JPH06174965A - Mode scramble method for multimode optical fiber - Google Patents

Abstract

PURPOSE:To provide the optical fiber as long as several km without damaging the optical fiber by fixing the coated fiber of the multimode optical fiber at a prescribed curvature and heating the fiber to melt the coated fiber of the optical fiber. CONSTITUTION:The coating of the multimode optical fiber is stripped to expose only the coated fiber 1 and the coated fiber is placed on a base 2 and a weight 3 is placed thereon to fix the coated fiber 1. A nichrome wire 4 is made to generate heat to melt and bend the coated fiber 1 of the optical fiber. Further, the coated fiber 1 of the multimode optical fiber bent by a mode scramble is put into a connector and is fixed by an epoxy resin. The coated fiber is bent by the mode scramble in such a manner, by which the worry about the flawing of the optical fiber is eliminated and the optical fiber as long as several km is prepd. The influence of bending and vibrating is hardly received by the joining state of a light source and the multimode optical fiber. A stable mode distribution is obtd. by taking out a higher mode and a radiation mode. The exact measurement having reproducibility is possible and measurement errors are decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mode scrambling method for multimode optical fibers.

[0002]

2. Description of the Related Art In a sensor using a multi-mode optical fiber for transmitting a signal, particularly an optical fiber sensor in which the amount of light is a signal amount, when the optical fiber is vibrated or an external force is applied to the optical fiber, the optical signal Attenuation occurs and the light intensity changes.

In particular, bending and vibration are likely to affect the bonding state of the light source and the multimode optical fiber.
When the numerical aperture of the incident angle is larger than that of the optical fiber,
Higher-order rays of light spend more time propagating near the boundary between the core and the cladding, causing more evanescent waves to seep into the cladding of the optical fiber. As a result, the damping increases. When the optical fiber is bent in such a state, a light ray having a large angle with respect to the axis of the optical fiber no longer satisfies the incident angle and is not reflected at all.

Since the existence of these unstable modes causes attenuation due to bending of the optical fiber, measures have been conventionally considered.

One method is to use an optical fiber of several kilometers to attenuate all unstable modes.

The other method is to bend the optical fiber 8 by sandwiching it with an uneven jig 7, as shown in FIG.

[0007]

However, the conventional method has a drawback that the apparatus becomes large because an optical fiber of several km is prepared, the optical fiber is damaged, and a large jig is used.

[0008]

SUMMARY OF THE INVENTION In the present invention, the core of a multimode optical fiber is fixed with a certain curvature,
By heating the bent part, multi-mode
The core of the optical fiber is once melted to obtain the mode scramble.

[0009]

According to the above method, there is no need to prepare an optical fiber of several kilometers or to damage the optical fiber.

Depending on the bonding state of the light source and the multimode optical fiber, it is less likely to be affected by bending and vibration.

[0011]

1 shows an example of a mode scrambling method according to the present invention. The coating of the multi-mode optical fiber is stripped off, and only the core wire 1 is placed. Since the core wire 1 of the optical fiber cannot be bent by itself, the nichrome wire 4 can be heated by passing a current through the nichrome wire 4, and the core wire 1 of the optical fiber can be melted and bent.

In the example of FIG. 2, the core wire 1 of the multi-mode optical fiber bent by the mode scramble is put in the connector 5 and hardened with the epoxy resin 6.

[0013]

According to the present invention, by bending with mode scrambling, an optical fiber of several km can be prepared,
There is no need to worry about damaging the optical fiber.

Further, since the high-order mode and the radiation mode can be taken out to the outside and stable mode distribution and reproducible and accurate measurement can be performed, the measurement error is reduced.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a mode scrambling method.

FIG. 2 is a sectional view showing an example of the inside of a connector of a multimode optical fiber sensor according to the present invention.

FIG. 3 is a diagram showing an example of a conventional mode scrambling method.

[Explanation of symbols]

 1 core wire 2 units 3 weight 4 nichrome wire 5 connector 6 epoxy resin 7 concave-convex jig 8 optical fiber

Claims (1)

[Claims] 1. A method of fixing a core wire of a multi-mode optical fiber with a certain curvature and heating a bent portion to melt the optical fiber once and bend it to obtain a mode scramble.