Patent Description:
Plasma Chemical Vapor Deposition (PCVD) is a plasma chemical vapor deposition method. The preparation of an optical fiber preform by PCVD process is to use microwave as a heat source and simultaneously use a holding furnace to heat a reaction liner tube and provide a constant temperature field. The reaction raw materials are SiCl<NUM> and O<NUM>, and GeCl<NUM> and C2F<NUM> are simultaneously used as dopants to participate in the reaction to adjust the refractive index of the preform. At the beginning of the reaction, the microwave activates the raw material gas to produce plasma, which recombines to release a large amount of heat and forms a thin layer of glass deposited on the inner surface of the liner tube. Repeated this many times, the thin layers of glass are stacked to form a hollow liner tube with a thickness of <NUM> to <NUM>. The liner tube is then fused and corroded by an electric furnace to finally form a solid preform. The length of the preform is generally <NUM> to <NUM>.

In the existing PCVD deposition process, the raw materials such as SiCl<NUM> and GeCl<NUM> are kept in a constant temperature and constant pressure state in a material cabinet. After the deposition starts, the vaporized raw material enters the liner tube through a gas-guide tube, and the microwave moves along the axial direction of the liner tube to vitrify the raw material, and the reacted tailings are pumped out from the other end of the liner tube by a vacuum pump. Generally, the preform obtained by the PCVD deposition has the problem of axial nonuniformity. The non-uniformity deposition position is generally concentrated at <NUM> to <NUM> at the gas end and <NUM> to <NUM> at the pump end of the preform. A common factor is the influence of holding furnace temperature setting in the PCVD deposition. The temperature setting value at the gas end of the holding furnace is generally higher than the intermediate temperature of the holding furnace. This is because the temperature of gas raw material when entering the glass liner tube is generally lower than <NUM>, and cold spots are easy to form in front of the microwave reaction zone of the liner tube. The cold spots are formed when the raw materials that are not fully vitrified adhere to the inner wall of the liner tube, which has a large stress effect and affects the quality of the preform. The temperature at the gas end is increased, and the gas raw material is fully preheated in the liner tube before entering the microwave action area, which can effectively reduce the formation of the cold spots. However, the increase of the temperature at the gas end will affect the deposition efficiency of Ge in this area. The Ge accelerates volatilization at high temperature and moves with the direction of air flow in the liner tube, and performs secondary deposition in the middle of the liner tube or turns into tailings and is pumped away by the vacuum pump. The optical refractive index of the preform is non-uniformity, and the refractive index of the gas end is smaller than the middle refractive index, and the optical fiber drawn from the gas end preform is more prone to the problem of unqualified optical fiber parameters. The temperature of the pump end of the holding furnace is generally higher, because in the process of the gas raw material in the liner tube flowing to the pump end, part of the heat is carried to the pump end. At the same time, the temperature at the pump end is artificially increased, so that the formation of cracks in the sedimentary layer or blockage of sedimentary pellets at the end of the liner tube by the reaction tailings can be avoided. However, the high temperature at the pump end also reduces the deposition efficiency of the Ge, which reduces the refractive index of the preform in this area.

At present, in view of the non-uniformity problem caused by low Ge doping efficiency caused by the high PCVD deposition temperature, the usual solution is to control the temperature to make the temperature field of the overall holding furnace tend to be uniform. Patent <CIT> discloses that both ends of the glass liner tube are welded with a gas end extension pipe and a pump end extension pipe, and a heating device for preheating pipe section is added on the gas end extension pipe, and the reaction gas passing through the preheating pipe section is preheated by the heating device to avoid the occurrence of the cracks in the sedimentary layer of the intake section. This method does not sufficiently preheat the gas raw material, and the extension pipe increases the cost of the optical fiber. US Patent <CIT> discloses that the holding furnace is moved along the axial direction of the liner tube. This method can improve the uniformity of the preform, but it will affect the effective rod length of the preform and increase the cost of the optical fiber. In addition, the equipment of this method is complicated.

