control leeway, the optical transmission characteristics can be designed as needed. In the core-cladding structure, at least one microstructure is introduced, such as a void structure in the cladding or a defect structure in the core. In this way, properties different from traditional optical fibers are obtained. The microstructure introduced in the present disclosure increases the design freedom of the optical fiber. The high refractive index core region is surrounded by a microstructure composed of quartz and voids. There is a large refractive index difference between glass and air or other gases, forming new characteristics of the optical fiber. The cladding structure has a relatively uniform refractive index in space. The refractive index of this region is designed and adjusted to meet the process requirements.

[0032] One embodiment of the present disclosure proposes a microstructured optical fiber preform, comprising:

[0033] A core region having a first index of refraction and a cladding region having a second index of refraction, the index of refraction of the cladding region being less than the index of refraction of the core region such that light transmitted through the optical fiber is substantially maintained within the core region, the cladding region including a plurality of non-periodically distributed voids therein.

[0034] In one embodiment, the voids are not less than 4% of the diameter of the optical fiber preform from the core region. In another embodiment, the void area percentage is not greater than 15% and not less than 3% in the void containing cladding region that is not more than 12% of the diameter of the optical fiber preform from the core region. The void area percentage is the ratio of the area containing voids to the cross-sectional area of the micro optical fiber preform. The non-periodically disposed voids include a cladding region in the void containing region having a void area percentage between 3% and 15% and an average number density of voids greater than 1 voids per square micron in the void containing region. The non-periodically disposed voids in the void containing region of the cladding preferably have a void area percentage greater than 6% in the void containing region to sufficiently lower the index of refraction of the cladding relative to the index of refraction of the core of the optical fiber to significantly improve the macrobend performance. The non-periodically disposed voids in the void containing region of the cladding preferably have an average number density of voids greater than 10 voids per square micron in the void containing region. When the average number density is greater, the bend performance is more uniformly improved along a longer length of the optical fiber.

[0035] In some preferred embodiments, a germanium doped core is used as the core of the optical fiber. However, the use of germanium and / or fluorine is not critical.

[0036] The non-periodically distributed voids or holes in the optical fiber formed by using the methods described herein are located in the cladding of the optical fiber. Such voids or holes serve to lower the index of refraction. By designing the consolidation parameters such that the maximum diameter of the voids or holes is less than the wavelength of the light to be transmitted along the length of the optical fiber (i.e., less than 1550 nanometers for optical fibers used in telecommunications applications), the optical fiber can be effectively used to transmit information of a particular wavelength. The term "non-periodically disposed" or "non-periodically distributed" means that the voids are randomly or non-periodically distributed over a portion of the optical fiber when a cross-section of the optical fiber is taken (e.g., a cross-section taken perpendicular to the longitudinal axis). Similar cross-sections taken at different points along the length of the optical fiber will show different cross-sectional void patterns, i.e., the various cross-sections will have different void patterns in which the distribution of the voids and the size of the voids do not match. That is, the voids are non-periodic, i.e., they are not periodically disposed within the structure of the optical fiber. The voids are elongated (slim) along the length of the optical fiber (i.e., parallel to the longitudinal axis), but do not extend the entire length of the optical fiber for a typical length of transmission optical fiber. The voids are less than 1 meter long along the length of the optical fiber.

[0037] A method for manufacturing a microstructured optical fiber, a preform loose body is formed by a conventional soot deposition method (e.g., an outside vapor deposition (OVD) method or a vapor axial deposition (VAD) method). The preform loose body is sintered under certain gas atmosphere and temperature conditions to form a microstructured optical fiber preform rod (in the form of a glass body) containing voids, and finally, the microstructured optical fiber preform rod is drawn into an optical fiber by a tower device. In this method, silica and doped silica particles are formed by burning in a flame and deposited in the form of soot. For OVD, silica particles are deposited on the outside of a cylindrical target rod layer by layer by passing a soot-laden flame across the axis of the cylindrical target rod to form a porous soot preform. The porous soot preform is then treated with a drying agent (e.g., chlorine) to remove water and metal impurities, and then consolidated or calcined at a temperature of 1100-1550°C in a consolidation furnace to form a glass blank containing voids or holes.

