FR2530234A1 - METHOD FOR MANUFACTURING SINGLE POLARIZED OPTICAL FIBERS - Google Patents

Abstract

IN THE SINGLE POLARIZATION OPTICAL FIBER MANUFACTURING PROCESS, A LOW MELTING POINT GLASS FILM WHICH WILL BE TRANSFORMED TO AN ELLIPTICAL LAYER IS FORMED ON THE INNER SURFACE OF A SILICA GLASS TUBE TO OBTAIN A SILICA GLASS TUBE PROVIDED WITH A FILM, THE RESULTING SILICA GLASS TUBE WITH A FILM IS PREFORMED TO OVAL SHAPE WITH AN ELLIPTICITY LESS THAN THAN THE ELLIPTICAL LAYER TO OBTAIN AN ELLIPTICAL SILICA GLASS TUBE WITH A FILM, A AME ROD IS INTRODUCED IN THE RESULTING SILICA GLASS ELLIPTICAL TUBE EQUIPPED WITH A FILM AND THESE TUBE AND THE SOUL ROD WHICH IS INTRODUCED THERE ARE HEATED SO AS TO BE MADE SOLIDARITY, WHILE REDUCING THE PRESSURE TO OBTAIN A PREFORM, AND RESULTING PREFORM IS SUBJECTED TO FILAMENT STRETCHING TO OBTAIN A SINGLE POLARIZATION OPTICAL FIBER.

Description

The present invention relates to a method of manufacturing

  cation of single polarized optical fibers, and in particular

  for a process for manufacturing polar optical fibers

  single or simple position in which the variation of ellip-

  length length is minimized.

  FIG. 1 is a section showing an optic fiber

  that with simple polarization in which the guide of the

  mière is carried out without variation of the single plane of polarization-

  tion and this single polarization optical fiber comprises a core 11 having a refractive index N 1, an elliptical sheath 12 having a refractive index N 2 (n 1> N 2) which surrounds the aforementioned core 11, a support 13 in silica glass placed outside the abovementioned elliptical sheath 12, and

  a plastic sheath 14 constituting the outer layer

  fiber optic The materials that make up the core 11

  and the elliptical sheath 12 are shown below.

  () Construction Materials Ame 11: (a) Sicl: (b) Si O 2 + B 203 (c) Sio + Ge O: (d) Si 2 + P 205 Elliptical sheath; (a) Sio 2 + B 203) ( (b) If O 2 + Ge O 2 + B 203) (In the case of these optical fibers with simple polarization, the anisotropic deformation generated by the difference of the coefficients of thermal expansion between the materials of the elliptical sheath 12 and of the support 13 is applied to core 11 so the difference in propagation constants in

  two directions perpendicular to each other and perpendicular

  culinary direction may be increased

  light, and thus the light guidance in simple mode can

  be performed without variation of the polarization plane.

  In the single polarization optical fibers mentioned above

  mentioned, however, there is a case where B 203, Ge O 2 or P 20

  (these substances increase the refractive index N 2) is

  porise from a layer deposited in the vapor state which becomes the core 11 by application inwards on the

  inner layer of the silica glass tube becoming the sup-

  port 13 to reduce its concentration in the case of the manufacture of optical fibers with, for example, a chemical vapor deposition (CVD) process As a result, the refractive index in the central part of the core 11 d 'A finished optical fiber decreases as shown in Figures 2 A or 2 B, so that the transmission characteristics are altered.

