JPH0534536A - Manufacture of optical fiber coupler - Google Patents

Abstract

PURPOSE:To provide the manufacturing method for an optical fiber coupler, for eliminating the influence of a Rayleigh scattered light to the utmost, at the time of monitoring a branching ratio. CONSTITUTION:This method is provided with a first process in which prior to heating and fusion of a coupler forming part 5, light of a prescribed quantity is made incident from one end of at least a 1 optical fiber 1, and on one end side of the 1 optical fiber 1, the light quantity of a Rayleigh scattered light of the 1 optical fiber 1 is detected, in a second process in which after heating and fusion of a coupler forming part 5 are started, light of a prescribed light quantity is made incident from one end side of the 1 optical fiber, allowed to pass through the coupler forming part, and also, reflected by the other end of the optical fiber, allowed to pass through the coupler forming part 5 again, and the light quantity of this reflected light is detected by one end side of plural pieces of optical fibers 1, respectively, and a third process in which the light quantity of each light detected in a second process is corrected, and based on a light quantity ratio of each light after the correction, a stop of drawing is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention forms a coupler by stretching a part of a plurality of optical fibers while heating and fusing them.
The present invention relates to a method for manufacturing an optical fiber coupler by the so-called fusion drawing method.

[0002]

2. Description of the Related Art An optical fiber coupler is a device for branching / coupling light between a desired plurality of optical fibers. After a part of the plurality of optical fibers are brought into close contact with each other, they are heated and melted,
It is manufactured by stretching. In order to obtain an optical fiber coupler having a desired branching ratio, it is necessary to manufacture it while monitoring the branching ratio in the melting and drawing steps.

As a method of monitoring this branching ratio, there are a commonly used transmission monitoring method and a reflection monitoring method which the applicant of the present invention applied for earlier (Japanese Patent Application No. 1-275616).

FIG. 4 shows an optical fiber coupler manufacturing apparatus using the transmission monitor method. As shown in the figure, bobbin 4
Two target optical fibers 40a, 4 wound around 1
0b is prepared, the coatings of the portions corresponding to the respective coupler forming portions 42 are removed, and the optical fiber couplers 43 are formed by bringing them into close contact with each other and heating, fusing, and stretching with a burner or the like. In order to control this drawing, one optical fiber 40
a light source 44 is connected to one end of a
Photodetectors 46 and 46 are connected to the other ends of a and 40b via V-groove connectors 45 and 45 for optical connection, respectively. Further, the photodetectors 46, 46 are connected to a computer 47, and the computer 47 is connected to a stretching controller 49 that controls a stretching jig 48.

The light incident on the optical fibers 40a and 40b from the light source 44 passes through the coupler forming section 42 and is detected by both photodetectors 46 and 46. The detection result is input to the computer 47, and the computer 47 calculates the branching ratio based on the light amounts of the both transmitted lights. When the branching ratio reaches a desired value, the stretching control device 49 is moved from the computer 47.
A control signal is output to the drawing control device 49 so that the drawing control device 49 stops the drawing of the drawing jig 48.

Next, FIG. 5 shows an apparatus for manufacturing an optical fiber coupler using the reflection monitor method. In this device, the photodetector 4 is provided at one end of each of the optical fibers 40a and 40b.
6, 46 are connected, and the light source 44 is connected to one of the optical fibers 40a via a measurement coupler 50 for branching the reflected light. And the photodetector 4
6, 46 are connected to the computer 47, and the computer 47
Is connected to a stretching control device 49 that controls the stretching jig 48. On the other hand, the other ends of both optical fibers 40a and 40b are open. Incidentally, reference numerals 51 and 51 in the figure are refractive index matching oils for antireflection.

The light incident on the optical fiber 40a from the light source 44 through the measuring coupler 50 passes through the coupler forming portion 42, is reflected by the open end of the optical fiber 40a, passes through the coupler forming portion 42 again, and is branched. Both photodetectors 46,
Detected at 46. This detection result is input to the computer 47, and the computer 47 calculates the branching ratio based on the light amounts of the two reflected lights. When the branching ratio reaches a desired value, a control signal is output from the computer 47 to the stretching control device 49, which causes the stretching control device 49 to stop the stretching of the stretching jig 48.

