Chapter 7 - Fiber Connections and Diagnostics

Fiber Connections and Diagnostics

To use fibers for photonics applications, light must usually be coupled from one fiber to another. The different ways of accomplishing this will be discussed in this chapter. The losses involved in making fiber connections will be considered, as well as diagnostic techniques for determining the degree of loss.

Connections between fibers can be classified into three types: a splice, a connector, or a coupler. In this section, each of these is briefly described.

Fiber Splice

A fiber splice is a permanent connection between fibers and is the optical equivalent of soldering wires together. In a mechanical splice, the fibers are typically held together in a "V groove" arrangement or in a tightly fitting capillary tube, as shown in Fig. 7-1. Index-matching fluid can be inserted between the fiber ends to reduce Fresnel reflection losses, and glue can be used to secure the alignment. An elastomeric splice is a type of mechanical splice having some elasticity in the capillary tube, which allows fibers of somewhat different dimensions to be joined.

The other type of splice is the fusion splice, in which the fiber ends are fused (melted) together to form a seamless junction. The fusion is accomplished with a fusion splicer, which is essentially an optical arc welder. In this process, a high-current, pulsed electrical discharge is created between closely spaced electrodes, which raises the temperature of the fiber to above the melting point of the glass. The duration of the pulse is carefully controlled to melt just enough glass to make the join, but not so much as to degrade the core-cladding structure. Slight misalignment of the two fibers tends to be self-correcting in this process, because the surface tension of the liquified fiber region acts to bring the fiber cores into proper alignment. Losses in a fusion splice can be quite low, in the 0.1 dB range.

Fiber Connections and Diagnostics

To use fibers for photonics applications, light must usually be coupled from one fiber to another. The different ways of accomplishing this will be discussed in this chapter. The losses involved in making fiber connections will be considered, as well as diagnostic techniques for determining the degree of loss.

Connections between fibers can be classified into three types: a splice, a connector, or a coupler. In this section, each of these is briefly described.

Fiber Splice

A fiber splice is a permanent connection between fibers and is the optical equivalent of soldering wires together. In a mechanical splice, the fibers are typically held together in a "V groove" arrangement or in a tightly fitting capillary tube, as shown in Fig. 7-1. Index-matching fluid can be inserted between the fiber ends to reduce Fresnel reflection losses, and glue can be used to secure the alignment. An elastomeric splice is a type of mechanical splice having some elasticity in the capillary tube, which allows fibers of somewhat different dimensions to be joined.

The other type of splice is the fusion splice, in which the fiber ends are fused (melted) together to...