JPS62134608A - Polarization plane maintaining optical fiber tape core - Google Patents

Abstract

PURPOSE:To obtain a polarization plane maintaining optical fiber tape core whose transmission characteristic is not degraded even if a side pressure is applied, by keeping an angle between the minor axis of the ellipse of an elliptic clad type polarization plane maintaining optical fiber and planes, which are arranged in parallel at prescribed intervals in the lengthwise direction, in the range from 45 deg.-90 deg.. CONSTITUTION:X and Y axes are taken in directions of major and minor axes of an elliptic clad respectively, and the x axis of a local coordinate system (x), (y) is inclined at an angle thetaF to the X axis, and an external force F is applied for an overall length L in the x-axis direction. In the figure, a core, the elliptic class, and a clad are indicated by 1, 2, and 3 respectively. A mode double refractive index B is varied in accordance with a principal stress difference DELTAsigmaE peculiar to the optical fiber and a principal stress difference DELTAsigmaF due to the external force F, and especially, the value B is minimum when the application direction of the external force, namely, the angle thetaF is in the range from 0 deg.-30 deg.. If the angle thetaF is selected to be in the range from 45 deg.-90 deg., said difference DELTAsigmaE of each elliptic clad optical fiber is not cancelled by said difference DELTAsigmaF even if a side pressure F/L is applied, and degradation in transmission characteristic such as reduction of the mode double refractive index and increase of mode coupling is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical fiber ribbon using a polarization maintaining optical fiber.

[Conventional technology] Polarization-maintaining optical fibers are capable of maintaining the linear polarization state of incident light in a completely stable manner over an oval radius, and therefore have been extensively researched and developed, including application to coherent source communication systems. is being vigorously advanced.

As one of these, many studies have been made on optical fiber ribbons using polarization-maintaining optical fibers. FIG. 6 is a cross-sectional view of an example of a polarization-maintaining optical fiber ribbon according to the prior art, in which 1 indicates the core of an elliptical clad polarization-maintaining fiber (hereinafter abbreviated as elliptical clad fiber);
2 is the elliptical cladding of the elliptic clad original fiber, 3 is the cladding of the elliptic clad original fiber, 4 is the subject resin of the elliptical clad optical fiber, and 5 is a planar shape parallel to the entire longitudinal direction of the five elliptic clad original fibers. It is a coating resin that is coated with the materials arranged in .

[Problem that the invention seeks to solve]

By converting polarization-maintaining optical fiber into fiber tape, it is possible to increase the density of polarization-maintaining optical fiber.
On the other hand, when pressure is applied to a polarization-maintaining optical fiber tape consisting of n elliptical clad optical fibers, the mode birefringence weakens.
The elliptical cladding fiber with large mode coupling is n
It has been statistically confirmed that cases in which one or more fibers exist in ice are far more common than cases in which none exist, and this is a major factor hindering the practical application of polarization preserving optical fiber tape. It has become.

The present invention aims to provide an optical fiber tape core that preserves the plane of polarization using an elliptical cladding fiber whose mode birefringence does not weaken and mode coupling does not increase even when lateral pressure is applied. It is something.

The present invention provides a means for solving all the problems of 1σ (oil-coated In the polarization-maintaining optical fiber tape, the short axis of each of the plurality of elliptical cladding-type polarization-maintaining source fibers and nine planes arranged in a plane parallel to the longitudinal direction and separated by the predetermined distance; The present invention is a polarization-maintaining optical fiber ribbon characterized in that the angle formed is always in the range of 45 degrees and 90 degrees.

Fig. 4 shows the coordinate thread of the elliptical clad optical fiber to which the lateral pressure F/L is applied. The direction in which the external force F is applied, which is the long axis and short axis of the elliptical cladding, is the X axis of the local coordinate system X-7 axis. The inclination of the local coordinate system (x, y) is expressed by the rotation angle OF from the X axis. Here, L is the length of the optical fiber to which the external force F is applied.

fcl is a core, 2 is an elliptical cladding, and 3 is a cladding.

Now, the mode birefringence B of the elliptic clad original fiber is
The following (1
It can be expressed as follows.

B=C! p(ΔtyF, “10ΔaF2−2ΔaE−Δu
F −coe2e+111)! +-(i) Friend, C
p is the relative photoelastic constant.

Further, ΔσE and ΔσF can be approximately expressed by the following equations (2) and (3).

Here, 6 is the ellipticity of the elliptic cladding, E and μtt'l
['f Young's modulus and Poisson's ratio, which are assumed to be the same in each layer of the circular-clad original fiber, Δα is the difference in thermal expansion coefficient between silica glass and elliptical cladding, ΔT (3T-To) i'i
Stress state '/3 ('j-ff?) & degree change in stress-free state (solidification temperature), D represents the outer diameter of the elliptical clad optical fiber.

FIG. 5 shows all the results of calculating the normalized birefringence B for all the heads using equation (1). Mathematical number 1: Used parameter i for self-calculation, F2 = 7750Kg/mm", 'p = (1
164, D=125pm, Cp=i44X10-'ra
nz/9, la-ΔT=15.0X10-'.

From FIG. 5, it can be seen that the mode birefringence has a minimum value and a local minimum value when the external force application direction is 0 degrees≦θF≦50 degrees. In particular, when θF = 0 degrees and the direction of external force application to the housing 9 is the long axis direction, the inherent stress difference of the elliptical clad optical fiber is completely canceled by the stress difference caused by the external force F.
The mode birefringence B may be zero.

