KR20010081941A - Method of making an optical fiber preform - Google Patents

Abstract

The glass suit 130 is deposited on the glass rod by the burner 140. The body is tensioned 126. Further deposition and pulling is performed. The final body is drawn out of fibers.

Description

Manufacturing Method of Fiber Optic Preforms

The known art discloses several methods for the fabrication of silica glass starter tubes and the fabrication of optical fiber preforms. The starter tube may be formed by heating the silica and extruding the silica through the opening. Starter tubes and optical fiber preforms are formed by depositing doped or undoped silica onto a target using one of several techniques, such as quartz chemical vapor deposition (MVCD), axial vapor deposition (VAD), and external vapor deposition (OVD). Can be made. Each of the methods is initiated by providing a rotating target, which is shaped in the form of a tube or steel bar and formed of glass, ceramic or other material. In some cases, the rod or tube is integral with the preform, but in other cases the rod is removed. A heat source, such as a gas burner or plasma source, is configured below, above or sideways across the rotating target. The heat source provides the energy required for the glass forming reaction to form glass particles. According to the method, the deposited glass particles are subjected to a drying and sintering step such as a next step, a VAD or OVD step. If in the MCVD step, the particles are melted into vitreous quartz by the same heat source.

When the target is mounted horizontally, the heat source moves along the length of the target so that a constant deposition is made up. If the target is a tube, the glass forming particles and material may be deposited on the inner or outer side of the tube, and the outer diameter remains constant when deposited on the inner side, but the outer diameter is deposited on the outer side. Will increase.

When the target is mounted vertically, the target rotates around the vertical axis, the burners are configured vertically above or laterally and the target is increased in the radial and axial directions. This constitutes a cylindrical output, and the diameter and length of the output increase as deposition continues.

Keck et al. US Pat. No. 3,737,292 describes a method of forming an optical fiber. The multilayer with the predetermined refractive index is formed by flame hydrolysis and is deposited on the outer wall of the starting rod or starting member. After the glass layer is deposited on the rods, the hollow cylinder is heated and configured to form the fibers.

USP 4,224,046 to Izawa et al. Describes a method for fabricating optical fiber preforms. The two vapor phase glass forming materials, oxygen, hydrogen and argon, are ejected upwards from the burner towards the vertically mounted rotating cylindrical starting member. Soot-shaped glass particles are formed by flame hydrolysis and are deposited on the lower end of the starting member. In order to maintain a constant gap between the growth end of the starting member and the burner, the starting member is gradually retracted upwards. At the end of the deposition, the soot glass preform is dried and sintered to form a clear glass preform.

US Pat. No. 4,217,027 to MacChesney et al. Describes the fabrication of preforms, termed quartz chemical vapor deposition (MCVD). In this method, steam consisting of chlorides or hydrides of silicon and germanium with oxygen is transferred into the glass tube. Chemical reactions between the chemicals form glass on the inner wall of the tube under suitable conditions, and the chemical reaction is induced by crossing the hot zone. Particles deposited in the tube melt in each path of the thermal zone.

Partus US Pat. No. 4,412,853 describes an MCVD method for forming an optical fiber preform starter tube. The method is disclosed with a horizontally mounted tubular rotating target, the target being formed of glass and having preselected composition and optical properties. Steam is supplied through the tubular target as a heat source configured beneath the tubular target and traveled along the length of the tubular target. This allows the reactants of the vapor to deposit and melt on the inner side of the tubular target. The deposited material has the same refractive index as the tubular target, but the composition is different. This means that the same effect can be achieved by using an external vapor oxidation method or an external vapor axis deposition method, and it is not described in any way.

USP 4,741,747 to Geittner et al. Describes Plasma Chemical Vapor Deposition (PCVD) for optical fiber fabrication. In the above PCVD method, the glass layer is deposited on the inner wall of the glass tube before the reactive gas mixture is passed at a pressure between 1 and 30 hPa and the plasma is moved back and forth inside the glass tube. After the glass layer is deposited, the glass tube shrinks to form a solid preform. The optical fiber can be extruded from the preform.

