Claims:CLAIMS

What is claimed is:

1. A fluorine doped core preform manufacturing method comprising:

dehydrating a porous soot preform in a gaseous atmosphere;

exposing the porous soot preform to a fluorine precursor to make a fluorine doped porous soot preform; and

sintering the fluorine doped porous soot preform to form the fluorine doped core preform, wherein the fluorine doped core preform is substantially a solid cylindrical body, wherein the fluorine doped core preform is defined by a radius and an outer periphery, wherein the outer periphery is defined by 100% of the radius, wherein the fluorine doped core preform has substantial concentration of fluorine from 60% of the radius to 100% of the radius.

2. The fluorine doped core preform manufacturing method as claimed in claim 1, wherein the porous soot preform is exposed to the fluorine precursor at a temperature less than 1350 degree Celsius.

3. The fluorine doped core preform manufacturing method as claimed in claim 1, wherein sintering of the fluorine doped porous soot preform requires a temperature of more than 1050 degree Celsius, wherein the temperature of more than 1050 degree Celsius is required after the dehydration of the porous soot preform.

4. The fluorine doped core preform manufacturing method as claimed in claim 1, wherein the fluorine precursor is one of C2F6, SiF4, and SF6, wherein the fluorine as a dopant used for lowering the refractive index of the fluorine doped core preform.

5. The fluorine doped core preform manufacturing method as claimed in claim 1, wherein the porous soot preform is a Germania doped preform.

6. The fluorine doped core preform manufacturing method as claimed in claim 1, wherein the gaseous atmosphere for the dehydration of the porous soot preform comprises chlorine and helium.

7. The fluorine doped core preform manufacturing method as claimed in claim 1, further comprising another step of drawing the fluorine doped core preform into core rods.

8. The fluorine doped core preform manufacturing method as claimed in claim 1, wherein the fluorine precursor has volume flow rate in range of about 0.5 standard litre per minute to 2.5 standard litre per minute.

9. The fluorine doped core preform manufacturing method as claimed in claim 1, wherein the dehydrated porous soot preform is exposed to the fluorine precursor for about 2.5 hours to 4.0 hours.

10. A fiber manufacturing method using a fluorine doped core preform, the fiber manufacturing method comprising:

manufacturing the fluorine doped core preform;

drawing the fluorine doped core preform into core rods, wherein the core rods are cylindrical in shape;

depositing silica over the core rods, wherein the deposition of the silica over each of the core rods is done to form a cladding of the core rod, wherein the cladding over the core rod forms a cylindrical structure;

sintering the core rods having the cladding of the pure silica to form a glass preform, wherein the glass preform is a solid preform body, wherein the glass preform has a core and a cladding, wherein the glass preform has a low refractive index region in the core; and

drawing the glass preform to form a fiber, wherein the fiber has a fiber core, wherein the fiber core has a low refractive index region.

11. The fiber manufacturing method as claimed in claim 10, wherein the silica over the core rods is one of pure silica and impure silica.

12. The fiber manufacturing method as claimed in claim 10, wherein the fiber has low refractive index region in the fiber core, wherein the fiber is drawn from the core rod with refractive index profile parameters, wherein the refractive index profile parameters comprising cladding to core diameter ratio (D/d) in a range of 3.1 to 4.2 before fluorine doping, core delta in a range of 0.35 to 0.37, trench delta in a range of – 0.27 to – 0.33, core alpha in a range of 4 to 8, and trench alpha in a range of 3-6.

13. The fiber manufacturing method as claimed in claim 10, wherein the low refractive index region in the fiber core is due to fluorine doping.

14. A fluorine doped core preform manufacturing method comprising:

dehydrating a porous soot preform in a gaseous atmosphere;

exposing the porous soot preform to a fluorine precursor to make the fluorine doped porous soot preform; and

sintering the fluorine doped porous soot preform to form the fluorine doped core preform, wherein the fluorine doped core preform is substantially a solid cylindrical body, wherein the fluorine doped core preform is defined by a radius and an outer periphery, wherein the outer periphery is defined by 100% of the radius, wherein the fluorine doped core preform has substantial concentration of fluorine from 60% of the radius to 100% of the radius,

wherein the fluorine doped porous soot preform is sintered at a temperature in a range of 1500 degree Celsius to 1585 degree Celsius.

15. The fluorine doped core preform manufacturing method as claimed in claim 14, wherein the fluorine precursor is one of C2F6, SiF4, and SF6, wherein the fluorine as a dopant used for lowering the refractive index of the fluorine doped core preform.

16. The fluorine doped core preform manufacturing method as claimed in claim 1, further comprising another step of dehydrating the fluorine doped preform in a gaseous atmosphere of chlorine and helium.

17. A bend insensitive optical fiber comprising:

a core region, wherein the core region of the bend insensitive optical fiber has refractive index profile parameters, wherein the refractive index profile parameters comprising cladding to core diameter ratio (D/d) in a range of 3.1 to 4.2 before fluorine doping, core delta in a range of 0.35 to 0.37, trench delta in a range of – 0.27 to – 0.33, core alpha in a range of 4 to 8, and trench alpha in a range of 3-6; and

a cladding region, wherein the cladding region is made of pure silica, wherein the cladding region made of pure silica.
Dated: 26th Day of March, 2019 Signature
Arun Kishore Narasani Patent Agent
PA/IN/1049
, Description:TECHNICAL FIELD

The present invention relates to the field of fiber optics and, in particular, relates to a method for manufacturing of bend insensitive optical fiber.

