Hot substrate deposition of fused silica

Fused silica injected or created by pyrolysis of SiCl4 are introduced in a powder state into a vacuum chamber. Pluralities of jet streams of fused silica are directed towards a plurality of heated substrates. The particles attach on the substrates and form shaped bodies of fused silica called preforms. For uniformity the substrates are rotated. Dopant is be added in order to alter the index of refraction of the fused silica. Prepared soot preforms are vitrified in situ. Particles are heated, surface softened and agglomerated in mass and are collected in a heated crucible and are softened and flowed through a heated lower throat. The material is processed into quartz plates and rods for wafer processing and optical windows.

SUMMARY OF THE INVENTION

Soot deposition on a plurality of substrates for fiber optic or any other high technology applications that require very high quality water-free synthetic fused silica such as optical wave guides, lenses and prisms for the deep ultraviolet spectrum are described here. Hot Substrate Deposition (HSD) of silica for fiber optic and other applications, processes and apparatus for superior quality synthetic fused silica fiber optic preforms that can be used in the MCVD (modified chemical deposition method) and OVD (outside vapor-phase deposition), VAD (vapor-phase axial deposition) applications are also part of this invention. The process allows for deposition of fused silica preforms of doped, undoped or modulation doped, and preforms in any radial profile of the index of refraction are also part of this invention. Controlled density of the deposited material as well as the provision for a plurality of substrates leads to increased productivity and higher yield production compared to the current processes for synthetic fused silica described in numerous patents. Water-free ultrapure synthetic fused silica having desired grain size is also part of this invention. Processes and apparatus for further processing of such synthetic fused silica into rods, tubes and plates for various applications are also part of this invention.

Fused silica and possibly various dopants are either created by pyrolysis of SiCl4or other compounds or they are introduced in a powder state into a vacuum chamber that might be at vacuum or desired pressure for the particular processes. Pluralities of jet streams of fused silica are directed towards a plurality of substrates heated to certain temperatures. The particles attach themselves on the substrates and form shaped bodies of fused silica called □preforms□. For uniformity purposes the substrates may be rotated clockwise (CW) or counterclockwise (CCW) and may be linearly moved with respect to the sources of fused silica streams. Fused silica streams from a fused silica powder or quartz powder may move with respect to the preform being fabricated. In one embodiment, the sources and preforms may both move linearly with respect to each other as well as relate with respect to each other. Depending on the substrate temperature of the silica preforms, the preforms may have different densities and states of compaction. Very thick layers are deposited in this way without cracking or peeling from the substrates. Dopant may be added in order to alter the index of refraction of the fused silica. If continuously added, the whole preforms may be doped. If added during certain time periods, one may create desired profiles of the index of refraction. The dopant may be added as part of the silica jet stream, through the surrounding deposition atmosphere or through the porous substrate. The dopant may be in solid, liquid or gaseous form.

Such prepared soot preforms are later vitrified in situ, or they are treated separately. Quartz material, doped, undoped, or preferentially doped to achieve a certain index of refraction profile is obtained. This material is further processed into quartz tubes for fiber optics and other applications, quartz rods for fused silica wafers for semiconductors and various optical applications and quartz plates for wafer processing and optical windows.

Processes and apparatus for making of metal oxides by oxidation of metal halides, formation of fiber optic preforms, doped and undoped, and making of high quality fused silica glass are described herein. Metal oxide, silicon dioxide in particular, is deposited on controlled temperature substrates made from graphite, silicon carbide, ceramic, quartz, metal and metal alloys. The substrates are tubular or rod-like in shape, having round, rectangular or polygonal cross-sections. The substrates and the deposited material are heated by means of resistive heating, RF heating or by any other means, and by any combination among them. The material is dried, doped (if needed), and densified. The material is later converted into high quality fused silica tubes, rods or quartz plates of desired sizes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides a controlled substrate temperature fused silica process and apparatus.

Process and apparatus for fused silica soot of desired size (doped and undoped), fiber optic preforms that are undoped, doped with the desired refractive index profile, or fully doped, fused silica tubes, fused silica fibers and rods and fused silica plates and fused silica members having desired shapes are described herein.

FIGS. 1,2and3show a plurality of substrates11at controlled temperature housed in a vacuum chamber1. A plurality of silica stream generators3are shown. The silica powder stream generators3represent burners for oxidation of chemical compounds into fused silica powder or silica powder injection units. Powder is made in separate chambers, or natural quartz powder may be injected in the chamber for preform deposition. Generators3, which may be burners for oxidation5of chemical compounds7such as SiCl4, SiF4 and others into fused silica particles, are either embedded in the chamber wall8or they are placed inside the chamber. The proximity of the silica particle providers or stream generators3to the collectors or substrates11as well as the distance of the substrates from the center9of the chamber are optimized based on the number of the substrates11, the number of the silica stream generators3and their relative positions. The chamber1may have round, rectangular or any other suitable shape that is needed or is useful to optimize the process. Vacuum ports13with valves15, vents17with valves19and a plurality of gas inlet ports21with valves23and inert gas ports22with valves24are also added to the chamber. The chamber may be vertical, horizontal, sloped and any other position or combination suitable for the new process. The chamber walls8may have a cooling jacket25for temperature control and appropriate venting apparatus for the gasses generated during the deposition. Appropriate openings are provided at one end, at each end or on one or two sides of the chamber for loading and unloading of the chamber.

