Fs-laser writing of waveguide Bragg gratings in phosphate glass
One of the hopes of femtosecond waveguide writing in glasses is to create fully integrated optical devices, in particular lasers. In its simplest form a laser consists of an optical cavity housing some gain medium and a pumping scheme. Research done in our group on fs-laser fabrication of photonic structures inside phospate glasses, as well as research by others, has already shown a host of active materials (gain media) that in which waveguiding structures can be created through femtosecond processing. In order to create the cavity mirrors for the laser there are many options but really only one that is capable of being completely integrated in the glass structure without extreme post-processing: waveguide Bragg gratings (WBGs). A Bragg grating structure has a periodic variation of its index of refraction which allows it to passively reflect, or transmit, certain wavelengths based upon its grating parameters. In fact one group has very recently been able to create a fully integrated laser cavity inside of a 2 cm piece of glass .
Schematic diagram of fs-laser writing of WBG in glass
In trying to create robust waveguide Bragg gratings there are several questions that need to be addressed:
how good of a waveguide can you make?
how good of an optical filter can you create?
how stable are these waveguide and filter structures?
here the necessary stability is really dependent on the end use of the devices.
For the past decade a lot of research has been put into answering the first question of waveguide quality. This leaves the other two questions left to answer. Using our new glass compositions as a host we are trying to create, using various techniques, waveguide Bragg gratings and to determine the differences in performance, stability, and overall usefulness of these devices.
 Graham D. Marshall, Peter Dekker, Martin Ams, James A. Piper, and Michael J. Withford, “Directly written monolithic waveguide laser incorporating a distributed feedback waveguide-Bragg grating,” Opt. Lett. 33, 956-958 (2008) http://www.opticsinfobase.org/abstract.cfm?URI=ol-33-9-956