JPS63121807A - Optical fiber - Google Patents

Abstract

PURPOSE:To extend the degree of freedom of constituting conditions for optimizing several characteristics of coating resin by forming an outermost peripheral clad layer contg. impurities which absorbs the light in the wavelength range applicable to optical communication, on the outermost periphery of the clad. CONSTITUTION:An outermost peripheral clad layer contg. impurities for absorbing the light in the wavelength range applicable to optical communication, particularly those having OH groups or transition metal ion such as Ni, Cr, Fe, Cu, Co, etc. is formed on the outermost peripheral layer of the clad in a quartz glass optical fiber comprising core and clad. For example, an outermost peripheral clad layer 3 contg. an impurity is formed on the external peripheral surface comprising a preform for single mode optical fiber of a clad 2 by melting a preform of optical fiber coated with SiO2 contg. Ni ion as transition metal ion by plasma vapor deposition in a heating furnace. Then, a resin curable with ultraviolet rays and having 1.42 refractive index is coated thereon, which is cured in an ultraviolet rays curing furnace to form a clad layer 4, thus an optical fiber is obtd. By this method, the degree of freedom of constituting conditions for optimizing several characteristics of the coating resin is extended.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical fiber composed of a core and a cladding for optical communication, and particularly relates to an improvement in the outer peripheral structure of the cladding.

[Conventional technology]

Since communication using an optical fiber is carried out by placing an optical fiber on the core mode light that propagates through the core, the cladding mode light that propagates through the cladding becomes a major interference during reception. Therefore, as a mechanism to facilitate attenuation of the cladding mode, conventionally, a coating layer having a refractive index higher than the refractive index of the cladding is used as the innermost layer of the coating layer applied around the cladding, that is, as an outer coating in contact with the cladding. By providing such a structure, light can easily pass from the cladding to the coating side. Figures 3a and 3b illustrate the cross-sectional structure and light propagation schematic diagram of a conventional optical fiber, where ■ is the core;
2 is a cladding, 4 is a covering layer having a refractive index higher than that of the cladding 2, and 5 is a covering layer having a refractive index lower than that of the covering layer 4. The arrow in Figure 3 indicates the light propagation of the cladding mode. , and the cladding mode is the coating layer 4.
is absorbed and attenuated.

[Problem that the invention seeks to solve]

In conventional optical fibers of this type, in order to attenuate the cladding mode, the innermost layer of the coating layer that is in direct contact with the cladding must have a refractive index higher than the refractive index of the cladding mode.

By the way, since the innermost layer of the coating layer is in direct contact with the cladding of the optical fiber, it must satisfy various characteristics such as special features such as attenuating the cladding mode, Young's modulus, elongation, curing characteristics, and temperature characteristics. . However, since the structure usually satisfies the requirement of having a higher refractive index than the cladding in order to attenuate the cladding mode, the constituent requirements of the coating resin to optimize the various characteristics mentioned above, that is, the chemical structure and There is a problem in that the degree of freedom in composition is unavoidably reduced.

[Means for solving problems]

In order to solve the conventional problems, the present invention provides a silica glass optical fiber consisting of a core and a cladding, in which the outermost layer of the cladding contains impurities, particularly OH groups or Ni, which absorb wavelength light in the wavelength range applicable to optical communications. Cr, Fe, C
It is characterized by having a structure including an outermost cladding layer mixed with impurities of transition metal ions such as u and Go.

[For production]

The present invention has a configuration in which the outermost layer of the cladding is mixed with an impurity that absorbs wavelength light in the wavelength range used for optical communication, so that the cladding mode propagating through the cladding is transmitted through the outermost layer of the cladding. Absorbed and attenuated.

Therefore, it is not necessary to make the refractive index of the innermost layer of the coating layer higher than the refractive index of the cladding, and the degree of freedom of the constituent elements for optimizing various properties of the coating resin is greatly expanded. Examples will be described below based on the drawings.

〔Example〕

FIGS. 1a and 1b illustrate schematic diagrams of the cross-sectional structure and light propagation of the optical fiber of the present invention, where 1 is the core, 2 is the cladding, and 3 is the outermost layer of the impurity-containing cladding. As shown by the arrow in FIG. 1, the cladding mode propagating through the cladding is absorbed and attenuated by the outermost layer 3 of the impurity-containing cladding.

