High power tunable Raman fiber laser at 1.2 μm waveband

Development of a high power fiber laser at special waveband, which is difficult to achieve by conventional rare-earth-doped fibers, is a significant challenge. One of the most common methods for achieving lasing at special wavelength is Raman conversion. Phosphorus-doped fiber (PDF), due to the phosphorus-related large frequency shift Raman peak at 40 THz, is a great choice for large frequency shift Raman conversion. Here, by adopting 150 m large mode area triple-clad PDF as Raman gain medium, and a novel wavelength-selective feedback mechanism to suppress the silica-related Raman emission, we build a high power cladding-pumped Raman fiber laser at 1.2 μm waveband. A Raman signal with power up to 735.8 W at 1252.7 nm is obtained. To the best of our knowledge, this is the highest output power ever reported for fiber lasers at 1.2 μm waveband. Moreover, by tuning the wavelength of the pump source, a tunable Raman output of more than 450 W over a wavelength range of 1240.6-1252.7 nm is demonstrated. This work proves PDF's advantage in high power large frequency shift Raman conversion with a cladding pump scheme, thus providing a good solution for a high power laser source at special waveband.

Phosphosilicate Fiber-Based Low Quantum Defect Raman Fiber Laser with Ultrahigh Spectral Purity

The phosphosilicate fiber-based Raman fiber laser (RFL) has great potential in achieving low-quantum defect (QD) high-power laser output. However, the laser’s performance could be seriously degraded by the Raman-assisted four-wave mixing (FWM) effect and spontaneous Raman generation at 14.7 THz. To find possible ways to suppress the Raman-assisted FWM effect and spontaneous Raman generation, here, we propose a revised power-balanced model to simulate the nonlinear process in the low-QD RFL. The power evolution characteristics in this low-QD RFL with different pump directions are calculated. The simulation results show that, compared to the forward-pumped low-QD RFL, the threshold powers of spontaneous Raman generation in the backward-pumped RFL are increased by 40% and the Raman-assisted FWM effect is well suppressed. Based on the simulation work, we change the pump direction of a forward-pumped low-QD RFL into backward pumping. As a result, the maximum signal power is increased by 20% and the corresponding spectral purity is increased to 99.8%. This work offers a way for nonlinear effects controlling in low-QD RFL, which is essential in its further performance scaling.