  Currently, direct-write waveguide fabrication is probably the most widely
studied application of femtosecond laser micromachining in transparent
dielectrics. Devices such as buried waveguides, power splitters, couplers,
gratings and optical amplifiers have all been demonstrated. Waveguide
properties depend critically on the sample material properties and writing
laser characteristics. In this paper we discuss the challenges facing
researchers using the femtosecond laser direct-write technique with specific
emphasis being placed on the suitability of fused silica and phosphate glass as
device hosts for different applications.
