JP4102702B2 - Manufacturing method of optical fiber coupler - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing an optical fiber coupler La for branching and coupling light propagated through the optical fiber, and more particularly to a method of manufacturing an optical fiber coupler La to reduce the temperature dependence of the insertion loss.
[0002]
[Prior art]
In the field of optical fiber communication, optical fiber couplers are widely used as optical devices for branching optical power into two or more branches. FIG. 10 is an external view (a) of a general optical fiber coupler and a CC cross-sectional view (b) at the optical coupling portion of the optical fiber coupler.
[0003]
As shown in FIG. 10 (a), the optical fiber coupler 101 prepares two optical fibers from which the intermediate coating is removed, and the two clads 105 exposed by the coating removal are parallel to each other at 1700 ° C. It was produced by melt drawing at the above high temperature.
[0004]
In the optical fiber coupler 101 having the above configuration, when light is incident from one end, it is branched at a predetermined branching ratio by the optical coupling portion and emitted from the other end. This branching ratio is determined by the mode coupling state between the optical fibers generated when the two optical fiber cores are brought close to each other. FIG. 11 is a schematic diagram showing an optical coupling state generated between such optical fibers. This optical fiber coupler 101 is a combination of port 1 and port 3 and port 2 and port 4 originally one continuous optical fiber. When the distance between the cores of two optical fibers is narrowed and fused using the Fused Taper Method, the light incident on the port 1 is coupled to the optical fiber on the port 2 side, Light is emitted.
[0005]
The types of the optical fiber coupler 101 shown in FIG. 11 can be classified into a wavelength flat type optical fiber coupler whose branching ratio hardly depends on the wavelength, and a WDM type optical fiber coupler that greatly depends on the wavelength. FIG. 12 is a graph showing optical coupling characteristics of the flat wavelength optical fiber coupler and the WDM optical fiber coupler. The branching ratio of the wavelength flat type optical fiber coupler can be arbitrarily set, but here, a general 3 dB branching is shown.
[0006]
In the wavelength flat type optical fiber coupler shown in FIG. 11, the propagation constant of the optical fiber from port 1 to port 3 and the propagation constant of the optical fiber from port 2 to port 4 are made different from each other, as shown in FIG. As shown, almost constant coupling characteristics in a wide light wavelength range are achieved.
[0007]
On the other hand, in the WDM type optical fiber coupler, the propagation constant of the optical fiber from the port 1 to the port 3 is equal to the propagation constant of the optical fiber from the port 2 to the port 4, and the coupling characteristic varies periodically depending on the wavelength. To do.
[0008]
Among such types of optical fiber couplers, in order to manufacture a wavelength flat type optical fiber coupler, the outer diameters of the optical fibers are different in advance so that the propagation constants of a plurality of optical fibers to be coupled are different. Need to be processed. For this purpose, it is necessary to reduce the diameter of only some of the same optical fibers used as the material of the optical fiber coupler.
[0009]
As shown in FIG. 10B, the cross section of such an optical fiber coupler 101 includes a first core 103a and a second core 103b contained in one clad 105, and one core (here) Then, the first core 103a) has a smaller cross-sectional area than the other core (second core 103b).
[0010]
Further, when the distance from the center point 0 of the cladding 105 to the center point of the first core 103a and the distance from _{L 1,} the center point 0 to the center point of the second core 103b and _{L 2,} the distance _{L 1} and The relationship L ₁ > L ₂ is established in the distance L ₂ , and the first core 103 a and the second core 103 b are arranged asymmetrically with respect to the X ₀ axis in the drawing in the clad 105.
[0011]
Further, the cladding diameter W ₂ which covers the periphery of the second core 103b is thicker than the cladding diameter W ₁ covers the peripheral portion of the first core 103a, to clad sectional shape in the drawing X ₀ axis as a whole The shape is asymmetric.
[0012]
Next, a manufacturing method of the wavelength flat type optical fiber coupler will be described in detail with reference to FIGS.
[0013]
First, as shown in FIG. 13 (a), as a first step, two silica optical fibers cut to a predetermined length (usually several meters) are prepared. Next, using a mechanical or chemical method, the coating 107 in the vicinity of the middle portion of each optical fiber is removed by a predetermined length (usually several tens of millimeters), and the clad 105 is exposed. FIG. 13B shows a cross-sectional view of the clad AA with the clad 105 exposed. At this time, the core outer diameter R ₀ and the clad outer diameter D ₀ of the two optical fibers have the same outer diameter.
