JPS5990027A - Measuring device for optical transmission loss of optical fiber - Google Patents

Abstract

PURPOSE:To enable the measurement of the uneven optical transmission loss of an optical fiber in its longitudinal direction without cutting the optical fiber by detecting the quantity of the light radiated from the side face of the optical fiber and measuring the optical transmission loss. CONSTITUTION:A measurement device is constituted of a light incident device A, a detection device B and an arithmetic device C. An optical fiber 22 drawn from a bobbin 23 passes through the device A and the device B, is taken off by a pair of nip rolls 25 driven at a specified speed and is taken up on a bobbin 24. A lens 30 is disposed in such a way that the image of a lamp is formed near the fiber 22 and a cover 32 is preferably made internal surface thereof of a material having a good reflectivity as it improves the efficiency of light incidence. Integration spheres 34, 35 are preferably of the spherical shape convered internally with a diffusion surface having a high reflectivity. An analog computer 40 calculates an optical transmission loss. It is possible to record continuously the fluctuation in the optical transmission loss of the optical fiber and to determine the distribution in the fiber axis direction by connecting a recorder 41 to the computer 40.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an apparatus for measuring optical transmission loss (absorption coefficient) of optical fibers.

Conventionally, optical transmission loss in optical m-fibers has been measured by the method shown in FIG. That is, first, the light from the lamp (2) is incident on one end surface (9) of the optical fiber It(+), the light emitted from the other end (10) is collected by the integrating sphere (3), and then the light converting element ( 6) into an electrical quantity, amplified by an amplifier (7), and read the indicated value with an indicator (8). This reading f
Let 1 be El. Next, from the end face (10) to the optical fiber (1
) The optical mtfn is cut at a plane (11) separated by a length L measured along the axis. Next, create a new end face (
11) is fixed with the holder (5) at the end face (1o) and at the rotation position, and the indicated value of the instruction At (8) is read. Let this reading value be E2.

Optical transmission loss (absorption coefficient) can be determined from El and E2 by applying Lambert-Beer's law, equation 0.

I + = I 2 exp (-KL)...
... ■Here, 11: Intensity of light reaching the end face (lO) 2: Intensity K of light reaching the end face (11):
Optical transmission loss (absorption coefficient) L: Length of the cut optical fiber ■, and I2 have a relationship with El and E2 as shown in the following equation.

E, -(1-ρ1)11...
・SE2 = (1-ρ2)I2...
・ ・j) Here, ρI = reflectance ρ of end face (10)
2: Reflectance of end surface (11)・, Substituting equation 21 and equation (■) into (sword equation) yields equation (■).

If the end face is cut or polished so that pl and p2 are equal, the optical transmission loss can be calculated from the following equation (5).

In this known method, the cut optical fibers cannot be used as products, so they cannot be used to detect all products, and they require a long period of time.

In addition, when the attenuation within the optical fiber is large, that is, when the product of the optical transmission loss and the length is large, the conventional method
It is difficult to obtain a constant value. For example, the optical transmission loss of current plastic optical fibers is the best, 3-1 x to C1n + 2-5 x for 99 letters.
The length of the product is approximately 11-10cm when wound on a bobbin.
-1. Even if the length is 1kI11, the attenuation of light is about 40
It is impossible to obtain a constant value of 411 with a normal stage.Also, even if it were possible to obtain a constant value of 411, it would be difficult to determine if the optical transmission loss is uniform over the entire length, or if there is a part in the middle where the optical transmission loss is large. Another drawback of the conventional method is that it cannot be determined whether the

The present invention provides an optical transmission loss measuring device for an optical fiber M[ that eliminates the drawbacks of the conventional method, and the gist of the invention is to A device that shines light from the side of the fiber and causes the light traveling inside the fixed part of the fiber to be directed to the person 114! 11 Optical fiber optical transmission equipped with a device for detecting light II; emitted when the light propagates through a fixed part A111 on both side surfaces of a part to be measured, and a device for calculating the ratio of these detected light velocities. Loss 4 (in the fixed device).

In the case of an optical fiber ideal for lighting, if you touch the light with a small spread from the end face on the - side, the opening angle is also small.
The incident light repeats the entire length 114 and is transmitted to the other end of Venus without emitting the light to the outside, and no matter how the light is irradiated from the outside of both end surfaces of the optical fiber, the optical It is said that it is impossible to generate light that travels through fibers by repeating total internal reflection.

