The tandem pumping technique has been proven effective in power scaling of fiber lasers, which enabled the most powerful high-brightness fiber lasers to date. However, further performance improvement of tandem-pumped fiber lasers is challenged by the contradiction between nonlinearity suppression and good beam quality maintaining. To address these challenges, researchers from worldwide devoted to expediting the development of high-power tandem-pumped fiber lasers, and a series of new results and new applications emerged in recent years. This paper will highlight the recent advances in the enabling techniques of high-brightness tandem-pumped fiber lasers and the new applications of tandem pumping since the first review paper on this topic in 2017. A brief outlook on the further development of tandem pumping technique is also given.
KEYWORDS: Optical pumping, Fiber lasers, High power fiber lasers, Coating, Optical amplifiers, Signal attenuation, Fusion splicing, Fiber amplifiers, High power fiber amplifiers, Optical engineering
We investigate a (2+1)×1 side-pumping combiner numerically and experimentally for high-power fiber laser based on tandem pumping for the first time. The influence of taper ratio and launch mode on the 1018-nm pump coupling efficiency and the leakage power into the coating of the signal fiber (LPC) is analyzed numerically. A side-pumping combiner is developed successfully by tapered-fused splicing technique based on the numerical analysis, consisting of two pump fibers (220/242 μm, NA=0.22) and a signal fiber (40/400 μm, NA=0.06/0.46). The total 1018-nm pump efficiency of the combiner is 98.1%, and the signal light insertion loss is <3%. The results show that, compared with laser diodes pumping, the combiner appears to have a better LPC performance and power handling capability when using 1018-nm fiber as the pump light. Meanwhile, an all-fiber MOPA laser based on tandem pumping with 1080-nm output of 2533 W and the slope efficiency of 82.8% is achieved based on the home-made combiner.
Ytterbium-doped fiber laser (YDFL) and Thulium doped fiber laser (TDFL) have been two kinds of the most widely
studied fiber laser in recent years. Although both silica-based Ytterbium-doped fiber and Thulium doped fiber have wide
emission spectrum band (more than 200 nm and 400 nm, respectively), the operation spectrum region of previously
demonstrated high power YDFL and TDFL fall into 1060-1100 nm and 1900-2050nm. Power scaling of YDFL and
TDFL operates at short-wavelength or long-wavelength band, especially for extreme wavelength operation, although is
highly required in a large variety of application fields, is quite challenging due to small net gain and strong amplified
spontaneous emission (ASE). In this paper, we will present study on extreme wavelength operation of high power YDFL
and TDFL in our group. Comprehensive mathematical models are built to investigate the feasibility of high power
operation and propose effective technical methods to achieve high power operation. We have achieved (1) Diodepumped
1150nm long wavelength YDFL with 120-watt level output power (2) Diode-pumped 1178nm long wavelength
YDFL operates at high temperature with 30-watt level output power (3) Random laser pumped 2153nm long wavelength
TDFL with 20-watt level output power (4) Diode-pumped 1018nm short wavelength YDFL with a record 2 kilowatt
output power is achieved by using home-made fiber combiner.
A high power single-frequency fiber amplifier with linear polarization is demonstrated based on the master oscillator power amplifier configuration, consisting of a single-frequency seed laser at 1064.1 nm and three-stage amplifiers. To suppress stimulated Brillouin scattering, a short piece of polarization-maintaining active fiber with large core diameter of 25 μm and high pump absorption coefficient is adopted in the main amplifier. Besides, step-distributed longitudinal strain is intentionally imposed on the active fiber to broaden the effective SBS gain spectrum and correspondingly improve the SBS threshold. As a result, a pump-limited single-frequency output of 414 W is obtained with no sign of SBS and mode instability, experimentally showing that the SBS threshold is improved by at least two times through introducing extra strain.. The slope efficiency of the main amplifier is about 80 %. The polarization degree is better than 98 % at all the power levels. To the best of our knowledge, this is the highest output power of single-frequency polarization-maintained fiber amplifier based on all-fiber structure.
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