JPH0525817B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method and apparatus for producing a stress-applied polarization-maintaining optical fiber base material with good polarization-maintaining properties used for coherent optical transmission or optical measurement. It is related to.

BACKGROUND TECHNOLOGY A stressed polarization-maintaining optical fiber with good polarization-maintaining properties includes a core, a cladding surrounding the core, and two cores arranged on opposite sides of the core, each having a thermal expansion coefficient different from that of the cladding, for example. The structure includes at least a stress applying section having a stress applying section. Such stress-applied polarization-maintaining optical fibers are conventionally
A method of forming a non-axisymmetric fan-shaped stress application part using the MCVD method (internal CVD method) (RDBirch et al.
al., Electron.Lett., Vol.18, No.24, PP.1036−
1038, 1982), or by the rod inch tube method as shown in Fig. 7, or by the perforated jacket method as shown in Fig. 8 (Y. Sasaki et al., Electron. Lett. .，
Vol. 19, No. 19, PP. 792-794, 1983).

For example, in the case of using the rod inch tube method as shown in FIG. A pair of glass preforms 4 for the stress-applying portion are arranged so as to sandwich the dummy glass rod 5 between them, and a dummy glass rod 5 is inserted into the remaining gap, which is then heated, melted, and drawn.

In addition, when using the perforated jacket method as shown in FIG. 8, a pair of stress-applying glass base materials are inserted into the jacket base material 6 in which the core 2 is formed in the center so as to sandwich the core 2 therebetween. It is produced by forming holes 7 and inserting stress-applying glass base materials 4 into the insertion holes 7, heating and melting and drawing.

Problems to be solved by the invention Among the conventional manufacturing methods described above,
Both the MCVD method, the rod inch tube method, and the perforated jacket method are not continuous manufacturing methods, and have the disadvantage that it is difficult to manufacture long fibers. In addition, the rod inch tube method or the perforated jacket method involves processes such as polishing the stress-applying base material and drilling high-precision holes to improve dimensional accuracy, which makes the manufacturing process complicated and increases the price. It was hot.

Therefore, the present invention eliminates these drawbacks and
It is an object of the present invention to provide a relatively simple method and apparatus for producing a long stress-applied polarization-maintaining optical fiber.

Means for Solving the Problems That is, according to the present invention, a porous glass base material for the core is formed at one end of the rotating support rod,
Glass particles for the intermediate layer are deposited on the peripheral surface of the porous glass base material for the core to form a porous glass base material for the intermediate layer, and then, on the peripheral surface of the porous glass base material for the intermediate layer, Fine glass particles for the stress-applying portion and fine glass particles for the cladding are deposited on the same plane intersecting the axis of the support rod from directions at angles to the axis, and the fine glass particles for the stress-applying portion and the glass fine particles for the cladding are deposited on the same plane intersecting the axis of the support rod. The intermediate glass particles are deposited intermittently during one rotation of the support rod so that glass particles of the same composition are deposited at positions axially symmetrical about the support rod. For a stress-applied polarization-maintaining optical fiber characterized in that a porous glass preform for a stress-applying member and a porous glass preform for a cladding are alternately formed on the circumferential surface of a porous glass preform for a layer. A method of making a base material is provided.

Furthermore, according to the present invention, a reaction container, an exhaust gas treatment device coupled to the reaction container, a support rod that moves up and down within the reaction container, a drive device that rotates and pulls up the support rod, and the support rod a torch for synthesizing a porous base material for a core, which is oriented along an axis through which the central axis of the support rod passes; a torch for synthesizing a porous glass base material for a stress-applying member, and a torch for synthesizing a porous glass base material for a stress applying member, which is oriented toward an axis through which the central axis of the support rod passes above the torch for synthesizing an intermediate layer porous glass base material; The torch for synthesizing the porous glass base material for the stress applying member and the torch for synthesizing the porous glass base material for the cladding are connected to the central axis of the support rod. The torch for synthesizing the porous glass base material for the stress applying member and the porous glass base material for the cladding are arranged at angles to each other with respect to the axis on the same plane that intersects the axis through which the An apparatus for producing a stress-applied polarization-maintaining optical fiber base material, comprising a control device that controls the amount of raw material supplied to the material synthesis torch in accordance with the rotation angle of the support rod. is provided.

