WO2020177355A1 - Single-mode optical fiber having ultra-low loss and large effective area and preparation method therefor - Google Patents

Abstract

A single-mode optical fiber that has ultra-low loss and a large effective area and a preparation method therefor. The optical fiber has an inner core layer, a depressed core layer, an outer core layer, an inner cladding layer, a depressed cladding layer and an outer cladding layer that are arranged successively from the inside to the outside, wherein: the inner core layer, the depressed core layer, the outer core layer, the inner cladding layer, and the depressed cladding layer use silica as a base material and have a dopant added thereto, and the outer cladding layer is pure silica; and the relative refractive index of the inner core layer is Δn₁, the relative refractive index of the depressed core layer is Δn₂, the relative refractive index of the outer core layer is Δn₃, the relative refractive index of the inner cladding layer is Δn₄, the relative refractive index of the depressed cladding layer is Δn₅, and the sizes of the relative refractive indices are: Δn₁>Δn₃>Δn₂>Δn₄>Δn₅. The present optical fiber is prepared by using an MCVD process and an OVD process, and the effective area, cut-off wavelength, attenuation, dispersion, bending loss and other comprehensive properties thereof are good.

Description

Single-mode optical fiber with ultra-low loss and large effective area and preparation method thereof

This application claims the priority of the invention patent application with application number 201910156066.2 filed with the State Intellectual Property Office of China on March 1, 2019, and the content of the priority text is expressly incorporated into this application by reference.

Technical field

The invention relates to a single-mode optical fiber with ultra-low loss and large effective area and a preparation method thereof, and belongs to the technical field of optical fiber transmission.

Background technique

Optical fiber is the medium of light transmission. After the optical signal is transmitted through the optical fiber, the reduction of optical power due to absorption, scattering, fiber structure, bending and other reasons is called optical fiber loss. Optical fiber loss is an important indicator of optical fiber transmission. The distance has a decisive influence. The level of optical fiber loss directly affects the transmission distance or the distance of the relay station. Therefore, reducing the optical fiber loss has great practical significance for optical fiber communication. Ultra-low loss optical fiber is mainly realized by adopting pure silicon core design, but for this pure silicon core design, it requires complicated viscosity matching inside the optical fiber, the manufacturing process is extremely complicated, and it is easy to cause internal defects in the fiber during the drawing process. The increased loss will also affect the realization of a large effective area of light. The current optical fiber usually adopts the core layer design of germanium-fluorine co-doped, but it will degrade the transmission performance of the optical fiber and affect the realization of the ultra-low loss performance index of the optical fiber.

The effective area of an optical fiber is used to measure the transmission capacity of light energy. A large effective area can effectively increase the transmission capacity of the optical fiber by changing the refractive index distribution of the fiber core and cladding, the size of the core and the duty cycle of the cladding. However, increasing the effective area of the optical fiber is accompanied by an increase in loss.

In the future transmission system of 400G or higher, the reduction of optical fiber loss and the increase of effective area will greatly improve the transmission quality of optical fiber and greatly reduce the construction and maintenance cost of the entire system. Therefore, the development and design of an optical fiber with ultra-low loss and large effective area has become an important issue in the field of optical fiber manufacturing.

Summary of the invention

The technical problem to be solved by the present invention is to provide a single-mode optical fiber with ultra-low loss and large effective area and a preparation method thereof in order to solve the technical problems of large loss and small effective area of the existing single-mode optical fiber.

The technical solutions adopted by the present invention to solve its technical problems are:

A single-mode fiber with ultra-low loss and large effective area. From the inside to the outside, it is an inner core layer, a sunken core layer, an outer core layer, an inner cladding layer, a sunken cladding layer and an outer cladding layer. Among them: inner core layer, sunken core layer The outer core layer, inner cladding layer, and sinking cladding use silica as the base material and adding dopants, and the outer cladding is pure silica; the relative refractive index of the inner core layer is △n ₁ , and the sinking core layer The relative refractive index is △n ₂ , the relative refractive index of the outer core layer is △n ₃ , the relative refractive index of the inner cladding layer is △n ₄ , the relative refractive index of the depressed cladding layer is △n ₅ , and the relative refractive index is : Δn ₁ >Δn ₃ >Δn ₂ >Δn ₄ >Δn ₅ .

