JPS62246836A - Method of forming soot for preform - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Behind the invention■ The present invention is directed to a leading waveguide and an optical waveguide base material (preform).
and their products, and in particular to providing such products by vapor deposition.

The method of manufacturing optical waveguides that is still in common use today is based on the decomposition of glass components in a flame to form a porous matrix of glassy particles called "soot." The "soot" matrix is transformed into a glassy state by sintering at high temperatures. This comes true as ``U Preform''. A predetermined combination (preform) of the core part and cladding part is
The wire is drawn under tension at elevated temperatures to a predetermined final diameter.

As the use of optical waveguides increases, the technological demands on communication systems also increase. In current technology, properties such as transmission loss of 0.4 dB/km, low dispersion, and precise cut-off wavelength are often required. In addition to the absence of microbubbles, this means that the refractive index profile defined by the geometry and materials of the core and cladding must be reliably and predictably controlled. However, the economics of the process used is also important, so the basic cost and yield must be at a satisfactory level.

Considering these factors, the conventionally used manufacturing method is
It is unsatisfactory from one or more points of view. The method that was widely used in the early days was the so-called ``filling method (internal vapor deposition method),'' which is also known as the ``build-up method.'' In this method, the soot material in the core is specially It is deposited inside a prepared silica tube, and the body is solidified after vitrification to make the interior dense before or during drawing.Preparing a hollow silica tube is expensive. However, the dimensions of the base material produced by this method are also ill.
guaranteed. Another method widely used today is the external deposition method, which is a radial deposition method. The external method requires [11] onto the mandrel and subsequent mandrel stripping before sintering. This operation is delicate and limits the length of the base material. Around 1977, the vapor deposition method (VAD method) was invented for continuous soot deposition and base material fabrication. This method is A cadem
Published by ic press Inc. (1985T
ingye 11 edition) book [Q pical l
"1ber Communication (Optical Fiber Communication) J (7) Vol. 1, lW97
m further Wk (D ”FiberF abduction
This method involves directing a flow of soot material toward a rotating target with a central vertical axis, and as the material is deposited into a solid cylinder, the flow and target This solid cylinder in the VAD method (vapor phase axial method) can be continuously sintered to form a glass starting rod if necessary. It is also possible to simultaneously deposit a coaxial soot cladding by impinging a flow of soot material radially across the contour of the cylinder. Although this manufacturing method is theoretically advantageous, it remains to be seen. The advantages obtained are also hampered by a number of practical factors and technical fill limitations: the axially upward flow of soot material must be directed from the side to prevent side deposition, and for this reason the secondary Accurate burner control must be performed using airflow and specific exhaust geometry, and if simultaneous radial deposition is used, the radial growth rate may be synchronized with the axial growth rate. If the chamber is unstable, the axial growth rate will not be uniform.Also, since both burners are in the same chamber, mixing of the paddy flows from both soot materials is unavoidable, resulting in a diffusion boundary layer between the core and cladding. exist.

When actually performing the VAD method, there are further fundamental restrictions. References and U.S. Patent No. 4°224.046
As described in the issue, the initial idea was that the flow of soot material should be coaxial (=0'') and vertical. However, Spray suggests that the angle should be approximately 40 degrees and the maximum absolute angle for growth should be 60 degrees (U.S. Pat. No. 4.367.085). In order to control the deposition, it was thought that the flow of soot material should be a II flow with a Reynolds number of less than about 100.According to published data, the deposition rate of glass particles is at a Reynolds number of 30-50 or higher. and decreases significantly above about 80. These operational constraints make it virtually impossible to increase deposition rates and reduce cost.

If the axial J3 and radial synchronous N product method of the core and cladding is used simultaneously with the outer sleeve to provide additional cladding, significant cost and performance obstacles arise. come. The ratio of cladding thickness 1 to core radius (a > 1) has significance both in terms of working surface and economics. Although it is possible to reduce the loss by increasing the ratio t/a, this cannot be adopted because the formation of the initial layer is the most costly and the cost of forming the core and cladding is prohibitive. Additionally, when OH ions are introduced into the boundary layer during the manufacturing process, they become water, and since water is directly proportional to light absorption, it is necessary to limit the hydroxyl ion content to keep losses low. be. Nevertheless, most fabricators using the VAD method fabricate with a core to cladding t/a ratio limit of 7 and combine this method with low hydroxyl ion sleeve tubes. The high cost is included both in the soot deposition section, which is limited in growth rate and size, and in the sleeve installation, which must be specially prepared. It is particularly desirable to remove these constraints.

