JPS63311206A - Optical fiber mode disturbing method and its element - Google Patents

Abstract

PURPOSE:To prevent an error in measurement from being generated, by producing a state equivalent to mode distribution in an optical fiber for a long distance by adding disturbance on a mode positively. CONSTITUTION:The propagation mode of light being propagated in the optical fiber can be disturbed by cutting the end face of the tip of the optical fiber 1 at a constant angle (alpha), forming a coarse plane 3 on the end face of the cut plane, and converting the propagation directions of a reflected light component and a refracted light component at the plane to the ones different from the incident direction of the light at random. Therefore, the mode of the light being propagated in the optical fiber 1 is disturbed by the coarse plane 3, and the light whose mode is disturbed in the direction different from that of incident light is taken out and measured as a transmission light component or the reflected light component effectively, thereby, it is possible to respond by a small element. In such a way, it is possible to facilitate the characteristic evaluating work of an optical fiber carrying path and to improve working accuracy.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a method for disturbing the propagation mode of light propagating in an optical fiber, and a function for uniformizing the propagation mode distribution of a multimode optical fiber. The present invention relates to an optical element having the following.

[Technical background] Light propagating through an optical fiber forms various modes. In this case, all allowed modes are equally excited, and optical power is frequently exchanged between each mode, which is said to be especially useful in maintaining the characteristics of multi-mode optical fibers. .

It is believed that this is achieved in long-distance optical fibers, but many modes have not yet grown to a range of tens of meters after the propagated light enters the optical fiber. If one attempts to evaluate the propagation loss, transmission band, and other characteristics of a long-distance optical fiber using a short optical fiber, errors will occur. In order to perform accurate loss and band measurements, it is said that the mode distribution must be uniform or excited to a degree close to uniformity throughout the permitted mode distribution. Therefore, conventionally, in order to perform such measurements, it has been necessary to use a long optical fiber called a dummy to sufficiently excite each mode before making measurements. This method allows measurement in a form closer to the practical fM, but
Since the long optical fiber is used, the measurement system becomes large-scale, which poses a practical problem. It was also difficult to downsize the device.

In addition, in order to equivalently produce the characteristics of an optical fiber, there is a method of measuring using a special sample in which the diameter of the optical fiber is periodically changed, or a method of bending the optical fiber in a zigzag pattern. A method of measuring the oscillation rate was also considered, but none of them had sufficient mode disturbance characteristics.

[Problems to be Solved by the Invention] As described above, in order to measure moats propagating in an optical fiber, a long optical fiber is required if it is to be put into practical use. Furthermore, in order to measure with an equivalently short sample, various difficult techniques must be used.

This invention was made in view of these points, and by actively adding disturbance to the modes, it is possible to create a state equivalent to the moat distribution in a long-distance optical fiber, thereby preventing errors in measurement. The purpose of the present invention is to provide a simple method and a device for the same.

[Means and effects for solving the problem] In this invention, the end face of the tip of the optical fiber is cut at a certain angle α,
By forming an S-plane on the end surface of this cut surface and randomly converting the propagation direction of the reflected light component and refracted light component on this surface to a direction different from the incident direction of the light, the light propagating inside the optical fiber is This disturbs the propagation mote of

Therefore, the mode of light propagating through the optical fiber is disturbed by the rough surface formed on the end face, and the mode is efficiently extracted and measured as a transmitted light component or reflected light component that is disturbed in a direction different from the incident light. Therefore, it is possible to deal with the problem using a small element.

[Example] Hereinafter, the present invention will be described in detail with reference to the drawings. 1st
In the figure, the tip of an optical fiber 1 is cut so as to form an angle α with this optical fiber. This angle α is 0″
The angle is within a range of 90°. Then, the cut surface 3 is formed into a rough surface having an appropriate roughness. Since the cut surface of the optical fiber immediately after cutting is a smooth surface, this rough surface is easily formed by scratching with sandpaper, sandpaper, etc. For example, the roughness characteristics of the cut surface 3 change depending on the rubbing direction of the sandpaper and the degree of roughness of the sandpaper, and it is possible to easily change the characteristics of the rough surface.

