Fibre Bragg gratings were written in large diameter (∼300-400 μm) air-clad optical fibre using an amplified Ti:Sapphire femtosecond laser (800 nm, 100 fs, 0-3 μJ/pulse) with the point-by-point method. Utilising multiphoton absorption, we induced modifications in the core of the air-clad fibre. By focusing the femtosecond laser close to the diffraction limit with a 20 × oil immersion microscope objective lens, the glass modification region is of the order of 1μm in the fibre, which has a 5 μm core diameter. A technique to avoid the scattering effect of the large air-silica index contrast, on the femtosecond radiation, was implemented. Grating rejection strengths of 20 dB were achieved with an accompanying insertion loss of 3-4 dB at 1085 nm.
|Number of pages||4|
|Journal||Glass Technology: European Journal of Glass Science and Technology Part A|
|Publication status||Published - Feb 2009|