In order to obtain particularly high quality, U.S. Patent No. 4,378.9
It is also known to use redeposition or "hybrid methods" as described in No. 85. In this manufacturing method, the outer cladding is formed by adding a soot layer. This method suffers from the aforementioned synchronization problems between axial and radial deposition.

Thus, while there are constant product and performance advances in optical waveguide technology, subtle and complex interrelationships inhibit further improvements. In addition to the above, the properties of signal transmission are substantially influenced by the shape of the refractive index profile. For single-mode transmission, which is widely used because of its large bandwidth potential, the t/a ratio needs to be precisely controlled and the interface should give a predictable "quasi-stepped" characteristic. It is. The VAD method in which simultaneous soot deposition is used cannot inherently provide the above characteristics, and therefore there may be large fluctuations in the cutoff wavelength and deterioration of the dispersion characteristics. Hydroxyl ion incorporation in the sleeving operation also requires the use of large t/a ratios to control the hydroxyl content within the fiber. Therefore, the #J manufacturing method is expensive, and the properties of the resulting fiber are not satisfactory.

According to the present invention, in a method of forming a soot for a preform by depositing a soot material, the rotational axis of the soot to be formed extends in the transverse direction, and the flow rate of the soot material is such that the soot material has a Reynolds number greater than 100. and is held at an angle greater than 60 degrees with respect to the rotation axis.

The method according to the invention utilizes a fast but laminar flow of soot material at an angle greater than 60° relative to a horizontally rotating initial target to form a core of uniform diameter. It is a deposition method. Radial deposition of the cladding is then used bus by bus until a matrix body with a predetermined t/a ratio is formed. After drying and sintering, this body may be sized to draw directly to a full length leading waveguide, or after drying, sintering, and drawing the initial body, additional cladding sections may be added. form,
It may be vitrified and then drawn to final dimensions.

In one embodiment of the invention, the core can have a higher refractive index than the pure silica cladding. However, in other embodiments according to the invention, the cladding can be fluoridated during sintering to make the cladding have a lower refractive index than the pure silica core. High deposition rates and low cost allow extremely long optical waveguides to be drawn from thin structures.
It is possible to produce a base material with a large diameter and a large quality m. Furthermore, the diameter of the core part is properly and strictly controlled ii+, so that the wall thickness of the cladding part II in the radial direction does not change in the longitudinal direction.
By lowering the burner temperature during deposition, removal of index-altering substances is minimized. The density is then kept approximately constant by increasing the burner temperature depending on the surface speed.

In a more particular embodiment of the method of the invention, a small pure silica starting member is rotated about a horizontal axis while the Reynolds number is increased by means of a flame hydrolysis burner at an angular displacement of more than 60 degrees relative to the starting member. Direct the flow of core soot material upward at a speed in the range of 100 or higher. Excess particulate matter is carried along the path of the impinging soot material flow.
It is discharged from vertically spaced discharge ports. When the target and forming core are initially reciprocated to form a bulbous soot tip, the burner and soot material flow are maintained along the central axis.

The soot tip is then withdrawn at a controlled speed by sensing the position of the end of the cylindrical core and adjusting the withdrawal mechanism on and off to maintain a more or less constant growth rate. Ru. The result is a core having a substantially constant diameter of approximately 2.5 cm in this example. For example 3
When a soot core portion with a predetermined thickness of 5 cm is formed,
Separate soot cladding is added by radial deposition to a thickness of at least twice the core radius. To form the cladding to a predetermined radial thickness, the core of the soot is rotated and reciprocated back and forth over the cladding burner. This manufacturing sequence eliminates the need to synchronize radial deposition with axial deposition and creates a soot core-cladding interface that is low in water M[ions and void-free. Both methods can be implemented at low cost and with high efficiency. The core portion and cladding portion formed to a predetermined thickness are then dried, solidified or vitrified by sintering, drawn, and cut to a diameter of 1 of the solidified or vitrified composite rod. An intermediate bar larger than /10 is formed. Next, a cladding portion is further formed on these rods (minus-order base material), and the thickness thereof is such that a predetermined cut-off wavelength characteristic is established in the guide waveguide after further solidification or final drawing of the glass. For example, diameter 125
In the case of a micron optical waveguide, the core portion is typically 9 microns, and the remainder is the cladding portion.