BACKGROUND

Over the last few years, there has been an exponential rise in the manufacturing of optical fibers due to an overgrowing demand of the optical fibers. The manufacturing of optical fibers has two major stages. The first stage involves the manufacturing of optical fiber preforms and the second stage involves drawing the optical fibers from the optical fiber preforms. In general, the quality of optical fibers depends on conditions of manufacturing. So, a lot of attention is paid towards the manufacturing of the optical fibers with good characteristic. These optical fiber preforms include an inner glass core surrounded by a glass cladding having a lower index of refraction than the inner glass core. Typically, the preform is manufactured by utilizing a substrate rod and one or more burners positioned below the substrate rod.

The presently available techniques for the production of the optical fiber have certain drawbacks. The most consistent problems which occur during the production of the optical fiber are excess time requirement and low bending performance of the drawn optical fiber. The optical fiber preform has to go through multiple stages for the production of the required optical fiber which results in the increase in time.

In light of the above stated discussion, there is a need for an optical fiber that overcomes the above stated disadvantages and increases the performance of the optical fibers.

OBJECT OF THE DISCLOSURE

A primary object of the present disclosure is to provide a method for the manufacturing of bend insensitive optical fiber using outside vapor deposition process.

Another object of the present disclosure is to provide the method for the manufacturing of optical fiber having low bending loss.

Yet another object of the present disclosure is to eliminate the multiple process stage required for the manufacturing of the bend insensitive optical fiber.

Yet another object of the present disclosure is to improve the characteristics of the optical fiber preform.

Yet another object of the present disclosure is to provide a cost effective method for the continuous manufacturing of the bend insensitive optical fiber.

Yet another object of the present disclosure is to provide the bend insensitive optical fiber which meets the requirement of ITU-T G.657 A2.

SUMMARY

In an aspect, the present disclosure provides a fluorine doped core preform manufacturing method. The method includes a first step of dehydrating a porous soot preform in a gaseous atmosphere. The method includes another step of exposing the porous soot preform to a fluorine precursor to make a fluorine doped porous soot preform. The method includes yet another step of sintering the fluorine doped porous soot preform to form the fluorine doped core preform. The fluorine doped core preform is substantially a solid cylindrical body. The fluorine doped core preform is defined by a radius and an outer periphery. The outer periphery is defined by 100 % of the radius. The fluorine doped core preform has substantial concentration of fluorine from 60% of the radius to 100% of the radius.

In an embodiment of the present disclosure, the porous soot preform is exposed to the fluorine precursor at a temperature less than 1350 degree Celsius.

In an embodiment of the present disclosure, the sintering of the fluorine doped porous soot preform requires a temperature of more than 1050 degree Celsius. The temperature of more than 1050 degree Celsius is required after the dehydration of the porous soot preform.

In an embodiment of the present disclosure, the fluorine precursor is one of C2F6, SiF4, and SF6, wherein the fluorine as a dopant used for lowering the refractive index of the fluorine doped core preform,

In an embodiment of the present disclosure, the porous soot preform is a Germania doped preform.

In an embodiment of the present disclosure, the gaseous atmosphere used for the dehydration of the porous soot preform includes chlorine and helium.

In an embodiment of the present disclosure, the fluorine doped core preform manufacturing method further includes another step of drawing the fluorine doped core preform into core rods.

In an embodiment of the present disclosure, the fluorine precursor has volume flow rate in range of about 0.5 standard litre per minute to 2.5 standard litre per minute.

In an embodiment of the present disclosure, the dehydrated porous soot preform is exposed to the fluorine precursor for about 2.5 hours to 4.0 hours.

In another aspect, the present disclosure provides a fiber manufacturing method using a fluorine doped core preform. The fiber manufacturing method includes a first step of manufacturing the fluorine doped core preform. The fiber manufacturing method includes another step of drawing the fluorine doped core preform into core rods. The core rods are cylindrical in shape. The fiber manufacturing method includes yet another step of depositing silica over the core rods. The deposition of the silica over each of the core rods forms a cladding of the core rod. The cladding is cylindrical in shape. The fiber manufacturing method includes yet another step of sintering the core rods having the cladding of the pure silica to form a glass preform. The glass preform is a solid preform body. The glass preform has a core and a cladding. The glass preform has a low refractive index region in the core. The fiber manufacturing method includes yet another step of drawing the glass preform to form a fiber. The fiber has a fiber core. The fiber core has a low refractive index region.

In an embodiment of the present disclosure, the silica over the core rods is one of pure silica and impure silica.