A plurality of power feeds for resistive heating29or RF coils31and appropriate power feedthroughs33and shields35are also included in the chamber.

The chamber may have plurality of particle provider ports37for introduction of soot39made during another operation or natural quartz powder.

The chamber and the substrate assembly may be rotated in respect to each other clockwise or counterclockwise and may be relatively axially moved at certain desired speeds, which are determined empirically. Each substrate may be rotated around its axis clockwise or counterclockwise at certain desired speeds. All rotations are aimed at establishing conditions for good thickness and uniformity properties of the deposited material in the porous perform41.

As shown inFIG. 3, substrates and preforms B1, B2and B3are spaced from a center by radius R1and from the chamber wall by a greater radius R2. The substrates and preforms41are relatively rotated42and moved44and46initially or as the preforms grow.

FIG. 4shows a tubular substrate11with deposited material43forming a preform41. Each substrate11may be made of solid, porous or perforated material made from silica, graphite, silicon carbide, ceramic, metal, metal alloys or combinations thereof. It may have round, rectangular or any other cross section. It may be tubular, solid or tubular with solid or tubular core made from the same or other material. The cross-sections of the substrates may be the same throughout the preforms or may vary in certain controlled manners to obtain silica members of desired shapes or sizes. The ends45may have the same cross section throughout, or the ends may have different dimensions or shapes. The ends45may be mechanically connected to the substrate11or they may be part of the substrate. A gas line47or vacuum line may be connected with the hollow portion of each substrate having tubular shape, with or without a central rod.

FIG. 4shows an apparatus consisting of a vacuum chamber51having a plurality pressure controls in the form of vacuum ports53, vent lines55, and gas ports57doping ports59for purging and doping purposes, plurality of power feedthroughs61with or without cooling lines63in them for resistive, RF65or any other form of heating the substrate11of the preform41and the preform itself. The chamber may have multiple heating zones67to accommodate the process being performed there. Rotation and translation assembly mechanisms60rotate62and translate64the substrate11and preform41. Slip rings66conduct power from source68to heat the substrate11.

InFIG. 4the dopant gases58surround the preform41, and purge or dopant gases56from purge or dopant line54flow outward from the porous substrate through the porous preform41.

InFIG. 5chamber51has three growing preforms41mounted on substrates11, which are mounted on independent rotation mechanisms or multiple rotators70, which rotate the preforms with respect to each other as the support ends45rotate62and translate64mechanisms70.

FIG. 6shows a preform41on a substrate11with the deposited soot43and an end attachment48. Heating element78connected to power source68heats the substrate11for controlled temperature deposition on the preform41.

As shown inFIG. 7, preforms41and substrates may have any specific shapes such as solid or tubular with round polygonal or square preforms and substrates with solid or hollow substrates, and they may employ solid, porous or tubular heating elements78.

FIG. 8shows several preferred end attachments48for substrates. The end attachments may be pinned, threaded or shrunk on the substrates, or they may be part of the substrate.

When the substrate is fused silica, the tube is ready to be used or ready to be softened and to be compacted and densified into a solid. When the substrate has desired core properties, the fused silica member may be transformed into fiber optic preform ready for fiber fabrication.

FIGS. 9A and 9Bshow a vitrified silica tube90on a heated substrate11and after removal from the substrate.

The substrate11may be heated, and the fused silica tube90may be slid off the substrate after a film is melted adjacent the substrate, after the end attachments48are removed.

The tubing90that is removed has a hole93and a tube wall95, as shown inFIG. 9A. It may be compressed into a solid doped or undoped fused silica rod.

InFIG. 10a vacuum chamber101is oriented vertically. A preform41is supported vertically on its substrate11which has generally hemispherical ends112. The preform41may be supported by the substrate rod itself, if the rod substrate cross-section is varied. A chamber seal and gas delivery assembly at the top102of the chamber has a rotation104and translation106mechanism103. A gas delivery system105with a valve107supplies purging or dopant gas to the hollow porous substrate. The preform is doped or undoped silica109having a controlled OH content. The chamber has a plurality of valved gas vents111, valved vacuum ports113, and valved dopant inlets115. Walls117of the chamber have appropriate heat shielding119and jacket cooling. Resistive or RF heating elements121provided in a plurality of heating zones123soften the silica, which flows125. The moving silica flows around end112of substrate11as purge gas127flows. The resultant fused silica member, in this case tube129, is rotated and pulled by mechanism130at the bottom131of the chamber101.

FIG. 11is similar toFIG. 10. A substrate power system133is added to heat the substrate11and to assist the heating elements121.

FIG. 12has a chamber101similar to the chambers shown inFIG. 10.

A movable shelf135may move inward and outward137and up and down139to control doping, heating and softening of the preform41, and to separate the chamber101into two chambers141and143. Lower chamber143has a separate set of valved ports144,145,147,149which precisely control the conditions in the lower chamber141. The shelf135divides the chamber101into separate heat zones151,153. In addition, heat outputs of heating elements121may be varied to create additional heat zones within zones151and153.