In the method and apparatus for producing a stress-applied polarization-maintaining optical fiber preform according to the present invention as described above, the porous glass preform for the stress-applying member on the peripheral surface of the porous glass preform for the intermediate layer. The porous glass preforms for the cladding are arranged alternately in the circumferential direction, but are formed so that the same preforms are continuous in the axial direction. Therefore, by heating the base material to make it transparent, jacketing it with a quartz glass tube and drawing it as necessary, stress applying members extend in the axial direction on opposite sides of the core. A polarization-maintaining optical fiber provided in this way can be manufactured. There is no need for high-precision polishing or drilling, and
Since the base material is produced by a shafting method, a long stress-applied polarization-maintaining optical fiber can be produced relatively easily.

Embodiments Hereinafter, embodiments of the method and apparatus for producing a preform for a stress-applied polarization-maintaining optical fiber according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 is an embodiment showing a schematic configuration of an apparatus for manufacturing a preform for a stress-applied polarization-maintaining optical fiber according to the present invention, which implements a method for manufacturing a pre-form for a stress-applied polarization-maintaining optical fiber according to the present invention. It is.

The illustrated apparatus has a reaction vessel 10 with a support rod 12 depending from the top thereof, the top of the support rod 12 being engaged with a drive 14 in the direction of arrow 16. arrow 18 while rotating to
It is designed so that it can be pulled up in the direction of

Furthermore, an exhaust gas treatment device 20 is connected to the reaction vessel 10 for removing surplus reaction gas, glass particles, etc. in the reaction vessel 10.

A support rod 1 is provided at the bottom of the reaction vessel 10.
A torch 22 for synthesizing a porous glass preform for a core is disposed toward the axis through which the central axis of No. 2 passes. Above the core porous base material synthesis torch 22, an intermediate layer porous glass base material synthesis torch 24 is arranged, similarly facing the axis through which the central axis of the support rod 12 passes.

Torch 24 for synthesizing the intermediate layer porous glass base material
Further above, a torch 26 for synthesizing a porous glass base material for a stress-applying member and a torch 28 for synthesizing a porous glass base material for a cladding are arranged in the same direction toward the axis through which the central axis of the support rod 12 passes. has been done. The torch 26 for synthesizing the porous glass base material for the stress applying member and the torch 28 for synthesizing the porous glass base material for the cladding are located in a plane substantially perpendicular to the axis through which the central axis of the support rod 12 passes. As shown in FIG. 2, the support rod 12 is disposed at a certain angle, for example, at a 90 degree angle, relative to the axis through which its central axis passes.

Further, electromagnetic valves V ₁ and V ₂ are provided in the conduit means extending to the raw material supply ports of the torch 26 for synthesizing the porous glass base material for the stress applying member and the torch 28 for synthesizing the porous glass base material for the cladding, respectively. is,
The opening and closing of these electromagnetic valves V ₁ and V ₂ is controlled by a control device 40 .

The stress-applying polarization-maintaining optical fiber preform manufacturing apparatus configured as described above operates as follows.

For example, the support rod 12 is placed at the lowest position and rotated by the drive device 14 at a rotational speed of 5 rpm. Oxygen gas is then applied to the torch 22 for synthesizing the porous base material for the core, which faces the lower end of the support rod 12.
At the same time, hydrogen gas is supplied at a rate of 4/min, and SiCl ₄ gas transported by argon gas is
100 c.c./min, and GeCl ₄ is supplied at a rate of 10 c.c./min. As a result, an H ₂ -O ₂ flame is formed in front of the torch 22 for synthesizing the porous base material for the core, and within the flame, SiCl ₄ and GeCl ₄ undergo a flame hydrolysis reaction, and SiO ₂ glass containing GeO ₂ is formed. Fine particles ( _SiO2 - _GeO2 ) are deposited on the lower end of the support rod 12, and a core porous glass preform 30 is formed on the lower end of the support rod 12.

