JPS5840689B2 - fiber optic terminal reflector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in optical fiber end reflectors.

Pulse-echo testing is useful for determining the length of optical transmission fibers and the location of fiber failures.

The principle of pulse echo testing will be explained with reference to FIG.

A laser oscillator 1 emits a pulsed optical signal.

This optical signal passes through the half square mirror 2 and the lens 3, enters the optical fiber from the input end A of the optical fiber 4, is transmitted therein, and reaches the far end B1.

At this time, reflection of the optical pulse occurs at the A end and the B end, and these reflected waves enter the photoelectric conversion element 6 from the lens 3 and the half mirror 2, where A.

The optical pulse reflected from the B end is converted into an electrical pulse and guided to the oscilloscope 7.

If the repetition frequency of the optical pulse and the sweep speed of the oscilloscope 7 are synchronized, reflected waves (pulses) from the A and B ends and a still image on the cathode ray tube of the oscilloscope will be displayed, as shown in A' in the figure. corresponds to the reflection at end A, and B' corresponds to the reflection at end B.

The time difference between A' and B' is equal to the time it takes for light to travel back and forth between A and B in optical fiber 4, so if you know the speed of light in the optical fiber, you can know the exact length between A and B. can.

If there is a fiber break point between 1 and AB, a reflected pulse from that point will appear between A'B' on the cathode ray tube, and the position of the break point can be determined.

As is clear from the above explanation, in this pulse echo measurement, it is fundamental to accurately display the reflected wave from the B end (far end) on the cathode ray tube.

However, the reflected wave at the B end travels in the opposite direction (
The conditions for transmission (to the A end) are narrow, and the reflected pulse from the B end can be captured with an oscilloscope only when the end face shape of the B end is special.

Next, to explain this situation using Figure 2, a is a case where the B end is a plane B perpendicular to the optical axis, b is a case where the surface is inclined B2, c is a complicated fracture surface B3. This is the case.

In the case of surface B, the reflected waves are clearly recognized because they are transmitted in the opposite direction through the fiber.

In the case of surface B2, when the inclination angle exceeds a certain value, the reflected wave escapes to the outside of the fiber and is no longer transmitted through the fiber, so that the reflected wave is no longer recognized.

In addition, in the case of B3, scattering occurs at the end face, and the energy of the reflected wave becomes weak, making it difficult to recognize the reflected wave.

An oscilloscope installed at the input end A side can capture the reflected waves at 18 points only when the B end is close to a plane perpendicular to the optical axis, as shown in the B1 plane in Figure 2 a. , this condition is much stricter than that on the A-end side.

Furthermore, since the reflected wave at the B end is affected by the transmission loss of the optical fiber and generally has small energy, special attention must be paid to the shape of the B end in pulse echo testing.

When cutting a fiber, it is difficult to cut it like B, but rather the cut and fracture planes like B2 and B3 are common, so in order to cut the fiber to a plane like B1, it is necessary to cut it many times. I had to recut it, which was quite inconvenient.

The present invention provides a pulse echo measurement auxiliary instrument that can generate reflected waves and increase the reflection level regardless of the shape of the B end. The significance of this method is extremely significant because the pulse echo at the B end can be detected to the maximum extent possible.

Next, the principle of the present invention will be explained with reference to FIGS. 3 and 4.

The bottom surface R of the container 9 is a mirror surface, and a liquid (hereinafter referred to as a matching liquid) having a refractive index close to that of the fiber 4 is filled in the container.

Put the far end B of the fiber 4 into this container. At this time, the fiber is inserted so that the bottom surface R of the vessel 9 and the optical axis of the fiber 4 are perpendicular.

In this way, regardless of the shape of the 8 surfaces at the far end, the light will be R
Since the optical pulse is reflected by the surface, the optical pulse with a high reflection level is transmitted within the optical fiber toward the input end, so that pulse-echo measurements can be performed satisfactorily.

The present invention is a reflector shown in FIG. 3, which is composed of a vessel 9 and a matching liquid 8, and is characterized in that the bottom surface of the vessel 9 is a mirror surface, and the diameter of the entrance of the vessel 9 is approximately equal to the outer diameter of the fiber. do.

Since the outer diameter of the fiber and the hole diameter of the vessel 9 are approximately equal, the optical axis of the optical fiber and the bottom surface R of the vessel are perpendicular to each other, resulting in good reflection and transmission.

Since the diameter of the fiber in the housing and the diameter of the hole are close, there is little matching liquid seeping out of the device.

Therefore, the device may be tilted, with the remote end of the fiber at the end of the device.
Since a good far-end reflecting section can be constructed simply by inserting the connector, handling is extremely easy.