[0014]
Next, as shown in FIG. 14, as a second step, one of the two optical fibers is thinned. The small-diameter size is intended to make a clad having a diameter of 125 μm, for example, approximately 110 μm in diameter. As a method for reducing the diameter, a pre-taper method or an etching method is generally used, but the diameter can also be reduced by a flame polishing method. The diameter reduction of the clad by the pretaper method is disclosed in Japanese Patent Publication No. 6-40167. According to this publication, the pretaper method is a method in which a predetermined portion of one optical fiber clad is melt-heated with a heat source and pre-stretched before the melt-stretching step to be performed in the next step, thereby obtaining a desired thinned cladding. is there. At this time, the propagation constant of the optical fiber changes. On the other hand, the etching method is disclosed in JP-A-6-265749. According to this publication, before the melt drawing process, only a predetermined portion of the other optical fiber clad is immersed in hydrogen fluoride (also referred to as HF or hydrofluoric acid), and the quartz constituting the clad is eluted to reduce the diameter. This is a method for obtaining a modified cladding. According to this, the propagation constant of the optical fiber at this time does not change. The flame polishing method is a method of obtaining a thin clad by heating the clad at a high temperature to 1700 ° C. or higher by using an oxyhydrogen (2H ₂ + O ₂ ) burner and vaporizing the quartz component of the surface layer. . Of the three stretching methods described above, FIG. 14B shows a BB cross section of the optical fiber clad 105a thinned by the pretaper method and the optical fiber 105b not thinned. As shown in the figure, a core outer diameter of the reduced diameter optical fiber 105a is R _1, the cladding outer diameter is D _1. A relationship of D ₀ > D ₁ is established between the clad diameter D ₀ before thinning and the clad diameter D ₁ after thinning. Similarly, the relationship of R ₀ > R ₁ holds for the core outer diameter.
[0015]
Next, as shown in FIG. 15, as a third step, the clad diameter-reduced optical fiber 105 a and the normal clad diameter optical fiber 105 b are bonded using a melt drawing method. The coupled optical fiber coupler 101 has a 2 × 2 shape as the number of ports sandwiching the optical coupling unit 109 in appearance. When the port 2 is unnecessary in actual use, the port 2 may be cut by an appropriate method and used in a state where the number of ports is 1 × 2 in appearance.
[0016]
According to the above manufacturing method, there is an advantage that a branching / coupling device can be manufactured with an optical fiber and that the structure is simple and can be used as a standard for optical branching / coupling for optical fiber communication.
[0017]
[Patent Document 1]
Japanese Patent Publication No. 6-40167 [0018]
[Patent Document 2]
Japanese Patent Laid-Open No. 6-265749
[Problems to be solved by the invention]
By the way, according to the conventional manufacturing method described above, the wavelength flat type optical fiber coupler can be manufactured. However, if the temperature change in the atmosphere where the wavelength flat type optical fiber coupler is actually installed is large, there is a problem that the insertion loss fluctuation due to the temperature change of the wavelength flat type optical fiber coupler becomes large.
[0020]
FIG. 16 shows a case where this wavelength flat type optical fiber coupler is applied to an optical amplifier placed in an optical line of a high-density wavelength division multiplexing (DWDM) transmission system of an optical communication network trunk system. FIG. According to this configuration, the input / output optical power level propagating through the optical fiber main line can be known. In general, this optical amplifier is often installed outdoors, and is exposed to external environmental changes. For this reason, if the insertion loss of a wavelength-flat type optical fiber coupler for input / output optical power monitoring varies due to temperature changes, it is as if the optical power propagating in the optical fiber main line has fluctuated, resulting in a system design problem. .
[0021]
FIG. 17 shows an optical power level of each wavelength emitted from a light source laser diode (hereinafter referred to as LD) of a DWDM transmission system in which a wavelength flat type optical fiber coupler is arranged at a subsequent stage of a wavelength poly-multiplexer. Therefore, a part is branched for monitoring. This apparatus is generally installed indoors, but there is still a problem that the monitor light fluctuates when the optical characteristics of the wavelength flat optical fiber coupler fluctuate due to a change in room temperature.
