Expanded single-mode fiber using graded index multimode fiber

A compact large Gaussian mode field diameter single-mode fiber is developed. This expanded single-mode fiber consists of splicing fibers with various lengths and characteristics. The principle of this optical arrangement is to excite the first mode of propagation of the multimode graded index to preserve a Gaussian field. The coupling properties are numerically analyzed, considering the effects of gap, radial offset, and tilt. The fiber connections loss between the same kinds of expanded single-mode fibers with a Gaussian mode field diameter of 18 µm is measured with an average of 0.55 dB. This large mode field diameter is preserved on a long length of fiber >20 cm.