Preferably, the radius of the inner core layer is r ₁ =4-6 μm, and the relative refractive index is Δn ₁ =0.35% to 0.55%; the radius of the depressed core layer is r ₂ =6-9 μm, and the relative refractive index is △ n ₂ ＝-0.25%～-0.15%; the radius of the outer core layer is r ₃ ＝9～15μm, the relative refractive index is △n ₃ ＝0.15%～0.3%; the radius of the inner cladding layer is r ₄ ＝15～20μm, The relative refractive index is △n ₄ ＝-0.4%～-0.3%; the radius of the depressed cladding is r ₅ ＝20～30μm, the relative refractive index is △n ₅ ＝-0.55%～-0.45%, and the outer cladding radius is r ₆ =70-85μm.

Preferably, the dopant added to the inner core layer and the outer core layer is P ₂ O ₅ or B ₂ O ₃ .

Preferably, the dopant added to the depressed core layer is a P ₂ O ₅ -F mixture, and the doping contribution Δn _P of P in the P ₂ O ₅ -F mixture is 0.2%-0.3%.

Preferably, the dopant added to the depressed core layer is a B ₂ O ₃ -F mixture, and the doping contribution Δn _B of B in the B ₂ O ₃ -F mixture is 0.2%-0.4%.

Preferably, the dopant added to the inner cladding layer is an Sb ₂ O ₃ -F mixture, and the Sb doping contribution Δn _{Sb in} the Sb ₂ O ₃ -F mixture is 0.05%-0.15%.

Preferably, the depressed cladding layer is a fluorine-doped silica glass layer.

The invention also provides a method for preparing a single-mode optical fiber with ultra-low loss and large effective area. The steps are as follows:

The inner cladding layer, the outer core layer, the sunken core layer and the inner core layer are sequentially deposited on the inner wall of the fluorine-doped quartz tube as the sunken cladding layer by the MCVD process to obtain the deposited tube;

The deposition tube is fused at high temperature into a prefabricated core rod with an inner core layer, a sinking core layer, an outer core layer, an inner cladding layer and a sinking layer;

The OVD process is used to deposit an outer coating on the preformed core rod, and after sintering, an optical fiber preform is prepared;

The optical fiber preform is directly drawn by wire, or drawn and then drawn into a single-mode fiber with ultra-low loss and large effective area.

Preferably, the inner surface of the fluorine-doped quartz tube is chemically etched before the inner cladding layer, the outer core layer, the sunken core layer and the inner core layer are deposited on the inner wall of the fluorine-doped quartz tube by using the MCVD process. The chemical etching method is: The quartz tube is heated to 600-700°C, and fluorine-containing gas is introduced into the fluorine-doped quartz tube to chemically etch the inner surface of the substrate tube.

Preferably, the melting temperature is 2300-2500°C, the temperature for depositing the inner cladding layer is 1800-2000°C, the temperature for depositing the core layer is 1600-1800°C, and the temperature for depositing the outer cladding layer is 1300-1500°C.

Preferably, the sintering treatment method is as follows: pass inert gas and chlorine gas into the sintering furnace, first raise the sintering furnace to 800-900°C at a heating rate of 20-30°C/min, keep it for 2-3 hours, and then increase the temperature for 15 The temperature rise rate of -20°C/min is increased to 1000-1100°C and the temperature is kept for 3-4 hours; finally, the chlorine gas is turned off, and the sintering furnace is raised to 1200-1300°C at a temperature rise rate of 8-12°C/min and the temperature is kept for 5-6 hours.