Therefore, the existing problem is that there is an urgent need to research and develop a system and a method for improving the uniformity of PCVD raw material gas deposition, and use thereof.

In view of the defects existing in the prior art, the purpose of the present invention is to provide a system and a method for improving the uniformity of PCVD raw material gas deposition, and use thereof. Through setting a PLC control unit connected with the microwave generator and the holding furnace, and adopting a control method in which the output power of the microwave generator is linked in real-time with the temperature of the holding furnace, the present invention realizes the adjustability of the output power of the microwave generator along the axial direction of the liner tube, so as to compensate for the uneven deposition of gas raw materials in the liner tube caused by the uneven distribution of the temperature field in the deposition section of the liner tube, and ensure the overall deposition uniformity of the deposition section of the liner tube. At the same time, the present invention can precisely control the vitrification conditions of the gas raw materials entering the deposition section of the liner tube, with a high degree of automation, and the invention is simple to operate and easy to implement. In addition, the effective rod length of the core rod of the optical fiber preform prepared by the present invention is increased, and the cost of rod manufacturing is reduced.

In order to achieve the above purpose, a first aspect of the present invention provides a system for improving the uniformity of PCVD raw material gas deposition, comprising:.

On the basis of the above technical solution, the set temperature at the real-time position during the movement of the microwave generator along the axial direction of the liner tube from the gas end area to the pump end area presents a trend of first increasing, then decreasing and then increasing.

On the basis of the above technical solution, the set temperature at the real-time position of the gas end area is not less than the temperature corresponding to the preset output power;
during the movement of the microwave generator along the axial direction of the liner tube from the gas end area to the pump end area: when the set temperature at the real-time position fed back by the temperature-measuring probe gradually decreases and falls to the temperature corresponding to the preset output power, the real-time position is the ending position of the gas end area or the starting position of the middle end area; and when the difference between the set temperature at the real-time position fed back by the temperature-measuring probe and the temperature at the previous real-time position shows a reverse mutation, the real-time position is the ending position of the middle end area or the starting position of the pump end area.

On the basis of the above technical solution, the set temperature Tgas at the real-time position of the gas end area is <NUM>≤Tgas≤<NUM>; the set temperature Tmiddle at the real-time position of the middle end area is <NUM>≤Tmiddle<<NUM>; and the set temperature Tpump at the real-time position of the pump end area is <NUM><Tpump≤ <NUM>.

On the basis of the above technical solution, the preset output power is <NUM>. 0kw; and the temperature corresponding to the preset output power is <NUM> to <NUM>.

According to the invention, the actual output power of the microwave generator is reduced at the starting position of the gas end area and the starting position of the pump end area.

On the basis of the above technical solution, the actual output power of the microwave generator is reduced to any value greater than <NUM>. 0kw and less than <NUM>. 0kw at the starting position of the gas end area and the starting position of the pump end area.

On the basis of the above technical solution, the actual output power of the microwave generator at the starting position of the gas end area is reduced to <NUM>. 5kw, and the actual output power of the microwave generator at the starting position of the pump end area is reduced to <NUM>.

On the basis of the above technical solution, the actual output power of the microwave generator at the starting position of the gas end area is reduced to <NUM>. 0kw, and the actual output power of the microwave generator at the starting position of the pump end area is reduced to <NUM>.

On the basis of the above technical solution, the lengths of the gas end area and the pump end area are both smaller than that of the middle end area.

On the basis of the above technical solution, the lengths of the gas end area and the pump end area are both <NUM> to <NUM>; and the length of the middle end area is <NUM> to <NUM>.

On the basis of the above technical solution, during the movement of the microwave generator along the axial direction of the liner tube from the pump end area to the gas end area, the actual output power of each area is maintained respectively to be the same as that of the corresponding area during the movement of the microwave generator along the axial direction of the liner tube from the gas end area to the pump end area.

