Optimization of Single-Mode Sapphire Waveguide Bragg Gratings
Mohan Wang, Patrick S. Salter, F.P. Payne, Tongyu Liu, Adrian Shipley, Zipei Song, Stephen Morris, Martin J. Booth, Julian Fells
Abstract
We demonstrate the fabrication and optimization of waveguide Bragg gratings on single-crystal sapphire substrates using femtosecond laser direct writing. The gratings are fabricated using modulated bursts and are embedded inside single-mode depressed cladding waveguides. Through design optimization, and fabrication parameter tuning, a depressed cladding waveguide with a loss of ∼0.8 dB/cm and a Bragg grating with a reflectivity of higher than 90% in the telecommunications wavelength band are demonstrated. The waveguide Bragg grating exhibits stable thermal properties under annealing at 1200°C. A sampled grating and a grating array are also demonstrated, showing the potential for more complex grating designs.