JP2945513B2 - Manufacturing method of optical fiber 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 forming 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 a so-called fusion drawing method.

[0002]

2. Description of the Related Art An optical fiber coupler is a device that branches and couples light between a desired plurality of optical fibers.
It is manufactured by stretching. In order to obtain an optical fiber coupler having a desired branching ratio, it is necessary to manufacture the optical fiber coupler while monitoring the branching ratio in the steps of melting and drawing.

[0003] As a method of monitoring the branching ratio, there are a transmission monitoring method generally used and a reflection monitoring method previously filed by the present applicant (Japanese Patent Application No. 1-275616).

FIG. 4 shows an apparatus for manufacturing an optical fiber coupler using this transmission monitoring method. As shown in FIG.
The two optical fibers 40a and 4 to be wound around 1
The optical fiber coupler 43 is formed by removing the coating of the portions corresponding to the respective coupler forming portions 42, bringing them into close contact with each other, heating, fusing, and stretching them with a burner or the like. To control this stretching, one of the optical fibers 40
A continuous light source 44 is connected to one end of a, and photodetectors 46, 46 are connected to the other ends of both optical fibers 40a, 40b via V-groove connectors 45, 45 for optical connection, respectively. I have. The photodetectors 46, 46 are
And the computer 47 is connected to a stretching control device 49 that controls a stretching jig 48.

[0005] From the continuous light source 44 to the optical fibers 40a, 4
The light incident on 0b passes through the coupler forming section 42,
The light is detected by the two photodetectors 46, 46. The detection result is input to the computer 47, and the computer 47 calculates the branching ratio based on the amounts of both transmitted lights. When the branching ratio reaches a desired value, a control signal is output from the computer 47 to the stretching control device 49, whereby the stretching control device 49 stops the stretching of the stretching jig 48.

FIG. 5 shows an apparatus for manufacturing an optical fiber coupler using the reflection monitor method. In this apparatus, a photodetector 4 is provided at one end of each of the optical fibers 40a and 40b.
6, 46 are connected, and a continuous light source 44 is connected to one of the optical fibers 40a via a measuring coupler 50 for splitting the reflected light. The photodetectors 46 and 46 are connected to a computer 47, and the computer 47 is connected to a stretching control device 49 that controls a stretching jig 48. On the other hand, the other ends of both optical fibers 40a and 40b are open. Reference numerals 51, 51 in the drawing denote refractive index matching oil for preventing reflection.

Light incident on the optical fiber 40 a from the continuous light source 44 via the measuring coupler 50 is transmitted to the coupler forming section 4.
After passing through No. 2, the light is reflected at the open end of the optical fiber 40a,
The light passes through the coupler forming section 42 again, is branched, and is detected by the photodetectors 46 and 46. The result of this detection is
The computer 47 calculates the branching ratio based on the amounts of the two reflected lights. Then, when the branching ratio reaches a desired value, a control signal is output from the computer 47 to the stretching control device 49, whereby the stretching control device 4
9 stops the stretching of the stretching jig 48.

[0008]

In the former manufacturing method, however, the manufactured optical fiber coupler 45 must be disconnected at any time, so that either one of the end of the light source 44 or the photodetector 46 is required. Needs 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 in connection work as in the transmission monitoring 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 appears remarkably, and this may cause a measurement error.

When pulse light is incident on a long optical fiber, Rayleigh scattering occurs over the entire length of the optical fiber. Therefore, Rayleigh scattered light returning to the incident end side (detected as reflected light) is shown in FIG. A waveform having a time dependency as shown in FIG. However, when the pulse light is repeatedly incident on the optical fiber and the transmission interval of the pulse is shortened, the Rayleigh scattered light of a plurality of pulses overlaps each other, and the above-described time dependence of the Rayleigh scattered light disappears.
On the other hand, since Fresnel reflection occurs only at the far end of the optical fiber, the Fresnel reflected light returns to the incident end side while maintaining the same waveform as at the time of incidence, even if repeated pulsed light enters. Therefore, if modulated light with a short time interval, that is, modulated light with a high modulation frequency, is used, the Rayleigh scattered light is a light of constant power having no time dependency, and the Fresnel reflected light is a modulated light of the same waveform and power as the incident light Is detected.