[0038] As shown in FIG. 1, one embodiment of the present disclosure proposes a method for manufacturing a microstructured optical fiber preform rod, including the following steps: Figure 1

[0039] S101: A chemical vapor deposition torch is used to spray silica towards a cylindrical target rod to deposit a preform loose body on the target rod;

[0040] S102: If the thickness of the preform loose body reaches a first specified value, while the low-temperature plasma torch is used to spray high-purity quartz powder towards the target rod, the chemical vapor deposition torch is continued to be used to spray silica towards the target rod to continue to deposit the preform loose body on the target rod;

[0041] S103: If the thickness of the preform loose body reaches a second specified value, the low-temperature plasma torch is stopped to spray high-purity quartz powder, and the chemical vapor deposition torch is continued to be used to spray silica towards the target rod to continue to deposit the preform loose body on the target rod;

[0042] S104: If the weight of the preform loose body reaches a third specified value, the preform loose body is subjected to high-temperature treatment to form the microstructured optical fiber preform rod.

[0043] The microstructured optical fiber preform rod is in the form of a glass body, and after the microstructured optical fiber preform rod is manufactured, the glass body (microstructured optical fiber preform rod) is drawn into a microstructured optical fiber by a tower device.

[0044] In step S101, the chemical vapor deposition torch is used to spray silica towards the cylindrical target rod to deposit the preform loose body on the target rod, so that the high-purity quartz powder sprayed by the low-temperature plasma torch in step S102 can easily adhere to the preform loose body. ​

[0045] Without the step S101 of spraying the silica from the chemical vapor deposition torch toward the cylindrical target rod, the high-purity quartz powder sprayed from the low-temperature plasma torch in step S102 is not easy to adhere to the cylindrical target rod.

[0046] In step S102, the high-purity quartz powder is the key to generating the voids. The low-temperature plasma torch does not perform a chemical process, and the chemical structure of the quartz powder is always SiO2. Only the physical form of the quartz powder is different from the silica particles sprayed from the chemical vapor deposition torch. In one embodiment, the high-purity quartz powder is a 5N quartz powder. The 5N quartz powder is a high-purity silicon-based material with a purity of up to 99.999%. This material contains almost no impurity elements, ensuring the special physical and chemical properties of high-purity silicon materials. The 5N quartz powder has excellent high purity, stability, and high-temperature resistance, and can operate stably in extreme environments. First, high purity: the purity of 5N indicates that the impurity content in the quartz powder is very low, which can meet the requirements of some application fields with high purity requirements; second, stability: due to high purity, the chemical and physical properties of the quartz powder are relatively stable and are not easy to change.

[0047] In the prior art, the silica powder layer (prepared by chemical vapor deposition) is shrunk by heating the powder layer with a relatively uniform particle size at a temperature lower than the melting point of the powder layer, so that the material spontaneously fills the interstitial space between the particles to densify and form a glass body with low free energy and stable performance. In general vapor deposition methods (such as the outside vapor deposition (OVD) method or the vapor axial deposition (VAD) method), silica particles are generated by chemical reaction in a flame and are deposited on the target rod in the form of soot through thermal migration.

[0048] In one embodiment of the present disclosure, a small amount of high-purity quartz powder (physically sprayed from a low-temperature plasma torch) with a relatively large particle size is doped in the silica powder layer (prepared by chemical vapor deposition) with a relatively uniform particle size. During layer-by-layer deposition, the particle size of the high-purity quartz powder can be on the order of millimeters, but the silica particle powder generated by chemical synthesis can be on the order of nanometers, which are not of the same order of magnitude. The high-purity quartz powder is relatively coarse, and the chemically generated silica is relatively fine. The preform loose body is relatively loose, so the high-purity quartz powder sprayed on the surface is fused into the deposited layer. Because the target rod is constantly rotating, a layer-by-layer deposited layer is formed on the surface of the target rod. As the number of layers increases, the outer diameter of the preform loose body gradually increases. During high-temperature densification, the particle size difference between the high-purity quartz powder and the powder layer causes the grain boundary to be distorted and dislocated, forming a glass body containing a certain amount of small voids. The presence of voids reduces the refractive index of the cladding layer, and the refractive index difference between the core region and the cladding layer meets the design requirements.

[0049] Further analysis: The silica generated by the chemical vapor deposition torch is small in size and small in gap due to the high temperature. In general, the silica generated by the chemical vapor deposition torch is smaller and less likely to generate gaps. In order to reduce the refractive index of the cladding layer, it is necessary to form larger gaps; in order to form larger gaps, the present disclosure aims to: enhance the adhesion performance of the particle surface. Because the inventors consider that particles with low surface activity are not easy to adhere to the target rod surface and have low deposition efficiency. In the low-temperature plasma in the non-thermodynamic equilibrium state, the electrons have high energy and can break the chemical bonds of the material surface molecules, improve the chemical reaction activity of the particles, and enhance the adhesion performance of the particle surface. The present disclosure can control the proportion of high-purity quartz powder sprayed by the low-temperature plasma torch and silica sprayed by the chemical vapor deposition torch on the surface of the deposited layer by adjusting the size of the inert gas flow of the low-temperature plasma torch, improve the activity of the particle surface, form a dense crosslinked layer, and further control the size and number of gaps. The high-purity quartz powder sprayed by the physical method has larger particle diameter, and further generates larger gaps during subsequent high-temperature calcination. In the cladding layer manufacturing, the distribution of the gaps is increased by increasing the sprayed high-purity quartz powder, so as to further adjust the refractive index difference of the core and cladding layer.

