Abstract
All-fiber lasers offer increased robustness and simplicity over other fiber laser systems. Current active Q-switching techniques for all-fiber lasers rely on electro-mechanical transducers to strain-tune an intra-cavity fiber-Bragg grating, which adds complexity and can lead to vibrational sensitivity. An all-optical technique for achieving active Q-switched operation is a more elegant approach and would maintain the inherent robustness and simplicity of an all-fiber laser system. In this work, we studied the optical tuning of a fiber-Bragg grating by resonant optical pumping and optimized it for application to active systems. We incorporated an optically-tunable fiber-Bragg grating into a fiber laser and demonstrated active Q-switching at 35 kHz with this all-optical, all-fiber laser system. We highlight the potential to operate at >300 kHz with the current embodiment. To our knowledge, this is the first demonstration of an optically-driven active Q-switch in a fiber laser. Further potential to operate at MHz frequencies is discussed.
Highlights
The incorporation of fiber-Bragg gratings (FBGs) into fiber lasers enables simple, compact and robust all-fiber laser cavities, eliminating the need for bulk-optic components
Pumping a fiber doped with rare-earth ions increases the refractive index of the core, which in accordance with the Bragg condition, shifts the Bragg wavelength of an FBG inscribed in that fiber
We show that the tunable FBG exhibits three optical tuning regimes: a long time-scale thermally-dominated regime, an electron-population dominated regime, and a fast thermal regime
Summary
The incorporation of fiber-Bragg gratings (FBGs) into fiber lasers enables simple, compact and robust all-fiber laser cavities, eliminating the need for bulk-optic components. We show that the tunable FBG exhibits three optical tuning regimes: a long time-scale thermally-dominated regime (limited to 1 second), an electron-population dominated regime (limited to the excited-state lifetime of 840 μs), and a fast thermal regime (limited to ~3 μs) By repetitively tuning this high-reflector (HR) FBG on- and off-resonance with a stabilized output-coupler (OC) FBG, the quality factor (Q) of the erbium fiber laser cavity was modulated, and the laser successfully Q-switched at repetition rates up to 35 kHz. We demonstrate that the diode driver is limiting the tuning rate, and show that the FBG is capable of tuning at frequencies greater than 300 kHz in the current embodiment. We highlight potential for this system to be scaled up to repetition rates exceeding 1 MHz
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