US Pat. No. 5,522,007 to Drouart et al. Describes the use of plasma deposition to form optical fiber preforms having high concentrations of hydroxyl ions. In this document, before the plasma generating gas enters one end of the plasma torch having an induction coil, hydroxyl ions are entrained in the plasma generating gas by allowing the gas to pass through the water tank. The plasma torch releases fused silica particles mixed with hydroxyl ions to the rotating substrate preform. This allows preforms to be formed with an average hydroxyl ion concentration of 50 to 100 ppm deposited on the target preform. According to Drouart et al., The technique allows optical fibers having attenuations of 0.32 dB / km and 0.915 dB / km, respectively, at 1310 nm and 1550 nm.

In addition to the large number of processing steps required for preform fabrication, another disadvantage of the method is that

1. MCVD and PCVD methods are slow in processing due to the low deposition rate of the above methods,

2. Preform size is limited due to the size of the deposition tube for MCVD and PCVD methods,

3. The OVD and VAD methods are based on flame hydrolysis, where excess water is generated and additional steps of drying and sintering are required to form high quality fiber optic preforms.

The present invention relates to a method for fabricating optical fiber preforms of single mode and multi mode designs using plasma external deposition methods.

1 is a diagram of an apparatus for plasma attachment.

FIG. 2 is a partial side view of a plasmatron used in the apparatus of FIG. 1; FIG.

3 is a plan view of a plasmatron similar to the plasmatron of FIG.

4 is a view illustrating a plasma flow form in the plasmatron of FIG. 3.

5 is a view of an optical fiber preform manufactured according to the method of the present invention.

* Sign Description

22 ... chamber 24 ... lathe

25 ... headstock 26,126 ... tailstock

30 ... target 32 ... carriage

34 ... tubular member 40,140 .. plasma source

56 ... support stand 58 ... stabilizer bar

60 ... inlet 64 ... inlet

66 ... outlet 70 ... plasma jet

130 ... workpiece 132 ... second bar

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing the optical fiber preform which is manufactured at low cost and has a low hydroxyl content by reducing the steps involved in the fabrication of the optical fiber preform, and provides a method for increasing the size of the preform and increasing the deposition rate. It is. These and other objects are achieved by the present invention for the formation of optical fiber preforms.

In one embodiment of the present invention, a plasma source is constructed proximate to the starting rod formed of the primary material. The starting rod is kept horizontal at both ends and is configured to rotate about the longitudinal axis of the starting rod. The plasma source is used to deposit the doped silica at a known first doping concentration. Doped silica is deposited along the length of the starting rod until the starting rod has grown to the desired diameter. The composite consisting of the starting rod and the doped silica is drawn and the thin region is extruded for use as a secondary rod. The secondary rod has a center formed of the primary material and an outer layer formed of doped silica. Additional silica with the same doping concentration is deposited, drawn and extruded on the secondary rod until the secondary rod reaches the desired diameter. The steps of deposition, drawing, extrusion and deposition can be repeated several times. The result is a doped silica rod having a center formed of a primary material of a first diameter, the silica rod having an annular layer formed of doped silica of a second outer diameter.

The doped silica rods will undergo another treatment. In particular, a plasma source is used to deposit the outer layer of doped silica on top of the doped silica rods, and the resulting structure is drawn and the thin area is extruded. The dopant used to form the outer layer may be selected to increase or decrease the refractive index of the silica.

If the dopant concentration changes as the outer layer is deposited, the outer layer is a graded layer. In this case, the dopant concentration is changed from the maximum, which is the initial concentration level when the outer layer is first deposited, to the minimum, which is the level when the deposition of the outer layer is complete.

If the dopant concentration does not change as the outer layer is deposited, the outer layer is a tiered layer. In this case, a second dopant concentration different from the first dopant concentration is used during the deposition of the outer layer.

According to another embodiment of the present invention, another treatment is performed on the composite consisting of the doped silica rods and the outer layer. The plasma source is used to deposit the coating layer on top of the outer layer. If the outer layer is graded, the coating layer may be formed of the same dopant and silica doped to the same minimum, complete concentration level. Optionally, the coating layer may be formed of pure silica or may be formed of silica doped with other dopant and third dopant concentrations. In addition, the coating layer may have a graded doping.

