Point by point femtosecond laser inscription of fibre and waveguide bragg gratings for photonic device fabrication

We present a flexible and rapid method for the production of Bragg gratings in a range of optical waveguides such as optical fibres and direct laser-written waveguides in bulk media. Using a low repetition rate (1 kHz) femtosecond laser, Bragg grating structures can be written in a point-by-point fashion (where each laser pulse inscribes one period of the Bragg structure) in both passive and active media be they fibre (FBG) or waveguide (WBG) based. Furthermore it is possible to control parameters such as the amplitude and chirp of the Bragg periods to create arbitrary reflection and transmission profiles. This technique can be coupled with existing fibre, rib waveguide and direct write waveguide technologies to create a range of photonic devices such as channel splitters, frequency combs, and signal amplifiers and conditioners for all-optical photonic signal processing. In initial tests 3 frequencies filter combs and Bragg grating reflectors with -53 dB insertion loss were written at arbitrary wavelengths in non-sensitised single mode fibre (SMF-28e) with process times between 30 and 90 seconds. These gratings are highly stable and withstand annealing to 600°C.