Based on the above findings, the polarization-maintaining optical fiber ribbon of the present invention has elliptical clad polarization-maintaining fibers separated by a predetermined distance and arranged on a plane parallel to the longitudinal direction. Since the angle θF between each elliptical clad optical fiber included in the fiber tape core and the short axis of the elliptical clad is in the range of 45 degrees ≦ θF ≦ 90 degrees, even if lateral pressure is applied, each elliptical clad light Since the inherent stress difference of the fiber is not canceled by the stress difference caused by the external force F, the characteristics as a polarization-maintaining optical fiber are affected, such as the mode birefringence B is weakened and the mode coupling is increased. It will not deteriorate.

〔Example〕

FIG. 1 shows an example of a cross-sectional view of a five-core polarization preserving fiber tape using an elliptical clad optical fiber according to the present invention. 1 is the core of an elliptical clad optical fiber, 2
The elliptical cladding of the I/i elliptical cladding original fiber, 5 is the cladding of the elliptical cladding optical fiber, the ellipticity of the elliptical cladding is 03%, the fiber outer diameter is 125 μm, and t. In addition, 4 is a fiber coating resin made of ultraviolet curing resin with a Young's modulus of 5 to 9/2, and the outer diameter of the outer diameter is 300 μm.
, 5 is a coating resin made of ultraviolet curable resin with a Young's modulus of 4 kg/m2, and the tape width after coating is 1.5 mm.
The tape thickness was α45.

Figure 2 shows 5
An outline of a method for manufacturing a polarization-maintaining optical fiber ribbon is shown. Oval clad optical fiber preform 61Fr: drawn in a spinning furnace 8, coated with a pressurized fiber chair 9, and cured with an ultraviolet ray lamp 10. As described above, the outer diameter of the T5-core elliptical clad optical fiber that is simultaneously drawn and coated with UV-curable resin is aligned and assembled using the guide roller 11 and the base 12, and coated with UV-curable resin using the pressure die 13 for tape. , the tape is cured with an ultraviolet lamp 14, and wound up with a winder 15. However, when attaching the elliptical clad optical fiber preform 6 to the preform support 7, the long axis direction of the elliptical clad of each elliptical clad optical fiber preform and the elliptical clad optical fiber preform 6 are attached to the preform support 7. Make sure that the alignment direction matches the direction in which they will be installed side by side. FIG. 3 shows a state in which the arrangement direction of the elliptical clad optical fiber preforms 6 and the short axis direction of each elliptical clad optical fiber preform 6 are perpendicular to each other, and the preforms 6 are attached to the preform support 7. 6 and 7 in Figure 3 have the same meanings as in Figure 2, 1 is an elliptical clad optical fiber preform, 1' is the core of the elliptical clad optical fiber preform, and 2' is an elliptical clad optical fiber preform. The elliptical cladding 5' is the cladding of the elliptical cladding optical fiber preform.

In the case of the elliptically clad polarization-maintaining optical fiber tape core of the present invention obtained as described above, the elliptical clad polarization-maintaining optical fibers are separated by a predetermined distance and arranged in a plane parallel to the longitudinal direction. Since the angle between the plane and the short axis of the elliptical clad of each elliptical clad optical fiber included in the polarization-maintaining optical fiber tape was in the range from 87 degrees ηλ to 90 degrees, lateral pressure was applied. Even if the 7Ff stress difference of each elliptical clad optical fiber is not canceled out by the stress difference caused by external force, the mode birefringence B will be weakened and mode coupling will be increased, resulting in polarization maintaining optical fibers. There was no deterioration in its properties.

That is, when a flat plate side pressure of 25 to 9/100 #l is applied to the optical fiber tape fabricated using the above method according to the present invention and which preserves the polarization plane, the mode birefringence is as follows for all five fibers. , t OX 10-'Gara 2,5 X 1 [)-
', and the transmission characteristics as a polarization-maintaining optical fiber did not deteriorate.

The angle between the short axis of the cladding and the plane is not always within the range of 45 degrees and 90 degrees, but is arbitrary as shown in Fig. 6, and the other flexibility is the same as in the above embodiment. In the polarization-maintaining optical fiber tape (comparative example) created by Tomokobei,
Similarly, when a flat plate side pressure of 9/100m+ is applied to 25, the mode birefringence is 1i 1. OX 10-' 7)h
2 out of 5 fibers recovered to about t 5 × 10−
On the other hand, α5 × 10-' ~ α8 × 10-4
The number of fibers was reduced to 3 out of 5.

From the above Examples and Comparative Examples, it is clear that the present invention can be used again.

〔Effect of the invention〕

As stated earlier, the polarization-maintaining optical fiber ribbon of the present invention has transmission characteristics as a polarization-maintaining optical fiber, such as weakening of mode birefringence and increased mode coupling even when lateral pressure is applied. It is an excellent NFC product that will not deteriorate.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the polarization-maintaining optical fiber ribbon of the present invention, FIG. Figure 5 shows the relationship between the arrangement direction of the elliptical clad optical fiber preform and the short axis direction of the elliptical clad in the manufacturing process shown in Figure 2. Figure 4 shows the relationship between the elliptical clad optical fiber preform and the minor axis direction of the elliptical clad in the manufacturing process shown in Figure 2. A diagram showing the coordinate system of the optical fiber, Fig. 5 shows the lateral pressure P/
FIG. 6, which is a graph showing the change in mode birefringence B with respect to L, is a cross-sectional view of an example of a conventional polarization-maintaining optical fiber ribbon.

Claims (1)

[Claims] In a polarization preserving optical fiber ribbon coated with resin, a plurality of elliptical clad polarization preserving optical fibers arranged in a plane parallel to each other in the longitudinal direction separated by a predetermined distance are coated with the elliptic clad polarization preserving optical fiber. The angle between the short axis of each elliptical clad of the plurality of optical fibers and a plane arranged parallel to the longitudinal direction and separated by the predetermined distance is always in the range of 45 degrees and 90 degrees. Polarization preserving optical fiber tape.