However, in the case of actual optical fibers, they contain more or less NK disturbance factors such as foreign objects and bubbles, so the light incident from the end face is transmitted while emitting even a small amount of light to the outside of the optical fiber. . At this time, the light 1i emitted to the outside is proportional to the incident light beam and has a size that allows practical measurement. Light that propagates internally through repeated total reflection can be used.

The principle of the present invention is shown in FIG. 2 by taking an example of an optical fiber having such characteristics.
(12) is an optical fiber, (13) is a lamp, (14) is an integrating sphere (left), (15) is an integrating sphere (right), (1B)
, (17) are photoelectric conversion elements, (1B) and (19) are amplifiers, (2o) is an indicator, and 11 (left) and (21) are indicator 1 (right). ■ Turn on the lamp (13) for (exempt)
This is the intensity of light that is incident on cross section a and travels to the right.

I (112,) and I (Q, r) are respectively I(Q
, ) propagates to the integrating spheres (14) and (+5), the intensity of \IL uniform light inside the optical fiber in the part surrounded by the integrating spheres of the item. L is along the axis of the optical fiber between the center line S of the integrating sphere (14) and the center line C of the integrating sphere (15).
A11 is a fixed length.

In such a device, the lamp (13) is turned on and the light I
Even when (1) is done, the above-mentioned Lamber 1-Beer's 91 law holds true, and the following equation 11 is obtained.

I (L r) = (Q, R) exp(-KL)
-old = (m where, K: Optical transmission loss (absorption coefficient) of the optical fiber between the cross section and the cross section C. I (Q4) and I (lr) are the intensity of light inside the optical fiber, so they can be directly measured. Although it is not possible to do so, the light "7' T
Due to the scattering factor contained inside the AX fibers, I(ul
) and I(Q,r), the scattered light emitted 114 to the side of the optical fiber can be collected by each integrating sphere. These are each converted into a photoelectric conversion element (If()
, (+7) to convert it into electrical quantity, and amplifier (+8),
(+9), it can be read as E (view) and E (lr) which are proportional to the light L1. Expressed as a formula, it is as follows.

E (f2. Exemption) - α (i) XI (1, Exemption)
...7) E (Q, r) = cx (r
) XI (Q, r) −・−・g
+where, α(Q,): Total photoelectric conversion efficiency of the optical fiber in the part surrounded by the integrating sphere (14) α(r): , f/1 Optical fiber in the part surrounded by the integrating sphere (15) The total photoelectric conversion efficiency α (ex), α (r) is further calculated by the following formula (%), where β (Q, ): inside of the optical fiber in the area surrounded by the integrating sphere (14). Scattered light radiation efficiency β (r) from inside to outside of the optical fiber surrounded by JA sphere (15) ll & scattered light scattering light efficiency IL): Collection of integrating sphere (14) Light efficiency y(r): Integral g(15) not t# Light efficiency δ(!Q,): Photoelectric conversion element (
16) Conversion efficiency δ(r): Conversion efficiency ε(Q,) of photoelectric conversion element (17): Amplification factor ε(r) of amplifier (18): Amplification factor β of amplifier (19) , β (r) is a constant determined by the roughness factor in 11, and it is a constant that it varies depending on the location of the optical fiber. .

ε (min) and ε (r) are constants determined by the structure of the device, and are constants that hardly vary over time.

Therefore, α(Q,) and α(r) are constants that vary depending on the location of the optical fiber, but if it is not necessary to determine Jull optical transmission loss with high precision, α(Q,) - α
There is no problem in assuming that (r), and ()) equation 1li
) can be substituted into the (Φ equation) and the optical transmission loss K can be reduced more easily than the i-multiple equation.

In addition, in the Jun method, if α(Q-) and α(r) cannot be placed equally, the length I of the optical fiber between the integrating spheres is increased, and the value of E(Kimi)/E(JLr) is Please listen carefully to α
Making (r)/α(9,) relatively small is 1-i
(It is Noh.

When used for the purpose of inspecting or monitoring optical transmission loss of optical fiber M#, it may be sufficient to measure relative changes in optical transmission loss. In such a case, the four polymorphisms can be modified as follows.

Here, C is a constant of a.

