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Classification of Techniques Used for Optical Fiber Connection/Splicing

Optical fibers are joined either by fusion/mechanical splice, which is a permanent joint, or by connectors, which can be disengaged repeatedly. Optical connectors are used mostly at joints that need to be switched for optical service operation and maintenance reasons, while permanent joints are in use mostly in other applications.

Mechanisms of Light Loss at Optical Fiber Joint

When joining optical fibers, the opposed cores must be properly aligned.
Optical fiber connector/splice loss occurs mostly in the following manner.

(1) Poor concentricity

Poor concentricity of joined optical fibers causes a connector/splice loss. In the case of general purpose single-mode fibers, the value of connector/ splice loss is calculated roughly as the square of the amount of misalignment multiplied by 0.2. (For example, if the light source wavelength is 1310nm, misalignment by 1 μm results in approximately 0.2 dB of loss.)

Poor concentricity

(2) Axial run-out

A connector/splice loss occurs due to an axial run-out between the light axes of optical fibers to be joined. For example, it is necessary to avoid an increased angle at fiber cut end when using an optical fiber cleaver before fusion splicing, since such an angle can result in splicing of optical fibers with run-out.

Axial run-out

(3) Gap

An end gap between optical fibers causes a connector/splice loss.
For example, if optical fiber end faces are not correctly butt-joined in mechanical splicing, a splice loss.

Gap

(4) Reflection

An end gap between optical fibers results in 0.6 dB of return loss at the maximum due to the change in refractive index from the optical fiber to the air. Cleaning optical fiber ends is important for optical connectors. In addition, the whole optical connector ends should be cleaned because loss can also occur due to dirt between optical connector ends.

Classification and Principles of Fusion Splices

Fusion splicing involves the melting and joining of optical fibers using heat generated by an electric arc between electrodes. Fusion splicing is classified into the two methods, as follows.

(1) Core alignment method(core alignment)

Optical fiber cores observed with a microscope are positioned with the help of image processing so that they are concentrically aligned.
Then, an electric arc is applied to the fiber cores. The fusion splicer used has cameras for observation and positioning in two directions.

Core alignment method

(2) Stationary V-groove alignment method (cladding alignment)

This fusion splicing method uses V-grooves produced with high precision to position and orient optical fibers and utilizes the surface tension of melted optical fibers for alignment effects (cladding alignment).
Splices made by this method achieve low loss thanks to the recent advancement of optical fiber production technology, which has improved the dimensional accuracy regarding the placement of core. This method is primarily used for splicing a multi-fiber cable in a single action.

Stationary V-groove alignment method

Notes on Fusion Splicing

Fusion splicing procedures comprise
(1) the fitting of a fiber protection sleeve, (2) removal of cover layers, (3) fiber cleaning, (4) fiber cleaving, (5) fusion splicing, and (6) reinforcing the splice.

(1) Fitting of Fiber Protection Sleeve

The fiber protection sleeve is used to protect optical fibers exposed at the splice. Make sure that one of the optical fibers is passed through the protection sleeve before fusion splicing.

(2) Removal of Cover Layers

Using a jacket remover, remove the cover layers to expose the fiber glass.

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(3) Fiber Cleaning

After cover layer removal, clean the fiber glass with alcohol.

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(4) Fiber Cleaving

Follow the optical fiber cleaver operating procedure to cut the fiber.

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(5) Fusion Splicing

Fusion-splice optical fibers following the operation manual of the fusion splicer.

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(6) Splice Reinforcing

Cover the optical fiber splice with the fiber protection sleeve.
Reinforce the fiber with the sleeve on the heater.

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