JPS62106339A - Method for measuring light transmission loss of optical fiber with high accuracy - Google Patents

Abstract

PURPOSE:To measure transmission loss by a light receiving part with good reproducibility and high accuracy, by passing an optical fiber through a light incident cylinder having a light reflective inner surface and two light condensing cylinders each having a light receiving part at the predetermined position thereof and a light reflective inner surface to allow light to be incident on said fiber from the light source provided to the fiber introducing part of the light incident cylinder. CONSTITUTION:An optical fiber F being a specimen to be measured is introduced into a light incident cylinder 1 by a guide roller 2 and the light from the light source P provided to the introducing part of said cylinder 1 is allowed to irradiate said fiber F. This fiber F is successively passed through a rear light attenuation part 6, a light condensing cylinder 3, a light transmission loss part 7, a light condensing cylinder 3' and an external light absorbing/light blocking part 8 to be taken up by a take-up part 9 and light transmission loss is measured by the light receiving parts 4, 4' provided to the cylinders 3, 3'. A light reflective surface 2 is formed to the entire peripheral inner surface of the cylinder 1. Light receiving parts 11 each comprising a spherical shell is provided to the cylindrical bodies of the cylinders 3, 3' and light reflective surfaces are respectively formed thereto and a voltmeter 15 is connected to the radiant light quantity detector 12 of the light receiving parts 11 through an amplifier 14.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method of measuring optical transmission loss of an optical fiber with high accuracy without destroying the optical fiber, and will be described in detail. The present invention relates to a non-destructive measuring method that can easily and conveniently measure the optical transmission loss of optical fibers, particularly optical fibers made of barbed polymers, with extremely high reproducibility and precision.

(Prior Art) Conventionally, light is applied from the side of a part of an optical fiber other than the part to be measured, and the light traveling inside the part to be measured is made incident.
A method of measuring by detecting the amount of light emitted when the incident light propagates through the part to be measured is detected at both side surfaces of the part to be measured and calculating the ratio of these emitted light amounts is disclosed in Japanese Patent Publication No. 1983-
It is known from the publication No. 18647.

However, although the measurement method disclosed herein is measurable in principle, in reality, even if the method disclosed herein is applied as it is, the optical transmission loss of optical fibers cannot be measured. It is extremely difficult to measure with good reproducibility and high precision, especially for organic materials where it is extremely difficult to introduce and advance the amount of light required for measurement inside the optical fiber even if light is irradiated from the side of the optical fiber. In the case of optical fibers made of polymers, highly accurate measurements are practically impossible.

First, optical fibers made of organic polymers have lower light transmittance than optical fibers made of glass, so even if light is incident on the side of the fiber, the incident light will not propagate and progress through the fiber. As the amount of light increases, the amount of light rapidly attenuates, making it impossible to detect the amount of light relevant to measurement, and as a result, it becomes impossible to measure optical transmission loss.

On the other hand, the position where the light is incident on the side of the fiber (light incidence point)
(1) Shorten the distance from the side of the fiber to the position where the amount of light that has propagated and progressed through the fiber is detected (called the light receiving point),
One possible method is to detect and measure the amount of emitted light from the side of the fiber at a position where the amount of light propagating and traveling through the fiber is large, but in this case, it is possible to detect and measure the amount of emitted light from the side of the fiber at a position where the amount of light propagating and traveling through the fiber is large. It was found that the waveform and intensity of the propagated and advanced light were unstable, making it impossible to accurately measure the optical transmission loss of the target optical fiber.

That is, FIG. 2 is a graph showing the amount of emitted light of an optical fiber made of an organic polymer at a distance from the light incident point to the light receiving point when light is incident from the side surface of the fiber, as described above. However, as shown in the figure, although it depends on the thickness of the optical fiber and the refractive index of the cladding and core that make up the optical fiber, it is independent of the amount (intensity) of light incident on the side of the optical fiber. The amount of light emitted from the side surface of the fiber at the light-receiving point does not stabilize until it passes a considerable distance from the light point. That is, the light that enters the fiber at the light incident point attenuates while rapidly changing the amount of light immediately after the light enters, and stabilizes after propagating and traveling a certain distance (hereinafter referred to as steady mode). Therefore, when measuring by setting the light receiving point as close as possible to the light incident point where the amount of radiant light propagating and traveling inside the fiber is large and the intensity is strong,
This is because the amount of light within the fiber fluctuates drastically, making it impossible to measure optical transmission loss values with high precision.

