JP3074495B2 - Manufacturing method of optical fiber type optical branch coupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical fiber type optical branching coupler used for optical communication, optical measurement, etc., and more particularly, to an optical fiber type optical coupler having a small branching ratio with a small wavelength dependency. The present invention relates to a method for manufacturing a branch coupler. An optical fiber type optical branching / coupling coupler having a small wavelength dependence of a branching ratio has an advantage that it can be used for a large capacity optical communication and the like because it has the same optical transmission characteristics in a wide wavelength range. .

[0002]

2. Description of the Related Art Conventionally, one of the manufacturing methods of an optical fiber type optical branching coupler having a small wavelength dependency of the branching ratio is as follows.
There is a method as disclosed in JP-A-63-108311. That is, two single-mode optical fibers are used, one optical fiber is uniformly reduced in diameter in advance, and the other optical fiber is fused without being reduced in diameter, along the two optical fibers in parallel. There is a method of stretching and thereby manufacturing an optical fiber type optical branching coupler.

According to this manufacturing method, when two optical fibers are fused and drawn, the coupling from one optical fiber to the other optical fiber is, for example, 1.5 times as shown in FIG.
Long wavelength light such as 5 μm is, for example, 1.30 μm
Is achieved faster than short wavelength light such as

Therefore, conventionally, the wavelengths of 1.55 μm and 1.3
In the case of manufacturing an optical fiber type optical branching / coupling coupler in which the branching ratio is set to 50% for both lights of 0 μm and the branching ratio is less dependent on the wavelength, the light of 1.55 μm wavelength is branched. At a point past the peak of the ratio and at a wavelength of 1.30μ
For the light of m, a method of stopping the fusion stretching just before the peak of the branching ratio is adopted.

[0005]

In practice, a wavelength of 1.5
5 μm light is incident on the input side of one of the optical fibers, and fusion-stretching is performed while monitoring the light intensity coming out on the output side of both optical fibers. When the branching ratio seems to have peaked, fusion is performed. Stretching has been stopped.

As described above, in the related art, a method is employed in which a stop is performed in the vicinity of a position that is empirically known while looking at a curve of the output with respect to time in advance.
When the curve changes due to disturbance, or when the curve changes irregularly due to noise from peripheral devices, there has been a problem that the determination of the stop is likely to be erroneous. For this reason, it has been extremely difficult to manufacture an optical fiber type optical branching coupler having a constant quality and a small branching ratio with a small wavelength dependency.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical fiber type optical branching coupler having a constant quality and a small branching ratio with a small wavelength, efficiently and at a high yield without relying on the skill of an operator. An object of the present invention is to provide a manufacturing method that can be manufactured stably.

[0008]

The above object is achieved by a method of manufacturing an optical fiber type optical branching coupler according to the present invention.
In summary, the present invention uses two single-mode optical fibers, one optical fiber is reduced in diameter, and the other optical fiber is arranged in parallel without reducing the diameter. In the method of manufacturing an optical fiber type optical branching coupler by fusing and stretching, at the time of fusing and stretching of both optical fibers, the light output on the output side of at least one of the optical fibers is detected by a detecting means, and this detection is performed. A method for manufacturing an optical fiber-type optical branching / coupling device characterized by firstly differentiating a signal and stopping fusion-stretching of both optical fibers when the signal value becomes substantially zero.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing an optical fiber type optical branching coupler according to the present invention will be described below in more detail with reference to the drawings.

According to this embodiment, as shown in FIG. 4, first, the same single mode optical fibers f ₁ and f ₂ having a core diameter d and a cladding outer diameter D are prepared, and the optical fiber f ₁ The outer diameter D of the clad is reduced to a predetermined diameter D ′ by etching to form a reduced diameter portion f ₁ ′. Etching, etchant station on hydrofluoric acid or hydrofluoric acid and etch pit preventing agent (e.g., ammonium fluoride) Pour a small amount of etchant such as a mixed solution is carried out by contacting the optical fiber f ₁ in the etching solution be able to. The etching conditions can be variously changed depending on the desired diameter reduction amount, but usually the etching temperature is 30 to 60 ° C. and the processing time is 5 to 30 minutes.

Although the diameter of the optical fiber f ₁ is reduced by etching, the present invention is not limited to this. For example, mechanical polishing using abrasive grains may be employed. Further, if the original cladding diameter D of the optical fiber f ₁ is produced in the outer diameter D 'of the reduced径後, the diameter reduction step can be used as this may be omitted.
Further, if necessary, the optical fiber f ₁ is can be reduced in diameter by pre stretched to a predetermined diameter by heating.

Next, the reduced diameter portion f ₁ ′ of the optical fiber f ₁
When, the optical fiber f ₂ are placed along parallel to the longitudinal direction, attached to a fused and extended stand, fused stretched.

The fusion-stretching treatment can be performed according to a usual method, for example, a flame burner, a heater laser,
Using an appropriate heating device such as a small electric furnace, generally 1300
While heating at a temperature of ２０００2000 ° C., the fusion stretching table can be obtained by pulling the optical fiber to both sides in the axial direction, for example, via a rack-pinion mechanism at a speed of, for example, 0.005 to 100 mm / min.