The support rod 12 is rotated by the drive device 14 at a rotation speed of 5 rpm and pulled upward in accordance with the growth rate of the porous glass base material 30 for core, so that the growth end surface of the base material is always kept constant. .

Oxygen gas is supplied at a rate of 5/min and hydrogen gas is supplied at a rate of 4/min onto the porous glass base material 30 for the core synthesized in this manner, and the raw material gas SiCl transported with argon gas ₄ is 200 c.c./
The torch 24 for synthesizing the intermediate layer porous glass base material is supplied at a rate of min.
A H ₂ -O ₂ flame is formed, SiCl ₄ gas is reacted within the flame, SiO ₂ glass particles are generated and deposited on the core porous base material 30 to form the intermediate layer porous glass base material 32. Form.

The intermediate layer porous glass base material 32 formed on the core porous glass base material 30 is supplied with oxygen gas at a rate of 5/min and hydrogen gas at a rate of 4/min.
SiCl ₄ gas was supplied at a rate of 200c.c./min and transported with argon gas at a rate of 200c.c./min.
Torch 26 for synthesizing porous glass base material for stress-applying members where _BBr3 gas is supplied at a rate of 100c.c./min
forms a _H2 - _O2 flame in front of the torch 26, reacts _SiCl4 and _BBr3 gas within the flame, and synthesizes and deposits _SiO2 - _B2O3 glass fine particles for the stress applying part _. .

Similarly, oxygen gas is supplied at a rate of 5/min, hydrogen gas is supplied at a rate of 4/min, and SiCl ₄ gas transported by argon gas is supplied at a rate of 200c.c./min.
The torch ₂₈ for synthesizing the porous glass base material for _cladding , which is supplied _at a ratio _of Synthesize and deposit glass particles.

As a result, on the intermediate layer porous glass base material 32,
A base material 34 consisting of porous glass for the stress applying member and porous glass for the cladding is formed.

As mentioned above, the torch 26 for synthesizing the porous glass base material for the stress applying member and the torch 28 for synthesizing the porous glass base material for the cladding are in the same horizontal plane and are at an angle of, for example, 90 degrees as shown in FIG. It is set up to have. When arranged in this way, the supply of SiCl 4 and BBr 3 to the torch 26 for synthesizing the porous glass base material for the stress applying member, and the supply of SiCl ₄ and BBr ₃ to the torch 28 for synthesizing the porous glass base material for the cladding.
The supply of SiCl ₄ is controlled by the control device 40 through the solenoid valve V ₁
and by controlling the opening and closing of V ₂ , the support rod 5
It is controlled so that the intermittent cycle is repeated at 1/4 of the time T required for one revolution. That is, when the support rod 12 is rotating at 5 rpm as described above, T is 12 seconds, so the control device 40 switches the solenoid valves V ₁ and V ₂ from open to closed every 3 seconds. , the feed of the material is controlled to repeat the interruption in 3 seconds.

With such intermittent control, as can be seen from FIG. A porous glass base material part 36A and a porous glass base material part 38A for cladding are formed. During the next 1/4T downtime, no glass synthesis material is supplied to the torches 26 and 28, and only the glass preform rotates. the result,
During the next 1/4T raw material supply time, the porous glass base material part 36 for the stress applying member that has already been deposited
A porous glass base material part 36B for a stress applying member and a porous glass base material part 38B for a cladding are formed at positions axially symmetrical to the porous glass base material part 38A for a stress applying member. During the raw material supply time that is further after the 1/4T rest period, the stress applying member porous glass base material part 36A and the cladding porous glass base material part 38A are formed again.