According to another embodiment of the present invention, a jacket is constructed in a composite consisting of doped silica rods, outer layer and coating layer. The jacket can be constructed by other plasma deposition, or by providing heat to the jacket construction material and shrinking the jacket construction material to the finished preform.

During plasma deposition, a dry plasma gas having a low concentration of hydroxyl is used for the formation of the plasma. A dopant source gas, such as a dry quartz source gas composed of SiCl ₄ , or a similar source gas having a low concentration of hydroxyl, GeCl ₄ co-doped with POCl ₃ or PCl ₅ , flows in close proximity to the plasma. This allows the material to be converted into silica (SiO ₂ ), or silica doped with germanium oxide (GeO ₂ ) or phosphorus pentoxide (P ₂ O ₅ ) O ₅ OOOO O, to be deposited on the target, in one simple step Allow to melt with glassy quartz.

Plasma external deposition apparatus 20 is shown in FIG. 1. The apparatus consists of a chamber 22 which is sealed to prevent the introduction of impurities into the final product. The shelf 24, which is available from Heathway Ltd. or Litton Engineering Lab, is located inside the chamber 22. The shelf 24 has a headstock 25 and a tailstock 26. A pair of spindle chucks 28 rotating in opposite directions to each other are provided on the spindle 25 and tailstock 26 and the ends of the elongate target 30 having a cylindrical outer wall are driven by the spindle chuck 28. It is fixed. The spindle chuck 28 rotates the target 30 according to the arrow A1. The carriage 32 is movably mounted to the shelf 24 so as to move in the direction along the target 30 or in the direction of the double arrow A2. The plasma source 40 is supported by the carriage 32. Accordingly, the carriage 32 moves the plasma source 40 along the length of the target 30. As a result, a material is attached on top of the target 30 to form the optical fiber spare part. The spindle chuck 28 rotates the target 30 such that the material is uniformly attached by the plasma source 40 around the target 30 to form a tubular member 34 having nearly complete outward facing walls. . In a preferred embodiment, the plasma source 40 located above the carriage 32 moves in both directions along a certain length of the target 30. As a result, the plasma source 40 moves along the portion of the target 30 and attaches the material.

Instead of moving the plasma source 40 along the length of the target, the target 30 is moved and the plasma source 40 remains stationary. To this end, the headstock 25 and tailstock 26 of the shelf reciprocate the target 30 such that all relevant parts of the target 30 move directly above the plasma source 40.

In another alternative embodiment, the plurality of plasma sources 40 are spaced apart along the length of the target 30. As a result, depending on whether the headstock 25 and tailstock 26 and carriage 32 are configured to move, the movement of headstock 25 and tailstock 26 of shelf 24 is reduced or The movement of the carriage 32 to which the plasma source 40 is attached can be reduced. In extreme cases where a plurality of plasma sources 40 are provided along the length of the target 30, movement of the headstock 25 and tailstock 26 or carriage 32 of the shelf may not be necessary.

In a preferred embodiment, the plasma source 40 is a plasmatron torch and the plasmatron torch is introduced into the interior through the dry plasma gas and the second gasline 44 introduced into the interior through the first gas line 42. Has a supply gas.

The plasma gas is composed of nitrogen and oxygen in a suitable suitable ratio. Air can be used as the plasma gas. In this case, the filtered air first passes through the first dryer 46 to remove moisture before passing through the first gas line 42. As a result, the hydroxyl concentration of the plasma gas is as small as 2.0 ppm or less. The total volume of gas delivered is controlled by a mass flow controller (MFC) or optionally a flow meter.