In other words, the reason why it is difficult to measure the non-destructive optical transmission loss of optical fibers made of organic polymers is that it is difficult to allow sufficient light to enter the fiber, and the amount of light that enters the fiber is subject to rapid fluctuations and attenuation. However, this can be said to be due to the fact that the amount of emitted light becomes significantly weaker at the position where the steady mode is reached.

(Problems to be Solved by the Invention) An object of the present invention is to increase the amount of incident light from the side surface of the optical fiber to increase the amount of emitted light at the light receiving point in the method for measuring non-destructive optical transmission loss of an optical fiber. At the same time, by increasing the distance from the light input point to the light receiving point, the light propagating and traveling inside the optical fiber is stabilized, that is, it is made to reach a steady mode, and the light is emitted from the side of the fiber at the point where the steady mode is reached. The purpose of the present invention is to provide an accurate and precise optical transmission loss measurement method for optical fibers by receiving and detecting the amount of light transmitted. It is an object of the present invention to provide a highly practical measurement method that can easily and easily measure optical transmission loss with high precision.

(Means for Solving the Problems) The object of the present invention is to achieve the invention described in the claims above, that is, to provide an optical fiber to a light-entering cylindrical body having a light-reflecting surface on the inner surface and a predetermined position. The optical fiber is made to pass continuously through at least two condensing cylindrical bodies each having a light-receiving part and a light-reflecting surface on the inner surface, and a light source is installed at the optical fiber introducing part to the light-incoming cylindrical body. guiding light from a light source into the cylindrical body, and irradiating light onto the side surface of the optical fiber to allow the light to enter the inside of the optical fiber;
By detecting the amount of light emitted when the incident light propagates inside the optical fiber from the light receiving portion of the two condensing cylindrical bodies, and measuring the optical transmission loss of the optical fiber from the ratio of the amounts of emitted light. can be achieved.

In the present invention, the optical fiber of the sample to be measured consists of a light-entering cylindrical body having a light-reflecting surface on its inner surface and at least two light-collecting cylindrical bodies each having a light-reflecting surface on its inner surface and having a light-receiving portion at a predetermined position. It is characterized by having optical fibers pass through the body continuously, increasing the distance between the light input point and the light reception point.

Hereinafter, the invention will be specifically explained based on the drawings. 1st
The figure is a side view showing one embodiment of the method for measuring optical transmission loss of an optical fiber of the present invention, particularly an optical fiber made of an organic polymer. In the figure, F is an optical fiber, P is a light source, and 1
2 is a light-entering cylindrical body, 2 is a guide roller having a light reflecting surface,
3.3' is a condensing cylindrical body, 4.4- is a light receiving section provided on the condensing cylindrical body, 6 is an optical attenuation section, 7 is an optical transmission loss section, and 8 is an external light absorbing section. The light shielding part 9 is a winding part of the optical fiber.

As shown in the figure, in the measurement method of the present invention, the optical fiber F of the sample to be measured is guided by a guide roller 2 and introduced into the light-entering cylindrical body 1. After being irradiated with light from a light source P provided in the fiber introduction part 1, a light attenuation part 6,
Concentrating cylindrical body 3, optical transmission loss section 7, condensing cylindrical body 3.3
-1 The sample to be measured is wound up by the winding part 9 through the external light absorbing/shading parts 8, respectively, and then placed in the light receiving parts 4 and 4- provided in the condensing cylinders 3 and 3-, respectively. The amount of light emitted from the optical fiber F is detected, and the optical transmission loss is calculated from the ratio.

