JPH0772344A - Optical fiber - Google Patents

Abstract

PURPOSE:To provide the polarization maintaining optical fiber from an ordinary optical fiber by heating and pressurizing the optical fiber having a circular shape in the section of a core and clad to an approximately elliptic shape in section. CONSTITUTION:This optical fiber is constituted by forming a single mode optical fiber 1 in an elliptic shape and consists of a core 3 and a clad 2. Since the polarized wave in parallel to the major axis (X-axis direction) and the polarized wave perpendicular thereto (Y-axis direction) vary in propagation constant, light propagates in the elliptic polarization maintaining optical fiber in the state of maintaining the polarization. The optical fiber 1 is made gradually elliptic by the groove width of a molding section 6 when the optical fiber 1 set at the molding part is inserted into a heating furnace 5 and the groove width of the molding section 6 is made successively smaller by an adjusting mechanism 8 outside the heating furnace 5 where the optical fiber 1 is heated to the same temp. as the process for production. The elliptic flatness of the core 3 is most adequately operated to obtain a high double refractive index, by which the double refractivity is imparted to the orthogonal polarized waves in the X- and Y-directions and the energy coupling thereof is suppressed. The optical fiber 1 made elliptic is thereafter taken up and the elliptic polarization maintaining optical fiber is thus produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization-maintaining optical fiber for transmitting a polarization required by an optical fiber application measuring instrument or a coherent optical transmission system while maintaining the polarization, and a single polarization plane. Only for fiber optic polarizers in which only one is propagated.

[0002]

2. Description of the Related Art With the progress of optical communication technology, optical fibers are currently used in various devices. Among them, in the optical integrated circuit used for various communication devices, it is assumed that the output from the optical fiber is linearly polarized light in the specified direction, and in various measuring devices, it propagates through the optical fiber. Light is required to be linearly polarized. Therefore, a polarization-maintaining optical fiber that propagates a linearly polarized wave while maintaining the polarization plane has been developed. 6 and 7 show a conventional example of this polarization-maintaining optical fiber. FIG. 6 shows a sectional view of an elliptic core optical fiber, and FIG. 7 shows a sectional view of a non-axisymmetric stress imparting optical fiber. .

As shown in FIG. 6, an elliptic core optical fiber 1
In No. 1, the cross section of the core 13 has an elliptical shape, and the propagation constant differs depending on whether the electric field is parallel to the major axis (X-axis direction) or perpendicular (Y-axis direction). The birefringence index B in these two directions has a relationship of B = (elliptical flatness) × (relative refractive index Δ) ² . However, the relative refractive index Δ is the refractive index n of the core 13.
1 and the refractive index n2 of the clad 12 are represented by the formula Δ = (n1 ² -n2 ² ) / 2n1 ² . Therefore, in the elliptic core optical fiber 11, a high birefringence B is obtained by manipulating the refractive indices n1 and n2 of the core 13 and the clad 12 and the elliptic flatness of the core 13 to obtain orthogonal polarization in the X and Y directions. Give birefringence to
These energy bonds can be suppressed.

On the other hand, in the non-axisymmetric stress-applying optical fiber 14 shown in FIG. 7, the core 16 has a circular cross section, but a pair of stress-applying members 17 provided in the clad 15 applies stress to the core 16 in one direction. In addition, this causes strain inside the core, and the originally isotropic core 16 becomes anisotropic, so that a high birefringence is obtained.

As described above, the conventional polarization maintaining optical fiber is
Two degenerate orthogonal polarization modes HE ₁₁ ^X and HE ₁₁
^The plane of polarization is preserved by giving birefringence to ^Y and suppressing energy coupling between these modes.

Further, it is possible to manufacture an optical fiber polarizer using these polarization-maintaining optical fibers to remove unnecessary orthogonal polarization components and extract only predetermined polarization components.

FIG. 8 is a perspective view showing a conventional example of an optical fiber polarizer. As shown in FIG. 8, the cladding 19 of the polarization-maintaining optical fiber 18 is partially removed by polishing or the like, and a metal film 22 is provided on the removed portion. In the optical fiber polarizer thus configured, the polarization mode in which the electric field oscillates in the direction parallel to the film surface of the metal film 22 is not attenuated by the metal film 22. On the other hand, the polarization mode in which the electric field vibrates perpendicularly to the film surface of the metal film 22 is attenuated by the metal film 22. Therefore, only the polarization mode in which the vibration direction of the electric field is parallel to the film surface of the metal film 22 passes, so that linearly polarized light is obtained.

