JPS58162831A - Method for measuring connection loss of optical fiber - Google Patents

Abstract

PURPOSE:To measure the connection loss of optical fibers, by shaping the part near the juncture of the fibers to be connected to an arc or coil shape, and measuring the connection loss from the ratio in the electric powers of the exit light before and after the connection thereof. CONSTITUTION:Two pieces of optical fibers 8, 9 to be connected are terminated and fibers 10, 11 are drawn out and are shaped to an arc or coil shape having 5-60mm. diameter to form shaped optical fibers 12, 13. The light of a light source 18 is irradiated to the fiber 12, and the light power from an exit end face 14 is measured. The exit end face 14 and the incident end face 15 and connected. The light power from the fiber 13 is measured with the photodetecting element 17 in a dark box 16. The above-mentioned results and the ratio between the light power to the optical fiber which is formed of the optical fiber of the same kind as the optical fibers to be connected and is formed into a coil shape and the light power which leaks to the outside of the optical fibers and is detected with a photodetector 17 are beforehand measured, and the connection loss of the optical fibers is measured.

Description

[Detailed description of the invention] The present invention relates to a method for measuring optical fiber splice loss.

As shown in FIG. 1, the conventional general optical fiber splice loss measurement method involves injecting light from one end of an optical fiber 1 using a stabilized light source 2, and measuring the optical power CP from the other end of the optical fiber 1. Then, after connecting the optical fiber 1 and the optical fiber 3 to be connected, the optical power (Pt) from one end of the source fiber 3 to be connected is measured, and the optical power (Pl) is measured.
This method measures the optical fiber connection loss by subtracting the optical transmission loss of the optical fiber 3 to be connected from the level difference between ) and (Pri).

This conventional method for measuring optical fiber splice loss allows the use of the same optical power measuring device when splicing is performed at the same location, and it is also possible to measure the optical transmission loss% of the optical fiber to be spliced with high accuracy. Therefore, it can be applied to the measurement of optical fiber connection loss of about 0.1 to 0.2 dB without any major problems.

However, the situation in which optical fibers are actually connected is
Normally, optical fiber cables of several hundred meters to one kilometer are connected one after another, and in this case, the original power before connection (Pt)'t = the measurement location, that is, the connection location, and the optical power after connection (Pg ) eThe measurement locations are several hundred meters to one kilometer apart. For this reason, the conventional optical fiber connection loss measuring method has the following drawbacks.

(1) The use of multiple optical power foot measuring instruments makes it difficult to measure with high precision, requiring inter-instrument calibration.

(2) Highly accurate measurement of the loss of connected optical fibers after installation is difficult for the above reasons and requires a large amount of man-hours.

(3) Personnel are required to measure the optical power after Wc continuation.

(4) After connection, it is necessary to transmit information on the optical power to the place to be connected by some means.

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-mentioned drawbacks and provide a method for measuring original fiber splice loss that can be measured only at the splicing location.

The method of measuring optical fiber splice loss of the present invention is to form the vicinity of the splicing part of two optical fibers to be connected into an arc shape or a coil shape vC9& with a diameter of 5 to (5Q mm), and irradiate the shaped part of one optical fiber with a light sound. The method is characterized in that the connection loss of the optical fiber is measured from the ratio of the optical power emitted from the tip of the optical fiber at that time to the optical power emitted from the other optical fiber shaping section after connection.

Next, the present invention will be explained in detail using the drawings.

-J export of optical fiber has a core 4 with an outer diameter of 50 to 100 μm, a cladding and a dome 5 with an outer diameter of 125 to 150 μm (only this core 4 and cladding 5 are called strands). The primary coating layer 6 has a diameter of 300 to 400 μm and an outer diameter of 0.
It is a coaxial structure consisting of a secondary coating layer 7 of 6 to 1 mm.

The light traveling through the optical fiber is transmitted to a distant place by total reflection at the interface between the core 4 and the cladding 5 or by repeated refraction in the core axial direction due to the gradient of the refractive index inside the core 4.

If the original fiber is bent here, the light incident on the interface between the core 4 and the cladding 5 at an angle exceeding the critical angle of total reflection will be transmitted to the cladding 5. - Leakage into the next coating layer 6 and the secondary coating layer 7,
Furthermore, a phenomenon of leakage to the outside of the optical fiber occurs. The degree of this leakage varies depending on the optical fiber structure and bending radius, but the optical loss due to bending of a general optical fiber is usually 2 to 5 dB when the bending radius is 5 mm. This shows that if light is irradiated onto a part of the optical fiber that has been bent in advance, the light will enter the core 4.

