JPH03168707A - Production of optical coupler - Google Patents

Abstract

PURPOSE:To produce an optical coupler having a specified wavelength pitch by controlling the drawing condition based on the monitored data on the branching ratio of the optical coupler when drawn. CONSTITUTION:Two optical fibers with a coat at its intermediate part removed are allowed to get close to each other in parallel, mounted on a drawing stage 40 and fixed. One end 20a of the fiber is irradiated with the light from sources 44 and 45 in an optical switch 46, other ends 20b and 20c are connected to power meters 47 and 48, and the uncoated regions are heated to fuse both ends together. At a certain point of time in drawing, the branching ratio monitored by an optical signal of plural wavelengths having a desired pitch is compared with that obtained when the optical coupler having a desired wavelength pitch is produced, the heating region or heating rate is feedback- controlled by a controller 49 based on the comparison result, and drawing is carried out. The optical coupler having a desired wavelength pitch is obtained in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for manufacturing an optical coupler, and in particular, the present invention relates to a method for manufacturing an optical coupler.
The present invention relates to a method of manufacturing an optical coupler that demultiplexes and multiplexes optical signals.

[Conventional technology]

As an optical coupler for demultiplexing and multiplexing optical signals, there is an optical fiber type multiplexing/demultiplexing optical coupler in which a plurality of optical fibers are melted and coupled together. As a conventional example of a method for manufacturing such an optical coupler, the method shown in FIG. 11 is known. In this conventional method, in a first step 10, the intermediate portions of the two optical fibers are uncoated. Second step 11
Then, the optical fibers from which the coating has been removed are placed close to each other so as to be parallel to each other, and then installed in a manufacturing device. Then, in the third step 12, the optical fiber. 1.31μm at one end of each
A light source capable of selectively injecting light with a wavelength of 1 or 1.55 μm is connected to the other end of the optical fiber, and a power meter is connected to each end. Next, in the fourth step 13, predetermined regions of the two optical fibers from which the coating has been removed are heated, and FM! Then, in a fifth step 14, it is stretched. During this stretching, the branching ratio is monitored while monitoring the output of the power meter, and when this branching ratio reaches a predetermined value (sixth step 15), the stretching is stopped (seventh step 16), and the heating (eighth step 17) to manufacture an optical coupler.

A method of monitoring the branching ratio to ensure where to stop the drawing is disclosed in Japanese Patent Laid-Open No. 63-17.
This is shown in Japanese Patent No. 5812.

In addition, the relationship between the heating region length of the fiber, which is a manufacturing condition for manufacturing a multiplexing/demultiplexing optical coupler, and the wavelength interval of demultiplexing/multiplexing (hereinafter referred to as wavelength pitch), which is one of the important characteristics of a multiplexing/demultiplexing optical coupler. The results of the study are presented by M.Eisenman, E.B.
E. Weldel) published a paper (SINGLE-MODE)
PUSED BICONICAL COUPLERS
FORWAVE LENGTH DIVISION M
ULTIPLEXING WITH IANNEL
SPACING BETWEEN 100ns AND
300ni).

In order to set the wavelength pitch of the light to be demultiplexed and multiplexed by the fiber-type demultiplexing/combining optical coupler to a predetermined value, we determined the width of the heating area that would be the optimal condition based on the above paper, and manufactured the optical coupler based on this. In addition, optical couplers were manufactured by accurately determining the timing to stop the stretching in accordance with the above-mentioned patent publication.

[Problem to be solved by the invention]

However, in the optical couplers manufactured as described above, the wavelength pitch varies depending on the actual fusion state, various heating conditions during stretching, etc. Therefore, it is difficult to manufacture optical couplers with a predetermined wavelength pitch. was difficult.

An object of the present invention is to solve the above problems and provide a method for manufacturing an optical coupler having a predetermined wavelength pitch.

[Means to solve the problem]

In the method for manufacturing an optical coupler of the present invention, the stretching conditions are controlled based on monitoring data of the branching ratio of the optical coupler during manufacture, so that the branching ratio of the optical coupler being manufactured is adjusted to at least 2 or more wavelengths during heating and stretching. The method is characterized in that heating and stretching is performed by controlling the moving width or moving speed of the heating means based on a comparison result between the observed branching ratio and a predetermined value while observing with light.