[0008]

However, the above-mentioned prior art has the following problems. For example, in order to manufacture an elliptic core optical fiber, it is necessary to prepare a preform as shown in FIG. 9 in advance and then draw the preform.

For example, in order to manufacture a polarization-maintaining optical fiber, a step of manufacturing a preform manufactured by a VAD method or the like consisting of a core, a first cladding and a second cladding, and then drawing this preform is necessary.

Further, for example, in the case of an optical fiber polarizer, the polarization maintaining optical fiber manufactured in the above steps needs to be further processed by polishing the clad and depositing a metal film.

There is a problem in that a large-scale device is required for the production of such a preform, the drawing process, and the polishing of the clad, and the process is also very complicated.

The present invention has been made in view of the above points, and an object thereof is to provide a polarization-maintaining optical fiber and an optical fiber polarizer obtained by processing an ordinary single mode optical fiber. .

[0013]

In order to solve the above problems, the present invention heats a normal single mode optical fiber (hereinafter referred to as an optical fiber) and applies pressure in one direction from the side surface of the optical fiber. , An optical fiber having a structure formed into a substantially elliptical shape.

Further, the present invention is an optical fiber having a structure in which a metal film is provided on the side surface in the minor axis direction of the elliptical cross section of an optical fiber having such a core and a clad having an elliptical cross section.

[0015]

In the optical fiber of the present invention having the above-mentioned substantially elliptical cross-section, the propagation constant differs between the polarized light parallel to the major axis (X-axis direction) and the polarized light vertical (Y-axis direction). , The plane of polarization is maintained in the optical fiber and the light propagates. That is,
Functions as a polarization maintaining optical fiber.

Further, in the optical fiber of the present invention having a structure provided with a metal film, polarized waves parallel to the short axis (Y-axis direction) of the elliptical cross section are attenuated by the metal film and parallel to the long axis (X).
Since only polarized light in the (axial direction) propagates, desired linearly polarized light can be obtained. That is, it functions as an optical fiber polarizer.

[0017]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a view showing the sectional structure of an elliptical polarization-maintaining optical fiber according to the first embodiment of the present invention. The single-mode optical fiber 1 has an elliptical configuration and includes a core 3 and a clad 2. In the elliptical polarization-maintaining optical fiber of the present invention, since the polarization constant parallel to the long axis (X-axis direction) and the vertical (Y-axis direction) have different propagation constants, the elliptical polarization-maintaining optical fiber In the optical fiber, light propagates while maintaining polarization.

Next, a method of manufacturing this elliptical polarization-maintaining optical fiber will be described.

FIG. 2 is a schematic view showing a method of manufacturing the above elliptical polarization-maintaining optical fiber. The optical fiber 1, the optical fiber feeding section 4, the heating furnace 5, the molding section 6, and the winding section 7 are used. Become. First, the optical fiber 1 is set in the molding unit 6. The molding section 6 has a groove having a width of about the diameter of the optical fiber, and an adjusting mechanism 8 capable of adjusting the groove width from outside the heating furnace 5. Next, the optical fiber 1 set in the molding unit 6 is inserted into the heating furnace 5. At this time, the heating furnace 5 is preheated to a temperature at which the optical fiber 1 is not completely melted, for example, in the case of a quartz optical fiber,
It is desirable to heat to about 600 ° C. The molding part 6 uses a material that does not melt at the heating temperature, for example, ceramics such as alumina or zirconia. The optical fiber 1 set in the molding section is inserted into the heating furnace 5, and when the optical fiber 1 is heated to the same temperature, the groove width of the molding section 6 is reduced by the adjusting mechanism 8 outside the heating furnace 5. Then, as shown in FIG. 3, the optical fiber gradually becomes elliptical depending on the groove width of the molding portion 6. By optimally manipulating the ellipticity of the core 3 here, a high birefringence B can be obtained, birefringence can be imparted to orthogonal polarized waves in the X and Y directions, and energy coupling between these can be suppressed. . Ovalized optical fiber 1
Is then wound to produce an elliptical polarization maintaining optical fiber.

As shown in the figure, the elliptical polarization-maintaining optical fiber of the present invention can be manufactured from a normal optical fiber, and is very simple and easy as compared with a conventional polarization-maintaining optical fiber manufacturing facility. A polarization maintaining optical fiber can be manufactured.