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

[0012]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for heating and forming a coupler forming section of a plurality of optical fibers.
When forming a coupler by stretching while fusing, in a method of manufacturing an optical fiber coupler that detects light passing through a coupler forming portion and controls stop of stretching based on the light, at least one of the first optical fiber A first step of inputting a predetermined amount of modulated light from one end side, and the modulated light passes through the coupler forming portion and is reflected at the other end side of the optical fiber;
A second step of detecting the reflected light at least at one end of any one of the optical fibers when the reflected light has passed through the coupler forming portion again; And a third step of controlling the stop of the stretching based on the ratio to the light amount.

In this case, in synchronization with the incident modulated light,
It is preferable that the reflected light is detected, and in this case, the reflected light is amplified and detected, and in this case, the amplification is preferably performed by a lock-in amplifier.

[0014]

When the modulated light is made incident from one end of the optical fiber and the modulated light synchronized with the reflected light reflected from the other end of the optical fiber is detected at one end,
Light can be incident and detected only at one end of the optical fiber, and by using modulated light for measurement and detecting this modulated light, reflected light due to Fresnel reflection and light due to Rayleigh scattering can be obtained. Can be detected separately.

In this case, if the reflected light is detected in synchronization with the incident modulated light, the reflected light due to Fresnel reflection can be selectively detected. In this case, if the detected modulated light is amplified, only the Fresnel reflected light to be measured can be amplified, and the influence of light due to Rayleigh scattering can be reduced.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an apparatus for manufacturing an optical fiber coupler for implementing the manufacturing method of the present invention will be described based on FIG. This manufacturing apparatus prepares two long single-mode optical fibers 1 wound around a bobbin 2 and unwinds them while unwinding the optical fiber coupler 3 having a 1: 1 branching ratio (50%).
Are continuously formed in large numbers. In this embodiment, 2
Although the same optical fiber 1 is used,
For the sake of simplicity, the description below will be described with the first optical fiber 1a at the top and the second optical fiber 1b at the bottom for convenience. Various devices for monitoring and controlling the branching ratio of the manufactured optical fiber coupler 3 are connected to one end of both optical fibers 1a and 1b, and the other end is open. The open end of the first optical fiber 1a is simply open, while the open end of the second optical fiber 1b is inserted into the antireflection index matching oil 4. The two optical fibers 1a and 1b
On the open end side, a coupler forming section 5 of both optical fibers 1a and 1b
Is configured. The coupler forming unit 5 includes the two optical fibers 1
After removing a portion of the coatings a and 1b, these portions are heat-sealed in close contact with a burner or the like, and further stretched to form the optical fiber coupler 3. For this reason, the coupler forming section 5 includes a stretching jig 8 having a burner 6 and a stretching table 7.
Attached to.

A modulated light source 10 is connected to one end of the first optical fiber 1a via a measuring coupler 9.
A modulation signal source 11 is connected to the front of the modulation light source 10. The modulated light source 10 is composed of a semiconductor laser or the like, and emits modulated light (pulse light) having a high modulation frequency by a signal from the modulated signal source 11. That is, based on the modulation signal from the modulation signal source 11, a desired pulse light from the modulation light source 11 enters from one end of the first optical fiber 1a via the measuring coupler 9 having a branching ratio of 50%. It is supposed to be. First of measurement coupler 9
One of the branches on the optical fiber 1a side is connected to the first optical fiber 1a as described above, while the other is inserted into the refractive index matching oil 4 to prevent the influence of reflection from this portion. I have. Conversely, one of the branches on the monitor device side of the measuring coupler 9 is connected to the modulated light source 10 as described above, and the other is connected to the first photodetector 12. On the other hand, a second photodetector 13 is connected to one end of the second optical fiber 1b. The first and second photodetectors 12 and 13 each include a light receiving element or the like, and photoelectrically convert reflected light guided to the photodetectors 12 and 13. That is, the reflected light reflected at the other end of the first optical fiber 1a passes through the coupler forming section 5 and is branched.
a and 1b. The branched reflected light is further branched by the measuring coupler 9 on the first optical fiber 1a side and detected by the first photodetector 12, and detected by the second photodetector 13 on the second optical fiber 1b side. It has become so.