  Figures 3 A to 3 C illustrate a manufacturing process

  cation of optical fibers with simple polarization by which one can avoid a lowering of the refractive index of the central part of the core 11 In FIG. 3 A, a glass rod 21 which will form the core 1 i is stretched while by heating the rod by means of a burner 22 at H 2-02 In FIG. 3B, a preform 27 comprising a layer 23 deposited in the vapor state, which has been shaped as an oval (while a tube of

  silica glass 24 is reduced to a round shape by the tension

  surface sion) is obtained by reducing the internal pressure of the silica glass tube 24 while heating a glass rod 21, the silica glass tube 24 having a layer 23 deposited in the vapor state which will form an elliptical sheath 12 by means of a burner 25 at H 2-02 so that the glass rod 21 has been introduced into the silica glass tube 24 Furthermore, in FIG. 3 C, the preform 27 having

  the shape shown in Figure 3B is subjected to a stretch

  ge in filament while being heated by a carbon heater 26 to obtain an optical fiber 28 with simple polarization (in this case, when the total amount of B 203 and p 205 of the elliptical sheath 12 is for example 7 moles, we

  performs a depression of -49 Pa to obtain an elliptical

40% t).

  According to the manufacturing process of optical fibers

  single polarization shown in Figures 3 A to 3 C,

  pendant, even if the internal pressure of the silicon glass tube

  ce 24 is reduced to -49 Pa so that the elliptical sheath 12

  has an ellipticity of 40%, there appears a case where the ellip-

  ticity of the elliptical sheath 12 varies according to the length in a range, for example, from 36 to 44%, because the tube of

  silica glass 24 has a dispersion of its characteristics

  characteristics (for example a spreading of the softening point due to the variation in composition) as a function

of the material according to its length.

  Therefore, the present invention proposes to provide a method of manufacturing single polarized optical fibers in which the ellipticity of the cladding

  elliptical does not vary according to its length.

  The present invention also proposes to provide a method for manufacturing optical fibers with simple polarization which does not involve a production unit.

  complex because of which there is no variation of ellip-

  length of the elliptical sheath layer.

  A process for manufacturing optical fibers with

  The simple embodiment according to the present invention consists in forming a vapor deposition layer which transforms into an elliptical layer on the inner surface of a tube.

  silica glass, to conform the pre-silica glass tube

  feeling the vapor deposition layer on its interior surface

  re in an oval shape with a lower ellipticity than

  that of the aforementioned elliptical layer, to introduce a ti-

  central ge in the silica glass tube thus ovalized to obtain a solid preform, and to subject the aforementioned solid preform to a filament drawing to produce a single polarized optical fiber, In the drawings,

  FIG. 1 is a section showing an optic fiber

  than single polarization; Figures 2 A and 2 B are explanatory diagrams each representing the refractive index of a core of the optical fiber indicated in Figure 1;

  Figures 3 A, 3 B and 3 C are diagrams

  each feeling the stages of a classic manufacturing process

  tion of single polarized optical fibers;

  Figures 4 A, 4 B and 4 C are diagrams showing

  tring the steps of one embodiment of the method

  bricating the single polarized optical fibers of the present invention, respectively;

  Figure 5 is a sectional view showing a figure

  bre with simple polarization made according to the present invention; and - Figures 6 A, 6 B and 6 C are diagrams showing the steps of another embodiment of the method

  for manufacturing single polarization optical fibers se-

  the present invention, respectively.

  The present invention will be described below in more detail with reference to the accompanying drawings showing the shapes

for carrying out the invention.

  Figures 4 A to 4 C illustrate a first form

  of the present invention in which the nu-

  reference number 31 designates a tube of pre-silica glass

  feeling, for example, an external diameter of 18 mm and a thickness of about 1.5 mm A film 32 in bottom glass

  melting point which forms an outer coating is reali-

  placed on the inside of the silica glass tube 31 to obtain

  a tube 33 made of silica glass provided with a film- (fi

gure 4 A).

  The film 32 made of low melting point glass is made of B 2 3 + Si O 2 glass or of glass containing at least two doping agents such as B 203, F, P 205, Ge O 2, etc., and the

  film is formed so that its melting point is

  less than other layers The thickness of the coat

  licule 32 in glass of low melting point is for example

about 200 micro meters.

  The interior of the tube 33 made of silica glass provided with a film is evacuated while heating the tube

  -filled with film to obtain an elliptical tube 34 de-

  formed with an ellipticity of 15% (Figure 4B).

