- A fiber-optic splicing method in which a fixture is used to align and join the ends of the fibers. When such splicing is used, a special gel with a matching refractive index may be used to fill the gaps. Even so, this method provides more losses than a fusion splice, in which the ends to be joined are cut, aligned, melted, and joined together. mechanical strain A lengthening, contraction, torsion, or other deformation resulting from an external stress or force. Also called strain.