A distance of 5 mm or less from the geometric center on a line passing through the center, and a distance of 511 m or less from the geometric center in the lateral direction.

Note that the starting member may rotate around a reference axis that is somewhat inclined with respect to the horizontal. This inclination is 30r1 or less with respect to the horizontal direction.

The relationship between the angle of flow of soot material and the impingement area with respect to the core of the growing soot, as well as other factors, are important in order to obtain high growth rates, uniform density and constant diameter. The flow of soot material is of substantially uniform cross-section and is directed along an axis displaced from the biaxial geometric center of the core.

The soot material rapidly deposited on the end E of the core forms a slightly convex, rounded end on the uniformly shaped cylindrical soot as the core is formed. Furthermore, the core part is
The density is approximately uniform throughout its radial and longitudinal directions.

In another embodiment of the invention, the axially deposited core has a diameter of l.
It is as small as C1m, and the cladding part is approximately 13mm thick.
CI is relatively large. A glass preform (preform) is formed by drying and sintering using a large furnace, and this preform is directly connected to a single-seven-mode optical waveguide having predetermined characteristics. J pull is possible. In the pond fabrication process, the actuation factors are changed during core deposition to warp the graded-end index multimode fiber.

According to another embodiment, the silica core is deposited by a high velocity, high incidence angle technique, then dried and sintered. The silica cladding is deposited to a predetermined thickness, but the solidification or vitrification takes place in the presence of a fluorinating agent, which diffuses only into the cladding and lowers the refractive index by a predetermined amount. . This method produced fluorosilicate fibers with transmission losses as low as 0.2 dB/- at 1.55 micron wavelength.

DETAILED DESCRIPTION OF THE EMBODIMENTS As shown in FIG. 1, most of the working parts of the apparatus according to the invention are mounted within a large enclosed deposition chamber 10. The first whisk 12 is made of a silica compound (Si C14 in this case)
This whisker 12 contains purified precursors such as
may be inside or outside the chamber 10. The silica glass precursor gas phase is ejected from the first whisk 12 by feeding a carrier gas, in particular oxygen or other suitable substances, under pressure into the first whisk 12. In this case, specifically, the purified precursor dope is a germanium compound GeC1!
A second whisk 14 containing 11 (additional substances) is included.

Dope precursor vapor is also ejected from the second whisk 14 by the O2m feeder. 02 Valve 15 during WI suspension
can shut off the second whisk 14 by operating this when necessary. The entrained glass forming the constituents in the gas phase stream is mixed and dissociated in a known manner by being sent to a first burner 16, which in this embodiment is held at a substantially fixed position δ relative to the deposition region. The first burner 16 generates a laminar soot material stream 17 and a soot material stream 1
7 is oriented upwardly at an angle of inclination of 65° to the horizontal axis of rotation. A narrow beam of light from laser 18 is deflected from mirror 19 to photodetector 20 . The $119 ray is at an angle intersecting the central geometric axis of the deposited material, as discussed below. However, the flow of soot material 17 is not directed toward the geometric center, but is offset from the geometric center both vertically and horizontally, as will be discussed in more detail below. The light beam can be positioned to intersect the central axis at an angle to the horizontal or vertical direction so as not to be obstructed by the FII&S instrument, and is shown only at an angle from the vertical position for clarity. . The chemical components in the soot material stream 17 are at a flow rate of 40 ft/Sec and -5
Other gases have a flow rate of about 25 ft/SeC. The exhaust port 22 directly above the target area is preset by a butterfly valve 24 in the exhaust path leading to the fan 25.
Collect the gas and unimpinged particles at a gas flow rate of about 300 ft/giin. An end burner 26 adjacent the first burner 16 assists in bringing the temperature of the deposition point to a predetermined height before deposition begins. Valve 28 is openable and openable to control the use of first burner 16 .