[0022]
FIG. 18 is a diagram for distributing optical signals (1490 nm, 1550 nm) transmitted from the station side by cascading wavelength-flat type optical fiber couplers in an equally branched manner to a large number of subscribers connected to the end. It is a figure which shows the structure of the equal branch splitter for PON. Since this form is mainly installed outdoors, it is necessary to reduce fluctuations in optical characteristics due to temperature changes over a wide wavelength range (1250 to 1600 nm) over a wide temperature range (−40 ° C. to + 85 ° C.). is there.
[0023]
The wavelength flat type optical fiber coupler manufactured by processing the outer diameters of the two optical fibers differently in advance is obtained by melting and stretching two optical fibers having different outer diameters. The shape of the optical coupling portion in which the fibers are integrated and reduced in diameter is inevitably an asymmetric shape. On the other hand, since the refractive index of the optical fiber and thus the quartz glass constituting the optical coupling part has a temperature dependency, the optical coupling state in the optical coupling part changes due to the temperature change, which causes the optical characteristics of the optical fiber coupler. Shows temperature dependence.
[0024]
For this reason, in the conventional wavelength flat type optical fiber coupler, since the shape of the optical coupling part and the arrangement of the core are asymmetric, the fluctuation of the optical coupling due to the change in the refractive index increases, and as a result, the temperature dependence of the optical characteristics increases. There is a problem. This temperature dependence is less than 0.1 dB with an insertion loss of a general 3 dB branch coupler, so it has hardly been a problem so far, but there is a demand for higher performance of optical components with the development of optical fiber communication technology. Therefore, the temperature dependence is required to be reduced more than ever.
[0025]
The present invention has been made in view of the above, as its purpose is to insertion loss temperature fluctuations to provide a method of manufacturing a very small optical fiber coupler la.
[0027]
[Means for Solving the Problems]
To achieve the above object, the present invention according to claim 1, the two optical fibers of identical structure cross section covering the core and the core cross-section having a substantially circular comprising a cladding having a substantially circular, mutually A method of manufacturing an optical fiber coupler having an optical coupling portion formed by melt-stretching adjacent portions formed along or parallel to each other and being aligned or twisted, wherein the two optical fibers include: A first diameter reduction process for reducing the diameter of one optical fiber to a predetermined cross-section outer diameter using a first diameter reduction method in which only the cladding is cut off, and the other optical fiber is reduced in diameter for both the core and the cladding. A second diameter reduction step for reducing the outer diameter to a predetermined cross section using the second diameter reduction method, and an optical fiber reduced in diameter in the first and second diameter reduction steps in parallel. Adjoining or twisting, adjoining or twisting together And summarized in that and a melt-drawing step of melt-drawing.
[0028]
The present invention described in claim 2 is the method of manufacturing the optical fiber coupler according to claim 1 , wherein the first diameter reduction method is an etching method or a flame polishing method, and the second diameter reduction method is a pretaper method. It is a summary.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0030]
FIG. 1 is an external view (a) of an optical fiber coupler 1 manufactured according to the present invention, and a CC cross-sectional view (b) at an optical coupling portion of the optical fiber coupler.
[0031]
As shown in FIG. 1 (a), an optical fiber coupler 1 is produced by melt-drawing two silica-based optical fibers from which coating has been removed in advance at a high temperature of 1700 ° C. or more along parallel. is there. At this time, the two optical fibers are obtained by reducing the diameter of an optical fiber having the same outer diameter at the same ratio by a different method.
[0032]
As shown in FIG. 1B, the cross section of the optical fiber coupler 1 includes a first core 3a and a second core 3b included in one clad 5, and the first core 3a The cross-sectional area is the same as the cross-sectional area of the second core 3b or a small cross-sectional area.
[0033]
Further, the distance L ₀ from the center point 0 of the clad 5 and the center point of the first core 3a, the distance L ₀ from the center point 0 to the center point of the second core 3b are both have equal distance . Therefore, the first core 3a and the second core 3b are arranged symmetrically with the center point 0 as a boundary.
[0034]
Further, the cladding diameter W ₀ that covers the peripheral portion of the first core 3a, to become a cladding diameter W ₀ are both the same size for covering the periphery of the second core 3b, the cladding cross-sectional shape as a whole Figure 1 (b ) in, and has a symmetrical shape with respect to X ₀ axis.
[0035]
The optical fiber used in the present invention is, for example, a single mode optical fiber having a cross-sectional diameter of 250 μm formed by coating a bare optical fiber having a core diameter of 10 μm and a cladding diameter of 125 μm with UV resin or the like. The optical fiber is not limited to this, and may be a dispersion shifted optical fiber, a polarization maintaining optical fiber, a multimode optical fiber, or the like.
