JPH05155642A - Production of expanded beam region forming single-mode fiber - Google Patents

Abstract

PURPOSE:To produce the subject fiber on which a beam size expanded region is previously formed at regular intervals over its entire length by heating the part of the fiber sufficiently shorter than the interval to a high temp. CONSTITUTION:An optical fiber preform is drawn to form a high-strength single- mode optical fiber (2-3) with a thin-film carbon formed around the clad over its entire length. The specified length of the fiber sufficiently smaller than a specified interval L is heated at a thousand several hundred degrees ( deg.C) for a specified time, and an expanded beam region forming single-mode fiber on which a beam size expanded region (2-4) having the beam size larger than that of the single-mode of its own is partially and periodically formed is produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous method for producing a single mode fiber with a partially enlarged beam size.

[0002]

2. Description of the Related Art In order to promote the introduction of single-mode optical fibers into various optical communication systems, simplification of connection technology between single-mode fibers and improvement of connection performance are important technical problems. In order to improve the connection characteristics between single-mode fibers, that is, to reduce the connection loss, it is necessary to precisely control the amount of misalignment between opposing fibers in the optical axis direction or in the direction perpendicular to the optical axis on the order of microns. Is. That is, the splice loss is determined by the degree of overlap of the beam size (mode field diameter) of the input / output fibers, and the mode field diameter of a normal single mode fiber is about 10 μm, so even if there is no spacing between fibers. In order to suppress the increase of splice loss to 0.5dB or less, it is necessary to highly accurately suppress the misalignment in the direction perpendicular to the optical axis to about 1μm, which hinders the economics involved in splicing and splicing work. It is a factor. As a method of relaxing the dimensional accuracy during optical axis alignment, in recent years, there has been a method of enlarging the mode field diameter in the vicinity of the input / emission side short part of the fiber to be opposed to about 20 to 30 μm, which is several times that of an ordinary fiber. Attempts have been made (eg JSHAPPER, et al., "TAPERS INSING
LE-MODE OPTICAL FIBRE BY CONTROLLED CORE DIFFUSIO
N ", ELECTRONICS LETTERS, Vol.24, No.4, 18th Februa
ry 1988 / K.SHIRAISHI et al., "FIBRE-EMBEDDED OPTICA
L ISOLATOR ", ELECTRONICS LETTERS, Vol.25, No.20,28
th September 1989). When these single-mode fibers with beam expansion regions are connected, the misalignment in the optical axis direction required to suppress the increase in splice loss to 0.5 dB or less is several hundred μm. The deviation in the vertical direction is significantly improved to a few μm. Moreover, even if an optical element of several hundred μm is inserted into the fiber gap due to the expansion of the mode field diameter, it is possible to suppress the increase in loss due to diffraction, and it is possible to realize an in-line type optical component with low insertion loss. In order to expand the mode field diameter of the fiber, the above-mentioned document reports a method of heating the fiber at a high temperature of several thousand and several hundred degrees Celsius for several minutes to several tens hours. This method is for refractive index control,
Injected into the core or cladding of the optical fiber
This is a method in which a dopant such as Ge or fluorine is diffused to the clad side or the core side at a high temperature to expand the refractive index distribution, that is, the mode field diameter. For heat diffusion, a bare fiber of a specified length is placed in an electric furnace and partially subjected to high temperature treatment, but handling bare fiber easily causes damage such as breakage, resulting in poor workability. In addition, there is a problem in that it is difficult to control the temperature distribution in the furnace and it is difficult to heat-treat a large number of fibers simultaneously with good reproducibility. Also, when applying this type of single mode optical fiber to connection products and optical parts at various places, as mentioned above, large-scale and expensive equipment such as an electric furnace and various manufacturing techniques are used for producing the fiber. However, it is difficult to obtain the fiber and it is difficult to apply it.

[0003]

SUMMARY OF THE INVENTION In order to solve the above-mentioned drawbacks of the prior art, the present invention provides a predetermined length along the length of a single mode fiber at a predetermined length which is sufficiently shorter than the predetermined length. It is an object of the present invention to provide a method for manufacturing an expanded beam region forming single mode fiber in which a portion of 1 is heated at a high temperature and the expanded region of the beam size is formed continuously continuously over a long length.

