Femtosecond laser modification of fused silica: the effect of writing polarization on Si-O ring structure.
A femtosecond laser with a 1 kHz repetition rate and two different polarization states was used to fabricate low-loss waveguides in fused silica. Investigations of chemically-mechanically polished waveguide regions using near-field scanning optical microscopy revealed the presence of modifications outside the glass regions directly exposed to a circularly polarized writing laser. These waveguides also exhibited refractive index contrast up to twice as large as that of waveguides written with linearly polarized radiation. The observed differences in refractive index were shown by Raman spectroscopy to correlate to an increased concentration of 3-member silicon-oxygen ring structures. We propose that the observed differences in material properties are due to the polarization dependence of photo-ionization rates in fused silica.
Little
Douglas J
DJ
Centre for Ultrahigh bandwidth Devices for Optical Systems, MQ Photonics Research Centre, Department of Physics, Macquarie University, New South Wales, 2109, Australia. dlittle@ics.mq.edu.au
Ams
Martin
M
Dekker
Peter
P
Marshall
Graham D
GD
Dawes
Judith M
JM
Withford
Michael J
MJ