Optically switched erbium fibre laser using a tunable fibre-Bragg grating

The ability to tune the Bragg wavelength of a fibre-Bragg grating (FBG) in an all-fibre laser can offer added functionality such as laser wavelength tunability, polarization selectivity, and Q-switching. Compared to current techniques which rely on mechanically straining the FBG to achieve Bragg-wavelength tunability, an all-optical technique for tuning an FBG offers potentially faster switching speeds and a more robust and simple cavity. All-optical tuning of the Bragg wavelength of an FBG has been demonstrated previously by resonant optical pumping; however this technique has only been applied to passive systems for switching applications. In this work, we have further investigated this optical-tuning process, experimentally identifying three time-scale regimes, and optimised it for application to active systems. Furthermore, we constructed an erbium all-fibre laser cavity consisting of an outputcoupler FBG and an optically-tunable, high-reflector FBG. The cavity pumping and the optical tuning of the FBG were kept independent. By repetitively tuning the high-reflector FBG onand off-resonance with the output-coupler FBG, we actively Q-switched the erbium fibre laser at repetition rates up to 35 kHz, limited only by our diode driver. We show that grating tuning at >300 kHz is possible with the existing embodiment, and discuss further potential to operate at MHz rates.