[0036]
As apparent from FIG. 1, two cores 3a, the center of 3b are equidistant L ₀ axisymmetric with respect to the center line X ₀ axis orthogonal to the major axis axis Y after the two optical fibers melt drawing is doing. By this structure, the influence on the optical coupling state due to the expansion / contraction of both cores 3a, 3b and the change in the relative refractive index of the cores 3a, 3b and the clad 5 due to temperature fluctuation is offset, and the optical coupling state is balanced. As a result, it is considered that the insertion loss temperature fluctuation amount can be kept small.
[0037]
Therefore, in the optical fiber coupler manufactured by the present invention, the distance L ₀ from the center point 0 of the clad 5 to the center point of the first core 3a and the center point 0 to the second point in the cross-sectional configuration of the optical coupling portion. The distance L ₀ to the center point of the core 3b is equidistant, and the first core 3a and the second core 3b are arranged symmetrically with respect to the cladding center point 0 as a boundary, thereby changing the optical coupling due to the refractive index change. As a result, the temperature dependence of the optical characteristics can be reduced.
[0038]
Next, with reference to FIG. 2 to FIG. 4, the manufacturing method of the optical fiber coupler of the present invention will be described in the order of steps.
[0039]
First, as shown in FIG. 2, in the method for manufacturing an optical fiber coupler, two silica optical fibers cut to a predetermined length (usually several meters) are prepared as a first step. Next, using a mechanical or chemical method, the coating 7 in the vicinity of the intermediate portion of the optical fiber is removed by a predetermined length (usually several tens of mm), and the cladding 5 is exposed. FIG. 2B shows a cross-sectional view of the clad AA with the clad 5 exposed. At this time, both the core outer diameter R ₀ and the clad outer diameter D ₀ of the two optical fibers are set to the same outer diameter.
[0040]
Next, as shown in FIG. 3, as the second step, the two optical fibers prepared in the first step are reduced in diameter using different methods. In other words, one of the optical fibers is reduced in diameter by using an etching method until a clad with a diameter of 125 μm is approximately 110 μm. The other optical fiber is thinned by using a pretaper method to make a clad having a diameter of 125 μm to a diameter of approximately 110 μm. The method for reducing the diameter is not limited to the pretaper method and the etching method, and a flame polishing method may be applied instead of the pretaper method, or a flame polishing method may be applied instead of the etching method. That is, at this time, the two optical fibers are reduced in diameter by different methods. FIG. 3B shows a cross-sectional view of the clad BB in a state where the diameter is reduced. As shown in the figure, only the clad of the optical fiber 5a is cut away using an etching method. Therefore, although cladding diameter is reduced to D _1, the outer diameter of the core 3a has a R ₀ having the same diameter as before diameter reduction. On the other hand the optical fiber 5b is because it extends collectively clad 5b and the core 3b with Puritepa method, the clad diameter is reduced to D _1, a core 3b diameter is also reduced to R _1.
[0041]
Next, as shown in FIG. 4, as a third step, the optical fiber 5a that has been thinned by an etching method and the optical fiber 5b that has been thinned by a pre-taper method are bonded together using a melt drawing method. FIG. 4B shows a cross-sectional view of the coupled optical coupling part 9 taken along the line C-C. According to this, since the optical fiber of the same outer diameter is reduced in a different method and at the same ratio, the distance from the cross-sectional center point 0 of the optical coupling portion 9 to the core 3a center point, The distance from the cross-sectional center point 0 of the optical coupling part 9 to the core 3b center point can be made equal. Thus, the cores 3a and 3b can be arranged symmetrically with the center point 0 as a boundary.
[0042]
Next, specifications of the optical fiber coupler having the above configuration will be described with reference to FIGS.
[0043]
As shown in FIGS. 5A to 5C, in the optical fiber coupler 1 in which two optical fibers are melt-bonded, the incident light intensity to the port 1 is P1 [mW], and the emitted light from the port 3 When the intensity is P3 [mW] and the intensity of light emitted from the port 4 is P4 [mW], the coupling ratio [%] (Coupling Ratio, hereinafter referred to as CR) of the two optical fibers is expressed by the equation (1) (or It can be calculated from FIG.