[0008]

In the former manufacturing method, the manufactured optical fiber coupler 45 must be separated at any time, so either one of the light source 44 side and the photodetector 46 side is connected. Need to be reconnected each time one optical fiber coupler 45 is manufactured. This connection work is time-consuming and requires skill, and if the proper connection is not made, it may affect the measurement error.

In the latter manufacturing method, there is no problem of connection work unlike the transmission monitor method, but the reflected light from the open end of the optical fiber 40a to be detected is weak Fresnel reflected light. Therefore, especially when the optical fiber 40a is long, the optical fiber 40a,
The influence of the Rayleigh scattered light within 40b remarkably appeared, which could cause a measurement error.

That is, when light is incident on the optical fiber, the light returning to the incident end side includes Fresnel reflected light reflected from the far end of the optical fiber and Rayleigh scattering generated over the entire length of the optical fiber. There is light. Here, the Fresnel reflected light power is P _r , the Fresnel reflectance is r, the optical fiber transmittance (emitted light power in the case of transmission / incident light power in the case of transmission) is α, and the incident light power is P ₀ . In this case, the Fresnel reflected light power is represented by P _r = P ₀ · α ² · r.

This means that if the optical fiber length becomes long and the transmittance of the optical fiber becomes small, the Fresnel reflected light power becomes extremely small. On the other hand, as shown in FIG. 6, the Rayleigh scattered light power increases proportionally as the optical fiber length increases. Therefore, when a long optical fiber is used, the effect of Rayleigh scattered light becomes remarkable. In this case, if only the Rayleigh scattered light power of the optical fiber can be measured in advance, it is possible to calculate only the Fresnel reflected light power among the reflected light powers including both.

The present invention has been made on the basis of such a principle, and an object thereof is to provide a method for manufacturing an optical fiber coupler in which the influence of Rayleigh scattered light is eliminated as much as possible in monitoring a branching ratio. .

[0013]

SUMMARY OF THE INVENTION To achieve the above object, the present invention provides a method for heating a coupler forming portion of a plurality of optical fibers by heating and
When forming a coupler by drawing while fusion-bonding, the amount of light passing through the coupler forming part is detected, and the stop of the drawing is controlled based on this, in the manufacturing method of the optical fiber coupler, heating of the coupler forming part. · At least 1 prior to fusing
A first step of causing a fixed amount of light to enter from one end of the optical fiber and detecting the amount of Rayleigh scattered light of the one optical fiber at the one end of the one optical fiber; After the heating / fusion is started, a certain amount of light is made incident from one end side of the optical fiber 1, passes through the coupler forming portion, is reflected at the other end of the optical fiber, and is again formed at the coupler forming portion. Through the second step of detecting the light quantity of the reflected light at one end side of each of the plurality of optical fibers, the light quantity of the light detected in the first step, and the second step. And a third step of correcting the light quantity of each light and controlling the stop of stretching based on the light quantity ratio of each light after the correction.

In this case, it is preferable to detect the amount of Rayleigh scattered light by suppressing Fresnel reflection at the other end of the one optical fiber. Further, in this case, the suppression of Fresnel reflection is preferably performed by immersing the other end of the one optical fiber in a refractive index matching agent.

[0015]

[Function] By detecting the amount of Rayleigh scattered light of one optical fiber at one end side of the one optical fiber prior to heating / fusion of the coupler forming portion, the Rayleigh scattered light generated in this optical fiber is numerically calculated. Can be understood. Next, after starting heating, fusing, and stretching of the coupler forming portion, a certain amount of light is made incident from one end side of the one optical fiber, and the amount of reflected light by this is adjusted to one of the plurality of optical fibers. By detecting each of them on the edge side and subtracting the detection value of the above Rayleigh scattered light from this detection value, it is possible to obtain the light amount of only Fresnel reflected light during the formation of the coupler. Then, if the branching ratio of the optical fiber coupler is calculated based on this light quantity, an accurate branching ratio can be obtained.