The feed gas consists of a source agent such as SiCl 4 and at least one carrier gas such as oxygen O 2 or nitrogen N 2. The carrier gas is introduced into the second dryer 48 to remove moisture. As a result, the hydroxyl concentration of the source gas is very small, 0.5 ppm. After the carrier gas is dried After the source delivery gas is dried, it proceeds to a mass flow controller (MFC) 81 before entering the foam generator 50 to capture the source drugs. Depending on the characteristics of the mass flow controller, a mass flow controller can be used downstream of the foam generator. Next, the gas flow of the delivery gas combined with the source gas proceeds to the second gas line 44. Optionally opening valve 52 allows doping gas to be guided into the gas flow prior to reaching the plasmatron torch.

In a preferred embodiment, the source agent is SiCl ₄ . The drug is selected for reactivity in the plasma. In particular, the SiCl ₄ is used in particular as a source of Si to form SiO ₂ attached on the target 30. The dopant may be a fluorine doping gas in the form of SiF ₄ or SiF ₆ . Fluorine dopants can lower the refractive index and change the viscosity of the quartz. Fluorine dopants also increase design flexibility for optical fiber spares. As is known, GeO ₂ or other equivalent material may be used as the dopant to increase the refractive index.

In a preferred embodiment, the source agent for GeO ₂ is GeCl ₄ . Since the medicament has similar physical and chemical properties of SiCl ₄ , the purity is GeO ₂ . Transfer function of GeCl ₄ is similar to that of SiCl _4. The delivery gas traveling from the dryer 48 may be divided into another branch controlled by the mass flow controller 82 before moving to the foam generator 83 to capture the source drug GeCl ₄ . Similar to the control action of the drug SiCl ₄ , a mass flow controller can also be located downstream of the foam generator. The gas flow may be supplied to gas line 44 and form a mixture before entering the plasmatron torch. In addition, the gas flow of GeCl ₄ may be directly guided to the plasmatron torch by a separate line 84. Using separate transmission lines has the advantage of minimizing the competitive chemical reaction between GeCl ₄ and SiCl ₄ . Other source agents for doping instead of germanium oxide (GeO ₂ ) or for co-doing with germanium oxide are doping with similar exponential doping, such as POCl ₃ , PCl ₅ and drugs containing aluminum and titanium. It is the same material.

Referring to FIG. 2, a side cross-section of the plasmatron torch 40 located below the target 30 is shown. The plasma torch 40 is constructed by a tubular torch housing composed of quartz. The housing has a diameter of 60 mm and a height of 220 mm. However, diameters of 40 to 80 mm and heights of 180 to 400 mm can be used.

A bronze induction coil 52 is provided around the upper portion of the housing 50. The coil 52 is constituted by a plurality of windings 54 having a diameter of approximately 72 mm and spaced apart from each other by a distance of 6 mm. The distance between the housing and the coil is between 2 and 10 mm. As shown by the uppermost winding portion 54 ', the uppermost portion of the coil 52 is separated from the outer surface of the tubular member 34 by a separation distance L of 30 to 55 mm in size.

When the crystal glass is attached, its outer diameter is increased. However, the plasma torch 40 is separated from the outer surface of the tubular member 34 by the distance L by adjusting the height of the support stand 56 is arranged.

When the crystal glass is attached, its outer diameter is increased. However, the distance L is maintained by adjusting the height of the support stand 56 on which the plasma torch 40 is arranged. Next, the support stand 56 is mounted to the carriage 32, and is moved laterally with the carriage. Initially, the support stand 56 is set at a predetermined height, and when the diameter of the attachment material increases during the attachment operation, the height is decreased. As a result, a predetermined distance is maintained between the plasma torch 40 and the attachment material. In order to measure the distance of the tubular member 34 growing radially from the carriage and to adjust the height of the support stand 56, an optical or other sensor mounted on the carriage 32 and connected to the controller can be used. have.

Plasma stabilizer bars 58 are configured on all sides of the top of the housing 50. Each stabilizer rod is formed from a crystal and consists of a U-shaped gutter extending laterally from the rim of the housing 50. Although a diameter of 40 to 80 mm and a length of 15 to 40 mm may be used, the stabilizer bar 58 extends 20 mm on the radially opposite side of the housing rim and has a diameter of 60 mm. When the plasmatron torch 40 is used, the stabilizer bar 58 is partially aligned with the target. By this arrangement, the reaction source drugs attached to the growing tubular member 34 are diffused.

