Abstract:
Fused silica injected or created by pyrolysis of SiCl 4  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.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/258,494, filed Dec. 29, 2000. 

   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 SiCl 4  or 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. 
   These and further and other objects and features of the invention are apparent in the disclosure, which includes the above and ongoing written specification, with the claims and the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic perspective representation of a porous preform-general chamber, which may be horizontal, vertical or any other position. 
       FIG. 2  shows a cross-sectional view of the chamber shown in  FIG. 1 , in which one or a plurality of deposition rods made from carbon, SiC, ceramic, graphite, metal or metal alloys, or combinations thereof may be rotated to collect the glass soot. 
       FIG. 3  is a cross-section showing spacing and movements of three or more substrates and preforms. 
       FIG. 4  is a longitudinal cross-section of the chamber showing relative longitudinal movements and rotations. 
       FIG. 5  show multiple preforms with rotation and translation in the silica powder streams in the chamber. 
       FIG. 6  shows a heated substrate and fused silica preform. 
       FIG. 7  shows several different cross-sections of preforms and substrates with heating and gas delivery elements. 
       FIG. 8  shows several different substrate end attachments of  FIG. 7  in further powder streams and forming a cladding layer. 
       FIG. 9A  shows vitrified silica on a heated substrate. 
       FIG. 9B  shows a vitrified silica tube member. 
       FIG. 10  is a cross-sectional vertical view of forming a fused silica tubular or solid preform member, which is formed as pulled from a melted porous or vitrified preform in a tubular preform forming chamber. 
       FIG. 11  shows a tube-forming chamber with a substrate heater. 
       FIG. 12  shows a tubular preform-forming chamber, such as shown in  FIG. 10 , with a recharging station for adding a preform for continuous article production. As shown in  FIG. 12 , the deposition tube has a straight end. After the above deposition tube is aligned with the lower deposition tube and the two are rotated together, the upper deposition tube is heated by radio frequency heating of the graphite, carbon based or SiC based tube, or a graphite, carbon based or SiC based heater within the tube, to soften the inside of the cylindrical porous preform and allow the cylindrical porous preform to slide down along the aligned tubes, recharging the working preform position. 
       FIG. 13  shows a chamber similar to that shown in  FIG. 12  with a substrate resistance heater. 
       FIG. 14  shows a single unit in which the porous preform is generated around a vertical porous or non porous deposition substrate. Silica stream generators, which are burners or powder delivery units, are connected for vertical and radial movements to ensure the desired distance and flow from the growing porous preform. The cylindrical porous preform is transferred to the lower fused silica tubular preform-forming chamber by opening the retractable shield and heating the deposition substrate with radio frequency heating, so that the center of the porous preform can be softened to allow the preform to slide down the deposition tube when ready. In the fused silica preform forming section, rotation is maintained under controlled heating, and the fused silica tube is pulled from the porous preform. 
       FIG. 15  shows chambers similar to those shown in  FIG. 14  with a substrate power delivery system in the lower chamber. 
       FIG. 16  shows chambers similar to those shown in  FIG. 15  with an electric field generator for further purification of the soft silica. 
       FIG. 17  shows a chamber with multiple heating zones for creating and melting soot and drawing a rod or tube from the melted soot. 
       FIG. 18  shows a chamber similar to that shown in  FIG. 17  with an electric field generator for unwanted impurities removal and plasma tube surface removal of the same impurities and other surface elements. 
       FIG. 19  shows a chamber similar to that shown in  FIG. 19  with an electric field generator and a plasma tube surface removal unit with gas introduction or withdrawal within the formed tube and with a double crucible with gas introduced in the second crucible. 
       FIG. 20  shows formation of a plate or sheet from a fused and vitrified silica tube-like preform. 
       FIG. 21  shows formation of a plate or sheet from a fused and vitrified silica rod-like preform. 
       FIG. 22  shows a combined system of  FIG. 19  and  FIG. 20  for continuous production of high quality plate or shaped type silica members. 