A first lock-in amplifier 14 is connected to the first photodetector 12 and a second lock-in amplifier 15 is connected to the second photodetector 13. The in-amplifiers 14 and 15 are connected to a computer 16 for calculating a branch ratio. The first and second lock-in amplifiers 14 and 15 amplify the Fresnel reflection component of the reflected light. Therefore, the first and second lock-in amplifiers 1
Reference numerals 4 and 15 are connected to a modulation signal source 11, and are synchronized with the modulation light source 10 by a signal from the modulation signal source 11. That is, of the reflected light detected by the photodetectors 12 and 13, the modulated light
And picks up only the modulated light that is incident on the. This amplification amplifies the reflected light of Fresnel reflection among the detected light, and Rayleigh scattered light is also detected, but the effect of Rayleigh scattered light is relatively increased by picking up and amplifying the Fresnel reflected light. Is smaller. Computer 16
Based on the amounts of the reflected lights amplified by the first and second lock-in amplifiers 14 and 15, the branching ratio is calculated by a calculation formula described later, and the calculated value is a desired branching ratio (in the case of the present embodiment). Is 50%), a control signal for stopping the stretching is output to the stretching control position 17 connected thereto.

The stretching control device 17 is connected to the stretching jig 8 and drives the stretching jig 8 based on a control signal from the computer 16. The stretching jig 8 is provided with a burner 6 for heating the coupler forming section 5 and a stretching table 7, whereby the coupler forming section 5 is heated, fused and stretched. When a control signal for stopping is input from the computer 16, the stretching control device 17 stops the stretching drive of the stretching jig 8 based on the stop signal.

Next, the principle of the monitoring method will be briefly described. First photodetector 12 before manufacturing optical fiber coupler
Assuming that the detected power (detected light amount) is P ₀ and the detected powers of the first and second photodetectors 12 and 13 during manufacture of the optical fiber coupler are P ₁ and P ₂ , respectively, the computer 16 calculates the power during manufacture. The branching ratio of the optical fiber coupler 3 (defined by the ratio of the branch-side optical power) is expressed by the following equation.

The 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 Note, alpha _1, the 1 alpha _2, respectively, a second double optical fiber 1
a, 1b transmittance (output light power / incident light power), S
₀ is the main line side transmittance of the measuring coupler 9 (main line outgoing light power / main line incident light power). Based on the above formula, the arithmetic processing of the computer 16 is performed, and when the desired branching ratio is reached, a signal to stop stretching is output. In this case, P ₀ , P ₁ and P ₂ are actually Are the first and second
The value is amplified by both lock-in amplifiers 14 and 15.

Here, a series of manufacturing steps will be described with reference to the flowchart of FIG. First, the coating of a part of the optical fiber 1 is removed to form the coupler forming section 5 (step 201). The coupler forming section 5 is fixed to the stretching tables 7, 7 of the stretching jig 8 on both sides (step 202). Followed by ON modulated light source 10 (step 203), the reflected light P ₀ reflected from the other end of the first optical fiber 1a is detected by the first light detector 12 (step 204). In this state, the coupler forming section 5 is heated by the burner 6, and this portion is fused (step 205) and further stretched (step 20).
6). In this stretching step, the first photodetector 12 and the second
P ₁ and P ₂ are detected by the photodetector 13 (step 207). These detected values are stored in the computer 16
The branching ratio is calculated by the computer 16 based on the value of the optical power (step 208).
The detection of P ₁ and P ₂ and the calculation of the branch ratio in this stretching step are repeated until the branch ratio becomes 50% (step 2).
09) When the branching ratio reaches 50%, a stop signal is output from the computer to the stretching stop device 17. The stretching stop device 17 stops the stretching of the stretching jig 8 based on the stop signal (step 210). The optical fiber coupler 3 thus formed is finally molded or bonded to a protection member (not shown) such as a quartz case (step 211).

By repeating the above steps as needed, the two long optical fibers 1 wound on the bobbin 2 respectively.
A large number of optical fiber couplers 3 are sequentially formed from a and 1b. In this case, if the measuring coupler 9 and the second photodetector 13 are connected to the first and second optical fibers 1a and 1b, respectively, when the first optical fiber coupler 3 is manufactured, The connection work can be omitted from the manufacture of the optical fiber couplers 3 and thereafter.