The second gas line 44 carrying the source drug is connected to the plasma torch 40 by the pair of injection parts 60. The injection portions 60 enter the housing at the same height along the housing 50 at a position between the top windings 54 ′ of the coil 52 and the stabilizer bar 58. Although a tube diameter of 3 to 10 mm is available with the plasma torch 40 of the present invention, the injection portions are constituted by a quartz tube having a diameter of 5 mm. In a preferred embodiment, a pair of injection portions 60 enter the housing 50 at the same height and are located radially across from each other. Instead of the two injection parts, three or more than four injection parts can be arranged in symmetry. In FIG. 2, two injection portions 60 are shown to be located just below the stabilizer rod. However, the above configuration is not essential, and referring to FIG. 3, the injection portions 60 are offset from the stabilizer bars 58 at an angle in the plan view of the plasma torch.

The first gas line 42 carrying the plasma gas is connected to the plasma torches 40 by the pair of plasma gas inlets 62. Plasma gas inlets 62 enter the housing at the same height close to the base of the housing. Although some range of diameters are sufficient for this purpose, the inlet 62 is constituted by a stainless steel tube having a 5 mm diameter.

Coolant inlet 64 and outlet 66 are also provided to plasmatron torch 40. In use, coolant, such as water, passes through inlet 64 and circulates within the outer wall of housing 50 and exits through outlet 66. The inlet and outlet of the coolant are formed from stainless steel and have a diameter of 5 mm. Like the plasma gas inlet and the inlet, the diameter is variable.

The plasma gas inlet 62, the coolant inlet 64, and the coolant outlet 66 are formed in the stainless steel chamber 68. The chamber 68 is a square block made of stainless steel on the side, which is 80 mm and has a height of about 40 mm. The chamber 68 is mounted on the support stand 56 and then on the carriage 32 to move along the target.

A high frequency generator (not shown) is electrically connected to the coil 52 to supply the coil with a variable power output up to 80 kW at a frequency of about 5.0 MHz. In a preferred embodiment, the generator is model No. T-80-3MC from Lepel Corporation. In order to supply energy to the plasma torch 40, the generator is operated with a power supply of 60 Hz, three-phase 460V. Alternatively a generator of model IG 60/5000 from Fritz Huttinger Electronic GmbH of Germany can be used.

Referring to FIG. 4, a plasma jet 70 formed inside the plasma torch 40 is shown when the dry plasma is supplied to the inlet 62 and converted into plasma. In fact, the plasma jet 70 is symmetrical around the longitudinal axis A 'of the torch. The positions of the injection parts 60 are formed such that the source medicine is introduced into the plasma immediately above the position V at which the vertical velocity of the plasma becomes zero. As a result, a structure is provided for the jet of the source drug to hydrodynamically and thermally flow into the boundary layer so as to effectively adhere to the growing tubular member 34. In a preferred embodiment this is also not necessary even if an injection section is introduced which flows laterally towards the inside of the housing. Instead, the source gas is introduced into the central portion of the plasma jet 70 by a water-cooled probe extending along the longitudinal axis A 'of the plasmatron torch 40.

Referring to FIG. 5, a known process that can be performed by a lathe 124, such as a precision modification of the model PFH842XXLS manufactured by Heathway and glassworking lathes, is shown. Headstock 125 and tailstock 126 of shelf 124 are movable longitudinally relative to each other. As a result, the final workpiece 130 of length L3 attached to the upper portion of the initial target can be yawably loaded and detached. More importantly, it is possible to pull a part of the workpiece into the second bar of reduced diameter equivalent to that of the original workpiece. Maintain the headstock 125 in the fixed state for the operation and the tailstock 126 is moved away from the headstock 125, the plasma supply source 140 is moved in the direction opposite to the direction of the headstock 126 . Optionally, a plasma source 140 or other heat source is arranged at the end of the workpiece 130 to soften the workpiece for the operation. Next, the main shaft 125 and the tailstock 126 are moved in the same direction but moved to the positions 125 'and 126' of the dotted line by different speeds by the distances L5 and L4. The result is a thin second rod 132, which may (but not necessarily) have the same diameter as the initial target, and is constructed. As is known to those skilled in the art, the second rod has the same cross-sectional component as the workpiece on which the second rod is operated, has a center, the density of the center is similar to the density of the original target, and the top of the target while the workpiece is being formed. It has an outer layer similar to the material attached to it.

