JPS58223102A - Optical fiber conserving plane of polarization and its manufacture - Google Patents

Abstract

PURPOSE:To attenuate unnecessary light shifting to the other optical axis speedily and to obtain a large quenching rate by providing a light absorbing part which contains transition elements diffused onto either one of characteristic axes of polarization differing in light propagation constant to the outer circumference of a jacket enclosing a core. CONSTITUTION:A couple of grooves 2 are formed at facing positions in the internal surface of a quartz pipe support 1; and quartz wires 3 containing a large quantity of a transition metal such as Fe, Cu, and Pd are inserted into the grooves 2 and an SiO2 glass film is deposited in the support 1 to a specific thickness and heated to form an intermediate collapse. Then, the elliptic jacket 5 containing much B2O3, a clad 6 of SiO2, and the core 1 in the form of an SiO2 layer containing GeO2 are deposited successively in the collapse and while the pressure in the collapse is reduced, a base material made solid by being heated is drawn to obtain a polarization-plane conserving optical fiber which has light absorving parts 4a and 4b of the quartz wire 3 on the short axis of the jeacket 5. Then, a polarized signal coincident with the long-axis direction of the jacket 5 is sent as a less-noise polarized signal of good quality because the polarization in the short-axis direction of the jacekt 5 due to variation in external stress of the optical fiber, etc., is absorbed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber used for optical communications, and more particularly to a polarization-maintaining optical fiber and a method for manufacturing the same.

By applying asymmetrical stress to the core of a single-mode optical fiber, we create eigenpolarization axes (hereinafter referred to as fast and slow axes) with different optical propagation constants, reducing the coupling of light between the two axes and changing the polarization of the incident polarization. Polarization-maintaining optical fibers, which can maintain wavefronts over long distances, have many features such as the ability to obtain information about the polarization plane of light that passes through both axes, so they are widely used for measurement and various types of sensors. Is possible.

The most common method of use is to input linearly polarized light in the fast axis or slow axis direction, and transmit various information on this linearly polarized light. Irregularities in the interface between claddings,
Alternatively, a phenomenon occurs in which some optical coupling occurs due to changes in external stress, and light leaks from the fast axis to the slow axis.

Note that the value obtained by converting the amount of light transferred from one axis to the other axis in Denbel terms is called the extinction ratio, and is used as a parameter indicating the conservation of the plane of polarization.

The light transferred to the other axis due to such optical coupling is
Since it acts like noise on the information signal, it is necessary to reduce this amount as much as possible. In conventional polarization-maintaining optical fibers, the rate of transmission loss was the same for light propagating along the fast axis and light propagating along the slow axis, so noise light once transferred to other axes does not attenuate as much, so a large extinction ratio can be obtained. However, it has had the disadvantage of permanently preventing optical signals from being damaged.

The present invention solves the drawbacks of the prior art described above, and provides a polarization-maintaining optical fiber that can quickly attenuate unnecessary light transferred to other axes and easily obtain a large extinction ratio, and a method for manufacturing the same. The purpose and first feature is that a light absorption section is provided around the core on either the fast axis or the slow axis other than the optical transmission axis, and the light absorption part is installed on either the fast axis or the slow axis other than the optical transmission axis, and the light absorption part is installed on either the fast axis or the slow axis other than the optical transmission axis. The reason is that the structure is such that the transmitted light is absorbed and attenuated.

However, the second feature is that a pair of grooves are provided in the axial direction on the inner surface of the support quartz tube, which is the outermost layer, and after inserting a quartz glass wire containing a transition element into this groove, a normal MOV
The method consists of sequentially depositing a jacket, a cladding, and a silica glass layer as a core, and drawing a solid base material by heating while reducing the pressure inside the core layer.

FIG. 1 is an explanatory diagram of a method for manufacturing a polarization-maintaining optical fiber, which is an embodiment of the present invention. A quartz glass wire 6 containing the above is inserted. The support 1 is heated to soften the quartz glass wire 6 and fit into the groove 2, thereby making the inner surface of the support 1 smooth.

FIG. 2 is a cross-sectional view of a polarization-maintaining optical fiber manufactured using the support 1 shown in FIG. ing. Further, a circular core 7 covered with a cladding 6 is installed in the center of the elliptical jacket 5.

When a polarized signal whose polarization plane coincides with the long axis direction of the elliptical jacket 5 is input into the core 7 of such a polarization maintaining optical fiber, the polarization plane coincides with the short axis direction of the elliptical jacket 5 due to the optical coupling due to the above-mentioned causes. Polarized light is generated.