Next, an example of a combination of devices used in carrying out the present invention will be explained based on FIG. The optical fiber (22) comes out of the bobbin (23), passes through a pre-loading device (A), a detection device (B),
- A pair of nin rollers (2
5) and wound onto a bobbin (24). The pre-loading device (^) includes a lamp (28) and a condensing lens (30).
), a light passenger seat cover (32) is incorporated. Detector (B) number 5 is integrating sphere (left) (34), integrating sphere (right)
(35), a photoelectric conversion element (3fl), and (37) are incorporated and housed within the measurement section cover (42). Photoelectric conversion element (3B).

A computing device (G) is connected to (37).

It is preferable that the lens (30) be arranged so that the image of the lamp appears close to the optical fiber (22), and that the cover (32) should have a mutually penetrating interior with good reflectivity, since this will increase the light incidence efficiency. It is preferable that the integrating spheres (34) and (35) have a spherical shape whose inner surface is covered with a diffusing surface having a high reflectance. The photoelectric conversion elements (36) and (37) usually use photomultiplier tubes,
Any type will do as long as there are enough ships.

Amplifiers (38) and (39) are installed if necessary. The analog computer (40) acts as a matchmaker and calculates the optical transmission loss. By connecting a recording 2t (41) to the analog computer (40), it is possible to continuously record fluctuations in the optical transmission loss of the optical fiber and determine the distribution in the fiber axis direction.

Note that the present invention is not limited to optical fibers, but can also be applied to threads, rods, thin 11-wire fibers,
It can also be applied to optical materials such as plates.

According to unreleased 1!1 configured as below-1, optical fiber #
Since the optical transmission loss is determined by detecting the amount of light radiated from the side surface of J1, there is no need to cut or comb the optical fiber. Therefore, in the case of long optical fibers or continuously manufactured optical fibers, by entering the light from the side, the optical transmission loss can be measured continuously over the length of the part to be measured while running the optical fiber. In other words, it is possible to measure the unevenness in the optical fiber's optical fiber loss in the length direction while keeping the optical fiber constant. Furthermore, by changing the wavelength of the incoming light, the spectral characteristics of optical transmission loss can also be determined, which brings about many powerful effects.

[Brief explanation of the drawing]

Fig. 1 is a partial longitudinal sectional side view of a device showing a conventional method for measuring optical transmission loss, Fig. 2 is a partial vertical sectional side view of a device illustrating the principle of the present invention, and Fig. ff13 is used to implement the present invention. 1 is a partially vertical side view showing a specific example of a device for
In the figure, (1) is an optical fiber, (2) is a lamp, (
3) is the integrating sphere, (4) and (5) are the Holter of the optical fiber M [
1 (6) is a photoelectric conversion element, (7) is an amplifier, (8) is an indicator L, (9), (10), (1, 1) is an end face of an optical fiber, (12) is an optical fiber, ( 13) is a lamp, (14)
, (15) is an integrating sphere, (1θ), (17) is a photoelectric conversion element, (1B), (1!II) is an amplifier, (20),
(21) is an indicator material] and (22) is an optical fiber. (23) is the winding bobbin of unmeasured optical 1aM#, (24
) is a bobbin wound with the optical fiber of the measurement method, (25) is a pair of rollers, (28) is a lamp, (30) is a condenser lens, (32) is a light entrance cover, (34), (
35) is an integrating sphere, (3B) and (37) are photoelectric conversion elements,
(39) is an amplifier, (40) is a recorder, and (42) is a measuring section cover. -“-Kei Salesne 1 Symphony 3, -i, F, -4 (Method) 1.・1
~Indication #+r Application No. 58-88707/2, Issue 1! Name of 11: Optical fiber optical transmission loss measuring device 3, Supplement 11: Person who performs! Relationship with case IX Patent applicant 19-inch IJ3ff, 2-chome, Kyobashi, Chuo-ku, Tokyo (603) Mitsubishi Rayon Co., Ltd. President and CEO Akio Kawasaki 4, Agent Address: 11-19, Kyobashi 2-3-chome, Chuo-ku, Tokyo 104 Showa October 1958 2511181-

Claims (1)

[Claims] A device that shines light from the side surface of the optical fiber in a portion other than the +1+1 constant part of the optical fiber and allows the light traveling inside the part to be measured to enter, and calculates the amount of light emitted when the input light propagates through the part to be measured. A device for determining optical transmission loss Wllll of an optical fiber, comprising a device for detecting on both side surfaces of a part to be measured, and a device for calculating the ratio of the detected light beams F.