The headstock 125 and tailstock 126 are movable by the shelf 124 to be sufficient to extend the second rod in the longitudinal direction to a distance L4 equal to the distance L3 of the workpiece to which the shelf is moved. . The second rod 132 can be cut from the workpiece mounted on the shelf 124 instead of the workpiece 130 and can be used as a target for continuous attachment with the plasma source 140. Thus, the first first generating target is used to form the first generating workpiece, and a second rod can be drawn from the workpiece as the second generating target. Therefore, the attachment action made on the upper part of the second generating target forms the second generating workpiece or the like. Plasma attach process on the target to form a workpiece, stretching one end of the workpiece to form a reduced diameter rod, and using the reduced diameter rod as a continuous target for another attachment operation The process can be repeated any number of times.

If the material attached on the target is invariant through the repetitive operation, the result of the Nro repeating steps is an Nth generating rod with a very small center, the center having the same components as the original target, and attached to the target. A circular layer refracting materials. For example, the first target has a diameter (D1), the first workpiece if it has a diameter D2 = D1 × M, the ratio of first target material within the first generation workpiece is 1 / M ^2. If a second target of diameter D1 is drawn from the workpiece and sufficient material is attached thereon to form a second workpiece of diameter D2, then the proportion of the first target material in the second workpiece is 1 / M ⁴ Therefore, if M is controlled during the attachment operation in accordance with the total number of repetitions, a workpiece having a predetermined ratio of the first target material is formed.

The method for forming a multimode optical fiber preform is described by the above repetition technique. Some dimensions are provided for more detailed description. However, many different values may be used in the actual process.

According to the method, the operation of providing a first target to be horizontally mounted on the shelf as shown in FIG. 5 is disclosed. The target is preferably formed from pure silica, which is commercially available from Heraeus Amersil of Georgia. F300 can be used. Optionally, silica that is formed by the latest process, generated n times and doped may be the first generation target. In a preferred embodiment, the first target has a length of 1 meter and a diameter D1 = 6 mm.

The silica doped with GeO ₂ is deposited on top of the first target of the description above. The dopant concentration for GeO ₂ depends on the required numerical aperture (NA) of the multimode optical fiber being formed. For example, the dopant concentration of the maximum GeO ₂ is about 10% to form a fiber with an NA of 0.2. The maximum GeO ₂ dopant concentration is about 18% to form a fiber having an NA of 0.275.

The dopant concentration is fixed at the same level during the attachment process, in which case a staircase is formed. Optionally, the dopant concentration can be changed gradually to form a separate layer. The process is controlled automatically by the introduction of a microprocessor dopant and by an adjustable rheometer. The stepped structure and the separated layers continue in successive workpiece generation operations, and the layers with different constant doping concentrations continue with each other. Thus, a separate layer may be attached on the first generating target, and a stepped layer may be attached on the second generating target formed after being stretched under the first generating workpiece. Similarly, a stepped layer is attachable on a separate layer and the layer is attached on the first first target. Also, a first staircase layer having a second doping concentration may be attached on top of the target, and a second staircase layer having a second doping concentration is attached on the next generation target. Other layers that are separated or have a stepped structure can be attached to all the tops of the structure.

In a preferred embodiment, silica is doped with 18% GeO ₂ with a first generation of 6 mm diameter until a workpiece with a length of 1 meter and a diameter D2 of 48 mm is formed (ie M = 8). It is attached as a staircase layer on the target. As a result, the first generation target has a cross-sectional area of about 64 times that of the first first generation target. The first generating workpiece is then drawn into 64 silica rods having a first generating doping structure, each rod having a length of 1 meter and a diameter of 6 mm. Each of the silica rods having a doping structure is used as a second generation target.

