High-temperature type IIa gratings in 12-ring photonic crystal fibre with germanosilicate core

The inscription of efficient Bragg gratings (>20 dB) in 12-ring photonic crystal fibre with a germanosilicate doped core without the need for hydrogen loading using 193 nm is demonstrated. We show the characteristic rollover from type I grating to type IIa – the first observation of a type IIa grating in structured optical fibre. The type IIa grating is shown to survive up to 700°C before any degradation in transmission or reflection takes place