High speed switching of a DFB grating in a twin-hole fibre

A distributed-feedback (DFB) grating was written in twin-hole fibres with internal electrodes. Due to the intrinsic birefringence, the grating has two ultra-narrow peaks (∼0.41 pm and ∼0.27 pm) corresponding to x- and y-polarization. The separation between them can vary from 40 pm to 104 pm when the temperature increases from room temperature to 96°C. The dominant contributions of the Bragg wavelength shift as the increasing temperature are the change in refracitive index of the fibre and the expansion of the substrate (largest). Under the current pulses excitation, full on-off switching with response time ∼2.5 ns has been achieved for x-polarization of the DFB grating.