Specialty Optical Fibers Handbook

drawn, surface tension forces also ensure that the geometry of the preform is

faithfully reproduced in the fiber.

8.5.2 PANDA Fiber

As benefits its origins as a modified telecommunications fiber, the starting

point for a PANDA fiber is a circularly symmetric ‘‘telecoms-type’’ preform,

into which two diametrically opposed holes have been drilled ultrasonically. The

PANDA preform is then completed by the insertion of a boron-doped stress rod

into each hole. These stress rods may be fabricated either by vapor deposition or

by a sol-gel process [25]. When drawn, the low melt viscosity of these stress rods

relative to the surrounding silica ensures that the ...