In an embodiment of the present disclosure, the fiber has low refractive index region in the fiber core. The fiber is drawn from the core rod with refractive index profile parameters. The refractive index profile parameters include cladding to core diameter ratio (D/d) in a range of 3.1 to 4.2 before fluorine doping, core delta in a range of 0.35 to 0.37. In addition, the refractive index profile parameters include trench delta in a range of – 0.27 to – 0.33, core alpha in a range of 4 to 8, and trench alpha in a range of 3-6.

In an embodiment of the present disclosure, the low refractive index region in the fiber core is due to the fluorine doping.

In yet another aspect, the present disclosure provides a fluorine doped core preform manufacturing method. The method includes a first step of dehydrating a porous soot preform in a gaseous atmosphere. The method includes another step of exposing the porous soot preform to a fluorine precursor to make a fluorine doped porous soot preform. The method includes yet another step of sintering the fluorine doped porous soot preform to form the fluorine doped core preform. The fluorine doped core preform is substantially a solid cylindrical body. The fluorine doped core preform is defined by a radius and an outer periphery. The outer periphery is defined by 100 % of the radius. The fluorine doped core preform has substantial concentration of fluorine from 60% of the radius to 100% of the radius. The fluorine doped porous soot preform is sintered at a temperature in a range of 1500 degree Celsius to 1585 degree Celsius.

In an embodiment of the present disclosure, the fluorine precursor is one of C2F6, SiF4, and SF6. The fluorine as a dopant used for lowering the refractive index of the fluorine doped core preform.

In an embodiment of the present disclosure, the fluorine doped core preform manufacturing method further includes another step of dehydrating the fluorine doped preform in a gaseous atmosphere of chorine and helium.

In yet another aspect, the present disclosure provides a bend insensitive optical fiber. The bend insensitive optical fiber includes a core region and a cladding region. The core region of the bend insensitive optical fiber with refractive index profile parameters includes cladding to core diameter ratio (D/d) in a range of 3.1 to 4.2 before fluorine doping. In addition, the refractive index profile parameters includes core delta in a range of 0.35 to 0.37, trench delta in a range of – 0.27 to – 0.33, core alpha in a range of 4 to 8, and trench alpha in a range of 3-6. The cladding region is made of pure silica. The cladding region has zero refractive index.

STATEMENT OF THE DISCLOSURE

In an aspect, the present disclosure provides a fluorine doped core preform manufacturing method. The method includes a first step of dehydrating a porous soot preform in a gaseous atmosphere. The method includes another step of exposing the porous soot preform to a fluorine precursor to make a fluorine doped porous soot preform. The method includes yet another step of sintering the fluorine doped porous soot preform to form a fluorine doped core preform. The fluorine doped core preform is substantially a solid cylindrical body. The fluorine doped core preform is defined by a radius and an outer periphery. The outer periphery is defined by 100 % of the radius. The fluorine doped core preform has substantial concentration of fluorine from 60% of the radius to 100% of the radius.

BRIEF DESCRIPTION OF FIGURES

Having thus described the disclosure in general terms, reference will now be made to the accompanying figures, wherein:

FIG. 1 illustrates a general overview of a system to manufacture a bend insensitive optical fiber, in accordance with various embodiments of the present disclosure;

FIG. 2 illustrates a flowchart for manufacturing of the bend insensitive optical fiber, in accordance with various embodiments of the present disclosure; and

FIG. 3 illustrates a refractive index profile of a core rod, in accordance with an embodiment of the present disclosure.

It should be noted that the accompanying figures are intended to present illustrations of exemplary embodiments of the present disclosure. These figures are not intended to limit the scope of the present disclosure. It should also be noted that accompanying figures are not necessarily drawn to scale.

DETAILED DESCRIPTION

In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present technology. It will be apparent, however, to one skilled in the art that the present technology can be practiced without these specific details. In other instances, structures and devices are shown in block diagram form only in order to avoid obscuring the present technology.

Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present technology. The appearance of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not other embodiments.

Moreover, although the following description contains many specifics for the purposes of illustration, anyone skilled in the art will appreciate that many variations and/or alterations to said details are within the scope of the present technology. Similarly, although many of the features of the present technology are described in terms of each other, or in conjunction with each other, one skilled in the art will appreciate that many of these features can be provided independently of other features. Accordingly, this description of the present technology is set forth without any loss of generality to, and without imposing limitations upon, the present technology.

FIG. 1 illustrates a general overview of a system 100 for manufacturing of an optical fiber preform, in accordance with various embodiments of the present disclosure. The system 100 is configured for the manufacturing of the optical fiber preform using outside vapor deposition process. In addition, the system 100 for the manufacturing of the optical fiber preform using outside vapor deposition technique includes a spindle rod 102, a rotating mechanism 104, one or more burners 106. Further, the system 100 includes a plurality of chemicals 108 and a guiding mechanism 110.

In general, the optical fiber preform is a large cylindrical body of glass having a core structure and a cladding structure. In addition, the optical fiber preform is a material used for fabrication of optical fibers. Accordingly, the optical fibers are used for a variety of purposes. The variety of purposes includes telecommunications, broadband communications, medical applications, military applications and the like. The optical fiber preform is the optical fiber in a large form. In general, the meticulously deposition of vapor around a long ceramic bait rod results in the formation of ultra-pure glass. In addition, when the bait rod removed, the perfect glass tube structure is known as a preform.