In addition, in order to clearly illustrate the technical solutions of the present invention, the definitions and descriptions of the terms involved in the present invention are as follows:

The relative refractive index Δn _i is defined by the following equation:

Among them, n _i is the absolute refractive index of the fiber at a specific position, and n _c is the absolute refractive index of pure silica glass.

The doping contribution of _Sb Δn _Sb is defined by the following equation:

Among them, n _Sb -n _c is the increase in refractive index caused by Sb doping when the dopant of the depressed core layer is Sb ₂ O ₃ -F mixture, and n _c is the absolute refractive index of pure silica glass.

The doping contribution of _B , Δn _B , is defined by the following equation:

Among them, n _B -n _c is the increase in refractive index of the inner cladding glass caused by B doping, and n _c is the absolute refractive index of pure silica glass.

The doping contribution of _P , Δn _P , is defined by the following equation:

Among them, n _P- n _c is the increase in refractive index of the inner cladding glass caused by P doping, and n _c is the absolute refractive index of pure silica glass.

The effective area A _{eff of the} optical fiber is defined by the following equation:

Among them, E is the electric field related to propagation, and R is the distance from the axis to the electric field distribution point.

Cut-off wavelength of optical cable λ _cc :

The IEC (International Committee) standard 60793-1-44 defines: the optical cable cut-off wavelength λ _cc is the wavelength at which the optical signal no longer propagates as a single-mode signal after 22 meters in the optical fiber. During the test, a circle with a radius of 14cm and two circles with a radius of 4cm are required to obtain data.

The beneficial effects of the present invention are:

The single-mode fiber with ultra-low loss and large effective area provided by the present invention has a suitable relative refractive index difference and radius, and its effective area, cut-off wavelength, attenuation, dispersion, bending loss and other comprehensive properties are good in the application band, and the cable cut-off wavelength can be To ensure that the optical signal propagates in a single mode in the optical fiber, the effective area of the optical fiber at the 1550nm wavelength is 165.1-181.3μm ² , the cable cutoff wavelength is equal to or less than 1321nm, and the attenuation at the 1550nm wavelength is equal to or less than 0.134dB/km , The dispersion at 1550nm wavelength is equal to or less than 14.3ps/nm*km, and the macrobending loss of 100 turns of R30mm bend radius at 1550nm wavelength is equal to or less than 0.0041dB. This fiber can be used for high-speed, large-capacity long-distance transmission And the long-distance transmission system without relay station, specifically:

(1) The fiber core layer is divided into inner core layer, sunken core layer and outer core layer. Further adding dopants into the inner core layer, sunken core layer and outer core layer can increase the effective area and reduce the attenuation coefficient of the fiber. Lower the cut-off wavelength;

(2) The inner cladding layer can prevent the fluoride ions, moisture and metal ions in the sinking layer from diffusing to the core layer, reducing the attenuation of the fiber;

(3) The fluorine-doped design of the depressed cladding can concentrate the optical power on the core layer of the fiber, which is beneficial to reduce the loss of light and improve the bending resistance of the fiber;

(4) The outer cladding layer of the outermost layer is designed with pure silicon dioxide, which reduces the proportion of fluorine-doped glass in the optical fiber, thereby reducing the manufacturing cost.

Description of the drawings

The present invention will be further described below in conjunction with the drawings and embodiments.

1 is a distribution diagram of the refractive index profile of the single-mode fiber of the present invention. The horizontal axis represents the cross-sectional radius of each layer of the fiber, and the vertical axis represents the relative refractive index corresponding to each layer.

detailed description

The present invention will now be described in further detail with reference to the drawings.