[0016]

First, an optical fiber coupler manufacturing apparatus for carrying out the manufacturing method of the present invention will be described with reference to FIG. This manufacturing apparatus prepares two long single-mode optical fibers 1 wound around a bobbin 2, and while unwinding them, an optical fiber coupler 3 with a 1: 1 branching ratio (50%).
Are formed continuously. 2 in this example
The optical fiber 1 of the book uses exactly the same one,
In order to make the following description easy to understand, for convenience sake, the one located above in the drawing will be referred to as the first optical fiber 1a, and the one located below will be described as the second optical fiber 1b. Various devices for monitoring and controlling the branching ratio of the optical fiber coupler 3 to be manufactured are connected to one end side of both optical fibers 1a and 1b, and the other end side is a refractive index matching oil for preventing Fresnel reflection. It is immersed in 4a and 4b. However, in this case, the other end of the second optical fiber 1b is always inserted in the index matching oil 4b, but the other end of the first optical fiber 1a is inserted in the index matching oil 4b in the manufacturing process described later.
It may be inserted into or removed from a.
That is, there are cases where the Fresnel reflection is suppressed at the end of the first optical fiber 1a and cases where the Fresnel reflection is actively performed. A coupler forming portion 5 of both optical fibers 1a and 1b is formed on the refractive index matching oils 4a and 4b side of both optical fibers 1a and 1b. The coupler forming unit 5 includes both optical fibers 1a and 1b.
After a part of the coating is removed, this portion is heated and fused by a burner or the like in a close contact state, and further stretched to form the optical fiber coupler 3. Therefore, this coupler forming unit 5
Is attached to a drawing jig 8 equipped with a burner 6 and a drawing table 7.

A light source 10 is connected to one end of the first optical fiber 1a through a measuring coupler 9, and the light source 1
0 is composed of a semiconductor laser or the like. A certain amount of light from the light source 10 is made to enter from one end of the first optical fiber 1a via the measuring coupler 9 having a branching ratio of 50%. First optical fiber 1a of measuring coupler 9
One of the side branches is connected to the first optical fiber 1a as described above, and the other side is inserted into the index matching oil 4c to prevent the influence of reflection from this portion. On the contrary, one of the branches of the measurement coupler 9 on the monitor device side is connected to the light source 10 as described above, and the other is connected to the first photodetector 1
Connected to 1. On the other hand, the second photodetector 12 is connected to one end of the second optical fiber 1b. First,
The second photodetectors 11 and 12 are each composed of a light receiving element and the like, and these are further connected to the computer 1 for calculating the branching ratio.
Connected to 3.

The reflected light reflected by the other end of the first optical fiber 1a passes through the coupler forming portion 5 and is branched, and the respective branched lights are guided to both optical fibers 1a and 1b. The branched reflected light is further branched by the measurement coupler 9 on the first optical fiber 1a side and detected by the first photodetector 11, and the second optical detector 12 on the second optical fiber 1b side.
It is detected by. In this case, the other end of the first optical fiber 1a described above is inserted into the index matching oil 4a to suppress Fresnel reflection, and the first photodetector 11
To detect only Rayleigh scattered light, and to take out Fresnel reflection from the index matching oil 4a positively,
In some cases, reflected light composed of Rayleigh scattered light and Fresnel reflection is detected.

First photodetector 11 and second photodetector 12
The detected value detected in step 1 is the computer 1 for calculating the branch ratio.
3, and the branching ratio is calculated by the calculation formula described later. Then, when this calculated value reaches a desired branching ratio (50% in the case of this embodiment), a control signal for stopping the stretching is output to the stretching control position 14 connected thereto.

The stretching controller 14 is connected to the stretching jig 8 and drives the stretching jig 8 based on a control signal from the computer 13. The drawing jig 8 is configured to include a burner 6 for heating the coupler forming section 5 and a drawing base 7, whereby the coupler forming section 5 is heated, fused and drawn. When a control signal for stopping is input from the computer 13, the stretching control device 14 stops the stretching drive of the stretching jig 8 based on this stop signal.