[Effect]

The wavelength pitch of the optical coupler depends on the heating conditions during stretching, specifically the moving width and moving speed of the heating means. Furthermore, the branching ratio of the optical coupler during manufacture changes periodically with respect to the amount of stretching, and furthermore, this amount of change differs depending on the injection wavelength.

Therefore, in the method for manufacturing an optical coupler of the present invention, the branching ratio of the optical coupler is adjusted by using at least two wavelengths of light having a wavelength pitch required for the optical coupler during the manufacturing of the optical coupler. monitor. Then, the branching ratio of the optical signal of each wavelength at a certain point during stretching is set to a predetermined value,
Specifically, it is compared with the branching ratio obtained during the manufacture of an optical coupler having a desired wavelength pitch, and based on the comparison result, feedback control of the heating conditions, specifically the heating region or heating rate, is performed. Then, by this feedback control, spreading is always performed under appropriate heating conditions, and an optical coupler having a desired wavelength pitch is manufactured.

〔Example〕

Embodiments according to the present invention will be described below with reference to the drawings.

Elements with the same reference numerals have the same functions, so duplicate explanations will be omitted.

FIG. 1 shows an example of a manufacturing flowchart of a method for manufacturing an optical coupler according to the present invention.

Further, FIG. 2 shows an example of a schematic configuration of an optical coupler manufacturing apparatus for carrying out the above manufacturing flowchart shown in FIG. 1.

As shown in FIG. 2, the optical coupler manufacturing device
The stretching stage 40 is movable in the axial direction (X direction) of the fixed optical fiber 2o, and can stretch the fixed optical fiber 20. Further, the head cover manufacturing apparatus is equipped with a burner 41 which is a heating means for heating the optical fiber 2o,
This burner 41 is fixed on a burner stage 42 that is movable in the axial direction (X direction) of the optical fiber 20 fixed to the stretching stage 40 and in the direction perpendicular to this axial direction (Z direction). It is possible to move in the direction. Further, this burner stage 42 is also movable, for example, on an arc with respect to the optical fiber 20 by combining the X and Z directions.

The burner 41 burns oxygen gas and hydrogen gas to generate heat, and the burner 41 includes a mass flow meter (flow rate controller) 43 that controls the amount of oxygen gas and hydrogen gas supplied to the burner 41, respectively.
Oxygen and hydrogen supply sources are connected via a and 43b.

Furthermore, in this optical coupler manufacturing equipment, 1.31 μm and 1.55 μm, which are to be multiplexed and demultiplexed, are added to the optical coupler during heating and stretching.
Light sources 44, 45 of light with a wavelength of μm and these light sources 44
, 45, one end 20 of the optical coupler is selectively producing light from 45.
It is equipped with an optical switch 46 for injecting from a. In addition, a power meter 947, 48 for observing the branching state of the injected light at the optical coupler is installed at the other end 20b of the optical coupler being manufactured.
, 20c. and,
These optical switch 46, power meters 47, 48, burner stage 42, stretching stage 40, and mass flow meters 43a, 43bG are connected to a control device 49, and this control device 49 is connected to a computer 50 that controls them.

Then, using this apparatus, the manufacturing flowchart illustrated in FIG. 1 is carried out.

In the manufacturing flowchart of the optical coupler according to the present invention shown in FIG. 1, first, in a first step 30, the coating at the intermediate portion of two optical fibers is removed, and in a second step 31, the optical fibers from which the coating has been removed are connected to each other. The optical fibers are mounted and fixed on the stretching stage 40 of the optical coupler manufacturing apparatus shown in FIG. Also, the other end of the optical fiber 20b120c
Power meters 47 and 48 are connected to the respective power meters 47 and 48, respectively. Next, in a fourth step 33, predetermined areas of the two optical fibers from which the coating has been removed are heated and fused. Next, in the fifth step 34, first, the traverse length p of the burner 41 and the burner speed 2 are set to predetermined initial values pSvo, and stretching is performed.

0 Next, in the sixth step 35, during this stretching, the optical switch 46 is first set to inject light with a wavelength of 1.31 μm from the light source 44 from one end 20a of the optical fiber, and the power meters 47 and 48 output Pl1P2. While monitoring the branching ratio. When this branching ratio reaches a predetermined value, for example 50%, the optical switch 46 is switched, light with a wavelength of 1.55 μm from the light source 45 is injected, and the branching ratio is measured.

