High mechanical strength fiber Bragg gratings made with infrared femtosecond pulses and a phase mask.

We report that by using 800 nm femtosecond pulses and the phase-mask technique, first-order fiber Bragg gratings with refractive index modulation in excess of 1×10(-3) can be written through both the acrylate and polyimide coatings of unloaded standard silica fibers without noticeable degradation of mechanical strength. We also demonstrate that the same experimental conditions can be applied for efficient FBG writing through the polyimide coating of pure silica core fibers, opening significant opportunities in the field of fiber sensors.