The development of femtosecond ultrafast fiber lasers with special wavelengths has progressed

Recently, the High Power Fiber Laser Technology Laboratory of Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences has made important progress in the development of femtosecond ultrafast fiber lasers of special wavelengths. The team reported for the first time a 978 nm femtosecond ytterbium fiber laser based on dispersion management and a fully polarized nine-figure cavity. The research results were published in Optics Letters under the title Generation of 978 nm dispersion-managed solitons from a polarization-maintaining Yb-doped figure-of-9 fiber laser.

978 nm ytterbium-doped femtosecond mode-locked fiber lasers have attracted much attention because of their unique application value. However, since the absorption cross-section of Yb3+ around the 978 nm wavelength is approximately equal to the emission cross-section, in order to obtain a high-performance laser output at this wavelength, problems such as laser self-absorption at 978 nm and amplified spontaneous emission (ASE) around 1030 nm must be overcome. In addition, Yb3+ has a relatively narrow gain bandwidth around 978 nm, which further increases the difficulty of obtaining femtosecond laser pulses at this wavelength. Therefore, achieving this 978 nm femtosecond fiber laser presents greater challenges than conventional ytterbium-doped mode-locked fiber lasers above 1 μm.

In order to solve the above problems, the research team used nonlinear magnifying ring mirror (NALM) technology based on the figure nine cavity structure to achieve a stable output of dispersion-managed soliton at 978 nm. In the experiment, the total dispersion in the cavity was effectively managed by controlling the parameters of each dispersion element in the laser cavity, and a filter was introduced to suppress the ASE at 1030 nm, and finally a highly coherent laser pulse with a spectral bandwidth of 14.4 nm and 175 fs was obtained. In addition, the laser cavity is composed of fully polarization preservation fiber devices, which can effectively resist environmental disturbances such as temperature and vibration, and ensure the long-term stability of mode-locked pulses. The numerical simulation results show that the spectral width of 978 nm dispersion-managed solitons is mainly limited by the gain bandwidth of Yb3+ around the relevant wavelength. In the future, nonlinear effects can be used to further broaden the spectrum outside the cavity, enabling a narrower pulse width laser output at this particular wavelength. The 978 nm mode-locked pulse realized in this study is the shortest pulse that can be output by ultrafast fiber lasers of relevant wavelengths reported so far, and has good application prospects in the fields of underwater communication and terahertz wave generation. (Source: Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences)

Figure 1.978 nm nine-cavity dispersion management soliton fiber laser experimental setup diagram

Figure 2. 978 nm nine-cavity fiber laser output pulse parameters. (a) spectrum, (b) pulse train, (c) emission spectrum, (d) autocorrelation signal, (e) extracavity compressed spectrum, and (f) autocorrelation signal.

Figure 3. Numerical simulation results. (a, b) spectral and temporal characteristics of output dispersion management solitons; (c, d) Time-frequency evolution of intracavity pulses.

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