Then, in the seventh step 36, this measured wavelength 1
．． Compare the branching ratio of the light of 55 μm with the value obtained during the manufacture of the optical power p plastic with a predetermined wavelength pitch, specifically λ −240 nm, and based on this comparison value, e.g. Then, the traverse length ρ or the burner speed ■ of the burner 41 is changed, and the extension is performed. Traverse length D from the fifth step 34 to the seventh step 36
Or repeat it a predetermined number of times while changing the burner speed V.

Then, in the eighth step 37, when the branching ratio reaches a predetermined value, specifically 100%, for the optical signal with a wavelength of 1.31 μm, the movement of the stretching stage 40 is stopped and the stretching is stopped. Then, in a ninth step 38, the optical coupler is heated and stretched and molded to complete the optical coupler.

The inventor investigated manufacturing conditions for stabilizing the wavelength pitch λ to a predetermined value, for example, 240 nm.

First, two optical fibers with a cladding diameter of 125 μm were
The relationship between the amount of stretching and the wavelength pitch was investigated by fusion and stretching in parallel. It is generally known that the relationship between the amount of stretching and the branching ratio is as shown in FIG. 3(a). That is, as shown in FIG. 3(a), the branching ratio changes periodically with respect to the amount of stretching, and the state of the change differs depending on the wavelength.

Therefore, the two optical fibers mentioned above are fused and stretched, and the wavelength is changed from one end as shown in FIG. 4(a).
. was injected and the outputs P1 and P2 were measured at the other end, a graph as shown in FIG. 5 was created, the values between the extreme values were measured, and the wavelength pitch λp was determined. As shown in FIG. 3(a), since the branching ratio changes periodically, there is a relationship between the number of times the optical coupler's branching ratio becomes 100% or 0% (hereinafter referred to as the number of transfers) and the wavelength bit λp. The results shown in FIG. 6 were obtained. In the graph shown in FIG. 6, point A is a state in which the number of transfers is once, that is, the optical signal is branched as shown in FIG. 4(a), and point B is a state in which the number of transfers is two,
That is, the optical signal is branched as shown in Figure 4(b), and the number of transfers at point C is three, that is, the optical signal is branched as shown in Figure 4(c). At point D, the number of transfers is four, that is, the optical signal is branched as shown in FIG. 4(d). From this figure, it can be seen that at point D, that is, when the number of transfers is four, the wavelength pitch λp is the required 1.31 μm and 1.31 μm.
It was found that the wavelength was close to 240 nm, which is 55 μm.

Furthermore, as shown in the paper by M. Eisenman et al. mentioned above, the wavelength pitch λ depends on the traverse length g of the burner 41. Therefore, the inventor investigated the relationship between the traverse length g1 of the burner 41, the moving speed V, the burner hole diameter h, and the wavelength pitches λ and p. Here, the traverse length g and the burner hole diameter h are specifically shown in Fig. 7(a) and Fig. 7(
This is the part shown in b). First, set the burner speed V to 2m.
m/sec, the number of transfers was 4 times, and the burner hole diameter h was 0.25 mm, and the relationship between the traverse length p and the wavelength pitch λ was investigated, and the results shown in FIG. 8 were obtained. From the graph shown in FIG. 8, the wavelength pitch λ depends on the traverse length g, and when the traverse length D is 5.2 mm, the wavelength pitch λ
was found to be close to 240 nm, which is the required wavelength of 1.31 μm and p of 1.55 μm.

Furthermore, the number of transfers is set to 4, and the traverse length g is set to 5.
2 mm, and the burner hole diameter h was 0.27 mm and 3.4 mm, respectively, and the relationship between the burner bead V of the burner 41 and the wavelength λ was investigated, and the results shown in FIG. 9 were obtained. From the results shown in FIG. 9, it was found that the wavelength λ depends on the burner speed V.

Based on these results, the branching ratio is monitored at at least two wavelengths during manufacturing during stretching, and the stretching conditions, specifically, the traverse length g1 burner speed V are controlled based on the monitoring results. We have realized a method for manufacturing an optical coupler according to the manufacturing flowchart shown below.

Hereinafter, a method for controlling the stretching conditions in the manufacturing method of the present invention will be explained using FIG. 3(b) and FIG. 10.

FIG. 3(b) shows the relationship between the branching ratio and the amount of stretching of the optical coupler during stretch manufacturing, and FIG. 10 shows the manufacturing process from the fifth step 34 to the eighth step 37 in FIG. A detailed manufacturing program flowchart is shown.

