  Broadband wavelength tuneability can ensure a new level of versatility for
laser systems and extend areas of their applications. Principle limitations of
achieving wide tuning wavelength ranges are generally defined by the spectral
bandwidth of the gain and traditional tuneability techniques, relying on
electrically controlled or bulk filters, reducing laser efficiency and
generation stability. In this work, we present nearly 90 nm tuneability in
ultrafast Tm-doped fibre laser within the span from 1873 to 1962 nm by
implementing variable feedback for efficient control of the excitation level of
the active medium and, hence, the gain spectrum. The highest laser efficiency
is observed with 20% feedback, generating 580-fs soliton pulses at 1877 nm
central wavelength with 1.5 nJ output pulse energy. By combining the nonlinear
Shrodinger equation and population inversion rate equations for the gain
medium, the developed numerical model helps to unveil nonlinear pulse evolution
under the influence of dynamically varying gain spectrum. The resulting laser
system presents a compact and straightforward approach to achieve laser
generation with a broad range tuneability of wavelength and operation regimes,
which is not impaired by the limitations on laser stability or power
performance and can be translated to other wavelength ranges.
