阅读说明：本技术 光纤预制棒及其制备方法、粉末棒沉积设备 (Optical fiber preform, preparation method thereof and powder rod deposition equipment ) 是由 钱宜刚 吴椿烽 沈一春 薛驰 薛济萍 于 2019-08-30 设计创作，主要内容包括：本发明提供一种光纤预制棒及其制备方法和粉末棒沉积设备,该方法通过内包层渐变式的掺氟分布可解决芯层、内包层、光学包层之间粘度匹配的制备工艺难点,特别是芯层与光学包层边界上粘度匹配；同时,实现粉末棒中各层氟化物的约束性扩散分布,保证各层折射率要求；中空粉末棒通过中心碱金属扩散,有利于降低芯层粘度,同时由于碱金属易扩散特性,在芯层扩散到外层的渐变过程,确保了芯层与内包层、光学包层之间的粘度匹配。(The invention provides an optical fiber preform, a preparation method thereof and powder rod deposition equipment, wherein the method can solve the difficulty of the preparation process of viscosity matching among a core layer, an inner cladding layer and an optical cladding layer through the gradual fluorine-doped distribution of the inner cladding layer, particularly the viscosity matching on the boundary of the core layer and the optical cladding layer; meanwhile, the constrained diffusion distribution of fluoride in each layer in the powder rod is realized, and the refractive index requirement of each layer is ensured; the hollow powder rod is advantageous to reducing the viscosity of the core layer through the diffusion of the central alkali metal, and simultaneously, the viscosity matching between the core layer and the inner cladding and the optical cladding is ensured in the gradual change process of the diffusion of the core layer to the outer layer due to the characteristic of easy diffusion of the alkali metal.)

1. A method for preparing an optical fiber preform, comprising the steps of:

sequentially forming a core layer, an inner cladding layer and an optical cladding layer which mainly comprise silicon dioxide on the surface of the target rod to obtain a powder rod, wherein the core layer also comprises germanium dioxide generated by reaction;

extracting the target rod to form a hollow powder rod, and then introducing alkali metal into the hollow part so as to diffuse the alkali metal into the powder rod to obtain an alkali metal doped powder rod;

sequentially carrying out three stages of dehydroxylation, sintering and vitrification on the alkali metal doped powder rod to form a glass rod with fluoride in the core layer, the inner cladding and the optical cladding in a constrained diffusion manner, wherein the sintering stage comprises a plurality of calcining stages, and the flow of introduced fluoride gas is set in each calcining stage and each vitrification stage according to the preset refractive index requirement;

and forming an outer cladding layer on the surface layer of the glass rod by adopting an axial vapor deposition process or an external vapor deposition process, and then sintering by doping fluorine to obtain the transparent optical fiber preform rod.

2. A method for preparing an optical fiber preform according to claim 1, wherein: and a step of extracting the target rod to form a hollow powder rod, then introducing alkali metal into the hollow part, and further diffusing the alkali metal into the powder rod to obtain an alkali metal-doped powder rod, wherein the alkali metal is carried by carrier gas and introduced into the hollow part of the hollow powder rod, the flow rate of the carrier gas is controlled to be 200 cc/min-500 cc/min, the environmental pressure of the carrier gas is controlled to be 5-15 pa, the environmental temperature is controlled to be 300-500 ℃, and the continuous introduction time of the alkali metal is controlled to be 4-6 h.

3. A method for preparing an optical fiber preform according to claim 2, wherein: the alkali metal comprises one or at least two combinations of lithium, sodium, potassium and rubidium alkali metal ions; the carrier gas comprises Ar and O₂、N₂One kind of (1).

4. A method for preparing an optical fiber preform according to claim 1, wherein: the sintering stage comprises a first calcining stage and a second calcining stage, the temperature rising rate of the first calcining stage is greater than that of the second calcining stage, and the temperature at the end of the first calcining stage is the same as the initial temperature of the second calcining stage.

5. The method for preparing an optical fiber preform according to claim 4, wherein: the temperature in the dehydroxylation stage is controlled to be 1200-1250 ℃; a first calcining stage, taking the temperature of the dehydroxylation stage as an initial temperature, and raising the temperature to 1300-1400 ℃ at a heating rate of 3-5 ℃/min; a second calcining stage, taking the temperature at the end of the first calcining stage as an initial temperature, and raising the temperature to 1450-1500 ℃ at a heating rate of 0.5-2 ℃/min; and (5) entering a vitrification stage, and keeping the temperature at the end of the second calcining stage for 2-6 h at constant temperature.

6. The method for preparing an optical fiber preform according to claim 5, wherein: the flow of fluoride gas introduced in the first calcining stage is 400 cc/min-600 cc/min; the flow of fluoride gas introduced in the second calcination stage is 600 cc/min-1000 cc/min; the flow rate of fluoride gas introduced in the vitrification stage is 300 cc/min-500 cc/min.

7. A method for preparing an optical fiber preform according to claim 1, wherein: and forming a core layer, an inner cladding and an optical cladding which mainly comprise silicon dioxide on the surface of the target rod in sequence to obtain the powder rod, wherein in the step of forming the core layer by reaction of germanium dioxide, reaction gas for forming the core layer comprises oxygen, hydrogen, silicon tetrachloride, germanium tetrachloride and Ar gas, and the flow rate of introducing the germanium tetrachloride is controlled to be 20-120 cc/min.

8. A method for preparing an optical fiber preform according to claim 1, wherein: forming a core layer, an inner cladding and an optical cladding which mainly comprise silicon dioxide on the surface of the target rod in sequence to obtain the powder rod, wherein in the step of forming the inner cladding by the core layer further comprising germanium dioxide generated by reaction, the reaction gas for forming the inner cladding comprises oxygen, hydrogen, silicon tetrachloride and Ar gas, the flow rate of the introduced silicon tetrachloride is controlled to be 4-12 g/min, and the reaction generatedThe density of the silicon dioxide powder is controlled to be 0.5-1.5 g/cm³The thickness of the inner cladding is 1/8-1 of the radius of the core layer.

