Optical fiber fusion splicing is a welded joint formed between two optical fibers. Fusion splicing is a permanent, low-loss, high-strength joint compared with other temporary joint such as a mechanical splice. Optical fiber fusion splices play a crucial role in the optical network.

The Ideal Fusion Splicing Process

The goal of fiber fusion splicing is to create a joint with minimum insertion loss yet with mechanical strength and long-term reliability that matches the fiber itself.

The ideal process of fusion splicing should be fast, inexpensive and should not require expensive equipment. But in reality the fusion splicing process needs trade-offs among different applications and requirements. For example, for undersea telecommunications, long-term reliability is the most important goal for a fusion splicing.

The Advantages of Optical Fiber Fusion Splicing

There are other approaches for interconnecting fibers such as fiber optic connectors and mechanical splicings. Compared to these two, fusion splicing has many advantages as explained below.

1. Fusion splicing is very compact

2. Fusion splicing has the lowest insertion loss

3. Fusion splicing has the lowest back reflection (optical return loss ORL)

4. Fusion splicing has the highest mechanical strength

5. Fusion splicing is permanent

6. Fusion splicing can withstand extreme high temperature changes

7. Fusion splicing prevents dust and other contaminants from entering the optical path

Types of Fusion Splicing

Fusion splicing environment and applications can be roughly divided into three types: 1. Field splicing 2. Factory splicing and 3. Laboratory splicing.

An important example of field splicing is the assembly of undersea fiber cables aboard fiber deployment ships. The example of factory splicing could be the assembly of fiber optic passive devices such as a WDM. An example of laboratory splicing is done by researchers fusion splicing the newest developed fibers to test their compatibility with existing industry standard fibers.

Fiber fusion splicing involves concepts from many subjects including optical waveguide theory, heat transfer, material science, mechanical engineering, fluid mechanics and more.

Introduction to the Fusion Splicing Process

The major steps involved in optical fiber fusion splicing can be summarized as the following.

1. Optical fiber stripping

The fiber cable jacket is removed and then the fiber polymer coating is stripped with fiber optic strippers.

2. Fiber cleaving

The fiber is cleaved with specialized tool called fiber cleaver. Two types of fiber cleaver exist: high precision fiber cleaver for single mode applications and field cleaver for multimode applications. A mirror like almost perfect end face is achieved by this cleaving process.

3. Fiber alignment

The fibers are laterally aligned to each other by step motor in a fusion splicer. This may involve rotating the fibers in polarization maintaining fiber splicings.

4. Fiber welding

The fibers are then heated with electric arc or other methods to the fiber glass's softening point and then both fibers are pressed together to form a solid joint.

5. Insertion loss estimation

The insertion loss is estimated based on the fusion quality and dimensions.

6. Pull tension strength testing

The fusion is pull proof tested when opening the fusion splicer cover.

7. Splice protection with fusion splice sleeve

The fusion splice joint is then protected with a heat shrink tube with a steel strength member inside to form a solid and reliable fiber joint.