A second aspect of the present invention provides a method for improving the uniformity of PCVD raw material gas deposition, which adopts the system for improving the uniformity of PCVD raw material gas deposition according to the first aspect of the present invention to perform the deposition on the PCVD raw material gas, and the method comprises the following steps:.

A third aspect of the present invention provides a use of the system for improving the uniformity of PCVD raw material gas deposition according to the first aspect of the present invention or of the method for improving the uniformity of PCVD raw material gas deposition according to the second aspect of the present invention in a preparation of a core rod of an optical fiber preform.

Compared with the prior art, the present invention has the following advantages:
Through setting a PLC control unit connected with the microwave generator and the holding furnace, and adopting a control method in which the output power of the microwave generator is linked in real-time with the temperature of the holding furnace, the present invention realizes the controllability of the output power of the microwave generator along the axial direction of the liner tube, so as to compensate for the uneven deposition of gas raw materials (especially GE) in the liner tube caused by the uneven distribution of the temperature field in the deposition section of the liner tube, and ensure the overall deposition uniformity of the deposition section of the liner tube. At the same time, the present invention can precisely control the vitrification conditions of the gas raw materials entering the deposition section of the liner tube, with a high degree of automation, and the invention is simple to operate and easy to implement. In addition, the effective rod length of the core rod of the optical fiber preform prepared by the present invention is increased, and the cost of rod manufacturing is reduced.

(Note: the abscissa in <FIG> and <FIG> is the length of the holding furnace, that is, the ideal length of the rod; the abscissa in <FIG> is the actual length of the core rod, which is <NUM>. Due to the influence of the deposition process, the actual length of the core rod is obtained through shrinking both ends inward on the basis of the ideal length of the rod. Therefore, the abscissas of <NUM> to <NUM> in <FIG> and <FIG> are no longer in one-to-one correspondence with the abscissas in <FIG> and <FIG>).

In the figure, the meanings of the reference numerals are as follows:
<NUM>-gas end interface; <NUM>-liner tube; <NUM>-holding furnace; <NUM>-microwave generator; <NUM>-pump end interface; <NUM>-deposition lathe bracket; <NUM>-translation platform; <NUM>-PLC control unit; <NUM>-gas end area; <NUM>-middle end area; <NUM>-pump end area.

For easier understanding, the present invention will be further described below in detail with reference to the drawings in combination with the embodiments. It should be understood that these embodiments are illustrative only and are not intended to limit the present invention.

In the existing PCVD deposition method, in order to avoid the generation of cracks and particles in the deposition area of the liner tube, a higher deposition temperature is usually used in the gas end area and the pump end area. Therefore, it is easy to cause the non-uniformity of axial doping of the gas raw materials (especially Ge), thereby reducing the effective length of the prepared core rod of the optical fiber preform and increasing the cost of rod manufacturing. In order to solve the above problems, the inventor found through a large number of experimental studies that through adopting a control method in which the output power of the microwave generator is linked in real-time with the temperature of the holding furnace, that is, the adjustability of the output power of the microwave generator along the axial direction of the liner tube, the non-uniformity deposition of gas raw materials (especially GE) in the liner tube caused by the uneven distribution of the temperature field in the deposition section of the liner tube can be compensated, and the effective rod length of the prepared core rod of the optical fiber preform is increased at the same time, which effectively reduces the cost of rod manufacturing. The present invention has been made based on the above findings.

As shown in <FIG> shows a schematic diagram of an existing conventional PCVD deposition system. The system comprises:.

In order to avoid cracks and particles in the deposition area of the liner tube, the method for PCVD deposition using this system comprises the following steps:.