In addition, with an optical fiber cable that accommodates multiple optical fibers, operations such as removing and replacing one optical fiber after measuring one optical fiber are easy, making it convenient to measure optical fibers one after another. It is.

Also, since the reflex level is a dog, the measurement accuracy is also increased.

The present inventor has recently developed the reflector described above, and the present invention relates to this improvement, and is characterized in that part or all of the wall surface in contact with the fiber is made into a spring shape.

This will be explained using a diagram.

In FIG. 5a, a cylindrical spring 10 is housed inside a cylindrical tube 9, and the bottom part 9' having a mirror surface R is assembled to the 9 as a screw.
It contains matching liquid 8.

b shows the state of actual use with the optical fiber 4 inserted into a.

c and d are perspective views of the spring 10, which functions as a spring by providing a plurality of slits 11 in parallel to its body.

The optical fiber 4 can be inserted with its coating.

Since the spring 10 is housed inside the tube, the outer diameter of the optical fiber is
Any type within a certain range can be used and can be held perpendicular to the mirror surface R.

Moreover, since there is a gap between the spring 10 and the container 90, when a fiber is inserted, air and excess matching liquid will be removed.
It is convenient because you can fill this gap.

FIG. 6 shows a tapered combination of the bottom 9' and the tube 9, which increases the accuracy of the perpendicularity between the hole wall surface and the bottom surface.

FIG. 7 shows a case in which the container 9 is integrated, and in this case, the mirror surface R may be formed as a vacuum-deposited metal film.

FIG. 8 shows a container whose inner surface has a wall surface with a triangular cross section, and one side of the triangle is constructed with a flat spring 10.

A matching liquid is contained within this tube, and the bottom surface is a mirror surface.

In this case, if the springs 10 are stacked four times on the inside, the fiber will be supported better.

Furthermore, in this case, care must be taken to prevent the matching liquid from seeping out at the bottom, and some kind of seal or the like is required.

FIG. 9 shows a structure in which six triangular reflectors are combined into one unit, and six leaf springs 10 are attached to a member 9.

This is suitable for measuring 6-core optical cables etc. all at once.

Figure 10a shows a vessel with a wall surface of a rectangular cross section;
Two leaf springs 10 are used.

In Fig. 11, the spring is not housed inside the vessel, and the inlet portion of the vessel is made into a spring-like shape. Fig. 11 shows a case in which the spring portion is in one stage, and Fig. 11 in Fig. 11 has a spring part in two stages.

Such a structure can be made by integrating the spring and the tube with the same material.

There are various embodiments mentioned above, and these may be made of metal, resin, or the like.

Furthermore, if the tube is made of resin, it is advantageous to make the tube transparent so that the state of the fiber and matching liquid can be seen.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the principle of the pulse echo measurement method, Fig. 2 a, b, c are various cutaway views of the optical fiber, Fig. 3,
FIG. 4 is an explanatory cross-sectional view of a terminal reflector of an optical fiber that has already been proposed, and FIGS. 5 to 11 are explanatory views of reflectors of various embodiments according to the present invention. 4: Optical fiber, 8: Matching liquid, 9 Two-terminal reflector,
R: Reflective mirror surface, 10: Spring, 11: Spring slit.

Claims (1)

[Claims] 1. The device has a hole into which an optical fiber having a diameter S thicker than the outer diameter of the optical fiber can be inserted, and the bottom surface of the container where the optical fiber hits is a mirror surface, and the refractive index of the optical fiber is inside the container. is equal to or
An optical fiber terminal reflector, characterized in that, in a container containing a liquid having a refractive index close to this, a part or all of the wall surface of the hole in contact with the optical fiber is made into a spring shape. 2. A patented terminal reflector characterized in that the above-mentioned device is a circular tube, and a circular tube-shaped spring having a plurality of slits is accommodated in the circular tube. 3. The optical fiber end reflector according to claim 1, wherein the vessel has a triangular inner cross section and one side is made of a plate spring. 4. Claim 1, characterized in that a plurality of cylindrical bodies described in Claims 2 and 3 above are integrated into one body.
Optical fiber terminal reflector as described in Section 2. 5. The optical fiber terminal reflector according to claim 1, wherein the device has two leaf springs housed on the inner surface of the rectangular cross section. 6. The optical fiber end reflector according to claim 1, wherein the inlet end of the reflector is spring-shaped. 7. The optical fiber terminal reflector according to claim 1, wherein the vessel is made of a transparent body. 8. The optical fiber terminal reflector according to claim 1, wherein the mirror surface on the bottom of the device is made of a vacuum-deposited metal film. 9. The optical fiber terminal reflector according to claim 1, wherein the reflector and the spring portion are integrated with the same material.