[0044]
CR = (P4 / P3 + P4) × 100 (1)
An insertion loss IL13 [dB] (Insertion Loss, hereinafter referred to as IL) received when light is propagated from port 1 to port 3 can be calculated from equation (2) (or FIG. 5C). .
[0045]
IL13 = −10 log ₁₀ (P3 / P1) (Formula 2)
Furthermore, the insertion loss IL14 [dB] received when light propagates from port 1 to port 4 can be calculated from equation (3) (or FIG. 5C).
[0046]
IL14 = -10log ₁₀ (P4 / P1) (Formula 3)
Next, FIG. 6 shows the temperature dependence measurement result of the insertion loss characteristic of the optical fiber coupler 1 of the present invention. In addition, FIGS. 7 and 8 show Comparative Examples 1 and 2, which are compared with an optical fiber coupler manufactured by a manufacturing method different from the present invention.
[0047]
With respect to the wavelength flat type optical fiber coupler manufactured by using the manufacturing method of the present invention, insertion loss was measured under the respective conditions of temperatures of −40 ° C., + 23 ° C., and + 85 ° C. As shown in FIG. 6, the difference between the maximum value and the minimum value of the insertion loss temperature with respect to the temperature change of −40 to + 85 ° C. is measured in the optical wavelength range of 1250 to 1600 nm, and the fluctuation amount is expressed as ΔIL13 (t), ΔIL14 (t ). As a result, the fluctuation amount ΔIL13 (t) and the fluctuation amount ΔIL14 (t) were both 0.02 dB or less.
[0048]
On the other hand, the temperature dependence characteristic of the insertion loss shown in FIG. 7 shows that the wavelength flat type optical fiber manufactured using an optical fiber whose cladding diameter is reduced to 110 μm by a pretaper method and a normal optical fiber having a cladding outer diameter of 125 μm. It is that of a coupler. In this optical fiber coupler, the insertion loss temperature variation with respect to the temperature change of −40 to + 85 ° C. in the light wavelength region of 1250 to 1600 nm was 0.08 dB on average.
[0049]
Further, the temperature dependence characteristics of the insertion loss shown in FIG. 8 indicate that the wavelength flat type optical fiber manufactured using an optical fiber whose cladding diameter is reduced to 110 μm by an etching method and a normal optical fiber having a cladding outer diameter of 125 μm. It is the characteristic of what produced the coupler. In this optical fiber coupler, the insertion loss temperature fluctuation with respect to the temperature change of −40 to + 85 ° C. in the light wavelength region of 1250 to 1600 nm was 0.09 dB on average.
[0050]
Therefore, from the above measurement results, when producing a wavelength flat type optical fiber coupler, the cladding diameters of a plurality of adjacent optical fibers are reduced in the pre-process for melt drawing and the cladding diameters are made equal. This indicates that the temperature dependence of the insertion loss can be made extremely small.
[0051]
Therefore, by the manufacturing method of the present invention, that is, the method of manufacturing an optical fiber coupler from a plurality of optical fibers that have been processed to have the same outer diameter in the portion constituting the optical coupling portion, the temperature of the optical characteristics is increased. An optical fiber coupler with reduced dependency can be obtained.
[0052]
The optical fiber coupler manufactured by the method of the present invention has a stable insertion loss characteristic in a wide temperature range (−40 to + 85 ° C.) over a wide optical wavelength band (1250 to 1600 nm), so that the change in environmental temperature is Applicable to large outdoor facilities.
[0053]
The above prototype measurement results were obtained for 2 × 2 or 1 × 2 (same for 2 × 1) optical fiber couplers, which are all made of two optical fibers. The present invention is an n × n, 1 × n (same as n × 1), m × n (same as n × m) multiport coupler made of a plurality of (n) optical fibers of 2 or more. Are all applicable. Here, n = 2, 3, 4... (Integer), m = 1, 2, 3... (Integer), and n> m.
[0054]
9A and 9B show a modification of the optical fiber coupler manufactured according to the present invention. FIG. 9A is a diagram showing an example of a diameter reduction process when three optical fibers are combined. FIG. 9B is a diagram showing an example of a diameter reduction process when four optical fibers are coupled.