9. A method for preparing an optical fiber preform according to claim 1, wherein: forming a core layer, an inner cladding and an optical cladding which mainly comprise silicon dioxide on the surface of the target rod in sequence to obtain the powder rod, wherein in the step of forming germanium dioxide by reaction on the core layer, the reaction gas for forming the optical cladding comprises oxygen, hydrogen, silicon tetrachloride and Ar gas, the flow rate of the introduced silicon tetrachloride is controlled to be 25 g/min-50 g/min, and the density of the silicon dioxide powder generated by reaction is controlled to be 0.2-0.6 g/cm³The total thickness of the optical cladding and the inner cladding is 3.0-10.5 times of the radius of the core layer.

10. A method for preparing an optical fiber preform according to claim 1, wherein: the step of fluorine-doped sintering comprises the steps of placing a glass rod coated with an outer cladding layer in a fluoride atmosphere for calcining, wherein the flow of fluoride is controlled to be 300-800 cc/min; the fluoride comprises SiF₄、CF₄、SF₆、C₂F₆、SOF₂、C₂F₂Cl₂One or a combination of at least two of (1).

11. An optical fiber preform obtained by the method for producing an optical fiber preform according to any one of claims 1 to 10, comprising, coaxially arranged from inside to outside:

a middle core layer with a radius of 4-6 μm and a refractive index of 0.03-0.12% relative to silicon dioxide;

the inner structure cladding has the radius of 5-8 mu m, and the refractive index of the inner structure cladding relative to the silicon dioxide is in linear gradient distribution;

an optical structure layer with a radius of 25-45 μm and a refractive index of-0.25 to-0.35% relative to silicon dioxide;

an outer cladding having a radius equal to 62.5 μm and a refractive index of-0.20 to-0.30% with respect to silicon dioxide.

12. A powder rod deposition equipment, includes blowtorch, deposition chamber, target rod and jib, the one end of target rod connect in the jib tip, the target rod stretches into the deposition chamber, the blowtorch sprays reaction gas stream deposition powder and attaches to on the target rod its characterized in that: the deposition chamber is communicated with the upper deposition cavity, the upper deposition cavity comprises an upper deposition cavity inner layer and an upper deposition cavity outer layer which are coaxially arranged, and an upper deposition cavity end cover which covers the end part far away from the deposition chamber, wherein the upper deposition cavity inner layer is used for accommodating the powder rod lifting space, and the upper deposition cavity outer layer is used for filling external gas.

13. The powder rod deposition apparatus of claim 12, wherein: the part of the upper deposition cavity end cover corresponding to the outer layer of the upper deposition cavity is provided with not less than 10 air holes for controlling the size of the air inlet flow.

14. The powder rod deposition apparatus of claim 12, wherein: the target rod comprises a hollow target rod and a solid target rod, and the first end of the hollow target rod is connected to the suspension rod; the first end part of the solid target rod is fixedly inserted into an inner hole of the second end part of the hollow target rod, the second end part of the solid target rod is a free end, and the target rod is driven by the suspender to rotate or move; the surface between the first end of the hollow target rod and the second end of the solid target rod is used for depositing to form a powder rod attached to the hollow target rod and the solid target rod, after deposition, the second end of the solid target rod is used as a clamping part, and the solid target rod is drawn out under the action of external force to form the hollow powder rod attached to the hollow target rod.

15. The powder rod deposition apparatus of claim 14, wherein: the first end part of the hollow target rod is an inlet for alkali metal and carrier gas thereof, and the inner hole of the free end of the hollow powder rod is an outlet for alkali metal and carrier gas thereof; the length of the hollow target rod is smaller than that of the solid target rod.

Technical Field

The invention relates to the technical field of optical communication, in particular to an optical fiber preform, a preparation method thereof and powder rod deposition equipment.

Background

In the future 400G and above transmission systems, reducing the optical fiber loss and obtaining a large effective area are one of the important issues in the field of optical fiber manufacturing. In the case of a silica optical fiber, attenuation at 600nm to 1600nm is mainly due to Rayleigh scattering, and attenuation a due to Rayleigh scattering_RCan be calculated from the following formula: a is_R＝R/λ⁴+ B. Wherein λ is wavelength, and R is Rayleigh scattering coefficient (dB/km/mum)⁴) And B is a corresponding constant.

In order to reduce the loss of the optical fiber, the most important process is to reduce the design of a core layer doped with germanium or a pure silicon core, and the rayleigh scattering of the optical fiber can be effectively reduced by reducing the doping concentration of the optical fiber. The rayleigh scattering R of the fiber is affected by the density fluctuation Rd in addition to the doping concentration Rc. The expression R ═ Rc + Rd. The pure silicon core design adopted in the traditional process is easy to cause viscosity mismatching between the core layer and the cladding layer to cause density fluctuation, and the loss of the optical fiber can be reduced only by reducing the viscosity matching between the core layer and the cladding layer while reducing the germanium doping of the core layer.

In order to obtain a large effective area, the method is mainly to reduce the refractive index of the core layer and increase the diameter of the core layer, but the effective area of the optical fiber can be increased by simply reducing the refractive index of the core layer and increasing the diameter of the core layer, but the increase of the cut-off wavelength and the deterioration of the attenuation and bending performance of the optical fiber cause the optical fiber to exceed relevant indexes. Furthermore, the refractive index of the core layer cannot be reduced by adopting a pure silicon core design.

Disclosure of Invention

In view of the above, there is a need to provide an ultra-low loss, large effective area optical fiber preform.

The technical scheme provided by the invention is as follows: a method for preparing an optical fiber preform, comprising the steps of:

sequentially forming a core layer, an inner cladding layer and an optical cladding layer which mainly comprise silicon dioxide on the surface of the target rod to obtain a powder rod, wherein the core layer also comprises germanium dioxide generated by reaction;

extracting the target rod to form a hollow powder rod, and then introducing alkali metal into the hollow part so as to diffuse the alkali metal into the powder rod to obtain an alkali metal doped powder rod;

sequentially carrying out three stages of dehydroxylation, sintering and vitrification on the alkali metal doped powder rod to form a glass rod with fluoride in the core layer, the inner cladding and the optical cladding in a constrained diffusion manner, wherein the sintering stage comprises a plurality of calcining stages, and the flow of introduced fluoride gas is set in each calcining stage and each vitrification stage according to the preset refractive index requirement;

and forming an outer cladding layer on the surface layer of the glass rod by adopting an axial vapor deposition process or an external vapor deposition process, and then sintering by doping fluorine to obtain the transparent optical fiber preform rod.