InFIG. 13a substrate power delivery system133is added to control precise heating on the substrate11. The heating elements121in the lower heat zone melt and flow125the soft silica from the lower preform. When silica is depleted from the lower preform, heat is increased on the substrate11to soften the inner layer of silica, and the upper part of the preform slides downward. A new preform can be added above shelf135, either via a door not shown here or through the chamber seal assembly.

FIG. 14shows the vacuum chamber165, which combines a vertically oriented chamber51such as shown inFIG. 4used for continuous production of glass material with a fused silica member-forming chamber101. After the necessary material preparation steps have been made appropriate pressure and atmosphere is introduced for the glass fabrication process, tubular or solid glass material having the desired cross sectional shape is made in the upper chamber167. The burners3or material feeders37feed material73as well as the glass preform41being made can rotate62. A retractable shelf holder169is placed under the growing refill preform41to prevent distractions in the tube formation process in lower chamber171. The preforms41might be used as produced or they may be dried, doped and densified before the fabrication of the fused silica fabrication process begins. Heat zones HZ1, HZ2, HZ3and HZ4control desired temperatures in chamber165.

FIG. 14shows process and apparatus for continuous fabrication of fused silica glass having either tubular, solid rod having the desired cross sections. The vacuum chamber165may constitute a plurality of interconnected chambers similar to chamber51and101. It also may be connected with a chamber for fused silica plate or bar production. Provisions for resistive, RF or any other heating of the substrate and the preform have been included. Multiple independently controlled heating zones HZ1-HZ4are used.

The upper chamber167serves for fabrication of the preform. The preform is later moved down to chamber171and used for continuous fabrication of fused silica glass in either tubular or solid rod form having the desired cross sections. Resistive or RF heating is used to decouple the preforms from the substrates, if needed.

FIG. 15shows a chamber165similar to that shown inFIG. 14. A plasma tube and/or fused silica member surface removal unit173is added either above or below the rotating and pulling mechanism130. A separate substrate heater175is added in the lower fabrication chamber.

FIG. 16is similar toFIG. 15. An electric field generator177with electrodes179and181is added to create an electric field across the silica flow125. Fused silica feed is softened and shaped therein. An ultrapure clear, bubble free tube, plate or bar is extracted from the chamber. Plasma process unit177removes unwanted impurities segregated on the surface layer by the electric field.

FIG. 17shows a chamber183for producing silica power185and other metal oxides from soot187having desired particle size. Fine oxide particles from generators such as in situ made from burners3or delivered through plurality of ports37on the chamber are heated in mass189and allowed to recombine. Depending on the time they stay hot and the distance the particles travel, they recombine into larger grains of desired size. Plasma plating using single or multiple stage plasma of the silica particles may be employed. The vacuum chamber183has multizone heating zones Z1-Z6. Resistive heating, RF heating, plasma or other heating methods of the grains may be employed.

The soot is collected in a crucible collector191with a heater193and a gas/dopant gas injector195, as shown inFIG. 17. It may be softened196in a heated throat198, funneled and flowed around a former197and filled/purged with gas199to form a tube21into chamber203.

Another chamber employing the new soot grain enlargement process for tube or rod fabrication is as shown inFIG. 18. In that embodiment, electric field generator177and electrodes179and181provide an electric field across the softened fused silica flow125. A plasma tube or fused silica member surface removal unit173is added in the embodiment.

FIG. 19shows a single or double crucible203in the chamber. A vacuum chamber183having plurality of vacuum ports, gas inlet ports, vent ports, and a fused silica feed material introduction port is heated by resistance or RF heating or any other means of heating, connected through plurality of feedthroughs. A second crucible203made from graphite, silicon carbide, ceramic material, metal, metal alloys or combinations thereof receives the material from the feed crucible191. A fused silica tube is produced. Pluralities of ultrasound generators are in contact with the crucible to provide proper mixing and outgassing. Additional vacuum ports are placed above the softened material to remove any gas bubbles. The chamber can be a single chamber or plurality of chambers.

FIG. 20shows apparatus for plate or any other fused silica member production.

FIGS. 21 and 22show forming a fused silica member210in a vacuum chamber211, which has two sections213and215. InFIG. 21, a softened fused silica tube217is fed into chamber section213. Heaters219around the chamber maintain required heat. In chamber section213a relatively high heat is maintained for flowing the softened fused silica into the desired form. A lower heat is maintained in chamber section215in which the fused silica form further solidifies.

FIG. 20shows a plate/bar fabrication chamber211. A vacuum chamber section213having plurality of valved vacuum ports221, gas inlet ports223, vent ports225and a fused silica feed material217introduction port227is heated by resistance of RF heating219or any other means of heating, connected through a plurality of feedthroughs. A crucible230made from graphite, silicon carbide, ceramic material, metal or metal alloys receives the material231from the feed tube217, softens, dopes, degassifies and solidifies the material. A fused silica plate or a bar210is produced. A plurality of ultrasound generators233are in contact with the crucible to provide proper mixing and outgassing. Additional vacuum ports235are placed above the softened material to remove any gas bubbles. The chamber can be a single chamber or plurality of chambers213,215with sequentially controlled heat zones. The shaped member210exits the chambers through pressure and heat seals237and239. Rollers240pull the shaped member out of the chambers.