   

   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 ,  2  and  3  show a plurality of substrates  11  at controlled temperature housed in a vacuum chamber  1 . A plurality of silica stream generators  3  are shown. The silica powder stream generators  3  represent 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. Generators  3 , which may be burners for oxidation  5  of chemical compounds  7  such as SiCl4, SiF4 and others into fused silica particles, are either embedded in the chamber wall  8  or they are placed inside the chamber. The proximity of the silica particle providers or stream generators  3  to the collectors or substrates  11  as well as the distance of the substrates from the center  9  of the chamber are optimized based on the number of the substrates  11 , the number of the silica stream generators  3  and their relative positions. The chamber  1  may have round, rectangular or any other suitable shape that is needed or is useful to optimize the process. Vacuum ports  13  with valves  15 , vents  17  with valves  19  and a plurality of gas inlet ports  21  with valves  23  and inert gas ports  22  with valves  24  are 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 walls  8  may have a cooling jacket  25  for 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 heating  29  or RF coils  31  and appropriate power feedthroughs  33  and shields  35  are also included in the chamber. 
   The chamber may have plurality of particle provider ports  37  for introduction of soot  39  made 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 perform  41 . 
   As shown in  FIG. 3 , substrates and preforms B 1 , B 2  and B 3  are spaced from a center by radius R 1  and from the chamber wall by a greater radius R 2 . The substrates and preforms  41  are relatively rotated  42  and moved  44  and  46  initially or as the preforms grow. 
     FIG. 4  shows a tubular substrate  11  with deposited material  43  forming a preform  41 . Each substrate  11  may 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 ends  45  may have the same cross section throughout, or the ends may have different dimensions or shapes. The ends  45  may be mechanically connected to the substrate  11  or they may be part of the substrate. A gas line  47  or vacuum line may be connected with the hollow portion of each substrate having tubular shape, with or without a central rod. 
     FIG. 4  shows an apparatus consisting of a vacuum chamber  51  having a plurality pressure controls in the form of vacuum ports  53 , vent lines  55 , and gas ports  57  doping ports  59  for purging and doping purposes, plurality of power feedthroughs  61  with or without cooling lines  63  in them for resistive, RF  65  or any other form of heating the substrate  11  of the preform  41  and the preform itself. The chamber may have multiple heating zones  67  to accommodate the process being performed there. Rotation and translation assembly mechanisms  60  rotate  62  and translate  64  the substrate  11  and preform  41 . Slip rings  66  conduct power from source  68  to heat the substrate  11 . 
   In  FIG. 4  the dopant gases  58  surround the preform  41 , and purge or dopant gases  56  from purge or dopant line  54  flow outward from the porous substrate through the porous preform  41 . 
   In  FIG. 5  chamber  51  has three growing preforms  41  mounted on substrates  11 , which are mounted on independent rotation mechanisms or multiple rotators  70 , which rotate the preforms with respect to each other as the support ends  45  rotate  62  and translate  64  mechanisms  70 . 
     FIG. 6  shows a preform  41  on a substrate  11  with the deposited soot  43  and an end attachment  48 . Heating element  78  connected to power source  68  heats the substrate  11  for controlled temperature deposition on the preform  41 . 
   As shown in  FIG. 7 , preforms  41  and 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 elements  78 . 
     FIG. 8  shows several preferred end attachments  48  for 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 9B  show a vitrified silica tube  90  on a heated substrate  11  and after removal from the substrate. 
   The substrate  11  may be heated, and the fused silica tube  90  may be slid off the substrate after a film is melted adjacent the substrate, after the end attachments  48  are removed. 
   The tubing  90  that is removed has a hole  93  and a tube wall  95 , as shown in  FIG. 9A . It may be compressed into a solid doped or undoped fused silica rod. 