The optical fiber preform includes a core section and a cladding section. The core section is an inner part of the optical fiber preform or the optical fiber and the cladding section is an outer part of the optical fiber preform or the optical fiber. Moreover, the core section and the cladding section are formed during the manufacturing stage of the optical fiber preform. The core section has a refractive index which is greater than a refractive index of the cladding section. In general, the core section has a higher refractive index than the cladding section. The refractive index is maintained as per a desired level based on a concentration of chemicals used for the production of the optical fiber preform. These chemicals are deposited over a surface of the initial material by performing flame hydrolysis. In an example, the initial material includes spindle rod or mandrel rod.

The system 100 includes a spindle rod 102. In general, the spindle rod 102 is a substrate rod configured to rotate about a longitudinal axis associated with the spindle rod 102. In addition, the spindle rod 102 rotates at a fixed rotational speed. In an embodiment of the present disclosure, the rotational speed of the spindle rod 102 may vary. In an example, the rotational speed of the spindle rod 102 is in revolutions per minute. In an embodiment of the present disclosure, the rotational speed is fixed at any instant of time of deposition. In another embodiment of the present disclosure, the rotational speed changes during the deposition process. Further, the spindle rod 102 is a cylindrical rod of any length used for the deposition of the chemicals around the circumference of the spindle rod 102. In an embodiment of the present disclosure, the spindle rod 102 is the initial material used for the manufacturing of the optical fiber preform. In an embodiment of the present disclosure, any type of rotating material may be utilized for the production of the optical fiber preform. In an example, the other type of rotating material includes a mandrel, a bait rod. In general, the spindle rod 102 is made of alumina or graphite or carbon. Further, the spindle rod 102 is associated with the rotating mechanism 104.

The system 100 includes the rotating mechanism 104. In an embodiment of the present disclosure, the spindle rod 102 is mechanically connected to the rotating mechanism 104. Moreover, one end of the spindle rod 102 is connected to the rotating mechanism 104. In an embodiment of the present disclosure, each end of the spindle rod 102 is connected to a corresponding end of the rotating mechanism 104. In addition, the rotating mechanism 104 is a device or a machine configured to rotate the spindle rod 102 or to traverse the spindle rod 102. In an embodiment of the present disclosure, the rotating mechanism 104 is configured to simultaneously rotate and traverse the spindle rod 102. The rotating mechanism 104 rotates the spindle rod 102 about the longitudinal axis associated with the spindle rod 102. In an embodiment of the present disclosure, the rotating mechanism 104 rotates the spindle rod 102 in a clockwise direction. In another embodiment of the present disclosure, the rotating mechanism 104 rotates the spindle rod 102 in an anti-clockwise direction.

The rotating mechanism 104 may include a lathe machine with each end of the spindle rod 102 mounted on the corresponding ends of the lathe machine. Examples of the lathe machine include but may not be limited to metal spinning lathe, glass working lathe, rotary lathe or any other type of lathe suitable for rotating the spindle rod 102. In an embodiment of the present disclosure, the rotating mechanism 104 may be a motor. The motor is an electric rotating motor configured to rotate the spindle rod 102 about the longitudinal axis of the spindle rod 102. Examples of the motor include DC motor, AC motor and the like.

In an embodiment of the present disclosure, the rotating mechanism 104 is controlled by an operator through a control unit. In an embodiment of the present disclosure, the operator monitors the revolutions made by the rotating mechanism 104 in real time. In an embodiment of the present disclosure, the operator keeps the revolutions per minute made by the rotating mechanism 104 constant. In another embodiment of the present disclosure, the operator keeps the revolutions per minute made by the rotating mechanism 104 variable. In addition, the rotating mechanism 104 is supplied with electrical power in real time. The electrical power is supplied for performing the rotation of the rotating mechanism 104 which eventually rotates the spindle rod 102.

In an embodiment of the present disclosure, the rotating mechanism 104 traverses the spindle rod 102 back and forth. Further, the traversing is done along the longitudinal axis of the spindle rod 102. Furthermore, the spindle rod 102 is traversed at an optimized traversing speed. Also, the spindle rod 102 traverses and rotates at the same time. In an embodiment of the present disclosure, the rotation and the traversing of the spindle rod 102 take place simultaneously. In an embodiment of the present disclosure, the spindle rod 102 may not traverse. The spindle rod 102 and the rotating mechanism 104 are associated with the one or more burners 106.

The system 100 includes the one or more burners 106. In addition, the one or more burners 106 are positioned below the spindle rod 102. In an embodiment of the present disclosure, each of the one or more burners 106 is placed at a suitable vertical distance from the spindle rod 102. In an embodiment of the present disclosure, the one or more burners 106 have a heating mechanism. Further, each of the one or more burners 106 deposits silica particles over the surface of the rotating spindle rod 102. The deposition of the silica particles is done to form multiple layers of porous soot over the surface of the spindle rod 102.