Thus, since the raw material gas is periodically interrupted in the torch 26 for synthesizing the porous glass base material for the stress-applying member and the torch 28 for synthesizing the porous glass base material for the cladding, the The SiO ₂ -B ₂ O ₃ regions and the SiO ₂ regions for the cladding exist alternately at 90° angles, while the respective base metal parts are continuous in the axial direction.

The porous base material thus obtained is dehydrated and made transparent using an electric furnace provided above the reaction vessel or elsewhere. The wavelength at which the transparent glass base material operates in a single mode (cutoff wavelength λc)
A stress-applied polarization-maintaining optical fiber is fabricated by jacketing it with a quartz glass tube having an appropriate inner and outer diameter, and drawing it.

By the above manufacturing method, the core diameter is 4 mm, the intermediate layer diameter is 8 mm, the cladding (stress applying part) diameter is 25 mm, the refractive index difference between the core and the intermediate layer is 0.3%, the _GeO2 molar concentration in the core is 3 mol%, and the stress applying part is B ₂ O ₃ molar concentration 10mol%
A glass base material was prepared. This is stretched to make the cladding diameter 12.5mm (core diameter 2mm), and the inner diameter
A quartz tube with a diameter of 12.7 mm and an outer diameter of 40 mm was jacketed and drawn to form a fiber. The fiber had an outer diameter of 200 μm, a core diameter of 10 μm, and a cutoff wavelength λc = 1.5 μm.
The mode birefringence B of this fiber is approximately 1.0 × 10 ^-4 , and the crosstalk in a short length (3 m) is -40 dB.
At a fiber length of 100 m, it was -30 dB.

Due to fluctuations in the stress-applying parts in the length direction,
Although the crosstalk was worse than that of fibers fabricated using conventional hole-drilling methods, this is not an essential problem, and crosstalk can be lowered even further than before by optimizing the fabrication conditions. The fact that a long stress-applied polarization-maintaining optical fiber can be manufactured according to the present invention is extremely significant.

In this embodiment, the rotation speed of the support rod was 5 rpm, and the intermittent interval of the raw material gas flow rate of the torches 10 and 11 was set to 3 seconds, but the rotation speed and the intermittent interval are not limited thereto.

That is, the angle between the torch 26 for synthesizing the porous glass base material for the stress applying member and the torch 28 for synthesizing the porous glass base material for the cladding does not need to be 90 degrees, and the glass particles from both torches are connected to the porous base material. It suffices if they can be deposited so that they do not overlap in the cross section.

For example, as shown in FIG. 4, a torch 26 for synthesizing a porous glass base material for a stress applying member and a torch 28 for synthesizing a porous glass base material for a cladding are arranged at an angle of 120 degrees. For example, if the base material is rotating in the direction of the arrow, during the first period of T/6,
Material is supplied to both torches, and during the next second period T/6, only the torch 25 for synthesizing the porous glass base material for the stress applying member is stopped, and the torch 28 for synthesizing the porous glass base material for the cladding is stopped. Continues to supply material to both torches, and then stops supplying material to both torches for a third period of T/6. Thereafter, the process returns to the initial T/6 period and supplies material to both torches.

A cross section of the base material thus formed is shown in FIG. As can be seen from FIG. 5, the porous glass base material portion 36 for the stress applying member extends over a range of 60 degrees, while the porous glass base material portion 38 for the cladding member extends in a range of 60 degrees.
extends over a range of 120 degrees.

Furthermore, as shown in FIG. 6, the torch 26 for synthesizing the porous glass base material for the stress applying member and the torch 28 for synthesizing the porous glass base material for the cladding may be arranged at an angle of 60 degrees. Again, assuming that the base metal is rotating in the direction of the arrow, material is supplied to both torches during the first T/6 period, and during the second T/6 period, the stress Only the torch 26 for synthesizing the porous glass base material for the application member is stopped, material is continued to be supplied to the torch 28 for synthesizing the porous glass base material for the cladding, and both torches are further supplied during the third period T/6. Suspension of supply of materials to. Thereafter, the process returns to the initial T/6 period and supplies material to both torches.