In the measurement method of the present invention, in order to effectively introduce a large amount of light into the optical fiber of the sample to be measured, and to propagate and advance within the optical fiber, the optical fiber has a cylindrical shape with a light reflecting surface on the inner surface. It is necessary to guide the light into the body and run it through the body, and it is necessary to use a cylindrical body for light entry and light collection that has a light reflecting surface on its inner surface (hereinafter simply referred to as a cylindrical body refers to both of these) ), it is possible to continuously, accurately and precisely measure the optical transmission loss of the optical fiber without destroying the running optical fiber.

The light is incident on the optical fiber running inside the cylindrical body by a light source P at the optical fiber introduction part at the end of the light entrance cylindrical body 1 where the optical fiber is introduced into the cylindrical body. The optical fiber is irradiated with light from this light source, but in order to mix as much of the irradiated light as possible into the optical fiber, the light source must be placed at the end of the light input tube. It is preferable to install the light source as close as possible to the running optical fiber and to irradiate the running optical fiber with light from the light source at a certain angle, for example, at an angle of about 20 to 30 degrees.

As a guide roller for guiding the optical fibers into the cylindrical body, it is preferable to provide a roller having a light reflecting surface on its surface, preferably a concave shape, in the optical fiber introduction part of the cylindrical body. By using a guide roller, the light from the light source can be more effectively and effectively introduced into the optical fiber.

An example of such a cylindrical body for light entry is shown in FIG. That is, FIG. 3 is a side sectional view showing one embodiment of the light-entering cylindrical body of the present invention, and in the figure, 1 is a cylindrical body, and 2 is a light reflecting surface provided on the entire inner circumference of the cylindrical body. The light reflecting surface may be a diffused light reflecting surface, but is more preferably a regular reflecting surface.

For example, a cylindrical body having such a regular reflective surface has an AQ on the inner circumferential surface of a cylindrical body 1 such as a glass tube.

It can be easily manufactured by depositing a metal such as AI, Au, Rh, Cu, or Ti and forming the light reflecting surface 2 on the inner peripheral surface of the cylindrical object.

The shapes of these light-incoming and light-collecting cylindrical bodies may be large enough to allow the optical fiber to pass through them smoothly.
Although not particularly limited, it is preferable to have a circular shape, and furthermore, it is easy to pass the optical fiber through these cylindrical bodies,
In addition, from the viewpoint of making it easier to clean the inner surface of these cylindrical bodies,
These cylindrical bodies can have a structure that can be divided and separated in the vertical direction.

The light-receiving section provided in the condensing cylindrical body collects the light emitted from the side surface of the optical fiber as the light introduced into the optical fiber by the condensing cylindrical body propagates and progresses inside the fiber. Although it is designed to emit light and detect it,
It is desirable that the light receiving section is designed to have the function of preventing the radiation from the optical fibers collected by the light collecting cylindrical body from being diffused and condensing the radiation. The function of preventing the emitted light from being diffused and concentrating the emitted light can be easily provided, for example, by making the light receiving section have a structure as shown in FIG. 4.

FIG. 4 is a sectional view showing one aspect of the light receiving section, and FIG.
10 is an optical fiber, 10 is a condensing cylindrical body, 11 is a light receiving part consisting of a spherical nucleus, 12 is a radiation amount detector, 13 is a light shielding body provided on the inner peripheral surface of the entrance of the condensing cylindrical body, and 14 is a An amplifier, 15 shows a voltmeter.

In such a measurement method of the present invention, as described above, these cylindrical bodies are used to introduce light into the fiber, and after the light propagating and traveling inside the fiber is shifted to the steady mode. , is characterized in that the amount of emitted light is detected and measured in the light receiving part of the condensing cylindrical body, and the amount of optical transmission loss is measured from the ratio thereof. Therefore, in order to shift to this steady mode, in the present invention, the light propagating inside the optical fiber is attenuated between the cylindrical body for entering the optical fiber and the cylindrical body for condensing light. , an optical attenuation section is provided for transitioning to a steady mode, and an optical transmission loss section for measuring optical transmission loss of the optical fiber is provided between the condensing cylindrical body and the condensing cylindrical body. It will be done. The light attenuator is provided mainly to cause the light propagating and traveling within the optical fiber to shift to a steady mode, but also has the function of absorbing and blocking light from the outside. In addition, these optical attenuation sections and optical transmission loss sections are designed to block or prevent external light from entering the optical fiber, which is the sample to be measured, as much as possible, for example, as shown in Figure 1. After passing through the cylindrical body and the condensing cylindrical body, the cylindrical body, optical attenuation section, optical transmission loss section, etc. provided between the cylindrical bodies, light attenuation section, optical transmission loss section, etc., are individually and/or as a whole until the optical fiber is wound up. It is desirable to cover the area, for example by installing blackout curtains or creating a dark room.

