The present invention relates to an optical fiber termination device used in an optical fiber communication circuit, and especially to an optical fiber termination device wherein a temperature rise is caused by high light power being terminated after passing through an optical fiber connected thereto.
If, in the prior art, one of a pair of optical fiber connector plugs used to optically connect optical fiber communication circuits together is detached from the other a light signal coming from a light source consisting of a laser device may reflect at the edge surface of the optical fiber built in the optical fiber connector plug to be connected to the light source, and the reflected light goes back to the light source. This type of reflection causes the laser diode to operate unstably since the reflected light is recombined with the light being generated in the light source.
The reflected light energy is remarkable, and is -12 dB with respect to incident light energy when the surface of the optical fiber at the edge thereof is orthogonal to the optical axis.
The optical fiber termination device is connected to the optical fiber edge in order to scatter the light going out of the optical fiber core so that the light signal might not reflect from the edge surface of the optical fiber.
FIGS. 5(a), 5(b) and 5(c) show cross-sectional views of an optical fiber termination device built in accordance with the technique in the prior art, as an example, which is to be used with the optical connector.
Optical fiber 22 is inserted into hole 23 at the center of optical connector ferrule 21 to be connected to the light source, and rear edge surface 24 of optical connector ferrule 21 is finished at right angle with respect to hole 23 by polishing optical fiber ferrule 21 and optical fiber 22 together.
Optical fiber termination device 25 consists of another ferrule and optical fiber 26 inserted into hole 28 at the center of that ferrule. The front edge surface of optical fiber termination device 25 is finished at right angle with respect to said hole 28 so that the front edge surface of optical fiber termination device 25 may contact the rear edge surface of optical connector ferrule 21. Rear edge surface 30 of said optical fiber termination device 25 is finished by polishing it at an angle greater than 8 degrees(or the threshold) with respect to a plane perpendicular to the optical axis of hole 28.
Consider that optical fibers 22 and 26 are inserted into alignment sleeve 31 after the rear edge surface of optical fiber ferrule 21 is contacted with front edge surface 29 of the other optical fiber ferrule. Light La is incident on core 32 of optical fiber 26 passing through core 35 of optical fiber 22 and is reflected from edge surface 30. The reflected light is scattered into clad 33 which surrounds core 32, as indicated by arrow Lb. This type of structure reduces the light energy reflecting from the rear edge surface of the optical fiber, and the light energy going into the light source can be reduced by -60 dB or more.
High light power is considered to be applied to the optical fiber termination device having such a structure as shown in FIGS. 5(a), 5(b) and 5(c) which are used to reduce the reflection of the light at the rear edge surface thereof where the light is to be terminated. The temperature of the optical fiber termination device rises around the rear edge surface thereof, at which the light energy can reflect, due to the scattering of the light into the clad layer. The temperature rise sometimes destroys the optical fiber termination device.
The objective of the present invention is therefore to provide the optical fiber termination device having a new type of structure which is free from temperature rise when used in high power light signal circuits.