Using the optical coupler manufacturing apparatus shown in FIG. 2, steps up to the fourth step 33 in the manufacturing flowchart shown in FIG. 1 are carried out.

Then, the optical switch 46 is connected to one end 20a of the optical fiber 20.
The setting is made so that light with a wavelength of 1.31 μm is injected. Next, in the computer 50, J (1. 31 μm
The number of times the branching ratio reaches, for example, 50% when light is injected at the wavelength of is set to "0" (step 50). Next, set the traverse length ρ to No, and set the burner speed V to V
o (step 51). While stretching in this state, a wavelength of 1.31
The branching ratio r in μm is monitored 1.31 (step 52). The branching ratio r gradually increases as shown in Figure 3, 1.31 (b). When the branching ratio r reaches a predetermined value, for example 50% (1.31), specifically when it reaches Sl in FIG. The optical switch 46 is switched so as to inject the liquid, and the branching ratio r' (1) is monitored using the power meters 44 and 45 and kept at a constant value (steps 1.55 to 54). That is, p1 is measured in FIG. 3(b). When manufacturing an optical coupler with a wavelength pitch of 240 nm for light with wavelengths of 1.55 μm and 1.31 μm, the branching ratio r is set to a predetermined value, for example, 1.55 μm for every 50% of 1.3 l. The value of the branching ratio of the optical coupler during manufacture in the optical signal, i.e. r 1.5. (
J) (J-1, 2, 3, 4) is measured in advance, and the branching ratio r' (1) at p is 1
1.55, and the traverse length g or barber speed V is changed according to this comparison value and stretching is continued.

Then, rlJ is added to the value of J (step 57).
Then, the optical switch 46 is changed so that light with a wavelength of 1.31 μm is injected again, and the branching ratio r 1 is monitored using the power meters 44 and 45, and stretching is continued while keeping the branching ratio r 2 at 1.31. And this branching ratio r is 1.3
Once a predetermined value, for example 50%, is reached, specifically 82 in FIG. Measure the value of the branching ratio r' (2) 1.55 at the signal, specifically the value of p2 in Figure 3 (b), compare it with the branching ratio r (2), and set the traverse 1.55 again. Change long g or burner speed V to J? 1'' and continue stretching. Then, until the value of J exceeds 4, every time the branching ratio r in the optical signal with a wavelength of 1.31 μm reaches a predetermined value, for example 50%, 1.31, that is, in FIG. Branching ratio r'- (3), branching ratio r' (
4) −1.55 1.55, specifically, find the branching ratio at p3 and p4 in Figure 3(b), and calculate the branching ratio "1.55(3)" and the branching ratio r', respectively.
(4) and branching ratio' 1.551.55 (3), based on the comparison value with branching ratio r (4) 1.5
5 Change the traverse l or burner bead V and continue the above stretching.

After the value of J exceeds 4, the value of the branching ratio r1,3■ is monitored (step 59). When the value reaches 100%, a stretching stop signal is issued (step 59), and the optical fiber is The stretching stage 40 fixing the is stopped.

Here, as a conversion formula for changing the traverse length p or Bernas bead V, for example, the traverse length p is g-u xα, (J)X (r' 1.55(J) /r (J) l
...■1.55 As a Bernas bead V, v my×α (J)× ■ (r' (J)/r (J)) ・
・・Branching ratio measured at a wavelength of 1.55 μm as in 1.55 1.55 and 1.
31μm and 1.55μm wavelength pitch λ -240n
The traverse length p or the burner speed V is corrected based on the ratio to the branching ratio measured in advance during manufacture of a multiplexing/demultiplexing coupler having m. Here α. ! (J) and αV(J) are coefficients for correcting the traverse length ρ and the Bernus bead ■, and are experimentally determined in advance.

In this way, during the manufacture of optical couplers, the stretching conditions that affect the wavelength pitch are fed back according to the state of the branching ratio at the time, and the wavelength pitch is controlled to the desired value. Perform stretching.

Using a 1.31-μm single-mode optical fiber, 1.31-μm and 1.55-μm multiplexing/demultiplexing couplers were prototyped by the above method, and variations in wavelength pitch were investigated.