A second development target is arranged inside the shelf and a second attachment layer is attached to form a second production workpiece having a diameter of 48 mm. The four second deposition process is performed at the same constant dopant concentration as the first deposition process. Maintaining the dopant concentration at the same level throughout the deposition process consists of a circular layer having the same composition as the center and the whole formed from the original target material, thereby forming a doped first generated silica rod. As a result, the optical properties of the first layer and the second optical layer of the first layer attached on the initial target are the same. The second generating workpiece is then drawn into the 144 silica bars of the second generating doping structure, each of which has a length of 1 meter and a diameter of 4 mm. Each of the rods can be used as the third generation target. The iteration process can continue with the deposition of another layer with the same dopant concentration. However, in some locations a workpiece with the required target material of the required ratio is formed, and then another iteration process is unnecessary. In fact, after the first generating workpiece is formed, the process can be reached.

In a preferred embodiment, an attachment layer of partition structure having an outer diameter of about 80 mm is attached on top of the third generation target having a diameter of 4 mm. The dopant concentration starts at the maximum of 18% GeO ₂ closest to the outer surface of the third generation target and gradually decreases to the minimum of about 0.1% GeO _{2 at} the outside of about 80 mm in diameter. The result is a third generating workpiece having a center formed from the original target and the same photo-tracking properties and two layers which cannot be clearly distinguished from each other, and a third layer of the division structure.

In a preferred embodiment, a third generating workpiece with a diameter of 80 mm undergoes another process to form the first optical fiber preform. Specifically, a cladding or barrier layer is attached on top of the third generating workpiece. The thickness of the cladding layer depends on the form of the final optical fiber preparation being manufactured. For 62.5 / 125 fiber preforms, the first preform that has been machined can have a final diameter of about 93 mm. For 50/125 fiber spares, the finished first preform has a final diameter of about 96 mm. The cladding layer is formed by doped silica at the minimum level of dopant concentration to form the third layer, that is, at a GeO ₂ concentration equal to 10% GeO ₂ . The structure with the first target material is then formed at the center, and a pair of uniformly doped second layers have the same optical properties, the separator structure layer has a dopant concentration that varies from maximum to minimum, and the cladding layer has a minimum value. Composed of doped silica.

Once the cladding layer is attached, the final preform has to be drawn to form the final preforms. Eight preform pieces of 1 meter length can be obtained from a single 62.5 / 125 preform with a diameter of 93 mm and a length of 1 meter, each of 12 preliminaries with a length of 1 meter from a 50/125 preform. Pieces of molded articles can be obtained, each with an outer diameter of 27 mm.

A jacketing layer may be attached on the cladding layer of the preform piece. The jacket layer preferably has the same refractive index as pure silica. The jacket layer may be attached by plasma external deposition using pure silica. Optionally a tube or sheet of pure silica of suitable diameter or width can be provided around the preform piece, and heat is applied to melt the jacket layer into the preform piece to form the final fiber prep.

In a preferred embodiment, the final optical preform has an outer diameter of about 56 mm. The final preform can then be drawn up to about 200 km as a fiber having a diameter of 125 μm.

Although the cladding layer, then the jacket layer, is attached for best performance, once stretched, a jacketing tube can be attached directly to the third generating workpiece without the cladding step.

A similar method for producing a single mode optical fiber preform can be achieved by the following procedure. The starting target may be an F300 rod purchased from Heraeus or a pure silica rod, which is an N-times generated rod of pure silica manufactured by the company. Fluorine-doped silica layers with a certain concentration are deposited on the target until the required diameter is reached. Single mode optical fibers can be drawn from the preform. There are a number of different glass index modifiers such as F, GeO _2, P ₂ O ₅ , TiO ₂ , Al ₂ O _3, etc., and according to a suitable combination, doped cores and / or doped claddings are prepared. The elements can be used to make. In a preferred embodiment, there is an N-times GeO ₂ doped rod with pure silica or a silica cladding layer deposited and doped thereon. When the required diameter is reached, the preform is completed.