Next, the principle of this monitoring method will be briefly described. First photodetector 11 before manufacture of optical fiber coupler
Let P _{0 be} the detection power (detection light amount) of the optical fiber coupler, and let P ₁ and P ₂ be the detection powers of the first and second photodetectors 11 and 12 during the manufacture of the optical fiber coupler, respectively. The branching ratio of the optical fiber coupler 3 (defined by the ratio of optical power on the branch line side) is expressed by the following equation.

Branching ratio = (s / t + s) × 100 [%] where t = (P ₁ / P ₀ ) ^1/2 s = (α ₁ / α ₂ ) S ₀ (P ₂ ² / P ₀ P ₁ ) ^1/2 where α ₁ and α ₂ are the first and second optical fibers 1 respectively
a, 1b transmittance (emitted light power / incident light power), S
₀ is the transmittance of the measuring coupler 9 on the main line side (main line output light power / main line input light power). The calculation processing of the computer 13 is performed based on the above calculation formula, and a signal for stopping the stretching is output when the desired branching ratio is reached. In reality, P ₀ , P ₁ and P ₂ are described below. The value is subtracted and corrected by the detection value of the Rayleigh scattered light in the step.

Here, a series of manufacturing steps will be described with reference to the flowchart of FIG. First, a part of the coating of the optical fiber 1 is removed to form the coupler forming portion 5 (step 201). The coupler forming portion 5 is fixed on both sides to the stretching tables 7 and 7 of the stretching jig 8 (step 202). Then the first
After immersing the other end of the optical fiber 1a in the index matching oil 4a (step 203), the light source 10 is turned on (step 204), and the Rayleigh scattered light generated in the first optical fiber 1a is converted into the first light. It is detected by the detector 11 (step 20)
5). Next, the other end of the first optical fiber 1a is pulled out from the refractive index matching oil 4a (step 206) to enable Fresnel reflection, and the reflected light P ₀ is detected by the first photodetector 11. (Step 207). Then, in this state, the coupler forming portion 5 is heated by the burner 6, and this portion is fused (step 208) and further stretched (step 2).
09). In this stretching process, the first photodetector 11 and the second photodetector 12 detect P ₁ and P ₂ , respectively (step 210). That is, these detected values are input to the computer 13 and the optical power values (P ₀ , P
_The branching ratio is calculated by the computer 13 on the basis of the detected values of Rayleigh scattered light that corrects these ( ₁ , P ₂ ) and these (step 211). And P in this stretching process
The detection of ₁ and P ₂ and the calculation of the branch ratio are repeated until the branch ratio reaches 50% (step 212), and the branch ratio becomes 50.
When the percentage reaches%, a stop signal is output from the computer 13 to the stretching stop device 14. The stretching stop device 14 stops the stretching of the stretching jig 8 based on this stop signal (step 213). The optical fiber coupler 3 thus formed is finally molded or adhered to a protective member (not shown) such as a quartz case (step 21).
4).

By repeating the above process as needed, two long optical fibers 1 each wound around the bobbin 2 are formed.
A large number of optical fiber couplers 3 are sequentially formed from a and 1b. In this case, if the measurement coupler 9 and the second photodetector 12 are respectively connected to the first and second optical fibers 1a and 1b when the first optical fiber coupler 3 is manufactured, The connection work can be omitted from the production of the optical fiber couplers 3 after the first.

By the manufacturing method of the embodiment described above,
The optical fiber coupler 3 was actually manufactured and the variation of the branching ratio was measured. In this manufacturing process, a super luminescent diode having a wavelength of 0.85 μm was used as the light source 10. Both the first and second optical fibers 1a and 1b were 0.85 μm band single mode fibers with a fiber length of 1 km, and the measurement coupler 9 was also a 0.85 μm band single mode coupler.