Further, the target rod is extracted to form a hollow powder rod, then alkali metal is introduced into the hollow part, and further the alkali metal is diffused into the powder rod to obtain the alkali metal doped powder rod, wherein the alkali metal is carried by carrier gas and introduced into the hollow part of the hollow powder rod, the flow rate of the carrier gas is controlled to be 200 cc/min-500 cc/min, the ambient pressure of the carrier gas is controlled to be 5-15 pa, the ambient temperature is controlled to be 300-500 ℃, and the continuous introduction time of the alkali metal is controlled to be 4-6 h.

Further, the alkali metal comprises one or at least two combinations of lithium, sodium, potassium and rubidium alkali metal ions; the carrier gas comprises Ar and O₂、N₂One kind of (1).

Further, the sintering stage comprises a first calcination stage and a second calcination stage, the temperature rise rate of the first calcination stage is greater than that of the second calcination stage, and the temperature at the end of the first calcination stage is the same as the initial temperature of the second calcination stage.

Further, the temperature in the dehydroxylation stage is controlled to be 1200-1250 ℃; a first calcining stage, taking the temperature of the dehydroxylation stage as an initial temperature, and raising the temperature to 1300-1400 ℃ at a heating rate of 3-5 ℃/min; a second calcining stage, taking the temperature at the end of the first calcining stage as an initial temperature, and raising the temperature to 1450-1500 ℃ at a heating rate of 0.5-2 ℃/min; and (5) entering a vitrification stage, and keeping the temperature at the end of the second calcining stage for 2-6 h at constant temperature.

Further, the fluoride gas in the first calcining stage is introduced at a flow rate of 400 cc/min-600 cc/min; the flow of fluoride gas introduced in the second calcination stage is 600 cc/min-1000 cc/min; the flow rate of fluoride gas introduced in the vitrification stage is 300 cc/min-500 cc/min.

Further, a core layer, an inner cladding layer and an optical cladding layer which are mainly composed of silicon dioxide are sequentially formed on the surface of the target rod to obtain the powder rod, wherein the core layer also comprises germanium dioxide generated by reaction, reaction gas for forming the core layer comprises oxygen, hydrogen, silicon tetrachloride, germanium tetrachloride and Ar gas, and the flow rate of introducing the germanium tetrachloride is controlled to be 20-120 cc/min.

Further, a core layer, an inner cladding and an optical cladding which are mainly composed of silicon dioxide are sequentially formed on the surface of the target rod to obtain the powder rod, wherein in the step of forming germanium dioxide by reaction on the core layer, the reaction gas for forming the inner cladding comprises oxygen, hydrogen, silicon tetrachloride and Ar gas, the flow rate of the introduced silicon tetrachloride is controlled to be 4 g/min-12 g/min, and the density of the silicon dioxide powder generated by reaction is controlled to be 0.5-1.5 g/cm³The thickness of the inner cladding is 1/8-1 of the radius of the core layer.

Further, a core layer, an inner cladding layer and an optical cladding layer which are mainly composed of silicon dioxide are sequentially formed on the surface of the target rod to obtain the powder rod, wherein in the step of forming germanium dioxide by reaction on the core layer, the reaction gas for forming the optical cladding layer comprises oxygen, hydrogen, silicon tetrachloride and Ar gas, the flow rate of the introduced silicon tetrachloride is controlled to be 25 g/min-50 g/min, and the density of the silicon dioxide powder generated by reaction is controlled to be 0.2-0.6 g/cm³The total thickness of the optical cladding and the inner cladding is 3.0-10.5 times of the radius of the core layer.

Further, the step of fluorine-doped sintering comprises the step of placing the glass rod coated with the outer cladding layer in a fluoride atmosphere for calcination, wherein the flow rate of fluoride introduction is controlled to be 300-800 cc/min; the fluoride comprises SiF₄、CF₄、SF₆、C₂F₆、SOF₂、C₂F₂Cl₂One or a combination of at least two of (1).

The invention also provides an optical fiber perform rod which is formed by the preparation method of the optical fiber perform rod, and the optical fiber perform rod sequentially comprises the following components in a coaxial arrangement from inside to outside:

a middle core layer with a radius of 4-6 μm and a refractive index of 0.03-0.12% relative to silicon dioxide;

the inner structure cladding has the radius of 5-8 mu m, and the refractive index of the inner structure cladding relative to the silicon dioxide is in linear gradient distribution;

an optical structure layer with a radius of 25-45 μm and a refractive index of-0.25 to-0.35% relative to silicon dioxide;

an outer cladding having a radius equal to 62.5 μm and a refractive index of-0.20 to-0.30% with respect to silicon dioxide.

The invention also relates to powder rod deposition equipment, which comprises a blast burner, a deposition chamber, a target rod and a hanging rod, wherein one end of the target rod is connected with the end part of the hanging rod, the target rod extends into the deposition chamber, the blast burner sprays reaction gas flow to deposit powder and is attached to the target rod, and the powder rod deposition equipment is characterized in that: the deposition chamber is communicated with the upper deposition cavity, the upper deposition cavity comprises an upper deposition cavity inner layer and an upper deposition cavity outer layer which are coaxially arranged, and an upper deposition cavity end cover which covers the end part far away from the deposition chamber, wherein the upper deposition cavity inner layer is used for accommodating the powder rod lifting space, and the upper deposition cavity outer layer is used for filling external gas.

Furthermore, the part of the upper deposition cavity end cover corresponding to the outer layer of the upper deposition cavity is provided with not less than 10 air holes for controlling the size of the air inlet flow.

Further, the target rods comprise a hollow target rod and a solid target rod, and a first end of the hollow target rod is connected to the suspension rod; the first end part of the solid target rod is fixedly inserted into an inner hole of the second end part of the hollow target rod, the second end part of the solid target rod is a free end, and the target rod is driven by the suspender to rotate or move; the surface between the first end of the hollow target rod and the second end of the solid target rod is used for depositing to form a powder rod attached to the hollow target rod and the solid target rod, after deposition, the second end of the solid target rod is used as a clamping part, and the solid target rod is drawn out under the action of external force to form the hollow powder rod attached to the hollow target rod.

Further, the inner diameter of the hollow target rod is equal to the rod diameter of the solid target rod.

Further, the hollow target rod and the solid target rod have the same outer diameter.