Furthermore, each of the one or more burners 106 correspond to a burner which performs combustion of hydrogen and oxygen along with other chemicals required for the production of the porous soot preform. Each burner of the one or more burners 106 is placed beneath the spindle rod 102. Further, each of the one or more burners 106 is an oxy hydrogen flame burner. Furthermore, the oxy hydrogen flame burner receives oxygen and hydrogen from corresponding inlets. The oxygen and hydrogen acts as the fuel for the production of porous soot preform. In an embodiment of the present disclosure, the oxy hydrogen flame burner receives the other chemicals through other inlets in order to react with hydrogen and oxygen to produce the silica particles. In an embodiment of the present disclosure, the silica particles correspond to soot. In an embodiment of the present disclosure, the plurality of chemicals 108 is used for the manufacturing of the optical fiber preform. In an embodiment of the present disclosure, the plurality of chemicals 108 includes oxygen, hydrogen, silicon tetrachloride and germanium tetrachloride. Further, the plurality of chemicals includes dopants such as Germania. In an embodiment of the present disclosure, the plurality of chemicals may include any suitable dopant used for providing desired characteristic to the optical fiber preform. In addition, the plurality of chemicals includes optical fiber cable. In an embodiment of the present disclosure, the silica particles correspond to soot.

Each of the one or more burners 106 traverses back and forth below the spindle rod 102. In addition, each of the one or more burners 106 traverses along the length of the spindle rod 102 at the optimized traversing speed. In another embodiment of the present disclosure, the one or more of burners 106 traverse relatively with the traversing and rotating spindle rod 102.

In an embodiment of the present disclosure, the optical fiber preform can be manufactured in each of the three cases. The first case is the spindle rod 102 traversing and rotating about the longitudinal axis of the spindle rod 102 and the one or more burners 106 remain at one position. The second case is the one or more burners 106 traversing parallel to the longitudinal axis of the spindle rod 102 and the spindle rod 102 rotate at one position. The third case is the relative traversing motion between the rotating spindle rod 102 and the one or more burners 106 about the longitudinal axis of the spindle rod 102. Each of the one or more burners 106 is associated with the guiding mechanism 110.

The system 100 includes the guiding mechanism 110. Each of the one or more burners 106 is connected to the guiding mechanism 110. In an embodiment of the present disclosure, the guiding mechanism 110 is placed adjacent to an arrangement of the one or more burners 106. In an embodiment of the present disclosure, the guiding mechanism 110 is placed below the rotating mechanism 104. In an embodiment of the present disclosure, the guiding mechanism 110 may be a part of the rotating mechanism 104.

The guiding mechanism 110 enables each of the one or more burners 106 to traverse along the length of the at least one spindle rod 102. Moreover, each of the one or more burners 106 traverses according to burner guide mechanics applied by the guiding mechanism 110. In an embodiment of the present disclosure, each of the one or more burners 106 moves over a fixed path according to the guiding mechanism 110. In an embodiment of the present disclosure, each of the one or more burners 106 is placed over a driving shaft. The driving shaft drives the one or more burners 106. Each of the one or more burners 106 is fixed on the driving shaft. In an embodiment of the present disclosure, the driving motor is connected to the driving shaft through a gear which enables the traversing motion of each of the one or more burners 106.

The guiding mechanism 110 enables the traversing speed to be optimized to the specific value corresponding to the number of revolutions made by the spindle rod 102 in the time taken to travel between the one or more burners 106. In an embodiment of the present disclosure, the optimization of the traversing speed against the number of revolutions is done automatically by the guiding mechanism 110. In an embodiment of the present disclosure, the traversing speed is optimized against each corresponding value of the number of revolutions made by the spindle rod 102.

The system 100 performs a method for the manufacturing of bend insensitive optical fiber. In addition the system 100 performs a continuous bend insensitive optical fiber manufacturing method. The method includes a first step of manufacturing a Germania doped porous soot preform using outside vapor deposition technique. The Germania doped porous soot preform is manufactured through a chemical reaction which takes place inside each of the one or more burners 106. The chemical reaction is done using the plurality of chemicals 108. In an embodiment of the present disclosure, the plurality of chemicals 108 includes oxygen, hydrogen, silicon tetrachloride and germanium tetrachloride. Further, the plurality of chemicals 108 includes one or more dopants for the manufacturing of porous soot preform. The plurality of chemicals includes Germania dopant. In an embodiment of the present disclosure, the plurality of dopants may include any suitable dopant required for the manufacturing of optical fiber preform.

In general, the combustion process produces a mixture of very small, oxidized glass particles called soot. In general, Germania is an inorganic compound with the chemical formula GeO2. In addition, the amorphous (glassy) form of GeO2 is similar to fused silica. The refractive index and optical dispersion properties of germanium dioxide (GeO2) makes it useful as an optical material for the core of fiber-optic lines. In addition, a mixture of silicon dioxide and germanium dioxide ("silica-germania") is used as an optical material for optical fibers. Further, the silica-Germania glasses have lower viscosity and higher refractive index than pure silica.

In an embodiment of the present disclosure, the core section of the optical fiber preform is manufactured using pure silica doped with Germania and the cladding section is manufactured using pure silica. In another embodiment of the present disclosure, the core section of the optical fiber preform is manufactured using pure silica doped with any suitable substance or element.

