JPS62272205A - Polarizing plane maintaining optical fiber - Google Patents

Abstract

PURPOSE:To improve a quenching ratio characteristic by dividing the refractive index distribution of an elliptical jacket in the circumferential direction thereof and constituting an optical fiber so as to have the refractive index lower than the reflective index of a clad in the major axis direction of the ellipse and the refractive index higher than a clad in the minor axis direction. CONSTITUTION:The clad 2 consisting of pure SiO2 glass is provided to the outside peripheral part of the core 1 consisting of the SiO2 glass added with Ge so as to enclose said part. The elliptical jacket 3 is provided to the outside peripheral part of the clad 2 so as to enclose the same. The elliptical jacket 3 consists of SiO2 glass added with P2O5 and B2O3 and has a large coefft. of expansion. The B2O3 is added at the higher ratio in the major X-axis direction thereof and the refractive index n1 lower than the refractive index n0 of the clad 2 is provided so that the cut off wavelength of the polarization mode in the major axis direction is longer. The P2O5 is added at the higher ratio in the minor Y-axis direction and the refractive index n2 higher than the refrac tive index n0 of the clad 2 is provided so that the cut off wavelength of the polarization mode in the minor axis direction is shorter. The quenching ratio is thus improved.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a polarization-maintaining optical fiber, and particularly to improvement of extinction ratio characteristics.

[Prior Art] Conventionally, elliptical jacket type fibers and panda type fibers as shown in FIGS. 5 and 6 have been used as polarization maintaining optical fibers.

In the elliptical jacket type fiber, the elliptical jacket 52 containing the cladding 51 is inside the support 62 containing the cladding 61 and in the panda type fiber.
The stress applying members 63 provided on both sides of the cores 53 and 6 are each made of a material having a large coefficient of thermal expansion, such as Sio2 glass added with B or P.
The structure is such that an anisotropic stress is applied to 4.

As a result, birefringence occurs in the cores 53 and 64, energy coupling between the two orthogonal polarization modes is suppressed, and only one polarization mode is propagated.

[Problems to be Solved by the Invention] However, in general, when manufacturing optical fibers, it is difficult to avoid variations in the refractive index and diameter in the longitudinal direction, and as a result, energy coupling occurs between two orthogonal polarization modes. Therefore, it was not possible to obtain a high extinction ratio of 1q. Therefore, if such a polarization-maintaining optical fiber is applied to a high-precision optical measurement system, the functionality of the system will deteriorate.

Therefore, if the birefringence of the fiber is increased in order to prevent energy coupling between orthogonal polarization modes, polarization dispersion will increase, and once mode coupling occurs, large pulse broadening will occur. This makes it particularly unsuitable for long-distance transmission systems.

Thus, an object of the present invention is to solve the problems of the above-mentioned prior art and to provide a polarization-maintaining optical fiber with an excellent extinction ratio.

[Means for Solving the Problems] In order to achieve the above object, the polarization-maintaining optical fiber of the present invention is provided with a cladding around the outer periphery of the core, and a cladding is provided on the outer periphery of the cladding. In a polarization maintaining optical fiber having a surrounding elliptical jacket, the refractive index distribution of the elliptical jacket is divided in the circumferential direction, and the refractive index distribution of the elliptical jacket is lower than the cladding in the major axis direction of the ellipse and above the cladding in the minor axis direction. It has a higher refractive index than the cladding.

[Function] By dividing the refractive index distribution of the elliptical jacket in the circumferential direction as described above, the elliptical jacket not only applies anisotropic stress to the core, but also suppresses the propagation of two orthogonal polarization modes. It has the function of directly realizing the characteristics.

Specifically, by making the elliptical jacket have a refractive index lower than that of the cladding in the major axis direction and higher than that of the cladding in the minor axis direction, the cutoff wavelength of the polarization mode in the major axis direction is long, and the cutoff wavelength of the polarization mode in the minor axis direction is long. The cutoff wavelength of the polarization mode becomes shorter.

Therefore, by bending or microbending this polarization maintaining optical fiber, an absolutely single polarization fiber can be easily constructed.

Note that the ellipticity of the elliptical jacket is preferably 10% or more in order to generate birefringence by applying stress to the core.

[Example] Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIGS. 1(a), 1(b), and 1(c) are cross-sectional views of a polarization-maintaining optical fiber according to an embodiment of the present invention, respectively.

They are a refractive index distribution diagram in the X-axis direction and a refractive index distribution diagram in the Y-axis direction. In the figure, reference numeral 1 denotes a core made of 5102 glass doped with Ge, and a cladding 2 made of pure 5i (h glass) is provided around the outer periphery of the core 1. An elliptical jacket 3 is provided around the outer periphery of the 5i0 to which P2O5 and 8203 are added.
2 glass has a large coefficient of thermal expansion, and in its major axis direction (X-axis direction), the amount of B2O3 added is large, and as shown in FIG. 1(b), it has a refractive index n1 lower than the refractive index no of the cladding 2. In the minor axis direction (Y-axis direction), the amount of P2O5 added is large, and as shown in FIG. 1(C), the refractive index n2 is higher than the refraction *no of the cladding 2.