FIG. 21shows a plate or bar forming chamber211similar to that sown inFIG. 20, in which the infeed is a solid rod241.

FIG. 22shows a fused silica plate, bar or otherwise shaped member210forming chamber211directly coupled to chamber183, such as shown inFIG. 19, for receiving the fused silica tube input directly from the output of chamber183.

The heating of the substrate may be accomplished by separate heaters positioned axially along or in the substrate. Alternatively if resistance heating is used, the heating wire may be varied in shape, form or size along the length of the substrate. The substrate may be linear or planar and may be made in one element or plural elements. A singe control or multiple independent controls may be used. The varied heating of the substrate may be used to effect uniformity of the preform in an axial direction. Alternatively the varied heating may be used to effect varied densities or porosities of the perform along it's length or per unit area.

EXAMPLES

Silica Glass Body Fabrication

Production of synthetic fused silica glass bodies having controlled density and desired size and shape have been of interest to the natural quartz or synthetic fused silica glass industry for some time. The densities of the formed silica body mainly depend on the temperature of the flame, the distance between the substrate and the burner, and rotational and translational speeds of the substrate. Densities between 10% and 30% have been reported by this approach. The size of the body and the optimal ratio between the wall thickness (Wt) and the outside diameter (Do), Wt/Do, as well as the ratio between the outside diameter (Do) and the Inside diameter (Di), Do/Di, and the way the body is held during the deposition depend greatly on the density of the body surface temperature and the body density.

To overcome the current limitations and to produce large glass bodies made from synthetic fused silica, natural quartz or combination thereof, substrate heating and surface heating has been introduced. The amount of the surface heating will greatly depend on the substrate temperature, the chamber pressure, the size of the quartz particles and their temperature at impact of the surface and the size of the quartz member fabricated. Silica preforms, doped or undoped, having desired density and optimized diameter ratio can be fabricated following the examples shown below.

Silica Body Fabrication

A heated substrate having temperature of about 1000°-1400° C. is subjected to plurality of silica particle stream either generated in situ by high temperature reactions of silica precursors, or fabricated in a separate process and then introduced via ports on the chamber in pure form, doped form, mixed with neutral gas, gas plasma or combination thereof. The so accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited, and layer by layer the silica member is formed. The silica particle stream may be doped or undoped. The temperature of the substrate might be sufficient to keep the surface of the so formed body at the same temperature. The silica body so formed is hot enough to allow for formation of a solid fused silica body. Densities between 80% and 100% may be expected as a result.

The substrate may be tubular or solid form having the desired diameter and cross section. Desired ratios between the outside and inside diameters may be obtained using this method. If tubular, the substrate may be solid or porous, depending on the dopant or reactive gas flow desired. This achieves optimized silica material-to-gas contact. The hot substrate may also serve as a heater for the dopant gas and increased reaction time. Porous substrates can also diminish the possibility of gas bubbles entrapment near the surface of the substrate.

Substrate and surface temperatures between about 700° C. and 1600° C. may result in various silica densities from 10% to 100%. Controlling the fused silica body temperature by controlling the substrate and surface temperature may result in control of the pore size and pore density in the material. If the variation is in the radial direction, exposure to dopant gas over periods of time will result in radial gradient of the dopant distribution. By doing so silica members having radially graded indexes of refraction may be fabricated.

If the substrate is other than a silica core, doped or undoped made from fused silica or natural quartz; the resulting silica member may be in tubular form or may be in solid form after collapsing the tube.

Employing non uniform substrate heating along the length of the body, one may obtain a silica member having variable density over its length.

Doped and Undoped Layer Combination Silica Body Fabrication

Rotating and translating, a substrate consisting of porous tubing is heated to a temperature of about 1300° C. and is subjected to plurality of silica particle stream introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited, and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

Introducing silicon tetra fluoride, SiF4, through the porous substrate and/or the chamber into the deposited porous silica material for about 0.3 to 6 hours at temperature of about 800-1400° C., the silica material is doped.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate. A vitrified tubular silica body having desired wall thickness is formed.

The so formed vitrified tubular silica body is heated to temperature of about 1300° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate. The newly deposited porous silica is vitrified, and a tubular silica body having desired doped inner wall thickness IWtand undoped other wall OWtdesired wall thickness is formed. The duration of the silica deposition for certain substrate cross sections and sizes can be adjusted to allow for various ratios between the wall thicknesses of the doped and undoped portion of the tubular member, e.g., 1:2, 1:3, 1:5, etc.

Doped Non-Porous and Undoped Porous Layer Combination Silica Body Fabrication

Rotating and translating, a substrate consisting of porous tubing is heated to a temperature of about 1300° C. and is subjected to plurality of silica particle stream introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited, and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

Introducing silicon tetra fluoride, SiF4, through the porous substrate and/or the chamber into the deposited porous silica material for about 0.3-6 hours at temperature of about 800-1400° C., the silica material is doped.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate. A vitrified tubular silica body having desired wall thickness is formed.