A single-mode fiber with ultra-low loss and large effective area. From the inside to the outside, it is the inner core layer, the outer core layer, the sunken core layer, the inner cladding layer, the sunken cladding layer and the outer cladding layer. Among them: inner core layer, sunken core layer , The outer core layer, inner cladding layer, and depressed cladding layer use silicon dioxide as the base material and add dopants; the radius of the inner core layer is r ₁ ＝4～6μm, and the relative refractive index of the inner core layer is △n ₁ =0.35 %～0.55%; the radius of the depressed core layer is r ₂ ＝6-9μm, the relative refractive index of the depressed core layer is △n ₂ ＝-0.25%～-0.15%; the radius of the outer core layer is r ₃ ＝9～15μm , The relative refractive index of the outer core layer is △n ₃ =0.15%～0.3%; the radius of the inner cladding layer is r ₄ =15-20μm, and the relative refractive index of the inner cladding layer is △n ₄ =-0.4%～-0.3%; The radius of the depressed layer is r ₅ ＝20～30μm, the relative refractive index of the depressed layer is △n ₅ ＝-0.55%～-0.45%, the outer cladding layer is pure silica, and the cladding layer radius is r ₆ ＝70- 85 μm; the relative refractive index is: Δn ₁ >Δn ₃ >Δn ₂ >Δn ₄ >Δn ₅ ;

The dopant added to the inner core layer and the outer core layer is at least one of Sb ₂ O ₃ , P ₂ O ₅ , and B ₂ O ₃ , and the dopant added to the depressed core layer is Sb ₂ O ₃ -F mixture or B ₂ O ₃ -F mixture, the doping contribution Δn _Sb of Sb in the Sb ₂ O ₃ -F mixture is 0.2%-0.3%, and the B doping in the B ₂ O ₃ -F mixture The impurity contribution Δn _B is 0.2%-0.4%;

The dopant added to the inner cladding layer is a P ₂ O ₅ -F mixture, and the P doping contribution Δn _{P in} the P ₂ O ₅ -F mixture is 0.05%-0.15%;

The depressed cladding layer closely surrounds the inner cladding layer, and the depressed cladding layer is a fluorine-doped silica glass layer.

The single-mode optical fiber of the present invention is prepared by the MCVD+OVD process, specifically:

Heat the fluorine-doped quartz tube to 600-700°C, and pass hydrogen fluoride gas into the fluorine-doped quartz tube to chemically etch the inner surface of the substrate tube;

The core rod is deposited by MCVD process and the depression layer structure is realized. The chemically etched fluorine-doped quartz tube is used as the deposition reaction tube. First, the inner cladding layer is deposited on the inner wall of the deposition reaction tube as the depression cladding layer, and then the outer core layer and the depression are sequentially deposited Core layer and inner core layer to obtain a deposition tube meeting the requirements of refractive index distribution. The temperature for depositing the inner cladding layer is 1800-2000°C, and the temperature for depositing the core layer is 1600-1800°C; after the deposition is completed, the deposited reaction tube is fused The MCVD process has the advantages of flexible operation, precise control of the flow of raw materials and the number of layers, etc., and can prepare optical fiber preforms with fine refractive index profiles.

Secondly, the OVD process is used to deposit an outer cladding layer on the prefabricated core rod. The temperature of the outer cladding layer is 1300-1500°C, and after sintering, an ultra-low loss large effective area optical fiber meeting the requirements is prepared; the sintering method is: Inert gas and chlorine gas are introduced into the sintering furnace. First, the sintering furnace is raised to 800-900℃ at a heating rate of 20-30℃/min, kept for 2-3h, and then raised to 1000 at a heating rate of 10-20℃/min -1100℃, heat preservation for 3-4h; finally, turn off the chlorine gas, make the sintering furnace rise to 1200-1300℃ at a heating rate of 5-15℃/min, and keep it for 5-6h; OVD process can improve production efficiency and is beneficial to large-scale produce.

Refer to Table 1 for optical fiber profile parameters of the various embodiments of the present invention, and refer to Table 2 for optical fiber performance parameters.