  Then, the elliptical silica glass tube re-

  sultant 34 provided with the film is held vertically,

  and a core rod 36 is introduced into the glass tube.

  re of elliptical silica 34 provided with the film (FIG. 4C).

  The core rod 36 is a solid rod produced by a VAD or similar method and it has an outside diameter, for example, of about 700 micrometers and has been previously coated with a film 35 of tall glass.

  melting point which will be transformed into an interior coating

  laughing. High melting point glass film 35

  is made in high purity Sio 2, in high pure Sio 2 -

  tee containing F, or the like, and it is necessary that the film 35 of glass of high melting point has a higher melting point than that of film 32 of glass of low melting point above, but the film of glass 35 does not necessarily have a higher melting point than

  of the silica glass tube 31 or of the core rod 36 The ma-

  Thirds combined as described above under the conditions indicated in Figure 4 C, are heated so as to be made integral, while reducing the pressure according to the desired ellipticity, so as to obtain an appropriate preform. As mentioned above, the silica glass tube 33 provided with its film has been previously treated to present

  an ellipticity of 15%, the rod-in-tube process is applied

  qué, then, when adjusting the degree of pressure reduction

  in the process, a preform having an ellip-

  ticity depending on this degree of pressure reduction.

  The preform thus prepared is subjected to stretching so that a single polarized optical fiber having an ellipticity of 40% to 60% is obtained. More particularly, a single polarized optical fiber having an ellipticity of 40% can be obtained by using a tube 33 made of silica glass provided with its film having an ellipticity of 15%, 4 moles of P 205 and 4 moles of B 203 are added to the film 32 of glass of low melting point, and the pressure is reduced to 9 , 8 Pa in the process On the one hand, when the total amount of P 205 and B 203 is 9 moles, it is possible to produce a single polarization optical fiber having an ellipticity of

50% at atmospheric pressure.

  The Applicant has further continued its research so that the elliptical tube 34 made of silica glass provided with its film having an ellipticity of 20% is shaped in

-30234

  further increasing the ellipticity of the tube 33 made of silica glass.

  Then, the core rod 36 covered with the film 35 in ver-

  re of high melting point is introduced into the tube 34 made of silica glass thus obtained, and they are put under vacuum and heated to give a preform in the same way as that

the described above.

  In this case, one also easily obtains a

  preform of an ellipticity of 20% or more.

  More specifically, the silica glass tube

  elliptical 34 with a film, having an elliptical

  20% tee and an internal diameter of 2 mm is conformed, the core rod 36 coated with a glass film and an external diameter of 700 Nom is introduced into the silica glass tube 34, the internal pressure prevailing in the glass tube

  resulting elliptical silica is reduced to 196 Pa in posi-

  vertical tion (total amount of P 205 and B 203 of 6 moles),

  and the silica glass tube and the core rod inside it

  pick are heated to obtain a preform A fiber op-

  simple polarized tick obtained by submitting the preform

  at a filament stretch has an ellipticity of 40% and a long

  coupling length of 4 mm at a wavelength of 0.63 Nm.

  When it is assumed that an ellipticity generally necessary for a single polarized optical fiber is

  between 40% and 60%, an ellipticity of the elliptical tube

  than in silica glass 34 provided with a film to which the pro-

  yielded to rod-in-tube must be applied, can be chosen

between 15% and 40%.

  In addition, a definition of ellipticity i is given below main axis secondary axis F = x 100 (%) main axis + secondary axis

  The term "ellipticity" used in this me-

  moire denotes that of the external shape of the exterior coating

  laughing 12 in the case of a single polarization optical fiber

  or its preform, while it designates that of its external form

  higher in the case of the elliptical tube made of silica glass 34

with its film.