Further, the inner diameter of the first end portion of the hollow target rod is larger than the inner diameter of the hollow target rod, and the outer diameter of the second end portion of the solid target rod is larger than the rod diameter of the solid target rod.

Further, the outer diameters of the hollow target rod and the solid target rod are equal, and the thickness of the first end part of the hollow target rod is half of that of the hollow target rod.

Further, the first end of the hollow target rod is an inlet for alkali metal and its carrier gas, and the inner bore of the free end of the hollow powder rod is an outlet for alkali metal and its carrier gas.

Further, the length of the hollow target rod is smaller than that of the solid target rod.

Compared with the prior art, the preparation process difficulty of viscosity matching among the core layer, the inner cladding and the optical cladding can be solved through the gradual fluorine-doped distribution of the inner cladding, and particularly the viscosity matching on the boundary of the core layer and the optical cladding is realized; meanwhile, the constrained diffusion distribution of fluoride in each layer in the powder rod is realized, and the refractive index requirement of each layer is ensured; the hollow powder rod is advantageous to reducing the viscosity of the core layer through the diffusion of the central alkali metal, and simultaneously, the viscosity matching between the core layer and the inner cladding and the optical cladding is ensured in the gradual change process of the diffusion of the core layer to the outer layer due to the characteristic of easy diffusion of the alkali metal.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

Fig. 1 is a flow chart illustrating a process for fabricating an optical fiber preform according to an embodiment of the present invention.

FIG. 2 is a schematic view of a powder rod deposition apparatus employed in the present invention.

Fig. 3 is a schematic end view of the upper deposition chamber shown in fig. 2.

FIG. 4 is a schematic view of the gasification chamber of the present invention.

FIG. 5 is a schematic view of the temperature control of the sintering stage of the present invention.

FIG. 6 is a schematic view showing the fluorine content control in the dehydroxylation, sintering and vitrification processes of the powder rod of the present invention.

FIG. 7 shows the fluorine doping amount and refractive index distribution of each layer of the glass rod of the present invention.

Fig. 8 is a schematic cross-sectional structure of an optical fiber preform according to the present invention.

FIG. 9 is a schematic cross-sectional view showing the refractive index of an optical fiber preform according to the present invention.

FIG. 10 is a schematic diagram showing the fluctuation of the rod diameter of the powder rods in different air inlet modes.

FIG. 11 is a graph showing the attenuation performance of optical fibers under different air-intake modes.

Description of reference numerals:

powder stick deposition apparatus 10

Core layer blowtorch 101

Inner cladding blowtorch 102

Optical cladding torch 103

Deposition chamber 104

Boom 105

Target rod 106

Solid target rod 1061

First end 1061b of a solid target rod

Second end 1061a of solid target rod

Hollow target rod 1062

First end 1062a of hollow target rod

Second end 1062b of hollow target rod

Powder stick 107

Hollow powder stick 1071

Hollow powder stick free end 1071a

Upper deposition chamber 108

Upper deposition chamber inner layer 108a

Upper deposition chamber outer layer 108b

Upper deposition chamber end cap 108c

Air hole 108d

Gasification cabinet 70

Gasification chamber 707

Air inlet 701

Pressure sensor 703

Gas outlet 705

Optical fiber preform 50

Middle core layer 501

Inner structural cladding 503

Optical structure layer 505

Outer structural cladding 509

The following detailed description further illustrates embodiments of the invention in conjunction with the above-described figures.

Detailed Description

So that the manner in which the above recited objects, features and advantages of embodiments of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. In addition, the features of the embodiments of the present application may be combined with each other without conflict.

In the following description, numerous specific details are set forth to provide a thorough understanding of embodiments of the invention, and the described embodiments are merely a subset of embodiments of the invention, rather than a complete embodiment. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without any creative effort belong to the protection scope of the embodiments of the present invention.

"VAD" herein refers to axial vapor deposition, and is used throughout to refer to: VApor Axial position, VAD for short.

Herein, "OVD" refers to the outside vapor deposition method, which is generally known as: outside vapor Deposition, OVD for short.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments of the present invention belong. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the embodiments of the invention.

Referring to fig. 1, a flow chart of a method for fabricating an optical fiber preform according to an embodiment of the present invention includes the following steps:

step S1: and sequentially forming a core layer r01 mainly composed of silicon dioxide, an inner cladding layer r02 and an optical cladding layer r03 on the surface of the target rod to obtain the powder rod, wherein the core layer r01 also comprises germanium dioxide generated by reaction. The germanium doping contributes to the refractive index by increasing the relative refractive index of the silica glass.

In a specific embodiment, the reaction gas for forming the core layer comprises oxygen, hydrogen, silicon tetrachloride, germanium tetrachloride and Ar gas, wherein the flow rate of the germanium tetrachloride is controlled to be 20-120 cc/min. The reaction gas for forming the inner cladding comprises oxygen, hydrogen, silicon tetrachloride and Ar gas, wherein the flow of the silicon tetrachloride is controlled to be 4 g/min-12 g/min, and the density of silicon dioxide powder generated by the reaction is controlled to be 0.5-1.5 g/cm³The thickness of the inner cladding is 1/8-1 of the radius of the core layer, namely (r02-r01)/r 01. The reaction gas for forming the optical cladding comprises oxygen, hydrogen, silicon tetrachloride and Ar gas, wherein the flow of the silicon tetrachloride is controlled to be 25 g/min-50 g/min, and the density of the silicon dioxide powder generated by the reaction is controlled to be 0.2-0.6 g/cm³The total thickness of the optical cladding and the inner cladding is 3.0-10.5 times of the radius of the core layer, namely (r03-r01)/r01, preferably 5.0-8.0 times. In the step, reaction gases can be respectively introduced or mixed gases are introduced, the raw materials react in flame at a high temperature to generate silicon dioxide particles or germanium dioxide and silicon dioxide particles, for example, the flow ratio of oxygen, hydrogen, silicon tetrachloride, germanium tetrachloride and Ar gases can be (1-3):3 (0.10-0.2): 1-1.5), and the flow ratio of oxygen, hydrogen, silicon tetrachloride and Ar gases can be (1-3):3:3 (1-1.5); the thickness and density of the deposited inner cladding and the optical cladding are optimally designed in the stepThe powder layers distributed in different density areas are combined, the components of the powder layers are similar, the core layer is doped as little as possible, the matching degree of the powder layers after viscosity regulation in the sintering process is high, density fluctuation is not easy to cause, and the design of a nearly pure silicon core or a low-germanium-doped core layer is achieved, so that Rayleigh scattering is reduced, and the loss of the final optical fiber is reduced.