Remarks: The following specific preparation conditions of the optical fibers of Examples 1 and 2 are: the fusion temperature is 2400°C, the temperature of the inner cladding layer is 1900°C, the temperature of the core layer is 1700°C, and the temperature of the outer cladding layer is 1400 ℃, the sintering treatment method is: pass helium and chlorine into the sintering furnace, first raise the sintering furnace to 850℃ at a heating rate of 25℃/min, keep it for 2.5h, and then raise it to 1050℃, heat preservation for 3.5h; finally, turn off the chlorine gas, make the sintering furnace rise to 1250℃ at a temperature increase rate of 10℃/min, and keep it for 5.5h;

The following specific preparation conditions for the optical fibers of Examples 3 and 4 are: the fusion temperature is 2300°C, the temperature of depositing the inner cladding layer is 1800°C, the temperature of depositing the core layer is 1600°C, and the temperature of depositing the outer cladding layer is 1300°C, The sintering treatment method is as follows: pass helium and chlorine into the sintering furnace, first raise the sintering furnace to 800℃ at a heating rate of 20℃/min, keep it for 3h, and then raise it to 1000℃ at a heating rate of 15℃/min. Keep the temperature for 4 hours; finally, turn off the chlorine gas, make the sintering furnace rise to 1200°C at a temperature rise rate of 8°C/min, and keep it for 6 hours;

The following specific preparation conditions of the optical fibers of Examples 5 and 6 are: the fusion temperature is 2500°C, the temperature for depositing the inner cladding layer is 2000°C, the temperature for depositing the core layer is 1800°C, and the temperature for depositing the outer cladding layer is 1500°C, The sintering treatment method is as follows: pass helium and chlorine into the sintering furnace, first raise the sintering furnace to 900°C at a heating rate of 30°C/min, hold for 2 hours, and then raise it to 1100°C at a heating rate of 20°C/min. Keep the temperature for 3 hours; finally, turn off the chlorine gas, make the sintering furnace rise to 1300°C at a heating rate of 12°C/min, and keep it for 5 hours.

Table 1 Fiber profile parameters of various embodiments of the present invention

Table 2 Optical fiber performance parameters of various embodiments of the present invention

It can be seen from Table 2 that the effective area of the single-mode optical fiber of the present invention at 1550nm wavelength is 165.1-181.3μm ² , the cut-off wavelength of the cable is 1279-1321nm, the attenuation at the wavelength of 1550nm is 0.123-0.134dB/km, and the attenuation at the wavelength of 1550nm is 0.123-0.134dB/km. The dispersion at the position is 12.32-14.30ps/nm*km, and the macrobending loss of the optical fiber with a bending radius of R30mm at a wavelength of 1550nm is 0.0034-0.0041dB; it can be seen that the effective area and cut-off wavelength of the single-mode optical fiber of the present invention The comprehensive performance parameters of, attenuation, dispersion, bending loss, etc. are good in the application band.

Taking the above-mentioned ideal embodiment according to the present invention as enlightenment, through the above-mentioned description content, relevant workers can make various changes and modifications without departing from the scope of the technical idea of the present invention. The technical scope of the present invention is not limited to the content of the description, and its technical scope must be determined according to the scope of the claims.

Claims (10)

