Specialty Optical Fibers Handbook

the guided mode expands into the holes or by using long period gratings (LPGs)

to couple light between core and cladding. A liquid plug is inserted into the holes,

and the holes are sealed by splicing to a standard fiber on both ends. The

structure is hence an air-hole fiber with a short section of the holes filled with

a liquid plug. On-fiber heaters are used to thermally control the air-filled sections

of the hole fiber. When heated, the air expands and displaces the fluid plug. In

this manner, the position of the fluid plug along the hole-fiber device can be

controlled.

The tapered devices are formed by heating and stretching a section of the fiber

to an outer diameter of approximately 50 mm, taking care that the holes do not

collapse, and that