Step S2: and (3) extracting the target rod to form a hollow powder rod, and then introducing alkali metal into the hollow part so as to diffuse the alkali metal into the powder rod to obtain the alkali metal doped powder rod.

In a specific embodiment, the alkali metal is carried by a carrier gas and is introduced into the hollow part of the hollow powder rod, the flow rate of the carrier gas is controlled to be 200 cc/min-500 cc/min, the environmental pressure of the carrier gas is controlled to be 5-15 pa, the environmental temperature is controlled to be 300-500 ℃, and the continuous introduction time of the alkali metal is controlled to be 4-6 h. The alkali metal comprises one or at least two combinations of lithium, sodium, potassium and rubidium alkali metal ions; the carrier gas comprises Ar and O₂、N₂One kind of (1). In the hollow powder rod of step S2, the alkali metal is doped in the center, so that the alkali metal diffuses outward in the core layer, which is beneficial to reducing the viscosity of the core layer, and meanwhile, the gradual change process from the core layer to the outer layer (inner cladding and optical cladding) is also realized, so as to ensure the viscosity matching between the core layer and the inner cladding and between the core layer and the optical cladding.

Step S3: and sequentially carrying out three stages of dehydroxylation, sintering and vitrification on the alkali metal doped powder rod to form the glass rod with fluoride in the core layer, the inner cladding and the optical cladding in a constrained diffusion manner, wherein the sintering stage comprises a plurality of calcining stages, and the flow of introduced fluoride gas is set in each calcining stage and each vitrification stage according to the preset refractive index requirement. The fluoride gas is defined to include SiF₄、CF₄、SF₆、C₂F₆、SOF₂、C₂F₂Cl₂One or a combination of at least two of the above gases.

In a specific embodiment, the sintering phase comprises a first calcination phase and a second calcination phase, the rate of temperature increase of the first calcination phase is greater than the rate of temperature increase of the second calcination phase, and the temperature at the end of the first calcination phase is the same as the starting temperature of the second calcination phase. The temperature T1 in the dehydroxylation stage is controlled to be 1200-1250 ℃; a first calcining stage, taking the temperature of the dehydroxylation stage as an initial temperature, and raising the temperature to 1300-1400 ℃ (T2) at a heating rate of 3-5 ℃/min; a second calcining stage, taking the temperature at the end of the first calcining stage as an initial temperature, and raising the temperature to 1450-1500 ℃ at a heating rate of 0.5-2 ℃/min (T3); and (5) entering a vitrification stage, keeping the temperature T3 at the end of the second calcining stage, and keeping the constant temperature for 2-6 h. The flow of fluoride gas introduced in the first calcining stage is 400 cc/min-600 cc/min; the flow of fluoride gas introduced in the second calcination stage is 600 cc/min-1000 cc/min; the flow rate of fluoride gas introduced in the vitrification stage is 300 cc/min-500 cc/min.

Referring to fig. 7, on the basis of the optimized design of thickness and density, in combination with the fluorine-doped sintering process, the content of fluoride in the glass rod is the least in the core layer and the most and uniformly distributed in the optical cladding layer, and the content of fluoride in the inner cladding layer gradually increases from the outer layer of the core layer to the inner layer of the optical cladding layer, i.e. the constrained diffusion of fluoride in the core layer, the inner cladding layer and the optical cladding layer is realized; meanwhile, the refractive index requirements of the core layer and the optical cladding layer are prevented from being influenced by the reduction of the refractive index of the core layer caused by the large diffusion of fluoride to the core layer without control. The fluoride comprises SiF₄、CF₄、SF₆、C₂F₆、SOF₂、C₂F₂Cl₂One or a combination of at least two of (1).

The fluorine-doped requirement in the optical cladding and the gradual change distribution of the fluoride in the inner cladding are realized through the process, a good transitional effect is achieved between the core layer and the optical cladding, and the viscosity of the core layer at the center and the viscosity of the optical cladding at the outer layer are effectively matched. The traditional ultra-low loss large-effective area optical fiber adopts a sinking auxiliary design method, the energy distribution in the optical fiber is Gaussian distribution, and the invention can effectively improve the diameter of an optical fiber mode field and increase the effective area of the optical fiber through the structural change of the refractive index of a core layer without reducing the refractive index of the core layer and increasing the diameter of the core layer.

Step S4: and forming an outer cladding layer on the surface layer of the glass rod by adopting an axial vapor deposition process or an external vapor deposition process, and then sintering by doping fluorine to obtain the transparent optical fiber preform rod.

In a specific embodiment, the step of fluorine-doped sintering comprises the steps of placing a glass rod coated with an outer cladding layer in a fluoride atmosphere for calcination, wherein the flow rate of fluoride introduction is controlled to be 300-800 cc/min; the fluoride comprises SiF₄、CF₄、SF₆、C₂F₆、SOF₂、C₂F₂Cl₂One or a combination of at least two of (1). The fluorine-doped design contributes to the refractive index by lowering the relative refractive index of the silica glass, and is advantageous for improving the bending resistance of the optical fiber.

As shown in fig. 8 and 9, the optical fiber preform 50 formed by the above-mentioned method includes, from inside to outside, coaxially arranged:

the intermediate core layer 501 has a radius r1 of 4-6 μm and a refractive index delta n1 of 0.03-0.12% relative to silicon dioxide;

the inner structure cladding 503 has a radius r2 of 5-8 μm, and has a refractive index delta n2 relative to silica in a gradual distribution;

an optical structure layer 505 having a radius r3 of 25 to 45 μm and a refractive index Δ n3 of-0.25 to-0.30% with respect to silica;

the outer cladding 509 has a radius r5 of 60 μm or more and a refractive index Δ n5 of-0.20 to-0.30%.

The powder rod deposition apparatus 10 employed in step S1 of the present invention will be described in detail below with reference to fig. 2 and 3.