1. A single-mode optical fiber with ultra-low loss and large effective area, which is characterized by inner core layer, sinking core layer, outer core layer, inner cladding layer, sinking cladding layer, and outer cladding layer from the inside to the outside. Among them: inner core layer The sunken core layer, the outer core layer, the inner cladding layer, and the sunken cladding layer use silicon dioxide as the base material and add dopants, and the outer layer is pure silicon dioxide; the relative refractive index of the inner core layer is △n ₁ , The relative refractive index of the sinking core layer is △n ₂ , the relative refractive index of the outer core layer is △n ₃ , the relative refractive index of the inner cladding layer is △n ₄ , and the relative refractive index of the sinking cladding layer is △n ₅ . The refractive index is: Δn ₁ >Δn ₃ >Δn ₂ >Δn ₄ >Δn ₅ .
2. The single-mode optical fiber with ultra-low loss and large effective area according to claim 1, wherein the radius of the inner core layer is r ₁ =4-6 μm, and the relative refractive index is Δn ₁ =0.35%-0.55% ; The radius of the depressed core layer is r ₂ ＝6-9μm, and the relative refractive index is △n ₂ ＝-0.25%～-0.15%; the radius of the outer core layer is r ₃ ＝9～15μm, and the relative refractive index is △n ₃ ＝0.15%～0.3%; the radius of the inner cladding layer is r ₄ ＝15～20μm, the relative refractive index is △n ₄ ＝-0.4%～-0.3%; the radius of the depressed cladding layer is r ₅ ＝20～30μm, the relative refractive index The rate is Δn ₅ = -0.55% to -0.45%, and the outer coating radius r ₆ = 70-85 μm.
3. The single-mode optical fiber with ultra-low loss and large effective area according to claim 1 or 2, wherein the dopant added to the inner core layer and the outer core layer is P ₂ O ₅ or B ₂ O ₃ .
4. The single-mode optical fiber with ultra-low loss and large effective area according to any one of claims 1 to 3, wherein the dopant added to the depressed core layer is P ₂ O ₅ -F mixture or B ₂ O ₃ -F mixture, the doping contribution Δn _P of P in the P ₂ O ₅ -F mixture is 0.2%-0.3%, and the doping contribution Δn _B of B in the B ₂ O ₃ -F mixture is 0.2% -0.4%.
5. The single-mode optical fiber with ultra-low loss and large effective area according to any one of claims 1-4, wherein the dopant added to the inner cladding layer is a mixture of Sb ₂ O ₃ -F, and the Sb ₂ O _The Sb doping contribution Δn _Sb in the _3- F mixture is 0.05%-0.15%.
6. The single-mode optical fiber with ultra-low loss and large effective area according to any one of claims 1-5, wherein the depressed cladding layer is a fluorine-doped silica glass layer.
7. A method for preparing a single-mode optical fiber with ultra-low loss and large effective area, which is characterized in that the preparation steps are as follows:

   The inner cladding layer, the outer core layer, the sunken core layer and the inner core layer are sequentially deposited on the inner wall of the fluorine-doped quartz tube as the sunken cladding layer by using the MCVD process to obtain the deposited tube;

   The deposition tube is fused at high temperature into a prefabricated core rod with an inner core layer, a sinking core layer, an outer core layer, an inner cladding layer and a sinking layer;

   The OVD process is used to deposit an outer coating on the preformed core rod, and after sintering, an optical fiber preform is prepared;

   The optical fiber preform is directly drawn by wire, or drawn and then drawn into a single-mode fiber with ultra-low loss and large effective area.
8. The method for preparing a single-mode optical fiber with ultra-low loss and large effective area according to claim 7, characterized in that the inner cladding layer, the outer core layer, the sunken core layer and the inner core layer are deposited on the inner wall of the fluorine-doped quartz tube by the MCVD process. , Chemically etch the inner surface of the fluorine-doped quartz tube. The method of chemical etching is: heat the fluorine-doped quartz tube to 600-700℃, and pass fluorine-containing gas into the fluorine-doped quartz tube to chemically etch the inner surface of the substrate tube .
9. The method for preparing a single-mode optical fiber with ultra-low loss and large effective area according to claim 7 or 8, characterized in that the fusion temperature is 2300-2500°C, the temperature of depositing the inner cladding is 1800-2000°C, and the core layer is deposited The temperature is 1600-1800℃, and the temperature for depositing the outer coating is 1300-1500℃.
10. The method for preparing a single-mode optical fiber with an ultra-low loss and large effective area according to any one of claims 7-9, wherein the sintering treatment method is: passing inert gas and chlorine gas into the sintering furnace, and first The sintering furnace is raised to 800-900°C at a heating rate of 20-30°C/min and kept for 2-3 hours, and then raised to 1000-1100°C at a heating rate of 15-20°C/min for 3-4 hours; finally, close With chlorine, the sintering furnace is raised to 1200-1300°C at a heating rate of 8-12°C/min, and the temperature is kept for 5-6 hours.

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