The so formed vitrified tubular silica body is heated to temperature of about 1300° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process. The duration of the silica deposition for certain substrate cross sections and sizes can be adjusted to allow for various ratios between the wall thicknesses of the doped and undoped portion of the tubular member, e.g., 1:2, 1:3, 1:5, etc.

Undoped Core and Fluorine Doped Cladding Fiber Optic Preform Fabrication

Rotating and translating, a substrate consisting of porous tubing is heated to a temperature of about 1300° C. and is subjected to plurality of silica particle stream introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate and maintained there for certain time interval. A vitrified tubular silica body having desired wall thickness is formed.

The so formed vitrified tubular silica body is heated to temperature of about 1300° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

Introducing silicon tetra fluoride, SiF4, through the porous substrate and/or the chamber into the deposited porous silica material for about 0.3-6 hours at temperature of about 800-1400° C., the silica material is doped.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate. The newly deposited porous silica is vitrified, and a tubular silica body having desired doped inner wall thickness IWtand undoped outer wall OWtdesired wall thickness is formed.

The substrate is transferred out of the deposition chamber area, and the substrate is removed. If wetting between the substrate and silica occurs, the substrate is heated to the softening point of the silica. The contact between the substrate and the silica member is melted and the substrate is removed.

The so formed silica member is collapsed and a solid rod like silica member is formed. Undoped core (high index of refraction material) surrounded by fluorine doped cladding (low index of refraction material) having desired diameter and length is formed. The duration of the silica deposition for certain substrate cross sections and sizes can be adjusted to allow for various ratios between the core diameter and the outside cladding layer diameter of the fiber optic preform, e.g., 1:2, 1:3, 1:5, etc. The length of the chamber and the translation capabilities can provide basis for fabrication fiber optic preforms that are up 6 inches or more in diameter and several meters in length.

Doped Core and Fluorine Doped Cladding Fiber Optic Preform Fabrication

Rotating and translating, a substrate consisting of porous tubing is heated to a temperature of about 1300° C. and is subjected to plurality of silica and dopant particle stream introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate and maintained there for certain time interval. A vitrified tubular silica body having desired wall thickness is formed.

The so formed vitrified tubular silica body is heated to temperature of about 1300° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

Introducing silicon tetra fluoride, SiF4, through the porous substrate and/or the chamber into the deposited porous silica material for about 0.3-6 hours at temperature of about 800-1400° C., the silica material is doped.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate. The newly deposited porous silica is vitrified, and a tubular silica body having desired doped inner wall thickness IWtand undoped outer wall OWtdesired wall thickness is formed.

The substrate is transferred out of the deposition chamber area and the substrate is removed. If wetting between the substrate and silica occurs, the substrate is heated to the softening point of the silica. The contact between the substrate and the silica member is melted, and the substrate is removed.

The so formed silica member is collapsed and a solid rod like silica member is formed. Undoped core (high index of refraction material) surrounded by fluorine doped cladding (low index of refraction material) having desired diameter and length is formed. The duration of the silica deposition for certain substrate cross section and size can be adjusted to allow for various ratios between the core diameter and the outside cladding layer diameter of the fiber optic preform, e.g., 1:2, 1:3, 1:5, etc. The length of the chamber and the translation capabilities can provide basis for fabrication fiber optic preforms that are up 6 inches or more in diameter and several meters in length.

Doped Core and Fluorine Doped Graded Index of Refraction Cladding Fiber Optic Preform Fabrication

Rotating and translating, a substrate consisting of porous tubing is heated to a temperature of about 1300° C. and is subjected to plurality of silica and dopant particle stream introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate and maintained there for certain time interval. A vitrified tubular silica body having desired wall thickness is formed.

The so formed vitrified tubular silica body is heated to temperature of about 1300° C. and is subjected to plurality of silica particle stream introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

Introducing silicon tetra fluoride, SiF4, through the porous substrate and/or the chamber into the deposited porous silica material for T1hours at temperature of 800-1400° C., the silica material is doped. T□ is about 0.3 to 2 hours.

The substrate and/or chamber temperature is raised to about 1400-1500° C. while rotating the substrate. The newly deposited porous silica is vitrified, and a tubular silica body having desired doped inner wall thickness IWtand undoped outer wall OWtdesired wall thickness is formed.

The so formed vitrified tubular silica body is heated to temperature of about 1300° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

Introducing silicon tetra fluoride, SiF4, through the porous substrate and/or the chamber into the deposited porous silica material for T2>T1hours at a temperature of about 1100° C.-1400° C., the silica material is doped. T2is about 0.4-4 hours.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate. The newly deposited porous silica is vitrified, and a tubular silica body having desired doped inner wall thickness IWtand undoped outer wall OWtdesired wall thickness is formed.

The so formed vitrified tubular silica body is heated to temperature of about 1300° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

Introducing silicon tetra fluoride, SiF4, through the porous substrate and/or the chamber into the deposited porous silica material for T3>T2hours at temperature of about 1100° C.-1400° C., the silica material is doped. T3is about 0.5-5 hours.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate. The newly deposited porous silica is vitrified, and a tubular silica body having desired doped inner wall thickness IWtand undoped outer wall OWtdesired wall thickness is formed.