According to the present invention, as shown in FIG. 1, when the two optical fibers f ₁ and f ₂ are fused and drawn, the LD light source 1 is connected to the input side of one of the optical fibers, in this embodiment, the optical fiber f _2.
From 00, monitor light of a predetermined wavelength, for example, 1.55 μm is incident, and the light output on the output side of at least one of the optical fibers is detected by detecting means, for example, a light receiving element 104 such as a photodiode , and converted into an electric signal. Convert.

The detection signal is transmitted to the computer 106, first differentiated by a differentiating circuit, and fusion splicing of both optical fibers is stopped when the value becomes substantially zero. This will be further described below.

FIG. 2 shows an example of an optical output from the output side of the optical fiber f ₂ and a curve obtained when the optical output is first-order differentiated.

In FIG. 2, the primary differential value increases as the fusion stretching proceeds and the light output increases. Furthermore, as the light output increases past the inflection point, the first derivative begins to decrease,
When the output reaches the peak, the first derivative becomes zero.

According to the present invention, even when the height of the output peak is not stable, the curve of the first derivative shows the same tendency as shown in FIG. 2 every time. Therefore, according to the present invention, even when the curve of the change of the light output with respect to time changes due to a disturbance or when the light output changes irregularly due to noise from peripheral equipment, it is possible to determine whether to stop the fusion stretching. There is no mistake.

As described above, the computer 106
Generates a stop signal when the first derivative becomes substantially zero, that is, when the first derivative becomes zero, or when the first derivative becomes a value close to zero. The stop signal is transmitted to the sequencer 108, and the heating device for fusion stretching is retracted via the sequencer 108, and the rack-pinion mechanism of the fusion stretching table is stopped.

With the above configuration, an optical branching coupler was actually manufactured, and the wavelength characteristics were evaluated. In the vicinity of the peak of the light output, the fusion / stretching was automatically stopped at the moment when the slope of the light output became the preset first derivative value, and as a result, the fusion / stretch was completed at almost the same timing each time. confirmed. Subsequently, the wavelength characteristics were evaluated using an optical spectrum analyzer. The results were as shown in FIG.

As can be seen from FIG. 3, the optical branching coupler obtained by the present invention has flat characteristics over a wide wavelength range of 1 micron band, that is, the wavelength dependence of the branching ratio is small, and It is understood that the fusion stretching was completed when the wavelength characteristics became smaller.

Further, the present invention will be described in detail with reference to examples.

Embodiment 1 As the single mode optical fibers f ₁ and f ₂ , an optical fiber having a core diameter (d) of 10 μm and a cladding diameter (D) of 125 μm is used, and the optical fiber f ₁ is made of hydrofluoric acid. Etching was performed at an etching temperature of 30 ° C. for a processing time of 10 minutes, and the cladding diameter was reduced to D ′ = 115 μm.

Next, the reduced diameter portion f ₁ ′ of the optical fiber f ₁
And the optical fiber f ₂ together with a flame torch for 1
While being heated to 500 to 1600 ° C., the wire was stretched at a rate of 0.8 mm / min by a length of about 5 mm to perform a fusion stretching process.

Simultaneously, 1.55 μm monitor light is incident on the input side of the optical fiber f ₂ from the LD light source 100, and the optical output on the output side of the optical fiber f ₂ is detected by the photodiode 104, and this electric signal is output. Was transmitted to the computer 106 provided with the differential operation circuit. This signal was first-order differentiated by a differentiating circuit of a computer, and fusion-stretching of both optical fibers was stopped when the value became zero.

In this way, a large number of optical fiber type optical couplers were manufactured. When the branching ratio of these optical fiber type optical branching couplers was measured at wavelengths of 1.55 μm and 1.30 μm, the branching ratio was approximately 50% at both wavelengths.

[0027]

As described above, according to the method for manufacturing an optical fiber type optical branching coupler according to the present invention, the operation such as differentiation is performed based on the data of the optical output of the optical fiber to be fused and drawn. Since the determination of the stop of the fusion stretching is automatically performed based on the result of the calculation, the determination of the stop is not mistaken.
For this reason, an optical fiber type optical branching / coupling coupler having a constant quality and a small branching ratio with a small wavelength can be manufactured at a high yield without relying on the skill of an operator.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a method for manufacturing an optical fiber type optical branching coupler according to the present invention.

FIG. 2 shows an example of a light output from an output side of an optical fiber to be fused and drawn, and a curve obtained when the light output is first-order differentiated.

FIG. 3 is a diagram showing a wavelength characteristic of a branching ratio of an optical fiber type optical branching coupler obtained by a manufacturing method of the present invention.

FIG. 4 is a diagram showing an example of an optical fiber used in the manufacturing method of the present invention.

FIG. 5 is a diagram showing a relationship between a coupling ratio, a wavelength, and an extension length in an optical fiber type optical branch coupler.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 LD light source 102 Fusing and stretching table 104 Detecting means (light receiving element) 106 Computer 108 Sequencer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 6/28

Claims (1)

(57) [Claims] 1. Two single-mode optical fibers are used, one optical fiber is reduced in diameter, and the other optical fiber is fused without being reduced in diameter. In the method of manufacturing an optical fiber type optical branch coupler by stretching, at the time of fusion stretching of both optical fibers,
Detecting the optical output on the output side of at least one of the optical fibers by the detecting means, first-order differentiating the detection signal, and stopping the fusion-stretching of the two optical fibers when the value becomes substantially zero. A method for producing an optical fiber type optical branching coupler.