Although the present invention has been described with reference to specific preferred embodiments, the above embodiments do not limit the present invention. By those skilled in the art, variations of the above embodiments are possible within the scope of the invention as set forth in the claims below.

Claims (20)

In the optical fiber preform manufacturing method, the method (a) constructing a target rod formed of a first material, (b) depositing a first silica layer doped with a first dopant having a first concentration on the target rod, the first silica layer being deposited to a predetermined first thickness, (c) drawing the target rod with the deposited first silica layer to a predetermined first diameter to form a doped silica rod, (d) (d1) a predetermined number of times or (d2) repeating steps (b) and (c) until the first material consists of a predetermined proportion of the doped silica rods, (e) depositing a second layer consisting of silica doped with a second dopant having a second concentration on the doped silica rod, the second silica layer being deposited to a predetermined second thickness to form an intermediate structure, (f) depositing a third layer over the intermediate structure, wherein the third layer is deposited to a predetermined third thickness to form a preform structure. The method of claim 1, (g) forming a jacket construction layer on the preform structure, wherein the jacket construction layer is comprised of pure silica and is formed to a predetermined fourth thickness. 3. The method of claim 2, comprising drawing the preform structure to a predetermined third diameter after step (f) and before step (g). The method of claim 1 wherein the first material is one of a group consisting of silica and silica doped with a dopant. 5. The method of claim 4 wherein the dopant is an index crystal material and is one of a group consisting of F, GeO ₂ , P ₂ O ₅ , TiO ₂ and Al ₂ O ₃ . The method of claim 1, In step (e) said second concentration is different from said first concentration, and said method comprises Maintaining the second concentration at a constant value as the second silica layer is deposited, thereby forming a step indicator profile at the index of refraction of the doped silica rod and the second silica layer. The method of claim 1, wherein the second concentration is varied as the second silica layer is deposited. 8. The method of claim 7, wherein the second dopant is fluorine and wherein the second concentration is varied from a minimum when the second silica layer is first deposited to a maximum when the deposition of the second silica layer is complete. How to feature. 8. The method of claim 7, wherein the second concentration is varied from a maximum when the second silica layer is first deposited to a minimum when the deposition of the second silica layer is complete. 10. The method of claim 9, wherein said maximum value of said second concentration is equal to said first concentration. 10. The method of claim 9, wherein the third layer deposited in step (f) is a coating layer deposited by plasma external deposition, wherein the coating layer consists of silica doped with the second dopant at the minimum value. 10. The method of claim 9, wherein the third layer deposited in step (f) is a coating layer deposited by plasma external vapor deposition, the coating layer consisting of silica doped with fluorine. The method of claim 1, wherein the third layer deposited in step (f) is a coating layer deposited by plasma external vapor deposition, the coating layer consisting of fluorine doped silica. The method of claim 9, (g) forming a jacket construction layer over the preform structure, wherein the jacket construction layer consists of pure silica and is formed to a predetermined fourth thickness. 15. The method of claim 14, comprising drawing the preform structure to a predetermined third diameter after step (f) and before step (g). The method of claim 1, wherein at least one of the deposition steps (b), (e), and (f) is performed by plasma external deposition, wherein the plasma external deposition is: A high frequency plasma tron composed of coils is formed, and the coil and the target are separated at an interval of 30 to 55 mm so that the plasma tron is selectively configurable along the length of the target, In order to form a plasma, a plasma gas having a hydroxyl content of 2 ppm or less is introduced into the plasma tron, Injecting a source gas consisting of at least SiCl ₄ and a dopant into a region in communication with the plasma, the source gas having a hydroxyl content of 0.5 ppm or less, Maintaining the gap between the target and the coil and depositing one or more reactants of the plasma and the source gas on the target. 17. The method of claim 16, wherein the source gas is introduced just above the point at which the vertical velocity of the plasma becomes zero in the plasmatron. 17. The method of claim 16, wherein the coil is comprised of a plurality of windings, the target being separated from the winding configured closest to the target by the spacing. 18. The method of claim 17, comprising drying the plasma gas before the plasma gas enters the plasmatron. The method of claim 1 wherein the first and second dopants and the first and second concentrations are the same.