The simplest way to create such an optical attenuation section and an optical transmission loss section is to increase the relative distance between the respective cylindrical bodies through which the optical fibers run and seal this section. This poses a problem in terms of equipment design because it requires a travel distance of . Therefore, it is convenient in terms of device design to provide, for example, a rotating drum at the entrance and exit of this cylindrical body, and to use this rotating drum as a light attenuation section and an optical transmission loss section to prevent external light from entering. It's advantageous. When using this rotating drum, it should be kept in mind that its small radius of curvature may cause mechanical damage to the optical fiber during light attenuation and light transmission loss, or light entering inside the truncated fiber. This is undesirable because the amount of light emitted from the optical fiber to the outside as radiation increases during its attenuation and optical transmission loss.

Therefore, although it depends on the thickness and transparency of the optical fiber, the drum used for the optical attenuation section and the optical transmission loss section may be
Those with a large radius of curvature, for example, approximately 25 to 3 in diameter
A range of 5 cm is preferable. The length of the optical fiber of the optical attenuator that converts the light incident on the optical fiber into a steady mode is the fiber diameter, and in the case of an optical fiber made of an organic polymer, the length of the core and cladding that constitute the fiber. Although it differs depending on the refractive index and needs to be determined appropriately, the length is usually at least about 10 m or more, preferably 13 m or more, and most preferably 17 m or more.

In this way, even if the optical fiber is provided with an optical attenuation section with a length of 10 m or more and the optical transmission loss section is made long, for example, even if this length is increased to 10 m or more as shown in the example, the optical It is surprising that it is possible to measure the emitted light of fibers. The length of the optical fiber of this light attenuation section is approximately 1
If it is shorter than 0 m, the attenuation of incident light, absorption of external light, and shielding will not be sufficient, and the light propagating and progressing within the optical fiber may not shift to a steady mode, leading to measurement errors and preventing highly accurate optical transmission. Loss values become difficult to measure. On the other hand, if the length is too long, the amount of light that propagates and travels within the optical fiber becomes too small, which is unfavorable in terms of measurement detection performance.

When measuring the optical transmission loss of an optical fiber according to the present invention, in addition to individually sealing the optical attenuation part, the optical transmission loss part, the light entrance and light collecting cylinders, etc., as shown in FIG. As such, it is preferable to provide an external light shielding section 8 to shield and prevent light from entering from the outside in order to improve measurement accuracy and measurement work. This external light shielding section 8 prevents and absorbs external light from entering not only the cylindrical body used in the measurement of the present invention but also the optical attenuation section and the optical transmission loss section, and protects each of these measurement sections, especially By blocking external light from entering the condensing cylindrical body, measurement accuracy can be improved, and it is also possible to perform measurements with the wound part of the optical fiber exposed to external light after measurement. Therefore, the workability after the measurement work is completed, especially when the measurement method is applied online to the production of optical fibers to greatly improve the workability when measuring the optical transmission loss value of the produced optical fibers.

Generally speaking, by providing a light-shielding or light-blocking component, such as a fabric-like material such as that provided in a camera magazine, especially a raised fabric, at the entrance and exit portion of the optical fiber to the cylindrical body, it is possible to prevent light from coming from sources other than the light source. Prevents external light from penetrating into the fibers and improves accuracy.

(Effects of the Invention) According to the present invention, the optical transmission loss of optical fibers, which was known in principle but difficult to measure with good reproducibility and high precision, can be actually measured. Moreover, according to the method of the present invention, the optical transmission loss of optical fibers made of organic polymers, which have optical properties inferior to those of inorganic optical fibers, can be continuously reproduced while running the optical fibers. It is possible to easily and simply measure the fibers with good quality and accuracy, and without destroying the fibers by cutting or the like.