An optical fiber 2 whose tip end is similarly cut at an angle .alpha. is arranged in a straight line so that the surface of the optical fiber 1 faces parallel to the rough surface.

Light propagating in the direction of arrow A in the optical fiber l is disturbed by the rough surface 3 provided on the end face, and the scattered light is transmitted in the direction of arrow B.
As shown in , it is cruel to pass through the second optical fiber 2 and take it out. At this time, the cutting angle α of the end face is α
By making the angle ≠90°, the reflected light component reflected by the rough surface 3 is prevented from returning to the first optical fiber 1.゛If this angle α is a small angle such as 0@<α≦10′, the area of the rough surface 3 formed on the end face of the optical fiber l will increase and the disturbance effect will increase, but on the other hand, it will be difficult to manufacture. becomes.

The refractive index difference Δn between the core and crat of optical fiber 1.2 is 1
%, the angle α is 10'<α<90
Should I change it to °? This is a condition to prevent the light component reflected by the rough surface 3 from returning to the original optical fiber l.

Next, as shown in FIG. 2, a second optical fiber 6 is installed in the optical fiber 5 whose end face is cut at an angle α and has a rough surface 7 in the direction of the reflected light reflected by the rough surface 7. At this time,
The second optical fiber 6 has an angle 2β which is twice the supplementary angle β of the above angle α.
It is joined so that Then, metal or the like is deposited on the rough surface 7 to form a reflective surface 8.

In this example, only the light component reflected by the rough surface 7 can be extracted from the second optical fiber 6, contrary to the example shown in FIG. Furthermore, the disturbance characteristics of the rough surface 7 can be easily readjusted without further cutting the optical fiber. Furthermore, it is possible to readjust the rough surface without actually measuring the effect.

FIG. 3 shows a perspective view of the optical fiber mode disturbance element shown in FIG. 2 described above housed in a case IO. The case 10 is fixed so that the rough surface 7 formed on the end face of the optical fiber is exposed on the side surface of the case 10. And this side of case 10 has i
ll is sealingly attached to the screw by 12.

In this case, the reflective film 8 is preferably installed on the lid 11. Therefore, it is possible to readjust the rough surface without loosening the screw 12, removing the lid, exposing the rough surface 7, and actually measuring the effect. Become.

[Effects of the Invention] As explained above, not only can the mode disturbance characteristics be controlled by quantitatively adjusting the rough surface, but since the measurement is performed using the optical fiber itself, it can be performed using extremely small elements. This not only greatly facilitates the work of evaluating the characteristics of optical fiber transmission lines at installation sites and laboratories, but also contributes to improving the viscosity of the work.

[Brief explanation of the drawing]

FIG. 1 is a side view of an optical fiber mode disturbance element showing one embodiment of the invention, and FIG. 2 is a side view of an optical fiber mode disturbance element showing another embodiment of the invention. FIG. 3 is a perspective view showing a state in which the optical fiber mode disturbance element is housed in a case. 1.5.6...Optical fiber 3.7...Rough surface

Claims (4)

[Claims] (1) Cut the end surface of the optical fiber tip at a certain angle α, form a rough surface on this cut surface, and make the propagation direction of the reflected light component and refracted light component on this surface different from the direction of light incidence. A method of perturbing the propagation mode of light propagating within an optical fiber by randomly changing the direction. (2) A first optical fiber whose end face of the fiber tip is cut at a certain angle α and a rough surface is formed on the cut face, and a second optical fiber which is connected in a straight line with the first optical fiber.
1. An optical fiber mode disturbance element characterized in that an optical fiber is disposed, and a transmitted light component subjected to mode disturbance by the second optical fiber is extracted. (3) The tips of the second optical fiber are coupled to the first fiber so that the angle is twice the supplementary angle β of the angle α, and the tip of the coupling portion is formed into a reflective rough surface. ,
An optical fiber mode disturbance element characterized in that a reflected light component on this surface is extracted from a second optical fiber. (4) The above feature, wherein the angle α of the surface is set to an angle other than 90 degrees, thereby preventing the reflected component of the light from this surface from returning to the first optical fiber. An optical fiber mode disturbance element according to claims 2 and 3.