All fiber mode-locked thulium-doped fiber laser using a novel femtosecond-laser-inscribed 45°-plane-by-plane-tilted fiber grating
Nithyanandan Kanagaraj, Antreas Theodosiou, Jan Aubrecht, Pavel Peterka, Michal Kamradek, Kyriacos Kalli, Ivan Kasik and Pavel Honzatko
Using the novel 45°-plane-by-plane-tilted fiber grating inscribed by a femtosecond laser as an in-line fiber polarizer, we demonstrate an all-fiber passively mode-locked thulium-doped fiber laser. We characterize the grating for polarization-dependent loss, indicating high contrast and broad operating wavelength. The 45°-tilted fiber grating together with polarization controller act as an artificial saturable absorber suitable for mode-locking through nonlinear polarization rotation. By properly pre-adjusting the polarization controller, stable mode-locking is achieved for a pump power in the range of 300 mW–400 mW at 1565 nm. Owing to the net anomalous dispersion, a stable mode-locked soliton pulse centered at 1870 nm with a pulse width of 862 fs is reported at a fundamental repetition rate of 22.34 MHz. A long-term stability test reveals that the laser is quite stable for 24 h under laboratory conditions, confirming the capabilities of the 45°-tilted fiber grating for stable laser operation.
Published in Laser Physics Letters – https://iopscience.iop.org/article/10.1088/1612-202X/ab39db/meta
All-fiber passively mode-locked ultrafast laser based on a femtosecond-laser-inscribed in-fiber Brewster device
Zinan Huang, Qianqian Huang, Antreas Theodosiou, Xi Cheng, Chuanhang Zou, Lilong Dai, Kyriacos Kalli, and Chengbo Mou
We report on an in-fiber Brewster device with a 45° tilted fiber grating (TFG) directly written by a plane-by-plane femtosecond laser inscription method. Up to 10 dB polarization-dependent loss was achieved, proving effective polarizing functionality. Furthermore, we employ it as an in-line polarizer to successfully mode lock a fiber laser through the nonlinear polarization rotation technique. A stable soliton pulse train has been generated at 1563.64 nm with a pulse width of 624 fs and pulse energy of 0.42 nJ. With proper polarization adjustment, the laser also can operate in a noise-like regime. The parameters of this kind of 45°-TFG can be flexibly customized owing to the high flexibility and controllability of the femtosecond laser-inscription approach. In particular, such in-fiber polarizing devices inscribed by femtosecond laser inscription without removing the fiber coating are extremely robust for fiber lasers working at a broad wavelength region including the mid-infrared.
Published in Optics Letters – https://www.osapublishing.org/ol/abstract.cfm?uri=ol-44-21-5177