Inside the deposition chamber 10, a relatively short silica seed rod 34 is centrally provided on a chuck 36 along the reference axis.

The tick 36 and the seed rod 34 are moved by a rotary drive machine 38 provided on the linear lateral movement mechanism 40, so that the tick 36 and the seed rod 34 are moved 1 to 1 with respect to the core position.
It is rotated at a predetermined speed of the 0 rotation valve. A position controller 42 that receives a signal from the photodetector 20 in the core deposition mode is capable of moving the lateral movement III structure 40 in one direction at a predetermined speed.

By bypassing the position controller 42, it is possible to cause the traverse mechanism 40 to reciprocate at a predetermined speed over any predetermined traverse length. In the core deposition mode, the seed rod 34 is initially short. It is reciprocated over a distance and then moved in one direction with alternating position control. The lateral movement mechanism 40 is also capable of reciprocating over almost its entire length, in this case 40 cm, for cladding deposition. .

In the deposition chamber 10, apart from the seed rod 34 along the reference axis,
Separately, a second burner 50 is used for depositing the cladding. When the valve 52 is opened, the particle-forming compound, in this case pure silica, is conveyed from the first whisk 12 to the second burner 50 by the 02 carrier gas. A second soot material stream 55 is subsequently generated which is directed perpendicular to the horizontal reference axis.

The formation of the core or starting rod for the optical waveguide base material mostly proceeds from conventional VAD techniques. First, the deposition chamber 10 is cleaned, mounted on the chuck 36 of the seed rod 34B, and centered on the axis of rotation. 1st bus 1
6 is determined in relation to the laser beam that determines the tip of the deposited 8% material for position control. The first burner 16 is then ignited, the pumping speed is maintained, and once conditions have stabilized, the seed rod 34 is rotated by the driver 38 at about 20 revolutions per minute to remove the first soot material containing core particles. is advanced into the path of stream 17. The soot material Fl flow 17 impinges on the tip of the seed rod 34 and its vicinity at a large angle of incidence, and the seed rod 34 is vibrated back and forth at a speed of about 45 cn/hr. A bulbous starting beam i60 grows on the free end of the seed rod 34 to a length of about 2 CI. When sufficient material is first deposited, this bulbous tip 60 forms a suitable base or anchor for the growth of the core portion 62. Note that the core portion of soot is sometimes referred to as a soot core portion.

The axial growth of the soot core portion 62 is initiated by the position controller 42 initially applying a constant withdrawal speed of 12 cm/hr. An initial stream of soot material 17 is injected into the end of the bulbous starting tip 60 to form the initial portion of the core portion 62 . The chemical composition of the soot material stream is 40 ft/
The flow rate of the soot material stream 17 is laminar, with a flow rate of 25 rt/sec for the other gases, a Reynolds number of about 1000, and a deposition rate of about 0.14 g.
r/win.

Although the high upward flow rate is accompanied by some over-injection, the gas bypassing the core section 62 is assisted by the upward natural convection tendency of the hot gas and is discharged from the outlet 22. Once deposition of the core 62 begins, the withdrawal rate of 12 cm/hr is slightly faster than the growth rate of the core 62, but the growth on the bulbous starting tip 60 is balanced. Next 1st place! v11
11 device 42 is switched to servo mode and the laser beam intersects the geometric center of the free end of core section 62. By withdrawing the core portion 62 so as to hold the free end of the core portion 62 in a fixed position as material is deposited, the position r11a is
i+ controller 42 is responsive to signals from photodetector 20.

To form a parent material with a diameter of approximately 2.5 CIll, this creates an unsteady withdrawal rate of 6 to 8 C1/hr.

The core part 62 continues to grow and grows to 20 cm (usually 20 to 3
Lateral mover 1f4 until the total length exceeds 3cm range)
40, the core portion 62 is pulled out. This discontinuous operation is carried out without intermixing particles and gases and without synchronizing the process, resulting in a better overall uII
ll becomes possible.