However, since the light absorption parts 4a and 4b exist in this direction and absorb light, the optically coupled noise signal is quickly attenuated, and only the normal signal that coincides with the long axis direction of the elliptical jacket 5 is transmitted. Therefore, it is possible to transmit high-quality polarized signals with less noise. That is, a signal with a large extinction ratio can be obtained.

Next, a method for manufacturing this polarization-maintaining optical fiber will be summarized. Support 1, which is the starting quartz tube in Figure 1, has an outer diameter of 2
Using a fused silica tube with a diameter of 0 mm and an inner diameter of 17#, a groove 2 having a width and depth of 0.2 rmO was made by treating it with hydrogen fluoride water, and a large amount of transition metals such as Fe', Ou, and Pd were added to this groove 2. Insert a quartz wire with a diameter of about 0.15 mm. This quartz wire is MC! which is used in normal optical fiber manufacturing. Using the VD method, a large amount of transition metal is mixed as an impurity into the starting material PoC1H to create a base material, which is then drawn into a wire, which is generally colored.

After forming support 1 in FIG. 1 in this way, MC
A 5i02 glass film is deposited on the inner surface of the support 1 to a thickness of 20 to 60 μm by the vD method and heated at a high temperature. In this case, the outer diameter of support 1, which is the starting quartz tube, is 1 to 2 m.
Although it is reduced in size, this is called the Intermediate Calabuse. This makes the inner surface of the support 1 smooth, and also diffuses the components of the quartz glass wire 6 containing the translucent metal into the vicinity, but when the product is manufactured, this part becomes the light absorption part 4a shown in FIG. , 4b, and absorbs light due to its coloring.

After that, the cladding 6, which is an elliptical jacket 5.8102 layer containing a large amount of B and 08 and giving an asymmetrical stress to the core 7, and the core 1, which is a SiO By doing this, a base material for a polarization-maintaining optical fiber having a cross-sectional structure as shown in FIG. 2 is obtained, and when this is drawn, a desired polarization-maintaining optical fiber is obtained.

An example of a polarization-maintaining optical fiber obtained in this way is that when used with light at a wavelength of 0.86 μm, the transmission loss of polarized light propagating along the first axis is 10 dB/km.
, the transmission loss of polarized light propagating along the slow axis is 60 dB/Km.
It quickly absorbs the light that leaks through optical coupling. The beat length, which indicates the preservation of the plane of polarization, was as small as 6 or less for light with a wavelength of 63 mm, and the extinction ratio was 40 dB or more at 1Kr11.

The polarization-maintaining optical fiber of this example can greatly differ the transmission loss of polarized light propagating in two orthogonal polarization planes, so disturbances applied to the transmission line can cause optical coupling and cause other polarization The light that has migrated to the wavefront is rapidly attenuated. Therefore, it has the effect that an excellent optical fiber with a large extinction ratio can be obtained.

The polarization-maintaining optical fiber of the present invention and its manufacturing method can quickly attenuate unnecessary light transferred to other polarization planes and easily obtain a large extinction ratio, and can be manufactured using conventional methods. The effect is that it is easily possible using .

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a method for manufacturing a polarization-maintaining optical fiber according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of a polarization-maintaining optical fiber manufactured using the support shown in FIG. 1. . 1: Support, 2: Groove, 6: Silica glass wire containing transition element, 4: Light absorption section, 5: Elliptical jacket, 6: Clad, 7: Core. 1st] 2nd (2) Run length/l □ l

Claims (1)

[Claims] 1. In a polarization-maintaining optical fiber in which asymmetric stress is applied to the core of a single-mode optical fiber to provide intrinsic polarization axes with different light propagation constants, any of the intrinsic polarization axes around the core 1. A polarization-maintaining optical fiber characterized in that a light absorbing portion is provided on one axis so that transmitted light leaked from the other axis is absorbed and attenuated by optical coupling. 2. The polarization-maintaining optical fiber according to claim 1, wherein the light absorbing portion is a portion containing a transition element diffused on the intrinsic polarization axis on the outer periphery of a jacket surrounding the upper core. 3. In a method for manufacturing polarization-maintaining optical fibers that have unique polarization axes with different optical propagation constants by applying an asymmetric stress to the core of a single-mode optical fiber, a pair of grooves are formed on the inner surface of a support quartz tube that is the outermost layer. After inserting a silica glass wire containing a transition element into this groove, a normal MO
A method for manufacturing a polarization-maintaining optical fiber, which comprises sequentially depositing a jacket, a cladding, and a quartz layer as a core by a VD method, and drawing the heated solid base material while reducing the pressure inside the core layer. .