In S1, in order to avoid the cracks and particles in the deposition area of the liner tube, it is usually necessary to set a gas end area and a pump end area to maintain a relatively high temperature. Moreover, the setting principle of each real-time position in the holding furnace <NUM> is as follows: the set temperature at the real-time position during the movement of the microwave generator <NUM> from the gas end area <NUM> to the pump end area <NUM> along the axial direction of the liner tube <NUM> is arbitrarily set in a trend of first increasing, then decreasing and then increasing. For example, the temperature distribution curve of the holding furnace can be set as shown in <FIG> (the measured temperature on the ordinate is also the set temperature), and the specific temperature every <NUM> along the axial direction of the liner tube from the starting position of the gas end is shown in Table <NUM>.

The preset output power is <NUM>. 0kw, and the temperature corresponding to the preset output power is <NUM>.

The set temperature at the real-time position of the gas end area <NUM> is not less than the temperature corresponding to the preset output power, and during the movement of the microwave generator <NUM> along the axial direction of the liner tube <NUM> from the gas end area <NUM> to the pump end area <NUM>: when the set temperature at the real-time position fed back by the temperature-measuring probe gradually decreases and falls to the temperature corresponding to the preset output power, the real-time position is the ending position of the gas end area <NUM> or the starting position of the middle end area <NUM>; and when the difference between the set temperature at the real-time position fed back by the temperature-measuring probe and the temperature at the previous real-time position shows a reverse mutation, the real-time position is the ending position of the middle end area <NUM> or the starting position of the pump end area <NUM>.

Therefore, under the temperature distribution curve shown in <FIG>, the position of <NUM> is the ending position of the gas end area <NUM> or the starting position of the middle end area <NUM>; and the position of <NUM> is the ending position of the middle end area <NUM> or the starting position of the pump end area <NUM>. That is, the length of the gas end area <NUM> is <NUM>, the starting position of the gas end area is taken as the original point, so that the area where the gas end area <NUM> is located is the area with the length of the liner tube of <NUM> to <NUM>. The length of the middle end area <NUM> is <NUM>, the starting position of the gas end area is taken as the original point, so that the area where the middle end area <NUM> is located is the area with the length of the liner tube of <NUM> to <NUM>. The length of the pump end area <NUM> is <NUM>, the starting position of the gas end area is taken as the original point, so that the area where the pump end area <NUM> is located is the area where the length of the liner tube is <NUM> to <NUM>.

When the system and method are applied to the preparation of the core rod of the optical fiber preform, the relative refractive index and core diameter test results of the obtained core rod are shown in solution <NUM> of <FIG>, respectively. When the output power of the microwave generator <NUM> is constant along the axial direction of the liner tube <NUM>, as shown in <FIG>, due to the large fluctuations in the temperature of the gas end area <NUM> and the temperature of the pump end area <NUM>, that is, the set temperature Tgas at the real-time position of the gas end area <NUM> is <NUM>≤Tgas≤<NUM>, the set temperature Tmiddle at the real-time position of the middle end area <NUM> is <NUM>≤Tmiddle<<NUM>, and the set temperature Tpump at the real-time position of the pump end area <NUM> is <NUM><Tpump≤<NUM>. As shown in <FIG>, the deposition efficiency of Ge in the raw material gas at both ends of the core rod is low. Since the qualified range of the refractive index of the entire core rod is <NUM>% to <NUM>%, the unqualified parts at both ends of the core rod are in the area with the length of the core rod of <NUM> to <NUM> and <NUM> to <NUM>, and the effective length of the core rod finally obtained is <NUM>.

As shown in <FIG> shows a schematic diagram of a PCVD deposition system in the present invention. The system comprises:.

The system further comprises a PLC control unit <NUM>, which is connected to the holding furnace <NUM> and the microwave generator <NUM>, and is configured to: during the movement of the microwave generator <NUM> along the axial direction of the liner tube <NUM> from the gas end area <NUM> to the pump end area <NUM>, according to the set temperature at the real-time position fed back by the temperature-measuring probe, determine an ending position of the gas end area <NUM> or a starting position of the middle end area <NUM>, the ending position of the middle end area <NUM> or the starting position of the pump end area <NUM>, change an actual output power of the microwave generator <NUM> at the starting position of the gas end area <NUM> and the starting position of the pump end area <NUM>, and keep the changed actual output power constant in the gas end area <NUM> and the pump end area <NUM>.