The method includes another step of dehydrating the Germania doped porous soot preform in a gaseous atmosphere of chlorine and helium with 5 % by volume chlorine percentage. In addition, the chlorine and inert gas like helium creates an atmosphere for the dehydration of the Germania doped porous soot preform. Further, chlorine gas with 5% by volume is used for removing hydroxyl (OH) group from the Germania doped porous soot preform. Furthermore, the reaction of Germania doped porous soot preform with chlorine leads to the removal of hydroxyl group and moisture from the Germania doped porous soot preform. Also, the addition of Cl2 gas in He atmosphere vaporizes trapped OH in form of HCl to achieve OH reduction in preform.

The Germania doped porous soot preform is dehydrated in the presence of gaseous atmosphere of chlorine and helium. In addition, the removal of moisture and hydroxyl group from the Germania doped porous soot preform depends on the dehydration temperature. In an embodiment of the present disclosure, the Germania doped porous soot preform is dehydrated at a temperature in a range of about 950 degree Celsius to 1150 degree Celsius.

The chlorine used for the dehydration of Germania doped porous soot preform has a volume flow rate in a range of about 1.5 standard litre per minute (hereinafter referred to as slpm) to 2 standard litre per minute (slpm). The helium used for the dehydration of Germania doped porous soot preform has a volume flow rate in a range of about 20 slpm to 40 slpm. In general, the volume flow rate is defined as the volume of fluid which passes per unit time. In general, the standard litre per minutes is a unit of volumetric flow rate of a gas at standard temperature and pressure (STP).

The method includes yet another step of exposing the dehydrated Germania doped porous soot preform to a fluorine precursor with 5% to 8% by volume to make fluorine doped porous soot preform. The dehydrated porous soot preform is exposed to the fluorine precursor at a temperature not more than 1350 degree Celsius for about 2.5 hours to 4.0 hours. In an embodiment of the present disclosure, the temperature and duration of exposing the preform to the fluorine precursor may vary according to the requirement. In an embodiment of the present disclosure, the fluorine precursor used to make the fluorine doped preform is selected from a group. The group includes C2F6, SiF4 and SF6. In addition, the fluorine as a dopant used for lowering the refractive index. Further, the fluorine precursor in the atmosphere has the volume flow rate in a range of about 0.5 Slpm to 2.5 Slpm. In an example, the dehydrated preform is exposed to the fluorine precursor to reduce the refractive index of the surface or cladding of the Germania doped porous soot preform. In an embodiment, the fluorine precursor is introduced from the bottom of a sintering machine along with helium gas which ensures the complete axial and radial distribution of fluorine precursor along the porous silica preform.

The method includes yet another step of exposing the fluorine doped porous soot preform to chlorine (Cl2) and helium (He) atmosphere for about 40 minutes 90 minutes. The volume flow rate of the chlorine lies within a range of about 0.2 slpm to 0.8 slpm. In addition, the volume flow rate of the helium lies within a range of about 20 slpm to 25 slpm. Further, the temperature of about 1100 degree Celsius to 1250 degree Celsius is maintained for exposing the fluorine doped porous soot preform to chlorine and helium. Furthermore, the duration and flow of the chlorine are fine-tuned to obtain a uniform fluorine doped trench profile with a run to run consistency. In an embodiment of the present disclosure, the gases such as SiCl4, Si2Cl6, Si2OCl6, SiCl3H, and CCl4 can be used as substitute for Cl2 though Cl2 is used in the current. In another embodiment of the present disclosure, the Cl2 can be replaced by any other suitable gases.

The method includes yet another step of dehydrating the fluorine doped porous soot preform in a gaseous atmosphere of chlorine and helium. The chlorine used for the dehydration of the fluorine doped preform makes fluorine to spread homogeneously within the soot body and to react with the SiO2. Furthermore, the chlorine used for the dehydration of the fluorine doped preform facilitates in the reduction of OH content and in the reduction of OH induced attenuation.

The method includes yet another step of sintering the fluorine doped porous soot preform at a temperature in a range of about 1500 degree Celsius to 1585 degree Celsius. The sintering of the fluorine doped porous soot preform is done to form a fluorine doped core preform. In general, the fluorine doped core preform is substantially a solid cylindrical body. The fluorine doped core preform is defined by a radius and an outer periphery. The outer periphery is defined by 100% of the radius. Further, the fluorine doped core preform has substantial concentration of fluorine from 60% of the radius to 100% of the radius.
In general, the sintering is defined as the heating of the compacted powder perform to a specific temperature (below the melting temperature of the principle powder particles while well above the temperature that would allow diffusion between the neighboring particles). In an embodiment of the present disclosure, the sintering of the fluorine doped porous soot preform requires a temperature of more than 1050 degree Celsius. The temperature of more than 1050 degree Celsius is required after the dehydration of the porous soot preform. In addition, the sintering facilitates the bonding action between the individual powder particles and increase the strength of the final part. Further, the heating process must be carried out in a controlled, inert or reducing atmosphere or in vacuum for very critical parts to prevent oxidation. Generally, the time, temperature and the atmosphere of the sintering furnace are major factors to control the sintering process. In general, the sintering process enhances the density of the fluorine doped preform by filling up the incipient holes and increasing the area of contact among the powder particles in optical fiber perform.