The so formed vitrified tubular silica body is heated to temperature of about 1300° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

Introducing silicon tetra fluoride, SiF4, through the porous substrate and/or the chamber into the deposited porous silica material for T4>T3hours at temperature of about 1100° C.-1400° C., the silica material is doped. T4is about 0.6 to 6 hours

The substrate and/or chamber temperature is raised to 1400-1600° C. while rotating the substrate. The newly deposited porous silica is vitrified and a tubular silica body having desired doped inner wall thickness IWtand undoped outer wall OWtdesired wall thickness is formed.

Repeat Steps 12-14 while further reducing the exposure to gaseous dopant, SiF4in this case.

The substrate is transferred out of the deposition chamber area and the substrate is removed. If wetting between the substrate and silica occurs, the substrate is heated to the softening point of the silica. The contact between the substrate and the silica member is melted and the substrate is removed.

The so formed silica member is collapsed and a solid rod like silica member is formed. Undoped core (high index of refraction material) surrounded by graded index of refraction fluorine doped cladding (low index of refraction material) having desired diameter and length is formed. The duration of the silica deposition for certain substrate cross section and size can be adjusted to allow for various ratios between the core diameter and the outside cladding layer diameter of the fiber optic preform, e.g., 1:2, 1:3, 1:5, etc. The length of the chamber and the translation capabilities can provide basis for fabrication fiber optic preforms that are up 6 inches or more in diameter and several meters in length.

Doped Core Having Graded Index of Refraction and Fluorine Doped Graded Index of Refraction Cladding Fiber Optic Preform Fabrication

Rotating and translating, a substrate consisting of porous tubing is heated to a temperature of about 1300° C. and is subjected to plurality of silica and dopant particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate and maintained there for certain time interval. A vitrified tubular silica body having desired wall thickness is formed.

Rotating and translating, a substrate consisting of porous tubing is heated to a temperature of about 1300° C. and is subjected to plurality of silica particle streams and reduced dopant particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate and maintained there for certain time interval. A vitrified tubular silica body having desired wall thickness is formed.

Rotating and translating, a substrate consisting of porous tubing is heated to a temperature of about 1300° C. and is subjected to plurality of silica particle streams and further reduced dopant particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. Porous silica body having about 25-35% solid glass density is obtained by this process.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate and maintained there for certain time interval. A vitrified tubular silica body having desired wall thickness is formed.

Repeat steps 4-6 further reducing the dopant levels in the deposited silica by lowering the dopant concentrations in the dopant particle streams, etc.

The so formed vitrified tubular silica body is heated to temperature of 1300° C. and is subjected to plurality of silica particle stream introduced via ports on the chamber. The so accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. Porous silica body having 25-35% solid glass density is obtained by this process.

Introducing silicon tetra fluoride, SiF4, through the porous substrate and/or the chamber into the deposited porous silica material for T1hours at temperature of about 1100° C.-1400° C. the silica material is doped. T1is about 0.3 to 2 hours.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate. The newly deposited porous silica is vitrified, and a tubular silica body having desired doped inner wall thickness IWtand undoped outer wall OWtdesired wall thickness is formed.

The so formed vitrified tubular silica body is heated to a temperature of about 1300° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. Porous silica body having about 25-35% solid glass density is obtained by this process

Introducing silicon tetra fluoride, SiF4, through the porous substrate and/or the chamber into the deposited porous silica material for T2>T1hours at temperature of about 1100° C.-1400° C. the silica material is doped. T2is about 0.4 to 4 hours.

The substrate and/or chamber temperature is raised to about 1400-1500° C. while rotating the substrate. The newly deposited porous silica is vitrified, and a tubular silica body having desired doped inner wall thickness IWtand undoped outer wall OWtdesired wall thickness is formed.

The so formed vitrified tubular silica body is heated to a temperature of about 1300° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

Introducing silicon tetra fluoride, SiF4, through the porous substrate and/or the chamber into the deposited porous silica material for T3>T2hours at temperature of about 1100° C.-1400° C. the silica material is doped. T3is about 0.6 to 6 hours.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate. The newly deposited porous silica is vitrified, and a tubular silica body having desired doped inner wall thickness IWtand undoped outer wall OWtdesired wall thickness is formed.

The so formed vitrified tubular silica body is heated to a temperature of about 1300° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having 25-35% solid glass density is obtained by this process.

Introducing silicon tetra fluoride, SiF4, through the porous substrate and/or the chamber into the deposited porous silica material for T4>T3hours at temperature of 1100° C.-1400° C., the silica material is doped. T4is about 0.6 to 6 hours

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate. The newly deposited porous silica is vitrified and a tubular silica body having desired doped inner wall thickness IWtand undoped outer wall OWtdesired wall thickness is formed.

Repeat Steps 12-14 while further reducing the exposure to gaseous dopant, SiF4 in this case.

The substrate is transferred out of the deposition chamber area and the substrate is removed. If wetting between the substrate and silica occurs, the substrate is heated to the softening point of the silica. The contact between the substrate and the silica member is melted and the substrate is removed.