FIG. 2 shows a cross-sectional structure of a specific embodiment of the optical fiber of the present invention. An optical fiber preform in which 5i02 containing Ni as an example of a transition metal ion was plasma-deposited on the outer peripheral surface of a single-mode optical fiber preform with a cladding 2 having a refractive index of 1.45 was heated and melted in a heating furnace. A line is drawn to have an outer diameter of 125 μmφ, and an ultraviolet curable resin with a refractive index of 1.42 is applied to the outside on which the impurity-mixed cladding outermost peripheral layer 3 is formed, and then the ultraviolet curable resin is cured in an ultraviolet oven to form the coating layer 4. An optical fiber with an outer diameter of 250 μmφ was prepared. The layer thickness of the outermost peripheral layer of the impurity-containing cladding was 2 μm. This produced optical fiber will be referred to as optical fiber sample 1.

In order to compare with optical fiber sample 1, a single mode optical fiber preform was drawn in the same manner as sample 1 described above without any treatment for impurities, and then coated with the same ultraviolet curing resin. Sample 2 of an optical fiber with an outer diameter of 250 μmφ and sample 3 of an optical fiber with an outer diameter of 250 μmφ coated with an ultraviolet curing resin having a refractive index of 1.54 were prepared.

The following table shows the results of measuring the amount of attenuation of each cladding mode of Samples 1.2 and 3 of the three types of optical fibers produced above. The cladding mode intensity was measured by NFP measurement to determine how many dB the light intensity attenuated at a position 5 μm away from the core center compared to the core center.

As is clear from the results shown in the above table, it was confirmed that the optical fiber having the structure of the present invention can eliminate the cladding mode even in the case of Sample 1 in which the refractive index of the coating layer is lower than the refractive index of the cladding.

In this example, transition metal ions such as Ni were mixed as impurities in the outermost layer of the cladding.
The same results were obtained even when transition metal ions such as e, Cu, and Co were mixed as impurities.

Furthermore, an optical fiber of the present invention was prepared in which OH groups were mixed as an example of other impurities. An oxygen/hydrogen flame was applied to the outer peripheral surface of a single-mode optical fiber preform whose cladding had a refractive index of 1.45 to mix OH groups into the outermost cladding layer, thereby forming an impurity-containing cladding outermost layer.

This preform is heated and melted in a heating furnace, and the outer diameter is 125μ.
A wire was drawn to mφ, and a coating layer of an ultraviolet curing resin similar to that of Example Sample 1 was applied. At this time, the layer thickness of the outermost peripheral layer of the OH group-containing hybrid was 4 μm. The cladding mode attenuation of this optical fiber is the result of NFP measurement similar to that described above.
2 dB/m, and similar to Sample 1, removal of the cladding mode was confirmed.

〔Effect of the invention〕

As described above, the optical fiber of the present invention has a structure in which the outermost cladding layer is mixed with an impurity that absorbs wavelength light in a wavelength range applicable to optical communication, so it is different from conventional optical fibers. Unlike fibers, it is not necessary to make the refractive index of the innermost layer in direct contact with the cladding layer higher than the refractive index of the cladding, which greatly expands the degree of freedom in configuration requirements for optimizing various properties of the coating resin. is big.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining an example of the optical fiber structure of the present invention, and FIG.
The figure is a cross-sectional structural diagram of an optical fiber embodiment of the present invention, and FIG. 3 is a diagram illustrating a conventional optical fiber structural example. 1... Core, 2... Clad, 3... Outermost layer of impurity-containing cladding, 4, 5... Coating layer Patent applicant Sumitomo Electric Industries, Ltd. Agent Patent attorney Tama Mushi Kugobe b Books FIG. 1 is a cross-sectional structural diagram of an embodiment of the optical fiber of the present invention. FIG. 3 is a diagram illustrating a conventional optical fiber structure.

Claims (3)

[Claims] (1) A silica glass optical fiber consisting of a core and a cladding, characterized in that the outermost periphery of the cladding is provided with an outermost cladding layer containing an impurity that absorbs wavelength light in a wavelength range applicable to optical communication. optical fiber. (2) The optical fiber according to claim 1, wherein the outermost clad layer contains an OH group as an impurity. (3) The optical fiber according to claim 1, wherein the outermost clad layer contains transition metal ions as impurities.