The base material thus formed also has a cross section similar to that shown in FIG. That is, the stress applying member porous glass base material part 36 extends over a 60 degree range, while the cladding porous glass base material part 3
8 extends over a range of 120 degrees.

As is clear from the above, the arrangement relationship between the torch 26 for synthesizing the porous glass base material for the stress applying member and the torch 28 for synthesizing the porous glass base material for the cladding is as follows.
The angle is not limited to 90 degrees, and the difference in angle between the two can be compensated for by changing the control timing of stopping the supply of raw materials.

The timing of supplying raw materials to the torch 26 for synthesizing the porous glass base material for the stress applying member and the torch 28 for synthesizing the porous glass base material for the cladding is determined according to the rotational speed of the support rod 12 and the angle of both torches. be done.

Furthermore, the amount of raw material supplied to each torch is not limited to the example described above, and the raw material to be supplied is not limited to the example described above, but can be selected according to the composition of the optical fiber to be manufactured. Ru.

For example, the compositions of the glass for the core, the glass for the intermediate layer, and the glass for the stress applying portion are SiO ₂ −GeO ₂ , SiO ₂
- Not limited to B ₂ O ₃ , SiO ₂ as core glass
−P ₂ O ₅ , SiO ₂ − for intermediate layer and stress applying part
By using GeO ₂ −B ₂ O ₃ or SiO ₂ −P ₂ O ₅ −B ₂ O ₃ , a larger birefringence can be obtained.
Polarization maintaining characteristics can be improved.

Further, by using SiO ₂ as the core glass and SiO ₂ -GeO ₂ -F as the intermediate layer and the stress applying part, the effect of fluorine is that it is resistant to radiation, making it suitable for use in outer space.

Effects of the Invention As explained above, the method and apparatus for manufacturing a stress-applied polarization-maintaining optical fiber according to the present invention relatively easily manufacture a stress-applied polarization-maintaining optical fiber without requiring high-precision processing. The base material can be manufactured continuously, improving properties and making it more economical, and it is also possible to lengthen the length, which is an original feature of the VAD method.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a stress-applied polarization-maintaining optical fiber preform manufacturing apparatus according to the present invention, and FIG. 2 is a stress-applied polarization-maintaining optical fiber preform manufacturing apparatus shown in FIG. FIG. 3 is a diagram showing the positional relationship between the torch for synthesizing the porous glass base material for the stress-applying member and the torch for synthesizing the porous glass base material for the cladding. FIG. 4 is a sectional view of the base material produced by the base material manufacturing device, and shows a torch for synthesizing the porous glass base material for the stress-applying member and a porous cladding material in the stress-applying polarization-maintaining optical fiber base material manufacturing device. A diagram showing a modified example of the positional relationship with a torch for synthesizing a glass base material,
FIG. 5 shows a stress-applying type polarization-maintaining optical fiber base material in which a torch for synthesizing a porous glass base material for a stress-applying member and a torch for synthesizing a porous glass base material for a cladding are arranged at the positions shown in FIG. FIG. 6 is a cross-sectional view of the base material made by the manufacturing device, and shows a torch for synthesizing the porous glass base material for the stress-applying member and the porous glass for the cladding in the stress-applying type polarization-maintaining optical fiber base material manufacturing device. FIG. 7 is a schematic diagram illustrating a conventional method for producing a stress-applied polarization-maintaining optical fiber by the rod inch tube method; FIG. 8 is a schematic diagram illustrating a conventional method for producing a preform for a stress-applied polarization-maintaining optical fiber by the perforated jacket method. [Main reference number], 1...jacketed quartz tube,
2... Core, 3... Glass base material for core, 4... Glass base material for stress imparting, 5... Dummy glass rod, 6... Jacket base material, 7... Insertion hole for stress imparting glass, DESCRIPTION OF SYMBOLS 10... Reaction container, 12... Support rod, 14... Drive device, 20... Exhaust gas treatment device, 22... Torch for synthesis of porous glass base material for core, 24... Porous glass base material for intermediate layer Synthesis torch, 26... Torch for synthesizing porous glass base material for stress applying member, 28... Torch for synthesizing porous glass base material for cladding, 40... Control device.