The so formed silica member is collapsed and a solid rod like silica member is formed. Undoped core (high index of refraction material) surrounded by graded index of refraction fluorine doped cladding (low index of refraction material) having desired diameter and length is formed. The duration of the silica deposition for certain substrate cross sections and sizes can be adjusted to allow for various ratios between the core diameter and the outside cladding layer diameter of the fiber optic preform, e.g., 1:2, 1:3, 1:5, etc. The length of the chamber and the translation capabilities can provide basis for fabrication fiber optic preforms that are up 6 inches or more in diameter and several meters in length. The radial distribution of the index of refraction in the core and the cladding will depend on the thickness of the doped layer deposited and on the pore density in the as deposited preform.

Doped Core Having Graded Index of Refraction and Fluorine Doped Cladding Having Graded Index of Refraction Fiber Optic Preform Fabrication

Rotating and translating, a substrate consisting of porous tubing is heated to a temperature of about 1300° C. and is subjected to plurality of silica and dopant particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate and maintained there for certain time interval. A vitrified tubular silica body having desired wall thickness is formed.

Rotating and translating, a substrate consisting of porous tubing is heated to a temperature of about 1300° C. and is subjected to plurality of silica particle stream and reduced concentration dopant particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% fused silica density is obtained by this process.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate and maintained there for certain time interval. A vitrified tubular silica body having desired wall thickness is formed.

Rotating and translating, a substrate consisting of porous tubing is heated to a temperature of about 1300° C. and is subjected to plurality of silica particle streams and further reduced concentration dopant particle stream introduced via ports on the chamber. The so accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% fused silica density is obtained by this process.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate and maintained there for certain time interval. A vitrified tubular silica body having desired wall thickness is formed.

Repeat steps 4-6 further reducing the dopant levels in the deposited silica by further lowering the dopant concentrations in the dopant particle stream. Repeat until the desired index of refraction profile in radial direction is obtained.

The so formed vitrified tubular silica body is heated to a temperature of about 1380° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 80-90% fused silica density is obtained by this process.

The so formed silica body is heated to a temperature of about 1370° C. and is subjected to plurality of silica particle stream introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 75-85% solid glass density is obtained by this process.

The so formed vitrified tubular silica body is heated to temperature of 1360° C. and is subjected to plurality of silica particle stream introduced via ports on the chamber. The so accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 65-75% fused silica density is obtained by this process.

The so formed vitrified tubular silica body is heated to a temperature of about 1330° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 50-60% fused silica density is obtained by this process.

The so formed vitrified tubular silica body is heated to a temperature of about 1300° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% fused silica density is obtained by this process.

Introducing silicon tetra fluoride, SiF4, through the chamber into the deposited porous silica material for about 0.3-6 hours at temperature of 1100° C.-1400° C. the silica material is doped. The amount of the SiF4penetrating the cladding will be proportional to the pore density and the exposure time at given temperature of the preform.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate. The newly deposited porous silica is vitrified, and a tubular silica body having desired cladding layer wall thickness is formed. Repeat until the desired index of refraction profile in radial direction is obtained.

The substrate is transferred out of the deposition chamber area and the substrate is removed. If wetting between the substrate and silica occurs, the substrate is heated to the softening point of the silica. The contact between the substrate and the silica member is melted and the substrate is removed.

The so formed silica member is collapsed and a solid rod like silica member is formed. Undoped core (high index of refraction material) surrounded by graded index of refraction fluorine doped cladding (low index of refraction material) having desired diameter and length is formed. The duration of the silica deposition for certain substrate cross sections and sizes can be adjusted to allow for various ratios between the core diameter and the outside cladding layer diameter of the fiber optic preform, e.g., 1:2, 1:3, 1:5, etc. The length of the chamber and the translation capabilities can provide basis for fabrication fiber optic preforms that are up 6 inches or more in diameter and several meters in length. The radial distribution of the index of refraction in the core and the cladding will depend on the thickness of the doped layer deposited and on the pore density in the deposited preform.

Fluorine Doped Cladding Having Graded Index of Refraction Fiber Optic Preform Fabrication Using Prefabricated Doped or Undoped Core Rod

Prefabricated silica doped or undoped rod is heated to a temperature of about 1400° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The so accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 90-100% fused silica density is obtained by this process.

Prefabricated silica doped or undoped rod is heated to a temperature of about 1380° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 80-90% fused silica density is obtained by this process.

The so formed silica body is heated to a temperature of about 1370° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 75-85% solid glass density is obtained by this process.

The so formed vitrified tubular silica body is heated to a temperature of about 1360° C. and is subjected to plurality of silica particle stream introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 65-75% fused silica density is obtained by this process.

The so formed vitrified tubular silica body is heated to a temperature of about 1330° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 50-60% fused silica density is obtained by this process.

The so formed vitrified tubular silica body is heated to a temperature of about 1300° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% fused silica density is obtained by this process.

Introducing silicon tetra fluoride, SiF4, through the chamber into the deposited porous silica material for about 0.3-6 hours at temperature of about 1100°-1400° C. the silica material is doped. The amount of the SiF4penetrating the cladding will be proportional to the pore density and the exposure time at given temperature of the preform.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate. The newly deposited porous silica is vitrified, and a tubular silica body having desired cladding layer wall thickness is formed. Repeat until the desired index of refraction profile in radial direction is obtained.