[0050] In one embodiment, the first specific value is preferably 3-10 layers; the difference between the second specific value and the first specific value is preferably 50-150 layers. The first specific value determines the distance between the gap and the core region. The second specific value determines the distance distribution range of the cladding region containing the gap and the core region. The first specific value and the second specific value are measured by a laser measuring instrument. During the deposition of the optical fiber preform, multiple layers of coating are usually deposited, and the coating material includes silica. The thickness of each layer can be determined according to specific needs, and in general cases, the thickness of each layer can be between several microns and several hundred microns. In the present disclosure, the concept of layer refers to the one-way running of each torch relative to the preformed loose body of the optical fiber preform during the deposition process.

[0051] Depositing 3-10 layers and 50-150 layers is to adjust the doping ratio between the high-purity quartz powder sprayed by the low-temperature plasma torch and the silica sprayed by the chemical vapor deposition torch on the deposited layer according to the process requirements, so as to generate a certain amount of gaps in the axial relative position of the cladding region of the optical fiber preform. The low-temperature plasma torch sprays high-purity quartz powder by physical means, which is melted into the preformed loose body at high temperature, and 50-150 layers are deposited. In this process, the chemical vapor deposition torch continuously sprays flame to generate silica, which melts the high-purity quartz powder into the loose body; solves the problem of not being able to generate gaps, and can form gaps in the cross section, and the formed gaps are mostly distributed in a non-periodic manner.

[0052] In one embodiment of the present disclosure, a threshold of weight is used instead of a threshold of thickness in terms of controlling the time node of stopping the deposition. Because the density of the loose body changes with the change of the deposition thickness, it is not accurate to control the thickness of the layer, so in this embodiment, a third specific value (a weight threshold for stopping the deposition of the chemical vapor deposition torch in step S104) is used to determine whether the dust of a sufficient thickness is deposited so that the deposition work of the chemical vapor deposition torch can be stopped. Since the optical fiber preform manufacturing system has integrated a weight sensor, the weight of the preformed loose body of the optical fiber preform can be measured and recorded in real time during the deposition process. For example, when the dynamic weight of the preformed loose body of the optical fiber preform reaches the third specific value within a unit time (e.g., 1 minute), the chemical vapor deposition torch can be stopped.

[0053] The silica sprayed by the chemical vapor deposition torch (chemical method) and the high-purity quartz powder sprayed by the low-temperature plasma torch (physical method) are deposited on the surface of the target rod, and the loose body is formed in the form of soot by burning in the flame. In one embodiment, during the high-temperature treatment of the preformed loose body, the water and metal impurities are removed by drying agent and strong oxidizing agent treatment, at least one inert gas is introduced to replace the air in the preformed loose body with pores, and calcination is carried out at a temperature of 1500-1550°C to form a microstructure optical fiber preform (in the form of a glass body) containing pores only in the cladding region. The at least one inert gas has a small molecular weight and strong permeability.

[0054] In one embodiment, the low-temperature plasma torch includes a Venturi tube connected to a cavity for storing high-purity quartz powder; when the high-purity inert gas passes through the Venturi tube, the low-temperature plasma torch sprays the high-purity quartz powder towards the target rod. The input of the low-temperature plasma torch is high-purity quartz powder and high-purity inert gas (containing at least one gas selected from the group consisting of nitrogen, argon, CO2, oxygen, chlorine, CF4, CO, SO2, krypton, and mixtures thereof), the output of the low-temperature plasma torch is high-purity quartz powder that is more fluffy and has larger particles, and the temperature of the low-temperature plasma torch is a temperature lower than 1500 degrees, such as 800 degrees, 900 degrees, 1000 degrees, 1100 degrees, 1100 degrees, 1200 degrees, 1300 degrees, or a temperature between the above values. The low-temperature plasma torch uses the Venturi effect to bring out the high-purity quartz powder as required by the process using high-purity inert gas, and the physical structure of the high-purity quartz powder is different from that of the conventional SiO2 dust obtained by deposition.