[0055]
Here, it is assumed that the optical fibers adjacent to each other are reduced in diameter by a different method when the diameter is reduced. That is, the cladding 5a is reduced in diameter by an etching method, the cladding 5b is reduced in diameter by a flame polishing method, and the cladding 5c is reduced in diameter by a pretaper method. At this time, even if the diameter reduction method is different, all the clad diameters must have the same outer diameter. Therefore, if it has the said structure, even if it is several optical fiber, the effect similar to the effect of the optical fiber coupler produced with two optical fibers can be acquired. At this time, if there are a plurality of optical fibers that are not used for the incident port, they may be reduced in diameter by the same method. FIG. 9C shows an example in the case of a 1 × 3 coupler.
[0056]
【The invention's effect】
Therefore, according to the present invention, it is possible insertion loss temperature dependency provides a method for producing a very small optical fiber coupler la.
[Brief description of the drawings]
FIG. 1 is an external view (a) of an optical fiber coupler manufactured according to the present invention and a CC cross-sectional view (b) of an optical coupling portion.
FIG. 2A is a view showing a coating removing process in the manufacturing process of the optical fiber coupler of the present invention, and FIG.
FIG. 3A is a diagram showing a cladding diameter-reducing step in the manufacturing process of the optical fiber coupler of the present invention, and FIG.
FIG. 4A is a diagram showing a fusion bonding process in the manufacturing process of the optical fiber coupler of the present invention, and FIG. 4B is a cross-sectional view taken along the line CC of the optical fiber coupler.
FIG. 5 is a specification definition of an optical fiber coupler.
FIG. 6 is a graph showing temperature dependence characteristics of insertion loss of an optical fiber coupler manufactured according to the present invention.
7 is a graph showing temperature dependence characteristics of insertion loss of Comparative Example 1. FIG.
8 is a graph showing temperature dependence characteristics of insertion loss of Comparative Example 2. FIG.
FIG. 9 is a diagram showing an example of a joint diameter reduction process for adjacent optical fibers.
10A is an external view of a conventional optical fiber coupler, and FIG. 10B is a cross-sectional view taken along line CC of the optical coupling portion.
FIG. 11 is an image diagram showing a propagation state in the optical fiber coupler.
FIG. 12 is a characteristic graph comparing characteristics of a flat wavelength optical fiber coupler and a WDM optical fiber coupler.
FIG. 13A is a view showing a coating removing process in a conventional manufacturing process of an optical fiber coupler, and FIG. 13B is a sectional view taken along line AA of the optical fiber coupler.
FIG. 14A is a diagram showing a cladding diameter reduction process in a conventional optical fiber coupler manufacturing process, and FIG. 14B is a cross-sectional view taken along line BB of the optical fiber coupler.
FIG. 15A is a diagram showing a melt-bonding process in a manufacturing process of a conventional optical fiber coupler, and FIG.
FIG. 16 is a diagram showing a configuration when a wavelength flat type optical fiber coupler is applied for input / output light monitoring in an optical amplifier.
FIG. 17 is a diagram showing a configuration in a case where a wavelength flat type optical fiber coupler is applied for in-line monitoring of an optical fiber main line.
FIG. 18 is a diagram showing a configuration when a flat wavelength optical fiber coupler is applied to a branching ratio splitter for a PON (Passive Optical Network).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Optical fiber coupler 3a, 3b ... Core 5 ... Cladding 7 ... Optical fiber coating 9 ... Optical coupling part 101 ... Optical fiber coupler 105a ... Clad thinning optical fiber 105b ... Normal clad diameter optical fiber 107 ... Optical fiber coating 109 ... Optical coupling part

Claims (2)

Two optical fibers having the same configuration consisting of a core having a substantially circular cross section and a clad having a substantially circular cross section covering the core are aligned or twisted in parallel with each other, and adjacent to each other. A method of manufacturing an optical fiber coupler having an optical coupling portion formed by melting and stretching a portion,
A first diameter reduction step of reducing one of the two optical fibers to a predetermined cross-section outer diameter using a first diameter reduction method in which only the cladding is cut off;
A second thinning step of thinning the other optical fiber to a predetermined cross-sectional outer diameter using a second thinning method in which both the core and the clad are thinned;
The optical fiber thinned in the first and second thinning steps, along or twisted in parallel, a melt stretching step of melt stretching the adjacent portion formed along the twisted or twisted,
An optical fiber coupler manufacturing method comprising: Wherein the first diameter reduction method is an etching method or flame polishing method of the optical fiber coupler according to claim 1, wherein the second diameter reduction process is characterized in that a Puritepa method.

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