The so formed silica member is vitrified and a solid rod like silica member is formed. Doped or undoped core (high index of refraction material) surrounded by graded index of refraction fluorine doped cladding (low index of refraction material) having desired diameter and length is formed. The duration of the silica deposition for certain substrate cross sections and sizes can be adjusted to allow for various ratios between the core diameter and the outside cladding layer diameter of the fiber optic preform, e.g., 1:2, 1:3, 1:5, etc. The length of the chamber and the translation capabilities can provide basis for fabrication fiber optic preforms that are up 6 inches or more in diameter and several meters in length. The radial distribution of the index of refraction in the core and the cladding will depend on the thickness of the doped layer deposited and on the pore density in the as deposited preform.

Process for Fabrication of Fluorine Doped Cladding Tube Having Graded Index of Refraction Fiber Optic Preform Fabrication

Rotating and translating, a substrate consisting of porous tubing is heated to a temperature of about 1400° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 90-100% fused silica density is obtained by this process.

Prefabricated silica doped or undoped rod is heated to a temperature of about 1380° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 80-90% fused silica density is obtained by this process.

The so formed silica body is heated to a temperature of about 1370° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The so accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 75-85% solid glass density is obtained by this process.

The so formed vitrified tubular silica body is heated to a temperature of about 1360° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 65-75% fused silica density is obtained by this process.

The so formed vitrified tubular silica body is heated to a temperature of about 1330° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 50-60% fused silica density is obtained by this process.

The so formed vitrified tubular silica body is heated to a temperature of about 1300° C. and is subjected to plurality of silica particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% fused silica density is obtained by this process.

Introducing silicon tetra fluoride, SiF4, through the porous substrate and the chamber into the deposited porous silica material for about 0.3-6 hours at temperature of about 1100° C.-1400° C., the silica material is doped. The amount of the SiF4penetrating the cladding will be proportional to the pore density and the exposure time at given temperature of the preform.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate. The porous silica is vitrified and a tubular silica body having desired cladding layer wall thickness is formed.

The substrate is transferred out of the deposition chamber area and the substrate is removed. If wetting between the substrate and silica occurs, the substrate is heated to the softening point of the silica. The contact between the substrate and the silica member is melted and the substrate is removed. The duration of the silica deposition for certain substrate cross sections and sizes can be adjusted to allow for various ratios between the inner diameter and the outside diameter of the tubing fiber optic preform, e.g., 1:2, 1:3, 1:5, etc. The length of the chamber and the translation capabilities can provide basis for fabrication doped tubing for fiber optic preforms that are up 12 inches or more in diameter and several meters in length. The radial distribution of the index of refraction in the cladding will depend on the thickness of the doped layer deposited and or the pore density in the as deposited preform.

Doped Core Having Graded Index of Refraction for Fiber Optic Preform Fabrication

Rotating and translating, a substrate consisting of porous tubing is heated to a temperature of about 1300° C. and is subjected to plurality of silica and dopant particle streams introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% solid glass density is obtained by this process.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate and maintained there for certain time interval. A vitrified tubular silica body having desired wall thickness is formed.

Rotating and translating, a substrate consisting of porous tubing is heated to a temperature of about 1300° C. and is subjected to plurality of silica particle streams and reduced concentration dopant particle stream introduced via ports on the chamber. The so accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% fused silica density is obtained by this process.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate and maintained there for certain time interval. A vitrified tubular silica body having desired wall thickness is formed.

Rotating and translating, a substrate consisting of porous tubing is heated to a temperature of about 1300° C. and is subjected to plurality of silica particle streams and further reduced concentration dopant particle stream introduced via ports on the chamber. The accelerated particles collide with the substrate and deposit themselves on the substrate. Subsequent particles deposit on the material already deposited and layer by layer the silica member is formed. A porous silica body having about 25-35% fused silica density is obtained by this process.

The substrate and/or chamber temperature is raised to about 1400-1600° C. while rotating the substrate and maintained there for certain time interval. A vitrified tubular silica body having desired wall thickness is formed.

Repeat steps 4-6 further reducing the dopant levels in the deposited silica by further lowering the dopant concentrations in the dopant particle stream. Repeat until the desired index of refraction profile in radial direction is obtained.

The substrate is transferred out of the deposition chamber area and the substrate is removed. If wetting between the substrate and silica occurs, the substrate is heated to the softening point of the silica. The contact between the substrate and the silica member is melted and the substrate is removed.

The so formed silica member is collapsed and a solid rod like silica member is formed. Graded index of refraction core having desired diameter and length is formed. The duration of the silica deposition for certain substrate cross sections and sizes can be adjusted to allow for various ratios between the inner diameter and the outside diameter of the tubing fiber optic preform, e.g., 1:2, 1:3, 1:5, etc. The length of the chamber and the translation capabilities can provide basis for fabrication doped cores for fiber optic preforms that are up 12 inches or more in diameter and several meters in length. The radial distribution of the index of refraction in the cladding will depend on the thickness of the doped layer deposited and on the pore density in the deposited preform.