In this prototype, an oxyhydrogen burner was used as a heating source to perform fusing and stretching. As for the stretching conditions, the fusion time was 3 minutes, and the initial traverse length po was 5.2 as shown in Figure 8.
mm, and 1 burnus bead Vo is 2 mm from Figure 9.
/sec, and the resolution of the burner speed is 1 μrn/sec.
sec and further J1α. ! (J), r, 5.
(J), 20 samples were manufactured using the values in Table 1 below, and the wavelength pitch λ was measured, and the results shown in Table 2 were obtained.

This wavelength bit λ is determined by fitting the change in the branching ratio of the manufactured optical coupler p as a sine wave, and finding it between the points where the branching ratio of each boat of the optical coupler is the minimum, without changing the burner speed V. Ta.

In addition, in order to confirm the effects of the present invention, we also investigated the traverse length 1)
=5.2mm, Bernas bead vs *2mm/s e
20 optical couplers were prototyped using the conventional method with c constant and without feedback, and the results shown in Table 2 were obtained.

Table 2 As shown in Table 2 above, the effects of the present invention were confirmed.

In addition, in the above prototype example, the traverse length g was changed and the burner bead V was kept constant.However, conversely, the burner speed V was changed based on the above formula (■), and the traverse length D was kept constant. We were able to obtain similar results even when we made a prototype by keeping the temperature at

The present invention is not limited to the above embodiments, and various modifications may be made.

Specifically, in the above embodiment, the burner is simply moved in the X direction, but the burner is moved in an arc shape with respect to the axial direction of the optical fiber to heat and melt the optical fiber, It is preferable to uniformize the amount of heat applied to the optical fiber. In this case, the depth of the arc is between 0.1 and 0.
．． It is preferable to keep it at about 5 mm.

Furthermore, in the above embodiment, an example is explained in which an optical coupler is manufactured without changing the hole diameter h of the burner, but the relationship between the burner speed V, traverse length D, and wavelength pitch λ depends on the burner hole diameter h. Different p comes. Therefore, depending on the case, various burner hole diameters h
It is necessary to experimentally determine the correction coefficients α, (J) and αv(J) for . Then, an optical coupler may be manufactured by preparing a plurality of burners with different hole diameters, changing the hole diameters during stretching, and performing heating and stretching.

Furthermore, in the above embodiment, the branching ratio r' (J)l
．． 55 and the branching ratio r (J), the heating 1.
Although the heating conditions are changed based on these differences, the value of r' may be measured when r' reaches a predetermined value of 1.55. 3
Control based on the ratio or difference between r' and r and '゛ of 3.
．． 33 1.33 You may also control it. In this case, the correction coefficient must be determined experimentally.

〔Effect of the invention〕

In the optical coupler manufacturing method of the present invention, as described above, it is possible to improve the control accuracy of the wavelength pitch of the demultiplexing/multiplexing optical coupler. Therefore, the optical coupler manufactured by this method has less variation in wavelength pitch, and it is easier to achieve the low loss and high crosstalk required for a multiplexing/demultiplexing optical coupler between wavelengths to be multiplexed/demultiplexed.

Further, such an optical coupler is effective when applied to a communication distributed system.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a manufacturing flowchart of a method for manufacturing an optical coupler according to the present invention, and FIG. 2 is a diagram showing a schematic configuration of an optical coupler manufacturing apparatus for carrying out the method for manufacturing an optical coupler shown in FIG. 1. , Figure 3 shows a wavelength of 1.31 μm 1 wavelength 16 5
Figure 4 showing the relationship between branching ratio and stretching amount at 5 μm.
The figure shows the relationship between the branching state of the optical coupler and the number of transfers, Figure 5 is a graph explaining the method for measuring the wavelength pitch λ, and Figure 6 shows the relationship between the number of transfers and the wavelength pitch λ.
7 is a diagram specifically explaining the traverse length p and the burner hole diameter h, and FIG. 8 is a diagram showing the relationship between the traverse length p and the wavelength pitch λ. 10 is a diagram showing the relationship between burner hole diameter h, burner speed ■, and wavelength pitch λ, FIG. It is a figure which shows the manufacturing flowchart of the manufacturing method of the conventional optical coverr.

Claims (1)

[Claims] 1. A step of removing part of the coating of at least two optical fibers and arranging them parallel to each other; a heating stretching step of heating and melting the coated removed portion of the optical fiber and stretching it using a heating means with a variable speed; Based on the comparison result between the observed branching ratio and a predetermined value while observing with light of the wavelength,
A method for manufacturing an optical coupler, which performs heating and stretching by controlling the moving width or moving speed of the heating means.