  Figure 5 illustrates a polarized optical fiber.

  tion made according to the present invention in which

  the reference number 41 designates a circular core, produced

  preferably made of Si O 2 glass + Ge O 2, or the like, 42 designates a coating having a circular section and made of Si O glass of high purity, 43 designates an elliptical sheath consisting essentially of glass with If O 2 +

  P 05 + B 203, 44 designates a support containing Si O as the principal

  component, and 45 denotes a plastic sheath, respectively. Figures 6 A to 6 C illustrate a second form

  of the present invention in which the reference

  digital reference 51 designates a silica glass tube, for example having an outside diameter of 18 mm and a thickness

about 1.5 mm.

  A glass film of low melting point 52 which will form an external coating is produced on the wall

  inside the silica glass tube 51.

  The film 52 made of low melting point glass is made of B O + Sio glass or glass containing

23 2

  at least two doping agents such as B 203, F P 205, Ge O 2, etc., and the film is formed in such a way that its point

  is lower than that of the other layers The thick-

  low-melting glass film 52 is

for example around 200 gm.

  A film 53 made of high melting point glass which will form an interior coating is also produced on the interior part of the film 52 made of low melting point glass in order to obtain a tube 54 made of silica glass provided with a

film (Figure 6 A).

  The film 53 in glass of high melting point is made of Si O 2 of high purity, in Si O, of high purity containing F, or similar element, and it is necessary that the film 53 of glass of high melting point has a higher melting point than that of the aforementioned low-melting glass film 52, but the glass film 53 does not necessarily have a higher melting point than that of the aforementioned silica glass tube 51 or the soul rod that

will be described below.

  A thickness for example of around 30 gm is suitable

  for film 53 in high melting point glass.

  The interior of the tube 54 made of silica glass with its

  film is evacuated while being heated to obtain

  nir a deformed elliptical tube 55 having an ellipticity

15% (Figure 6 B).

  Then, the elliptical silica glass tube re-

  sultant 55 with a film is held vertically,

  and a core rod 56 is introduced into this tube (FIG. 6C).

  The core rod 56 is a solid rod manufactured by

  a VAD process, or analogous process, and it has a di-

  external meter, for example around 700 Nm.

  The combined materials, as described above under the conditions shown in Figure 6C, are heated to

  so as to be made integral, while reducing the pres-

  according to the desired ellipticity, so as to obtain a

appropriate preform.

  As mentioned above, the silica glass tube 54 provided with a film has been previously treated to present

  an ellipticity of 15 to 40%, we apply the rod-

  in-tube, then when adjusting the degree of pressure reduction

  In the process, you can easily get a preform

  having the predetermined ellipticity.

  The preform thus prepared is subjected to drawing

  filament to be able to produce a polarized optical fiber

  simple tion with an ellipticity of 40 to -60%.

  The Applicant has further pursued its research in such a way that the elliptical tube made of silica glass 55

  provided with a film, having an ellipticity of 20% or

  mé by further increasing the ellipticity of the glass tube of si-

  file 54 provided with a film Next, the core rod 56 is in-

  troduit in the tube 55 thus obtained, then one makes the vacuum -

  and we heat to get a preform in the same way as

described above.

  In this case, the elliptical tube 55 made of silicon glass

  this provided with the film, having an ellipticity of 20% and an internal diameter of 2 mm is shaped, the core rod 56 having an external diameter of 700 Nom is introduced into the tube 55, the internal pressure of the glass tube of resulting elliptical silica is reduced to 196 Pa in the vertical state (the total amount of P 205 and B 203 being 6 moles), and

  the silica glass tube and the core rod which is introduced therein

  are heated to form a preform A single polarized optical fiber obtained by subjecting the preform to stretching has an ellipticity of 40% and a coupling length

  of 4 mm at a wavelength of 0.63 Nom.

  As described above, according to the present invention,

  a silica glass tube fitted with a film was previously

  nicely shaped to the oval so that even if the tu-

  be in silica glass has any variability over

  its length, its elliptical layer can be shaped regularly

  As a result, single polarized optical fiber

  of the present invention can suppress the variation of the el-

  In addition, the advantages of the present invention other than those described above are

mentioned below.