   In  FIG. 10  a vacuum chamber  101  is oriented vertically. A preform  41  is supported vertically on its substrate  11  which has generally hemispherical ends  112 . The preform  41  may be supported by the substrate rod itself, if the rod substrate cross-section is varied. A chamber seal and gas delivery assembly at the top  102  of the chamber has a rotation  104  and translation  106  mechanism  103 . A gas delivery system  105  with a valve  107  supplies purging or dopant gas to the hollow porous substrate. The preform is doped or undoped silica  109  having a controlled OH content. The chamber has a plurality of valved gas vents  111 , valved vacuum ports  113 , and valved dopant inlets  115 . Walls  117  of the chamber have appropriate heat shielding  119  and jacket cooling. Resistive or RF heating elements  121  provided in a plurality of heating zones  123  soften the silica, which flows  125 . The moving silica flows around end  112  of substrate  11  as purge gas  127  flows. The resultant fused silica member, in this case tube  129 , is rotated and pulled by mechanism  130  at the bottom  131  of the chamber  101 . 
     FIG. 11  is similar to  FIG. 10 . A substrate power system  133  is added to heat the substrate  11  and to assist the heating elements  121 . 
     FIG. 12  has a chamber  101  similar to the chambers shown in  FIG. 10 . 
   A movable shelf  135  may move inward and outward  137  and up and down  139  to control doping, heating and softening of the preform  41 , and to separate the chamber  101  into two chambers  141  and  143 . Lower chamber  143  has a separate set of valved ports  144 ,  145 ,  147 ,  149  which precisely control the conditions in the lower chamber  141 . The shelf  135  divides the chamber  101  into separate heat zones  151 ,  153 . In addition, heat outputs of heating elements  121  may be varied to create additional heat zones within zones  151  and  153 . 
   In  FIG. 13  a substrate power delivery system  133  is added to control precise heating on the substrate  11 . The heating elements  121  in the lower heat zone melt and flow  125  the soft silica from the lower preform. When silica is depleted from the lower preform, heat is increased on the substrate  11  to soften the inner layer of silica, and the upper part of the preform slides downward. A new preform can be added above shelf  135 , either via a door not shown here or through the chamber seal assembly. 
     FIG. 14  shows the vacuum chamber  165 , which combines a vertically oriented chamber  51  such as shown in  FIG. 4  used for continuous production of glass material with a fused silica member-forming chamber  101 . 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 chamber  167 . The burners  3  or material feeders  37  feed material  73  as well as the glass preform  41  being made can rotate  62 . A retractable shelf holder  169  is placed under the growing refill preform  41  to prevent distractions in the tube formation process in lower chamber  171 . The preforms  41  might be used as produced or they may be dried, doped and densified before the fabrication of the fused silica fabrication process begins. Heat zones HZ 1 , HZ 2 , HZ 3  and HZ 4  control desired temperatures in chamber  165 . 
     FIG. 14  shows process and apparatus for continuous fabrication of fused silica glass having either tubular, solid rod having the desired cross sections. The vacuum chamber  165  may constitute a plurality of interconnected chambers similar to chamber  51  and  101 . 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 HZ 1 -HZ 4  are used. 
   The upper chamber  167  serves for fabrication of the preform. The preform is later moved down to chamber  171  and 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. 15  shows a chamber  165  similar to that shown in  FIG. 14 . A plasma tube and/or fused silica member surface removal unit  173  is added either above or below the rotating and pulling mechanism  130 . A separate substrate heater  175  is added in the lower fabrication chamber. 
     FIG. 16  is similar to  FIG. 15 . An electric field generator  177  with electrodes  179  and  181  is added to create an electric field across the silica flow  125 . Fused silica feed is softened and shaped therein. An ultrapure clear, bubble free tube, plate or bar is extracted from the chamber. Plasma process unit  177  removes unwanted impurities segregated on the surface layer by the electric field. 
     FIG. 17  shows a chamber  183  for producing silica power  185  and other metal oxides from soot  187  having desired particle size. Fine oxide particles from generators such as in situ made from burners  3  or delivered through plurality of ports  37  on the chamber are heated in mass  189  and 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 chamber  183  has multizone heating zones Z 1 -Z 6 . Resistive heating, RF heating, plasma or other heating methods of the grains may be employed. 