Once the core portion 62 of a predetermined length is formed, the first burner 1
6 is extinguished, and the second burner 50 is ignited and stabilized. Next, the lateral movement mechanism 40 is operated to reciprocate the core portion 62 over its entire length while facing the second burner 50 . The core portion 62 is rotated by the rotary drive device 38.
Rotated at a zero rotation valve speed, the second burner 50 is maintained at a substantially constant distance of approximately 17.5 cm from the axis of rotation of the core portion 62. The core portion 62 is then moved back and forth along the horizontal axis relative to the second clad soot material flow 55 by moving the lateral movement mechanism 40 at a rate of about 250 cs/hr. Deposition of pure silica soot particles is carried out at an average rate of about 2.5 g+7+gin obtained by flame hydrolysis of the gas phase entrained by the carrier gas from the first bubbler 12. The thin contact layer with a thickness of about 51 cm is the core P! By gradually increasing the gas/oxygen flow rate during the first 15 minutes of operation time, the deposition temperature at the surface of the core section 62 is gradually raised to normal operating levels until the I62 is deposited on the core section 62. This allows the temperature to be lowered, thereby avoiding the removal of germanium from the soot core portion 62, but even at the lower temperature, the clad particles that are initially deposited are firmly bonded to the surface of the core soot.The core portion Unless the diameter of the core 62 is held exactly constant, the surface will wave in the longitudinal direction, but the cladding will also perfectly conform to this variation in the surface of the core 62. The boundary layer between the outer cladding 64 and the outer cladding 64 is in the nature of a very thin transition layer with approximately constant properties and a very low moisture content, a factor which depends on the refractive index of the final optical waveguide. (It is quite heavy compared to Ii and water M group ion-containing products.

Deposition of the cladding portion 65 is continued until a final diameter 17 of about 10.5 cm is obtained, giving a ratio of cladding thickness [) to core radius <a> of 2:1 in this example. This soot base material has a thickness of 35 Cllfi and is approximately 550 (J
r' has quality 1, and there is no internal discontinuity. When the cladding is added, the surface velocity increases, but the rate of increase decreases with increasing radius. The burner temperature is increased over time, generally corresponding to the surface speed, so as to remain constant.

According to the manufacturing process shown in Figure 2, the soot base material is first
It is dried in a hydrophilic (here chlorine) atmosphere at 50°C and then sintered in a chlorine atmosphere at 1450°C into a transparent glass rod matrix approximately 3.8 cm in diameter.

The glass rod preform is then drawn in a nearly anhydrous furnace atmosphere at 2000 DEG C. into starting rods having a diameter of about 9 mm. These vitreous rods are over 1710 mm in diameter of the dried and sintered product. The starting rod forms a usable rod with a total length of approximately 150 cm, which is typically 4040-5.
It is divided into Q lengths. The rods are inspected for refractive index distribution, cladding to core diameter ratio and glass quality. Handles are attached to the ends of these individual rods with appropriate properties to clean their exteriors.

When the t/a ratio is greater than or equal to about 2, the base material is subjected to reciprocating and rotational motion in an oxygen flame and flame polished to provide a clean surface for further cladding. t/a
If the ratio is about 1, it is cleaned by dry etching.

In the second cladding step, the first glass base material rod is again rotated in front of the second burner 50 and reciprocated to form another 11 cm thick cladding portion on the wire rod. Ru.

Once formed to the appropriate diameter, the redeposited rod is then dried and sintered as before to form a final fiber preform approximately 5.5° in diameter. Such a matrix is itself a commercial product, since most manufacturers prefer to draw their own optical waveguides. To form the optical waveguide, the parent material is conventionally drawn to a final fiber diameter of 125 μm for 1300a+1 wavelength operation. These optical waveguide fibers with a silica-germanium core and a silica cladding have a t/a ratio of about 13, a transmission loss of 1, and less than 0 dB/lv (typically 0°4
dB/kllll), and 1285-133On-
(7) Dispersion at wavelengths in the Ii range is 3,5 ps/
It is a ψ-mode fiber with less than nap/kge.