[0004]

The present invention is a method of manufacturing a high-strength single-mode optical fiber in which thin-film carbon is formed over the entire length, and a predetermined interval is provided to obtain a beam size larger than the beam size peculiar to this single-mode fiber. Regions having a large beam size are periodically formed, and the protective resin layer is partially colored so that the beam size enlarged portion can be identified. A single-mode fiber in which the beam size expansion region is periodically formed over a long length is superior in reproducibility and mass productivity to the one obtained by heat-treating a conventional short bare fiber in an electric furnace. The application of the single mode fiber is also much easier.

[0005]

EXAMPLE FIG. 1 shows a single mode fiber preform (1-
From (1) to an outer diameter of 125 μm φ, on the surface of the fiber (1-2) drawn using the drawing furnace (1-3), by the vapor phase growth system (1-5) for carbon thin film deposition, It shows a process of continuously forming several hundreds of carbon thin film layers. 1-4 and 1-7 are fiber outer diameter measuring instruments. An optical fiber with a carbon thin film formed by depositing a thin carbon layer on the surface in this way (1-8)
Has excellent mechanical strength and can be wound directly onto a drum (1-6) as shown in FIG.

The carbon thin film-formed optical fiber (1-8) produced in FIG. 1 is then subjected to the steps shown in FIG.
A portion of the illustrated beam size expansion region (2-4) is locally heated to a few hundreds of hundreds of degrees Celsius by the heating device (2-5) at a predetermined interval L. By this heating, for example, Ge contained in the core portion of the fiber is diffused to the cladding side, the refractive index is also distributed to the cladding side, and as a result, the beam size is expanded. The extent to which the beam size is expanded is proportional to the heating temperature and the heating time. A plurality of heating devices are arranged at the intervals, and after the fibers are heated for a predetermined time,
It is wound by a drum, moved through the interval, stopped, and heated again. By repeating this, the heating time is accumulated and the beam size is expanded to a predetermined size. When the fiber is heated and transferred while rotating the drum at a low speed, the outer diameter is likely to be deformed due to the softening of the fiber.However, by stopping the fiber during heating like this method, It becomes possible to prevent deformation. In FIG. 2, 2-1 is a drum and 2-
2 is a capstan, and 2-3 is a carbon thin film-formed optical fiber. As described above, in order to facilitate the protection and handling of the carbon thin film-formed fiber in which the beam expansion region is formed at the predetermined interval L, in the step shown in FIG. 3, a protective resin layer (3-4 ) Is formed. That is, FIG.
In the above, the carbon thin film forming fiber (3-2) in which the beam size expansion region is partially formed is the resin coating device (3
-3), a protective resin layer (3-4) is formed on the surface,
Further, a predetermined coloring paint is applied to the surface of the protective resin layer in the same area portion by a sprayer or a roller type coloring device (3-5) so that the enlarged beam size area can be identified. In FIG. 3, 3-1 is a drum and 3-6 is a colored portion.

FIG. 4 shows a cross section of a single-mode optical fiber core wire with a partial beam size expansion region produced by the steps shown in FIGS. 1 to 3 above, and 4-1 is obtained by heating. The beam size expansion area, 4-2 is the protective resin layer, 4-3 is the colored part for identifying the beam expansion area applied to the surface of the protective resin layer, and 4-4 is a single area with a periodic beam size expansion area. The mode fiber cores are shown respectively. Such a single-mode optical fiber with a partial beam expansion region is cut at the colored part that shows the beam expansion region, the resin layer is removed over a specified length to expose the clad layer, and it is inserted and fixed in a ferrule or the like. It is applied to optical connectors.

There are various methods for partially heating the fiber at a high temperature as shown in FIG. That is, FIG.
, (A) shows heating means by gas burner or discharge, (b) shows high frequency or heater heating means, and (c) shows self heating means using part of carbon thin film forming fiber as a resistor. Any of these methods or a combination thereof can efficiently locally heat the fiber. In FIG. 5, 5-1 is a beam size expansion region, 5-2 is a burner or discharge heating device, 5-3 is a resistance or high frequency heating device, and 5-4 is an electrode.

