Several methods of preparing twin-core fibers (TCFs) that can be easily spl
iced to standard single-core single-mode fiber are proposed. Unlike the con
ventional TCF preparation methods that are used to fabricate a TCF with bot
h cores placed symmetrically with respect to the fiber axis, these methods
result in twin-core fibers that have one core in the fiber center. Experime
ntal results obtained with the TCF fabricated by using one of the designs a
re presented.