To obtain high growth rates, uniform soot deposition, and controlled diameters using high velocity and large angle of incidence flow of soot material, multiple complex factors must be considered.

Referring now to FIGS. 3 and 4, an ideal core 62 would preferably have slightly convex ends and a fairly constant diameter. The geometric center of the front end face of the core section 62 is the target point of the laser beam used to measure the growth of the core section 62. This is a point of symmetry,
Although essentially a point of symmetry should be tracked, in core deposition according to the present invention, the center of chemical component flow is instead
As can be seen in Figure 3, it deviates from the geometric center along the reference axis, and as can be seen in Figure 4, it also deviates in the horizontal direction.

Although the over-injection from the soot material stream 17 is not clearly visible in the diagram, the flow pattern in and beyond the target area is important.

Along the upward path of the soot after passing the direct impingement area, the flow flows along the convex end surface of the core portion 26 for a distance just as the flow is drawn in the direction of the outlet 22 . This flow is also initially somewhat diffused in the collision region. Deposition occurs further downstream along this arc adjacent to the flow of soot material and at a lower temperature than the direct impingement area.

The center of the flow 17 of soot material is at a point on the reference axis inwardly spaced a distance d from the front edge surface and the geometric center of the core portion 62 . This means that the true center of soot material flow is below the reference axis, as can be seen from FIGS. 3 and 4. The spacing between the source of the soot material stream 17 and a line perpendicular to the soot material flow through the geometric center is 4.875" (13,4 cm). The distance d between the geometric center and the intersection of the center line of the soot material flow 17 with the reference axis is 1
/8″ (0,313c+++). It was found that the optimum growth rate is obtained when the soot material flow 17 is directed to the geometric center, keeping the same angle, even though the shapes are almost similar. The growth rate is equal to nothing. If the distance jld is too large while keeping the angle the same, the core will have a soft outer layer, which will cause cracks and deteriorate the refractive index distribution.

As shown in FIG. 3, the free end of the core portion 62 has a concave shape as shown by the dotted line, and the growth rate rapidly decreases to ρ. If the angle 8 is larger than the optimum value, the edge of the core portion 62 will become flat as shown by the point ta line, and the diameter and growth rate will be substantially reduced.

In particular, as can be seen from FIG. 4, the density distribution J3 and refractive index distribution of the core portion 62 are determined by the horizontal deviation (t') of the center of the soot material flow 17 with respect to the geometric center of the core i62.
further controlled by For this example and conditions, the distance 1(t) should be less than or equal to 0.5 CI < 0, 35 c
m (0,138") seems to be optimal. As can be seen in FIG. It has a nearly constant value over the cross section. If the value of t is −0, the value of the refractive index decreases from the center of the core to both sides (dotted line), while if t is larger than the optimal value (dotted line), the refractive index decreases from the center to both sides (dotted line). The rate distribution exhibits high values near the edges of the core.Neither condition is acceptable when the excursion is substantially large.

When the soot material flow spacing and gas flow for chemical components and other gases are in the conditions described above, and when the withdrawal speed is servo ultll, the method can achieve zero deposition rate.
．． A substantially constant growth rate can be obtained with 14or/1g1n.

The Reynolds number is approximately 1000, but in all cases substantially greater than 80, and the flow within the soot stream is laminar.

A high quality core and starting Orad are formed simultaneously such that the body is formed with a soot/soot boundary layer between the core and the cladding. This manufacturing method has substantial slow-flow advantages over prior art techniques that require the use of high quality silica-based tubes or sleeve tubes at substantial cost. The manufacturing method according to the invention and the waveguide obtained thereby also provide substantial benefits with respect to the optical properties of the waveguide obtained.

The refractive index distribution shown in FIG. 6 helps in understanding the excellent optical properties. The high refractive index of the core portion and the low refractive index of the cladding portion are comparative values and are not adjusted for BiO. The sawtooth trajectory is due to instrument instability in the 20 micron step readings. The nature of the transition line between high and low levels is critical to obtaining the "quasi-step" distribution required for single-mode fiber properties, and in this type of fabrication method an infinite slope (i.e. vertical) It is essentially impossible to obtain. However, as can be seen from FIG. 6, the gradient of the transition line is steep, and there is almost no disturbance at either the bottom or the top.