  (1) A solid optical fiber with simple polarization

  can be obtained because his soul is not formed according to the pro-

  transferred CVD modified (internal vapor deposition), but by pro

yielded rod-in-tube.

  (2) A single polarized optical fiber having

  an ellipticity of 40 to 60% and not varying according to its length

  can easily be made by adjusting the degree of

  pressure reduction in the case where the silicon glass tube

  this and the core rod are solidified so as to be integral.

  This is due to the fact that the silica glass tube provided with a film has an ellipticity of 15 to 40%, and

  then apply the rod-in-tube process to it.

Claims (8)

  1 Process for the manufacture of optical fibers   simple production, characterized in that it consists in: forming a glass film of low melting point which will be transformed into an elliptical layer, on the inner surface of a silica glass tube to obtain a silica glass tube provided with a film; ovalizing said silica glass tube to give it an ellipticity lower than that of said elliptical layer o to obtain an elliptical silica glass tube provided with a film;   to introduce a core rod into said elliptical tube   than in silica glass provided with a film and to heat the   said tube and the core rod which is introduced therein so as to make them integral, while reducing the pressure to obtain a preform; and   to subject said preform to drawing in a fila-   to obtain a single polarization optical fiber pos-   seducing an elliptical layer having a predetermined ellipticity born.   2 Process for the manufacture of optical fibers   the simple version according to claim 1, characterized in that   that the ellipticity of said elliptical tube made of silica glass   nor of a film is between 15 and 40%.   3 Process for the manufacture of polarized optical fibers   simple risation according to claim 1, characterized in that   that the ellipticity of said elliptical layer is included in- be 40 and 60%.   4 Process for the manufacture of optical fibers   simple version, characterized in that it consists of:   to form a glass film of low melting point   sion which will be transformed into an elliptical layer, on the inner surface of a silica glass tube to obtain a silica glass tube provided with a film; to ovalize said silica glass tube to give it an ellipticity lower than that of said layer   elliptical to obtain an elliptical silica glass tube that provided with a film; -   to introduce a core rod coated with a glass film of high melting point which will form a coating layer in the elliptical tube made of silica glass provided with a film and to heat said elliptical tube made of silica glass provided with its film and said soul stem therein   introduced so as to make them united while reducing   pressure to obtain a preform; and   to subject said preform to drawing in a fila-   to obtain a pre-polarized single polarized optical fiber   feeling an elliptical layer having an ellipticity predeter- mined -   Process for manufacturing single-polarized optical fibers according to claim 4, characterized in   that the ellipticity of said elliptical tube made of silica glass   nor of its film is between 15 and 40%.   6 Process for the manufacture of optical fibers   the simple arrangement according to claim 4, characterized in that   that the ellipticity of said elliptical layer is included in- be 40 and 60%.   7 Process for the manufacture of optical fibers   larisation simple, characterized in that it consists in successively forming a glass film of   low melting point which will be transformed into an ellip-   tick and a glass film of high melting point which will be transformed into a coating layer, on the internal surface of a silica glass tube to obtain a silica glass tube provided with a film; ovalizing said silica glass tube provided with a film to give it an ellipticity lower than that of said elliptical layer in order to obtain an elliptical silica glass tube provided with a film;   to introduce a core rod into said elliptical tube   than in silica glass provided with a film and to heat the   said tube and said core rod which is introduced therein so as to   make them united, while reducing the pressure to obtain hold a preform; and   to subject said preform to drawing in a fila-   to obtain a single polarization optical fiber of which * 1 2530234   the elliptical layer has a predetermined ellipticity.   8 Process for the manufacture of optical fibers   the simple arrangement according to claim 7, characterized in that the ellipticity of said elliptical tube made of silica glass provided with a film is between 15 and 40%.   9 Process for the manufacture of optical fibers with   the simple arrangement according to claim 7, characterized in that   that the ellipticity of said elliptical layer is included in- be 40 and 60%.