In an embodiment of the present disclosure, the Germania doped preform is exposed to the fluorine precursor in the sintering furnace preceded and followed by the dehydration process. In an embodiment of the present disclosure, the sintering of the fluorine doped preform is done in a gaseous atmosphere of chlorine and helium having volume flow rate of 0.30 to 1.00 slpm and 15 to 25 slpm respectively.

The method includes yet another step of drawing the fluorine doped preform into core rods with pure silica cladding. In an embodiment of the present disclosure, the cladding over the core rods may not be of pure silica. In addition, the core rods are drawn continuously from the fluorine doped preform. In other words, the drawing of core rods from the fluorine doped preform is a continuous process. The cladding of pure silica over the core rods is formed using outside vapor deposition (OVD) technique. In general, the drawing can be defined as the heating of preform within the furnace to make it soft and allowing it to be pulled into a fiber. In an embodiment of the present disclosure, the fluorine doped preform is drawn into the core rods with pure silica cladding. In an embodiment of the present disclosure, the fluorine doped preform is drawn into the core rods at a temperature in a range of about 1650 degree Celsius to 1900 degree Celsius. In an embodiment of the present disclosure, the drawing process is performed for about 4 to 5 hours for the manufacturing of core rods in a range of about 6 to 10. In another embodiment of the present disclosure, the temperature, time and number of drawn core rods may vary according to the requirement.

The method includes yet another step of drawing the core rods having cladding of pure silica into a glass preform. The glass preform is a solid preform body. The glass preform has a core and a cladding. In addition, the glass preform has a low refractive index region in the core.

The method includes yet another step of drawing the fiber from the glass preform. The fiber is drawn from the glass preform after sintering the core rod along with the pure silica cladding. In an embodiment of the present disclosure, the cladding region and the core region of the glass preform is sintered to draw the fiber. The fiber has a fiber core region and cladding region. The fiber core has a low refractive index region.

In an embodiment of the present disclosure, the core region of the bend insensitive optical fiber corresponds to the core rod. Refractive index parameters of the core rod are the parameter for the core region of the bend insensitive optical fiber. The refractive index profile parameters include cladding to core diameter ratio (D/d) in a range of 3.1 to 4.2 before fluorine doping, core delta in a range of 0.35 to 0.37. In addition, the refractive index profile parameters include trench delta in a range of – 0.27 to – 0.33, core alpha in a range of 4 to 8, and trench alpha in a range of 3-6. The cladding of the fiber is made of pure silica. The cladding region of the fiber made of pure silica. In an embodiment, the cladding region of the fiber is made of impure silica with a suitable value of refractive index.
The method used for the manufacturing of the bend insensitive optical fiber leads to a reduction in overall process time with increase in ease of operation with relaxation in bend insensitive optical fiber parameters. In general, the bend insensitive optical fibers are the optical fibers which are insensitive to stress, particularly bending. In addition, the bend sensitive optical fibers when stressed by bending, light in the outer part of the core is no longer guided in the core of the fiber. The stress on the bend sensitive optical fibers creates a higher loss in the stressed section of the fiber. The bend insensitive optical fiber parameters includes cladding to core diameter ratio (D/d), core delta, core trench delta and core alpha. The drawn bend insensitive optical fiber complies with specific telecommunication standards. The telecommunication standards are defined by International Telecommunication Union-Telecommunication (hereinafter “ITU-T”). In an embodiment of the present disclosure, the drawn bend insensitive optical fiber is compliant with G.657 recommendation standard set by the ITU-T. Furthermore, the ITU-T G.657 recommendation describes a geometrical, mechanical and transmission characteristics of a single mode optical fiber.

The ITU-T G.657 standard defines a plurality of optical characteristics associated with the bend insensitive optical fiber. The plurality of parameters associated with the bend insensitive optical fiber is optimized for achieving the plurality of optical characteristics in a pre-defined range. In an embodiment of the present disclosure, the plurality of optical characteristics is achieved in the pre-defined range by altering the concentration of the one or more dopants. The plurality of optical characteristics include but may not be limited to an attenuation, zero dispersion wavelength, zero dispersion slope, cable cutoff wavelength, mode field diameter, bending losses and effective area.

In general, the attenuation is a loss of optical power as light travels inside the core region of the drawn bend insensitive optical fiber. The attenuation in the drawn bend insensitive optical fiber is based on a plurality of factors. The plurality of factors includes but may not be limited to absorption, scattering, bending losses and the like. Moreover, the absorption and the scattering of the light in the drawn bend insensitive optical fiber are intrinsic in nature. Also, the attenuation due to the bending losses of the drawn bend insensitive optical fiber is extrinsic in nature. Further, the zero dispersion wavelength (hereinafter as “ZD wavelength”) is a wavelength at which the value of dispersion coefficient is zero. In general, ZD wavelength is the wavelength at which material dispersion and waveguide dispersion cancel one another.