Because there are some dimensional variations within the core resulting from the deposition process, the slope of the transition line is not exactly vertical.

During core deposition, temperature control is important in order to control the refractive index distribution υIwJ. Figure 7 shows the influence of temperature on the distribution. If the lfi degree is lower than the optimum temperature, the 1 distribution (dotted curve) has side slopes at large angles to the vertical, and the peak refractive index is only near the center of the core. If the temperature is above a predetermined level, the index of refraction of the middle core is depressed, but the outer core has a large index of refraction and the side slopes are reasonably vertical. However, as a result of this temperature dependence, it is possible to obtain graded index fibers by using lower temperatures than would be required for constant index through the core. In addition, in this variation, the relative orientation of the soot material flow to the free end of the core and the chemical composition of the soot material flow will also change during deposition. Therefore, in a typical example, the soot material flow will impinge closer to the center of the core, and germanium particles will also be more common in a typical example.

The burner 16 used for core deposition is shown in FIG. 8 along with the relative positions of the gas flows. A stream of soot material 17 emerges from a central aperture 70, around which an inner ring of orifices 72 forms an inner shield for oxygen flow. The middle ring of orifices 74 for the combustible gas and aX forms a slightly converging circular flame. Finally, the outer shielding oxygen is ejected from the orifices 76 of the outer ring.

This arrangement maintains the flow of soot material at a nearly constant diameter,
This forms the frame necessary for dissociation.

As can be seen from Figure 9, when the initial crud deposition temperature is high, the bottom level of the transition between the cladding and the steep gradient in the core boundary layer becomes more gradual (as shown by the dotted line). . It is believed that the germanium dopant will be removed and the core will shrink unless the cladding boundary layer is deposited at a temperature lower than the standard temperature, even at the cost of some manufacturing time.

One advantage of the manufacturing method according to the invention is that a complete soot/soot matrix is produced, sintered, and drawn directly into optical waveguides. To this end, the flow of soot material moves close to the core so that the core is formed to a diameter of only about 1 cm+.

The cladding is then deposited to about 14CI to a predetermined t/
When the composite core/clad structure is then dried and sintered, it has a diameter of about 7 m, from which it can be drawn directly to the leading waveform size.

Furthermore, it will be appreciated that numerous alternatives can be used at various stages of the present manufacturing process. While keeping the angle between the core soot material flow and the axis of rotation of the core constant, the reference axis is tilted relative to the horizontal axis to direct the soot material flow to a near-vertical or completely vertical position. It is also possible to direct the discharge port to the side, and the shape of the discharge port can be changed to meet the requirements, and a gap is provided around the core part to form a function of sucking out excess injection. The vitrified rod is cleaned by a variety of methods including dry gas etching, high power laser beam polishing, or flame polishing. In another manufacturing method according to the invention, as shown in FIG. 10, even low loss (0.2 dB/km) optical waveguides are fabricated by using a pure silica core and a low index cladding. In the first step, a soot core of pure silica is deposited, similar to the embodiment of FIG. This base material is then dried and sintered, and a cladding, also consisting of silica soot, is deposited thereon to a predetermined thickness. This soot layer is then dried at 1150° C. in a hydrophilic atmosphere. Therefore, in order to infiltrate a certain fluorine component into the soot at the same time as solidification or vitrification, in other words, to form a fluorosilicate-impregnated cladding, a fluorinated atmosphere (
Zone sintering is carried out using SFe). Subsequently, another group of silica soot is added and then dried,
It is sintered to obtain a predetermined total cladding thickness.

An example of sintering in a fluorinated atmosphere is 1450°C.
There is an atmosphere of helium and sulfur hexafluoride in the temperature range of .

Drying and sintering take place in a closed furnace into which a gas stream is injected at a controlled rate to maintain the base material at an IJITI temperature. For drying, the oven is heated for at least 20 minutes.
[To a range of 1000-1150℃, 350 s
ec+e chlorine flow, 7000 sec helium flow,
and 14 Q 5CC− of oxygen flow, then 3
It remains in the same state for 0 minutes. Thereafter, the base material is withdrawn while maintaining the same flow conditions, but the withdrawal takes place within 10 minutes.

