Annealing properties of waveguides and bragg gratings fabricated in a phosphate glass host using the femtosecond-laser direct-write technique

Femtosecond-laser direct-write waveguide lasers are a significantly enabling technology in the fields of sensing, communications, defense and integrated quantum optics. We recently demonstrated distributed feedback (DFB) monolithic waveguide lasers with high output powers (of order 100 mW) and optical conversion efficiencies of 17%. However for their general acceptance in the above fields, waveguide lasers need to have proven stability, lifetimes and resilience to changing external environmental conditions. The environmental sensitivity of integrated DFB or distributed Bragg reflector (DBR) waveguide-lasers is considerably greater than platforms based on amplifying waveguides and external gratings because changes in the refractive index profile of the waveguide-Bragg grating (WBG) effect both the laser wavelength and the output power due to the changing reflectivity of the grating structures. In this paper we investigate the refractive index properties of WBGs written in a Ytterbium doped phosphate glass host to determine the effects of pump-laser field and bulk thermal annealing.