[0055] In one embodiment, the low temperature plasma torch is within a distance of no more than 200 mm from the chemical vapor deposition torch. The number of the chemical vapor deposition torches is at least two, and the gas outlet angles of the chemical vapor deposition torches are the same or deviate from each other by a first angle, wherein the first angle can be no more than 2°; or the first angle can be no more than 5°; or the first angle can be no more than 10°.

[0056] In one embodiment, the number of the low temperature plasma torches is at least one, and the gas outlet angles of the low temperature plasma torches are the same or deviate from each other by a second angle, wherein the second angle can be no more than 2°; or the second angle can be no more than 5°; or the second angle can be no more than 10°.

[0057] In one embodiment, when the various torches are unidirectionally operated relative to the preform loose body of the optical fiber during the deposition process, the preform loose body rotates or moves, but the torches do not rotate or move.

[0058] In one embodiment, the chemical vapor deposition torch adopts a bottom spray angle or a top spray angle, or deviates from the bottom spray angle or the top spray angle by a third angle, wherein the third angle can be no more than 2°; or the third angle can be no more than 5°; or the third angle can be no more than 10°.

[0059] In one embodiment, the low temperature plasma torch adopts a bottom spray angle or a top spray angle, or deviates from the bottom spray angle by a fourth angle, wherein the fourth angle can be between 0° and 150°, and no more than 150°.

[0060] Wherein, the bottom spray angle means that the torch sprays vertically upward from the bottom, and the spraying direction of the torch is the vertical direction; the top spray angle means that the torch sprays downward from the top, and the spraying direction forms an angle of 90-150 degrees with the vertical direction,

[0061] In one specific embodiment, some torches are closer to the head of the target rod, some torches are closer to the tail of the target rod, and some torches are closer to the center of the target rod; in general, the torches are basically in the middle part of the target rod. The target rod moves up and down or rotates, but the three torches basically spray vertically on a line, and the distance between the torches is very small. These torches include chemical vapor deposition torches or low temperature plasma torches.

[0062] The method of the present disclosure uses direct and indirect methods to produce silica particles and attach them to the target rod to make a preform loose body. The specific process is: 1. Feed the chemical raw materials (such as hydrogen, oxygen, and silicon tetrachloride) into two or more chemical vapor deposition torches, and generate silica by chemical reaction, depositing on the outside of the cylindrical target rod layer by layer, with the number of deposited layers controlled between 3-10 layers; 2. Another group of low-temperature plasma torches physically spray high-purity quartz powder into the preform loose body at high temperature, depositing 50-150 layers, while the chemical vapor deposition torches continue to generate silica by spraying flames, and the high-purity quartz powder is melted into the preform loose body; 3. After the high-purity quartz powder reaches a certain level, the low-temperature plasma torch stops spraying high-purity quartz powder, and the chemical vapor deposition torch continues to deposit by feeding chemical raw materials, and finally completes the preform loose body. This porous preform loose body is then treated with a drying agent (such as chlorine) in a sintering furnace to remove water and metal impurities, while at least one inert gas with a small molecular weight and high permeability (such as helium, nitrogen, deuterium, CO2, argon, etc.) or their mixture is fed in to replace the air in the porous loose body, reducing the larger voids, and calcining at a temperature of 1500-1550°C to form a microstructured optical fiber preform rod (in the form of a glass body) containing voids only in the cladding region. In order to generate sufficient voids, the present disclosure uses multiple torches during vapor deposition, with at least two torches using chemical reaction to generate silica particles, and at least one torch using physical method to spray high-purity quartz powder into the powder at high temperature. During the sintering process, the surface energy drives the viscous flow sintering, and due to the incompatibility of the two phases, many closed pores are generated during the densification process, leaving one or more hollow voids in the preform. These voids will not close during the drawing operation of drawing the optical fiber from the preform, and finally a multi-void microstructured optical fiber is formed.

[0063] Through the manufacturing method of the present disclosure, a microstructured optical fiber can be made such that the voids are located therein, forming the cladding of the optical fiber. The optical fiber is composed of a core region with a first refractive index and a cladding region with a second refractive index, the refractive index of the cladding region being lower than that of the core region, so that the light transmitted through the optical fiber is basically maintained within the core region.

[0064] Using the techniques disclosed herein, voids can be formed in the cladding in a predominantly non-periodic distribution. By non-periodic distribution, it is meant that when a cross-section of the fiber is observed, the voids are randomly or non-periodically distributed over a portion of the fiber. Cross-sections taken at different locations along the length of the fiber will exhibit different cross-sectional void patterns, i.e., each cross-section will have a slightly different randomly oriented void pattern, distribution, and size. The voids extend along the length of the fiber, but do not mean that the voids are long enough, but rather that there are many voids of different sizes extending along the entire length of the fiber.