Claims (1)

[Claims] 1. A porous glass base material for a core is formed at one end of a rotating support rod, and glass fine particles for an intermediate layer are deposited on the circumferential surface of the porous glass base material for a core to form an intermediate layer. Next, on the peripheral surface of the porous glass base material for the intermediate layer, on the same plane intersecting the axis of the support rod, from directions mutually angular with respect to the axis. , depositing glass fine particles for the stress applying part and glass fine particles for the cladding, and intermittently stopping the deposition of the glass fine particles for the stress applying part and the glass fine particles for the cladding during one revolution of the support rod; A porous glass base material for the stress applying member and a porous cladding material are formed on the circumferential surface of the porous glass base material for the intermediate layer so that glass fine particles having the same composition are deposited at axially symmetrical positions about the support rod. 1. A method for producing a preform for a stress-applied polarization-maintaining optical fiber, the method comprising forming a base material for a stress-applied polarization-maintaining optical fiber alternately. 2 The porous base material for the core is SiO ₂ −GeO ₂ , SiO ₂ −
Formed from P ₂ O ₅ or SiO ₂ , the intermediate layer is formed from SiO ₂ ,
_SiO2 - _GeO2 -F, _SiO2 - _{GeO2 - B2O3} , _SiO2-
It is formed from P ₂ O ₅ −B ₂ O ₃ and the stress applying part is made of SiO ₂ −
B ₂ O ₃ , SiO ₂ −P ₂ O ₅ −B ₂ O ₃ , SiO ₂ −GeO ₃ −
B ₂ O ₃ , SiO ₂ −GeO ₂ −F to form a cladding.
A method for producing a stress-applied polarization-maintaining optical fiber base material according to claim 1, characterized in that the base material is formed from SiO ₂ . 3. A reaction vessel, an exhaust gas treatment device coupled to the reaction vessel, a support rod that moves up and down within the reaction vessel, a drive device that rotates and pulls up the support rod, and an axis along which the central axis of the support rod passes. A torch for synthesizing a porous base material for a core is oriented, and a torch for synthesizing an intermediate layer porous glass base material is oriented toward an axis through which the central axis of the support rod passes above the torch for synthesizing a porous base material for a core. and a torch for synthesizing a porous glass base material for a stress applying member and a porous glass base material for a cladding, which are oriented toward an axis through which the central axis of the support rod passes above the torch for synthesizing the intermediate layer porous glass base material. The torch for synthesizing the porous glass base material for the stress applying member and the torch for synthesizing the porous glass base material for the cladding are the same torch that intersects the axis through which the central axis of the support rod passes. The torches are arranged at angles to each other with respect to the axis on a plane, and further include raw materials for the torch for synthesizing the porous glass base material for the stress applying member and the torch for synthesizing the porous glass base material for the cladding. 1. An apparatus for producing a preform for a stress-applied polarization-maintaining optical fiber, characterized in that a control device is provided for controlling the supply amount of the preform in accordance with the rotation angle of the support rod. 4. The torch for synthesizing the porous glass base material for the stress applying member and the torch for synthesizing the porous glass base material for the cladding are arranged on the same plane substantially perpendicular to the axis through which the central axis of the support rod passes. A method for producing a preform for a stress-applied polarization-maintaining optical fiber according to claim 3, characterized in that: 5. The torch for synthesizing the porous glass base material for the stress applying member and the torch for synthesizing the porous glass base material for the cladding are arranged at an angle of 90 degrees,
The control device controls the time T for one rotation of the support rod.
The method is characterized in that the torch for synthesizing the porous glass base material for the stress applying member and the torch for synthesizing the porous glass base material for the cladding are both supplied with raw materials and stopped for every 1/4T period. A method for producing a preform for a stress-applied polarization-maintaining optical fiber according to claim 3 or 4.