FIG. 6 shows an example in which a single mode optical fiber manufactured by the manufacturing method of the present invention is cut in a beam size expansion region and applied to various optical parts. b) shows an example applied to a semiconductor laser diode module, and (c) shows an example applied to fiber collimation.

That is, in FIG. 6 (a), in the single mode optical fiber core wire (6-4) with a partial beam expansion region, the protective resin layer is removed in the vicinity of the colored part (6-3), and the beam size is reduced. The cladding of the enlarged region (6-1) is exposed and inserted into and fixed in the small diameter hole of the ferrule (6-5). The ferrule tip is optically polished, and the connector housing (6-7) is mounted around the ferrule metal fitting (6-6) to complete the optical connector plug (6-8). The single mode fiber mounted optical connector plugs whose beam size is expanded at the tip end are connected by the adapter (6-9) as shown in the figure, but the beam size of the opposing fiber is expanded. Therefore, the dimensional accuracy of the precision ferrule (6-5), which is the heart of the connector article, is greatly eased to the order of several μm from the conventional submicron order, which can contribute to the economicalization of the connector. Further, deterioration of the connectivity due to temperature fluctuations, shocks and vibrations, and even the inclusion of minute dust into the connection portion is significantly alleviated as compared with a fiber having a normal mode size, and high reliability of the connector becomes possible.

FIG. 6B shows an example in which a single mode optical fiber manufactured by the manufacturing method of the present invention is cut in a beam size expansion region and applied to a semiconductor laser diode module. In Fig. 6 (b), 6-2 is a single mode fiber with a periodic beam size expansion region, 6-10 is a semiconductor laser diode chip, 6-11 is a spherical lens, 6-12.
Is a heat sink and 6-13 is a stem. The beam size of the semiconductor laser diode is 1 μm to 2 μm, and when it is combined with an ordinary single mode fiber having a beam size of 10 μm, good coupling efficiency can be obtained due to the difference in beam size. For this reason, a coupling system is adopted in which a lens is arranged over the entire surface of the laser diode and the size of the emitted beam is made the same as that of the fiber to enhance the coupling efficiency. The same strict dimensional accuracy is required as in the connection of one mode. The dimensional accuracy, that is, the tolerance indicating the rate of deterioration of the coupling efficiency with respect to the optical axis shift is relaxed in the connection between optical elements having a large beam size. For this reason, as shown in the figure, the assembly workability of the laser diode can be greatly improved by the coupling structure in which the beam expansion region forming fiber and the lens capable of obtaining the beam size of this fiber are arranged in the vicinity of the entire surface of the laser. ..

When the beam-size expanding fibers are arranged opposite to each other, it is good for diffraction and the increase in connection loss is greatly alleviated, and a fiber type collimator having a structure without using a lens can be formed.

FIG. 6 (c) shows that the partial beam size expanding fibers according to the present invention are arranged opposite to each other, and the optical path of the collimated beam formed in the space between the fibers is controlled by the prism (6-14). Optical switch circuit. It should be noted that the single mode optical fiber forming the beam size expansion region is not restricted in terms of the relative refractive index difference, the presence or absence of a dispersion shift condition, and the presence or absence of a polarization preserving function.

[0014]

As described above, according to the present invention, a high-strength single-mode optical fiber formed by depositing thin-film carbon over the entire length is heated at a predetermined interval in a plurality of places at a high temperature to partially heat the same. The beam size expansion area is periodically and collectively formed, and after the protective resin layer is applied to the fiber, the same area on the protective resin layer surface is colored so that the beam size expansion area can be identified. Is a method for producing a partially expanded beam size single-mode optical fiber, which enables the beam size expansion region to be periodically formed over a long length with good reproducibility, and is also applied to optical circuit components. It is possible to improve the property.

[Brief description of drawings]

FIG. 1 is a diagram showing a step of forming a carbon thin film layer on a clad surface by a vapor phase growth apparatus in a drawing step of an optical fiber preform.

FIG. 2 is a diagram showing a process of heating a drawn carbon thin film fiber at high temperature at a plurality of locations at a predetermined interval L by a plurality of heating devices at the same time to periodically form a beam size expansion region. Is.

FIG. 3 is a diagram showing a step of applying a protective resin layer to the outer periphery of the expanded beam size forming fiber and coating the expanded beam size area identifying colored portion.