According to 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 superluminescent diode having a wavelength of 0.85 μm is used as the modulated light source 10, and a rectangular modulated signal of 200 kHz is input from the modulated signal source 10 to output a rectangular pulse light having a frequency of 200 kHz. I made it. Each of the first and second optical fibers 1a and 1b has a fiber length of 0.8 km having a length of 1 km.
5 μm band single mode fiber, measuring coupler 9
Was also a 0.85 μm band single mode coupler.

Under the above conditions, while monitoring the branching ratio, optical fiber couplers having various branching ratios were manufactured, and the manufactured optical fiber couplers were measured for the branching ratio by a transmission method. FIG. 3 shows the measurement results. The plots with black circles are optical fiber couplers manufactured by the reflection monitor method of the present embodiment, and the plots with white circles are manufactured by the conventional reflection monitor method shown in FIG. An optical fiber coupler. According to the measurement results, the reflection monitoring method and the transmission monitoring method of the present embodiment completely match, and according to the reflection monitoring method of the present embodiment, an optical fiber coupler with an accurate branching ratio was manufactured. You can see that. On the other hand, the conventional reflection monitoring method is different from the transmission monitoring method, and it can be confirmed that the branch ratio of the optical fiber coupler using the conventional reflection monitoring method is somewhat inaccurate. Thus, it was confirmed that the reflection monitoring method of the present example was able to remove the influence of Rayleigh scattered light.

[0026]

As described above, according to the present invention, modulated light is made incident on the optical fiber forming the optical fiber coupler, the reflected light reflected at the other end is detected, and the amount of the detected reflected light is detected. The stop of the extension of the coupler forming section is controlled based on the ratio of the incident light and the amount of incident modulated light, which simplifies the connection work between the optical fiber and the monitor device, and also reflects the reflected light due to Fresnel reflection. And the light due to Rayleigh scattering can be detected separately. If only the reflected light due to Fresnel reflection is selectively detected, the influence of Rayleigh scattered light can be reduced and an optical fiber coupler with an accurate branching ratio can be manufactured. can do.

[Brief description of the drawings]

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

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

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

FIG. 4 is an explanatory view showing an outline of an optical fiber coupler manufacturing apparatus which has performed a conventional manufacturing method.

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

FIG. 6 is a diagram showing characteristics of Rayleigh scattered light with respect to pulsed light.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical fiber 1a ... 1st optical fiber 1b ... 2nd optical fiber 3 ... Optical fiber coupler 5 ... Coupler forming part 10 ... Modulated light source 12 ... 1st detector 13 ... 2nd detector 14 ... 1st lock-in amplifier 15: second lock-in amplifier 16: computer 17: stretching control device

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroaki Takimoto 1 Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Sumitomo Electric Industries, Ltd. Yokohama Works (72) Inventor Hiroshi Suganuma 1st Tayacho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries Hiroshima Yokota (72) Inventor Hiroshi Yokota 1-chome, Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries, Ltd.Yokohama Works (72) Kazuhiko Arimoto 7-31, Omorinishi 7-chome, Ota-ku, Tokyo (56) References JP-A-3-136008 (JP, A) JP-A-4-328505 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 6 / 28

Claims (4)

(57) [Claims] 1. A coupler forming section for a plurality of optical fibers,
When forming a coupler by stretching while heating and fusing, a method of manufacturing an optical fiber coupler that detects light passing through the coupler forming portion and controls the stop of the stretching based on the light, A first step of injecting a predetermined amount of modulated light from one end of the optical fiber, and the modulated light passes through the coupler forming portion, is reflected at the other end of the optical fiber, and is again When passing through the coupler forming section, this reflected light is converted into at least one arbitrary light.
A second step of detecting at one end side of the optical fiber, and a third step of controlling the stop of the stretching based on a ratio between the detected amount of reflected light and the amount of incident modulated light. A method of manufacturing an optical fiber coupler, comprising: 2. The method according to claim 1, wherein the detection of the reflected light is performed in synchronization with the incident modulated light. 3. The method according to claim 2, wherein the reflected light is amplified and detected. 4. The method according to claim 3, wherein the amplification is performed by a lock-in amplifier.