   The soot is collected in a crucible collector  191  with a heater  193  and a gas/dopant gas injector  195 , as shown in  FIG. 17 . It may be softened  196  in a heated throat  198 , funneled and flowed around a former  197  and filled/purged with gas  199  to form a tube  21  into chamber  203 . 
   Another chamber employing the new soot grain enlargement process for tube or rod fabrication is as shown in  FIG. 18 . In that embodiment, electric field generator  177  and electrodes  179  and  181  provide an electric field across the softened fused silica flow  125 . A plasma tube or fused silica member surface removal unit  173  is added in the embodiment. 
     FIG. 19  shows a single or double crucible  203  in the chamber. A vacuum chamber  183  having 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 crucible  203  made from graphite, silicon carbide, ceramic material, metal, metal alloys or combinations thereof receives the material from the feed crucible  191 . 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. 20  shows apparatus for plate or any other fused silica member production. 
     FIGS. 21 and 22  show forming a fused silica member  210  in a vacuum chamber  211 , which has two sections  213  and  215 . In  FIG. 21 , a softened fused silica tube  217  is fed into chamber section  213 . Heaters  219  around the chamber maintain required heat. In chamber section  213  a relatively high heat is maintained for flowing the softened fused silica into the desired form. A lower heat is maintained in chamber section  215  in which the fused silica form further solidifies. 
     FIG. 20  shows a plate/bar fabrication chamber  211 . A vacuum chamber section  213  having plurality of valved vacuum ports  221 , gas inlet ports  223 , vent ports  225  and a fused silica feed material  217  introduction port  227  is heated by resistance of RF heating  219  or any other means of heating, connected through a plurality of feedthroughs. A crucible  230  made from graphite, silicon carbide, ceramic material, metal or metal alloys receives the material  231  from the feed tube  217 , softens, dopes, degassifies and solidifies the material. A fused silica plate or a bar  210  is produced. A plurality of ultrasound generators  233  are in contact with the crucible to provide proper mixing and outgassing. Additional vacuum ports  235  are placed above the softened material to remove any gas bubbles. The chamber can be a single chamber or plurality of chambers  213 ,  215  with sequentially controlled heat zones. The shaped member  210  exits the chambers through pressure and heat seals  237  and  239 . Rollers  240  pull the shaped member out of the chambers. 
     FIG. 21  shows a plate or bar forming chamber  211  similar to that sown in  FIG. 20 , in which the infeed is a solid rod  241 . 
     FIG. 22  shows a fused silica plate, bar or otherwise shaped member  210  forming chamber  211  directly coupled to chamber  183 , such as shown in  FIG. 19 , for receiving the fused silica tube input directly from the output of chamber  183 . 
   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&#39;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 (W t ) and the outside diameter (D o ), W t /D o , as well as the ratio between the outside diameter (D o ) and the Inside diameter (D i ), D o /D i , 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. 
   Example No. 1 
   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. 
   Example No. 2 
   Doped and Undoped Layer Combination Silica Body Fabrication 
   Step 1. 
   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. 
   Step 2. 
   Introducing silicon tetra fluoride, SiF 4 , 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. 
   Step 3. 
   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. 
   Step 4. 
   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. 
   Step 5. 
   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 IW t  and undoped other wall OW t  desired 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. 
   Example No. 3 
   Doped Non-Porous and Undoped Porous Layer Combination Silica Body Fabrication 
   Step 1. 
   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. 
   Step 2. 
   Introducing silicon tetra fluoride, SiF 4 , 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. 
   Step 3. 
   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. 
   Step 4. 
   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. 
   Example No. 4 
   Undoped Core and Fluorine Doped Cladding Fiber Optic Preform Fabrication 
   Step 1. 
   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. 
   Step 2. 
   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. 