FIG. 4 is a surface showing a structure of a single mode optical fiber core wire with a partial mode size expansion region completed by the above process.

5A is an explanatory diagram of a gas burner or discharge heating method as a heating method in the step shown in FIG. 2. FIG. (b)
FIG. 3 is an explanatory diagram of a resistance or high frequency heating method as a heating method in the step shown in FIG. (c) is an explanatory view of a self-heating method of carbon thin film forming fiber specific resistance as a heating method in the process shown in FIG. 2.

FIG. 6A is a diagram showing an example in which a single-mode optical fiber manufactured by the manufacturing method of the present invention is cut in a beam size expansion region and applied to an optical connector. (b) is a diagram showing an example in which a single mode optical fiber manufactured by the manufacturing method of the present invention is cut in a beam size expansion region and applied to a semiconductor laser module. (c) is a diagram showing an example in which a single mode optical fiber manufactured by the manufacturing method of the present invention is cut in a beam size expansion region and applied to an optical switch circuit.

[Explanation of symbols]

1-1 Single-mode fiber preform 1-2 Drawing silica fiber 1-3 Drawing furnace 1-4 Fiber outer diameter measuring instrument 1-5 Vapor phase growth equipment for carbon thin film deposition 1-6 Drum 1-7 Fiber outer diameter Measuring instrument 1-8 Carbon thin film forming optical fiber 2-1 Drum 2-2 Capstan 2-3 Carbon thin film forming optical fiber 2-4 Beam size expansion area 2-5 Heating device 3-1 Drum 3-2 Periodic beam size Carbon thin film fiber with expansion area 3-3 Resin coating equipment 3-4 Protective resin layer 3-5 Coloring equipment 3-6 Colored area 4-1 Beam size expansion area 4-2 Protective resin layer 4-3 Colored area 4-4 Single-mode fiber core with periodic beam size expansion region 5-1 Beam size expansion region 5-2 Gas burner or discharge heating device 5-3 Resistor or high frequency heating device 5-4 Electrode 6-1 Beam size expansion region 6-2 Period Single-mode fiber with dynamic beam size expansion area 6-3 Coloring section 6 -4 Single-mode fiber core wire with periodic beam size expansion area 6-5 Ferrule 6-6 Ferrule metal fitting 6-7 Connector plug housing 6-8 Connector plug 6-9 Adapter 6-10 Semiconductor laser diode chip 6-11 Ball lens 6-12 Heat sink 6-13 Stem 6-14 Prism

Claims (4)

[Claims] 1. A high-strength single-mode optical fiber in which thin-film carbon is formed over the entire length of the outer peripheral surface of a clad by an optical fiber preform drawing process, and a predetermined interval is provided, which is sufficiently smaller than this interval. Heating a range of lengths to a few hundreds of degrees Celsius for a predetermined time to periodically form a beam size expansion region having a beam size that is partially larger than the beam size specific to the single mode fiber. And a method of manufacturing a single mode fiber for forming an expanded beam region. 2. The method for manufacturing an expanded beam region forming single mode fiber according to claim 1, wherein when forming the expanded beam region by heating, a carbon thin film formed high strength single mode optical fiber wound on a drum is formed. In the process of being wound on the other drum via a plurality of capstans, the optical fibers are stopped at a portion of a plurality of heating devices provided between the capstans for a predetermined period of time, and then heated. The expanded beam area forming single mode fiber characterized by forming a beam expanded area at a predetermined interval over a long length by winding the length again and then stopping again to reheat the same place, and repeating this. Production method. 3. The method for manufacturing an expanded beam region forming single mode fiber according to claim 1, wherein a protective resin layer is applied to an outer peripheral surface of the carbon thin film forming single optical mode fiber having a partially expanded beam size. When forming
A method for manufacturing an expanded beam region forming single mode fiber, characterized in that the resin layer in the expanded beam size region is colored so that the expanded beam size region can be identified. 4. The method of manufacturing an expanded beam region forming single mode fiber according to claim 1, wherein the heating method of the fiber is any one of gas burner, electric furnace, high frequency heating, and resistance heating of carbon thin film forming fiber itself. A method of manufacturing an expanded beam region forming single mode fiber characterized by using a method.