Thermo-optic behaviour of intrinsically single-mode low-numerical aperture (NA) ytterbium-doped fibre. (28th May 2019)

• Record Type: Journal Article
• Authors: Zhang, Fangfang; Xing, Yingbin; Liao, Lei; Wang, Yibo; Xu, Haozhen; Chen, Yisha; Dai, Nengli; Yang, Luyun; Li, Haiqing; Li, Jinyan
• Is Part Of: Laser physics. Volume 29:Number 7(2019)
• Publication Date: 2019-05-28
• Subjects: thermal effects -- low-numerical aperture (NA) fibre -- fibre amplifier -- mode instability; Lasers -- Periodicals; 621.36605
• DOI: 10.1088/1555-6611/ab2116
• Languages: English
• ISSNs: 1054-660X

Abstract

Abstract: A simplified model based on the finite-element method is proposed to study the thermo-optic behavior in high-power fiber amplifiers. It is shown that thermally induced refractive index change results in a thermal lens effect and ultimately leads to multimode behavior even in an intrinsically single-mode fiber. Besides, experimental investigations were carried out to characterize the thermo-optic behavior of an intrinsically single-mode large mode area 20/400 ytterbium-doped fiber with core numerical aperture (NA) ~ 0.04 in an all-fiber amplifier. Output power up to 1.68 kW was achieved with a deterioration of beam quality from M 2 < 1.1 to 1.7. It is explained that due to the uneven distribution of axial heat load, an intrinsically single-mode fiber gradually turns into a combination of a multi-mode fiber and a single-mode fiber with the growing heat load and then the leakage core modes trigger transverse mode instability. Moreover, a near diffraction-limited output power of 1.35 kW from an all-fiberized low-NA fiber amplifier is obtained.