FIG. 4A shows a perspective view of an optical fiber polarizer according to the first embodiment of the present invention, and FIG. 4B shows A of the optical fiber polarizer according to the first embodiment of the present invention. -A sectional drawing is shown.

The optical fiber polarizer of the present invention is an optical fiber 1.
The metal film 10 was provided on the side surface of the optical fiber parallel to the major axis (X-axis direction) of the elliptical cross section by using the elliptical polarization-maintaining optical fiber in which the intermediate portion of the above was molded as described above. Due to the metal film 10 provided on the side surface of the optical fiber, polarized waves parallel to the minor axis (Y-axis direction) of the elliptical polarization-maintaining optical fiber are attenuated, and only polarized waves parallel to the major axis (X-axis direction) are attenuated. Since it propagates, linearly polarized light can be obtained. The metal film 10 is formed by a thin film forming means such as a sputtering method or a vacuum deposition method, and the thickness of the metal is not particularly limited as long as the electric field of light does not leak to the outside of the metal film 10. good. The optical fiber polarizer of the present invention does not require the polishing step of the optical fiber clad, which is necessary for the production of the conventional optical fiber type polarizer, and the production thereof is easy.

FIG. 5 is a sectional view of an optical fiber polarizer according to another embodiment of the present invention. Another embodiment of the present invention uses a conventional polarization-maintaining optical fiber and transforms it into an elliptical shape whose major axis is the direction in which the stress applying portions are aligned (X-axis direction), and then the major axis (X The metal film 10 was provided on the side surface of the optical fiber parallel to the axial direction). The light propagating through the polarization-maintaining optical fiber is attenuated by the metal film 10 provided on the side surface of the optical fiber, and the polarization parallel to the minor axis (Y-axis direction) of the polarization-maintaining optical fiber is attenuated and parallel to the major axis. Since only the polarized light (X-axis direction) propagates, linearly polarized light can be obtained. The other optical fiber polarizer of the present invention can easily add a polarizer function to the middle of the optical path without splicing loss in the system using the conventional polarization maintaining optical fiber.

[0025]

As described above in detail, according to the optical fiber having the elliptical cross-section according to the present invention and the optical fiber having the structure provided with the metal film, the following excellent effects are obtained. Have. The optical fiber in which the optical fiber has an elliptical cross section does not require a special material, and a polarization-maintaining optical fiber can be obtained from an ordinary optical fiber. The optical fiber in which the optical fiber is formed into an elliptical cross section can obtain a polarization-maintaining optical fiber that can be easily manufactured without requiring large-scale equipment for manufacturing, as compared with the conventional manufacturing equipment for polarization-maintaining optical fiber. The optical fiber provided with the metal film can provide an optical fiber polarizer which can be easily manufactured without a complicated clad polishing step as in the past. Since the optical fiber polarizer provided with the metal film can add a polarizer function in the optical fiber optical path without cutting the optical fiber, it is possible to realize a highly reliable optical fiber polarizer without loss. it can.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing the structure of an elliptical polarization-maintaining optical fiber according to a first embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a manufacturing apparatus for explaining an optical fiber molding method according to the present invention.

FIG. 3 is a schematic cross-sectional view showing a molding part of a manufacturing apparatus for explaining the optical fiber molding method according to the present invention.

4A and 4B show a structure of an optical fiber polarizer according to a second embodiment of the present invention, where FIG. 4A is a side sectional view and FIG.
FIG.

FIG. 5 is a sectional view showing the structure of an optical fiber polarizer according to a third embodiment of the present invention.

FIG. 6 is a cross-sectional view showing a conventional example of a polarization maintaining optical fiber.

FIG. 7 is a cross-sectional view showing another conventional example of a polarization maintaining optical fiber.

FIG. 8 is a perspective view showing a conventional example of an optical fiber polarizer.

FIG. 9 is a sectional view of a preform for producing a conventional elliptic core optical fiber.

[Explanation of symbols]

 1, 11 Optical fiber 2, 12, 15, 19 Clad 3, 13, 16, 20 Core 10, 22 Metal film 14 Non-axisymmetric stress applying optical fiber 17, 21 Stress applying member 18 Polarization maintaining optical fiber

Claims (2)

[Claims] 1. An optical fiber having a substantially elliptical cross section formed by heating and pressing an optical fiber whose core and clad have circular cross sections. 2. An optical fiber having a cross section of a core and a clad that is substantially elliptical, and a metal film is provided on an outer peripheral surface that is substantially parallel to the major axis of the ellipse.