In order to improve the uniformity of the PCVD raw material gas deposition, the method for PCVD deposition using this system comprises the following steps:.

In S1, the set temperature of each real-time position in the holding furnace <NUM>, which is the same as that of the comparative example <NUM>, is set, and the temperature distribution curve thereof is shown in <FIG>. The preset output power is <NUM>. 0kw, and the temperature corresponding to the preset output power is <NUM>.

Therefore, under the temperature distribution curve shown in <FIG>, the position of <NUM> is the ending position of the gas end area <NUM> or the starting position of the middle end area <NUM>; and the position of <NUM> is the ending position of the middle end area <NUM> or the starting position of the pump end area <NUM>. That is, the length of the gas end area <NUM> is <NUM>, the starting position of the gas end area is taken as the original point, so that the area where the gas end area <NUM> is located is the area with the length of the liner tube of <NUM> to <NUM>. The length of the middle end area <NUM> is <NUM>, the starting position of the gas end area is taken as the original point, so that the area where the middle end area <NUM> is located is the area with the length of the liner tube of <NUM> to <NUM>. The length of the pump end area <NUM> is the length of the remaining liner tube <NUM>, i.e., <NUM>, the starting position of the gas end area is taken as the original point, so that the area where the pump end area <NUM> is located is the area where the length of the liner tube is <NUM> to <NUM>.

In order to adjust the relative refractive index of the core rod at both ends of the holding furnace <NUM>, when the temperature of the holding furnace <NUM> is constant, this comparative example compensates for the influence of temperature on the deposition efficiency of Ge through adjusting the axial output power of the microwave. Therefore, in S4 of this comparative example, the actual output power of the microwave generator <NUM> in the gas end area <NUM> is set to <NUM>. 0kw, and the actual output power of the microwave generator <NUM> in the pump end area <NUM> is set to <NUM>. At the same time, the actual output power of the microwave generator <NUM> in the middle end area <NUM> is maintained to be the preset output power of <NUM>.

When the system and method are applied to the preparation of the core rod of the optical fiber preform, the relative refractive index and core diameter test results of the obtained core rod are shown in solution <NUM> of <FIG>, respectively. As shown in <FIG>, compared with the solution <NUM> of the comparative example <NUM>, in the solution <NUM> provided by this comparative example, the deposition efficiency of Ge in the raw material gas at both ends of the core rod is lower. Since the qualified range of the refractive index of the entire core rod is <NUM>% to <NUM>%, the unqualified parts at both ends of the core rod are in the area with the length of the core rod of <NUM> to <NUM> and <NUM> to <NUM>, and the effective length of the core rod finally obtained is <NUM>. In addition, as shown in <FIG>, since the actual output power of the microwave at both ends of the holding furnace <NUM> is improved, compared with the core diameter data in the solution <NUM> of the comparative example <NUM>, the core diameter of the comparative example <NUM> in the gas end area of <NUM> to <NUM> is improved compared with that of the solution <NUM>.

The PCVD deposition system and method provided in this embodiment are the same as those in Comparative Example <NUM>, except that in S4, the actual output power of the microwave generator <NUM> in the gas end area <NUM> is set to <NUM>. 5kw, and the actual output power of the microwave generator <NUM> in the pump end area <NUM> is set to <NUM>. At the same time, the actual output power of the microwave generator <NUM> in the middle end area <NUM> is maintained to be the preset output power of <NUM>.

During the deposition of the raw material gas, in this embodiment, atomization phenomenon is observed on the inner surface of the gas end area <NUM> of the liner tube <NUM>, which is caused by insufficient actual output power of the microwave.