   Step 3. 
   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. 
   Step 4. 
   Introducing silicon tetra fluoride, SiF 4 , 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. 
   Step 5. 
   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 IW t  and undoped outer wall OW t  desired wall thickness is formed. 
   Step 6. 
   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. 
   Step 7. 
   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. 
   Example No. 5 
   Doped Core and Fluorine Doped Cladding Fiber Optic Preform Fabrication 
   Step 1. 
   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. 
   Step 2. 
   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. 
   Step 3. 
   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. 
   Step 4. 
   Introducing silicon tetra fluoride, SiF 4 , 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. 
   Step 5. 
   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 IW t  and undoped outer wall OW t  desired wall thickness is formed. 
   Step 6. 
   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. 
   Step 7. 
   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. 
   Example No. 6 
   Doped Core and Fluorine Doped Graded Index of Refraction Cladding Fiber Optic Preform Fabrication 
   Step 1. 
   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. 
   Step 2. 
   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. 
   Step 3. 
   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. 
   Step 4. 
   Introducing silicon tetra fluoride, SiF 4 , through the porous substrate and/or the chamber into the deposited porous silica material for T 1  hours at temperature of 800-1400° C., the silica material is doped. T□ is about 0.3 to 2 hours. 
   Step 5. 
   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 IW t  and undoped outer wall OW t  desired wall thickness is formed. 
   Step 6. 
   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. 
   Step 7. 
   Introducing silicon tetra fluoride, SiF 4 , through the porous substrate and/or the chamber into the deposited porous silica material for T 2 &gt;T 1  hours at a temperature of about 1100° C.-1400° C., the silica material is doped. T 2  is about 0.4-4 hours. 
   Step 8. 
   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 IW t  and undoped outer wall OW t  desired wall thickness is formed. 
   Step 9. 
   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. 
   Step 10. 
   Introducing silicon tetra fluoride, SiF 4 , through the porous substrate and/or the chamber into the deposited porous silica material for T 3 &gt;T 2  hours at temperature of about 1100° C.-1400° C., the silica material is doped. T 3  is about 0.5-5 hours. 
   Step 11. 
   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 IW t  and undoped outer wall OW t  desired wall thickness is formed. 
   Step 12. 
   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. 
   Step 13. 
   Introducing silicon tetra fluoride, SiF 4 , through the porous substrate and/or the chamber into the deposited porous silica material for T 4 &gt;T 3  hours at temperature of about 1100° C.-1400° C., the silica material is doped. T 4  is about 0.6 to 6 hours 
   Step 14. 
   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 IW t  and undoped outer wall OW t  desired wall thickness is formed. 
   Steps 15-17. 
   Repeat Steps 12-14 while further reducing the exposure to gaseous dopant, SiF 4  in this case. 
   Step 18. 
   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. 
   Step 19. 
   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. 
   Example No. 7 
   Doped Core Having Graded Index of Refraction and Fluorine Doped Graded Index of Refraction Cladding Fiber Optic Preform Fabrication 
   Step 1. 
   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. 
   Step 2. 
   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. 
   Step 3. 
   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. 
   Step 4. 
   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. 
   Step 5. 
   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. 
   Step 6. 
   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. 
   Step 7-9. 
   Repeat steps 4-6 further reducing the dopant levels in the deposited silica by lowering the dopant concentrations in the dopant particle streams, etc. 
   Step 10. 
   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. 
   Step 11. 
   Introducing silicon tetra fluoride, SiF 4 , through the porous substrate and/or the chamber into the deposited porous silica material for T 1  hours at temperature of about 1100° C.-1400° C. the silica material is doped. T 1  is about 0.3 to 2 hours. 
   Step 12. 
   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 IW t  and undoped outer wall OW t  desired wall thickness is formed. 
   Step 13. 
   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 
   Step 14. 