That is, the measuring method of the present invention can be used to produce optical fibers.
Since it can be measured online, it can be said to be an extremely useful method industrially.

The present invention will be specifically described below based on Examples.

Example 1 The optical transmission loss value is approximately 380 dB/Km, and the diameter is 5
Using an optical fiber having a 0.00 micron core made of polymethyl methacrylate, the optical transmission loss of the optical fiber was measured by the measuring means shown in FIG.

In Figure 1, no external light shielding part is provided, the length of the optical fiber in the light attenuation part is 10 m, the length of the optical fiber in the optical transmission loss part is 10 m, and the length of the optical fiber between the light incident point and the light receiving point is 10 m. The optical transmission loss value of the optical fiber was measured at a distance of 3 m, and the optical transmission loss value was 800 dB/Km.

By correcting this measured value using a calibration curve,
It was possible to easily measure a value close to the optical transmission loss value of the above optical fiber.

Next, the length of the optical fiber in the light attenuation section (corresponding to the distance between the light incident point and the light receiving point) is 15 m, the length of the optical fiber in the light transmission loss section is 10 m, and the length of the optical fiber in the external light blocking section is 15 m. Assuming that the length of the fiber was 10 m, the optical transmission loss of the optical fiber was determined to be 400 dB/Km.

This value directly indicates the optical transmission loss value of the optical fiber itself without correcting the returned measured value, and it has been found that the measurement method of the present invention is a measurement method that shows extremely high accuracy and reliability. Ta.

On the other hand, for comparison, in FIG. 1, the optical transmission loss of the above optical fiber was measured without using any cylindrical body or guide of the present invention, but it was found that sufficient light entered the fiber. Therefore, the light could not be detected with sufficient sensitivity at the two light receiving points, resulting in measurement being impossible.

[Brief explanation of drawings]

FIG. 1 is a side view showing one embodiment of the method for measuring optical transmission loss of an optical fiber according to the present invention. In the figure, F is an optical fiber, P is a light source, 1 is a cylindrical body for light entrance, 2 is a guide roller having a light reflecting surface, 3.3' is a condensing cylindrical body, 4.4' is a light receiving part provided on the condensing cylindrical body, 6 is a light attenuating part, and 7 is a light attenuating part. An optical transmission loss section, 8 is an external light absorption/shading section, and 9 is an optical fiber winding section. FIG. 2 is a graph showing the amount of emitted light of the optical fiber at the distance from the light incident point to the light receiving point when light is incident from the fiber side of the optical fiber made of an organic polymer. FIG. 2 is a side sectional view showing one aspect of the light-incoming cylindrical body of FIG. FIG. 4 is a sectional view showing one aspect of the light receiving part of the condensing cylindrical body, where F is an optical fiber, 10 is a cylindrical body, 11 is a light receiving part consisting of a spherical nucleus, and 12 is a radiation light amount detector. , 13 is a light shield provided on the inner peripheral surface of the cylindrical body, 14 is an amplifier, and 15 is a voltmeter.

Claims (3)

[Claims] (1) An optical fiber is passed through at least two light-concentrating cylindrical bodies, each having a light-reflecting surface on its inner surface and a light-receiving section at a predetermined position; A light source is installed at the optical fiber introduction part to the light entrance cylindrical body, and the light source irradiates the side surface of the optical fiber to cause the light to enter the optical fiber, and the incident light propagates inside the optical fiber. The method of measuring optical transmission loss of an optical fiber is characterized in that the amount of light emitted from the light receiving portion of the two condensing cylinders is detected and the optical transmission loss of the optical fiber is measured from the ratio of the amounts of emitted light. High precision measurement method. (2) A highly accurate measuring method for optical transmission loss of an optical fiber according to claim 1, wherein a fiber guide having a light reflecting surface is provided at a position where light is irradiated from a light source onto the side surface of the optical fiber. (3) In claims 1 and 2, a light attenuator for stabilizing the light propagating and traveling through the optical fiber is provided between the light-incoming cylindrical body and the light-collecting cylindrical body. A highly accurate measurement method for optical transmission loss of optical fibers.