Investigation of ultrafast laser photonic material interactions:   challenges for directly written glass photonics
  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. 
M. Ams, G.D. Marshall, P. Dekker, M. Dubov, V.K. Mezentsev, I. Bennion   and M.J. Withford