The dispersion slope of the drawn bend insensitive optical fiber is the rate of change of dispersion with respect to the wavelength. In addition, the zero dispersion slope related to the drawn bend insensitive optical fiber is the slope at zero dispersion wavelength. The mode field diameter (hereinafter as “MFD”) of the drawn bend insensitive optical fiber is a section of fiber where most of the light energy travels. In general, MFD defines a section or area of the drawn bend insensitive optical fiber in which the optical signals travel. The MFD is an expression of distribution of the optical power. The effective area of the drawn bend insensitive optical fiber corresponds to an optical effective area at a wavelength of 1550 nm. The drawn bend insensitive optical fiber transmits a single mode of optical signal above a pre-defined cutoff wavelength known as cable cutoff wavelength. In general, cutoff wavelength is defined as the wavelength above which any given mode cannot propagate.

The MFD of the drawn bend insensitive optical fiber obtained has a pre-defined standard value. In an embodiment of the present disclosure, the pre-defined standard value of MFD lies in a range of about 8.2 µm to 9 µm. The ZD wavelength of the drawn bend insensitive optical fiber obtained has a pre-defined standard value. In an embodiment of the present disclosure, the pre-defined standard value of ZD wavelength lies in a range of about 1300 nm to 1324 nm. Furthermore, the bending losses associated with the drawn bend insensitive optical fiber has a pre-defined standard value. In an embodiment of the present disclosure, the pre-defined standard value of bending losses at 15 mm diameter bend is less than 0.5 dB/turn, preferably less than 0.2 dB/turn for the wavelength of 1550 nanometers. Moreover, the cable cutoff wavelength has a pre-defined value less than 1260 nanometers.

In an embodiment of the present disclosure, Vapor axial deposition (VAD) process is used for the manufacturing of the bend insensitive optical fiber. In another embodiment of the present disclosure, any suitable process is used for the manufacturing of the bend insensitive optical fiber. In general, the vapor axial deposition process is used to manufacture a porous glass preform. In the vapor axial deposition process, the porous glass preform is fabricated by the deposition of fine glass material onto the end surface of a starting material through flame hydrolysis. The starting material such as SiCl4, GeCl4, SiF4 pulled upward in axial direction and the porous glass preform is grown in the same direction. The porous glass preform is heated to create a transparent fiber preform.

FIG. 2 illustrates a flowchart 200 for a fiber manufacturing method using a fluorine doped core preform, in accordance with various embodiments of the present disclosure. It may be noted that to explain the process steps of the flowchart 200, references will be made to the system elements of the FIG. 1. The flowchart 200 initiates at step 202. Following step 202, at step 204, manufactures the fluorine doped core preform. At step 206, draw fluorine doped core preform into core rods. At step 208, deposits silica over the core rods. At step 210, sinters the core rods having cladding of the pure silica to form a glass preform. At step 212, draw the glass preform into fibers. The flowchart 200 terminates at step 214.

It may be noted that the flowchart 200 is explained to have above stated process steps; however, those skilled in the art would appreciate that the flowchart 200 may have more/less number of process steps which may enable all the above stated embodiments of the present disclosure.

FIG. 3 illustrates a refractive index profile 300 of a core rod, in accordance with various embodiments of the present disclosure. The refractive index profile 300 illustrates a relationship between the refractive index of the core rod and the radial distance of the core rod. In an embodiment of the present disclosure, the refractive index profile 300 shows the change in the refractive index of the core rod with the radial distance of the core rod. In an embodiment of the present disclosure, d is the diameter of the core region of the core rod. In addition, D is the diameter of the cladding region with trench region formed due to the fluorine doping on the cladding region of the core rod. Further, D1 is the diameter of the cladding region of the core rod without fluorine doping. The core region has index of refraction ?1. The index of refraction of the core region is represented as core delta ?1 (as shown in FIG. 3). The core delta ?1 has the value in a range of about 0.35 to 0.37. The cladding region before fluorine doping has index of refraction ?2 (as shown in FIG. 3). Further, the cladding region has clad delta ?2. The clad delta ?2 has value 0. Further, the trench region (cladding region after fluorine doping) has index of refraction ?3 (as shown in FIG. 3). The trench region has the trench delta ?3. The trench delta ?3 has the value in a range of about - 0.27 to - 0.33. In general, the trench region is a downdopant region in the core rod. Downdopant is a type of dopant which has the tendency to decrease the refractive index of glass with respect to pure. The cladding to core diameter ratio (D/d) of the core rod measured before fluorine doping is in the range of about 3.1 to 4.2. The cladding to core diameter ratio (D1/d) of the core rod is in the range of about 2 to 2.8 after fluorine doping. The core rod has the core region with an alpha parameter. The alpha parameter of the core region of the core rod is in a range of about 4 to 8. Also, the trench alpha in a range of about 3-6. In general, the refractive index or index of refraction of a material is a dimensionless number that describes how light propagates through that medium. In general, the alpha parameter is a non-dimensional parameter that is indicative of the shape of the refractive index profile.

The refractive index profile of the core rod is given by

Here n (r) is the refractive index at radial parameter ‘r’ and delta-i (?i) is the percentage of normalized index difference defined as:

.

is in the range of about 3 to 6.