The apparatus includes a target rod 106, a deposition chamber 104, an optical cladding torch 103, an inner cladding torch 102, a core torch 101, a hanger bar 105, and an upper deposition chamber 108. Wherein, the upper part of the deposition chamber 104 is provided with an upper deposition cavity 108, a hanger rod 105 is arranged in the upper deposition cavity 108, the hanger rod 105 is provided with a hook, the hanger rod 105 is connected with a lifting mechanism (not shown), the target rod 106 is hung on the hook of the hanger rod 105 connected with the lifting mechanism, one side of the lower part of the deposition chamber 104 is sequentially provided with an optical cladding torch 103, an inner cladding torch 102 and a core layer torch 101, and the torches (103, 102 and 101) spray air flow towards the target rod 106, thereby reacting layer by layer to form powder to be attached on the target rod 106. In a specific embodiment, the upper deposition chamber 108 is divided into two chambers, an upper deposition chamber inner layer 108a and an upper deposition chamber outer layer 108b, the ends of which are provided with upper deposition chamber end caps 108c (shown in FIG. 3). The upper deposition cavity outer layer 108b is mainly filled with external air, the upper deposition cavity inner layer 108a is mainly used for accommodating a powder rod lifting space, the upper deposition cavity end cover 108c is used for sealing the powder rod accommodating space and preventing air flow from entering, and the part of the upper deposition cavity end cover 108c, corresponding to the upper deposition cavity outer layer 108b, is provided with not less than 10 air holes 108d for controlling the size of air flow. So divide into inside and outside two rooms with upper portion deposit cavity 108, effectively get into the cavity separation with powder stick accommodation space and gas, avoid along with the increase of powder stick rod footpath, be used for the space reduction that gas pours into in the upper portion deposit cavity and the cavity pressure fluctuation that arouses, cause the rod footpath of powder stick 107 to produce undulantly, the rod footpath of above-mentioned structural design can effectively improve powder stick 107 is undulantly.

FIG. 2 shows target rod 106 comprising a hollow target rod 1062 and a solid target rod 1061, with hollow target rod 1062 comprising two ends, a hollow target rod first end 1062a and a hollow target rod second end 1062b, respectively; the solid target rod 1061 also includes two ends, a solid target rod first end 1061b and a solid target rod second end 1061 a; the first end 1062a of the hollow target rod is connected to the boom 105; the first end 1061b of the solid target rod is inserted and fixed in the inner hole of the second end 1062b of the hollow target rod, the second end 1061a of the solid target rod is a free end, and the target rod 106 is driven by the suspension rod 105 to rotate or move; the surface between the hollow target rod first end 1062a and the solid target rod second end 1061a is used to deposit a powder rod 107 attached to the hollow target rod 1062 and the solid target rod 1061, and after deposition, the solid target rod second end 1061a acts as a grip to draw the solid target rod 1061 out under an external force to form a hollow powder rod 1071 attached to the hollow target rod 1062. The length of the hollow target rod 1062 is less than the length of the solid target rod 1061. In specific embodiments, the inner diameter of the hollow target rod 1062 is the same as the rod diameter of the solid target rod 1061, or the outer diameter of the hollow target rod 1062 is the same as the outer diameter of the solid target rod 1061. When the latter, in particular, the inner diameter of the first end 1062a of the hollow target rod is larger than the inner diameter of the hollow target rod 1062, and the outer diameter of the second end 1061a of the solid target rod is larger than the rod diameter of the solid target rod 1061; for example, the hollow target rod 1062 and the solid target rod 1061 have the same outer diameter, and the thickness of the hollow target rod first end 1062a is half the thickness of the hollow target rod 1062. The above embodiments are not exclusive, and the outer diameters are preferably equal.

Deposition process of powder rod: oxygen, hydrogen, silicon tetrachloride, germanium tetrachloride and Ar gas are introduced into the core layer blowtorch 101, and silicon dioxide and germanium dioxide are formed through high-temperature reaction and attached to the end face of the target rod to form a loose core layer with a certain density. The silicon dioxide layer with a certain thickness surrounding the surface of the core layer is an inner cladding, and oxygen, hydrogen, silicon tetrachloride and Ar gas are introduced into the inner cladding blowtorch 102. The silica layer with a certain thickness surrounding the surface of the inner cladding layer is an optical cladding, oxygen, hydrogen, silicon tetrachloride and Ar gas are introduced into the optical cladding torch 103, and the powder body is deposited to a set length and then stops being deposited. In the process of introducing, the purpose of controlling the thickness and the density of the inner cladding and the optical cladding can be achieved by controlling the flow rate of the silicon tetrachloride, the flow rate ratio of the hydrogen and the oxygen of the inner cladding and the optical cladding torches (102, 103), and the like.

After the deposition of the powder rod is completed, the solid target rod 1061 is extracted and then moved to the gasification chamber 70 to be doped with the alkali metal. The gasification chamber 70 used in step S2 of the present invention will be described in detail with reference to fig. 7.

The gasification cabinet 70 comprises a gasification chamber 707, an air inlet 701 and a pressure sensor 703 are arranged at the top end of the gasification chamber 707, an air outlet 705 is arranged at the bottom side of the gasification chamber 707, a hollow target rod 1062 carries a hollow powder rod 1071 to enter the gasification chamber 707 and then is sealed, and a first end 1062a of the hollow target rod is arranged outside the gasification chamber 707. The first end 1062a of the hollow target rod is the inlet for the alkali metal and its carrier gas, and the inner bore of the free end 1071a of the hollow powder rod is the outlet for the alkali metal and its carrier gas, and the alkali metal diffuses from the core layer to the inner cladding and the optical cladding from the inside to the outside. External air enters the gasification chamber 707 through the air inlet 701, and the mixed gas after sufficient reaction is discharged through the air outlet 705. The flow rate of the carrier gas is controlled to be 200 cc/min-500 cc/min, the pressure of the inner cavity of the gasification cabinet 70 is controlled to be 5-15 pa, the reaction temperature in the gasification cabinet 70 is controlled to be 300-500 ℃, and the constant temperature duration of the gasification treatment of the hollow powder rod 1071 is 4-6 h.

Alkali metal doping process: the hollow powder rod 1071 is moved into the gasification cabinet 70, the carrier gas carries out alkali metal, the alkali metal is introduced into the hollow powder rod 1071 from top to bottom, the alkali metal is contacted and enters gaps or holes of the core layer powder and further diffuses from inside to outside, meanwhile, external gas (protective atmosphere and the like) is introduced into the gas inlet 701, the gas pressure in the gasification chamber 707 is kept in a control range, and the gas which is fully reacted is discharged from the gas outlet 705 until a preset doping design is formed and then is stopped.