   Introducing silicon tetra fluoride, SiF 4 , through the porous substrate and/or the chamber into the deposited porous silica material for T 2 &gt;T 1  hours at temperature of about 1100° C.-1400° C. the silica material is doped. T 2  is about 0.4 to 4 hours. 
   Step 15. 
   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 IW t  and undoped outer wall OW t  desired wall thickness is formed. 
   Step 16. 
   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. 
   Step 17. 
   Introducing silicon tetra fluoride, SiF 4 , through the porous substrate and/or the chamber into the deposited porous silica material for T 3 &gt;T 2  hours at temperature of about 1100° C.-1400° C. the silica material is doped. T 3  is about 0.6 to 6 hours. 
   Step 18. 
   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 IW t  and undoped outer wall OW t  desired wall thickness is formed. 
   Step 19. 
   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. 
   Step 20. 
   Introducing silicon tetra fluoride, SiF 4 , through the porous substrate and/or the chamber into the deposited porous silica material for T 4 &gt;T 3  hours at temperature of 1100° C.-1400° C., the silica material is doped. T 4  is about 0.6 to 6 hours 
   Step 21. 
   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 IW t  and undoped outer wall OW t  desired wall thickness is formed. 
   Step 22-24. 
   Repeat Steps 12-14 while further reducing the exposure to gaseous dopant, SiF4 in this case. 
   Step 25. 
   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. 
   Step 26. 
   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. 
   Example No. 8 
   Doped Core Having Graded Index of Refraction and Fluorine Doped Cladding Having Graded Index of Refraction Fiber Optic Preform Fabrication 
   Step 1. 
   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. 
   Step 2. 
   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. 
   Step 3. 
   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. 
   Step 4. 
   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. 
   Step 5. 
   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. 
   Step 6. 
   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. 
   Step 7-9. 
   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. 
   Step 10. 
   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. 
   Step 11. 
   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. 
   Step 12. 
   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. 
   Step 13. 
   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. 
   Step 14. 
   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. 
   Step 15. 
   Introducing silicon tetra fluoride, SiF 4 , 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 SiF 4  penetrating the cladding will be proportional to the pore density and the exposure time at given temperature of the preform. 
   Step 16. 
   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. 
   Step 17. 
   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. 
   Step 18. 
   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. 
   Example No. 9 
   Fluorine Doped Cladding Having Graded Index of Refraction Fiber Optic Preform Fabrication Using Prefabricated Doped or Undoped Core Rod 
   Step 1. 
   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. 
   Step 2. 
   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. 
   Step 3. 
   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. 
   Step 4. 
   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. 
   Step 5. 
   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. 
   Step 6. 
   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. 
   Step 7. 
   Introducing silicon tetra fluoride, SiF 4 , 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 SiF 4  penetrating the cladding will be proportional to the pore density and the exposure time at given temperature of the preform. 
   Step 8. 
   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. 
   Step 26. 
   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. 
   Example No. 10 
   Process for Fabrication of Fluorine Doped Cladding Tube Having Graded Index of Refraction Fiber Optic Preform Fabrication 
   Step 1. 
   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. 
   Step 2. 
   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. 
   Step 3. 
   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. 
   Step 4. 
   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. 
   Step 5. 
   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. 
   Step 6. 
   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. 
   Step 7. 
   Introducing silicon tetra fluoride, SiF 4 , 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 SiF 4  penetrating the cladding will be proportional to the pore density and the exposure time at given temperature of the preform. 
   Step 8. 
   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. 
   Step 9. 
   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. 
   Example No. 11 
   Doped Core Having Graded Index of Refraction for Fiber Optic Preform Fabrication 
   Step 1. 
   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. 
   Step 2. 
   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. 
   Step 3. 
   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. 
   Step 4. 
   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. 
   Step 5. 
   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. 
   Step 6. 
   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. 
   Step 7-9. 
   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. 
   Step 10. 
   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. 
   Step 11. 
   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. 
   While the invention has been described with reference to specific embodiments, modifications and variations of the invention may be constructed without departing from the scope of the invention, which is defined in the following claims.