[0065] By the manufacturing methods disclosed herein, a microstructured optical fiber can be made in which the maximum size of any void within a region having greater than 70% of the power fraction of light is less than the wavelength of the light to be transmitted for the telecommunication application. By maximum size, it is meant the largest diameter of any particular void in a perpendicular cross-section as viewed along the axis of the fiber. For example, optical fibers have been made in which greater than 90% of the region has all of the voids with a maximum diameter less than or equal to 1550 nm.

[0066] By the manufacturing methods disclosed herein, a microstructured optical fiber can be made in which the microstructured optical fiber can be made with a cladding region having voids in which the void area percentage is in the range of 3% to 15%.

[0067] By the manufacturing methods disclosed herein, primarily silica core optical fibers are made, i.e., optical fibers having a relatively pure silica core region surrounded by a cladding region having voids. Alternatively, refractive index adjusting dopants, such as fluorine containing materials alone or in combination, can be used to further adjust the core-cladding refractive index difference.

Claims

1. A method of manufacturing a microstructured optical fiber preform, for manufacturing a microstructured optical fiber preform, characterized by, The manufacturing method comprises the following steps: S101: spraying silica towards the target rod by a chemical vapor deposition torch to deposit a preform loose body on the target rod; S102: if the thickness of the preform loose body reaches a first specific value, continue to spray silica towards the target rod by the chemical vapor deposition torch while spraying high-purity quartz powder towards the target rod by a low-temperature plasma torch to continue to deposit the preform loose body on the target rod; wherein the first specific value is 3-10 layers; S103: if the thickness of the preform loose body reaches a second specific value, stop spraying high-purity quartz powder by the low-temperature plasma torch, but continue to spray silica towards the target rod by the chemical vapor deposition torch to continue to deposit the preform loose body on the target rod; wherein the difference between the second specific value and the first specific value is 50-150 layers; S104: if the weight of the preform loose body reaches a third specific value, perform high-temperature treatment on the preform loose body to form the microstructured optical fiber preform rod; wherein the third specific value is a preset weight threshold; Wherein the microstructured optical fiber preform rod has a core region with a first refractive index and a cladding region with a second refractive index, the refractive index of the cladding region is smaller than that of the core region, so that the light transmitted through the optical fiber is basically maintained within the core region, and a plurality of non-periodically distributed voids are included in the cladding region.

2. The manufacturing method of the microstructured optical fiber preform rod according to claim 1, characterized in that: The low-temperature plasma torch comprises a Venturi tube connected with a cavity for storing high-purity quartz powder; When high-purity inert gas passes through the Venturi tube, the low-temperature plasma torch sprays high-purity quartz powder towards the target rod.

3. The manufacturing method of the microstructured optical fiber preform rod according to claim 1, characterized in that: The distance between the low-temperature plasma torch and the chemical vapor deposition torch is not greater than 200 mm.

4. The manufacturing method of the microstructured optical fiber preform rod according to claim 1, characterized in that: The number of the chemical vapor deposition torches is at least 2, and the gas outlet angles of the chemical vapor deposition torches are the same or deviate from each other by a first angle.

5. The manufacturing method of the microstructured optical fiber preform rod according to claim 4, characterized in that: The first angle is not greater than 2°.

6. The manufacturing method of the microstructured optical fiber preform rod according to claim 4, characterized in that: The first angle is not greater than 5°.

7. The manufacturing method of the microstructured optical fiber preform rod according to claim 4, characterized in that: The first angle is not greater than 10°.

8. The manufacturing method of the microstructured optical fiber preform rod according to claim 1, characterized in that: The number of the low-temperature plasma torches is at least 1, and the gas outlet angles of the low-temperature plasma torches and the at least 1 chemical vapor deposition torch are the same or deviate from each other by a second angle.

9. The manufacturing method of the microstructured optical fiber preform rod according to claim 8, characterized in that: The second angle is not greater than 2°.

10. The method of claim 8, wherein the second angle is not more than 5°.

11. The method of claim 8, wherein the second angle is not more than 10°.

12. The method of claim 1, wherein the preform is formed by drying and treating the preform with a strong oxidizing agent to remove water and metal impurities, replacing air in the preform with at least one inert gas, and calcining the preform at a temperature of 1500 to 1550 °C to form the microstructured optical fiber preform containing voids only in the cladding region. ​ ​ ​

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