In the embodiment according to the present invention, as shown in FIG. 3, the source fiber cable 8 and the source fiber cable 9 to be connected are terminal-treated, and the optical fibers 10 and 11 are taken out and shaped into rings or coils of appropriate diameters. Shaped optical fiber 12.1
3. The shaped optical fiber 12 is irradiated with light from the light source 18, and the optical power (Ps) from the original fiber output end face 14 is determined. Measure.

Next, the optical fiber input end face 14 and the optical fiber input end face 15 are connected by a fusion splicing method or a butt splicing method. Next, the light receiving element 17 set in the dark box 16 receives the optical power (P4) from the connected shaped optical fiber 13? Measure. Using the above results and the same type of optical fiber as the optical fiber to be connected, the ratio of the optical power to the coiled original fiber and the optical power leaking outside the optical fiber and detected by the light receiving element 17 was measured in advance. Measure the optical fiber splice loss by

At this time, the shaped optical fiber 12 and the light source 18t' may be stored in a dark box, or in order to reduce the influence of the secondary coating, the shaped optical fiber 12 and 13e may be immersed in a liquid having the same refractive index as the secondary coating. good.

In addition, in calculating the splice loss, in addition to the method described above, one optical fiber is matched against the output end face 14 and the optical fiber input end face 15', and while monitoring the original power with the light receiving element 17, the original power is maximized. Slightly move the optical fiber output end face 14 or the optical fiber input end face 15, connect the optical fibers at the maximum nine points using a fusion splicing method, etc., measure the optical power (P6) with the light receiving element 17, and measure the optical power (P5). ) and the optical power (Pg) to calculate the amount of loss reduction from the theoretical abutment loss of the optical fiber, and measure the splice loss of the optical fiber.

Further, the embodiment has a great advantage when used as a monitor for the alignment quality of a single mode optical fiber having an extremely small core diameter (approximately 10 μm).

A silica-based optical fiber At having a step-type refractive index distribution with a core diameter of 50 μm and a core diameter of 125 μm and a secondary coating diameter of 400 μm and an eccentricity of the core, core, and core within 1.0 μm, and a diameter of 10 m for each source fiber to be connected is used. One coiled optical fiber is irradiated with white light source light, and an optical power meter light receiving section is set in close proximity to the other coiled optical fiber, which is set in a dark box.

In this state, each optical fiber is set in the arc discharge type original fiber fusion splicer, and the end face of the optical fiber is ? After lightly hitting the optical power and measuring the optical power, connect the optical fibers completely and then measure the optical power again. As a result, the loss reduction calculated from the optical power change before and after connection is 0.3 to Q, 4 dB.
It became. This means that the loss due to butt before connection is 9
．． 3dB (theoretical value due to Fresnel loss) ~Q, l5dB
Considering that the optical fiber connection loss is about 0 to 0.2 dB
This indicates that it can be confirmed that the

As described above, the optical fiber splice loss measuring method according to the present invention has the following effects.

(1) Optical fiber connection loss can be measured only at the connection location, which is not necessary to connect the original fiber cable. (2) There is no need to measure the loss of the optical fiber to be connected, which can reduce the number of work hours.

(3) Errors caused by inter-instrument calibration of optical power measuring instruments are eliminated.

(4) #The optical power information transmission means is disabled! .

(5) Axis alignment of single-mode optical fibers can be performed only at the connection location.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing a conventional method for measuring optical fiber connection slip loss, Fig. 2 (al and (bl) are horizontal and vertical cross-sectional views of a general optical fiber, and Fig. 3 is an illustration of an optical fiber connection according to the present invention. 1 is an explanatory diagram showing an example of a loss measurement method. 1. Original fiber, 2. Stabilized light source, 3.
...Connected optical fiber, 4...Core, 5...
...Clad, 6...-Next coating layer, 7...
. . . Secondary coating layer, 8 . . . Optical fiber cable, 9 . . . Connected optical fiber cable, 10.
...Optical fiber, 11... Optical fiber, 1
2... Shaped optical fiber, 13... Shaped optical fiber, 14... Optical fiber output end surface, 1
5... Optical fiber entrance end face, 16... Dark box, 17... Light receiving element, 18... Light source.

Claims (1)

[Claims] Total diameter near the connecting part of two optical fibers to be connected: 5 to 60 mm
The optical fiber is shaped into a 1'nm arc or coil shape, and light is irradiated to one optical fiber shaper to compare the optical power output from the tip of the optical fiber and the output from the other optical fiber shaper after connection. A method for measuring optical fiber splice loss, characterized by measuring splice loss of an optical fiber from a ratio of emitted light power.