Sintering: [The culms were carried out with a dry flow of chlorine as low as 50 sec, a constant helium flow of 70,005 ecIl, a sulfur hexachloride flow of 1,355 ec-1, and a temperature of 1,200 sec.
It begins with a 40 minute heating step increasing from 0.degree. C. to 1450.degree. The base material is then sintered at 1450°C for 180 minutes, with a constant flow rate of 0.2 cm/s.
Pass through the hot region at a speed of in. The flow is then interrupted and the base material is cooled from 1450°C to 1000°C in 30 minutes.

Although various shapes and modifications according to the present invention have been described above with reference to the drawings, the present invention is not limited thereto, but includes all methods and modifications thereof within the scope of the claims.

[Brief explanation of drawings]

FIG. 1 is a combination diagram of a simplified perspective view and a block diagram of an apparatus according to the present invention for manufacturing an optical waveguide base material, FIG. 2 is a block diagram of steps in the optical waveguide manufacturing method according to the present invention, and FIG. The figures do not show the collision angle and how the deposited material changes depending on the collision angle. A more detailed side view of the soot flow and the end of the core; FIG. 5 is a diagram showing the change in refractive index distribution with respect to the deviation (1) of the collision position from the axis; FIG. A distribution diagram of the true refractive index read from the wave path. Figure 7 is a diagram showing the influence of controlling the temperature (T) during core deposition on the refractive index distribution. Figure 8 is a diagram used for core deposition. FIG. 9 is an enlarged side view showing the burner and the shape of the soot material flow; FIG. 9 is a diagram showing the change in refractive index distribution when the cladding temperature is changed; FIG. This is a diagram of the manufacturing method. 10... Deposition chamber 16... Core soot burner 7.
... Core soot material flow 18 ... Laser 20 ... Photo detection B 22 ... Discharge port 8 ... Rotation drive device
34... Bait member (seed rod) 40... Lateral movement mechanism 42
... Position controller 50 ... Clad soot burner 55 ... Clad soot material flow 60 ... Bulb-shaped starting part

Claims (12)

[Claims] (1) A method of forming a preform soot by depositing soot material, in which the axis of rotation of the soot to be formed extends in the transverse direction, the flow of soot material has a flow velocity such that the Reynolds number is greater than 100, and A method characterized in that the method is held at an angle greater than 60 degrees with respect to the axis of rotation. (2) A method according to claim 1, wherein the soot material impingement area at the soot end where the soot material is deposited is radially offset with respect to the geometric center of the soot end. (3) The method according to claim 2, wherein the soot end portion is a convex portion. (4) The method according to any one of claims 1 to 3, wherein the soot consists of a core portion and a cladding portion, and the core portion is formed by depositing a core soot material. (5) cladding soot material is deposited on the outer surface of the core portion by radial flow of the cladding soot material to form a cladding portion coaxial with the core portion;
The method described in section. (6) The method according to any one of claims 1 to 5, wherein the flow of soot material is directed upward and undeposited soot material is discharged from above the soot. (7) Surrounding the clad soot material during the initial deposition of the clad soot material over the previously deposited core soot material to limit the surface temperature until the initial cladding is formed on the core surface of the soot. 6. A method as claimed in claim 5, in which the mixed flow of gas and oxygen is gradually increased. (8) As the core of the soot is formed, by varying the position of the core relative to the flow during deposition in order to keep the end position and final diameter of the core constant. and when the cladding portion of the soot is formed, by reciprocating the core portion axially relative to the flow of the cladding soot material;
6. The method of claim 5, wherein a cladding is deposited. (9) The method according to any one of claims 1 to 7, wherein the rotation axis is horizontal. (10) Claim 1, wherein the rotation axis is inclined.
7. The method according to any one of items 7 to 7. (11) A method according to any one of claims 1 to 10, wherein the starting part of the soot is formed into a bulbous shape, after which the deposition of soot material continues in a cylindrical shape. (12) The method according to claim 2, in which the center of flow of the soot material is kept a certain distance away from the rotation axis, which is the geometric center of the soot end.