Furthermore, this is enclosed on the outer periphery of this oval jacket 3!
A support 4 made of pure 5102 glass is provided to do so.

The polarization maintaining optical fiber having such a configuration is manufactured as follows.

First, as shown in FIG. 2, P2O5 is placed on the inner surface of the quartz tube 5.
-8202 doped 5i02 glass layer 6 is deposited by MCVD with increased P2O5 doping. At this time, since the quartz tube 5 is not rotated, the quartz tube 5 is heated only from the top and bottom directions in the drawing, and is deposited on the upper and lower inner surfaces of the quartz tube 5.

Next, the quartz tube 5 is rotated 90'' in the circumferential direction, and then a P2O5-8203-doped SiO2 glass layer 7 is applied to the upper and lower parts of the inner surface of the quartz tube 5, that is, the parts that have not yet been laminated. The quartz tube 5 is enlarged and deposited by the MCVD method.In this case as well, the quartz tube 5 is kept fixed without being rotated.

To prevent this, a core rod with a cladding (not shown) is inserted into the quartz tube 5, and the quartz tube 5 is contracted (carabous) while reducing the pressure, so that the glass layer 7 is aligned in the longitudinal direction of the glass FIJ.
An elliptical jacket portion with 6 located in the minor axis direction is formed to obtain an optical fiber preform. Then, the refractive index distribution of the core portion was measured, and the quartz tube was further overjacketed or the outer diameter of the wire was adjusted to form an optical fiber so as to obtain the desired cutoff wavelength.

In this way, the refractive index difference between core 1 and cladding 2 is reduced to 0.
7%, the refractive index in the major axis direction of the elliptical jacket 3 is -0.2% with respect to the cladding 2, and the refractive index in the minor axis direction is the same as that of the cladding 2.
A polarization-maintaining optical fiber of +0.2% with respect to the above was manufactured.

When the cutoff wavelength of this optical fiber was measured, it was 1.15 μs in the polarization mode in the long axis direction (X-axis direction) and 1.0 μs in the polarization mode in the short axis direction (Y-axis direction).

Furthermore, in order to construct an absolutely single polarization fiber, the manufactured optical fiber was coiled into a coil with a diameter of 30 am+.
When we measured the optical loss wavelength characteristics after winding it with m windings, we found that there was a large difference in attenuation between the two orthogonal polarization modes in the 1.3-wavelength band, as shown in Figure 3, and an extinction ratio characteristic of -45 dB was obtained. It was done. In other words, it has become possible to perform substantially absolute single polarization transmission in this wavelength band.

In the above example, after depositing the P2O5-8203-added 5ith glass layers 6 and 7 on the inner surface of the quartz tube 5 having a circular cross section, the glass layers 6 and 7 were changed into an elliptical cross-sectional shape when they were shrunk. P2O5-8203 is added to the inner surface of the quartz tube 15 having an elliptical cross section as shown in FIG.
i02 glass layers 16 and 17 may be deposited.

Furthermore, when constructing an absolutely single-polarized fiber, instead of winding the polarization-maintaining optical fiber of the present invention into a coil as described above, the outer periphery of the fiber is coated with plastic, and micro-bending is caused by the contraction of the fiber. You can also use

〔Effect of the invention〕

As explained above, according to the present invention, the following excellent effects are exhibited.

(1) Extremely high extinction ratio characteristics can be obtained, and substantially absolute single polarization transmission can be performed.

(Thus, by applying the polarization-maintaining optical fiber of the present invention to optical communication systems, optical measurement systems, etc. that utilize polarization and phase, it is possible to improve the functionality and accuracy of the system. , it is also suitable for long-distance transmission systems.

[Brief explanation of drawings]

FIGS. 1A to 1C are cross-sectional views of polarization-maintaining optical fibers according to embodiments of the present invention. A refractive index distribution diagram in the X-axis direction and a refractive index distribution diagram in the Y-axis direction,
Figure 2 shows the example fiber! A cross-sectional view for explaining the LJ manufacturing method, FIG. 3 is an optical loss wavelength characteristic diagram when the fiber of the example is coiled, FIG. 4 is a cross-sectional view showing the manufacturing method of another example, and FIG. and FIG. 6 are cross-sectional views of general polarization-maintaining optical fibers. In the figure, 1 is the core, 2 is the cladding, 3 is the oval jacket,
4 is support.

Claims (2)

[Claims] (1) In a polarization maintaining optical fiber in which a cladding is provided around the outer periphery of the core and an elliptical jacket is provided around the outer periphery of the cladding, the refractive index of the elliptical jacket is 1. A polarization-maintaining optical fiber characterized in that the distribution is divided in the circumferential direction of the ellipse, and the refractive index is lower than that of the cladding in the major axis direction of the ellipse and higher than that of the cladding in the minor axis direction. (2) The polarization-maintaining optical fiber according to claim 1, wherein the elliptical jacket has an ellipticity of 10% or more.