Under the above conditions, optical fiber couplers having various branching ratios were manufactured while monitoring the branching ratio, and the branching ratios of the manufactured optical fiber couplers were measured by the transmission method. FIG. 3 shows the measurement results. The plots with black circles are optical fiber couplers manufactured by the reflection monitor method of this embodiment, and the plots with white circles are manufactured by the conventional reflection monitor method shown in FIG. It is an optical fiber coupler. According to this measurement result, the reflection monitor method and the transmission monitor method of the present embodiment are completely in agreement, and according to the reflection monitor method of the present embodiment, an optical fiber coupler having an accurate branching ratio was manufactured. I understand. On the other hand, the conventional reflection monitor method and the transmission monitor method are deviated from each other, and it can be confirmed that the branching ratio of the optical fiber coupler based on the conventional reflection monitor method is somewhat inaccurate. Thus, it was confirmed that the reflection monitor method of the present example could eliminate the influence of Rayleigh scattered light.

[0027]

As described above, according to the present invention, the Rayleigh scattered light generated in the optical fiber is detected in advance, and the monitor in the drawing operation of the coupler forming section is based on the detected value of the Rayleigh scattered light. Since the detection value of reflected light is corrected, the influence of Rayleigh scattered light can be eliminated as much as possible, and an optical fiber coupler with an accurate branching ratio can be manufactured.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an outline of an optical fiber coupler manufacturing apparatus that carries out a manufacturing method of the present invention.

FIG. 2 is a flowchart showing a manufacturing process of an optical fiber coupler.

FIG. 3 is a diagram showing a comparison between an optical fiber coupler manufactured by the manufacturing method of the present invention and an optical fiber coupler manufactured by a conventional method.

FIG. 4 is an explanatory diagram showing an outline of an optical fiber coupler manufacturing apparatus that carries out a conventional manufacturing method.

FIG. 5 is an explanatory diagram showing an outline of an optical fiber coupler manufacturing apparatus that implements a conventional manufacturing method.

FIG. 6 is a diagram showing the relationship between the length of an optical fiber and the Rayleigh scattered light power.

[Explanation of symbols]

1 ... Optical fiber 1a ... 1st optical fiber 1b ... second optical fiber 3 ... Optical fiber coupler 4a ... Refractive index matching oil 5: Coupler forming section 10 ... Light source 11 ... First detector 12 ... Second detector 13 ... Computer 14 ... Stretching control device

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroaki Takimoto             Sumitomoden 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd. Yokohama Works (72) Inventor Hiroshi Suganuma             Sumitomoden 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd. Yokohama Works (72) Inventor Hiroshi Yokota             Sumitomoden 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd. Yokohama Works (72) Inventor Kazuhiko Arimoto             Sumiden             Within Opcom Co., Ltd.

Claims (3)

[Claims] 1. A coupler forming section for a plurality of optical fibers,
When forming a coupler by stretching while heating and fusing, the amount of light passing through the coupler forming part is detected, and in the method for producing an optical fiber coupler controlling the stop of stretching based on this, Prior to heating and fusing the coupler forming part, at least one end of the one optical fiber is made to enter a certain amount of light, and Rayleigh scattering of the one optical fiber is performed at one end side of the one optical fiber. A first step of detecting the light amount of light, and after starting heating / fusion of the coupler forming portion, a constant light amount of light is made incident from one end side of the one optical fiber to make the coupler forming portion. Through the optical fiber, the optical fiber is reflected by the other end of the optical fiber, and is allowed to pass through the coupler forming portion again to detect the amount of the reflected light at one end of each of the plurality of optical fibers. The process, the first A third step of correcting the light quantity of each light detected in the second step with the light quantity of the light detected in the step of (3) and controlling the stop of the stretching based on the light quantity ratio of each light after the correction. A method of manufacturing an optical fiber coupler, comprising: 2. The manufacturing of the optical fiber coupler according to claim 1, wherein the detection of the amount of the Rayleigh scattered light is performed by suppressing Fresnel reflection at the other end of the one optical fiber. Method. 3. The method for manufacturing an optical fiber coupler according to claim 2, wherein the Fresnel reflection is suppressed by immersing the other end of the one optical fiber in a refractive index matching agent. .