When the system and method are applied to the preparation of the core rod of the optical fiber preform, the relative refractive index and core diameter test results of the obtained core rod are shown in solution <NUM> of <FIG>, respectively. As shown in <FIG>, compared with the solution <NUM> of the comparative example <NUM>, in the solution <NUM> provided by this embodiment, the deposition efficiency of Ge in the raw material gas at both ends of the core rod is significantly improved, and the unqualified parts at both ends of the core rod are in the area with the length of the core rod are <NUM> to <NUM> and <NUM> to <NUM>, and the effective length of the core rod is <NUM>, which is significantly improved. In addition, as shown in <FIG>, the core diameter in the solution <NUM> of the present embodiment has no obvious change compared with that in the solution <NUM> of the comparative example <NUM>.

The PCVD deposition system and method provided in this embodiment are the same as those in the comparative example <NUM>, except that in S4, the actual output power of the microwave generator <NUM> in the gas end area <NUM> is set to <NUM>. 0kw, and the actual output power of the microwave generator <NUM> in the pump end area <NUM> is set to <NUM>. At the same time, the actual output power of the microwave generator <NUM> in the middle end area <NUM> is maintained to be the preset output power of <NUM>.

During the deposition of the raw material gas, in this embodiment, normal deposition is observed on the inner surface of the gas end area <NUM> of the liner tube <NUM> in this embodiment.

When the system and method are applied to the preparation of the core rod of the optical fiber preform, the relative refractive index and core diameter test results of the obtained core rod are shown in solution <NUM> of <FIG>, respectively. As shown in <FIG>, compared with the solution <NUM> of the comparative example <NUM>, in the solution <NUM> provided by this embodiment, the deposition efficiency of Ge in the raw material gas at both ends of the core rod is significantly improved, and the unqualified parts at both ends of the core rod are in the area with the length of the core rod od <NUM>-<NUM> and <NUM>-<NUM>, and the effective length of the core rod is <NUM>, which is significantly improved. In addition, as shown in <FIG>, the core diameter in the solution <NUM> of the present embodiment has no obvious change compared with that in the solution <NUM> of the comparative example <NUM>.

Claim 1:
A system for improving the uniformity of Plasma Chemical Vapor Deposition (PCVD) raw material gas deposition, comprising:
a liner tube (<NUM>);
a microwave generator (<NUM>), which is sleeved on an outside of the liner tube (<NUM>), and is configured to reciprocate along an axial direction of the liner tube (<NUM>);
a holding furnace (<NUM>), which is sleeved on the outside of the microwave generator (<NUM>), and a temperature-measuring probe is arranged therein and is configured to measure a set temperature at each real-time position in the holding furnace (<NUM>) during an axial movement of the microwave generator (<NUM>) along the liner tube (<NUM>);
wherein the holding furnace (<NUM>) is successively provided with a gas end area (<NUM>), a middle end area (<NUM>) and a pump end area (<NUM>) along the axial direction of the liner tube (<NUM>);
a preset output power of the microwave generator (<NUM>) in each area is the same;
the system further comprises a PLC control unit (<NUM>), which is connected to the holding furnace (<NUM>) and the microwave generator (<NUM>), and is configured to:
during the movement of the microwave generator (<NUM>) along the axial direction of the liner tube (<NUM>) from the gas end area (<NUM>) to the pump end area (<NUM>), according to the set temperature at the real-time position fed back by the temperature-measuring probe, determine an ending position of the gas end area (<NUM>) or a starting position of the middle end area (<NUM>), and the ending position of the middle end area (<NUM>) or the starting position of the pump end area (<NUM>), reduce an actual output power of the microwave generator (<NUM>) at the starting position of the gas end area (<NUM>) and the starting position of the pump end area (<NUM>), and keep the reduced actual output power constant in the gas end area (<NUM>) and the pump end area (<NUM>).