JPH01169410A - Optical fiber - Google Patents

Abstract

PURPOSE:To improve a bending light loss characteristic by constituting the title optical fiber of a central core having a specific refractive index difference DELTAto a core and clad and a peripheral core which has the specific refractive index difference DELTA' smaller than the specific refractive index difference DELTA and is added to the periphery of the central core. CONSTITUTION:The core of the optical fiber is formed of the central core 1 and the peripheral core 2 added to the outside circumference of the central core 1. The optical fiber is constituted by disposing the clad 3 to the outside of the peripheral core 2. Namely, the core is constituted of the entire part added with the peripheral core 2 having the specific refractive index difference DELTA' smaller than the specific refractive index difference DELTA of the central core 1 with respect to the clad to the outside circumference of the central core 1. The max. specific refractive index difference of the cores maintains about the same mode field diameter as the mode field diameter of the conventional optical fiber according to this constitution and the bending light loss is improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an optical fiber having a zero dispersion wavelength in the vicinity of 1.3 μm, and in particular to a core structure of a single mode optical fiber with improved bending optical loss characteristics. It is related to.

[Conventional technology]

Optical fibers widely used in optical fiber cables and the like have a zero dispersion wavelength of around 1.3 μm. The refractive index distribution shape of such conventional optical fibers is a simple step type, and the relative refractive index difference of the core is 0.
It is 3% to 0.4%.

FIG. 2 shows the refractive index distribution shape of this type of conventional optical fiber. 1 is the central core, 3 is the cladding portion, Δ〃 is the relative refractive index difference, and a is the radius of the central core 1.

[Problem that the invention seeks to solve]

When a conventional optical fiber having the refractive index distribution illustrated in FIG. 2 is used to form a cable, there is a problem that microbending loss and bending light loss when storing the excess length of the cable connection portion increase.

FIG. 3 shows the transmission loss characteristics with respect to wavelength before and after making a cable using a conventional optical fiber. ■Characteristics before cableization and ■Characteristics after cableization.

[Means for solving problems]

The present invention solves the conventional problems and provides an optical fiber with improved bending optical loss characteristics, and has a zero dispersion wavelength of 1.3.
In a single mode optical fiber having a cladding on the outer periphery of a core in the vicinity of μm, the core has a central core having a relative refractive index difference Δ with respect to the cladding, and a central core having a relative refractive index difference Δ′ smaller than the relative refractive index difference Δ. and a peripheral core added to the periphery of the central core, the refractive index of the central core having a distribution that decreases from the center of the core toward the outer circumference, and It is characterized by including an embodiment in which the maximum relative refractive index difference of the central core is in the range of 0.25% to 0.4%.

[For production]

In order to make the conventional optical fiber with the simple step refractive index distribution shown in Fig. 2 more resistant to bending, it is possible to reduce the core diameter and increase the relative refractive index difference. Optical fibers with such a core structure have the following problems. That is, as the amount of dopant in the core or cladding increases, scattering loss increases. Furthermore, by reducing the core diameter, the mode field diameter becomes smaller, which is disadvantageous when connecting optical fibers. Furthermore, the zero dispersion wavelength is significantly shifted toward longer wavelengths based on the relative refractive index difference and core diameter.

In order to solve the above problems, the optical fiber of the present invention has the following advantages:
Since the core is made up of the outer periphery of the central core and a peripheral core with a relative refractive index difference Δ′ smaller than the relative refractive index difference Δ with respect to the central core with respect to the cladding, the maximum relative refractive index difference of the central core is the same as that of the conventional At the same level as a simple step type optical fiber,
It acts to improve the bending optical loss characteristics while keeping the mode field diameter at the same level. Examples will be described below based on the drawings.

〔Example〕

FIGS. 1a and 1b are diagrams showing the refractive index distribution of an embodiment of the optical fiber of the present invention. FIG. 1A shows an example showing the refractive index distribution of the basic type, and FIG. 1A shows an example showing the modified refractive index distribution of the basic type.

As shown in FIG. 1a, the core of the optical fiber of this embodiment is formed by a central core 1 and a peripheral core 2 added to the outer periphery of the central core 1. As shown in FIG. A cladding 3 is arranged outside the peripheral core 2. The optical fiber having such a configuration can improve bending optical loss without reducing the mode field diameter due to the influence of the peripheral core 2.

FIG. 4 is a diagram comparing the relationship between the bending optical loss and the bending diameter of the optical fiber for the optical fiber A according to the embodiment of the present invention and the conventional optical fiber B. That is, in the optical fiber according to the embodiment of the present invention shown in FIG. 1a and the conventional optical fiber B shown in FIG.
．． The bending optical loss when the specifications are determined as follows so that the mode field diameter is 25 μm and the mode field diameter is 9.011 m is shown using the bending diameter as a parameter.

That is, in the optical fiber A of this example, the relative refractive index difference of the central core is Δ=0.36%, and the relative refractive index difference of the peripheral core is Δ
' = 0.08%, core diameter 2 b -10,2, cr
mφ, a/b = 0.75, and in the conventional optical fiber B, the refractive index difference Δ” of the center core was set to 0.35%, and the center core diameter 2a = 8.3 μmφ.

Note that the zero dispersion wavelength is 1.31 for optical fiber A in this example.
μm, which is about the same as 1.30 μm for conventional optical fiber B.

As can be seen from FIG. 4, by using the optical fiber of the present invention, the bending optical loss can be improved by half while keeping the cutoff wavelength, mode field diameter, and zero dispersion wavelength at the same level.

The above has described an optical fiber according to an embodiment of the present invention having the refractive index distribution shown in FIG. However, the same improvement effect was observed.

〔Effect of the invention〕

As explained above, in the optical fiber according to the present invention, the entire core is formed from the central core and the peripheral cores having a relative refractive index difference smaller than the relative refractive index difference between the central core. It has the advantage of being able to maintain the index difference and mode field diameter to the same extent as conventional optical fibers and improve bending optical loss.

[Brief explanation of the drawing]

Figures 1a and b are the refractive index distribution of the optical fiber according to the present invention, Figure 2 is the refractive index distribution of the conventional optical fiber, Figure 3 is the change in optical transmission loss before and after being made into a cable, and Figure 4 is the optical FIG. 3 is a diagram showing bending optical loss with respect to the bending diameter of the fiber. 1... Central core, 2... Peripheral core, 3... Clad Patent applicant Sumitomo Electric Industries Co., Ltd. Agent Patent attorney Kugobe Tamamushi Refractive index distribution of optical fiber embodiment of the present invention No. 111g
1 Refractive index distribution of conventional optical fiber No. 211ii1 1.0 13 1.5 Wavelength (pm)
Changes in optical transmission loss before and after cable formation Fig. 3 Bending diameter (mm-) Bending optical loss system for optical 7 eyer bending diameter Fig. 4

Claims (2)

[Claims] (1) In a single mode optical fiber having a cladding on the outer periphery of a core having a zero dispersion wavelength of around 1.3 μm, the core includes: a central core having a relative refractive index difference Δ with respect to the cladding; and a central core having a relative refractive index difference Δ with respect to the cladding. An optical fiber comprising a peripheral core added around the central core and having a smaller relative refractive index difference Δ'. (2) The optical fiber according to claim 1, wherein the central core has a distribution in which the refractive index decreases from the center of the core toward the outer circumference.