The process of forming the optical fiber preform 50 using the method of the present invention and the properties thereof are comparatively analyzed with reference to specific examples and comparative examples.

Example 1:

firstly, preparing a core layer, an inner cladding and an optical cladding by VAD vapor deposition process, and introducing GeCl into the core layer in the deposition process₄The gas flow rate is controlled at 30 cc/min; SiCl in the inner cladding₄The flow rate is controlled at 5g/min, and the powder density is controlled at 1.3g/cm³(ii) a SiCl in optical cladding₄The flow rate is controlled at 25g/min, and the powder density is controlled at 0.6g/cm³。

After the deposition of the powder rod is finished, extracting the solid target rod, moving the solid target rod into a gasification cabinet, introducing KBr carried by carrier gas Ar from an opening of the hollow quartz target rod, controlling the flow of Ar at 500cc/min, controlling the pressure of the gasification cabinet at 15pa, controlling the temperature of the gasification cabinet at 300 ℃, and keeping the temperature constant for 4 hours.

Then the powder rod doped with alkali metal is subjected to dehydroxylation, sintering and vitrification treatment in a sintering furnace. Firstly, the dehydroxylation temperature is controlled at 1200 ℃; after the end of the dehydroxylationEntering a sintering stage 1, the glass transition temperature is increased to 1300 ℃ at a heating rate of 3 ℃/min, and CF is added at the same time₄The gas flow is controlled at 400 cc/min; after the temperature is increased to 1300 ℃, the sintering stage 2 is carried out, the glass transition temperature is increased to 1450 ℃ at the temperature increasing rate of 0.5 ℃/min, and simultaneously CF₄The gas flow is controlled at 600 cc/min; after the temperature is raised to 1450 ℃; entering a constant temperature stage, keeping the temperature for 2h, CF₄The gas flow was controlled at 300cc/min and the powder rod was further sintered into a transparent glass body.

The glass rod is treated through OVD gas phase synthesis to reach the target weight or rod diameter, and through further fluorine doping and sintering, CF₄The gas flow rate was controlled at 400cc/min and the soot rod was fabricated into a transparent ultra-low loss optical fiber preform 50.

Refractive index profile characteristics:

the intermediate core layer 501: Δ n1 ═ 0.04%, r1 ═ 4.5 μm;

the inner structure cladding 503 is a fluorine-doped transition region, and r2 is 5.5 μm;

the optical structure layer 505: Δ n3 ═ 0.26%, r3 ═ 28 μm;

outer structural cladding 509: Δ n4 ═ 0.20%, r4 ═ 62.5 μm.

Optical fiber performance test results: the effective area of the optical fiber is 145 μm²1550nm attenuation 0.164dB/km, cable wavelength 1440 nm.

Example 2:

firstly, preparing a core layer, an inner cladding and an optical cladding by VAD vapor deposition process, and introducing GeCl into the core layer in the deposition process₄The gas flow rate is controlled at 60 cc/min; SiCl in the inner cladding₄The flow rate is controlled at 8g/min, and the powder density is controlled at 0.8g/cm³(ii) a SiCl in optical cladding₄The flow rate is controlled at 35g/min, and the powder density is controlled at 0.4g/cm³。

After the deposition of the powder rod is finished, extracting the solid target rod, moving the solid target rod into a gasification cabinet, and passing KCl through carrier gas O₂Carrying, introducing from the opening of the hollow quartz target rod, O₂The flow rate is controlled at 400cc/min, the pressure of the gasification cabinet is controlled at 10pa, the temperature of the gasified silicon is controlled at 400 ℃, and the temperature is kept constant for 4 h.

Then doping is carried outThe powder rod of alkali metal is dehydroxylated, sintered and vitrified in a sintering furnace. Firstly, the dehydroxylation temperature is controlled at 1200 ℃; after the dehydroxylation is finished, the sintering stage 1 is carried out, the vitrification temperature is increased to 1350 ℃ at the heating rate of 4 ℃/min, and simultaneously SiF is added₄The gas flow rate is controlled at 500 cc/min; after the temperature is raised to 1350 ℃, the sintering stage 2 is carried out, the glass transition temperature is raised to 1450 ℃ at the temperature raising rate of 1 ℃/min, and simultaneously SiF is added₄The gas flow is controlled at 800 cc/min; after the temperature is raised to 1450 ℃; and entering a constant temperature stage, keeping the temperature for 4 hours, controlling the SiF4 gas flow at 400cc/min, and further sintering the powder rod into a transparent glass body.

The glass rod is treated through OVD gas phase synthesis to reach the target weight or rod diameter, deposition is completed, fluorine-doped sintering and SiF₄The gas flow rate was controlled at 500cc/min and the soot rod was fabricated into a transparent ultra-low loss optical fiber preform 50.

Refractive index profile characteristics:

the intermediate core layer 501: Δ n1 ═ 0.08%, r1 ═ 5.0 μm;

the inner structure cladding 503 is a fluorine-doped transition region, and r2 is 6.2 μm;

optical structured cladding 505: Δ n3 ═ 0.30%, r3 ═ 36 μm;

outer structural cladding 509: Δ n4 ═ 0.23%, r4 ═ 62.5 μm.

Optical fiber performance test results: effective area of optical fiber is 140 μm²1550nm attenuation 0.163dB/km, cable wavelength 1510 nm.

Example 3:

firstly, preparing a core layer, an inner cladding and an optical cladding by VAD vapor deposition process, and introducing GeCl into the core layer in the deposition process₄The gas flow is controlled at 100 cc/min; SiCl in the inner cladding₄The flow rate is controlled at 12g/min, and the powder density is controlled at 0.6g/cm³(ii) a SiCl in optical cladding₄The flow rate is controlled at 45g/min, and the powder density is controlled at 0.2g/cm³。

After the deposition of the powder rod is finished, extracting the solid target rod, moving the solid target rod into a gasification cabinet, and enabling KBr to pass through carrier gas O₂Carrying, introducing from the opening of the hollow quartz target rod, O₂The flow rate is controlled at 300cc/min, the pressure of the gasification cabinet is controlled at 7pa, the temperature of the gasified silicon is controlled at 500 ℃, and the temperature is kept for 6 h.

Then the powder rod doped with the alkali metal is subjected to dehydroxylation, sintering and vitrification treatment in a sintering furnace. Firstly, the dehydroxylation temperature is controlled at 1250 ℃; after the dehydroxylation is finished, the sintering stage 1 is carried out, the vitrification temperature is increased to 1400 ℃ at the heating rate of 5 ℃/min, and simultaneously CF₄The gas flow is controlled at 600 cc/min; after the temperature is raised to 1400 ℃, the sintering stage 2 is carried out, the vitrification temperature is raised to 1500 ℃ at the temperature raising rate of 1.8 ℃/min, and simultaneously CF₄The gas flow is controlled at 1000 cc/min; after the temperature is raised to 1500 ℃; entering a constant temperature stage, keeping the temperature for 6h, CF₄The gas flow was controlled at 500cc/min and the powder rod was further sintered into a transparent glass body.

The glass rod is treated through OVD gas phase synthesis to reach the target weight or rod diameter, and through further fluorine doping and sintering, CF₄The gas flow rate was controlled at 800cc/min and the soot rod was fabricated into a transparent ultra-low loss optical fiber preform 50.

Refractive index profile characteristics:

the intermediate core layer 501: Δ n1 ═ 0.12%, r1 ═ 5.5 μm;

the inner structure cladding 503 is a fluorine-doped transition region, and r2 is 7.5 μm;

optical structured cladding 505: Δ n3 ═ 0.33%, r3 ═ 45 μm;

outer structural cladding 509: Δ n4 ═ 0.30%, r4 ═ 62.5 μm.

Optical fiber performance test results: effective area of optical fiber is 132 μm²1550nm attenuation 0.162dB/km, cable wavelength 1480 nm.

Comparative example 1:

the procedure and parameter settings for this example were essentially the same as in example 3, except that: in step S1, conventional VAD vapor deposition chamber deposition is used, i.e. gas flow enters the lower chamber from the upper powder body chamber, and is in the same chamber with the powder body.

For the powder rods formed by different air-inlet modes, a plurality of groups of samples are prepared under the process conditions of example 3 and comparative example 1, and the thicknesses of the optical cladding and the inner cladding in each sample are respectively testedThe magnification of the respective core layer rod diameters, in which the rod diameters of all the core layers are identical, is shown in fig. 10. It can be seen that the rod diameters of the powder rods adopting the air inlet mode of the invention are basically consistent, the results of 22 groups of samples are maintained between 7.20 and 7.30 times, and the fluctuation is small; in contrast, the conventional air intake method of comparative example 1 was employed, and the diameter of the powder rod was greatly fluctuated within a range of 7.10⁺Multiple to 7.50⁺The multiples varied, 5 samples were clearly higher than 7.40 times, and the remaining 17 samples were not substantially higher than 7.40 times, and were very unstable. Therefore, the results show that the air inlet mode of the invention helps to reduce the fluctuation of the rod diameter of the powder rod, and the design and control of the thickness and the density are easier to realize.

Refractive index profile characteristics:

a middle core layer: Δ n1 '═ 0.12%, r 1' ═ 5.4 μm;

the inner structure cladding is a fluorine-doped transition region, and r 2' is 7.6 mu m;

optical structure cladding: Δ n3 '═ 0.33%, r 3' ═ 45 μm;

outer structural cladding: Δ n4 '— 0.30%, r 4' — 62.5 μm.

Optical fiber performance test results: effective area of optical fiber is 132 μm²1550nm attenuation 0.165dB/km, cable wavelength 1490 nm.

We also tested the attenuation at 1550nm for comparison with optical fibres shaped with different modes of air entry, as shown in figure 11. The results show that the 16 samples of example 3 had an attenuation of substantially between 0.155 and 0.165dB/km, more precisely between 0.158 and 0.162 dB/km. The attenuation of the 16 groups of the comparative example 1 is up to more than 0.175dB/km, the lowest value is about 0.158dB/km, the average value is larger than that of the 16 groups of the example 3, the reproducibility of the sample is poor, and the qualified rate is difficult to control. Therefore, the air inlet mode has influence on the attenuation of the optical fiber, and the constant ratio among the core layer, the inner cladding layer and the optical cladding layer of the core rod can be realized by controlling the deposition air flow of the powder rod, so that the longitudinal instability of the attenuation caused by the longitudinal fluctuation of the core rod is avoided.

In conclusion, the preparation method of the optical fiber preform rod is simple, can effectively control and realize the quantitative production of the optical fiber with ultralow loss and large effective area, has excellent performance, and the effective area reaches 120-²1550nm attenuation lower than 0.165dB/km and cable wavelength lower than 1530nm are the preferred materials for optical fibers in transmission systems of 400G and above in the future. The method has the advantages that: (1) after the thickness and density of the inner cladding and the optical cladding are optimally designed in VAD deposition, powder layer combination distributed in different density areas is realized, and the constrained diffusion of the fluoride in the core layer, the inner cladding and the optical cladding is realized by combining a linear sintering fluorine-doped process; meanwhile, the refractive index requirements of the core layer and the optical cladding layer are prevented from being influenced by the reduction of the refractive index of the core layer caused by the large diffusion of fluoride to the core layer without control; (2) the fluorine-doped requirement in the optical cladding and the gradual change type distribution of the fluoride of the inner cladding are realized through the process, a good transitional effect is achieved between the core layer and the optical cladding, and the viscosity of the core layer at the center and the viscosity of the optical cladding at the outer layer are effectively matched; (3) the hollow powder rod is doped with alkali metal through the center, so that the diffusion of the alkali metal to the outside of the core layer is realized, the viscosity of the core layer is favorably reduced, meanwhile, the gradual change process from the core layer to the outer layer is also realized, and the viscosity matching between the core layer and the inner cladding layer and the optical cladding layer is ensured. (4) The upper portion cavity divide into inside and outside two rooms, effectively gets into the cavity separation with powder stick accommodation space and gas, avoids increasing along with the powder stick, and simultaneously, outer outdoor upper cover plate adopts foraminiferously, can tie the air input, and the air current turbulent flow in the deposit cavity is improved by a wide margin to this kind of structure, reaches the effect that effectively improves the stick footpath fluctuation of powder stick.

Although the embodiments of the present invention have been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the embodiments of the present invention.